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1

Time scales and relaxation dynamics in quantum-dot lasers  

SciTech Connect

We analyze a three-variable rate equation model that takes into account carrier capture and Pauli blocking in quantum dot semiconductor lasers. The exponential decay of the relaxation oscillations is analyzed from the linearized equations in terms of three key parameters that control the time scales of the laser. Depending on their relative values, we determine two distinct two-variable reductions of the rate equations in the limit of large capture rates. The first case leads to the rate equations for quantum well lasers, exhibiting relaxation oscillations dynamics. The second case corresponds to dots nearly saturated by the carriers and is characterized by the absence of relaxation oscillations.

Erneux, Thomas; Viktorov, Evgeny A.; Mandel, Paul [Universite Libre de Bruxelles, Optique Nonlineaire Theorique, Campus Plaine, Code Postal 231, 1050 Brussels (Belgium)

2007-08-15

2

Relation between the dispersion of ?-relaxation and the time scale of ?-relaxation at the glass transition  

Microsoft Academic Search

Dielectric spectra of several typical molecular glass-formers, showing one or more secondary processes resolved in the glassy state, have been measured at different temperatures. We found that the genuine Johari–Goldstein ?-relaxation is connected to the structural relaxation. In fact, a clear correlation was found between the structural relaxation time, the Johari–Goldstein relaxation time and the dispersion of the structural relaxation

Simone Capaccioli; Daniele Prevosto; Khadra Kessairi; Mauro Lucchesi; Pierangelo Rolla

2007-01-01

3

Growing Point-to-Set Length Scale Correlates with Growing Relaxation Times in Model Supercooled Liquids  

NASA Astrophysics Data System (ADS)

It has been demonstrated recently that supercooled liquids sharing simple structural features (e.g. pair distribution functions) may exhibit strikingly distinct dynamical behavior. Here we show that a more subtle structural feature correlates with relaxation times in three simulated systems that have nearly identical radial distribution functions but starkly different dynamical behavior. In particular, for the first time we determine the thermodynamic “point-to-set” length scale in several canonical model systems and demonstrate the quantitative connection between this length scale and the growth of relaxation times. Our results provide clues necessary for distinguishing competing theories of the glass transition.

Hocky, Glen M.; Markland, Thomas E.; Reichman, David R.

2012-06-01

4

Thermodynamic scaling of ?-relaxation time and viscosity stems from the Johari-Goldstein ?-relaxation or the primitive relaxation of the coupling model  

NASA Astrophysics Data System (ADS)

By now it is well established that the structural ?-relaxation time, ??, of non-associated small molecular and polymeric glass-formers obey thermodynamic scaling. In other words, ?? is a function ? of the product variable, ??/T, where ? is the density and T the temperature. The constant ? as well as the function, ?? = ?(??/T), is material dependent. Actually this dependence of ?? on ??/T originates from the dependence on the same product variable of the Johari-Goldstein ?-relaxation time, ??, or the primitive relaxation time, ?0, of the coupling model. To support this assertion, we give evidences from various sources itemized as follows. (1) The invariance of the relation between ?? and ?? or ?0 to widely different combinations of pressure and temperature. (2) Experimental dielectric and viscosity data of glass-forming van der Waals liquids and polymer. (3) Molecular dynamics simulations of binary Lennard-Jones (LJ) models, the Lewis-Wahnström model of ortho-terphenyl, 1,4 polybutadiene, a room temperature ionic liquid, 1-ethyl-3-methylimidazolium nitrate, and a molten salt 2Ca(NO3)2.3KNO3 (CKN). (4) Both diffusivity and structural relaxation time, as well as the breakdown of Stokes-Einstein relation in CKN obey thermodynamic scaling by ??/T with the same ?. (5) In polymers, the chain normal mode relaxation time, ?N, is another function of ??/T with the same ? as segmental relaxation time ??. (6) While the data of ?? from simulations for the full LJ binary mixture obey very well the thermodynamic scaling, it is strongly violated when the LJ interaction potential is truncated beyond typical inter-particle distance, although in both cases the repulsive pair potentials coincide for some distances.

Ngai, K. L.; Habasaki, J.; Prevosto, D.; Capaccioli, S.; Paluch, Marian

2012-07-01

5

Thermodynamic scaling of ?-relaxation time and viscosity stems from the Johari-Goldstein ?-relaxation or the primitive relaxation of the coupling model.  

PubMed

By now it is well established that the structural ?-relaxation time, ?(?), of non-associated small molecular and polymeric glass-formers obey thermodynamic scaling. In other words, ?(?) is a function ? of the product variable, ?(?)/T, where ? is the density and T the temperature. The constant ? as well as the function, ?(?) = ?(?(?)/T), is material dependent. Actually this dependence of ?(?) on ?(?)/T originates from the dependence on the same product variable of the Johari-Goldstein ?-relaxation time, ?(?), or the primitive relaxation time, ?(0), of the coupling model. To support this assertion, we give evidences from various sources itemized as follows. (1) The invariance of the relation between ?(?) and ?(?) or ?(0) to widely different combinations of pressure and temperature. (2) Experimental dielectric and viscosity data of glass-forming van der Waals liquids and polymer. (3) Molecular dynamics simulations of binary Lennard-Jones (LJ) models, the Lewis-Wahnström model of ortho-terphenyl, 1,4 polybutadiene, a room temperature ionic liquid, 1-ethyl-3-methylimidazolium nitrate, and a molten salt 2Ca(NO(3))(2)·3KNO(3) (CKN). (4) Both diffusivity and structural relaxation time, as well as the breakdown of Stokes-Einstein relation in CKN obey thermodynamic scaling by ?(?)/T with the same ?. (5) In polymers, the chain normal mode relaxation time, ?(N), is another function of ?(?)/T with the same ? as segmental relaxation time ?(?). (6) While the data of ?(?) from simulations for the full LJ binary mixture obey very well the thermodynamic scaling, it is strongly violated when the LJ interaction potential is truncated beyond typical inter-particle distance, although in both cases the repulsive pair potentials coincide for some distances. PMID:22830715

Ngai, K L; Habasaki, J; Prevosto, D; Capaccioli, S; Paluch, Marian

2012-07-21

6

Times of development and relaxation of artificial small-scale irregularities  

SciTech Connect

For the interpretation of results of studies of high-power shortwave action on the ionospheric F-layer plasma in the complex temporal regime of the pump wave radiation, it is necessary to know the characteristics of development and relaxation of the spectrum of the artificial ionospheric turbulence in the small-scale range. Results of the experimental studies are considered, and a comparison is made between the times of development and relaxation of artificial small-scale irregularities and their spectral charcteristics under the action of high-power radio waves at frequencies of 4.785 and 2.95 MHz on the ionospheric F-layer.

Belikovich, V.V.; Erukhimov, L.M.; Zyuzin, V.A.; Korobkov, Yu.S.; Maksimenko, O.M.; Nasyrov, A.M.; Sergeev, E.N.; Frolov, V.L.; Shavin, P.B.

1988-09-01

7

Time scale bridging in atomistic simulation of slow dynamics: viscous relaxation and defect activation  

NASA Astrophysics Data System (ADS)

Atomistic simulation methods are known for timescale limitations in resolving slow dynamical processes. Two well-known scenarios of slow dynamics are viscous relaxation in supercooled liquids and creep deformation in stressed solids. In both phenomena the challenge to theory and simulation is to sample the transition state pathways efficiently and follow the dynamical processes on long timescales. We present a perspective based on the biased molecular simulation methods such as metadynamics, autonomous basin climbing (ABC), strain-boost and adaptive boost simulations. Such algorithms can enable an atomic-level explanation of the temperature variation of the shear viscosity of glassy liquids, and the relaxation behavior in solids undergoing creep deformation. By discussing the dynamics of slow relaxation in two quite different areas of condensed matter science, we hope to draw attention to other complex problems where anthropological or geological-scale time behavior can be simulated at atomic resolution and understood in terms of micro-scale processes of molecular rearrangements and collective interactions. As examples of a class of phenomena that can be broadly classified as materials ageing, we point to stress corrosion cracking and cement setting as opportunities for atomistic modeling and simulations.

Kushima, A.; Eapen, J.; Li, Ju; Yip, S.; Zhu, T.

2011-08-01

8

Sensitivity of the simulated precipitation to changes in convective relaxation time scale  

NASA Astrophysics Data System (ADS)

The paper describes the sensitivity of the simulated precipitation to changes in convective relaxation time scale (TAU) of Zhang and McFarlane (ZM) cumulus parameterization, in NCAR-Community Atmosphere Model version 3 (CAM3). In the default configuration of the model, the prescribed value of TAU, a characteristic time scale with which convective available potential energy (CAPE) is removed at an exponential rate by convection, is assumed to be 1 h. However, some recent observational findings suggest that, it is larger by around one order of magnitude. In order to explore the sensitivity of the model simulation to TAU, two model frameworks have been used, namely, aqua-planet and actual-planet configurations. Numerical integrations have been carried out by using different values of TAU, and its effect on simulated precipitation has been analyzed. The aqua-planet simulations reveal that when TAU increases, rate of deep convective precipitation (DCP) decreases and this leads to an accumulation of convective instability in the atmosphere. Consequently, the moisture content in the lower- and mid- troposphere increases. On the other hand, the shallow convective precipitation (SCP) and large-scale precipitation (LSP) intensify, predominantly the SCP, and thus capping the accumulation of convective instability in the atmosphere. The total precipitation (TP) remains approximately constant, but the proportion of the three components changes significantly, which in turn alters the vertical distribution of total precipitation production. The vertical structure of moist heating changes from a vertically extended profile to a bottom heavy profile, with the increase of TAU. Altitude of the maximum vertical velocity shifts from upper troposphere to lower troposphere. Similar response was seen in the actual-planet simulations. With an increase in TAU from 1 h to 8 h, there was a significant improvement in the simulation of the seasonal mean precipitation. The fraction of deep convective precipitation was in much better agreement with satellite observations.

Mishra, S. K.; Srinivasan, J.

2010-10-01

9

The Waveform Relaxation Method for Time-Domain Analysis of Large Scale Integrated Circuits  

Microsoft Academic Search

The Waveform Relaxation (WR) method is an iterative method for analyzing nonlinear dynamical systems in the time domain. The method, at each iteration, decomposes the system into several dynamical subsystems each of which is analyzed for the entire given time interval. Sufficient conditions for convergence of the WR method are proposed and examples in MOS digital integrated circuits are given

Ekachai Lelarasmee; Albert E. Ruehli; Alberto L. Sangiovanni-vincentelli

1982-01-01

10

On the role of cloud adjustment time scale in simulating precipitation with Relaxed Arakawa-Schubert convection scheme  

NASA Astrophysics Data System (ADS)

The precipitation by Relaxed Arakawa-Schubert cumulus parameterization in a General Circulation Model (GCM) is sensitive to the choice of relaxation parameter or specified cloud adjustment time scale. In the present study, we examine sensitivity of simulated precipitation to the choice of cloud adjustment time scale (?adj) over different parts of the tropics using National Center for Environmental Prediction (NCEP) Seasonal Forecast Model (SFM) during June-September. The results show that a single specified value of ?adj performs best only over a particular region and different values are preferred over different parts of the world. To find a relation between ?adj and cloud depth (convective activity) we choose six regions over the tropics. Based on the observed relation between outgoing long-wave radiation and ?adj, we propose a linear cloud-type dependent relaxation parameter to be used in the model. The simulations over most parts of the tropics show improved results due to this newly formulated cloud-type dependent relaxation parameter.

Jain, Deepesh Kumar; Chakraborty, Arindam; Nanjundiah, Ravi S.

2012-01-01

11

Measurement of magnetic nanoparticle relaxation time  

PubMed Central

Purpose: Nanoparticle relaxation time measurements have many applications including characterizing molecular binding, viscosity, heating, and local matrix stiffness. The methods capable of in vivo application are extremely limited. The hypothesis investigated by the authors was that the relaxation time could be measured quantitatively using magnetic spectroscopy of nanoparticle Brownian motion (MSB). Methods: The MSB signal (1) reflects the nanoparticle rotational Brownian motion, (2) can be measured from very low nanoparticle concentrations, and (3) is a function of the product of the drive frequency and the relaxation time characterizing Brownian motion. To estimate the relaxation time, the MSB signal was measured at several frequencies. The MSB signal for nanoparticles with altered relaxation time is a scaled version of that for reference nanoparticles with a known relaxation time. The scaling factor linking the altered and reference MSB measurements is the same factor linking the altered and reference relaxation times. The method was tested using glycerol solutions of varying viscosities to obtain continuously variable relaxation times. Results: The measured relaxation time increased with increasing viscosity of the solution in which the nanoparticles resided. The MSB estimated relaxation time matched the calculated relaxation times based on viscosity with 2% average error. Conclusions: MSB can be used to monitor the nanoparticle relaxation time quantitatively through a scale space correlation of the MSB signal as a function of frequency.

Weaver, John B.; Kuehlert, Esra

2012-01-01

12

Modeling the collective relaxation time of glass-forming polymers at intermediate length scales: Application to polyisobutylene  

NASA Astrophysics Data System (ADS)

In a recent paper [V. N. Novikov, K. S. Schweizer, and A. P. Sokolov, J. Chem. Phys. 138, 164508 (2013)] a simple analytical ansatz has been proposed to describe the momentum transfer (Q) dependence of the collective relaxation time of glass-forming systems in a wide Q-range covering the region of the first maximum of the static structure factor S(Q) and the so-called intermediate length scale regime. In this work we have generalized this model in order to deal with glass-forming systems where the atomic diffusive processes are sub-linear in nature. This is for instance the case of glass-forming polymers. The generalized expression considers a sub-linear jump-diffusion model and reduces to the expression previously proposed for normal diffusion. The generalized ansatz has been applied to the experimental results of the Q- and temperature-dependence of polyisobutylene (PIB), which were previously published. To reduce the number of free parameters of the model to only one, we have taken advantage of atomistic molecular dynamics simulations of PIB properly validated by neutron scattering results. The model perfectly describes the experimental results capturing both, Q- and temperature-dependences. Moreover, the model also reproduces the experimental Q-dependence of the effective activation energy of the collective relaxation time in the temperature range of observation. This non-trivial result gives additional support to the way the crossover between two different relaxation mechanisms of density fluctuations is formulated in the model.

Colmenero, Juan; Alvarez, Fernando; Khairy, Yasmin; Arbe, Arantxa

2013-07-01

13

Modeling the collective relaxation time of glass-forming polymers at intermediate length scales: application to polyisobutylene.  

PubMed

In a recent paper [V. N. Novikov, K. S. Schweizer, and A. P. Sokolov, J. Chem. Phys. 138, 164508 (2013)] a simple analytical ansatz has been proposed to describe the momentum transfer (Q) dependence of the collective relaxation time of glass-forming systems in a wide Q-range covering the region of the first maximum of the static structure factor S(Q) and the so-called intermediate length scale regime. In this work we have generalized this model in order to deal with glass-forming systems where the atomic diffusive processes are sub-linear in nature. This is for instance the case of glass-forming polymers. The generalized expression considers a sub-linear jump-diffusion model and reduces to the expression previously proposed for normal diffusion. The generalized ansatz has been applied to the experimental results of the Q- and temperature-dependence of polyisobutylene (PIB), which were previously published. To reduce the number of free parameters of the model to only one, we have taken advantage of atomistic molecular dynamics simulations of PIB properly validated by neutron scattering results. The model perfectly describes the experimental results capturing both, Q- and temperature-dependences. Moreover, the model also reproduces the experimental Q-dependence of the effective activation energy of the collective relaxation time in the temperature range of observation. This non-trivial result gives additional support to the way the crossover between two different relaxation mechanisms of density fluctuations is formulated in the model. PMID:23902018

Colmenero, Juan; Alvarez, Fernando; Khairy, Yasmin; Arbe, Arantxa

2013-07-28

14

Detection of nano-second internal motion and determination of overall tumbling times independent of the time scale of internal motion in proteins from NMR relaxation data.  

PubMed

The usual analysis of (15)N relaxation data of proteins is straightforward as long as the assumption can be made that the backbone of most residues only undergoes fast (ps), small amplitude internal motions. If this assumption cannot be made, as for example for proteins which undergo domain motions or for unfolded or partially folded proteins, one needs a method to establish for each residue whether it undergoes fast (ps) or slow (ns) internal motion. Even then it is impossible to determine the correct overall tumbling time, tau(m)(0), via the usual method from the ratio of the longitudinal and transverse relaxation times, if the majority of residues do not undergo fast, small amplitude internal motions. The latter problem is solved when tau(m)(0) can be determined independent of the time scale, tau(i), or the amplitude, S(2), of the internal motion. We propose a new protocol, called PINATA, for analyzing (15)N relaxation data acquired at minimally two field strengths, where no a priori assumption about time scales or amplitude of internal motions needs to be made, and overall tumbling can either be isotropic or anisotropic. The protocol involves four steps. First, for each residue, it is detected whether it undergoes ps- or ns-internal motion, via the combination of the ratio of the longitudinal relaxation time at two fields and the hetero-nuclear NOE. Second, for each residue tau(m)(0) and the exchange broadening, Rex, are iteratively determined. The accuracy of the determination of tau(m)(0) is ca. +/-0.5 ns and of Rex ca +/- 0.7 s(-1), when the relaxation data are of good quality and tau(m)(0)>5 ns, S(2)>0.3, and tau(i)< approximately 3 ns. Third, given tau(m)(0) and Rex, step 1 is repeated to iteratively improve on the internal motion and obtain better estimates of the internal parameter values. Fourth, final time scales and amplitudes for internal motions are determined via grid search based fitting and chi(2)-analysis. The protocol was successfully tested on synthetic and experimental data sets. The synthetic dataset mimics internal motions on either fast or slow time scales, or a combination of both, of either small- or large amplitude, superimposed onto anisotropic overall motion. The procedures are incorporated into MATLAB scripts, which are available on request. PMID:14512728

Larsson, Göran; Martinez, Gary; Schleucher, Jürgen; Wijmenga, Sybren S

2003-12-01

15

Fast-time scale dynamics of Outer membrane protein A by extended model-free analysis of NMR relaxation data  

PubMed Central

In order to better understand the dynamics of an integral membrane protein, backbone amide 15N NMR dynamics measurements of the ?-barrel membrane protein OmpA have been performed at three magnetic fields. A total of nine relaxation data sets were globally analyzed using an extended model-free formalism. The diffusion tensor was found to be prolate axially symmetric with an axial ratio of 5.75, indicating a possible rotation of the protein within the micelle. The generalized order parameters gradually decreased from the mid-plane towards the two ends of the barrel, counteracting the dynamic gradient of the lipids in a matching bilayer, and were dramatically reduced in the extracellular loops. Large-scale internal motions on the ns time scale indicate that entire loops most likely undergo concerted (“sea anemone”-like) motions emanating from their anchoring points on the barrel. The case of OmpA in DPC micelles also illustrates inherent limitations of analyzing the data with even the most sophisticated current models of the model-free formalism. It is likely that conformational exchange processes on the ms-µs also play a role in describing the motions of some residues, but their analysis did not produce unique results that could be independently verified.

Liang, Binyong; Arora, Ashish; Tamm, Lukas K.

2009-01-01

16

Implications of Electron Momentum Relaxation Time Scales for Modeling of Transient Electric Fields in the Lower Ionosphere  

NASA Astrophysics Data System (ADS)

Thomas et al. [JGR, A12306, 2008] has reported lightning-driven electric (E) field pulses at 75-130 km altitude recorded during rocket experiment in 1995 from Wallops Island, Virginia. The measurements were compared to a 2D electromagnetic model of Cho and Rycroft [JASTP, 60,871,1998]. Thomas et al.[2008] indicated that the observed field magnitudes were an order of magnitude lower than predicted by the model and questioned validity of the electromagnetic pulse mechanism of elves. The goal of the present work, which utilizes Monte Carlo and FDTD electromagnetic modeling, is to emphasize range of validity of the local field approximation (LFA) employed in the Cho and Rycroft's [1998] model and other similar models for the cases when weak (~10 mV/m as reported in [Thomas et al., 2008]) E field pulses are considered. Glukhov et al. [GRL, 23, 2193, 1996] and Sukhorukov et al. [GRL, 23, 2911, 1996] performed Monte Carlo simulations for large E fields ~10V/m at typical altitudes of elves, which fully confirmed validity of models of elves based on LFA [Taranenko et al., GRL, 20, 2675, 1993; Inan et al., GRL, 23, 133, 1996]. We demonstrate that the time of relaxation of the momentum of the electron distributions subjected to the external E field scales approximately as 1/E and exceeds 10s of microseconds for E<1V/m at typical altitudes of elves and sprite halos. The weak, ~10mV/m (<18kHz), E field transients observed in the lower ionosphere [Thomas et al., 2008] can not be accurately described in the framework of the self-consistent electron mobility model based on the LFA [e.g.,Cho and Rycroft, 1998]. At lower ionospheric altitudes LFA in which electron mobility reaches equilibrium value defined by the magnitude of the reduced applied E field is only valid for relatively large fields E>1 V/m when fast (10 kHz) processes are considered. The models of elves relying on LFA [e.g., Taranenko et al., 1993; Inan et al., 1996] generally require E>1 V/m for production of observable optical emissions at lower ionospheric altitudes and therefore remain valid, in agreement with original conclusions reached by Glukhov et al. [1996] and Sukhorukov et al. [1996]. Two additional factors may have contributed to the low field magnitudes reported in [Thomas et al., 2008]: 1) The measurements were conducted on September 2, 1995 around evening hours (9:22 PM local time) at which the lower ionosphere likely exhibited enhancement of electron density in comparison with night time conditions employed in modeling; 2) The NLDN deduced peak currents were employed in modeling with lightning current rise time 60 microseconds while NLDN is generally sensitive to LF radiation, which for a typical -CG is emitted during the initial 1-5 microseconds from a vertical part of the return stroke channel a few tens to a few hundreds of meters above the ground [Krider et al., J. Appl. Meteorol., 15, 301, 1976; Orville, BAMS, 2, 180, 2008]. The low pass filtering with 18 kHz cutoff applied to data reported in [Thomas et al., 2008] may contributed to underestimation of magnitudes of observed lightning induced pulses. Modeling results will be presented which illustrate these effects and allow to reach a good agreement with observations in a subset of the cases reported in [Thomas et al., 2008].

Pasko, V. P.

2009-12-01

17

A computational atomistic study of the relaxation of ion-bombarded c-Si on experimental time-scales: an application of the kinetic Activation Relaxation Technique  

NASA Astrophysics Data System (ADS)

The kinetic activation relaxation technique (kinetic ART) method, an off-lattice, self-learning kinetic Monte Carlo (KMC) algorithm with on-the-fly event search,ootnotetextL. K. B'eland, P. Brommer, F. El-Mellouhi, J.-F. Joly and N. Mousseau, Phys. Rev. E 84, 046704 (2011). is used to study the relaxation of c-Si after Si^- bombardment at 3 keV. We describe the evolution of the damaged areas at room-temperature and above for periods of the order of seconds, treating long-range elastic deformations exactly. We assess the stability of the nanoscale structures formed by the damage cascade and the mechanisms that govern post-implantation annealing.

Béland, Laurent Karim; Mousseau, Normand

2012-02-01

18

Scale properties as a basis of power law relaxation processes  

NASA Astrophysics Data System (ADS)

Computer simulations of first-order relaxation processes show that the spatial configurations of the system acquire an invariant shape once the stationary regime is attained. Inspired by them we find that, in any first-order relaxation process, if the interaction that governs the system fulfils a simple scale property, then the relaxation will end up by following a stationary process described by a power law. A scaling law and some invariants are obtained for the time evolution of the system in such a case.

Fondado, A.; Mira, J.; Rivas, J.

2007-04-01

19

Comprehensive description of NMR cross-correlated relaxation under anisotropic molecular tumbling and correlated local dynamics on all time scales.  

PubMed

A simple general expression for the NMR cross-correlated relaxation rate under anisotropic molecular tumbling is presented for globular proteins. The derivation includes effects of fast and slow motion of the interaction tensors and correlation between them. Expressions suitable for practical analysis are tailored in dependence of standard order parameters of the individual interactions. It is shown that these order parameters must be sensitive to slow motion (slower than molecular tumbling) for detection of slow correlated motion. Such order parameters are those obtained from residual dipolar couplings but not those obtained from T1, T2, and heteronuclear Nuclear Overhauser Enhancement measurements. PMID:20614970

Vögeli, Beat

2010-07-01

20

Dielectric polarization evolution equations and relaxation times  

SciTech Connect

In this paper we develop dielectric polarization evolution equations, and the resulting frequency-domain expressions, and relationships for the resulting frequency dependent relaxation times. The model is based on a previously developed equation that was derived using statistical-mechanical theory. We extract relaxation times from dielectric data and give illustrative examples for the harmonic oscillator and derive expressions for the frequency-dependent relaxation times and a time-domain integrodifferential equation for the Cole-Davidson model.

Baker-Jarvis, James; Riddle, Bill; Janezic, Michael D. [NIST, Electromagnetics Division, MS 818.01, Boulder, Colorado 80305 (United States)

2007-05-15

21

Time of Relaxation. I. Unbounded Medium.  

National Technical Information Service (NTIS)

The classical problem of relaxation time in an infinite, uniform, stellar medium is reinvestigated by a method that includes the time dependence of interaction, in contrast to the original treatment in which all collisions were considered to be very brief...

J. P. Ostriker A. F. Davidsen

1968-01-01

22

A Numerical Test of the Relaxation Time.  

National Technical Information Service (NTIS)

The relaxation time of a simplified model of a stellar cluster is derived analytically and compared with many numerical examples, using up to 2500 field stars. The derivation closely resembles that of Chandrasekhar; it assumes independent binary encounter...

E. M. Standish K. Aksnes

1969-01-01

23

Rounded stretched exponential for time relaxation functions.  

PubMed

A rounded stretched exponential function is introduced, C(t)=exp{(tau(0)/tau(E))(beta)[1-(1+(t/tau(0))(2))(beta/2)]}, where t is time, and tau(0) and tau(E) are two relaxation times. This expression can be used to represent the relaxation function of many real dynamical processes, as at long times, t>tau(0), the function converges to a stretched exponential with normalizing relaxation time, tau(E), yet its expansion is even or symmetric in time, which is a statistical mechanical requirement. This expression fits well the shear stress relaxation function for model soft soft-sphere fluids near coexistence, with tau(E)relaxation (both the modulus and viscosity forms). It is shown that both the dielectric spectra and dynamic shear modulus imaginary parts approach the real axis with a slope equal to 0 at high frequency, whereas the dynamic viscosity has an infinite slope in the same limit. This indicates that inertial effects at high frequency are best discerned in the modulus rather than the viscosity Cole-Cole plot. As a consequence of the even expansion in time of the shear stress relaxation function, the value of the storage modulus derived from it at very high frequency exceeds that in the infinite frequency limit (i.e., G(infinity)). PMID:19968353

Powles, J G; Heyes, D M; Rickayzen, G; Evans, W A B

2009-12-01

24

Probing relaxation times in graphene quantum dots.  

PubMed

Graphene quantum dots are attractive candidates for solid-state quantum bits. In fact, the predicted weak spin-orbit and hyperfine interaction promise spin qubits with long coherence times. Graphene quantum dots have been extensively investigated with respect to their excitation spectrum, spin-filling sequence and electron-hole crossover. However, their relaxation dynamics remain largely unexplored. This is mainly due to challenges in device fabrication, in particular concerning the control of carrier confinement and the tunability of the tunnelling barriers, both crucial to experimentally investigate decoherence times. Here we report pulsed-gate transient current spectroscopy and relaxation time measurements of excited states in graphene quantum dots. This is achieved by an advanced device design that allows to individually tune the tunnelling barriers down to the low megahertz regime, while monitoring their asymmetry. Measuring transient currents through electronic excited states, we estimate a lower bound for charge relaxation times on the order of 60-100 ns. PMID:23612294

Volk, Christian; Neumann, Christoph; Kazarski, Sebastian; Fringes, Stefan; Engels, Stephan; Haupt, Federica; Müller, André; Stampfer, Christoph

2013-01-01

25

Scale properties as a basis of power law relaxation processes  

Microsoft Academic Search

Computer simulations of first-order relaxation processes show that the spatial configurations of the system acquire an invariant shape once the stationary regime is attained. Inspired by them we find that, in any first-order relaxation process, if the interaction that governs the system fulfils a simple scale property, then the relaxation will end up by following a stationary process described by

A. Fondado; J. Mira; J. Rivas

2007-01-01

26

Influence of Ionic Solutes Upon Relaxation Times.  

National Technical Information Service (NTIS)

Sin-lattice relaxation times were measured by the 'direct' N.M.R. method for dilute aqueous solutions of Ni(II) in presence of cyanide, halide, acetone, t-butyl alcohol, trimethyl phosphate, edta and trien, for some of these solutes in the absence of para...

V. Gold

1964-01-01

27

Conformational exchange on the microsecond time scale in alpha-helix and beta-hairpin peptides measured by 13C NMR transverse relaxation.  

PubMed

13C-NMR relaxation experiments (T(1), T(2), T(1)(rho), and NOE) were performed on selectively enriched residues in two peptides, one hydrophobic staple alpha-helix-forming peptide GFSKAELAKARAAKRGGY and one beta-hairpin-forming peptide RGITVNGKTYGR, in water and in water/trifluoroethanol (TFE). Exchange contributions, R(ex), to spin-spin relaxation rates for (13)C(alpha) and (13)C(beta) groups were derived and were ascribed to be mainly due to peptide folding-unfolding. To evaluate the exchange time, tau(ex), from R(ex), the chemical shift difference between folded and unfolded states, Deltadelta, and the populations of these states, p(i), were determined from the temperature dependence of (13)C chemical shifts. For both peptides, values for tau(ex) fell in the 1 micros to 10 micros range. Under conditions where the peptides are most folded (water/TFE, 5 degrees C), tau(ex) values for all residues in each respective peptide were essentially the same, supporting the presence of a global folding-unfolding exchange process. Rounded-up average tau(ex) values were 4 micros for the helix peptide and 9 micros for the hairpin peptide. This 2-3-fold difference in exchange times between helix and hairpin peptides is consistent with that observed for folding-unfolding of other small peptides. PMID:11258895

Nesmelova, I; Krushelnitsky, A; Idiyatullin, D; Blanco, F; Ramirez-Alvarado, M; Daragan, V A; Serrano, L; Mayo, K H

2001-03-01

28

Crossover time in relative fluctuations characterizes the longest relaxation time of entangled polymers  

NASA Astrophysics Data System (ADS)

In entangled polymer systems, there are several characteristic time scales, such as the entanglement time and the disengagement time. In molecular simulations, the longest relaxation time (the disengagement time) can be determined by the mean square displacement (MSD) of a segment or by the shear relaxation modulus. Here, we propose the relative fluctuation analysis method, which is originally developed for characterizing large fluctuations, to determine the longest relaxation time from the center of mass trajectories of polymer chains (the time-averaged MSDs). Applying the method to simulation data of entangled polymers (by the slip-spring model and the simple reptation model), we provide a clear evidence that the longest relaxation time is estimated as the crossover time in the relative fluctuations.

Uneyama, Takashi; Akimoto, Takuma; Miyaguchi, Tomoshige

2012-09-01

29

Crossover time in relative fluctuations characterizes the longest relaxation time of entangled polymers.  

PubMed

In entangled polymer systems, there are several characteristic time scales, such as the entanglement time and the disengagement time. In molecular simulations, the longest relaxation time (the disengagement time) can be determined by the mean square displacement (MSD) of a segment or by the shear relaxation modulus. Here, we propose the relative fluctuation analysis method, which is originally developed for characterizing large fluctuations, to determine the longest relaxation time from the center of mass trajectories of polymer chains (the time-averaged MSDs). Applying the method to simulation data of entangled polymers (by the slip-spring model and the simple reptation model), we provide a clear evidence that the longest relaxation time is estimated as the crossover time in the relative fluctuations. PMID:22998286

Uneyama, Takashi; Akimoto, Takuma; Miyaguchi, Tomoshige

2012-09-21

30

Discontinuous Galerkin and Nonconforming in Time Optimized Schwarz Waveform Relaxation  

Microsoft Academic Search

\\u000a In many fields of applications such as reactive transport or ocean-atmosphere coupling, models with very different spatial\\u000a and time scales have to be coupled. Optimized Schwarz Waveform Relaxation methods (OSWR), applied to linear advection-reaction-diffusion\\u000a problems in [1, 8], provide efficient solvers for this purpose. They have two main advantages: first, they are global in time\\u000a and thus permit non conforming

Laurence Halpern

31

Ageing and relaxation times in disordered insulators  

NASA Astrophysics Data System (ADS)

We focus on the slow relaxations observed in the conductance of disordered insulators at low temperature (especially granular aluminum films). They manifest themselves as a temporal logarithmic decrease of the conductance after a quench from high temperatures and the concomitant appearance of a field effect anomaly centered on the gate voltage maintained. We are first interested in ageing effects, i.e. the age dependence of the dynamical properties of the system. We stress that the formation of a second field effect anomaly at a different gate voltage is not a "history free" logarithmic (lnt) process, but departs from lnt in a way which encodes the system's age. The apparent relaxation time distribution extracted from the observed relaxations is thus not "constant" but evolves with time. We discuss what defines the age of the system and what external perturbation out of equilibrium does or does not rejuvenate it. We further discuss the problem of relaxation times and comment on the commonly used "two dip" experimental protocol aimed at extracting "characteristic times" for the glassy systems (granular aluminum, doped indium oxide...). We show that it is inoperable for systems like granular Al and probably highly doped InOx where it provides a trivial value only determined by the experimental protocol. But in cases where different values are obtained like in lightly doped InOx or some ultra thin metal films, potentially interesting information can be obtained, possibly about the "short time" dynamics of the different systems. Present ideas about the effect of doping on the glassiness of disordered insulators may also have to be reconsidered.

Grenet, T.; Delahaye, J.; Cheynet, M. C.

2012-07-01

32

Detection of weak signals through nonlinear relaxation times for a Brownian particle in an electromagnetic field.  

PubMed

The detection of weak signals through nonlinear relaxation times for a Brownian particle in an electromagnetic field is studied in the dynamical relaxation of the unstable state, characterized by a two-dimensional bistable potential. The detection process depends on a dimensionless quantity referred to as the receiver output, calculated as a function of the nonlinear relaxation time and being a characteristic time scale of our system. The latter characterizes the complete dynamical relaxation of the Brownian particle as it relaxes from the initial unstable state of the bistable potential to its corresponding steady state. The one-dimensional problem is also studied to complement the description. PMID:21867143

Jiménez-Aquino, J I; Romero-Bastida, M

2011-07-25

33

Time resolved scattering relaxation mechanisms of microcavity polaritons  

NASA Astrophysics Data System (ADS)

We study the polariton relaxation dynamics for different scattering mechanisms as: Phonon and electron scattering procesess. The relaxation polariton is obtained at very short times by solving the Boltzman equation. Instead of the well-known relaxation process by phonons, we show that the bottleneck effect relaxes to the ground state more efficiently at low pump power intensity when the electron relaxation process is included. In this way, we clearly demonstrate that different relaxation times exist, for which any of these two mechanism is more efficient to relax the polariton population to the ground state.

Chaves, F.; Rodríguez, F. J.

2005-11-01

34

A Scale Measuring the Ability To Relax Others.  

ERIC Educational Resources Information Center

|The present research developed and validated a self-reported instrument called the "Relaxing Others Scale" (ROS), which is designed to identify individuals who possess the ability to relax others. A second part of the study involved assessing the construct validity of the ROS. Participants in the study were male and female dormitory residents,…

Oliver, Peter V.; Boudreau, Louis A.

35

Evidence for the universal scaling behaviour of a freely relaxing DNA molecule  

NASA Astrophysics Data System (ADS)

Relaxation measurements on a fluorescently labelled free DNA molecule after stretching by a Poiseuille flow in a capillary vessel reveal universal scaling features: at intermediate times the scaling exponent of the decay law for the molecule length as a function of time is found to be 0.51 ± 0.05. This law is in agreement with the prediction of the Brochard-Wyart "stem and flower" model for the relaxation of a stretched polymer chain.

Manneville, S.; Cluzel, Ph.; Viovy, J.-L.; Chatenay, D.; Caron, F.

1996-11-01

36

Cluster Size Distribution and Relaxation Long Time Tails  

NASA Astrophysics Data System (ADS)

Relaxation phenomena such as the dielectric, magnetic and mechanical relaxation of many disordered physical systems exhibit universal features in particular for long time one often observes an exponential behavior known as long time tail relaxation. We show that if individual clusters in these materials have a relaxation time proportional to the cluster size, the existence of a stable probability size distribution with a long tail power law changes dramatically the relaxation rate, from an initial exponential relaxation to a long time tail t-?. In this case it is the morphology of the system which determines its kinetics.

Vasquez, Alexis; Sotolongo, Oscar; Brouers, Francois

1997-08-01

37

Geological Time Scale  

NSDL National Science Digital Library

This document describes how geologic time is approached in discussions of geologic topics. The uses of relative time and absolute time are compared, and a geologic time scale is provided to represent both concepts. References are provided.

38

Clustered continuous-time random walks: diffusion and relaxation consequences  

PubMed Central

We present a class of continuous-time random walks (CTRWs), in which random jumps are separated by random waiting times. The novel feature of these CTRWs is that the jumps are clustered. This introduces a coupled effect, with longer waiting times separating larger jump clusters. We show that the CTRW scaling limits are time-changed processes. Their densities solve two different fractional diffusion equations, depending on whether the waiting time is coupled to the preceding jump, or the following one. These fractional diffusion equations can be used to model all types of experimentally observed two power-law relaxation patterns. The parameters of the scaling limit process determine the power-law exponents and loss peak frequencies.

Weron, Karina; Stanislavsky, Aleksander; Jurlewicz, Agnieszka; Meerschaert, Mark M.; Scheffler, Hans-Peter

2012-01-01

39

Probing Microsecond Time Scale Dynamics in Proteins by Methyl 1H Carr-Purcell-Meiboom-Gill Relaxation Dispersion NMR Measurements. Application to Activation of the Signaling Protein NtrCr  

PubMed Central

To study microsecond processes by relaxation dispersion NMR spectroscopy, low power deposition and short pulses are crucial and encourage the development of experiments that employ 1H Carr?Purcell?Meiboom?Gill (CPMG) pulse trains. Herein, a method is described for the comprehensive study of microsecond to millisecond time scale dynamics of methyl groups in proteins, exploiting their high abundance and favorable relaxation properties. In our approach, protein samples are produced using [1H, 13C]-d-glucose in ?100% D2O, which yields CHD2 methyl groups for alanine, valine, threonine, isoleucine, leucine, and methionine residues with high abundance, in an otherwise largely deuterated background. Methyl groups in such samples can be sequence-specifically assigned to near completion, using 13C TOCSY NMR spectroscopy, as was recently demonstrated (Otten, R.; et al. J. Am. Chem. Soc.2010, 132, 2952?2960). In this Article, NMR pulse schemes are presented to measure 1H CPMG relaxation dispersion profiles for CHD2 methyl groups, in a vein similar to that of backbone relaxation experiments. Because of the high deuteration level of methyl-bearing side chains, artifacts arising from proton scalar coupling during the CPMG pulse train are negligible, with the exception of Ile-?1 and Thr-?2 methyl groups, and a pulse scheme is described to remove the artifacts for those residues. Strong 13C scalar coupling effects, observed for several leucine residues, are removed by alternative biochemical and NMR approaches. The methodology is applied to the transcriptional activator NtrCr, for which an inactive/active state transition was previously measured and the motions in the microsecond time range were estimated through a combination of backbone 15N CPMG dispersion NMR spectroscopy and a collection of experiments to determine the exchange-free component to the transverse relaxation rate. Exchange contributions to the 1H line width were detected for 21 methyl groups, and these probes were found to collectively report on a local structural rearrangement around the phosphorylation site, with a rate constant of (15.5 ± 0.5) × 103 per second (i.e., ?ex = 64.7 ± 1.9 ?s). The affected methyl groups indicate that, already before phosphorylation, a substantial, transient rearrangement takes place between helices 3 and 4 and strands 4 and 5. This conformational equilibrium allows the protein to gain access to the active, signaling state in the absence of covalent modification through a shift in a pre-existing dynamic equilibrium. Moreover, the conformational switching maps exactly to the regions that differ between the solution NMR structures of the fully inactive and active states. These results demonstrate that a cost-effective and quantitative study of protein methyl group dynamics by 1H CPMG relaxation dispersion NMR spectroscopy is possible and can be applied to study functional motions on the microsecond time scale that cannot be accessed by backbone 15N relaxation dispersion NMR. The use of methyl groups as dynamics probes extends such applications also to larger proteins.

2010-01-01

40

Relaxation dynamics of scale-free polymer networks  

NASA Astrophysics Data System (ADS)

We focus on polymer networks with a scale-free topology. In the framework of generalized Gaussian structures, by making use of the eigenvalue spectrum of the connectivity matrix, we determined numerically the averaged monomer displacement under external forces and the mechanical relaxation moduli (storage and loss modulus). First, we monitor these physical quantities and additionally the eigenvalue spectrum for structures of different sizes, but with the same ?, which is a parameter that measures the connectivity of the structure. Second, we vary the parameter ?, and we keep constant the size of the structures. This allows us to study in detail the crossover behavior from a simple linear chain to a starlike structure. As expected we encounter a more chainlike behavior for high values of ?, while for small values of ? a more starlike behavior is observed. In the intermediate time (frequency) domain, we encounter regions of constant slope for some intermediate values of ?.

Galiceanu, M.

2012-10-01

41

Parametrization of the relaxation time in crystalline graphite  

NASA Astrophysics Data System (ADS)

The band theory of Slonczewsky, Weiss, and McClure (SWMc) is combined with an electron-phonon interaction to determine the relaxation time in crystalline graphite as a function of the interaction parameters. The transition probability between Bloch functions, which include atomic displacements due to thermal vibration of the lattice, is evaluated. Wave functions are expanded at each atomic site, leading to a simple relationship between the electron-phonon interaction and the relaxation time. The splitting of the relaxation time parallel and perpendicular to the graphite plane is introduced through the transition probability. The Komatsu dispersion relation, for parallel and perpendicular acoustic phonons, is adjusted through experimental measurement. Relaxation times are evaluated as a function of energy for temperatures between 25 and 300 K, giving results that depend on the interaction parameters used. Both parallel and perpendicular relaxation times are of the same order of magnitude, and the parallel relaxation time agrees with the one calculated using Ono's theory.

Luiggi, Ney J.; Barreto, Willians

1986-08-01

42

Energy relaxation times in a Nb persistent current qubit  

Microsoft Academic Search

We measured the energy relaxation time in a Nb superconducting persistent current qubit using a time-resolved fast measurement scheme. The energy relaxation time is longer than 10?s, showing a strong potential of realizing quantum computation with Nb-based superconducting qubits.

Yang Yu; William D. Oliver; D. Nakada; Janice C. Lee; Karl K. Berggren; T. P. Orlando

2005-01-01

43

Full-spectrum phonon relaxation times in crystalline Si from molecular dynamics simulations  

NASA Astrophysics Data System (ADS)

The lattice vibrations of a periodic silicon crystal are simulated by a molecular dynamics simulation. The history of atomic displacements and velocities obtained is used to compute the amplitudes of all phonon modes supported by the lattice. The phonon amplitude autocorrelation coefficients are found to decay exponentially in time, in agreement with single-mode relaxation time models for phonon scattering. However, the relaxation times extracted from the correlation curves are found to differ significantly from the empirical formulas currently used in models for microscale thermal transport, suggesting that improved relaxation time models are needed for accurate predictions in complex small-scale heat transfer systems.

Zhao, Hong; Freund, Jonathan B.

2008-08-01

44

GSA Geologic Time Scale  

NSDL National Science Digital Library

This Geological Society of America (GSA) site contains a detailed geologic time scale as an educational resource. It may be downloaded to a larger size, and includes all Eras, Eons, Periods, Epochs and ages as well as magnetic polarity information.

1999-01-01

45

Integration on time scales  

Microsoft Academic Search

In this paper we study the process of Riemann and Lebesgue integration on time scales. The relationship of the Riemann and Lebesgue integrals is considered and a criterion for Riemann integrability is established.

Gusein Sh. Guseinov

2003-01-01

46

A Mesozoic time scale  

Microsoft Academic Search

We present an integrated geomagnetic polarity and stratigraphic time scale for the Triassic, Jurassic, and Cretaceous periods of the Mesozoic Era, with age estimates and uncertainty limits for stage boundaries. The time scale uses a suite of 324 radiometric dates, including high-resolution Ar-40\\/Ar-39 age estimates. This framework involves the observed ties between (1) radiometric dates, biozones, and stage boundaries, and

Felix M. Gradstein; Frits P. Agterberg; James G. Ogg; Jan Hardenbol; Paul van Veen; Jacques Thierry; Zehui Huang

1994-01-01

47

Dynamics of continuous-time random walk, fractal time dispersion, and fractional exponential time relaxation  

NASA Astrophysics Data System (ADS)

This paper attempts to establish the dynamics of a microscopic model for a continuous-time random walk. The waiting-time distribution Q(t) is derived from the time-dependent perturbation theory of quantum mechanics for the walker's motion coupled with the media. The walker's motion includes the hopping of a localized particle and a spin (or dipole) flip. The medium is modeled as a harmonic heat bath. The walker moves among a set of degenerate localized states. The scaling behavior of the effective spectrum at low frequency with index ? is modeled by using stochastic theory. It is found that Q(t)=exp(-at(2-?)) for 0<=?<2 and Q(t)~t-? for ?=2. The applications of our theory include dispersion diffusion, the transient drift of hopping control light excitation in a-Si:H, and thermoremanent magnetization relaxation in spin glasses.

Liu, Fu-Sui; Chao, Wen

1989-10-01

48

Primary and secondary relaxation time dispersions in fragile supercooled liquids  

NASA Astrophysics Data System (ADS)

The relaxation time dispersions of the primary (?) and secondary (?) dielectric relaxations are studied for molecular glass-forming liquids regarding their dependence on structural relaxation time [or lack thereof observed as time-temperature superposition (TTS)], their changes with fragility, and a possible correlation of the values for the ? and ? processes. Toward more fragile liquids, the width w? of the ? peak at the glass transition temperature Tg is known to increase significantly. Additionally, we observe that TTS extends over a broader range of peak relaxation times in the case of higher fragility, with the approach to exponential (Debye) relaxation being delayed to faster dynamics. The width w? of the ? relaxation at Tg is somewhat lower for more fragile liquids and appears correlated with that of the primary relaxation. The extrapolated coincidence of the dispersions of the ? and ? processes occurs at the fragility “limit” of m=170 , implying that w??w? for all molecular supercooled liquids. Materials of high fragility are also those with no clear low-frequency cutoff in the relaxation time distribution—i.e., their susceptibilities require Havriliak-Negami instead of Cole-Davidson fits. For sorbitol, the value of w? is seen to change steadily through the ?-? -merging region, whereas w? displays a kink at the crossover temperature.

Wang, Li-Min; Richert, Ranko

2007-08-01

49

Relaxation Time of High-Density Amorphous Ice  

NASA Astrophysics Data System (ADS)

Amorphous water plays a fundamental role in astrophysics, cryoelectron microscopy, hydration of matter, and our understanding of anomalous liquid water properties. Yet, the characteristics of the relaxation processes taking place in high-density amorphous ice (HDA) are unknown. We here reveal that the relaxation processes in HDA at 110-135 K at 0.1-0.2 GPa are of collective and global nature, resembling the alpha relaxation in glassy material. Measured relaxation times suggest liquid-like relaxation characteristics in the vicinity of the crystallization temperature at 145 K. By carefully relaxing pressurized HDA for several hours at 135 K, we produce a state that is closer to the ideal glass state than all HDA states discussed so far in literature.

Handle, Philip H.; Seidl, Markus; Loerting, Thomas

2012-06-01

50

A NOTE ON UNIQUENESS IN THERMOELASTICITY WITH ONE RELAXATION TIME  

Microsoft Academic Search

Uniqueness for a general initial boundary-value problem of linear dynamic thermoelasticity with one relaxation time is established using the associated conservation law involving higher-order time derivatives.

Józef Ignaczak

1982-01-01

51

Time-Temperature Superposition of Structural Relaxation in a Viscous Metallic Liquid  

NASA Astrophysics Data System (ADS)

Bulk metallic glass-forming Pd40Ni10Cu30P20 has been investigated in its equilibrium liquid by quasielastic neutron scattering. The quasielastic signal exhibits a structural relaxation as known from nonmetallic viscous liquids. Even well above the melting point, the structural relaxation is nonexponential and obeys a universal time-temperature superposition. From the mean relaxation times average diffusivities have been determined, resulting in values on a 10-10 m2 s-1 scale, 3 orders of magnitude slower than in simple metallic liquids.

Meyer, A.; Busch, R.; Schober, H.

1999-12-01

52

Origin of the relaxation time in dissipative fluid dynamics  

SciTech Connect

We show how the linearized equations of motion of any dissipative current are determined by the analytical structure of the associated retarded Green's function. If the singularity of Green's function, which is nearest to the origin in the complex-frequency plane, is a simple pole on the imaginary frequency axis, the linearized equations of motion can be reduced to relaxation type equations for the dissipative currents. The value of the relaxation time is given by the inverse of this pole. We prove that, if the relaxation time is sent to zero, or equivalently, the pole to infinity, the dissipative currents approach the values given by the standard gradient expansion.

Denicol, Gabriel S.; Noronha, Jorge; Niemi, Harri; Rischke, Dirk H. [Institut fuer Theoretische Physik, Goethe University, 60438 Frankfurt am Main (Germany); Department of Physics, Columbia University, New York, New York 10027 (United States) and Instituto de Fisica, Universidade Federal do Rio de Janeiro, C. P. 68528, 21945-970, Rio de Janeiro (Brazil); Frankfurt Institute for Advanced Studies (FIAS), 60438 Frankfurt am Main (Germany); Institut fuer Theoretische Physik, Goethe University, and Frankfurt Institute for Advanced Studies (FIAS), 60438 Frankfurt am Main (Germany)

2011-04-01

53

Frequency-independent order parameter relaxation time in TGS crystals  

Microsoft Academic Search

The acoustical anomalies near phase transition of TGS crystals are studied within the frequency range of 17-670 MHz. The frequency independence of order parameter relaxation time is shown contrary to the frequency dependence established before.

E. V. Charnaya; A. A. Kuleshov; A. K. Radzhabov; I. K. Rakhimov; L. A. Shuvalov

1993-01-01

54

Proton-nuclear magnetic resonance relaxation times in brain edema  

SciTech Connect

Proton relaxation times of protein solutions, bovine brain, and edematous feline brain tissue were studied as a function of water concentration, protein concentration, and temperature. In accordance with the fast proton exchange model for relaxation, a linear relation could be established between R1 and the inverse of the weight fraction of tissue water. This relation also applied to R2 of gray matter and of protein solutions. No straightforward relation with water content was found for R2 of white matter. Temperature-dependent studies indicated that in this case, the slow exchange model for relaxation had to be applied. The effect of macromolecules in physiological relevant concentrations on the total relaxation behavior of edematous tissue was weak. Total water content changes predominantly affected the relaxation rates. The linear relation may have high clinical potential for assessment of the status of cerebral edema on the basis of T1 and T2 readings from MR images.

Kamman, R.L.; Go, K.G.; Berendsen, H.J. (Univ. of Groningen (Netherland))

1990-01-01

55

Technique for Measuring Hippocampal T2 Relaxation Time  

Microsoft Academic Search

PURPOSE: To implement and validate methods for producing calculated coronal T2 maps with complete coverage of the hippocampus and the rest of the brain. METHODS: T2 relaxation times were estimated on three occasions for 12 quality assessment test objects with the use of fast spin-echo (FSE) and conventional spin-echo (CSE) sequences. Hippocampal T2 relaxation times were measured in 15 healthy

John S. Duncan; Philippa Bartlett; Gareth J. Barker

1996-01-01

56

Intraband relaxation time in quantum-well lasers  

Microsoft Academic Search

Intraband relaxation time, which causes spectral broadening of optical gain and spontaneous emission spectra, is estimated theoretically for quantum-well lasers. Carrier-carrier and carrier-longitudinal optical (LO) phonon scattering mechanisms are considered, and it is shown that hole-hole electron-hole, and hole-LO phonon scattering are dominant in spectral broadening. Intraband relaxation time determined by all of these mechanisms increases slightly with the decrease

M. Asada

1989-01-01

57

Relaxation time and elasticity during polymerization with DER 332  

NASA Astrophysics Data System (ADS)

To complement a study of the dielectric relaxation time's relation with the velocity of propagation of hypersound wave in a polymerizing liquid [K. Venkateshan and G. P. Johari J. Chem. Phys.125, 014907 (2006)], we report results of an analogous study by using the same diglycidylether of bisphenol-A that had been used for measuring the velocity. The data show that the logarithmic relaxation time increases linearly with the square of the velocity of propagation of transverse hypersound wave.

Venkateshan, K.; Johari, G. P.

2006-10-01

58

Multiple-relaxation-time lattice Boltzmann models in three dimensions.  

PubMed

This article provides a concise exposition of the multiple-relaxation-time lattice Boltzmann equation, with examples of 15-velocity and 19-velocity models in three dimensions. Simulation of a diagonally lid-driven cavity flow in three dimensions at Re = 500 and 2000 is performed. The results clearly demonstrate the superior numerical stability of the multiple-relaxation-time lattice Boltzmann equation over the popular lattice Bhatnagar-Gross-Krook equation. PMID:16214687

D'Humières, Dominique; Ginzburg, Irina; Krafczyk, Manfred; Lallemand, Pierre; Luo, Li-Shi

2002-03-15

59

The Geologic Time Scale  

NSDL National Science Digital Library

This site contains a large, easy to read, detailed geologic time scale for the Phanerozoic Eon (544 million years ago - Present). This is the period of time, also known as an eon, between the end of the Precambrian and today. The Phanerozoic begins with the start of the Cambrian period, 544 million years ago. It encompasses the period of abundant, complex life on Earth. The chart includes the Era, Period or System, and the Epoch or Series and features a brief description of each.

60

Web Geologic Time Scale  

NSDL National Science Digital Library

The University of California-Berkeley Museum of Paleontology (last mentioned in the June 16, 1995 Scout Report) has recently updated its Web Geologic Time Scale, an online feature that helps users learn about the geologic timeline and explore related museum exhibits. The familiar geologic timeline appears on the main page of the Web site, with hypertext links for each division of time. Every page of the Web Geologic Time Machine site is liberally sprinkled with links to related UCMP Web pages; think of it as a portal to all online information available from the museum. Altogether, this Web site provides a well-organized and comprehensive resource for learning how the planet has changed over time, and would be a great addition to earth or life sciences classroom material for a broad range of grades.

1994-01-01

61

Effectiveness of Slow Relaxation Dynamics in Finite-Time Optimization by Simulated Annealing  

Microsoft Academic Search

The origin of the specific temperature beneficial to finite-time optimization by simulated annealing is discussed on the analogy of the dynamics of complex physical systems. Rate-cycling experiments are introduced and performed on practical time scales on the random Euclidean traveling salesman problems. In the present systems, the effective relaxation dynamics and the resulting good optimization performance are not only dependent

M. Hasegawa

2008-01-01

62

Design of self-refocused pulses under short relaxation times  

Microsoft Academic Search

The effect of using self-refocused RF pulses of comparable duration to relaxation times is studied in detail using numerical simulation. Transverse magnetization decay caused by short T2 and longitudinal component distortion due to short T1 are consistent with other studies. In order to design new pulses to combat short T1 and T2 the relaxation terms are directly inserted into the

Bashar Issa

2009-01-01

63

Calorimetric study of the conformational relaxation times in polystyrene  

Microsoft Academic Search

The temperature dependence of the relaxation times of the structural relaxation process of polystyrene is determined by temperature-modulated\\u000a differential scanning calorimetry (TMDSC) and by conventional differential scanning calorimetry (DSC) in the latter by modelling\\u000a the experimental heat capacity curves measured in heating scans after different thermal histories. The good agreement between\\u000a both measuring techniques in the temperature interval just above

M. Salmerón; C. Torregrosa; A. Vidaurre; J. M. Meseguer Dueñas; M. Monleón Pradas; J. L. Gómez Ribelles

1999-01-01

64

Real-time relaxation and kinetics in hot scalar QED: Landau damping  

SciTech Connect

The real time evolution of non-equilibrium expectation values with soft length scales {approximately}k{sup {minus}1}{gt}(eT){sup {minus}1} is solved in hot scalar electrodynamics, with a view towards understanding relaxational phenomena in the QGP and the electroweak plasma. We find that the gauge invariant non-equilibrium expectation values relax via {ital power laws} to asymptotic amplitudes that are determined by the quasiparticle poles. The long time relaxational dynamics and relevant time scales are determined by the behavior of the retarded self-energy not at the small frequencies, but at the Landau damping thresholds. This explains the presence of power laws and not of exponential decay. In the process we rederive the HTL effective action using {ital non-equilibrium} field theory. Furthermore we obtain the influence functional, the Langevin equation and the fluctuation-dissipation theorem for the soft modes, identifying the correlators that emerge in the classical limit. We show that a Markovian approximation fails to describe the dynamics {ital both} at short and long times. We find that the distribution function for soft quasiparticles relaxes with a power law through Landau damping. We also introduce a novel kinetic approach that goes beyond the standard Boltzmann equation by incorporating off-shell processes and find that the distribution function for soft quasiparticles relaxes with a power law through Landau damping. We find an unusual dressing dynamics of bare particles and anomalous (logarithmic) relaxation of hard quasiparticles. {copyright} {ital 1998} {ital The American Physical Society}

Boyanovsky, D. [Department of Physics and Astronomy, University of Pittsburgh, Pittsburgh , Pennsylvania 15260 (United States); de Vega, H.J. [LPTHE, Universite Pierre et Marie Curie (Paris VI) et Denis Diderot (Paris VII), Tour 16, 1er. etage, 4, Place Jussieu, 75252 Paris, Cedex 05 (France); Holman, R.; Kumar, S.P. [Department of Physics, Carnegie-Mellon University, Pittsburgh, Pennsylvania 15213 (United States); Pisarski, R.D. [Department of Physics, Brookhaven National Laboratory, Upton, New York 11973 (United States)

1998-12-01

65

Time scales in fragmentation  

SciTech Connect

The problem of fragmentation of excited finite systems is explored in the frame of classical molecular dynamics experiments of two-dimensional Lennard-Jones drops. The main objective of this work is to get information about the relative value of the relevant characteristic time scales (CTS) for this kind of process. We investigate the CTS for fragment formation, the stabilization of the radial flux, and the internal {open_quotes}temperature.{close_quotes} It is found that the asymptotic fragments are realized early in phase space, when the system is still dense, by the time the radial flux attains its asymptotic value. It is also shown that the temperature of the system during the breakup is quite homogenous with respect to the expected profile if local thermal equilibration takes place. Special emphasis is put on the investigation of the time scale of stabilization of the statistical properties of the mass spectrum, which is related to the kind of information carried by the asymptotic fragments. {copyright} {ital 1997} {ital The American Physical Society}

Strachan, A.; Dorso, C.O. [Departamento de Fisica, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Pabellon I, Ciudad Universitaria, Nunez 1428, Buenos Aires (Argentina)

1997-02-01

66

Evaluation of brain edema using magnetic resonance proton relaxation times  

SciTech Connect

Experimental and clinical studies on the evaluation of water content in cases of brain edema were performed in vivo, using MR proton relaxation times (longitudinal relaxation time, T1; transverse relaxation time, T2). Brain edema was produced in the white matter of cats by the direct infusion method. The correlations between proton relaxation times obtained from MR images and the water content of white matter were studied both in autoserum-infused cats and in saline-infused cats. The correlations between T1 as well as T2 and the water content in human vasogenic brain edema were also examined and compared with the data obtained from the serum group. T1 and T2 showed good correlations with the water content of white matter not only in the experimental animals but also in the clinical cases. The quality of the edema fluid did not influence relaxation time and T1 seemed to represent almost solely the water content of the tissue. T2, however, was affected by the nature of existence of water and was more sensitive than T1 in detecting extravasated edema fluid. It seems feasible therefore to evaluate the water content of brain edema on the basis of T1 values.

Fu, Y.; Tanaka, K.; Nishimura, S. (Baba Memorial Hospital, Osaka (Japan))

1990-01-01

67

Electron spin relaxation times of phosphorus donors in silicon  

Microsoft Academic Search

Pulsed electron paramagnetic resonance measurements of donor electron spins\\u000ain natural phosphorus-doped silicon (Si:P) and isotopically-purified 28Si:P\\u000ashow a strongly temperature-dependent longitudinal relaxation time, T1, due to\\u000aan Orbach process with DeltaE = 126 K. The 2-pulse echo decay is exponential in\\u000a28Si:P, with the transverse relaxation (decoherence) time, T2, controlled by\\u000athe Orbach process above ~12 K and by

A. M. Tyryshkin; S. A. Lyon; A. V. Astashkin; A. M. Raitsimring

2003-01-01

68

Use of relaxation time as a marker for arterial distensibility.  

PubMed

Arterial stiffening is associated with a number of known cardiovascular risk factors, including advancing age, increased systolic blood pressure (SBP), diabetes, hypertension, heart failure, myocardial infarction, and obesity. Many methodologies, both invasive and noninvasive, have been applied to the assessment of the stiffening of large elastic arteries in vivo, but there is no economically and/or universally accepted means of screening patients for atherosclerosis. From preliminary studies, a novel parameter, arterial relaxation time, has been identified as a potential indicator for inferring the elasticity of arteries. Preliminary measurements of arterial relaxation time of six normotensive subjects are significantly less than measurements of four hypertensive subjects. PMID:19163440

Winchester, C C; Chou, N Y; Winchester, L W

2008-01-01

69

Similarity and scaling in creep and load relaxation of single-crystal halite (NaCl)  

Microsoft Academic Search

This work explores the physical basis for Hart's mechanical equation of state in high-temperature plasticity. The experiments seek to identify a possible microstructural basis for the “hardness” parameters associated with load relaxation curves. The experiments also seek to examine the microstructural basis for scaling in load relaxation data and to explore the relationship between creep and load relaxation. Constant stress

Donald S. Stone; Thawatchai Plookphol; Reid F. Cooper

2004-01-01

70

Similarity and scaling in creep and load relaxation of single-crystal halite (NaCl)  

Microsoft Academic Search

This work explores the physical basis for Hart's mechanical equation of state in high-temperature plasticity. The experiments seek to identify a possible microstructural basis for the ``hardness'' parameters associated with load relaxation curves. The experiments also seek to examine the microstructural basis for scaling in load relaxation data and to explore the relationship between creep and load relaxation. Constant stress

Donald S. Stone; Thawatchai Plookphol; Reid F. Cooper

2004-01-01

71

Scaling of ?-relaxation in the equilibrium liquid state of sorbitol  

Microsoft Academic Search

The Johari–Goldstein dielectric ?-relaxation has been studied in the molecular liquid, sorbitol. In the narrow temperature interval in which ?- and ?-relaxation are separated (still being in the equilibrium liquid state), it is shown that ?-relaxation has a temperature-dependence of loss peak frequency and magnitude, which differs from what is found in the glassy state. Within experimental error the ?-peak

Niels Boye Olsen

1998-01-01

72

Distribution of relaxation times in ?-phase polyvinylidene fluoride  

Microsoft Academic Search

In this paper, a recently developed numerical method to analyze dielectric-spectroscopy data is applied to ?-phase polyvinylidene fluoride (PVDF). The numerical procedure is non-parametric and does not contain any of the extensively used empirical formulas mentioned in the literature. The method basically recovers the unknown distribution of relaxation times of the generalized dielectric function representation by simultaneous application of the

Enis Tuncer; Michael Wegener; Reimund Gerhard-Multhaupt

2005-01-01

73

Multiple-Relaxation-Time Lattice Boltzmann Models in 3D.  

National Technical Information Service (NTIS)

This article provides a concise exposition of the multiple-relaxation-time lattice Boltzmann equation, with examples of fifteen-velocity and nineteen-velocity models in three dimensions. Simulation of a diagonally lid-driven cavity flow in three dimension...

D. dHumieres I. Ginzburg L. S. Luo M. Krafczyk P. Lallemand

2002-01-01

74

Relaxation time distributions for an anomalously diffusing particle  

NASA Astrophysics Data System (ADS)

As well known, the generalized Langevin equation with a memory kernel decreasing at large times as an inverse power law of time describes the motion of an anomalously diffusing particle. Here, we focus attention on some new aspects of the dynamics, successively considering the memory kernel, the particle's mean velocity, and the scattering function. All these quantities are studied from a unique angle, namely, the discussion of the possible existence of a distribution of relaxation times characterizing their time decay. Although a very popular concept, a relaxation time distribution cannot be associated with any time-decreasing quantity (from a mathematical point of view, the decay has to be described by a completely monotonic function).Technically, we use a memory kernel decaying as a Mittag-Leffler function (the Mittag-Leffler functions interpolate between stretched or compressed exponential behaviour at short times and inverse power law behaviour at large times). We show that, in the case of a subdiffusive motion, relaxation time distributions can be defined for the memory kernel and for the scattering function, but not for the particle's mean velocity. The situation is opposite in the superdiffusive case.

Pottier, Noëlle

2011-08-01

75

A Geologic Time Scale 2004  

Microsoft Academic Search

A successor to A Geologic Time Scale 1989 (Cambridge, 1990), this volume introduces the theory and methodology behind the construction of the new time scale, before presenting the scale itself in extensive detail. An international team of over forty stratigraphic experts develops the most up-to-date international stratigraphic framework for the Precambrian and Phanerozoic eras. A large wallchart summarizing the time

Felix M. Gradstein; James G. Ogg; Alan G. Smith

2005-01-01

76

Length-scale dependent relaxation shear modulus and viscoelastic hydrodynamic interactions in polymer liquids  

NASA Astrophysics Data System (ADS)

A quantitative theory of hydrodynamic interactions in unentangled polymer melts and concentrated solutions is presented. The study is focussed on the pre-Rouse transient time regimes (t < ?R, the Rouse relaxation time) where the hydrodynamic response is governed mainly by the viscoelastic effects. It is shown that transient viscoelastic hydrodynamic interactions are not suppressed (screened) at large distances and are virtually independent of polymer molecular mass. A number of transient regimes of unusual and qualitatively different behavior of isotropic and anisotropic hydrodynamic response functions are elucidated. The regimes are characterized in terms of two main length-scale dependent characteristic times: momentum spreading time ?i ~ r4/3 and viscoelastic time ?* ~ r4. It is shown that for t > ?i the viscoelastic hydrodynamic interactions can be described in terms of the time or length scale dependent effective viscosity which, for t < ?R and/or for r < Rcoil, turns out to be much lower than the macroscopic ``polymer'' viscosity ?m. The theory also involves a quantitative analysis of the length-scale dependent stress relaxation in polymer melts. The general predictions for hydrodynamic interactions in thermostated systems with Langevin friction are obtained as well.

Semenov, A. N.; Farago, J.; Meyer, H.

2012-06-01

77

Lyapunov instability versus relaxation time in two coupled oscillators  

SciTech Connect

We consider the relation between relaxation time and the largest Lyapunov exponent in a system of two coupled oscillators, one of them being harmonic. It has been found that in a rather broad region of parameter space, contrary to the common expectation, both Lyapunov exponent and relaxation time increase as a function of the total energy. This effect is attributed to the fact that above a critical value of the total energy, although the Lyapunov exponent increases, Kolmogorov-Arnold-Moser tori appear and the chaotic fraction of phase space decreases. We examine the required conditions and demonstrate the key role of the dispersion relation for this behavior to occur. This study is useful, among other things, in the understanding of the damping of nuclear giant resonances.

Papachristou, P. K.; Mavrommatis, E.; Diakonos, F. K. [Department of Physics, University of Athens, GR-15771, Athens (Greece); Constantoudis, V. [Institute of Microelectronics (IMEL), NCSR 'Demokritos', P. O. Box 60228, Aghia Paraskevi, Attiki, 15310 (Greece); Physics Department, National Technical University, Athens (Greece); Wambach, J. [Institut fuer Kernphysik, Technische Universitaet Darmstadt, Schlossgartenstr. 9, D-64289 Darmstadt (Germany)

2006-01-15

78

Distribution of relaxation times in alpha-phase polyvinylidene fluoride  

Microsoft Academic Search

In this paper, a recently developed numerical method to analyze dielectric-spectroscopy data is applied to $\\\\alpha$-phase polyvinylidene fluoride (PVDF). The numerical procedure is non-parametric and does not contain any of the extensively used empirical formulas mentioned in the literature. The method basically recovers the unknown distribution of relaxation times of the generalized dielectric function representation by simultaneous application of the

E. Tuncer; M. Wegener; R. Gerhardmulthaupt

2005-01-01

79

Ultrafast time-resolved broadband fluorescence studies of the benzene-tetracyanoethylene complex: solvation, vibrational relaxation, and charge recombination dynamics.  

PubMed

The charge-transfer (CT) state relaxation dynamics of the benzene-tetracyanoethylene (BZ-TCNE) complex was studied with broadband ultrafast time-resolved fluorescence spectroscopy implemented by optical Kerr gating in three solvents of different polarities. The CT state of the BZ-TCNE complex is reached via femtosecond laser excitation, and the subsequent temporal evolutions of the fluorescence spectra were measured. Analyses of various time-dependent spectral properties revealed rapid relaxations along solvent and vibrational coordinates in competition with charge recombination (CR). By comparing the results in solvents of different polarities, we partially separated solvation and vibrational relaxation dynamics and explored the solvent-dependent CR dynamics. Time-dependent dynamic fluorescence Stokes shift (TDFSS) measurements unveiled the solvation and vibrational relaxation contributions to the observed spectral relaxation. The biphasic and slow time scales of the vibrational contributions identified in TDFSS suggested nonstatistical and hindered intramolecular vibrational-energy redistribution that can be attributed to the unique structural properties of EDA complexes. The slowest spectral relaxation of 10-15 ps identified in TDFSS was ascribed to relaxation of the BZ(+)-TCNE(-) intermolecular vibrations, which is equivalent to a structural relaxation from the initial Franck-Condon configuration to the equilibrium CT-state structure. The time scales of vibrational relaxation indicate that a fraction of the CT-state population undergoes CR reactions before complete vibrational/structural equilibrium is achieved. In carbon tetrachloride, a nonexponential temporal profile was observed and attributed to vibrational nonequilibrium CR. In dichloromethane, polar solvation greatly accelerates CR reactions, and a slower reaction-field-induced structural relaxation gives rise to a pronounced biexponential decay. The equilibrium CR time constants of the BZ-TCNE CT state are 29 ps, 150 ps, and 68 ps in dichloromethane, carbon tetrachloride, and cyclohexane, respectively. PMID:23865400

Chiu, Chih-Chung; Hung, Chih-Chang; Chen, Chien-Lin; Cheng, Po-Yuan

2013-08-07

80

Length-Scale-Dependent Relaxation in Colloidal Gels  

SciTech Connect

We use molecular dynamics computer simulations to investigate the relaxation dynamics of a simple model for a colloidal gel at a low volume fraction. We find that due to the presence of the open spanning network this dynamics shows at low temperature a nontrivial dependence on the wave vector which is very different from the one observed in dense glass-forming liquids. At high wave vectors the relaxation is due to the fast cooperative motion of the branches of the gel network, whereas at low wave vectors the overall rearrangements of the heterogeneous structure produce the relaxation process.

Gado, Emanuela Del [Dipartimento di Scienze Fisiche, Universita di Napoli 'Federico II', 80125 Naples (Italy); Kob, Walter [Laboratoire des Colloiedes, Verres et Nanomateriaux, UMR5587 CNRS, Universite Montpellier 2, 34095 Montpellier (France)

2007-01-12

81

Transient photovoltage and dielectric relaxation time in porous silicon  

NASA Astrophysics Data System (ADS)

Transient photovoltage (PV) measurements have been carried out on free-standing porous silicon of different porosity. For porous silicon of low porosity, fast charge-carrier separation takes place in the surface space-charge region. A retarded component arises in the PV transients due to limitation of the separation of charge carriers by interparticle transport. For nanoporous silicon, the fast component is absent and the PV transients are retarded strongly in time. The maximum of the retarded PV transients is correlated with the dielectric relaxation time which was obtained by using dc conductivity measurements. This opens opportunities to a contactless electrical characterization of porous semiconductors and its application.

Duzhko, V.; Koch, F.; Dittrich, Th.

2002-06-01

82

Remarks concerning bulk viscosity of hadron matter in relaxation time ansatz  

NASA Astrophysics Data System (ADS)

The bulk viscosity is calculated for hadron matter produced in heavy-ion collisions, being described in the relaxation time approximation within the relativistic mean-field-based model with scaled hadron masses and couplings. We show how different approximations used in the literature affect the result. Numerical evaluations of the bulk viscosity with three considered models deviate not much from each other confirming earlier results.

Khvorostukhin, A. S.; Toneev, V. D.; Voskresensky, D. N.

2013-10-01

83

Measurement of Relaxation Times of Concentration Fluctuations by the Electric Field on Critical Opalescence.  

National Technical Information Service (NTIS)

Measurements of the electric field effect on the critical opalescence were extended to a study of the phenomena in the scattered light. Relaxation times were obtained which when integrated over all scattering angles can be related to the relaxation times ...

C. C. Gravatt

1967-01-01

84

Relaxivity of Gd-based contrast agents on X nuclei with long intrinsic relaxation times in aqueous solutions.  

PubMed

The relaxivity of commercially available gadolinium (Gd)-based contrast agents was studied for X-nuclei resonances with long intrinsic relaxation times ranging from 6 s to several hundred seconds. Omniscan in pure 13C formic acid had a relaxivity of 2.9 mM(-1) s(-1), whereas its relaxivity on glutamate C1 and C5 in aqueous solution was approximately 0.5 mM(-1) s(-1). Both relaxivities allow the preparation of solutions with a predetermined short T1 and suggest that in vitro substantial sensitivity gains in their measurement can be achieved. 6Li has a long intrinsic relaxation time, on the order of several minutes, which was strongly affected by the contrast agents. Relaxivity ranged from approximately 0.1 mM(-1) s(-1) for Omniscan to 0.3 for Magnevist, whereas the relaxivity of Gd-DOTP was at 11 mM(-1) s(-1), which is two orders of magnitude higher. Overall, these experiments suggest that the presence of 0.1- to 10-microM contrast agents should be detectable, provided sufficient sensitivity is available, such as that afforded by hyperpolarization, recently introduced to in vivo imaging. PMID:17448617

van Heeswijk, Ruud B; Laus, Sabrina; Morgenthaler, Florence D; Gruetter, Rolf

2007-04-19

85

Relaxivity of Gd-based contrast agents on X nuclei with long intrinsic relaxation times in aqueous solutions  

PubMed Central

The relaxivity of commercially available gadolinium-based contrast agents was studied for X-nuclei resonances with long intrinsic relaxation times ranging between 6 and several hundred seconds. Omniscan in pure 13C formic acid had a relaxivity of 2.9 mM-1 s-1, whereas its relaxivity on glutamate C1 and C5 in aqueous solution was ?0.5 mM-1 s-1. Both relaxivities allow the preparation of solutions with a predetermined short T1 suggest that in vitro substantial sensitivity gains in their measurement can be achieved. 6Li has a long intrinsic relaxation time, on the order of several minutes, which was strongly affected by the contrast agents. Relaxivity ranged from ?0.1 mM-1 s-1 for Omniscan to 0.3 for Magnevist, whereas the relaxivity of Gd-DOTP was at 11 mM-1 s-1 two orders of magnitude higher. Overall these experiments suggest that the presence of 0.1-10 ?M contrast agents should be detectable, provided sufficient sensitivity is available, such as that afforded by hyperpolarization, recently introduced to in vivo imaging.

van Heeswijk, Ruud B.; Laus, Sabrina; Morgenthaler, Florence D.; Gruetter, Rolf

2007-01-01

86

Relaxation time for electron-dislocation scattering for noble and polyvalent metals  

Microsoft Academic Search

An analysis is presented of the relaxation time for electron-dislocation scattering for the polyvalent and noble metals. It is shown that for these metals the relaxation time is significantly anisotropic, i.e., its magnitude varies markedly with position over the Fermi surface. This anisotropy of the relaxation time results from the nonsphericity of the Fermi surface for these metals and from

A. Bergmann; M. Kaveh; N. Wiser

1981-01-01

87

Fluorescence Lifetimes: Effect of Precision of Relaxation Times from Fluorescence Depolarization Data  

Microsoft Academic Search

The fluorescence lifetime ? enters into the Perrin-Weber equation used to determine rotational relaxation times of proteins by the steady-state depolarization method. If is either too short or too long, the relaxation time cannot be measured with precision. With reasonable assumptions as to photometric precision, it has been possible to compute the precision of relaxation time assays for different lifetime:relaxation

Raymond F. Chen

1982-01-01

88

Meso-scale model for structural relaxation in the glass transition region  

NASA Astrophysics Data System (ADS)

Nonlinear volume relaxation of amorphous materials was demonstrated in the classic series of experiments by Kovacs (1963) and any acceptable theory of structural relaxation must be able to describe this data set. It is generally believed that the phenomenological models of the KAHR type achieve at least semi-quantitative fit to the Kovacs data if at the expense of parameters lacking physical significance. In fact, two crucial pieces of information have been omitted. First, the temperature dependence of the relaxation times for equilibrium material at atmospheric pressure must fit the experimental data (WLF). If this is enforced in the phenomenological models, then the fit to the Kovacs data becomes disastrous. Second, a viable model should be able to describe experimental data at elevated pressures as well. If experimentally observed pressure dependence of Tg is employed in all the traditional models, then the prediction of the Kovacs data cannot be achieved. We present novel meso-scale model which simultaneously predicts Kovacs data, temperature dependence of log(a) function, and the pressure dependence of Tg.

Medvedev, Grisha; Caruthers, James

2001-03-01

89

Understanding scale invariance in a minimal model of complex relaxation phenomena  

NASA Astrophysics Data System (ADS)

We report on the computer study of a lattice system that relaxes from a metastable state. Under appropriate nonequilibrium randomness, relaxation occurs by avalanches, i.e., the model evolution is discontinuous and displays many scales in a way that closely resembles the relaxation in a large number of complex systems in nature. Such apparent scale invariance simply results in the model from summing over many exponential relaxations, each with a scale which is determined by the curvature of the domain wall at which the avalanche originates. The claim that scale invariance in a nonequilibrium setting is to be associated with criticality is therefore not supported. Some hints that may help in checking this experimentally are discussed.

Hurtado, P. I.; Marro, J.; Garrido, P. L.

2006-02-01

90

Bayesian relaxed clock estimation of divergence times in foraminifera.  

PubMed

Accurate and precise estimation of divergence times during the Neo-Proterozoic is necessary to understand the speciation dynamic of early Eukaryotes. However such deep divergences are difficult to date, as the molecular clock is seriously violated. Recent improvements in Bayesian molecular dating techniques allow the relaxation of the molecular clock hypothesis as well as incorporation of multiple and flexible fossil calibrations. Divergence times can then be estimated even when the evolutionary rate varies among lineages and even when the fossil calibrations involve substantial uncertainties. In this paper, we used a Bayesian method to estimate divergence times in Foraminifera, a group of unicellular eukaryotes, known for their excellent fossil record but also for the high evolutionary rates of their genomes. Based on multigene data we reconstructed the phylogeny of Foraminifera and dated their origin and the major radiation events. Our estimates suggest that Foraminifera emerged during the Cryogenian (650-920 Ma, Neo-Proterozoic), with a mean time around 770 Ma, about 220 Myr before the first appearance of reliable foraminiferal fossils in sediments (545 Ma). Most dates are in agreement with the fossil record, but in general our results suggest earlier origins of foraminiferal orders. We found that the posterior time estimates were robust to specifications of the prior. Our results highlight inter-species variations of evolutionary rates in Foraminifera. Their effect was partially overcome by using the partitioned Bayesian analysis to accommodate rate heterogeneity among data partitions and using the relaxed molecular clock to account for changing evolutionary rates. However, more coding genes appear necessary to obtain more precise estimates of divergence times and to resolve the conflicts between fossil and molecular date estimates. PMID:21723398

Groussin, Mathieu; Pawlowski, Jan; Yang, Ziheng

2011-06-23

91

Theory of long-scale cooperative relaxation of polymer networks. Hydrodynamic interaction effects  

Microsoft Academic Search

The theory of relaxation properties of polymer networks is considered for specific long-scale cooperative motions of network chains, which have characteristic scales greater than chain dimensions between cross-links. Long-range hydrodynamic interactions between the incompressible effective viscous medium and the network moving with respect to this medium are taken into account. Two types of relaxation spectra arise. The first type of

Yuli Ya. Gotlib; Andrew A. Gurtovenko

2000-01-01

92

Resolving distribution of relaxation times in poly(propylene glycol) on the crossover region  

NASA Astrophysics Data System (ADS)

In this article, a recently developed numerical technique [E. Tuncer and S. M. Guba?ski, IEEE Trans. Dielectr. Electr. Insul. 8, 310 (2001)] is applied to poly(propylene glycol) (PPG) complex dielectric data to extract more information about the molecular relaxation processes. The method is based on a constrained-least-squares (C-LSQ) data fitting procedure together with the Monte Carlo method. We preselect the number of relaxation times with no a priori physical assumption, and use the Debye single relaxation as ``kernel,'' then the obtained weighting factors at each MC step from the C-LSQ method builds up a relaxation time spectrum. When the analysis is repeated for data at different temperatures a relaxation image is created. The obtained relaxation are analyzed using the Lorentz (Cauchy) distribution, which is a special form of the Lévy statistics. In the present report the ? and ? relaxations are resolved for the PPG. A comparison of the relaxations to those earlier reported in the literature indicate that the presented method provides additional information compared to methods based on empirical formulas. The distribution of relaxation times analysis is especially useful to probe the crossover region where the ? and ? relaxations merge and the results show that the relaxation after the crossover region at higher temperatures is Arrhenius-type as the ? relaxation. Moreover, this relaxation is more likely to be the continuation of the ? relaxation, but with a different activation energy.

Tuncer, Enis; Furlani, Maurizio; Mellander, Bengt-Erik

2004-03-01

93

Stability of Pulsar Time Scale.  

NASA Astrophysics Data System (ADS)

It is well known, that stability of pulsar period in the barycenter of Solar system depends on different effects. The stability is determined by both physical conditions in pulsar and processes along the way of signal propagation which affect the pulse time of arrival (TOA). In the presentation it will be discussed stability of pulsar time scale based on the long term millisecond pulsar timing. It will be considered an influence of the propagation conditions along the pulsar signal way. In this presentation it will be considered an influence of microlensing to TOA, as well. This effect can put a natural limit for pulsar time scale stability.

Sazhin, M. V.; Pshirkov, M. S.

2006-08-01

94

Longitudinal complex dielectric polarizability and relaxation times of polar molecules in a biaxial liquid crystal phase  

NASA Astrophysics Data System (ADS)

The longitudinal relaxation time and the complex dielectric polarizability of rod-like molecules with dipole moment parallel to the long axis in a biaxial nematic liquid crystal are calculated using as model the rotational Brownian motion in a mean field potential so reducing the problem to a set of linear differential-recurrence relations for the appropriate equilibrium orientational correlation functions. The solution of this set is obtained by matrix continued fractions. Simple analytic equations (based on the exponential separation of the time scales of the intrawell and overbarrier (interwell) relaxation processes), allowing one to understand the qualitative behavior of the system and accurately predicting the longitudinal complex polarizability for a wide range of the barrier height and anisotropy parameters, are proposed.

Kalmykov, Yuri; Coffey, William; Ouari, Bachir; Titov, Sergey

2006-03-01

95

Feasibility Study of Real-Time Scheduling Using the Lagrangean Relaxation Method Under an APS Environment  

NASA Astrophysics Data System (ADS)

Advanced Planning and Scheduling (APS) has been widely recognized as a promising method for solving real production planning and scheduling problems. Based on the proposal of a real-time job shop scheduling mechanism under an APS environment, which adopts the Lagrangean relaxation method as the optimization logic, the present paper describes a feasibility study of this mechanism by evaluating its calculation speed and re-scheduling quality. Numerical experiments have been carried out for various models having different scales, as well as different densities and strengths of random events, such as the arrival of new jobs or changes to the due dates for existing jobs. The results of experiments show that the proposed scheduling mechanism has the potential to satisfy the real-time scheduling requirements, not only in terms of calculation speed and solution quality, but also with respect to predictability of the calculation load. Finally, an improvement to the Lagrangean relaxation method is proposed to improve re-scheduling quality.

Shin, Kaikou; Kuroda, Mitsuru; Natsuyama, Kouichi

96

Relativistic dissipative hydrodynamics from kinetic theory with relaxation-time approximation  

NASA Astrophysics Data System (ADS)

Starting from the Boltzmann equation with the relaxation time approximation for the collision term and using a Chapman-Enskog-like expansion for the distribution function close to equilibrium, we derive hydrodynamic evolution equations for the dissipative quantities directly from their definition. Although the form of the equations is identical to those obtained in traditional Israel-Stewart approaches employing Grad's 14-moment approximation and the second moment of the Boltzmann equation, the coefficients obtained are different. In the case of a one-dimensional scaling expansion, we demonstrate that our results are in better agreement with a numerical solution of the Boltzmann equation as compared to Israel-Stewart results. We also show that including approximate higher-order corrections in viscous evolution significantly improves this agreement, thus justifying the relaxation time approximation for the collision term.

Jaiswal, Amaresh

2013-05-01

97

Communication: Correlation of the instantaneous and the intermediate-time elasticity with the structural relaxation in glassforming systems  

NASA Astrophysics Data System (ADS)

The elastic models of the glass transition relate the increasing solidity of the glassforming systems with the huge slowing down of the structural relaxation and the viscous flow. The solidity is quantified in terms of the instantaneous shear modulus G?, i.e., the immediate response to a step change in the strain. By molecular-dynamics simulations of a model polymer system, one shows the virtual absence of correlations between the instantaneous elasticity and the structural relaxation. Instead, a well-defined scaling is evidenced by considering the elastic response observed at intermediate times after the initial fast stress relaxation. The scaling regime ranges from sluggish states with virtually pure elastic response on the picosecond time scale up to high-mobility states where fast restructuring events are more apparent.

Puosi, F.; Leporini, D.

2012-01-01

98

Stability of Pulsar Time Scale  

Microsoft Academic Search

It is well known, that stability of pulsar period in the barycenter of Solar system depends on different effects. The stability is determined by both physical conditions in pulsar and processes along the way of signal propagation which affect the pulse time of arrival (TOA). In the presentation it will be discussed stability of pulsar time scale based on the

M. V. Sazhin; M. S. Pshirkov

2006-01-01

99

Magnetic resonance imaging (MRI) and relaxation time mapping of concrete  

NASA Astrophysics Data System (ADS)

The use of Magnetic Resonance Imaging (MRI) of water in concrete is presented. This thesis will approach the problem of MR imaging of concrete by attempting to design new methods, suited to concrete materials, rather than attempting to force the material to suit the method. A number of techniques were developed, which allow the spatial observation of water in concrete in up to three dimensions, and permits the determination of space resolved moisture content, as well as local NMR relaxation times. These methods are all based on the Single-Point Imaging (SPI) method. The development of these new methods will be described, and the techniques validated using phantom studies. The study of one-dimensional moisture transport in drying concrete was performed using SPI. This work examined the effect of initial mixture proportions and hydration time on the drying behaviour of concrete, over a period of three months. Studies of drying concrete were also performed using spatial mapping of the spin-lattice (T1) and effective spin-spin (T2*) relaxation times, thereby permitting the observation of changes in the water occupied pore surface-to-volume ratio (S/V) as a function of drying. Results of this work demonstrated changes in the S/V due to drying, hydration and drying induced microcracking. Three-dimensional MRI of concrete was performed using SPRITE (Single-Point Ramped Imaging with T1 Enhancement) and turboSPI (turbo Single Point Imaging). While SPRITE allows for weighting of MR images using T 1 and T2*, turboSPI allows T2 weighting of the resulting images. Using relaxation weighting it was shown to be possible to discriminate between water contained within a hydrated cement matrix, and water in highly porous aggregates, used to produce low-density concrete. Three dimensional experiments performed using SPRITE and turboSPI examined the role of self-dessication, drying, initial aggregate saturation and initial mixture conditions on the transport of moisture between porous aggregates and the hydrated matrix. The results demonstrate that water is both added and removed from the aggregates, depending upon the physical conditions. The images also appear to show an influx of cement products into cracks in the solid aggregate. (Abstract shortened by UMI.)

Beyea, Steven Donald

2001-07-01

100

Two typical time scales of the piston effect  

Microsoft Academic Search

The existence of a fourth mode of heat transfer near the critical point, named the piston effect, has been known for more than a decade. The typical time scale of temperature relaxation due to this effect was first predicted by Onuki [Phys. Rev A 41, 2256 (1990)], and this author's formula has been extensively used since then to predict the

Pierre Carlès; Kokou Dadzie

2005-01-01

101

Deep Time: The Geologic Time Scale  

NSDL National Science Digital Library

This page examines the issues involved in teaching students about the geologic time scale. There are suggestions for tackling troublesome issues in class as well as activities that can be used to clarify how geoscientists look at deep time. Five main concepts with which students struggle when thinking about Deep Time are addressed here: imagining or comprehending big numbers; the difference between relative and numerical age; the concept of "timescales"; the ways we know about the age of the Earth and other materials; and resolving perceived issues with religious beliefs.

2007-01-01

102

Developing an IGS time scale.  

PubMed

Currently, the International GPS Service (IGS) provides a set of clock products for both satellites and tracking receivers, tabulated at 5-min intervals. These products allow users to determine consistent coordinates and clock values for an isolated GPS receiver with an internal accuracy at the few-cm level. However, because the underlying time scale for the IGS combined clocks is based on a linear alignment to broadcast GPS Time for each day separately, the day-to-day stability of this reference is poor. We show the results of a new filter package written to automate the production of an integrated IGS frequency scale based on a dynamically weighted ensemble of the included frequency standards. The new scale is loosely steered to GPS Time. PMID:12839170

Senior, Ken; Koppang, Paul; Ray, Jim

2003-06-01

103

Growth strains and stress relaxation in alumina scales during high temperature oxidation  

SciTech Connect

A novel X-ray technique was used, exploiting synchrotron radiation at the Advanced Photon Source at Argonne National Laboratory, to investigate the growth stresses in {alpha}-Al{sub 2}O{sub 3}. In-situ measurements of Debye-Scherrer diffraction patterns from the scale were recorded during oxidation and cooling, and the elliptical distortion of the diffraction rings was analyzed to yield the in-plane strain. Fe-28Al, Fe-40Al, Fe-40Al-0.2Hf, Fe-20Cr-10Al and Ni-50Al (at. %) were studied. Data were acquired in air at temperatures between 950-1100 C and during cool down. In all cases, the steady stage growth strain was relatively low (<0.1%) and was either tensile or compressive depending on the alloy. A higher tensile strain often existed during the initial oxidation period when transition alumina was present. Thermal stresses imposed on NiAl by reducing the sample temperature to 950 C for a period of time showed noticeable stress relaxation by creep. Different degrees of relaxation were also found during cooling depending on alloy composition and scale microstructure. On all Fe-based alloys, the first formed {alpha}-Al{sub 2}O{sub 3} was highly textured with the degree of texture decreasing with further oxidation. The relationships between stress development, scale wrinkling, oxide phase changes, and the effect of reactive element addition on growth stresses are discussed. Results are compared with other reports of growth stresses in Al{sub 2}O{sub 3} scales.

Hou, P.Y.; Paulikas, A.P.; Veal, B.W.

2004-03-23

104

Similarity and scaling in creep and load relaxation of single-crystal halite (NaCl)  

NASA Astrophysics Data System (ADS)

This work explores the physical basis for Hart's mechanical equation of state in high-temperature plasticity. The experiments seek to identify a possible microstructural basis for the "hardness" parameters associated with load relaxation curves. The experiments also seek to examine the microstructural basis for scaling in load relaxation data and to explore the relationship between creep and load relaxation. Constant stress creep and load relaxation tests were conducted on [100] oriented single crystals of halite at 700°C and stresses between 0.6 and 3 MPa. Load relaxation tests were performed at 400°C up to a stress level of 13 MPa. After testing, specimens were sectioned, and dislocation densities and subgrain size distributions were measured. Results at 700°C reveal that distributions of subgrain size in crystals crept at different stress levels are similar to each other; that is, they have the same shape but different average subgrain sizes depending on stress level. Hardness curves obtained from load relaxation experiments at different levels of work hardening were found to correspond to different average subgrain size. Load relaxation data from 700°C and 400°C belong to a single-parameter family of curves, with hardness curves translating onto each other with a scaling slope m = 0.33 ± 0.05. Subgrain size distributions generated in creep are statistically identical to those from load relaxation. The hardness parameter, ?*, specified as the (apparent) high-strain rate limit of stress in the load relaxation data, is approximately 50Gb/DI, where G is the shear modulus, b is the Burgers vector, and DI is the mean intercept subgrain diameter. During creep under constant stress the subgrain size evolves until a steady value is approached. The experimental data lend credence to Hart's interpretation that load relaxation data represent (nearly) constant "structure" with subgrain size playing the role of the structural variable.

Stone, Donald S.; Plookphol, Thawatchai; Cooper, Reid F.

2004-12-01

105

The Concise Geologic Time Scale  

Microsoft Academic Search

This concise handbook presents a summary of Earth's history over the past 4.5 billion years as well as a brief overview of contemporaneous events on the Moon, Mars and Venus. The authors have been at the forefront of chronostratigraphic research and initiatives to create an international geologic time scale for many years, and the charts in this book present the

James G. Ogg; Gabi Ogg; Felix M. Gradstein

2008-01-01

106

Developing an IGS time scale  

Microsoft Academic Search

Currently, the International GPS Service (IGS) provides a set of clock products for both satellites and tracking receivers, tabulated at 5-min intervals. These products allow users to determine consistent coordinates and clock values for an isolated GPS receiver with an internal accuracy at the few-cm level. However, because the underlying time scale for the IGS combined clocks is based on

Ken Senior; Paul Koppang; Jim Ray

2003-01-01

107

Developing an IGS time scale  

Microsoft Academic Search

Currently, the International GPS Service (IGS) provides a set of clock products for both satellites and tracking receivers, tabulated at 5-minute intervals. These products provide users with sufficient information to determine consistent coordinates and clock values for an isolated GPS receiver with a precision at roughly the 5-cm level. However, because the underlying time scale for the IGS combined clocks

Ken Senior; Paul Koppang; Demetrios Matsakis

2001-01-01

108

The Offset-Saturation NMR Experiment for Measuring Spin Relaxation Times and Application to Chemical Exchange  

Microsoft Academic Search

NMR spin relaxation times T$\\\\sb1$ and T$\\\\sb2$ provide useful information regarding molecular motions and dynamics. The spin-spin relaxation time T$\\\\sb2$ in particular is important for measuring rates of chemical exchange, but has proven difficult to measure. A facile offset-saturation experiment for the simultaneous measurement of T$\\\\sb1$ and T$\\\\sb2$ NMR spin relaxation times is presented in this thesis. Errors determined as

Gregory Joseph Duns

1994-01-01

109

The offset-saturation NMR experiment for measuring spin relaxation times and application to chemical exchange  

Microsoft Academic Search

NMR spin relaxation times T$\\\\sb1$ and T$\\\\sb2$ provide useful information regarding molecular motions and dynamics. The spin-spin relaxation time T$\\\\sb2$ in particular is important for measuring rates of chemical exchange, but has proven difficult to measure. A facile offset-saturation experiment for the simultaneous measurement of T$\\\\sb1$ and T$\\\\sb2$ NMR spin relaxation times is presented in this thesis. Errors determined as

Gregory Joseph Duns

1994-01-01

110

Comparison of Viscosities from the Chapman -- Enskog & Relaxation Time Methods  

NASA Astrophysics Data System (ADS)

Viscosity to entropy ratios of hadrons and the quark-gluon system control the elliptic flow observed in relativistic heavy-ion collisions. Here we establish the extent to which results from different approximation schemes for shear viscosities agree (or disagree) by choosing classic examples in which the elastic scattering cross sections are specified. The two different approximation schemes chosen are the Chapman-Enskog [1] and the Relaxation Time [2] methods. These test studies are performed for (i) a hard sphere gas (?= a^2/(4?), where a is the hard sphere radius), (ii) the Maxwell gas (?= m?(?)/2g) with m being the mass of the particles, ?(?) is an arbitrary function of ?, and g is the relative velocity), (iii) chiral pions (?= 5s/(48?f^4?), where s is the squared c.m. energy and f? is the pion-decay constant, and (iv) massive pions (here ?(?) is taken from experiments). Where possible, analytical results are obtained in either the non-relativistic or extremely relativistic cases. [4pt] [1] M. Prakash, et. al, Physics Report 227, 6 (1993) 321 -- 366. [0pt] [2] P. Chakraborty and J. I. Kapusta, arxiv:1006.0257v1 (2010).

Wiranata, Anton; Prakash, Madappa

2010-10-01

111

Phonon relaxation times extracted from first principles thermal conductivity calculations  

NASA Astrophysics Data System (ADS)

The lattice thermal conductivity of semiconductors, ?L, is a key component in assessing a material's utility for thermoelectric applications. Calculations of ?L commonly employ phonon relaxation times, ?ph. Over the past few decades, a variety of mathematical forms have been used for these?phs to represent the phonon-phonon scattering [1], which dominates the behavior of ?L around and above room temperature. However, these forms have typically been obtained in a low frequency/low temperature approximation where umklapp scattering is weak and outside the thermal regime of interest for thermoelectrics. Recently we have developed a first principles approach that accurately calculates ?L using no adjustable parameters [2]. In this presentation, we use our ab initio results for Si, Ge and diamond to examine the accuracy of the different models for ?ph, and we identify alternative models. [1] See for example, M. Asen-Palmer et al., Phys. Rev. B 56, 9431 (1997), and references therein. [2] D. A. Broido, M. Malorny, G. Birner, N. Mingo and D. A. Stewart, Appl. Phys. Lett. 91, 231922 (2007).

Broido, D. A.; Ward, A.

2009-03-01

112

Time scales in cognitive neuroscience.  

PubMed

Cognitive neuroscience boils down to describing the ways in which cognitive function results from brain activity. In turn, brain activity shows complex fluctuations, with structure at many spatio-temporal scales. Exactly how cognitive function inherits the physical dimensions of neural activity, though, is highly non-trivial, and so are generally the corresponding dimensions of cognitive phenomena. As for any physical phenomenon, when studying cognitive function, the first conceptual step should be that of establishing its dimensions. Here, we provide a systematic presentation of the temporal aspects of task-related brain activity, from the smallest scale of the brain imaging technique's resolution, to the observation time of a given experiment, through the characteristic time scales of the process under study. We first review some standard assumptions on the temporal scales of cognitive function. In spite of their general use, these assumptions hold true to a high degree of approximation for many cognitive (viz. fast perceptual) processes, but have their limitations for other ones (e.g., thinking or reasoning). We define in a rigorous way the temporal quantifiers of cognition at all scales, and illustrate how they qualitatively vary as a function of the properties of the cognitive process under study. We propose that each phenomenon should be approached with its own set of theoretical, methodological and analytical tools. In particular, we show that when treating cognitive processes such as thinking or reasoning, complex properties of ongoing brain activity, which can be drastically simplified when considering fast (e.g., perceptual) processes, start playing a major role, and not only characterize the temporal properties of task-related brain activity, but also determine the conditions for proper observation of the phenomena. Finally, some implications on the design of experiments, data analyses, and the choice of recording parameters are discussed. PMID:23626578

Papo, David

2013-04-19

113

Time scales in cognitive neuroscience  

PubMed Central

Cognitive neuroscience boils down to describing the ways in which cognitive function results from brain activity. In turn, brain activity shows complex fluctuations, with structure at many spatio-temporal scales. Exactly how cognitive function inherits the physical dimensions of neural activity, though, is highly non-trivial, and so are generally the corresponding dimensions of cognitive phenomena. As for any physical phenomenon, when studying cognitive function, the first conceptual step should be that of establishing its dimensions. Here, we provide a systematic presentation of the temporal aspects of task-related brain activity, from the smallest scale of the brain imaging technique's resolution, to the observation time of a given experiment, through the characteristic time scales of the process under study. We first review some standard assumptions on the temporal scales of cognitive function. In spite of their general use, these assumptions hold true to a high degree of approximation for many cognitive (viz. fast perceptual) processes, but have their limitations for other ones (e.g., thinking or reasoning). We define in a rigorous way the temporal quantifiers of cognition at all scales, and illustrate how they qualitatively vary as a function of the properties of the cognitive process under study. We propose that each phenomenon should be approached with its own set of theoretical, methodological and analytical tools. In particular, we show that when treating cognitive processes such as thinking or reasoning, complex properties of ongoing brain activity, which can be drastically simplified when considering fast (e.g., perceptual) processes, start playing a major role, and not only characterize the temporal properties of task-related brain activity, but also determine the conditions for proper observation of the phenomena. Finally, some implications on the design of experiments, data analyses, and the choice of recording parameters are discussed.

Papo, David

2013-01-01

114

Relaxation time of terahertz magnons excited at ferromagnetic surfaces.  

PubMed

The temporal and spatial properties of terahertz magnons excited at ferromagnetic fcc Co(100) and bcc Fe(110) surfaces are investigated experimentally. The magnon lifetime is found to be a few tens of femtoseconds at low wave vectors, which reduces significantly as the wave vector approaches the Brillouin zone boundary. Surprisingly, the lifetime is very similar in both systems, in spite of the fact that the excitation energy in the Co(100) film is by a factor of two larger than in the Fe(110) film. The magnon wave packets propagate only a few nanometers within their lifetime. In addition to the fact that our results describe the damping mechanism in ultrafast time scales, they may provide a way to predict the ultimate time scale of magnetic switching in nanostructures. PMID:23002772

Zhang, Y; Chuang, T-H; Zakeri, Kh; Kirschner, J

2012-08-24

115

Can inertial electrostatic confinement work beyond the ion-ion collisional time scale.  

National Technical Information Service (NTIS)

Inertial electrostatic confinement systems are predicated on a non-equilibrium ion distribution function. Coulomb collisions between ions cause this distribution to relax to a Maxwellian on the ion-ion collisional time-scale. The power required to prevent...

W. M. Nevins

1995-01-01

116

Spectral and relaxation-time measurements in the HMBA CrV radical at 150 GHz  

Microsoft Academic Search

Spectral and relaxation characteristics of the HMBA CrV complex for polarized nuclear targets have been performed. Long time stability of the HMBA CrV complex in I.2 propylene glycol solution is investigated. Spin-lattice relaxation time and spectral diffusion rate versus concentration have been obtained.

A. A. Vertiy; Yu. P. Popkov; V. P. Shestopalov

1984-01-01

117

Spectral and relaxation-time measurements in the HMBA CrV radical at 150 GHz  

NASA Astrophysics Data System (ADS)

Spectral and relaxation characteristics of the HMBA CrV complex for polarized nuclear targets have been performed. Long time stability of the HMBA CrV complex in I.2 propylene glycol solution is investigated. Spin-lattice relaxation time and spectral diffusion rate versus concentration have been obtained.

Vertiy, A. A.; Popkov, Yu. P.; Shestopalov, V. P.

1984-02-01

118

Molecular dynamics study of the thermal and the density effects on the local and the large-scale motion of polymer melts: Scaling properties and dielectric relaxation  

NASA Astrophysics Data System (ADS)

Results from a molecular dynamics simulation of a melt of unentangled polymers are presented. The translational motion, the large-scale and the local reorientation processes of the chains, as well as their relations with the so-called ``normal'' and ``segmental'' dielectric relaxation modes are thoroughly investigated in wide temperature and pressure ranges. The thermodynamic states are well fitted by the phenomenological Tait equation of state. A global time-temperature-pressure superposition principle of both the translational and the rotational dynamics is evidenced. The scaling is more robust than the usual Rouse model. The latter provides insight but accurate comparison with the simulation calls for modifications to account for both the local chain stiffness and the nonexponential relaxation. The study addresses the issue whether the temperature or the density is a dominant control parameter of the dynamics or the two quantities give rise to comparable effects. By examining the ratio |??|/?P between the isochronic and isobaric expansivities, one finds that the temperature is dominant when the dynamics is fast. If the relaxation slows down, the fluctuations of the free volume increase their role and become comparable to those of the thermal energy. Detectable cross-correlation between the ``normal-mode'' and the ``segmental'' dielectric relaxations is found and contrasted with the usual assumption of independent modes.

Barbieri, A.; Campani, E.; Capaccioli, S.; Leporini, D.

2004-01-01

119

Universal bound on dynamical relaxation times and black-hole quasinormal ringing  

SciTech Connect

From information theory and thermodynamic considerations a universal bound on the relaxation time {tau} of a perturbed system is inferred, {tau}{>=}({Dirac_h}/2{pi})/{pi}T, where T is the system's temperature. We show that black holes comply with the bound; in fact they may actually saturate it. Thus, when judged by their relaxation properties, black holes are the most extreme objects in nature, having the maximum relaxation rate which is allowed by quantum theory.

Hod, Shahar [Ruppin Academic Center, Emeq Hefer 40250 (Israel) and Hadassah Institute, Jerusalem 91010 (Israel)

2007-03-15

120

Two typical time scales of the piston effect.  

PubMed

The existence of a fourth mode of heat transfer near the critical point, named the piston effect, has been known for more than a decade. The typical time scale of temperature relaxation due to this effect was first predicted by Onuki [Phys. Rev A 41, 2256 (1990)], and this author's formula has been extensively used since then to predict the thermal behavior of near-critical fluids. Recent studies, however, pointed out that the critical divergence of the bulk viscosity could have a strong influence on piston-effect-related processes. In this paper, we conduct a theoretical analysis of near-critical temperature relaxation showing that the piston effect is not governed by one (as was until now believed) but by two typical time scales. These two time scales exhibit antagonistic asymptotic behaviors as the critical point is approached: while the classical piston-effect time scale (as predicted by Onuki ) goes to zero at the critical point (critical speeding up), the second time scale (related to bulk viscosity) goes to infinity (critical slowing down). Based on this property, an alternative method for measuring near-critical bulk viscosity is proposed. PMID:16089870

Carlès, Pierre; Dadzie, Kokou

2005-06-28

121

Time Scales in the Approach to Equilibrium of Macroscopic Quantum Systems  

NASA Astrophysics Data System (ADS)

We prove two theorems concerning the time evolution in general isolated quantum systems. The theorems are relevant to the issue of the time scale in the approach to equilibrium. The first theorem shows that there can be pathological situations in which the relaxation takes an extraordinarily long time, while the second theorem shows that one can always choose an equilibrium subspace, the relaxation to which requires only a short time for any initial state.

Goldstein, Sheldon; Hara, Takashi; Tasaki, Hal

2013-10-01

122

Electric Field Effect on the Critical Opalescence. Ii. Relaxation Times of Concentration Fluctuations.  

National Technical Information Service (NTIS)

In an investigation of the effect of electric fields on the critical opalescence, time-dependent phenomena were observed which are related to theoretical relaxation times of concentration fluctuations for a binary mixture. Rectangular dc pulses of 25 to 6...

P. Debye C. C. Gravatt M. Ieda

1966-01-01

123

Electric Field Effect on the Critical Opalescence. Ii. Relaxation Times of Concentration Fluctuations.  

National Technical Information Service (NTIS)

In an investigation of the effect of electrical fields on the critical opalescence, time dependent phenomena were observed which are related to theoretical relaxation times of concentration fluctuations for a binary mixture. Rectangular DC pulses of 25 to...

P. Debye C. C. Gravatt M. Ieda

1966-01-01

124

Dielectric relaxations of poly(acrylic acid)-graft-poly(ethylene oxide) aqueous solution: analysis coupled with scaling approach and hydrogen-bonding complex.  

PubMed

Dielectric properties of poly(acrylic acid)-graft-poly(ethylene oxide) (PAA-g-PEO) aqueous solution were measured as a function of concentration and temperature over a frequency range of 40 Hz to 110 MHz. After subtracting the contribution of electrode polarization, three relaxation processes were observed at about 20 kHz, 220 kHz, and 4 MHz, and they are named low-, mid- and high-frequency relaxation, respectively. The relaxation parameters of these three relaxations (dielectric increment ?? and relaxation time ?) showed scaling relations with the polyelectrolyte concentration. The mechanisms of the three relaxations were concluded in light of the scaling theory: The relaxations of low- and mid frequency were attributed to the fluctuation of condensed counterions, while the high-frequency relaxation was ascribed to the fluctuation of free counterions. Based on the dielectric measurements of varying temperatures, the thermodynamic parameters (enthalpy change ?H and entropy change ?S) of the three relaxations were calculated and these relaxation processes were also discussed from the microscopic thermodynamical view. In addition, the impacts of PEO side chains on the conformation of PAA-g-PEO chains were discussed. PEO side chains greatly strengthen the hydrogen-bonding interactions between PAA-g-PEO chains, resulting in the chains overlapping at a very low concentration and the formation of a hydrogen-bonding complex. Some physicochemical parameters of PAA-g-PEO molecules were calculated, including the overlap concentration, the effective charge of the chain, the friction coefficient, and the diffusion coefficient of hydrogen counterions. PMID:23679439

Li, Jingliang; Zhao, Kongshuang; Liu, Chunyan

2013-04-10

125

Investigating low frequency dielectric properties of a composite using the distribution of relaxation times technique  

SciTech Connect

The distribution of relaxation times approach, a less frequently employed dielectric data analysis technique, is utilized to better understand the relaxation characteristics of composites consisting of metal-coated, hollow glass spheres dispersed in a paraffin wax matrix. The dielectric properties of the composite samples are measured by means of impedance spectroscopy in the frequency range 0.1mHz to 10 MHz. The application of a mixture law is not appropriate for the analysis of the frequency-dependent properties of the considered system on this broad frequency range. However, utilization of the distribution of relaxation times procedure to study the dielectric behaviour shows clear trends in the mixtures' relaxation spectra. Relaxation processes of the paraffin wax and those specific to the composites are found from the extracted distribution of relaxation times spectra. The influence of the filler concentration, q, on the dielectric properties is examined; a relaxation with a narrow distribution at intermediate frequencies becomes broad with the addition of the filler. This relaxation, in the form of the low-frequency-dispersions (also known as constant phase angle) phenomenon, dominates the dielectric properties of the composites with high bead concentration, q > 0:15. The variation in dielectric properties of individual samples whose bead concentrations q are nominally the same is discussed in terms of possible microstructural variations.

Tuncer, Enis [ORNL

2006-01-01

126

Investigating low-frequency dielectric properties of a composite using the distribution of relaxation times technique  

SciTech Connect

The distribution of relaxation times approach, a less frequently employed dielectric data analysis technique, is utilized to better understand the relaxation characteristics of composites consisting of metal-coated, hollow glass spheres dispersed in a paraffin wax matrix. The dielectric properties of the composite samples are measured by means of impedance spectroscopy in the frequency range 0.1 mHz to 10 MHz. The application of a mixture law is not appropriate for the analysis of the frequency-dependent properties of the considered system on this broad frequency range. However, utilization of the distribution of relaxation times procedure to study the dielectric behaviour shows clear trends in the mixtures' relaxation spectra. Relaxation processes of the paraffin wax and those specific to the composites are found from the extracted distribution of relaxation times spectra. The influence of the filler concentration, q, on the dielectric properties is examined; a relaxation with a narrow distribution at intermediate frequencies becomes broad with the addition of the filler. This relaxation, in the form of the low-frequency-dispersions (also known as constant phase angle) phenomenon, dominates the dielectric properties of the composites with high bead concentration, q>0.15. The variation in dielectric properties of individual samples whose bead concentrations q are nominally the same is discussed in terms of possible microstructural variations.

Tuncer, Enis [ORNL; Bowler, Nicola [Center for Nondestructive Evaluation, Ames, Iowa; Youngs, I. J. [DSTL, Porton Down, Salisbury, Wiltshire, UK; Lymer, K. P. [QinetiQ Ltd, Hampshire, UK

2006-01-01

127

Optimal Sampling Strategies for the Measurement of Spin–Spin Relaxation Times  

Microsoft Academic Search

It is shown how Cramér–Rao theory may be used to determine the optimal sampling pattern for measuring the NMR spin–spin relaxation time,T2. The results may also be applied to the measurement of any other exponential decay, including some pulse sequences for measuring the spin–lattice relaxation time,T1. The optimal sampling pattern involves placing 22% of the sample points at zero time

J. A. Jones; P. Hodgkinson; A. L. Barker; P. J. Hore

1996-01-01

128

A model of elastic and relaxation polarization of ferroelectrics with a distribution of domain walls over relaxation times and natural frequencies  

NASA Astrophysics Data System (ADS)

A model that takes into account the distribution of domain walls over natural frequencies and relaxation times (or activation energies) is proposed. It is demonstrated that the function of the distribution of domain walls over natural frequencies and relaxation times ƒ(?0, ?) (or potential barriers ƒ(?0, W 0)) can be calculated from the spectral-temperature dependence of the complex permittivity ?*(?, T).

Tilles, V. F.; Metal'Nikov, A. M.; Pecherskaya, R. M.

2009-07-01

129

Role of relaxation and time-dependent formation of x-ray spectra  

NASA Astrophysics Data System (ADS)

A fundamental problem of x-ray spectroscopy is the role of relaxation of the electronic subsystem in the field of the transient core hole. The main intention of the present study is to explore the dynamics due to core-hole relaxation in the whole time domain, and to find out how it is manifested in finite molecular systems in comparison with solids. A technique is developed based on a reduction of the Noziéres-De Dominicis equation to a set of linear algebraic equations. The developed time-dependent formalism is applied to a numerical investigation of a one-dimensional tight-binding model. The formation of the x-ray profiles is explored on the real time scale, and the role of interaction with the core hole, band filling, and the final-state rule are investigated for systems of different size. The formation of spectra of the infinite translational invariant system is studied by extensions of the finite systems. We found that the dynamics of finite systems, like molecules, differs qualitatively from solids: Contrary to the latter the time lapse of the Noziéres-De Dominicis domain for finite systems is squeezed between the inverse bandwidth and the revival time, which is proportional to the system size. For small molecules this means that there is no time for a ``Mahan-Noziéres-De Dominicis singularity'' to develop. Comparison with the strict solution of the Noziéres-De Dominicis equation shows that the adiabatic approximation describes x-ray absorption and emission considerably better than the fast approximation. This explains the suppression of the relaxation effects in x-ray emission of, e.g., gas phase and surface adsorbed molecules, but also that these effects are essential for the absorption case. There is still a quantitative distinction between the adiabatic approximation and the strict approach, which becomes more important for larger systems. Adopting the so-called finite state rule by von Barth and Grossman also for molecules, an almost complete numerical agreement between this rule and the strict x-ray-absorption and emission profiles for systems of different sizes is obtained. The simulations indicate that the final-state rule correction is important mainly near the absorption edge and at the top of the emission band.

Privalov, Timofei; Gel'mukhanov, Faris; Ågren, Hans

2001-10-01

130

Secondary and primary relaxations in hyperbranched polyglycerol: a comparative study in the frequency and time domains.  

PubMed

The non-Debye relaxation behavior of hyperbranched polyglycerol was investigated by broadband dielectric spectroscopy. A thorough study of the relaxations was carried out paying special attention to truncation effects on deconvolutions of overlapping processes. Hyperbranched polyglycerol exhibits two relaxations in the glassy state named in increasing order of frequency beta and gamma processes. The study of the evolution of these two fast processes with temperature in the time retardation spectra shows that the beta absorption is swallowed by the alpha in the glass-liquid transition, the gamma absorption being the only relaxation that remains operative in the liquid state. In heating, a temperature is reached at which the alpha absorption vanishes appearing the alphagamma relaxation. Two characteristics of alpha absorptions, decrease of the dielectric strength with increasing temperature and rather high activation energy, are displayed by the alphagamma process. Williams' ansatz seems to hold for these topologically complex macromolecules. PMID:17902934

Garcia-Bernabé, Abel; Dominguez-Espinosa, Gustavo; Diaz-Calleja, Ricardo; Riande, Evaristo; Haag, Rainer

2007-09-28

131

The effect of fast electronic relaxation times on the 1H and 7Li magnetic relaxation dispersion modulated by the translational encounter of cation/cation pairs  

NASA Astrophysics Data System (ADS)

1H and 7Li magnetic relaxation dispersion data are presented, showing the field dependence of the spin-lattice relaxation rates of (H 3C) 4N + and Li(H 2O) n+ in Gd(III) and Mn(II) solutions. The limit of short electronic relaxation time is observed for Gd(III) up to about 7 T, in contrast to Mn(II) solutions wherein the intermolecular contribution to nuclear relaxation is dominated by relative translational diffusion. These results contradict the assumption made by Fries et al. (Chem. Phys. Lett. 286 (1998) 93) that the electron relaxation times may be neglected in the analysis of tetramethylammonium proton relaxation rates in Gd(III) solutions.

Dinesen, T. R. J.; Bryant, R. G.

1999-04-01

132

Relaxation Time Mapping of Short T * 2Nuclei with Single-Point Imaging (SPI) Methods  

Microsoft Academic Search

New techniques for quantitative mapping ofT1,T2, andT*2are proposed, based on thesingle-pointimaging (SPI) method, for materials with short nuclear magnetic resonance relaxation times which cannot be imaged with traditional methods. Relaxation times extracted from two-dimensional images of uniform doped agarose phantoms (T*2? 60–210 ?s) as well as hardened mortar (T*2? 220 ?s) and polymers (T*2? 20–100 ?s), using these techniques, agreed

Steven D. Beyea; Bruce J. Balcom; Pablo J. Prado; Albert R. Cross; Christopher B. Kennedy; Robin L. Armstrong; Theodore W. Bremner

1998-01-01

133

Rat brain metabolite relaxation time estimates using magnetic resonance spectroscopy at two different field strengths  

Microsoft Academic Search

The in vitro and in vivo longitudinal (T1) and transversal (T2) relaxation times of the singlet resonances of the three major metabolites: N-acetylaspartate, creatine and choline, in healthy rat brains were estimated at 4.7T and 7T. Field-dependent variations in the T1 and T2 relaxation time values were observed with high significance, since the measurements were performed under near-identical experimental conditions.

Cristina Cudalbu; Adrian Rengle; Olivier Beuf; Sophie Cavassila

2008-01-01

134

1 H NMR relaxation times of skeletal muscle metabolites at 3 T  

Microsoft Academic Search

This study reports proton relaxation times of water and metabolites in soleus and tibialis anterior muscles of young healthy volunteers at 3 T. The results are in agreement with data reported for 1.5 and 4 T, showing a steady increase of spin-lattice relaxation times of water, creatine and lipids with B 0 and no effect of B 0 on spin–spin

M. Krššák; M. Roden; V. Mlynárik; M. Meyerspeer; E. Moser

2004-01-01

135

Non-Fermi liquid behavior of thermal relaxation time in degenerate electron plasma  

NASA Astrophysics Data System (ADS)

The thermal relaxation time (??ee) for the degenerate electron plasma has been calculated by incorporating non-Fermi liquid corrections both for the thermal conductivity and specific heat capacity. Perturbative results are presented by making expansion in T/mD with next to leading order corrections. We see that the next to leading order non-Fermi liquid corrections further reduce the decrease in relaxation time due to the leading order corrections.

Sarkar, Sreemoyee; Dutt-Mazumder, Abhee K.

2013-04-01

136

What is the time scale for ?-helix nucleation?  

PubMed

Helix formation is an elementary process in protein folding, influencing both the rate and mechanism of the global folding reaction. Yet, because helix formation is less cooperative than protein folding, the kinetics are often multiexponential, and the observed relaxation times are not straightforwardly related to the microscopic rates for helix nucleation and elongation. Recent ultrafast spectroscopic measurements on the peptide Ac-WAAAH(+)-NH(2) were best fit by two relaxation modes on the ?0.1-1 ns time scale, (1) apparently much faster than had previously been experimentally inferred for helix nucleation. Here, we use replica-exchange molecular dynamics simulations with an optimized all-atom protein force field (Amber ff03w) and an accurate water model (TIP4P/2005) to study the kinetics of helix formation in this peptide. We calculate temperature-dependent microscopic rate coefficients from the simulations by treating the dynamics between helical states as a Markov process using a recently developed formalism. The fluorescence relaxation curves obtained from simulated temperature jumps are in excellent agreement with the experimentally determined results. We find that the kinetics are multiphasic but can be approximated well by a double-exponential function. The major processes contributing to the relaxation are the shrinking of helical states at the C-terminal end and a faster re-equilibration among coil states. Despite the fast observed relaxation, the helix nucleation time is estimated from our model to be 20-70 ns at 300 K, with a dependence on temperature well described by Arrhenius kinetics. PMID:21480610

De Sancho, David; Best, Robert B

2011-04-11

137

Assessment of the Holland model for silicon phonon-phonon relaxation times using lattice dynamics calculations  

NASA Astrophysics Data System (ADS)

We assess the ability of the Holland model to accurately predict phonon-phonon relaxation times from bulk thermal conductivity values. First, lattice dynamics calculations are used to obtain phonon-phonon relaxation times and thermal conductivities for temperatures ranging from 10 K to 1000 K for Stillinger-Weber silicon. The Holland model is then fitted to these thermal conductivities and used to predict relaxation times, which are compared to the relaxation times obtained by lattice dynamics calculations. We find that fitting the Holland model to both total and mode-dependent thermal conductivities does not result in accurate mode-dependent phonon-phonon relaxation times. Introduction of Umklapp scattering for longitudinal modes resulted in improved prediction of mode-dependent relative contributions to thermal conductivity, especially at high temperatures. However, assumptions made by Holland regarding the frequency-dependence of phonon scattering mechanisms are found to be inconsistent with lattice dynamics data. Instead, we introduce a simple method based on using cumulative thermal conductivity functions to obtain better predictions of the frequency-dependence of relaxation times.

Zhu, Zimu; Romero, David A.; Sellan, Daniel P.; Nabovati, Aydin; Amon, Cristina H.

2013-05-01

138

Rotational relaxation time of polyelectrolyte xanthan chain via single molecule tracking method  

NASA Astrophysics Data System (ADS)

Effect of solvent viscosity on the longest rotational relaxation time of xanthan molecule has been examined using a single molecule tracking method. Incorporating inverted epi-fluorescence microscope and chargedcoupled device (CCD) camera, various features of xanthan ( i.e., radius of gyration, orientation angle, etc.) were interpreted by image processing algorithm from the captured real xanthan images. From the best-fit of the autocorrelation function on the orientation angle, the longest rotational relaxation time was effectively determined. Rotational relaxation time increases with the medium solvent viscosity due to the slow movement of xanthan molecule. It is confirmed that there is a good agreement between experiments and Brownian dynamics simulations on the relaxation patterns of xanthan chain.

Lee, Jeong Yong; Jung, Hyun Wook; Hyun, Jae Chun

2012-12-01

139

Stability of Rasch Scales Over Time  

Microsoft Academic Search

Item response theory (IRT) methods are generally used to create score scales for large-scale tests. Research has shown that IRT scales are stable across groups and over time. Most studies have focused on items that are dichotomously scored. Now Rasch and other IRT models are used to create scales for tests that include polytomously scored items. When tests are equated

Catherine S. Taylor; Yoonsun Lee

2009-01-01

140

Scaling regimes of composite rainfall time series  

Microsoft Academic Search

The scaling behaviour of rainfall is analysed both for a range of scales in time and for a given scale in intensity using the statistics of the Fourier transform and the cumulative probability distribution. The analyses are applied to sets of long time series of daily rainfall (26 (8) files of 45 (90) years at 13 European stations) and sets

Klaus Fraedrich; Chris Larnder

1993-01-01

141

Entanglement and confinement effects constraining polymer chain dynamics on different length and time scales  

Microsoft Academic Search

With the time constants usually considered to be characteristic for polymer dynamics, namely ?s (the segment fluctuation time), ?e (the entanglement time), and ?R (the longest Rouse relaxation time), the time scales of particular interest: (i) t?s; (ii) ?st?e; and (iii) ?et?R will be discussed and compared with experimental data. These ranges correspond to the chain-mode length scales: (i) ?b;

Rainer Kimmich

2010-01-01

142

Determination of 13 C ? relaxation times in uniformly 13 C\\/ 15 N-enriched proteins  

Microsoft Academic Search

Relaxation times of 13Ca carbons of uniformly 13C\\/15N-enriched probes have been investigated. The relaxation behaviour was analyzed in terms of a multispin system. Pulse sequences for the determination of T1, T2 and the heteronuclear NOE of 13Ca in uniformly 13C\\/15N-enriched ribonuclease T1 are presented. The experiments performed in order to obtain T1 and the heteronuclear NOE were similar to those

Jan Engelke; Heinz Rüterjans

1995-01-01

143

Two-Relaxation-Time Lattice Boltzmann Scheme: About Parametrization,Velocity, PressureandMixed Boundary Conditions  

Microsoft Academic Search

We develop a two-relaxation-time (TRT) Lattice Boltzmann model for hy- drodynamic equations with variable source terms based on equivalent equilibrium functions. A special parametrization of the free relaxation parameter is derived. It controls, in addition to the non-dimensional hydrodynamic numbers, any TRT macro- scopic steady solution and governs the spatial discretization of transient flows. In this framework, the multi-reflection approach

Irina Ginzburg; Frederik Verhaeghe; Dominique d'Humieres

144

Strain-induced enhancement of spin relaxation times in [110] and [111] grown quantum wells  

Microsoft Academic Search

We derive the strain-dependent Hamiltonian of the conduction band for semiconductor quantum wells grown along [110] and [111] directions. We propose and demonstrate theoretically that by properly controlling the strain of InGaAs\\/InP quantum wells, the spin relaxation from the Dyakonov-Perel mechanism can be suppressed in [110] and [111] quantum wells. The spin relaxation time can be enhanced by more than

Shu-Wei Chang; Shun-Lien Chuang

2005-01-01

145

Longitudinal relaxation time detection using a high-Tc superconductive quantum interference device magnetometer  

Microsoft Academic Search

The parameters to optimize the measurement of longitudinal relaxation time detection using a high-Tc superconductive quantum interference device magnetometer are investigated. These parameters include the prepolarization field, Bp, the prepolarization time, TBp, and the delay time, Td, to turn on pulses after turning off the prepolarization field. Furthermore, the decreasing of magnetization with the increasing Td of the applied pulse

Shu-Hsien Liao; Herng-Er Horng; Hong-Chang Yang; Shieh-Yueh Yang

2007-01-01

146

Phase relaxation in slowly changing environments: Evaluation of the Kubo-Anderson model for a continuous-time random walk  

NASA Astrophysics Data System (ADS)

The Kubo-Anderson model is a stochastic model of phase relaxation of an ensemble of systems in a fluctuating environment. This model is usually studied under the assumption that the system-environment interaction is a Gaussian stochastic process. This assumption only holds if the environment changes a very large number of times on the time scale of the system's motion. This paper reviews our work on the Kubo-Anderson model for the case where this interaction is a continuous-time random walk. A continuous-time random walk is a simple model for a `slowly changing environment', i.e., one which makes a relatively small number of changes on the time scale of the system's motion. We present the key results from this model and show how to apply them to common problems in magnetic resonance spectroscopy and and non-linear optical spectroscopy.

Packwood, Daniel M.

2013-02-01

147

Multiple time scale based reduction scheme for nonlinear chemical dynamics  

NASA Astrophysics Data System (ADS)

A chemical reaction is often characterized by multiple time scales governing the kinetics of reactants, products and intermediates. We eliminate the fast relaxing intermediates in autocatalytic reaction by transforming the original system into a new one in which the linearized part is diagonal. This allows us to reduce the dynamical system by identifying the associated time scales and subsequent adiabatic elimination of the fast modes. It has been shown that the reduced system sustains the robust qualitative signatures of the original system and at times the generic form of the return map for the chaotic system from which complex dynamics stems out in the original system can be identified. We illustrate the scheme for a three-variable cubic autocatalytic reaction and four-variable peroxidase-oxidase reaction.

Das, D.; Ray, D. S.

2013-07-01

148

Dominant time scale for brittle fragmentation of vesicular magma by decompression  

Microsoft Academic Search

Brittle fragmentation was examined in a vesicular material analogous to magma, in this case, maltose syrup with bubbles. All the key time scales for magma fragmentation are controlled in the experiment using a rapid decompression facility. It was found that the onset of fragmentation can be well characterized using the Maxwell relaxation time ?r and the decompression time ?tdec, in

Masaharu Kameda; Hideaki Kuribara; Mie Ichihara

2008-01-01

149

Relaxation time, diffusion, and viscosity analysis of model asphalt systems using molecular simulation.  

PubMed

Molecular dynamics simulation was used to calculate rotational relaxation time, diffusion coefficient, and zero-shear viscosity for a pure aromatic compound (naphthalene) and for aromatic and aliphatic components in model asphalt systems over a temperature range of 298-443 K. The model asphalt systems were chosen previously to represent real asphalt. Green-Kubo and Einstein methods were used to estimate viscosity at high temperature (443.15 K). Rotational relaxation times were calculated by nonlinear regression of orientation correlation functions to a modified Kohlrausch-Williams-Watts function. The Vogel-Fulcher-Tammann equation was used to analyze the temperature dependences of relaxation time, viscosity, and diffusion coefficient. The temperature dependences of viscosity and relaxation time were related using the Debye-Stokes-Einstein equation, enabling viscosity at low temperatures of two model asphalt systems to be estimated from high temperature (443.15 K) viscosity and temperature-dependent relaxation time results. Semiquantitative accuracy of such an equivalent temperature dependence was found for naphthalene. Diffusion coefficient showed a much smaller temperature dependence for all components in the model asphalt systems. Dimethylnaphthalene diffused the fastest while asphaltene molecules diffused the slowest. Neat naphthalene diffused faster than any component in model asphalts. PMID:18035887

Zhang, Liqun; Greenfield, Michael L

2007-11-21

150

Can inertial electrostatic confinement work beyond the ion-ion collisional time scale?  

SciTech Connect

Inertial electrostatic confinement systems are predicated on a non-equilibrium ion distribution function. Coulomb collisions between ions cause this distribution to relax to a Maxwellian on the ion-ion collisional time-scale. The power required to prevent this relaxation and maintain the IEC configuration for times beyond the ion-ion collisional time scale is shown to be at least an order of magnitude greater than the fusion power produced. It is concluded that IEC systems show little promise as a basis for the development of commercial electric power plants.

Nevins, W.M.

1995-01-01

151

Can inertial electrostatic confinement work beyond the ion--ion collisional time scale?  

SciTech Connect

Inertial electrostatic confinement (IEC) systems are predicated on a nonequilibrium ion distribution function. Coulomb collisions between ions cause this distribution to relax to a Maxwellian on the ion--ion collisional time scale. The power required to prevent this relaxation and maintain the IEC configuration for times beyond the ion--ion collisional time scale is shown to be greater than the fusion power produced. It is concluded that IEC systems show little promise as a basis for the development of commercial electric power plants. {copyright} {ital 1995} {ital American} {ital Institute} {ital of} {ital Physics}.

Nevins, W.M. [Lawrence Livermore National Laboratory, Livermore, California 94550 (United States)

1995-10-01

152

Fast timing closure by interconnect criticality driven delay relaxation  

Microsoft Academic Search

Due to decreasing transistor sizes and increasing clock frequency, interconnect delay is a dominant factor in achieving timing closure in deep sub-micron designs. Techniques like wire pipelining and retiming can manage delay of timing critical wires. The latency of the system, however, limits the total pipelining in the design. New techniques are, thus, needed at synthesis stage to consider the

Love Singhal; Elaheh Bozorgzadeh

2005-01-01

153

Exciton spin relaxation time in quantum dots measured by continuous-wave photoluminescence spectroscopy  

NASA Astrophysics Data System (ADS)

We demonstrate a method of measuring the exciton spin relaxation time in semiconductor nanostructures by continuous-wave photoluminescence. We find that for self-assembled CdTe quantum dots (QDs) the degree of circular polarization of emission is larger when exciting polarized excitons into the lower energy spin state (?--polarized) than in the case when the excitons are excited into the higher energy spin state (?+-polarized). A simple rate equation model gives the exciton spin relaxation time in CdTe QDs equal to ?S=4.8+/-0.3 ns, significantly longer than the QD exciton recombination time ?R=300 ps.

Mackowski, S.; Nguyen, T. A.; Jackson, H. E.; Smith, L. M.; Kossut, J.; Karczewski, G.

2003-12-01

154

Correlation Times Measurements from Tin-Proton Dipolar Interactions: A 1H NMR Spin-Lattice Relaxation Study  

Microsoft Academic Search

The simultaneous analysis of nuclear relaxation behaviour of Sn-H and Sn-H dipolar vectors from the proton spinlattice relaxation rates of the relative satellite peaks may yield a very accurate calculation of correlation times. The dipolar interaction between the proton and the bound tin nucleus is differently observed on the Sn and Sn satellite resonances in the H partially relaxed spectra.

N. Niccolai; M. Rustici; A. Bonci; M. Scarselli; P. Neri; A. Brandi; A. Goti; A. Guarna; F. de Sarlo

1990-01-01

155

The Time of Relaxation in Crystals of Rochelle Salt  

Microsoft Academic Search

A semiquantitative theory of the action of mechanical and electrical forces is given, using the concept of two relaxtion times. The theory is shown to offer qualitative explanations of numerous features of the experimental results such as the phenomenon of \\

R. D. Schulwas-Sorokin; M. V. Posnov

1935-01-01

156

Estimates of expansion time scales  

NASA Astrophysics Data System (ADS)

Monte Carlo simulations of the expansion of a spacefaring civilization show that descendants of that civilization should be found near virtually every useful star in the Galaxy in a time much less than the current age of the Galaxy. Only extreme assumptions about local population growth rates, emigration rates, or ship ranges can slow or halt an expansion. The apparent absence of extraterrestrials from the solar system suggests that no such civilization has arisen in the Galaxy.

Jones, E. M.

157

Calibrated Tree Priors for Relaxed Phylogenetics and Divergence Time Estimation  

PubMed Central

The use of fossil evidence to calibrate divergence time estimation has a long history. More recently, Bayesian Markov chain Monte Carlo has become the dominant method of divergence time estimation, and fossil evidence has been reinterpreted as the specification of prior distributions on the divergence times of calibration nodes. These so-called “soft calibrations” have become widely used but the statistical properties of calibrated tree priors in a Bayesian setting hashave not been carefully investigated. Here, we clarify that calibration densities, such as those defined in BEAST 1.5, do not represent the marginal prior distribution of the calibration node. We illustrate this with a number of analytical results on small trees. We also describe an alternative construction for a calibrated Yule prior on trees that allows direct specification of the marginal prior distribution of the calibrated divergence time, with or without the restriction of monophyly. This method requires the computation of the Yule prior conditional on the height of the divergence being calibrated. Unfortunately, a practical solution for multiple calibrations remains elusive. Our results suggest that direct estimation of the prior induced by specifying multiple calibration densities should be a prerequisite of any divergence time dating analysis.

Heled, Joseph; Drummond, Alexei J.

2012-01-01

158

Determination of NMR relaxation times (T1 and T2) from multislice, multiecho MR imaging  

Microsoft Academic Search

In proton MR imaging the determination of fundamental MR constants such as spin lattice (T1) and spin spin (T2) relaxation times is essential for an understanding of image contrast and for insight into the question of optimal field vis a vis disease state. Multislice, multiecho imaging is attractive because imaging time per slice is reduced; however, slice selecting radiofrequency (RF)

K. Wilkins; F. S. Prato; D. J. Drost; T. Keys

1985-01-01

159

Comparing Entropic and Multiple Relaxation Times Lattice Boltzmann Methods for Blood Flow Simulations  

Microsoft Academic Search

We compare the Lattice BGK, the Multiple Relaxation Times and the Entropic Lattice Boltzmann Methods for time harmonic flows. We measure the stability, speed and accuracy of the three models for Reynolds and Womersley numbers that are representative for human arteries. The Lattice BGK shows predictable stability and is the fastest method in terms of lattice node updates per second.

Joost B. W. Geerdink; Alfons G. Hoekstra

2009-01-01

160

Comparing Entropic and Multiple Relaxation Times Lattice Boltzmann Methods for blood flow simulations  

Microsoft Academic Search

We compare the Lattice BGK, the Multiple Relaxation Times and the Entropic Lattice Boltzmann Methods for time harmonic flows. We measure the stability, speed and accuracy of the three models for Reynolds and Womersley numbers that are representative for human arteries. The Lattice BGK shows predictable stability and is the fastest method in terms of lattice node updates per second.

JOOST B. W. GEERDINK; ALFONS G. HOEKSTRA

2009-01-01

161

A discrete-time nonlinear Wiener model for the relaxation of soft biological tissues  

Microsoft Academic Search

The present paper is devoted to introducing discrete-time models for the relaxation function of soft biological tissues. Discrete-time models are suitable for the analysis of sampled data and for digital simulations of continuous systems. Candidate models are searched for within both linear ARX structures and nonlinear Wiener models, consisting of an ARX element followed in cascade by a polynomial function.

Virginio Quaglini; Fabio Previdi; Roberto Contro; Sergio Bittanti

2002-01-01

162

Static Electric Susceptibility and Dielectric Relaxation Time near the Transition Points in NaNO2  

Microsoft Academic Search

The precise temperature dependence of the ralaxation time of the polarization in NaNO2 has been given through a new approach, in which the relaxation time is derived from the imaginary part of the complex dielectric constant in the low frequency region. On the way of this experimental procedure, it was found that the measurement of the static electric susceptibility should

Ichiro Hatta

1970-01-01

163

Spectrum of Volume Relaxation Times in Boron Oxide.  

National Technical Information Service (NTIS)

Time-index of refraction isotherms were measured for B2O3 glass starting from both a high and a low temperature in the transformation region. The equilibrium index values at teach temperature, obtained from both types of approach curve, were identical. Th...

L. Boesch A. Napolitano P. B. Macedo

1969-01-01

164

Multiple time scales in survival analysis  

Microsoft Academic Search

In some problems in survival analysis there may be more than one plausible measure of time for each individual. For example mileage may be a better indication of the age of a car than months. This paper considers the possibility of combining two (or more) time scales measured on each individual into a single scale. A collapsibility condition is proposed

David Oakes

1995-01-01

165

Multiple time scale methods in tokamak magnetohydrodynamics  

SciTech Connect

Several methods are discussed for integrating the magnetohydrodynamic (MHD) equations in tokamak systems on other than the fastest time scale. The dynamical grid method for simulating ideal MHD instabilities utilizes a natural nonorthogonal time-dependent coordinate transformation based on the magnetic field lines. The coordinate transformation is chosen to be free of the fast time scale motion itself, and to yield a relatively simple scalar equation for the total pressure, P = p + B/sup 2//2..mu../sub 0/, which can be integrated implicitly to average over the fast time scale oscillations. Two methods are described for the resistive time scale. The zero-mass method uses a reduced set of two-fluid transport equations obtained by expanding in the inverse magnetic Reynolds number, and in the small ratio of perpendicular to parallel mobilities and thermal conductivities. The momentum equation becomes a constraint equation that forces the pressure and magnetic fields and currents to remain in force balance equilibrium as they evolve. The large mass method artificially scales up the ion mass and viscosity, thereby reducing the severe time scale disparity between wavelike and diffusionlike phenomena, but not changing the resistive time scale behavior. Other methods addressing the intermediate time scales are discussed.

Jardin, S.C.

1984-01-01

166

Probing of structural relaxation times in the glassy state of sucrose and trehalose based on dynamical properties of two secondary relaxation processes  

SciTech Connect

Time-dependent isothermal dielectric measurements were carried out deeply in the glassy state on two very important saccharides: sucrose and trehalose. In both compounds two prominent secondary relaxation processes were identified. The faster one is an inherent feature of the whole family of carbohydrates. The slower one can also be detected in oligo- and polysaccharides. It was shown earlier that the {beta} process is the Johari-Goldstein (JG) relaxation coupled to motions of the glycosidic linkage, while the {gamma} relaxation originates from motions of the exocyclic hydroxymethyl unit. Recently, it was shown that the JG relaxation process can be used to determine structural relaxation times in the glassy state [R. Casalini and C. M. Roland, Phys. Rev. Lett. 102, 035701 (2009)]. In this paper we present the results of an analysis of the data obtained during aging using two independent approaches. The first was proposed by Casalini and Roland, and the second one is based on the variation of the dielectric strength of the secondary relaxation process during aging [J. K. Vij and G. Power, J. Non-Cryst. Solids 357, 783 (2011)]. Surprisingly, we found that the estimated structural relaxation times in the glassy state of both saccharides are almost the same, independent of the type of secondary mode. This finding calls into question the common view that secondary modes of intramolecular origin do not provide information about the dynamics of the glassy state.

Kaminski, K.; Adrjanowicz, K.; Paluch, M. [Institute of Physics, Silesian University, Uniwersytecka 4, PL-40-007 Katowice (Poland); Kaminska, E. [Department of Pharmacognosy and Phytochemistry, Medical University of Silesia, Jagiellonska 4, PL-41-200 Sosnowiec (Poland)

2011-06-15

167

Probing of structural relaxation times in the glassy state of sucrose and trehalose based on dynamical properties of two secondary relaxation processes.  

PubMed

Time-dependent isothermal dielectric measurements were carried out deeply in the glassy state on two very important saccharides: sucrose and trehalose. In both compounds two prominent secondary relaxation processes were identified. The faster one is an inherent feature of the whole family of carbohydrates. The slower one can also be detected in oligo- and polysaccharides. It was shown earlier that the ? process is the Johari-Goldstein (JG) relaxation coupled to motions of the glycosidic linkage, while the ? relaxation originates from motions of the exocyclic hydroxymethyl unit. Recently, it was shown that the JG relaxation process can be used to determine structural relaxation times in the glassy state [R. Casalini and C. M. Roland, Phys. Rev. Lett. 102, 035701 (2009)]. In this paper we present the results of an analysis of the data obtained during aging using two independent approaches. The first was proposed by Casalini and Roland, and the second one is based on the variation of the dielectric strength of the secondary relaxation process during aging [J. K. Vij and G. Power, J. Non-Cryst. Solids 357, 783 (2011)]. Surprisingly, we found that the estimated structural relaxation times in the glassy state of both saccharides are almost the same, independent of the type of secondary mode. This finding calls into question the common view that secondary modes of intramolecular origin do not provide information about the dynamics of the glassy state. PMID:21797367

Kaminski, K; Adrjanowicz, K; Kaminska, E; Paluch, M

2011-06-13

168

Nuclear Magnetic Resonance Relaxation Times and Plasmalemma Water Exchange in Ivy Bark  

PubMed Central

Measurement of nuclear magnetic resonance (NMR) relaxation times (transverse [T2] and longitudinal [T1]) for Hedera helix L. cv. Thorndale (ivy) bark water indicates the presence of at least two populations of water with different relaxation characteristics. One population of water with short T2 and T1 was found to be composed of both hydration water and extracellular free water. The second population of water with long T2 and T1 was identified as intracellular bulk water. NMR relaxation of extracellular water protons is controlled by cell wall surface effects, possibly due to binding of paramagnetic cations by the cell walls. NMR relaxation of intracellular water protons is controlled by both water exchange to the extracellular environment and chemical exchange with a population of protons that is chemically shifted from that of the bulk water. The relaxation time of intracellular water is not measurably affected, either by intracellular paramagnetic ions or by increased viscosity of intracellular water. Manganese flux into the cells occurs at 1.7 × 10?15 moles cm?2 seconds?1 and is independent of extracellular Mn2+ concentration in the range 5 to 20 mm. The intracellular-extracellular water exchange time of ivy bark was found to be predominantly limited by membrane water permeability. A diffusional water permeability coefficient (Pd) of approximately 3 × 10?2 cm seconds?1 was calculated for ivy cell membranes at 20 C.

Stout, Darryl G.; Steponkus, Peter L.; Cotts, Robert M.

1978-01-01

169

Retrieval of transverse relaxation time distribution from spin-echo data by recurrent neural network  

NASA Astrophysics Data System (ADS)

Inversion of transverse relaxation time decay curve from spin-echo experiments was carried out using Hopfield neural network, to obtain the transverse relaxation time distribution. The performance of this approach was tested against simulated and experimental data. The initial guess, necessary for the integration procedure, was established as the analytical Laplace inversion. Together with errors in the simulated data, inversion was also carried out with errors in this initial guess. The probability density function, calculated by the neural network, is used in multiple sclerosis diagnostics.

Sebastião, R. C. O.; Braga, J. P.

2005-11-01

170

Assessment of nonradiative relaxation time and characteristic diffusion time of neodymium, erbium and cobalt doped low silica calcium aluminosilicate glasses  

Microsoft Academic Search

Nonradiative relaxation time (?) and characteristic diffusion time (??) of Nd, Er and Co doped low silica calcium aluminosilicate (LSCA) glasses were assessed by means of photoacoustic spectroscopy. The results are interpreted in terms of frequency dependence predicted by the theory of Rosencwaig and Gersho. Whereas ? varied between 7.2ms and 36ms, the values of ?? lied between 0.25ms and

L. Mota; J. A. Sampaio; M. G. da Silva; H. Vargas

2011-01-01

171

Boiling temperature as a scaling parameter for the microscopic relaxation dynamics in molecular liquids.  

PubMed

At sufficiently high temperatures, the center-of-mass microscopic diffusion dynamics of liquids is characterized by a single component, often with weak temperature dependence. In this regime, the effective cage made by the neighbor particles cannot be sustained and readily breaks down, enabling long-range diffusion. As the temperature is decreased, the cage relaxation becomes impeded, leading to a higher viscosity with more pronounced temperature dependence. On the microscopic scale, the sustained caging effect leads to a separation between a faster in-cage relaxation component and a slower cage-breaking relaxation component. The evidence for the separate dynamic components, as opposed to a single stretched component, is provided by quasielastic neutron scattering experiments. We use a simple method to evaluate the extent of the dynamic components separation as a function of temperature in a group of related aromatic molecular liquids. We find that, regardless of the glass-forming capabilities or lack thereof, progressively more pronounced separation between the in-cage and cage-breaking dynamic components develops on cooling down as the ratio of Tb/T, where Tb is the boiling temperature, increases. This reflects the microscopic mechanism behind the empirical rule for the glass forming capability based on the ratio of boiling and melting temperatures, Tb/Tm. When a liquid's Tb/Tm happens to be high, the liquid can readily be supercooled below its Tm because the liquid's microscopic relaxation dynamics is already impeded at Tm, as evidenced by a sustained caging effect manifested through the separation of the in-cage and cage-breaking dynamic components. Our findings suggest certain universality in the temperature dependence of the microscopic diffusion dynamics in molecular liquids, regardless of their glass-forming capabilities. Unless the insufficiently low (with respect to Tb) melting temperature, Tm, intervenes and makes crystallization thermodynamically favorable when cage-breaking is still unimpeded and the structural relaxation is fast, the liquid is likely to become supercooled. The propensity to supercooling and eventually forming a glass is thus determined by a purely thermodynamic factor, Tb/Tm. PMID:23869489

Mamontov, Eugene

2013-08-02

172

Direct visualization of short transverse relaxation time component (ViSTa).  

PubMed

White matter of the brain has been demonstrated to have multiple relaxation components. Among them, the short transverse relaxation time component (T2<40ms; T2(?)<25ms at 3T) has been suggested to originate from myelin water whereas long transverse relaxation time components have been associated with axonal and/or interstitial water. In myelin water imaging, T2 or T2(?) signal decay is measured to estimate myelin water fraction based on T2 or T2(?) differences among the water components. This method has been demonstrated to be sensitive to demyelination in the brain but suffers from low SNR and image artifacts originating from ill-conditioned multi-exponential fitting. In this study, a novel approach that selectively acquires short transverse relaxation time signal is proposed. The method utilizes a double inversion RF pair to suppress a range of long T1 signal. This suppression leaves short T2(?) signal, which has been suggested to have short T1, as the primary source of the image. The experimental results confirm that after suppression of long T1 signals, the image is dominated by short T2(?) in the range of myelin water, allowing us to directly visualize the short transverse relaxation time component in the brain. Compared to conventional myelin water imaging, this new method of direct visualization of short relaxation time component (ViSTa) provides high quality images. When applied to multiple sclerosis patients, chronic lesions show significantly reduced signal intensity in ViSTa images suggesting sensitivity to demyelination. PMID:23796545

Oh, Se-Hong; Bilello, Michel; Schindler, Matthew; Markowitz, Clyde E; Detre, John A; Lee, Jongho

2013-06-22

173

Time derivatives of the spectrum: Relaxing the stationarity assumption  

NASA Astrophysics Data System (ADS)

Spectrum analysis of seismic waveforms has played a significant role towards the understanding of multiple aspects of Earth structure and earthquake source physics. In recent years the multitaper spectrum estimation approach (Thomson, 1982) has been applied to geophysical problems providing not only reliable estimates of the spectrum, but also estimates of spectral uncertainties (Thomson and Chave, 1991). However, these improved spectral estimates were developed under the assumption of local stationarity and provide an incomplete description of the observed process. It is obvious that due to the intrinsic attenuation of the Earth, the amplitudes, and thus the frequency contents are changing with time as waves pass through a seismic station. There have been incredible improvements in different techniques to analyze non-stationary signals, including wavelet decomposition, Wigner-Ville spectrum and the dual-frequency spectrum. We apply one of the recently developed techniques, the Quadratic Inverse Theory (Thomson, 1990, 1994), combined with the multitaper technique to look at the time derivatives of the spectrum. If the spectrum is reasonably white in a certain bandwidth, using QI theory, we can estimate the derivatives of the spectrum at each frequency. We test synthetic signals to corroborate the approach and apply it the records of small earthquakes at local distances. This is a first approach to try and combine the classical spectrum analysis without the assumption of stationarity that is generally taken.

Prieto, G. A.; Thomson, D. J.; Vernon, F. L.

2005-12-01

174

Fragile-Strong Fluid Crossover and Universal Relaxation Times in a Confined Hard-Disk Fluid  

NASA Astrophysics Data System (ADS)

We show that a system of hard disks confined to a narrow channel exhibits a fragile-strong fluid crossover located at the maximum of the isobaric heat capacity and that the relaxation times for different channel widths fall onto a single master curve when rescaled by the relaxation times and temperatures of the crossover. Calculations of the configurational entropy and the inherent structure equation of state find that the crossover is related to properties of the jamming landscape for the model but that the Adam-Gibbs relation does not predict the relaxation behavior. We also show that a facilitated dynamics description of the system, where kinetically excited regions are identified with local packing arrangements of the disks, successfully describes the fragile-strong crossover.

Yamchi, Mahdi Zaeifi; Ashwin, S. S.; Bowles, Richard K.

2012-11-01

175

Only through perturbation can relaxation times be estimated  

NASA Astrophysics Data System (ADS)

Estimation of model parameters is as important as model building, but is often neglected in model studies. Here we show that despite the existence of well known results on parameter estimation in a simple homogenous Ornstein-Uhlenbeck process, in most practical situations the methods suffer greatly from finite sample sizes and especially the estimator of the time constant of the system is degraded. Therefore an alternative solution is of paramount importance. We present such a solution based on perturbation of the system, observing trajectories far from equilibrium. The results are illustrated on computer experiments based on applications in neuroscience and pharmacokinetics, which show a striking improvement of the quality of estimation. The results are important for judicious designs of experiments to obtain maximal information from each data point, especially when samples are expensive or difficult to obtain.

Ditlevsen, Susanne; Lansky, Petr

2012-11-01

176

Distribution of relaxation times from dielectric spectroscopy using Monte Carlo simulated annealing: Application to ?-PVDF  

NASA Astrophysics Data System (ADS)

The existence of a distribution of relaxation times has been widely used to describe the relaxation function versus frequency in glass-forming liquids. Several empirical distributions have been proposed and the usual method is to fit the experimental data to a model that assumes one of these functions. Another alternative is to extract from the experimental data the discrete profile of the distribution function that best fits the experimental curve without any a priori assumption. To test this approach a Monte Carlo algorithm using the simulated annealing is used to best fit simulated dielectric loss data, ?''(?), generated with Cole-Cole, Cole-Davidson, Havriliak-Negami, and Kohlrausch-Williams-Watts (KWW) functions. The relaxation times distribution, G(ln(?)), is obtained as an histogram that follows very closely the analytical expression for the distributions that are known in these cases. Also, the temporal decay functions, ?(t), are evaluated and compared to a stretched exponential. The method is then applied to experimental data for ?-polyvinylidene fluoride over a temperature range 233 K<=T<=278 K and frequencies varying from 3 MHz to 0.001 Hz. These data show the existence of two relaxation processes: the fast segmental ?a process associated with the glass transition and a ?c mode, which is slower and due to changes in conformation that can occur in the crystalline regions. The experimental curves are fitted by the simulated annealing direct signal analysis procedure, and the relaxation times distributions are calculated and found to vary with temperature. The decay function is also evaluated and it shows clearly its bimodal character and a good agreement with a KWW function with a temperature dependent ? for each mode. The relaxation plots are drawn for each mode and the Vogel-Tammann-Fulcher and Arrhenius parameters are found. The fragility parameter for polyvinylidene flouride (PVDF) is found to be 87, which characterizes this polymer as a relatively structurally strong material.

Bello, A.; Laredo, E.; Grimau, M.

1999-11-01

177

Determining the structural relaxation times deep in the glassy state of the pharmaceutical Telmisartan.  

PubMed

By using the dielectric relaxation method proposed recently by Casalini and Roland (2009 Phys. Rev. Lett. 102 035701), we were able to determine the structural ?-relaxation times deep in the glassy state of the pharmaceutical, Telmisartan. Normally, deep in the glassy state ?(?) is so long that it cannot be measured but ?(?), which is usually much shorter, can be directly determined. The method basically takes advantage of the connection between the ?-relaxation and the secondary ?-relaxation of the Johari-Goldstein kind, including a relation between their relaxation times ?(?) and ?(?), respectively. Thus, ?(?) of Telmisartan were determined by monitoring the change of the dielectric ?-loss, ?'', with physical aging time at temperatures well below the vitrification temperature. The values of ?(?) were compared with those expected by the coupling model (CM). Unequivocal comparison cannot be made in the case of Telmisartan because its ?-loss peak is extremely broad, and the CM predicts only an order of magnitude agreement between the primitive relaxation frequency and the ?-peak frequency. We also made an attempt to analyze all isothermal and aging susceptibility data after transformation into the electric modulus representation. The ?(?) found in the glass state by using the method of Casalini and Roland in the modulus representation are similar to those obtained in the susceptibility representation. However, it is remarkable that the stretching parameter ?(KWW - M) = 0.51 in the electric modulus representation gives more precise fits to the aging data than in the susceptibility representation with ?(KWW) = 0.61. Our results suggest that the electric modulus representation may be useful as an alternative to analyze aging data, especially in the case of highly polar glassformers having a large ratio of low frequency and high frequency dielectric constants, such as the Telmisartan studied. PMID:21389498

Adrjanowicz, K; Paluch, M; Ngai, K L

2010-03-12

178

Determining the structural relaxation times deep in the glassy state of the pharmaceutical Telmisartan  

NASA Astrophysics Data System (ADS)

By using the dielectric relaxation method proposed recently by Casalini and Roland (2009 Phys. Rev. Lett. 102 035701), we were able to determine the structural ?-relaxation times deep in the glassy state of the pharmaceutical, Telmisartan. Normally, deep in the glassy state ?? is so long that it cannot be measured but ??, which is usually much shorter, can be directly determined. The method basically takes advantage of the connection between the ?-relaxation and the secondary ?-relaxation of the Johari-Goldstein kind, including a relation between their relaxation times ?? and ??, respectively. Thus, ?? of Telmisartan were determined by monitoring the change of the dielectric ?-loss, ?'', with physical aging time at temperatures well below the vitrification temperature. The values of ?? were compared with those expected by the coupling model (CM). Unequivocal comparison cannot be made in the case of Telmisartan because its ?-loss peak is extremely broad, and the CM predicts only an order of magnitude agreement between the primitive relaxation frequency and the ?-peak frequency. We also made an attempt to analyze all isothermal and aging susceptibility data after transformation into the electric modulus representation. The ?? found in the glass state by using the method of Casalini and Roland in the modulus representation are similar to those obtained in the susceptibility representation. However, it is remarkable that the stretching parameter ?KWW - M = 0.51 in the electric modulus representation gives more precise fits to the aging data than in the susceptibility representation with ?KWW = 0.61. Our results suggest that the electric modulus representation may be useful as an alternative to analyze aging data, especially in the case of highly polar glassformers having a large ratio of low frequency and high frequency dielectric constants, such as the Telmisartan studied.

Adrjanowicz, K.; Paluch, M.; Ngai, K. L.

2010-03-01

179

Determination of Dielectric Relaxation Time of Langmuir-Films by a Whole-Curve Method Using the Maxwell Displacement Current  

NASA Astrophysics Data System (ADS)

A whole-curve method using the Maxwell displacement current (MDC) is presented for determining the dielectric relaxation time ? of floating monolayers on the water surface. The dielectric relaxation time of 4-cyano-4'-alkyl-biphenyle (5CB) monolayers was examined. It was revealed that the dielectric relaxation time ? of 5CB monolayers depends on the molecular area, and shows a good agreement with the theoretical relaxation time in the isotropic polar orientational phase, which was calculated using a rodlike columnar molecule model.

Sato, Yoko; Wu, Chen-Xu; Majima, Yutaka; Iwamoto, Mitsumasa

1998-10-01

180

Relaxation time effects on dynamic conductivity of alloyed metallic thin films in the infrared band  

NASA Astrophysics Data System (ADS)

The behavior of nanoscale infrared antenna elements depends upon the dynamic conductivity of thin metallic films. Spectroscopic ellipsometer measurements of noble metal films show that when the product of the incident radiation frequency and the relaxation time is greater than unity, anomalous dynamic electron transport effects occur. In this regime electron scattering increases the conductivity of alloyed metallic films as demonstrated by ellipsometry measurements of films from the Au-Cu system. A binary alloy thin film was fabricated with equal parts of Au and Cu, and the dynamic conductivity was measured to be 300% larger than the high frequency conductivity of pure Au or pure Cu films at wavelengths in the 3-5 ?m band. When electronic scattering is reduced, ellipsometer measurements of Au and Cu films taken near 4 K demonstrate that the IR conductivity decreases to 20% of the value measured at 300 K at wavelengths in the 3-5 ?m band. Using measured dc relaxation times, a model to explain deviations from Drude behavior was developed using the theory of the anomalous skin effect and frequency dependent relaxation time. This model was in quantitative agreement with the measured data. The ability to design an alloyed metallic thin film using a calculated ideal dc relaxation time to produce the greatest possible dynamic conductivity for infrared antennas and metamaterials was demonstrated.

Shelton, D. J.; Sun, T.; Ginn, J. C.; Coffey, K. R.; Boreman, G. D.

2008-11-01

181

REFLECTION OF THERMOELASTIC WAVES AT A SOLID HALF-SPACE WITH TWO RELAXATION TIMES  

Microsoft Academic Search

The effect of two relaxation times, following Green and Lindsay's theory, on the reflection of thermoelastic waves at a homogeneous, isotropic, and thermally conducting elastic solid half-space is studied. The results for the partition of the energy for various values of the angle of incidence are presented and compared with that of Lord and Shulman's theory to show the importance

Surendra B. Sinha; Khaled A. Elsibai

1996-01-01

182

STATE SPACE FORMULATION FOR GENERALIZED THERMOELASTICITY WITH ONE RELAXATION TIME INCLUDING HEAT SOURCES  

Microsoft Academic Search

The equations of generalized thermoelasticity with one relaxation time for one-dimensional problems including heat sources are cast into matrix form using the state space and Laplace transform techniques. The resulting formulation is applied to a problem for the whole space with a plane distribution of heat sources. It is also applied to a semispace problem with a traction-free surface and

Hany H. Sherief

1993-01-01

183

7Li relaxation time measurements at very low magnetic field by 1H dynamic nuclear polarization  

Microsoft Academic Search

Dynamic nuclear polarization (DNP) of water protons was used to measure the relaxation time of lithium at very low magnetic field as a demonstration of the use of DNP for nuclei less abundant than water protons. Lithium (Li+) was chosen because it is an efficient treatment for manic-depressive illness, with an unknown action mechanism. After having recalled the theoretical basis

Nadir Zeghib; Daniel Grucker

2001-01-01

184

Relaxation time of the Cooper pairs near Tc in cuprate superconductors  

Microsoft Academic Search

It is first shown that the thermal fluctuation effects on the transport and on the thermodynamic observables above the superconducting transition may provide, when they are analyzed simultaneously and consistently, a powerful tool to access the relaxation time, tau0, of the Cooper pairs with wave vector k = 0 in high-temperature cuprate superconductors (HTSC). Then, we apply this procedure to

M. V. Ramallo; C. Carballeira; J. Viña; J. A. Veira; T. Mishonov; D. Pavuna; F. Vidal

1999-01-01

185

Linear relaxation times of stochastic processes driven by non-Gaussian noises  

Microsoft Academic Search

The linear relaxation time (LRT) associated with steady-state correlation functions is studied for Langevin equations with non-Gaussian noises: dichotomous Markov noise and Poissonian white shot noise. Exact results for arbitrary models are obtained and compared with results for Gaussian noises. Some general features of LRTs are discussed. The concept of dynamic effective diffusion is introduced and the existence of an

J. Casademunt; J. M. Sancho

1989-01-01

186

Very long nuclear relaxation times of spin polarized helium 3 in metal coated cells  

Microsoft Academic Search

We obtained very long relaxation times T1 of up to 120 h for the nuclear polarization of an optically pumped helium 3 gas. The glass containers were internally coated with metallic films such as bismuth or cesium. These findings will have applications in the field of helium magnetometers and polarized targets.

Werner Heil; Hubert Humblot; Ernst Otten; Matthias Schafer; Reinhard Sarkau; Michèle Leduc

1995-01-01

187

Spin time-relaxation within strongly coupled paramagnetic systems exhibiting paramagnetic–ferrimagnetic transitions  

Microsoft Academic Search

The purpose of the present work is a quantitative study of the spin time relaxation within superweak ferrimagnetic materials exhibiting a paramagnetic–ferrimagnetic transition, when the temperature is changed from an initial value Ti to a final one Tf very close to the critical temperature Tc. From a magnetic point of view, the material under investigation is considered to be made

M. Chahid; M. Benhamou

2000-01-01

188

On the measurement of the width of the distribution of relaxation times in polymer glasses  

Microsoft Academic Search

A new method to determine the width of the distribution of relaxation times (DRT) based on calorimetric measurements by temperature modulated differential scanning calorimetry (TMDSC) is presented. The simulation of the glass transition by TMDSC, taking into account a DRT, shows that the inflectional slope of the complex heat capacity, Cp? depends sensitively on the stretched exponential parameter ? of

S Montserrat; J. M Hutchinson

2002-01-01

189

SOLVING THE TRAVELING REPAIRMAN PROBLEM WITH DIFFERENTIATED WAITING TIMES THROUGH LAGRANGIAN RELAXATION  

Microsoft Academic Search

In this paper we present a formulation of the traveling repairman problem with difierentiated waiting times that is derived from the extended disaggregated ?ow formulation for the asymmetric traveling salesman problem. We focus on the usage of the Lagrangian approach as a mechanism of speeding up the solution of the linear relaxation by a simplex method. We show some computational

Ana Maria Rocha; Edite M. G. P. Fernandes

190

Dependence of Nuclear Quadrupole Relaxation Times in Ionic Crystals on the Phonon Spectrum  

Microsoft Academic Search

Nuclear quadrupole relaxation times are calculated for the halogen and alkali nuclei in a number of alkali halides using lattice phonon density curves computed by Karo. The calculated values of T1 at room temperature are generally lower than those obtained using the Debye model and in better agreement with experiment. The variation of T1 with temperature has also been calculated

S. K. Joshi; R. Gupta; T. P. Das

1964-01-01

191

Towards quantitative measurements of relaxation times and other parameters in the brain  

Microsoft Academic Search

The nature and physical significance of the relaxation times T1 and T2 and of proton density are described. Methods of measuring T1 and T2 are discussed with emphasis on the establishment of precision and the maintenance of accuracy. Reported standards of success are briefly reviewed. We expect sensitivities of the order of 1% to be achievable in serial studies. Although

P. S. Tofts; E. P. G. H. Boulay

1990-01-01

192

A convenient way of measuring nuclear spin-lattice relaxation times based on the null method  

Microsoft Academic Search

Describes a method for measuring the nuclear spin-lattice relaxation time T1 by the free precession technique, which offers certain practical advantages, particularly in the measurement of relative values of T1. The method is a simple modification of the original signal-growth technique of Carr and Purcell. Instead of measuring the time constant for the signal growth or the time required for

S. K. Ghosh; E. Tettamanti; A. Panatta

1980-01-01

193

FDTD Modeling of Wave Propagation in Cole-Cole Media With Multiple Relaxation Times  

Microsoft Academic Search

A finite-difference time-domain (FDTD) method for simulating wave propagation in Cole-Cole dispersive media with multiple relaxation times is presented. The main difficulty that the proposed method circumvents is the presence of fractional derivatives in the time-domain representation of the polarization relation. The latter is approximated by a set of auxiliary differential equations using Pad approximants, where each approximant corresponds to

Ioannis T. Rekanos; Theseus G. Papadopoulos

2010-01-01

194

Enhancement of spin relaxation time in hydrogenated graphene spin-valve devices  

NASA Astrophysics Data System (ADS)

Hydrogen adsorbates in graphene are interesting as they are not only strong Coulomb scatterers, but they also induce a change in orbital hybridization of the carbon network from sp2 into sp3. This change increases the spin-orbit coupling and is expected to largely modify spin relaxation. In this work, we report the change in spin transport properties of graphene due to plasma hydrogenation. We observe an up to threefold increase of spin relaxation time ?S after moderate hydrogen exposure. This increase of ?S is accompanied by the decrease of charge and spin diffusion coefficients, resulting in a minor change in spin relaxation length ?S. At high carrier density, we obtain ?S of 7 ?m, which allows for spin detection over a distance of 11 ?m. After hydrogenation, a value of ?S as high as 2.7 ns is measured at room temperature.

Wojtaszek, M.; Vera-Marun, I. J.; Maassen, T.; van Wees, B. J.

2013-02-01

195

Performance of Relaxed-Clock Methods in Estimating Evolutionary Divergence Times and Their Credibility Intervals  

PubMed Central

The rapid expansion of sequence data and the development of statistical approaches that embrace varying evolutionary rates among lineages have encouraged many more investigators to use DNA and protein data to time species divergences. Here, we report results from a systematic evaluation, by means of computer simulation, of the performance of two frequently used relaxed-clock methods for estimating these times and their credibility intervals (CrIs). These relaxed-clock methods allow rates to vary in a phylogeny randomly over lineages (e.g., BEAST software) and in autocorrelated fashion (e.g., MultiDivTime software). We applied these methods for analyzing sequence data sets simulated using naturally derived parameters (evolutionary rates, sequence lengths, and base substitution patterns) and assuming that clock calibrations are known without error. We find that the estimated times are, on average, close to the true times as long as the assumed model of lineage rate changes matches the actual model. The 95% CrIs also contain the true time for ?95% of the simulated data sets. However, the use of incorrect lineage rate model reduces this frequency to 83%, indicating that the relaxed-clock methods are not robust to the violation of underlying lineage rate model. Because these rate models are rarely known a priori and are difficult to detect empirically, we suggest building composite CrIs using CrIs produced from MultiDivTime and BEAST analysis. These composite CrIs are found to contain the true time for ?97% data sets. Our analyses also verify the usefulness of the common practice of interpreting the congruence of times inferred from different methods as a reflection of the accuracy of time estimates. Overall, our results show that simple strategies can be used to enhance our ability to estimate times and their CrIs when using the relaxed-clock methods.

Battistuzzi, Fabia U.; Filipski, Alan; Hedges, S. Blair; Kumar, Sudhir

2010-01-01

196

Effects of relaxation time on start-up time for starting flow of Maxwell fluid in a pipe  

Microsoft Academic Search

Although the analytical solution of the starting flow of Maxwell fluid in a pipe has been derived for a long time, the effect\\u000a of relaxation time ? on start-up time t\\u000a s of this flow is still not well understood. Especially, there exist a series of jumps on the t\\u000a s–? curve. In this paper we introduce a normalized mechanical

Zhen Li; Keqin Zhu

2010-01-01

197

Simulation of lid-driven cavity flows by parallel lattice Boltzmann method using multi-relaxation-time scheme  

Microsoft Academic Search

Two-dimensional near-incompressible steady lid-driven cavity flows (Re = 100-7,500) are simulated using multi-relaxation-time (MRT) model in the parallel lattice Boltzmann BGK Bhatnager-Gross-Krook method (LBGK). Results are compared with those using single-relaxation-time (SRT) model in the LBGK method and previous simulation data using Navier-Stokes equations for the same flow conditions. Effects of variation of relaxation parameters in the MRT model, effects

J.-S. Wu; Y.-L. Shao

2004-01-01

198

Imperfect scaling of time and space–time rainfall  

Microsoft Academic Search

Scale invariance is the most fertile concept to be introduced in stochastic rainfall modeling in 15 years. In particular, a form of scale invariance called multifractality has been exploited to construct parsimonious representations of rainfall in time and space and address fundamental problems of hydrology such as rainfall extremes, downscaling, and forecasting. However, several authors have observed that rainfall is

Daniele Veneziano; Pierluigi Furcolo; Vito Iacobellis

2006-01-01

199

Scale anomaly as the origin of time  

NASA Astrophysics Data System (ADS)

We explore the problem of time in quantum gravity in a point-particle analogue model of scale-invariant gravity. If quantized after reduction to true degrees of freedom, it leads to a time-independent Schrödinger equation. As with the Wheeler-DeWitt equation, time disappears, and a frozen formalism that gives a static wavefunction on the space of possible shapes of the system is obtained. However, if one follows the Dirac procedure and quantizes by imposing constraints, the potential that ensures scale invariance gives rise to a conformal anomaly, and the scale invariance is broken. A behaviour closely analogous to renormalization-group (RG) flow results. The wavefunction acquires a dependence on the scale parameter of the RG flow. We interpret this as time evolution and obtain a novel solution of the problem of time in quantum gravity. We apply the general procedure to the three-body problem, showing how to fix a natural initial value condition, introducing the notion of complexity. We recover a time-dependent Schrödinger equation with a repulsive cosmological force in the `late-time' physics and we analyse the role of the scale invariant Planck constant. We suggest that several mechanisms presented in this model could be exploited in more general contexts.

Barbour, Julian; Lostaglio, Matteo; Mercati, Flavio

2013-05-01

200

Development of the time management environment (TiME) scale  

Microsoft Academic Search

Purpose – The purpose of this paper is to propose an integrative model of time management, and in particular develop a scale to measure organizational variables which would facilitate and support time management practices. The research also examined whether the time management environment is related to turnover intentions and stress. Design\\/methodology\\/approach – Three studies are reported. Study 1 sampled 262

Christopher D. B. Burt; Alexandra Weststrate; Caroline Brown; Felicity Champion

2010-01-01

201

Ion-Beam Sculpting Time Scales  

NASA Astrophysics Data System (ADS)

A study of ion sculpting dynamics in SiO2 and SiN using periodically pulsed ion beams reveals material transport that depends strongly on the time structure of the pulsed beams. It is found that significant nanoscale matter transport can occur over second long time scales after the ion beam has been extinguished. A simple phenomenological model described the dynamics of ion beam sculpting in terms of two material time scales. The model accounts for the surprising observation of enhanced matter transport affected by pulsed ion beams over continuous ion beam exposure.

Stein, Derek; Li, Jiali; Golovchenko, Jene A.

2002-12-01

202

Time scales involved in emergent market coherence  

NASA Astrophysics Data System (ADS)

In addressing the question of the time scales characteristic for the market formation, we analyze high-frequency tick-by-tick data from the NYSE and from the German market. By using returns on various time scales ranging from seconds or minutes up to 2 days, we compare magnitude of the largest eigenvalue of the correlation matrix for the same set of securities but for different time scales. For various sets of stocks of different capitalization (and the average trading frequency), we observe a significant elevation of the largest eigenvalue with increasing time scale. Our results from the correlation matrix study can be considered as a manifestation of the so-called Epps effect. There is no unique explanation of this effect and it seems that many different factors play a role here. One of such factors is randomness in transaction moments for different stocks. Another interesting conclusion to be drawn from our results is that in the contemporary markets the emergence of significant correlations occurs on time scales much smaller than in the more distant history.

Kwapie?, J.; Dro?d?, S.; Speth, J.

2004-06-01

203

Experimental determination of the distribution of relaxation time for thermally activated transition in thin film magnetic recording media  

NASA Astrophysics Data System (ADS)

Although grain size distribution has significant effects on the time decay behavior of thin film magnetic recording media, the grains size itself is not a truly independent parameter due to intergranular exchange coupling. Relaxation time incorporates the interaction. Its distribution will determine the time decay performance of thin film magnetic recording media. An algorithm is proposed to determine the unique distribution of relaxation time in magnetic recording media directly from the experimental data without any presumption. It was found for the first time that the distribution of relaxation time is very well described by Weibull distribution.

Yang, Cheng; Sivertsen, John M.; Li, Tan; Judy, Jack H.

1999-04-01

204

Time scales of turbulent relative dispersion  

NASA Astrophysics Data System (ADS)

Tracers in a turbulent flow separate according to the celebrated t3/2 Richardson-Obukhov law, which is usually explained by a scale-dependent effective diffusivity. Here, supported by state-of-the-art numerics, we revisit this argument. The Lagrangian correlation time of velocity differences increases too quickly for validating this approach, but acceleration differences decorrelate on dissipative time scales. Phenomenological arguments are used to relate the behavior of separations to that of a “local energy dissipation,” defined as the average ratio between the cube of the longitudinal velocity difference and the distance between the two tracers. This quantity is shown to stabilize on short time scales and this results in an asymptotic diffusion ?t1/2 of velocity differences. The time of convergence to this regime is shown to be that of deviations from Batchelor's initial ballistic regime, given by a scale-dependent energy dissipation time rather than the usual turnover time. It is finally demonstrated that the fluid flow intermittency should not affect this long-time behavior of the relative motion.

Bitane, Rehab; Homann, Holger; Bec, Jérémie

2012-10-01

205

Optimal time scale for spike-time reliability  

PubMed Central

Use of spike timing to encode information requires that neurons respond with high temporal precision and with high reliability. Fast fluctuating stimuli are known to result in highly reproducible spike times across trials, whereas constant stimuli result in variable spike times. Here, we have investigated how spike-time reliability depends on the time scale of fluctuations of the input stimuli in real neurons (mitral cells in the olfactory bulb and pyramidal cells in the neocortex) as well as in neuron models (integrate-and-fire and Hodgkin-Huxley) with intrinsic noise. In all cases we found that for firing frequencies in the beta/gamma range, spike reliability is maximal when the input includes fluctuations on the time scale of a few milliseconds (2-5 ms), coinciding with the time scale of fast synapses, and decreases substantially for faster and slower inputs. In addition, we show mathematically that the existence of an optimal time scale for spike-time reliability is a general feature of neurons. Finally, we comment how these findings relate to the mechanisms that cause neuronal synchronization.

Galan, Roberto F.; Ermentrout, G. Bard; Urban, Nathaniel N.

2008-01-01

206

Time resolved infrared absorption studies of geminate recombination and vibrational relaxation in OClO photochemistry  

NASA Astrophysics Data System (ADS)

Ultrafast time-resolved infrared absorption studies of aqueous chlorine dioxide (OClO) photochemistry are reported. Following photoexcitation at 401 nm, the evolution in optical density at frequencies between 1000 to 1100 cm-1 is monitored to investigate vibrational energy deposition and relaxation along the asymmetric-stretch coordinate following the reformation of ground-state OClO via geminate recombination of the primary photofragments. The measured kinetics are compared to two proposed models for the vibrational-relaxation dynamics along the asymmetric-stretch coordinate. This comparison demonstrates that the perturbation model derived from molecular dynamics studies is capable of qualitatively reproducing the observed kinetics, where the collisional model employed in previous UV-pump, visible probe experiments demonstrates poor agreement with experiment. The ability of the perturbation model to reproduce the optical-density evolution observed in these studies demonstrates that for aqueous OClO, frequency dependence of the solvent-solute coupling is important in defining the level-dependent vibrational relaxation rates along the asymmetric-stretch coordinate. The absence of optical-density evolution corresponding to the population of higher vibrational levels (n>8) along the asymmetric-stretch coordinate suggests that following geminate recombination, energy is initially deposited into a local Cl-O stretch, with the relaxation of vibrational energy from this coordinate providing for delayed vibrational excitation of the asymmetric- and symmetric-stretch coordinates relative to geminate recombination, as previously observed.

Bolinger, Joshua C.; Hayes, Sophia C.; Reid, Philip J.

2004-09-01

207

Hydrogen bonding and related association in linear aliphatic amino alcohols as probed by carbon-13 spin-lattice relaxation times  

Microsoft Academic Search

Carbon-13 chemical shifts and spin-lattice relaxation data obtained in a number of solvents for five linear aliphatic amino alcohols are presented. The purpose of monitoring the relaxation behavior was to learn about inter- and intramolecular association as a function of concentration and solvent. An analyses of the Tâ, C13 spin-lattice relaxation time, data reveals that intermolecular OH-OH hydrogen bonding competes

Ulf Edlund; Clive Holloway; George C. Levy

1976-01-01

208

Relationships between induced polarization relaxation time and hydraulic properties of sandstone  

NASA Astrophysics Data System (ADS)

We investigated electrical and physical-chemical properties of six sandstone samples with contrasting mineralogical characteristics and with hydraulic conductivity varying in a wide range. The electrical data were obtained from time domain spectral induced polarization (IP) measurements. We inverted the IP decays to relaxation time distributions, and then compared the modal relaxation times with the dominant pore throat diameters obtained from the Mercury Injection Capillary Pressure (MICP) data. We found a positive logarithmic relationship between the relaxation time and the pore throat diameter. Also, we found the normalized chargeability (an integral IP parameter) to be positively correlated with the clay content. These two results suggest that the polarization of our sandstones is controlled by the pore throat distribution, and by the clay content. The logarithmic relationship contradicts previous theories, and is not universal. Adopting an approach of Kruschwitz and her co-workers, we calculated the effective diffusivity from IP and MICP data, and we found the effective diffusivity values ranging from 2.9 × 10-13 to 1.6 × 10-10 m2s-1. High diffusivity values, typical of surface diffusion, were obtained for clean sandstones. Low diffusivity values were obtained for clayey sandstones, and they were one to two orders of magnitude lower than those characteristic of the surface diffusion. We proposed two mechanisms to explain the `slow' diffusion: (1) the effect of surface tortuosity of pore throats filled with clay minerals and (2) the effect of pore geometry. These two effects represent an obstacle in assessing the pore throat diameter and hydraulic conductivity of sandstones with large specific surface and clay content on the basis of spectral IP measurements. However, we believe that the sandstones featuring `slow' diffusion can be discriminated based on the integral polarization parameters, and that the relaxation time remains a valuable parameter for assessing hydraulic properties of clean sandstones.

Titov, Konstantin; Tarasov, Andrey; Ilyin, Yuri; Seleznev, Nikita; Boyd, Austin

2010-03-01

209

Nuclear spin-lattice relaxation-time reduction in small particles  

NASA Astrophysics Data System (ADS)

A method is described of reducing the nuclear spin-lattice relaxation time in a polycrystalline solid without the introduction of any paramagnetic impurities. It relies on the fact that the relaxation times of nuclei on a surface are usually much shorter than those in the bulk due to greater freedom of movement. Simply reducing the particle size by grinding or other methods is shown to be effective in markedly reducing the spin-lattice relaxation time of all the nuclei in the specimen because of the good thermal contact between like nuclei in the interior and surface of small particles. The nuclear quadrupole resonance (NQR) of 14N, 2D, or 23Na was measured for the same specimens with different particle sizes by nuclear quadrupole double resonance to ensure that the chemical structure of the compound did not alter due to the grinding. In all samples studied, except sodium thiosulphate, the NQR spectrum was unaffected by the grinding except that the time necessary to collect the data was reduced. In the case of sodium thiosulphate a marked change in the NQR spectrum was observed despite the fact that no change in chemical composition could be detected. Data is presented which demonstrates the effectiveness of the technique and a simple model of the underlying mechanism is described.

Rabbani, S. R.; Edmonds, D. T.

1994-09-01

210

Imperfect scaling of time and space time rainfall  

NASA Astrophysics Data System (ADS)

Scale invariance is the most fertile concept to be introduced in stochastic rainfall modeling in 15 years. In particular, a form of scale invariance called multifractality has been exploited to construct parsimonious representations of rainfall in time and space and address fundamental problems of hydrology such as rainfall extremes, downscaling, and forecasting. However, several authors have observed that rainfall is scale invariant only in approximation and within limited ranges. Here, we make a systematic analysis of the deviations of time and space time rainfall from multifractality. We use a flexible multiplicative cascade model, which produces multifractality as a special case while allowing deviations from scale invariance to occur. By fitting the model to rainfall records from different climates and over land or ocean, we find significant and consistent departures from multifractality in both the alternation of wet and dry conditions and the fluctuations of precipitation intensity when it rains. The fractal dimension of the rain support increases with increasing rain rate and the (multiplicative) fluctuations are larger at smaller scales and for lighter rainfall. A plausible explanation of these departures from scaling is that the rate of water vapor condensation in the atmosphere is a multifractal process in three space dimensions plus time, but multifractality is destroyed when the condensation rate is integrated to produce rainfall intensity at fixed altitudes.

Veneziano, Daniele; Furcolo, Pierluigi; Iacobellis, Vito

2006-05-01

211

A new nonlocal traffic flow model with anticipation-dependent relaxation time, equilibrium velocity and variance  

NASA Astrophysics Data System (ADS)

We derived a nonlocal kinetic traffic model from a generalized car-following model with multiple look-ahead through the BBGKY hierarchy. A nonlocal hydrodynamical model was obtained consistently by the method of kinetic theory. The novel feature of nonlocality in equilibrium velocity and variance as well as in relaxation time was discovered. Simulation results showed that traffic hysteresis was induced by anticipation-dependent equilibrium velocity, relaxation time and equilibrium variance, indicating a 2D-region of synchronized flow. When drivers looked farther ahead, the amplitude of stop-and-go traffic reduced, and the resulting equilibrium velocity and flow increased, thus traffic stabilized as expected. Numerical results also indicated the existence of optimum anticipation vision. Finally, the model could also capture the physical nonlinear dynamic characteristics of metastability and the stop-and-go phenomenon in traffic flow.

Qiu, Yuzhuo; Chen, Senfa

2010-12-01

212

Transport relaxation time and quantum lifetime in selectively doped GaAs/AlAs heterostructures  

NASA Astrophysics Data System (ADS)

Low-temperature dependences of the transport relaxation time (?tr) and quantum lifetime (?q) on the density of the two-dimensional electron gas ( n e ) in GaAs quantum wells with AlAs/GaAs lateral superlattice barriers have been studied. An exponential increase in the quantum lifetime with increasing electron density has been observed. It has been shown that the sharp increase in the quantum lifetime correlates with the appearance of X electrons in the AlAs/GaAs lateral superlattice barriers. It has been established that the ratio of the transport relaxation time to the quantum lifetime in the studied structures nonmonotonically depends on the density: the ratio ?tr/?q first increases linearly with n e and then decreases. This behavior is not described by the existing theories.

Dmitriev, D. V.; Strygin, I. S.; Bykov, A. A.; Dietrich, S.; Vitkalov, S. A.

2012-06-01

213

Measuring non-radiative relaxation time of fluorophores with biomedical applications by intensity-modulated laser-induced photoacoustic effect  

PubMed Central

Modulated tone-burst light was employed to measure non-radiative relaxation time of fluorophores with biomedical importance through photoacoustic effect. Non-radiative relaxation time was estimated through the frequency dependence of photoacoustic signal amplitude. Experiments were performed on solutions of new indocyanine green (IR-820), which is a near infrared dye and has biomedical applications, in two different solvents (water and dimethyl sulfoxide (DMSO)). A 1.5 times slower non-radiative relaxation for the solution of dye in DMSO was observed comparing with the aqueous solution. This result agrees well with general finding that non-radiative relaxation of molecules in triplet state depends on viscosity of solvents in which they are dissolved. Measurements of the non-radiative relaxation time can be used as a new source of contrast mechanism in photoacoustic imaging technique. The proposed method has potential applications such as imaging tissue oxygenation and mapping of other chemophysical differences in microenvironment of exogenous biomarkers.

Soroushian, Behrouz; Yang, Xinmai

2011-01-01

214

Nuclear magnetic relaxations times of 3He IN 3He4He solutions  

Microsoft Academic Search

The longitudinal and transverse relaxation times T1 and T2 of the nuclear spins of 3He in solution in 4HE for high and low temperatures are calculated and shown to be equal for reasonable external magnetic fields. The result is compared with experimental data. Research supported by the Air Force of Scientific Research, U.S. Air Force under AFOSR Grant No. AF-AFOSR-869-65

C. C. Sung

1967-01-01

215

Waiting time after non-depolarizing relaxants alter muscle fasciculation response to succinylcholine  

Microsoft Academic Search

The purpose of the study was to determine the effect of non-depolarizing muscle relaxants and waiting time on muscle fasciculations\\u000a after succinylcholine in anaesthetized patients. Adult men and women, 60–80 kg, received pretreatment doses of atracurium\\u000a 5 mg (n = 160), pancuronium 1 mg (n = 123), d-tubocurarine 3 mg (n = 97), or vecuronium 1 mg (n = 62).

Alfred C. Pinchak; Charles E. Smith; Lee S. Shepard; Louise Patterson

1994-01-01

216

Determination of discrete relaxation and retardation time spectra from dynamic mechanical data  

Microsoft Academic Search

A powerful but still easy to use technique is proposed for the processing and analysis of dynamic mechanical data. The experimentally determined dynamic moduli,G'(?) andG?(?), are converted into a discrete relaxation modulusG(t) and a discrete creep complianceJ(t). The discrete spectra are valid in a time window which corresponds to the frequency window of the input data. A nonlinear regression simultaneously

M. Baumgaertel; H. H. Winter

1989-01-01

217

Evaluation of water content by spatially resolved transverse relaxation times of human articular cartilage  

Microsoft Academic Search

Non-invasive assessment of cartilage properties, specifically water content, could prove helpful in the diagnosis of early degenerative joint diseases. Transverse relaxation times T2 of human articular cartilage (34 cartilage slices of three donors) were measured on a pixel-by-pixel basis in a clinical whole body MR system in vitro. In vivo feasibility to measure quantitative T2 maps was shown for human

S Lüssea; H Claassen; T Gehrke; J Hassenpflug; M Schünke; M Heller; C.-C Glüer

2000-01-01

218

Two-relaxation-time lattice Boltzmann method for the anisotropic dispersive Henry problem  

Microsoft Academic Search

This study develops a lattice Boltzmann method (LBM) with a two-relaxation-time collision operator (TRT) to cope with anisotropic heterogeneous hydraulic conductivity and anisotropic velocity-dependent hydrodynamic dispersion in the saltwater intrusion problem. The directional-speed-of-sound technique is further developed to address anisotropic hydraulic conductivity and dispersion tensors. Forcing terms are introduced in the LBM to correct numerical errors that arise during the

Borja Servan-Camas; Frank T.-C. Tsai

2010-01-01

219

A new relaxation algorithm for the time optimal control problem of step motors  

Microsoft Academic Search

The free end-velocity time-optimal control of a bifilar-wound hybrid step motor is considered. The necessary conditions for the optimal control are derived from motor, load, and driver circuit models using Pontryagin's minimum principle. A reduced-order relaxation method, involving forward\\/backward integrations, is presented for finding the solution to the nonlinear two-point boundary value problem specified by the necessary conditions, including generation

R. H. Brown; Y. Zhu; X. Feng

1989-01-01

220

Discontinuous Galerkin and Nonconforming in Time Optimized Schwarz Waveform Relaxation for Heterogeneous Problems  

Microsoft Academic Search

We consider the question of domain decomposition for evolution problems with discontinuous coefficients.We design a method\\u000a relying on four ingredients: extension of the optimized Schwarz waveform relaxation algorithms as described in [1], discontinuous\\u000a Galerkin methods designed in [7], time windows, and a generalization of the projection procedure given in [6]. We so obtain\\u000a a highly performant method, which retains the

Laurence Halpern; Caroline Japhet

221

Brain T2 relaxation times correlate with regional cerebral blood volume  

Microsoft Academic Search

We previously reported cerebellar and putaminal transverse relaxation time (T2) differences in children with ADHD and in adults with childhood trauma. As brain T2 can be altered by deoxyhemoglobin concentration ([dHb]) and because [dHb] is proportional to regional cerebral blood volume (rCBV), at steady state we attributed those differences to rCBV changes. Studies in other species have established a correlation

C. M. Anderson; M. J. Kaufman; S. B. Lowen; M. Rohan; P. F. Renshaw; M. H. Teicher

2005-01-01

222

Relaxation-time approximation for a Boltzmann gas in Robertson-Walker universe models  

Microsoft Academic Search

Given Einstein's theory of gravitation, the relaxation-time approximation for a general-relativistic Boltzmann equation is studied with a view to demonstrating its usefulness in the context of Robertson-Walker universe models. Solutions of the full nonlinear equations for the metric and the distribution function are examined, together with their relation to linearized perturbations. Emphasis is placed on finding analogs of the exact

Zbigniew Banach; Hanna Makaruk

1995-01-01

223

T2 relaxation time study of iron overload in b-thalassemia  

Microsoft Academic Search

Myocardial iron deposition occurs as a result of blood transfusion therapy in b-thalassemia major patients. Since this deposition\\u000a causes various cardiac complications, it is of interest to assess the iron content of the myocardium in relation to the clinical\\u000a picture of the patients. Two different MRI indices were used to achieve this purpose: the T2 relaxation time and the heart\\/skeletal

S. I. Mavrogeni; E. D. Gotsis; V. Markussis; N. Tsekos; C. Politis; E. Vretou; D. Kremastinos

1998-01-01

224

Phenomenological approach on wave propagation in dielectric media with two relaxation times  

NASA Astrophysics Data System (ADS)

In this paper dielectric phenomena with two relaxation times are discussed. By assuming a sinusoidal form for induction vector D a sinusoidal electric field is generated and it depends on unknown phenomenological coefficients whose expressions together to their numerical values as functions of frequency are obtained. Moreover, electromagnetic wave propagation is analysed obtaining wave vector as function of the aforementioned coefficients. The results are applied to a Vinylidene Chloride-Vinyl Chloride (VDC-VC) to test the applicability of the model.

Ciancio, V.; Farsaci, F.; Rogolino, P.

2009-02-01

225

Hot band rotational relaxation time in carbonyl sulfide by transient infrared–microwave double resonance  

Microsoft Academic Search

Rotational relaxation time (T) has been measured for pure carbonyl sulfide (16O 12C 32S) in a highly vibrationally and rotationally excited state (031f0, J = 24). A pulsed CO2 laser [P9(24)] line was used to excite the OCS gas: (011f0, J = 25) ? (031f0, J = 24). The transient population difference between l-doublet states (031f0, J = 24) and

John W. Leap; Paul D. Coleman

1982-01-01

226

Multi relaxation time lattice Boltzmann simulations of deep lid driven cavity flows at different aspect ratios  

Microsoft Academic Search

In this paper, the multi relaxation time (MRT) lattice Boltzmann equation (LBE) was used to compute lid driven cavity flows at different Reynolds numbers (100–7500) and cavity aspect ratios (1–4 cavity width depth). Steady solutions were obtained for square cavity flows, however for deep cavity flows at 1.5 and 4 cavity width depth, unsteady solutions prevail at Re=7500, where periodic

Li-Song Lin; Yi-Cheng Chen; Chao-An Lin

2011-01-01

227

Compression stress relaxation apparatus for the long-time monitoring of the incremental modulus  

NASA Astrophysics Data System (ADS)

A compression apparatus for aging experiments on soft rubbers and foams is presented. The sample is compressed between two parallel surfaces and held there for long-time relaxation studies. The specific purpose of the test is twofold: possible exposure of the sample to aggressive environment under compression during aging and measurement of sample modulus without unloading, i.e., while leaving the sample under constant compression at all times. To determine the restoring force in the compressed sample, the compression strain is modulated with an incremental strain while measuring the force response. The total force gives the compression modulus, and the slope of the force-strain curve allows the determination of the incremental modulus. Stress relaxation data for silicon foam, Dow Corning S-5370 RTV, with 68% void fraction are shown. The modulus of the compressed sample decays over long experimental times of several days. The decay can be described by two relaxation modes, a short mode at 1500 s and a long mode at about 105 s. The incremental modulus changes sharply in the first 1000 s (first mode) and then levels off. The apparatus consists of two self-contained components, the removable sample holder (compression jig) and the stationary test station, which performs the modulation of the strain and all measurements (restoring force and incremental modulus). This allows separation of functions. The apparatus design specifically focused on the control of the incremental strain modulation.

Horst, Roland H.; Stephens, Thomas S.; Coons, James E.; Winter, H. Henning

2003-11-01

228

Generalized Mittag-Leffler relaxation: clustering-jump continuous-time random walk approach.  

PubMed

A stochastic generalization of renormalization-group transformation for continuous-time random walk processes is proposed. The renormalization consists in replacing the jump events from a randomly sized cluster by a single renormalized (i.e., overall) jump. The clustering of the jumps, followed by the corresponding transformation of the interjump time intervals, yields a new class of coupled continuous-time random walks which, applied to modeling of relaxation, lead to the general power-law properties usually fitted with the empirical Havriliak-Negami function. PMID:18763915

Jurlewicz, Agnieszka; Weron, Karina; Teuerle, Marek

2008-07-02

229

TimeScale Modification of Speech Signals  

Microsoft Academic Search

This paper presents methods for independently modifying the time and pitch scale of acoustic sig- nals, with an emphasis on speech signals. The algorithms developed here use parametric (sinu- soidal) modelling techniques introduced by other authors, but new perspectives on the role of vocal tract decomposition and maintaining phase relationships between sinusoidal tracks are derived that achieve improved output quality

Brett Ninness; Soren John Henriksen

2008-01-01

230

Carrier Concentrations and Relaxation Spectroscopy: New Information from Scaling Properties of Conductivity Spectra in Ionically Conducting Glasses  

NASA Astrophysics Data System (ADS)

A new kind of scaling analysis for the conductivity spectra of glasses without any arbitrary parameters is presented. By applying this method to sodium borate glasses of different compositions, we find strong indications for the existence of a universal ionic relaxation process as well as for a strong electrolyte behavior. Our results enable us to show that the often used electric modulus formalism is misleading when relaxation mechanisms on a microscopic level are concerned. A more meaningful discussion can be based on the log-log dependence of the conductivity on frequency.

Roling, B.; Happe, A.; Funke, K.; Ingram, M. D.

1997-03-01

231

The effect of physical ageing on the relaxation time spectrum of amorphous polymers: the fractional calculus approach  

Microsoft Academic Search

Empirical models corresponding to a constitutive equation with fractional derivatives are proposed for linear viscoelastic polymers. For these models, the relaxation modulus, the dynamic moduli, the relaxation time spectra, and other material functions can be calculated as a function of a few parameters that characterise the behaviour of a viscoelastic polymer. The fractional calculus approach allows us to calculate the

M. Alcoutlabi; J. J. Martinez-Vega

1999-01-01

232

Distribution of relaxation times from dielectric spectroscopy using Monte Carlo simulated annealing: Application to alpha-PVDF  

Microsoft Academic Search

The existence of a distribution of relaxation times has been widely used to describe the relaxation function versus frequency in glass-forming liquids. Several empirical distributions have been proposed and the usual method is to fit the experimental data to a model that assumes one of these functions. Another alternative is to extract from the experimental data the discrete profile of

A. Bello; E. Laredo; M. Grimau

1999-01-01

233

Reducing the parallel solution time of sparse circuit matrices using reordered Gaussian elimination and relaxation  

NASA Astrophysics Data System (ADS)

Using parallel processors to reduce the execution times of classical circuit simulation programs like SPICE and ASTAP has been the focus of much current research. In these efforts, good parallel speed increases were achieved for linearized system construction, but it has been difficult to get good parallel speed increases for sparse matrix solution. In this paper we examine two approaches for reducing parallel sparse matrix solution time; the first based on pivot ordering algorithms for Gaussian elimination, and the second based on relaxation algorithms. In the section on Gaussian elimination sparse matrix solution, we present a pivot ordering algorithm which increases the parallelism of Gaussian elimination compared to the commonly used Markowitz method. The performance of the new algorithm is compared to other suggested ordering algorithms for a collection of circuit examples. The minimum number of parallel steps for the solution of a tridiagonal matrix is derived, and it is shown that this optimum is nearly achieved by the ordering heuristics which attempt to maximize parallelism. In the section on relaxation, we present an optimality result about Gauss-Jacobi over Gauss-Seidel relaxation on parallel processors.

Smart, David; White, Jacob

1988-03-01

234

Structure formation, melting, and optical properties of gold/DNA nanocomposites: Effects of relaxation time  

NASA Astrophysics Data System (ADS)

We present a model for structure formation, melting, and optical properties of gold/DNA nanocomposites. These composites consist of a collection of gold nanoparticles (of radius 50 nm or less) which are bound together by links made up of DNA strands. In our structural model, the nanocomposite forms from a series of Monte Carlo steps, each involving reaction-limited cluster-cluster aggregation (RLCA) followed by dehybridization of the DNA links. These links form with a probability peff which depends on temperature T and particle radius a. The final structure depends on the number of monomers (i.e., gold nanoparticles) Nm, T, and the relaxation time. At low temperature, the model results in a RLCA cluster. But after a long enough relaxation time, the nanocomposite reduces to a compact, nonfractal cluster. We calculate the optical properties of the resulting aggregates using the discrete dipole approximation. Despite the restructuring, the melting transition (as seen in the extinction coefficient at wavelength 520 nm) remains sharp, and the melting temperature TM increases with increasing a as found in our previous percolation model. However, restructuring increases the corresponding link fraction at melting to a value well above the percolation threshold. Our calculated extinction cross section agrees qualitatively with experiments on gold/DNA composites. It also shows a characteristic “rebound effect,” resulting from incomplete relaxation, which has also been seen in some experiments. We discuss briefly how our results relate to a possible sol-gel transition in these aggregates.

Park, Sung Yong; Stroud, D.

2003-12-01

235

Temperature dependence of relaxation times and temperature mapping in ultra-low-field MRI  

NASA Astrophysics Data System (ADS)

Ultra-low-field MRI is an emerging technology that allows MRI and NMR measurements in microtesla-range fields. In this work, the possibilities of relaxation-based temperature measurements with ultra-low-field MRI were investigated by measuring T1 and T2 relaxation times of agarose gel at 50 ?T-52 mT and at temperatures 5-45 °C. Measurements with a 3 T scanner were made for comparison. The Bloembergen-Purcell-Pound relaxation theory was combined with a two-state model to explain the field-strength and temperature dependence of the data. The results show that the temperature dependencies of agarose gel T1 and T2 in the microtesla range differ drastically from those at 3 T; the effect of temperature on T1 is reversed at approximately 5 mT. The obtained results were used to reconstruct temperature maps from ultra-low-field scans. These time-dependent temperature maps measured from an agarose gel phantom at 50 ?T reproduced the temperature gradient with good contrast.

Vesanen, Panu T.; Zevenhoven, Koos C. J.; Nieminen, Jaakko O.; Dabek, Juhani; Parkkonen, Lauri T.; Ilmoniemi, Risto J.

2013-10-01

236

Continuum approach to self-similarity and scaling in morphological relaxation of a crystal with a facet  

NASA Astrophysics Data System (ADS)

The morphological relaxation of axisymmetric crystal surfaces with a single facet below the roughening transition temperature is studied analytically for diffusion-limited (DL) and attachment-detachment-limited (ADL) kinetics with inclusion of the Ehrlich-Schwoebel barrier. The slope profile F(r,t) , where r is the polar distance and t is time, is described via a nonlinear, fourth-order partial differential equation (PDE) that accounts for step line-tension energy g1 and step-step repulsive interaction energy g3 ; for ADL kinetics, an effective surface diffusivity that depends on the step density is included. The PDE is derived directly from the step-flow equations and, alternatively, via a continuum surface free energy. The facet evolution is treated as a free-boundary problem where the interplay between g1 and g3 gives rise to a region of rapid variations of F , a boundary layer, near the expanding facet. For long times and g3/g1scales as (g3/g1)-1/6 , and (f) the change of the facet radius from its limit as g3/g1?0 scales as (g3/g1)1/3 . For ADL kinetics a boundary layer can still be defined, with thickness that varies as (g3/g1)3/8 . Our scaling results are in excellent agreement with kinetic simulations.

Margetis, Dionisios; Aziz, Michael J.; Stone, Howard A.

2005-04-01

237

Biogeographic Kinetics: Estimation of Relaxation Times for Avifaunas of Southwest Pacific Islands  

PubMed Central

When species diversity S on an island is displaced from the equilibrium value by injection or removal of species, S relaxes to equilibrium by an imbalance between immigration and extinction rates. Estimates of exponential relaxation times, tr, for avifaunas of New Guinea satellite islands are calculated from analysis of four “experiments of nature”: recolonization of exploded volcanoes, contraction in island area due to rising sea level, severing of land bridges, and disappearance of landbridge relict species. tr is in the range 3,000-18,000 years for avifaunas of islands of 50-3000 square miles (130-7800 km2), and increases with island area. Immigration coefficients decrease and extinction coefficients increase with increasing S. The results may be relevant to the design of rainforest preserves.

Diamond, Jared M.

1972-01-01

238

Interfacial layers from the protein HFBII hydrophobin: dynamic surface tension, dilatational elasticity and relaxation times.  

PubMed

The pendant-drop method (with drop-shape analysis) and Langmuir trough are applied to investigate the characteristic relaxation times and elasticity of interfacial layers from the protein HFBII hydrophobin. Such layers undergo a transition from fluid to elastic solid films. The transition is detected as an increase in the error of the fit of the pendant-drop profile by means of the Laplace equation of capillarity. The relaxation of surface tension after interfacial expansion follows an exponential-decay law, which indicates adsorption kinetics under barrier control. The experimental data for the relaxation time suggest that the adsorption rate is determined by the balance of two opposing factors: (i) the barrier to detachment of protein molecules from bulk aggregates and (ii) the attraction of the detached molecules by the adsorption layer due to the hydrophobic surface force. The hydrophobic attraction can explain why a greater surface coverage leads to a faster adsorption. The relaxation of surface tension after interfacial compression follows a different, square-root law. Such behavior can be attributed to surface diffusion of adsorbed protein molecules that are condensing at the periphery of interfacial protein aggregates. The surface dilatational elasticity, E, is determined in experiments on quick expansion or compression of the interfacial protein layers. At lower surface pressures (<11 mN/m) the experiments on expansion, compression and oscillations give close values of E that are increasing with the rise of surface pressure. At higher surface pressures, E exhibits the opposite tendency and the data are scattered. The latter behavior can be explained with a two-dimensional condensation of adsorbed protein molecules at the higher surface pressures. The results could be important for the understanding and control of dynamic processes in foams and emulsions stabilized by hydrophobins, as well as for the modification of solid surfaces by adsorption of such proteins. PMID:22480400

Alexandrov, Nikola A; Marinova, Krastanka G; Gurkov, Theodor D; Danov, Krassimir D; Kralchevsky, Peter A; Stoyanov, Simeon D; Blijdenstein, Theodorus B J; Arnaudov, Luben N; Pelan, Eddie G; Lips, Alex

2012-03-20

239

Dielectric relaxation in metal-coated particles: the dramatic role of nano-scale coatings  

Microsoft Academic Search

Insulating materials filled with conducting particles permit tailoring of electrical, electromagnetic and thermal properties of the resulting composite. When the filler particles are small and metallic, a dielectric relaxation due to interfacial polarization is commonly observed at optical or smaller wavelengths. Here, experimental results are presented in which the dielectric relaxation is shifted to microwave frequencies as a result of

I J Youngs; N Bowler; K P Lymer; S Hussain

2005-01-01

240

Longitudinal rotating frame relaxation time measurements in infarcted mouse myocardium in vivo.  

PubMed

Longitudinal relaxation time in the rotating frame (T1?) was measured using continuous wave irradiation in normal and infarcted mouse myocardium in vivo. Significant increase in T1? was found after 7 days of infarction when compared with reference myocardium or in myocardium before infarction. Cine MRI and histology were performed to verify the severity of infarction. The time course of T1? in the infarct fits better with granulation and scar tissue formation than necrosis and edema. The results of the study show that T1? could potentially be a noninvasive quantitative marker for tissue remodeling after ischemic damage. PMID:22736543

Musthafa, Haja-Sherief N; Dragneva, Galina; Lottonen, Line; Merentie, Mari; Petrov, Lyubomir; Heikura, Tommi; Ylä-Herttuala, Elias; Ylä-Herttuala, Seppo; Gröhn, Olli; Liimatainen, Timo

2012-06-26

241

Dielectric relaxation studies of methyl cellulose with phenol derivatives in non-polar solvents using time domain reflectometry  

NASA Astrophysics Data System (ADS)

Dielectric relaxation measurements of methyl cellulose with substituted phenols p-cresol, m-cresol and o-cresol mixture in different non-polar solvents CCl4, benzene and 1,4-dioxan for different concentrations over the frequency range of 10 MHz-20 GHz at 303 K have been carried out using Time Domain Reflectometry (TDR). Dielectric parameters such as static permittivity (?0) and relaxation time (?) were determined and discussed to yield information on the molecular structure and dynamics of the mixture. The dielectric constant and relaxation time were found to be high for methyl cellulose with p-cresol in CCl4 compared with the other mixtures.

Mohan Kumar, P.; Malathi, M.; Khirade, P. W.

2009-11-01

242

Two-exponential analysis of spin-spin proton relaxation times in MR imaging using surface coils  

Microsoft Academic Search

Proton relaxation time measurements were performed on a standard whole body MR imager operating at 1.5 T using a conventional surface coil of the manufacturer. A combined CP\\/CPMG multiecho, multislice sequence was used for the T1 and T2 relaxation time measurements. Two repetition times of 2000 ms (30 echoes) and 600 ms (2 echoes) with 180 degrees-pulse intervals of 2

Lothar R. Schad; Gunnar Brix; Wolfhard Semmler; F. L. Gueckel; Walter J. Lorenz

1989-01-01

243

Multi-scale dynamics and relaxation of a tethered membrane in a solvent by Monte Carlo simulations  

NASA Astrophysics Data System (ADS)

A tethered membrane modeled by a flexible sheet dissipates entropy as it wrinkles and crumples. Nodes of a coarse grained membrane are connected via multiple pathways for dynamical modes to propagate. We consider a sheet with nodes connected by fluctuating bonds on a cubic lattice. The empty lattice sites constitute an effective solvent medium via node-solvent interaction. Each node execute its stochastic motion with the Metropolis algorithm subject to bond fluctuations, excluded volume constraints, and interaction energy. Dynamics and conformation of the sheet are examined at a low and a high temperature with attractive and repulsive node-node interactions for the contrast in an attractive solvent medium. Variations of the mean square displacement of the center node of the sheet and that of its center of mass with the time steps are examined in detail which show different power-law motion from short to long time regimes. Relaxation of the gyration radius and scaling of its asymptotic value with the molecular weight are examined.

Pandey, Ras; Anderson, Kelly; Farmer, Barry

2006-03-01

244

Millisecond Time-Resolved Changes Occurring in Ca2+-regulated Myosin Filaments upon Relaxation  

PubMed Central

Summary Contraction of many muscles is activated in part by the binding of Ca2+ to, or phosphorylation of, the myosin heads on the surface of the thick filaments. In relaxed muscle, the myosin heads are helically ordered and undergo minimal interaction with actin. On Ca2+ binding or phosphorylation, the head array becomes disordered, reflecting breakage of the head-head and other interactions that underlie the ordered structure. Loosening of the heads from the filament surface enables them to interact with actin filaments, bringing about contraction. On relaxation the heads return to their ordered positions on the filament backbone. In scallop striated adductor muscle, the disordering that takes place on Ca2+ binding occurs on the millisecond timescale, suggesting that it is a key element of muscle activation. Here we have studied the reverse process. Using time-resolved negative staining electron microscopy we show that the rate of re-ordering on removal of Ca2+ also occurs on the same physiological timescale. Direct observation of images, together with analysis of their Fourier transforms, shows that activated heads regain their axial ordering within 20 msec and become ordered in their final helical positions within 50 msec. This rapid reordering suggests that re-formation of the ordered structure, and the head-head and other interactions that underlie it, is a critical element of the relaxation process.

Zhao, Fa-Qing; Craig, Roger

2008-01-01

245

Time scales of memory, learning, and plasticity.  

PubMed

After only about 10 days would the storage capacity of our nervous system be reached if we stored every bit of input. The nervous system relies on at least two mechanisms that counteract this capacity limit: compression and forgetting. But the latter mechanism needs to know how long an entity should be stored: some memories are relevant only for the next few minutes, some are important even after the passage of several years. Psychology and physiology have found and described many different memory mechanisms, and these mechanisms indeed use different time scales. In this prospect we review these mechanisms with respect to their time scale and propose relations between mechanisms in learning and memory and their underlying physiological basis. PMID:23160712

Tetzlaff, Christian; Kolodziejski, Christoph; Markelic, Irene; Wörgötter, Florentin

2012-11-18

246

11B MAS NMR spectroscopic study of structural relaxation, aging, and memory effect at the atomic scale in a borosilicate glass.  

PubMed

Relaxation kinetics of boron coordination environments in a borosilicate glass in response to temperature jumps has been monitored using (11)B magic-angle spinning (MAS) NMR spectroscopy. The relaxation time scale of the BO4/BO3 ratio is found to be closely comparable with those of the bulk properties, namely, refractive index and viscosity, showing a close connection with one another. Samples partially equilibrated at a low temperature, when subjected to a positive temperature jump, display an initial rapid decrease followed by an increase in the BO4/BO3 ratio. This reversal in the trend of the variation of the BO4/BO3 ratio has been interpreted to be the signature of a memory effect, and the implications are discussed within the framework of the potential energy landscape model of glassy dynamics. PMID:17661507

Uzun, Sezen Soyer; Sen, Sabyasachi

2007-07-28

247

Assessment of nonradiative relaxation time and characteristic diffusion time of neodymium, erbium and cobalt doped low silica calcium aluminosilicate glasses  

NASA Astrophysics Data System (ADS)

Nonradiative relaxation time ( ?) and characteristic diffusion time (??) of Nd, Er and Co doped low silica calcium aluminosilicate (LSCA) glasses were assessed by means of photoacoustic spectroscopy. The results are interpreted in terms of frequency dependence predicted by the theory of Rosencwaig and Gersho. Whereas ? varied between 7.2 ms and 36 ms, the values of ?? lied between 0.25 ms and 0.7 ms. For the neodymium doped LSCA glass, a decrease in ?? was observed as the ion concentration was increased. The results indicates that rare earth ion acts as network modifier, disrupting the glass lattice.

Mota, L.; Sampaio, J. A.; da Silva, M. G.; Vargas, H.

2011-01-01

248

Estimation of water retention parameters from nuclear magnetic resonance relaxation time distributions  

PubMed Central

[1] For characterizing water flow in the vadose zone, the water retention curve (WRC) of the soil must be known. Because conventional WRC measurements demand much time and effort in the laboratory, alternative methods with shortened measurement duration are desired. The WRC can be estimated, for instance, from the cumulative pore size distribution (PSD) of the investigated material. Geophysical applications of nuclear magnetic resonance (NMR) relaxometry have successfully been applied to recover PSDs of sandstones and limestones. It is therefore expected that the multiexponential analysis of the NMR signal from water-saturated loose sediments leads to a reliable estimation of the WRC. We propose an approach to estimate the WRC using the cumulative NMR relaxation time distribution and approximate it with the well-known van-Genuchten (VG) model. Thereby, the VG parameter n, which controls the curvature of the WRC, is of particular interest, because it is the essential parameter to predict the relative hydraulic conductivity. The NMR curves are calibrated with only two conventional WRC measurements, first, to determine the residual water content and, second, to define a fixed point that relates the relaxation time to a corresponding capillary pressure. We test our approach with natural and artificial soil samples and compare the NMR-based results to WRC measurements using a pressure plate apparatus and to WRC predictions from the software ROSETTA. We found that for sandy soils n can reliably be estimated with NMR, whereas for samples with clay and silt contents higher than 10% the estimation fails. This is the case when the hydraulic properties of the soil are mainly controlled by the pore constrictions. For such samples, the sensitivity of the NMR method for the pore bodies hampers a plausible WRC estimation. Citation: Costabel, S., and U. Yaramanci (2013), Estimation of water retention parameters from nuclear magnetic resonance relaxation time distributions, Water Resour. Res., 49, 2068-2079, doi:10.1002/wrcr.20207.

Costabel, Stephan; Yaramanci, Ugur

2013-01-01

249

Influence of aging time of oleate precursor on the magnetic relaxation of cobalt ferrite nanoparticles synthesized by the thermal decomposition method  

NASA Astrophysics Data System (ADS)

Cobalt ferrite nanoparticles are of interest because of their room temperature coercivity and high magnetic anisotropy constant, which make them attractive in applications such as sensors based on the Brownian relaxation mechanism and probes to determine the mechanical properties of complex fluids at the nanoscale. These nanoparticles can be synthesized with a narrow size distribution by the thermal decomposition of an iron-cobalt oleate precursor in a high boiling point solvent. We studied the influence of aging time of the iron-cobalt oleate precursor on the structure, chemical composition, size, and magnetic relaxation of cobalt ferrite nanoparticles synthesized by the thermal decomposition method. The structure and thermal behavior of the iron-cobalt oleate was studied during the aging process. Infrared spectra indicated a shift in the coordination state of the oleate and iron/cobalt ions from bidentate to bridging coordination. Aging seemed to influence the thermal decomposition of the iron-cobalt oleate as determined from thermogravimmetric analysis and differential scanning calorimetry, where shifts in the temperatures corresponding to decomposition events and a narrowing of the endotherms associated with these events were observed. Aging promoted formation of the spinel crystal structure, as determined from X-ray diffraction, and influenced the nanoparticle magnetic properties, resulting in an increase in blocking temperature and magnetocrystalline anisotropy. Mossbauer spectra also indicated changes in the magnetic properties resulting from aging of the precursor oleate. Although all samples exhibited some degree of Brownian relaxation, as determined from complex susceptibility measurements in a liquid medium, aging of the iron-cobalt oleate precursor resulted in crossing of the in-phase ??and out-of-phase ?? components of the complex susceptibility at the frequency of the Brownian magnetic relaxation peak, as expected for nanoparticles that relax through a single relaxation mechanism. The resulting nanoparticles would be suitable for sensors based on the Brownian relaxation mechanism and in determining mechanical properties of complex fluids at the size scale of the nanoparticles.

Herrera, Adriana P.; Polo-Corrales, Liliana; Chavez, Ermides; Cabarcas-Bolivar, Jari; Uwakweh, Oswald N. C.; Rinaldi, Carlos

2013-02-01

250

Postmortem MRI of Human Brain Hemispheres: T2 Relaxation Times during Formaldehyde Fixation  

PubMed Central

Unlike in vivo imaging, postmortem MRI allows for invasive examination of the tissue specimen immediately following the MR scan. However, natural tissue decomposition and chemical fixation cause the postmortem tissue’s MRI properties to be different from those found in vivo. Moreover, these properties change as postmortem fixation time elapses. The goal of this study was to characterize the T2 relaxation changes that occur over time in cadaveric human brain hemispheres during fixation. Five hemispheres immersed in formaldehyde solution were scanned on a weekly basis for three months postmortem, and once again at six months postmortem. The T2 relaxation times were measured throughout the hemispheres. Over time, T2 values near the edges of the hemispheres decreased rapidly after death, while T2 values of deep tissue decreased more slowly. This difference is likely due to the relatively large distance from the hemisphere surface, and other barriers limiting diffusion of formaldehyde molecules to deep tissues. In addition, T2 values in deep tissue did not continuously decay to a plateau, but instead reached a minimum and then increased to a plateau. This final increase may be due to the effects of prolonged tissue decomposition, a hypothesis that is supported by numerical simulations of the fixation process.

Dawe, Robert J.; Bennett, David A.; Schneider, Julie A.; Vasireddi, Sunil K.; Arfanakis, Konstantinos

2009-01-01

251

Determining the in vivo transverse relaxation time of GABA in the human brain at 7T.  

PubMed

PURPOSE: To measure in vivo transverse relaxation times (T(2) ) of gamma-aminobutyric acid (GABA) at 7T using the experimental spectral-editing method. MATERIALS AND METHODS: Experiments were performed at 7T in a 10 mM GABA phantom to determine the intrinsic TE-dependence of the edited signal. Then the same method was applied with editing-based suppression of coedited macromolecular signals to five healthy volunteers to determine T(2) of GABA in vivo. RESULTS: From in vivo data acquired at multiple echo times, the in vivo GABA T(2) relaxation time was estimated to be 63 ± 19 msec. CONCLUSION: We present a measurement of the T(2) of edited GABA signal at 7T by first using phantom measurements to determine the echo time-dependence of edited signal. The method is purely experimental and does not rely on prior knowledge of coupling constants or simulation of realistic experiments. J. Magn. Reson. Imaging 2013;. © 2013 Wiley Periodicals, Inc. PMID:23239232

Intrapiromkul, Jarunee; Zhu, He; Cheng, Ying; Barker, Peter B; Edden, Richard A E

2012-12-13

252

Modified scaling principle for rotational relaxation in a model for suspensions of rigid rods  

NASA Astrophysics Data System (ADS)

We have performed simulations of the model of infinitely thin rigid rods undergoing rotational and translational diffusion, subject to the restriction that no two rods can cross one another, for various concentrations well into the semidilute regime. We used a modification of the algorithm of Doi et al. [J. Phys. Soc. Jpn. 53, 3000 (1984)] that simulates diffusive dynamics using a Monte Carlo method and a nonzero time step. In the limit of zero time step, this algorithm is an exact description of diffusive dynamics subject to the noncrossing restriction. For a wide range of concentrations in the semidilute regime, we report values of the long time rotational diffusion constant of the rods, extrapolated to the limit of zero time step, for various sets of values of the infinite dilution (bare) diffusion constants. These results are compared with the results of a previous simulation of the model by Doi et al. and of previous simulations of rods with finite aspect ratio by Fixman and by Cobb and Butler that had been extrapolated to the limit of infinitely thin rods. The predictions of the Doi-Edwards (DE) scaling law do not hold for this model for the concentrations studied. The simulation data for the model display two deviations from the predictions of the DE theory that have been observed in experimental systems in the semidilute regime, namely, the very slow approach toward DE scaling behavior as the concentration is increased and the large value of the prefactor in the DE scaling law. We present a modified scaling principle for this model that is consistent with the simulation results for a broad range of concentrations in the semidilute regime. The modified scaling principle takes into account two physical effects, which we call ``leakage'' and ``drift,'' that were found to be important for the transport properties of a simpler model of nonrotating rods on a lattice [Y.-L. S. Tse and H. C. Andersen, J. Chem. Phys. 136, 024904 (2012)].

Tse, Ying-Lung Steve; Andersen, Hans C.

2013-07-01

253

Electron Spin Relaxation Time Measurements Using Radiofrequency Longitudinally Detected ESR and Application in Oximetry  

NASA Astrophysics Data System (ADS)

Longitudinally detected ESR (LODESR) involves transverse ESR irradiation with a modulated source and observing oscillations in the spin magnetization parallel to the main magnetic field. In this study, radiofrequency-LODESR was used for oximetry by measuring the relaxation times of the electron. T1e and T2e were measured by investigating LODESR signal magnitude as a function of detection frequency. We have also predicted theoretically and verified experimentally the LODESR signal phase dependence on detection frequency and relaxation times. These methods are valid even for inhomogeneous lines provided that T1e>>T2e. We have also developed a new method for measuring T1e, valid for inhomogeneous spectra, for all values of T1e and T2e, based on measuring the spectral area as a function of detection frequency. We have measured T1e and T2e for lithium phthalocyanine crystals, for the nitroxide TEMPOL, and for the single line agent Triarylmethyl (TAM). Furthermore, we have collected spectra from aqueous solutions of TEMPOL and TAM at different oxygen concentrations and confirmed that T1e values are reduced with increased oxygen concentration. We have also measured the spin-lattice electronic relaxation time for degassed aqueous solutions of the same agents at different agent concentrations. T1e decreases as a function of concentration for TAM while it remains independent of free radical concentration for TEMPOL, a major advantage for oxygen mapping. This method, combined with the ability of LODESR to provide images of exogenous free radicals in vivo, presents an attractive alternative to the conventional transverse ESR linewidth based oximetry methods.

Panagiotelis, Ioannis; Nicholson, Ian; Hutchison, James M. S.

2001-03-01

254

Electron spin relaxation time measurements using radiofrequency longitudinally detected ESR and application in oximetry.  

PubMed

Longitudinally detected ESR (LODESR) involves transverse ESR irradiation with a modulated source and observing oscillations in the spin magnetization parallel to the main magnetic field. In this study, radiofrequency-LODESR was used for oximetry by measuring the relaxation times of the electron. T1e and T2e were measured by investigating LODESR signal magnitude as a function of detection frequency. We have also predicted theoretically and verified experimentally the LODESR signal phase dependence on detection frequency and relaxation times. These methods are valid even for inhomogeneous lines provided that T1e>T2e. We have also developed a new method for measuring T1e, valid for inhomogeneous spectra, for all values of T1e and T2e, based on measuring the spectral area as a function of detection frequency. We have measured T1e and T2e for lithium phthalocyanine crystals, for the nitroxide TEMPOL, and for the single line agent Triarylmethyl (TAM). Furthermore, we have collected spectra from aqueous solutions of TEMPOL and TAM at different oxygen concentrations and confirmed that T1e values are reduced with increased oxygen concentration. We have also measured the spin-lattice electronic relaxation time for degassed aqueous solutions of the same agents at different agent concentrations. T1e decreases as a function of concentration for TAM while it remains independent of free radical concentration for TEMPOL, a major advantage for oxygen mapping. This method, combined with the ability of LODESR to provide images of exogenous free radicals in vivo, presents an attractive alternative to the conventional transverse ESR linewidth based oximetry methods. PMID:11273754

Panagiotelis, I; Nicholson, I; Hutchison, J M

2001-03-01

255

What controls the relaxation time? Lessons learnt from simple liquids' quasiuniversality  

NASA Astrophysics Data System (ADS)

The relaxation time of a supercooled liquid is extremely temperature and density dependent, approaching hours upon cooling or compression. Is this quantity controlled by the entropy, is it controlled by high-frequency elastic properties as assumed in the shoving and related elastic models, or by another physical property? It is far from certain that there is a simple and generally valid answer to this question for glass-forming liquids with quite different chemistry, but as physicists we like to think that this is the case. The talk summarizes recent results [1] on the quasiuniversality of simple liquids, where a simple liquid is defined as a system with strong virial / potential-energy correlations in the equilibrium NVT fluctuations. Such systems, which include e.g. the Lennard-Jones liquid, have good isomorphs. An isomorph is a curve in the phase diagram along which structure, dynamics, and some thermodynamic properties in reduced units are invariant to a good approximation [2-5]. It was recently conjectured [1] that simple liquids have almost the same isomorphs in the sense that these systems are characterized by a quasiuniversal one-parameter family of reduced-coordinate constant-potential-energy manifolds encoding all isomorph invariants. The entropy is the logarithm of the area of this manifold and the high-frequency elastic properties are basically the surface's curvature. Since the relaxation time is also encoded in the manifold, both quantities will appear to ``control'' the relaxation time, as will any isomorph invariant.[4pt] References: [1] J. C. Dyre, arXiv:1208.1748 (2012).[0pt] [2] N. Gnan et al., J. Chem. Phys. 131, 234504 (2009).[0pt] [3] N. Gnan et al., Phys. Rev. Lett. 104, 125902 (2010).[0pt] [4] U. R. Pedersen et al., Phys. Rev. Lett. 105, 157801 (2010).[0pt] [5] T. Ingebrigtsen et al., Phys. Rev. X 2, 011011 (2012).

Dyre, Jeppe

2013-03-01

256

Magnetic Resonance Imaging Relaxation Time Measurements of the Placenta at 1.5 T  

PubMed Central

Placental insufficiency is a major cause of fetal growth restriction (FGR) and accumulating evidence indicates several aspects of placental morphology are altered in this condition. MRI provides quantitative indices that may be used in non-invasive assessment of the human placenta, such as relaxation time measurements, T1 and T2. We hypothesised that placental relaxation times relate to alterations in placental tissue morphology and hence may be useful in identifying the changes associated with FGR. We report on the first phase of testing this hypothesis, in a study of women in normal pregnancy. Aims To assess relaxation time measurements in the placenta in normal pregnancy and correlate these with gestational age and stereological analyses of placental morphology following delivery. Methods 30 women underwent MRI examination (1.5 T) between 20 and 41 weeks gestation. Placental T1 and T2 measurements were acquired from a mid-depth placental region, co-localised to a structural scan. Fixed, wax-embedded sections of these placentas collected at delivery were stained with hematoxylin/ eosin and subjected to stereological analysis. Results Placental T1 and T2 show a significant negative correlation with gestation, (Pearson correlation p=0.01, 0.03 respectively). 17 placentas were analysed stereologically. In the group as a whole there was no significant correlation between T1 and T2 and morphological features. However, in a subset of 7 pregnancies scanned within a week of delivery, a significant positive correlation was observed between the fibrin volume density and the ratio of fibrin: villous volume densities and T2 (Spearman correlation p=0.02, 0.03 respectively). Discussion The correlations between placental T1 and T2 and gestation show that these variables are clearly influenced by changes in placental structure. Fibrin might be a key component but further work is needed to fully elucidate the major structural influences on placental T1 and T2.

Wright, Caroline; Morris, David M; Baker, Philip N; Crocker, Ian P; Gowland, Penny A; Parker, Geoff J; Sibley, Colin P

2013-01-01

257

Apparent Diffusion Coefficient, Fractional Anisotropy and T2 Relaxation Time Measurement  

Microsoft Academic Search

Background:  Quantification of apparent diffusion coefficient (ADC), fractional anisotropy (FA), and T2 relaxation time are increasingly\\u000a important for neuroradiologic applications. A transfer of the values established for 1.5-T to 3-T MRI must be supported by\\u000a a dedicated comparison with special emphasis on possible differences in the spatial distribution.\\u000a \\u000a \\u000a \\u000a Material and Methods:  In the present study, brain scans were carried out in 16

Xiao-Qi Ding; Jürgen Finsterbusch; Oliver Wittkugel; Christian Saager; Einar Goebell; Thies Fitting; Ulrich Grzyska; Hermann Zeumer; Jens Fiehler

2007-01-01

258

Time-resolved chloroquine-induced relaxation of supercoiled plasmid DNA.  

PubMed

Herein, we report on the in vitro change of DNA conformation of plasmids bound to a 3-aminopropyl-modified mica surface and monitoring the events by atomic force microscopy (AFM) imaging under near physiological conditions. In our study, we used an intercalating drug, chloroquine, which is known to decrease the twist of the double helix and thus altered the conformation of the whole DNA. During our experiments, a chloroquine solution was added while imaging a few highly condensed plasmid nanoparticles in solution. AFM images recorded after the drug addition clearly show a time-resolved relaxation of these bionanoparticles into a mixture of loose DNA strands. PMID:21766217

Mahut, Marek; Leitner, Michael; Ebner, Andreas; Lämmerhofer, Michael; Hinterdorfer, Peter; Lindner, Wolfgang

2011-07-16

259

Age distribution and iron dependency of the T2 relaxation time in the globus pallidus and putamen  

Microsoft Academic Search

Heavily T2-weighted spin echo sequences of the brain show age-dependent low signal intensity in many extrapyramidal nuclei. Although it has been suggested that this low intensity results from non-haem iron, the specific influence of non-haem iron on the T2 relaxation time has not been quantified and remains controversial. The T2 relaxation times of the globus pallidus and putamen were measured

C. Schenker; D. Meier; W. Wiclnnann; P. Boesiger; A. Valavanis

1993-01-01

260

An open-source software tool for the generation of relaxation time maps in magnetic resonance imaging  

Microsoft Academic Search

BACKGROUND: In magnetic resonance (MR) imaging, T1, T2 and T2* relaxation times represent characteristic tissue properties that can be quantified with the help of specific imaging strategies. While there are basic software tools for specific pulse sequences, until now there is no universal software program available to automate pixel-wise mapping of relaxation times from various types of images or MR

Daniel R Messroghli; Andre Rudolph; Hassan Abdel-Aty; Ralf Wassmuth; Titus Kühne; Rainer Dietz; Jeanette Schulz-Menger

2010-01-01

261

MEASUREMENT OF THE RELAXATION TIME ?21 OF A Y3Al5O12:Nd3+ CRYSTAL  

Microsoft Academic Search

The relaxation time of the transition from the lower laser level 4I11\\/2 to the ground state 4I9\\/2 of the Nd3+ ions was determined experimentally for a crystal of Y3Al5O12:Nd3+. The relaxation time was measured by two independent methods. The value obtained, ?21 ? 3·10–7 sec, was associated with the very broad (up to ~ 900 cm–1) phonon spectrum of the

A A Zlenko; V A Sychugov; G P Shipulo

1973-01-01

262

Nuclear Spin of Phosphorus Donors in Silicon: Spin Relaxation Times and Environmental Decoupling  

NASA Astrophysics Data System (ADS)

All shallow donors in silicon (and their various isotopes) have non-zero nuclear spins and thus, both the electron and nuclear spins of neutral donors have been proposed for coding, manipulating and storing quantum information. We have recently demonstrated that the spin of electrons bound to donors have extremely long coherence times of at least T2e= 60ms at liquid helium temperatures which permits 10^6 single-qubit operations before the electron spin decoheres [1]. Here we extend this work and demonstrate that spin states of both the electron and nucleus of a ^31P donor can be accurately controlled using resonant microwave and RF pulses in pulsed electron nuclear double resonance (ENDOR) experiments. We measure the spin relaxation times of the ^31P nuclear spin and observe long longitudinal relaxation times T1n= 70s at 6K, limited by hyperfine interaction with the electron spin residing on the donor. We implement a recently proposed bang-bang strategy which decouples the nuclear spin from a decohering environment, through repeated manipulation of the coupled electron spin [2]. This highlights the potential benefits of physical ‘qubit’ systems beyond the simple 2-level structure. [1] A. M. Tyryshkin et al. PRB, 68, 193207 (2003); [2] J. J. L. Morton et al. Nature Physics in press (2005)

Tyryshkin, Alexei; Lyon, Stephen; Morton, John; Ardavan, Arzhang

2006-03-01

263

The dependence of the time constant of left ventricular isovolumic relaxation (tau) on pericardial pressure.  

PubMed

The purpose of this study was to investigate the dependence of tau, the time constant of left ventricular (LV) isovolumic relaxation, on pericardial pressure and to compare values of tau as determined by the methods of previous investigators and by a standard exponential curve fit. All of the more recent methods involve an additional parameter--the pressure to which the exponential relaxation finally declines (PB, the pressure intercept in the method of Craig and Murgo and the asymptote in the exponential fits). An additional purpose of the study was to determine the relation of these parameters to pericardial pressure. In eight closed-chest anesthetized dogs, tau was calculated from intracavitary (Plv) and transmural LV pressure (Plv = Plv-Pper) by each method as pericardial (Pper) and LV end-diastolic pressure were changed by pericardial infusion and intravenous volume loading. The time constant determined by the method of Weiss et al was dependent on pericardial pressure; the time constants determined by the other methods were not. PB and the asymptotes were found to be similar and to increase almost equally with pericardial pressure. When pericardial pressure was zero, these values were approximately -20 mm Hg. Thus, both these parameters seem to indicate the same baseline pressure, a pressure that increases pari passu with pericardial pressure. Reported changes in the value of tau calculated from intracavitary LV pressure by the method of Weiss et al may reflect factors other than changes in LV diastolic function. PMID:2306816

Frais, M A; Bergman, D W; Kingma, I; Smiseth, O A; Smith, E R; Tyberg, J V

1990-03-01

264

Average relaxation time of internal spectrum for carbosilane dendrimers: Nuclear magnetic resonance studies  

NASA Astrophysics Data System (ADS)

A new theoretical description of the interior mobility of carbosilane dendrimers has been tested. Experiments were conducted using measurements of the 1H NMR spin-lattice relaxation time, T1H, of two-, three- and four-generation carbosilane dendrimers with three different types of terminal groups in dilute chloroform solutions. Temperature dependences of the NMR relaxation rate, 1/T1H, were obtained for the internal CH2 - groups of the dendrimers in the range of 1/T1H maximum, allowing us to directly evaluate the average time of the internal spectrum for each dendrimer. It was found that the temperature of 1/T1H maximum is practically independent of the number of generations, G; therefore, the theoretical prediction was confirmed experimentally. In addition, the average time of the internal spectrum of carbosilane dendrimers was found to be near 0.2 ns at room temperature, and this value correlates well with the values previously obtained for other dendrimer structures using other experimental techniques.

Markelov, Denis A.; Matveev, Vladimir V.; Ingman, Petri; Lähderanta, Erkki; Boiko, Natalia I.

2011-09-01

265

Real-time measurement of Brownian relaxation of magnetic nanoparticles by a mixing-frequency method  

NASA Astrophysics Data System (ADS)

A detection scheme for real-time Brownian relaxation of magnetic nanoparticles (MNPs) is demonstrated by a mixing-frequency method in this paper. MNPs are driven into the saturation region by a low frequency sinusoidal magnetic field. A high frequency sinusoidal magnetic field is then applied to generate mixing-frequency signals that are highly specific to the magnetization of MNPs. These highly sensitive mixing-frequency signals from MNPs are picked up by a pair of balanced built-in detection coils. The phase delays of the mixing-frequency signals behind the applied field are derived, and are experimentally verified. Commercial iron oxide MNPs with the core diameter of 35 nm are used for the measurement of Brownian relaxation. The results are fitted well with Debye model. Then a real-time measurement of the binding process between protein G and its antibody is demonstrated using MNPs as labels. This study provides a volume-based magnetic sensing scheme for the detection of binding kinetics and interaction affinities between biomolecules in real time.

Tu, Liang; Jing, Ying; Li, Yuanpeng; Wang, Jian-Ping

2011-05-01

266

Average relaxation time of internal spectrum for carbosilane dendrimers: nuclear magnetic resonance studies.  

PubMed

A new theoretical description of the interior mobility of carbosilane dendrimers has been tested. Experiments were conducted using measurements of the (1)H NMR spin-lattice relaxation time, T(1H), of two-, three- and four-generation carbosilane dendrimers with three different types of terminal groups in dilute chloroform solutions. Temperature dependences of the NMR relaxation rate, 1/T(1H), were obtained for the internal CH(2)-groups of the dendrimers in the range of 1/T(1H) maximum, allowing us to directly evaluate the average time of the internal spectrum for each dendrimer. It was found that the temperature of 1/T(1H) maximum is practically independent of the number of generations, G; therefore, the theoretical prediction was confirmed experimentally. In addition, the average time of the internal spectrum of carbosilane dendrimers was found to be near 0.2 ns at room temperature, and this value correlates well with the values previously obtained for other dendrimer structures using other experimental techniques. PMID:21974558

Markelov, Denis A; Matveev, Vladimir V; Ingman, Petri; Lähderanta, Erkki; Boiko, Natalia I

2011-09-28

267

Is it the grain size or the characteristic pore size that controls the induced polarization relaxation time of clean sands and sandstones?  

NASA Astrophysics Data System (ADS)

There is a wide range of evidence to suggest that permeability can be constrained through of induced polarization measurements. For clean sands and sandstones, current mechanistic models of induced polarization predict a relationship between the low-frequency time constant inferred from induced polarization measurements and the grain diameter. A number of observations do, however, disagree with this and indicate that the observed relaxation behavior is rather governed by the so-called dynamic pore radius ?. To test this hypothesis, we have developed a set of new scaling relationships, which allow the relaxation time to be computed from the pore size and the permeability to be computed from both the Cole-Cole time constant and the formation factor. Moreover, these new scaling relationships can be also used to predict the dependence of the Cole-Cole time constant as a function of the water saturation under unsaturated conditions. Comparative tests of the proposed new relationships with regard to various published experimental results for saturated clean sands and sandstones as well as for partially saturated clean sandstones, do indeed confirm that the dynamic pore radius ? is a much more reliable indicator of the observed relaxation behavior than grain-size-based models.

Revil, André; Koch, Kristof; Holliger, Klaus

2012-05-01

268

Direct measurement of dipole-dipole/CSA cross-correlated relaxation by a constant-time experiment  

PubMed Central

Relaxation rates in NMR are usually measured by intensity modulation as a function of a relaxation delay during which the relaxation mechanism of interest is effective. Other mechanisms are often suppressed during the relaxation delay by pulse sequences which eliminate their effects, or cancel their effects when two data sets with appropriate combinations of relaxation rate effects are added. Cross-correlated relaxation (CCR) involving dipole-dipole and CSA interactions differ from auto-correlated relaxation (ACR) in that the signs of contributions can be changed by inverting the state of one spin involved in the dipole-dipole interaction. This property has been exploited previously using CPMG sequences to refocus CCR while ACR evolves. Here we report a new pulse scheme that instead eliminates intensity modulation by ACR and thus allows direct measurement of CCR. The sequence uses a constant time relaxation period for which the contribution of ACR does not change. An inversion pulse is applied at various points in the sequence to effect a decay that depends on CCR only. A 2-D experiment is also described in which chemical shift evolution in the indirect dimension can share the same constant period. This improves sensitivity by avoiding the addition of a separate indirect dimension acquisition time. We illustrate the measurement of residue specific CCR rates on the non-myristoylated yeast ARF1 protein and compare the results to those obtained following the conventional method of measuring the decay rates of the slow and fast-relaxing 15N doublets. The performances of the two methods are also quantitatively evaluated by simulation. The analysis shows that the shared constant-time CCR (SCT-CCR) method significantly improves sensitivity.

Liu, Yizhou; Prestegard, James H.

2008-01-01

269

Dynamic time scale for the Lagrangian subgrid-scale model based on Rice's formula  

NASA Astrophysics Data System (ADS)

The dynamic formulation of Smagorinsky's subgrid-scale model for Large Eddy Simulations (LES) requires averaging to avoid instability due to extreme fluctuations. For complex-geometry flows a Lagrangian approach is often useful [see Meneveau, Lund, and Cabot, JFM 319 (1996)]. However, an ad-hoc choice of the relaxation timescale must be made, often based on resolved strain-rates and stresses at the grid- scale. Recently, Park and Mahesh [Phys. Fluids 21, 065106 (2009)] proposed the attractive notion of using statistics of the error signal itself to determine a timescale dynamically. We extend this approach by using Rice's formula to dynamically estimate the time between mean-crossings of the error signal and set the averaging timescale to be twice this value. The approach requires accumulating Lagrange-averaged square error and its time-derivative squared, which is done using the Eulerian approximation as proposed in the original model. For validation, LES of flow in a channel and through an array of cubes are compared with experimental results. Distributions of the dynamic coefficient, error, and dynamic timescale are shown as a function of distance from the wall. Computational efficiency and memory requirements are also discussed.

Verhulst, Claire; Meneveau, Charles

2011-11-01

270

Relaxation Time and Dissipation Interaction in Hot Planet Atmospheric Flow Simulations  

Microsoft Academic Search

We elucidate the interplay between Newtonian thermal relaxation and numerical dissipation, of several different origins, in flow simulations of hot extrasolar planet atmospheres. Currently, a large range of Newtonian relaxation, or \\

Heidar Th. Thrastarson; James Y. K. Cho

2011-01-01

271

Relaxation Time and Dissipation Interaction in Hot Planet Atmospheric Flow Simulations  

Microsoft Academic Search

We elucidate the interplay between Newtonian thermal relaxation and numerical dissipation, of several different origins, in flow simulations of hot extrasolar planet atmospheres. Currently, a large range of Newtonian relaxation, or \\

Heidar Thor Thrastarson; James Y. K. Cho

2010-01-01

272

NMR of Absorbed Systems. I. A Systematic Method of Analyzing NMR Relaxation-Time Data for a Continuous Distribution of Nuclear Correlation Times  

Microsoft Academic Search

Methods are outlined for the systematic analysis of NMR relaxation-time data in terms of the continuous distribution of nuclear-correlation-time theories of Odajima and Resing. It is shown how unique values of the two significant parameters of these theories—the width parameter ? and the apparent rigid-lattice second-moment parameter ?02—can be obtained if a minimum occurs in the spin–lattice relaxation-time data. While

L. J. Lynch; K. H. Marsden; E. P. George

1969-01-01

273

Bulk viscosity and relaxation time of causal dissipative relativistic fluid dynamics  

SciTech Connect

The microscopic formulas of the bulk viscosity {zeta} and the corresponding relaxation time {tau}{sub {Pi}} in causal dissipative relativistic fluid dynamics are derived by using the projection operator method. In applying these formulas to the pionic fluid, we find that the renormalizable energy-momentum tensor should be employed to obtain consistent results. In the leading-order approximation in the chiral perturbation theory, the relaxation time is enhanced near the QCD phase transition, and {tau}{sub {Pi}} and {zeta} are related as {tau}{sub {Pi}={zeta}}/[{beta}{l_brace}(1/3-c{sub s}{sup 2})({epsilon}+P)-2({epsilon}-3P)/9{r_brace}], where {epsilon}, P, and c{sub s} are the energy density, pressure, and velocity of sound, respectively. The predicted {zeta} and {tau}{sub {Pi}} should satisfy the so-called causality condition. We compare our result with the results of the kinetic calculation by Israel and Stewart and the string theory, and confirm that all three approaches are consistent with the causality condition.

Huang Xuguang; Rischke, Dirk H. [Frankfurt Institute for Advanced Studies, D-60438 Frankfurt am Main (Germany); Institut fuer Theoretische Physik, J.W. Goethe-Universitaet, D-60438 Frankfurt am Main (Germany); Kodama, Takeshi [Instituto de Fisica, Universidade Federal do Rio de Janeiro, Caixa Postale 68528, 21945-970, Rio de Janeiro (Brazil); Koide, Tomoi [Frankfurt Institute for Advanced Studies, D-60438 Frankfurt am Main (Germany)

2011-02-15

274

On the nonlinear variation of dc conductivity with dielectric relaxation time  

NASA Astrophysics Data System (ADS)

The long-known observations that dc conductivity ?dc of an ultraviscous liquid varies nonlinearly with the dielectric relaxation time ?, and the slope of the log ?dc against log ? plot deviates from -1 are currently seen as two of the violations of the Debye-Stokes-Einstein equation. Here we provide a formalism using a zeroth order Bjerrum description for ion association to show that in addition to its variation with temperature T and pressure P, impurity ion population varies with a liquid's equilibrium dielectric permittivity. Inclusion of this electrostatic effect modifies the Debye-Stokes-Einstein equation to log(?dc?)=constant+log ?, where ? is the T and P-dependent degree of ionic dissociation of an electrolytic impurity. Variation of a liquid's shear modulus with T and P would add to the nonlinearity of ?dc-? relation, as would a nonequivalence of the shear and dielectric relaxation times, proton transfer along the hydrogen bonds, or occurrence of another chemical process. This is illustrated by using the data for ultraviscous acetaminophen-aspirin liquid.

Johari, G. P.; Andersson, Ove

2006-09-01

275

Theory of the ac spin valve effect: a new method to measure spin relaxation time  

NASA Astrophysics Data System (ADS)

Parallel (P) and antiparallel (AP) configurations of FNF junctions have, in a dc regime, different resistivities (RAP>RP), giving rise to the giant magnetoresistance (GMR) effect, which can be explained within the spin injection drift-diffusion model. We extend the model to include ac phenomena and predict new spin dynamical phenomenon; the resonant amplification and depletion of spin accumulation in the P and AP configurations, respectively. As the major new effect, the spin valve magnetoimpedance of the FNF junction oscillates with the driving ac frequency, which leads to negative GMR effect (|ZAP|<|ZP|). We show that from the spin-valve oscillation periods, measured all electrically in the GHz regime, the spin relaxation times could be extracted without any magnetic field and sample size changes (contrary to other techniques). For thin tunnel junctions the ac signal becomes pure Lorentzian, also enabling one to obtain the spin relaxation time of the N region from the signal width. This work, was published in Physical Review Letters,10, 176604 (2011).

Kochan, Denis; Gmitra, Martin; Fabian, Jaroslav

2012-02-01

276

A Metric for Judicious Relaxation of Timing Constraints in Soft Real-Time Systems  

Microsoft Academic Search

For soft real-time systems, timing constraints are not as stringent as those in hard real-time systems: some constraint violations are permitted as long as the amount of violation is within a given limit. The allowed flexibility for soft real-time systems can be utilized to improve system's other quality-of-service (QoS) properties, such as energy consumption. One way to enforce constraint violation

Yue Yu; Shangping Ren; Xiaobo Sharon Hu

2009-01-01

277

The Study of Relationship between Listening to Music and Mood Change Musical Tempo and Melody, Preference Music Influence on a Mood Scale and Relaxation State  

Microsoft Academic Search

The present study examined relationship between listening to music and relaxation by changing tempo and melody. Four musical tasks were varied in tempo (fast or slow) and melody (complex and simple). Participants listened to one version of musical tasks and completed measures of mood scale, relaxation state and musical preference. Results of the experiment indicated that listening to music decreased

NAITO Masatomo

278

The Geologic Time Scale: The Development of Life through time  

NSDL National Science Digital Library

This text assists in understanding time relationships and how life on Earth has changed over time. The dates shown were compiled from several available sources. The first page shows some important events in Earth history, presented in the order in which they occurred. The data are also shown on the scale of a calendar year. On the second sheet is a chart showing the geologic eras, systems, and series. On the chart, each dot, number, or letter represents 1 million years. The dots get older as you read down the chart, or to the right along a row. They represent millions of years before present (mybp) and show the ages of the oldest known fossils of selected animals or the time of an event. Not all of the items are shown on the chart because of space limitations.

279

Time sequence and time scale of intermediate mass fragment emission  

SciTech Connect

Semiperipheral collisions in the {sup 124}Sn+{sup 64}Ni reaction at 35 MeV/nucleon were studied using the forward part of the Charged Heavy Ion Mass and Energy Resolving Array. Nearly completely determined ternary events involving projectilelike fragments (PLF), targetlike fragments (TLF), and intermediate mass fragments (IMF) were selected. A new method of studying the reaction mechanism, focusing on the analysis of the correlations between relative velocities in the IMF+PLF and IMF+TLF subsystems, is proposed. The relative velocity correlations provide information on the time sequence and time scale of the neck fragmentation processes leading to production of IMFs. It is shown that the majority of light IMFs are produced within 40-80 fm/c after the system starts to reseparate. Heavy IMFs are formed at times of about 120 fm/c or later and can be viewed as resulting from two-step (sequential) neck rupture processes.

De Filippo, E.; Pagano, A.; Cardella, G.; Lanzano, G.; Papa, M.; Pirrone, S.; Politi, G. [INFN, Sezione di Catania and Dipartimento di Fisica e Astronomia, Universita di Catania (Italy); Wilczynski, J. [A. Soltan Institute for Nuclear Studies, Swierk/Warsaw (Poland); Amorini, F.; Anzalone, A.; Baran, V.; Bonasera, A.; Cavallaro, S.; Colonna, M.; Di Toro, M.; Giustolisi, F.; Iacono-Manno, M.; La Guidara, E.; Lanzalone, G.; Maiolino, C. [INFN, Laboratori Nazionali del Sud and Dipartimento di Fisica e Astronomia, Universita di Catania (Italy)] [and others

2005-04-01

280

Parametric instabilities in picosecond time scales  

SciTech Connect

The coupling of intense laser light with plasmas is a rich field of plasma physics, with many applications. Among these are inertial confinement fusion (ICF), x-ray lasers, particle acceleration, and x-ray sources. Parametric instabilities have been studied for many years because of their importance to ICF; with laser pulses with duration of approximately a nanosecond, and laser intensities in the range 10{sup 14}--10{sup 15}W/cm{sup 2} these instabilities are of crucial concern because of a number of detrimental effects. Although the laser pulse duration of interest for these studies are relatively long, it has been evident in the past years that to reach an understanding of these instabilities requires their characterization and analysis in picosecond time scales. At the laser intensities of interest, the growth rate for stimulated Brillouin scattering (SBS) is of the order of picoseconds, and of an order of magnitude shorter for stimulated Raman scattering (SRS). In this paper the authors discuss SBS and SRS in the context of their evolution in picosecond time scales. They describe the fundamental concepts associated with their growth and saturation, and recent work on the nonlinear treatment required for the modeling of these instabilities at high laser intensities.

Baldis, H.A. [Lawrence Livermore National Lab., CA (United States); Rozmus, W. [Alberta Univ., Edmonton, AB (Canada). Dept. of Physics; Labaune, C.; Mounaix, Ph.; Pesme, D.; Baton, S. [Ecole Polytechnique, Palaiseau (France); Tikhonchuk, V.T. [P.N. Lebedev Physics Inst., Moscow (Russian Federation)

1993-03-01

281

The role of the kinetic parameter in the stability of two-relaxation-time advection–diffusion lattice Boltzmann schemes  

Microsoft Academic Search

In general, explicit numerical schemes are only conditionally stable. A particularity of lattice Boltzmann multiple-relaxation-time (MRT) schemes is the presence of free (“kinetic”) relaxation parameters. They do not appear in the transport coefficients of the modelled second-order (macroscopic) equations but they have an impact on the effective accuracy and stability of the algorithm. The simplest uniform choice (the well known

A. Kuzmin; I. Ginzburg; A. A. Mohamad

2011-01-01

282

Two-relaxation-times Lattice Boltzmann schemes for solute transport in unsaturated water flow, with a focus on stability  

Microsoft Academic Search

We develop two-relaxation-times Lattice Boltzmann schemes (TRT) with two relaxation functions ?±(r?,t) for solving highly non-linear equations for groundwater modeling in d-dimensions, namely, the Richards equation for water content distribution ?(r?,t) in unsaturated flow and the associated transport equation for solute concentration C(r?,t), advected by the local Darcian water flux. The method is verified against the analytical solutions and the

H. Hammou; I. Ginzburg; M. Boulerhcha

2011-01-01

283

Computation of effective electron–phonon relaxation times in a high- T c superconductor using the measured track radii  

Microsoft Academic Search

Energy relaxation processes after fast heavy ions passage through YBa2Cu3O7?? single crystal have been calculated. Effective times ? of electron–atom energy relaxation have been determined as fitting parameters for each pair of the measured track radius and the value of dE\\/dx. The latter quantity has been chosen over the interval of 20–40 keV\\/nm. The calculated results are compared with short pulse

I. N Goncharov; B. F Kostenko; V. P Philinova

2001-01-01

284

Computation of effective electron-phonon relaxation times in a high-Tc superconductor using the measured track radii  

Microsoft Academic Search

Energy relaxation processes after fast heavy ions passage through YBa2Cu3O7-delta single crystal have been calculated. Effective times \\/tau of electron-atom energy relaxation have been determined as fitting parameters for each pair of the measured track radius and the value of \\/dE\\/dx. The latter quantity has been chosen over the interval of 20-40 keV\\/\\/nm. The calculated results are compared with short

I. N. Goncharov; B. F. Kostenko; V. P. Philinova

2001-01-01

285

Unusual longitudinal relaxation time behaviour of colloidal solutions of superparamagnetic nanoparticles  

NASA Astrophysics Data System (ADS)

Superparamagnetic nanoparticles are very interesting objects having many applications among which MRI contrast agents are one of the more important. In this work the longitudinal relaxation times of Endorem and Lumirem, two colloidal solutions of iron oxide nanoparticles used as contrast agents for magnetic resonance imaging were measured at magnetic field intensities similar to the ones used in MRI. T1 was seen to depend on nanoparticle concentrations as expected but, for the Lumirem, also on the time spend by the sample under the influence of the static magnetic field. The T1 evolution was measured for colloidal solutions both different concentrations and different viscosities. The strange T1 dependence is presented and discussed relating to the nanoparticles superparamagnetic properties. It is shown that one of the possible reasons for the fact is the formation of local field enhanced linear arrays of SPIO.

Carvalho, A.; Taborda, A.

2007-12-01

286

Vibrational relaxation pathways in porous silicon: A time-resolved infrared spectroscopic study  

NASA Astrophysics Data System (ADS)

We have used a free electron laser to measure the picosecond vibrational dynamics of the SiH, SiH2 , and O3SiH stretching modes in porous silicon. A three beam pump-probe technique has been employed to make temperature dependent measurements of the population relaxation times. We demonstrate that both bending modes and scissors modes play important roles as does the vibrational bath provided by the pore walls themselves. Using a forward box, two beam photon echo technique we have measured the homogeneous dephasing times of all modes which have dynamic linewidths in the range 0.6-1.2cm-1 . The inferred pure dephasing rates are dominated by the elastic scattering of acousticlike Si-Si vibrations.

Jobson, K. W.; Wells, J.-P. R.; Vinh, N. Q.; Phillips, P. J.; Pidgeon, C. R.; Dijkhuis, J. I.

2006-10-01

287

Spin-drag relaxation time in one-dimensional spin-polarized Fermi gases  

SciTech Connect

Spin propagation in systems of one-dimensional interacting fermions at finite temperature is intrinsically diffusive. The spreading rate of a spin packet is controlled by a transport coefficient termed 'spin drag' relaxation time {tau}{sub sd}. In this paper we present both numerical and analytical calculations of {tau}{sub sd} for a two-component spin-polarized cold Fermi gas trapped inside a tight atomic waveguide. At low temperatures we find an activation law for {tau}{sub sd}, in agreement with earlier calculations of Coulomb drag between slightly asymmetric quantum wires, but with a different and much stronger temperature dependence of the prefactor. Our results provide a fundamental input for microscopic time-dependent spin-density functional theory calculations of spin transport in one-dimensional inhomogeneous systems of interacting fermions.

Rainis, Diego; Polini, Marco; Tosi, M. P. [NEST-CNR-INFM and Scuola Normale Superiore, I-56126 Pisa (Italy); Vignale, G. [Department of Physics and Astronomy, University of Missouri, Columbia, Missouri 65211 (United States)

2008-01-15

288

NMR relaxation times of trabecular bone—reproducibility, relationships to tissue structure and effects of sample freezing  

NASA Astrophysics Data System (ADS)

Nuclear magnetic resonance (NMR) spectroscopy provides a potential tool for non-invasive evaluation of the trabecular bone structure. The objective of this study was to determine the reproducibility of the NMR relaxation parameters (T2, Carr-Purcel-T2, T1?) for fat and water and relate those to the structural parameters obtained by micro-computed tomography (?CT). Especially, we aimed to evaluate the effect of freezing on the relaxation parameters. For storing bone samples, freezing is the standard procedure during which the biochemical and cellular organization of the bone marrow may be affected. Bovine trabecular bone samples were stored at -20 °C for 7 days and measured by NMR spectroscopy before and after freezing. The reproducibility of NMR relaxation parameters, as expressed by the coefficient of variation, ranged from 3.1% to 27.9%. In fresh samples, some correlations between NMR and structural parameters (Tb.N, Tb.Sp) were significant (e.g. the relaxation rate for T2 of fat versus Tb.Sp: r = -0.716, p < 0.01). Freezing did not significantly change the NMR relaxation times but the correlations between relaxation parameters and the ?CT structural parameters were not statistically significant after freezing, suggesting some nonsystematic alterations of the marrow structure. Therefore, the use of frozen bone samples for NMR relaxation studies may provide inferior information about the trabecular bone structure.

Prantner, Viktória; Isaksson, Hanna; Närväinen, Johanna; Lammentausta, Eveliina; Nissi, Mikko J.; Avela, Janne; Gröhn, Olli H. J.; Jurvelin, Jukka S.

2010-12-01

289

Length, time, and energy scales of photosystems.  

PubMed

The design of photosynthetic systems reflects the length scales of the fundamental physical processes. Energy transfer is rapid at the few angstrom scale and continues to be rapid even at the 50-A scale of the membrane thickness. Electron tunneling is nearly as rapid at the shortest distances, but becomes physiologically too slow well before 20 A. Diffusion, which starts out at a relatively slow nanosecond time scale, has the most modest slowing with distance and is physiologically competent at all biologically relevant distances. Proton transfer always operates on the shortest angstrom scale. The structural consequences of these distance dependencies are that energy transfer networks can extend over large, multisubunit and multicomplex distances and take leaps of 20 A before entering the domain of charge separating centers. Electron transfer systems are effectively limited to individual distances of 15 A or less and span the 50 A dimensions of the bioenergetic membrane by use of redox chains. Diffusion processes are generally used to cover the intercomplex electron transfer distances of 50 A and greater and tend to compensate for the lack of directionality by restricting the diffusional space to the membrane or the membrane surface, and by multiplying the diffusing species through the use of pools. Proton transfer reactions act over distances larger than a few angstroms through the use of clusters or relays, which sometimes rely on water molecules and which may only be dynamically assembled. Proteins appear to place a premium on robustness of design, which is relatively easily achieved in the long-distance physical processes of energy transfer and electron tunneling. By placing cofactors close enough, the physical process is relatively rapid compared to decay processes. Thus suboptimal conditions such as cofactor orientation, energy level, or redox potential level can be tolerated and generally do not have to be finely tuned. The most fragile regions of design tend to come in areas of complex formation and catalysis involving proton management, where relatively small changes in distance or mutations can lead to a dramatic decrease in turnover, which may already be limiting the overall speed of energy conversion in these proteins. Light-activated systems also face a challenge to robust function from the ever-present dangers of high redox potential chemistry. This can turn the protein matrix and wandering oxygen molecules into unintentional redox partners, which in the case of PSII requires the frequent, costly replacement of protein subunits. PMID:12629967

Moser, Christopher C; Page, Christopher C; Cogdell, Richard J; Barber, James; Wraight, Colin A; Dutton, P Leslie

2003-01-01

290

7Li relaxation time measurements at very low magnetic field by 1H dynamic nuclear polarization.  

PubMed

Dynamic nuclear polarization (DNP) of water protons was used to measure the relaxation time of lithium at very low magnetic field as a demonstration of the use of DNP for nuclei less abundant than water protons. Lithium (Li+) was chosen because it is an efficient treatment for manic-depressive illness, with an unknown action mechanism. After having recalled the theoretical basis of a three-spin system comprising two nuclei-the water proton of the solvent, the dissolved Li+ ion and the free electron of a free radical-we have developed a transient solution in order to optimize potential biological applications of Li DNP. The three-spin model has allowed computation of all the parameters of the system-the longitudinal relaxation rate per unit of free radical concentration, the dipolar and scalar part of the coupling between the nuclei and the electron. and the maximum signal enhancement achievable for both proton and lithium spins. All these measurements have been obtained solely through the detection of the proton resonance. PMID:11580174

Zeghib, N; Grucker, D

2001-09-01

291

Acute and repair stage characteristics of magnetic resonance relaxation times in oxygen-induced pulmonary edema.  

PubMed

Proton magnetic relaxation times, T1 and T2, were determined for rat lungs exposed to 80% oxygen for a duration of 2 weeks. The transverse magnetization decay curve of the lung tissue was multiexponential. A linear combination of two decay curves with different T2 values fits the multiexponential decay suggesting that there are at least two different components of tissue water in the lung. Remarkable prolongation of T1 and T2 was demonstrated as lung injuries progressed in the acute stage of pulmonary edema. Both 1/T1 and 1/T2 were significantly correlated with 1/water content of the lung tissue. In the repair stage, T1 and T2 were significantly shortened. Shortening coincided with the spontaneous resolution of pulmonary edema. Relaxation rates showed no significant correlation with 1/water content in this stage. These results indicate that the physical state of water in the tissue is affected not only by the water content but also by the derangement of macromolecules in pulmonary edema. T2 was more sensitive than T1 for detecting pulmonary damage. PMID:3231071

Shioya, S; Haida, M; Tsuji, C; Ohta, Y; Yamabayashi, H; Fukuzaki, M; Kimula, Y

1988-12-01

292

Charge and momentum transfer in supercooled melts: why should their relaxation times differ?  

PubMed

The steady-state values of the viscosity and the intrinsic ionic conductivity of quenched melts are computed, in terms of independently measurable quantities. The frequency dependence of the ac dielectric response is estimated. The discrepancy between the corresponding characteristic relaxation times is only apparent; it does not imply distinct mechanisms, but stems from the intrinsic barrier distribution for alpha-relaxation in supercooled fluids and glasses. This type of intrinsic "decoupling" is argued not to exceed four orders in magnitude for known glassformers. The origin of the discrepancy between the stretching exponent beta, as extracted from epsilon(omega) and the dielectric modulus data, is explained. The actual width of the barrier distribution always grows with lowering the temperature. The contrary is an artifact of the large contribution of the dc-conductivity component to the modulus data. The methodology allows one to single out other contributions to the conductivity, as in "superionic" liquids or when charge carriers are delocalized, implying that in those systems, charge transfer does not require structural reconfiguration. PMID:17492870

Lubchenko, Vassiliy

2007-05-01

293

Spin-spin Relaxation Time Measurements of 2D 3He on Graphite  

NASA Astrophysics Data System (ADS)

Spin-spin relaxation time (T2) and magnetic susceptibility (?) of the second layer 3He adsorbed on Grafoil, exfoliated graphite, preplated with a monolayer 4He are studied by pulsed-NMR in a density range of 0.68 <= ? <= 5.28 nm-2. The temperature dependence of ?(T) and ?(T = 0) show Fermi fluid behaviour and no evidence of self-condensation are found even at the lowest density ? = 0.68 nm-2. Density dependence of T2 at f = 5.5 MHz shows a broad maximum of 5.7 ms around ? = 3 nm-2. Since the decrease of T2 in dilute side can not be expected in the ideal 2D fluid, it can be understood as the relaxation caused by a small amount of solid 3He at heterogeneity of the substrate. We also measured the Larmor frequency dependence of T2 at ? = 5.28 nm-2. 1/T2 has a f-linear dependence similarly to the earlier study on a first layer solid 3He [14]. From a comparison between our result and the earlier one, this linearity is almost independent of the particle motion. Now, it could be caused by a microscopic magnetic field inhomogeneity arisen from the mosaic angle spread and diamagnetism of the graphite substrate.

Sato, D.; Naruse, K.; Matsui, T.; Fukuyama, Hiroshi

2012-12-01

294

EDITORIAL: Special issue on time scale algorithms  

NASA Astrophysics Data System (ADS)

This special issue of Metrologia presents selected papers from the Fifth International Time Scale Algorithm Symposium (VITSAS), including some of the tutorials presented on the first day. The symposium was attended by 76 persons, from every continent except Antarctica, by students as well as senior scientists, and hosted by the Real Instituto y Observatorio de la Armada (ROA) in San Fernando, Spain, whose staff further enhanced their nation's high reputation for hospitality. Although a timescale can be simply defined as a weighted average of clocks, whose purpose is to measure time better than any individual clock, timescale theory has long been and continues to be a vibrant field of research that has both followed and helped to create advances in the art of timekeeping. There is no perfect timescale algorithm, because every one embodies a compromise involving user needs. Some users wish to generate a constant frequency, perhaps not necessarily one that is well-defined with respect to the definition of a second. Other users might want a clock which is as close to UTC or a particular reference clock as possible, or perhaps wish to minimize the maximum variation from that standard. In contrast to the steered timescales that would be required by those users, other users may need free-running timescales, which are independent of external information. While no algorithm can meet all these needs, every algorithm can benefit from some form of tuning. The optimal tuning, and even the optimal algorithm, can depend on the noise characteristics of the frequency standards, or of their comparison systems, the most precise and accurate of which are currently Two Way Satellite Time and Frequency Transfer (TWSTFT) and GPS carrier phase time transfer. The interest in time scale algorithms and its associated statistical methodology began around 40 years ago when the Allan variance appeared and when the metrological institutions started realizing ensemble atomic time using more than one single atomic clock. An international symposium dedicated to these topics was initiated in 1972 as the first International Symposium on Atomic Time Scale Algorithms and it was the beginning of a series: 1st Symposium: organized at the NIST (NBS at that epoch) in 1972, 2nd Symposium: again at the NIST in 1982, 3rd Symposium: in Italy at the INRIM (IEN at that epoch) in 1988, 4th Symposium: in Paris at the BIPM in 2002 (see Metrologia 40 (3), 2003) 5th Symposium: in San Fernando, Spain at the ROA in 2008. The early symposia were concerned with establishing the basics of how to estimate and characterize the behavior of an atomic frequency standard in an unambiguous and clearly identifiable way, and how to combine the reading of different clocks to form an optimal time scale within a laboratory. Later, as atomic frequency standards began to be used as components in larger systems, interest grew in understanding the impact of a clock in a more complex environment. For example, use of clocks in telecommunication networks in a Synchronous Digital Hierarchy created a need to measure the maximum time error spanned by a clock in a certain interval. Timekeeping metrologists became interested in estimating time deviations and time stability, so they had to find ways to convert their common frequency characteristics to time characteristics. Tests of fundamental physics provided a motivation for launching atomic frequency standards into space in long-lasting missions, whose high-precision measurements might be available for only a few hours a day, yielding a series of clock data with many gaps and outliers for which a suitable statistical analysis was necessary to extract as much information as possible from the data. In the 21st century, the field has been transformed by the advent of atomic-clock-based Global Navigation Satellite Systems (GNSS), the steady increase in precision brought about by rapidly improving clocks and measurement systems, and the growing number of relatively inexpensive small clock ensembles. Although technological transformations have raised the

Matsakis, Demetrios; Tavella, Patrizia

2008-12-01

295

Time scales in nuclear giant resonances  

SciTech Connect

We propose a general approach to characterise fluctuations of measured cross sections of nuclear giant resonances. Simulated cross sections are obtained from a particular, yet representative, self-energy that contains all information about fragmentations. Using a wavelet analysis, we demonstrate the extraction of time scales of cascading decays into configurations of different complexity of the resonance. We argue that the spreading widths of collective excitations in nuclei are determined by the number of fragmentations as seen in the power spectrum. An analytic treatment of the wavelet analysis using a Fourier expansion of the cross section confirms this principle. A simple rule for the relative lifetimes of states associated with hierarchies of different complexity is given.

Heiss, W. D. [National Institute for Theoretical Physics, Stellenbosch Institute for Advanced Study, and Institute of Theoretical Physics, University of Stellenbosch, 7602 Matieland (South Africa); Nazmitdinov, R. G. [Department de Fisica, Universitat de les Illes Balears, E-07122 Palma de Mallorca (Spain); Bogoliubov Laboratory of Theoretical Physics, Joint Institute for Nuclear Research, RU-141980 Dubna (Russian Federation); Smit, F. D. [iThemba LABS, Post Office Box 722, Somerset West 7129 (South Africa)

2010-03-15

296

Optimum synthesis for time scale generation.  

PubMed

A time scale can be regarded as a synthesis of readings from precise clocks. Usually such synthesis is based on the principle of weighted averaging, which balances the contribution of each clock according to its noise level. It is well known that there are five different noise processes in precise clocks. Therefore, a good synthesis should balance each of those noise levels. Most existing algorithms control only one or two noise types. If an algorithm can control all five noise types simultaneously, we consider it to be optimum. The key point of constructing an optimum algorithm is the separation of all five noise types. In this paper, an optimum algorithm is presented using the half-integrating/half-differentiating model by which the five noise types are separated correctly. Performances of the new algorithm are demonstrated with simulated and real data. PMID:18238481

Zhu, S; Wei, G

1999-01-01

297

Dielectric susceptibility measurements of the primary and secondary relaxation in polybutadiene  

Microsoft Academic Search

We present data on the dielectric relaxation in the random copolymer polybutadiene. There are two distinct peaks in the imaginary part of the dielectric susceptibility, one of which is attributable to an alpha relaxation and the other to a Johari-Goldstein beta relaxation. The bifurcation of these two relaxations explains the previously reported decoupling of microscopic and macroscopic time scales in

Robert D. Deegan; Sidney R. Nagel

1995-01-01

298

Time Horizon and Social Scale in Communication  

NASA Astrophysics Data System (ADS)

In 2009 our center (CRED) published a first version of The Psychology of Climate Change Communication. In it, we attempted to summarize facts and concepts from psychological research that could help guide communication. While this work focused on climate change, most of the ideas are at least partly applicable for communication about a variety of natural hazards. Of the many examples in this guide, I mention three. Single-action bias is the human tendency to stop considering further actions that might be needed to deal with a given hazard, once a single action has been taken. Another example is the importance of group affiliation in motivating voluntary contributions to joint action. A third concerns the finding that group participation enhances understanding of probabilistic concepts and promotes action in the face of uncertainty. One current research direction, which goes beyond those included in the above publication, focuses on how time horizons arise in the thinking of individuals and groups, and how these time horizons might influence hazard preparedness. On the one hand, individuals sometimes appear impatient, organizations look for immediate results, and officials fail to look beyond the next election cycle. Yet under some laboratory conditions and in some subcultures, a longer time horizon is adopted. We are interested in how time horizon is influenced by group identity and by the very architecture of planning and decision making. Institutional changes, involving long-term contractual relationships among communities, developers, insurers, and governments, could greatly increase resilience in the face of natural hazards. Communication about hazards, in the context of such long-term contractual relationships might look very different from communication that is first initiated by immediate threat. Another new direction concerns the social scale of institutions and of communication about hazards. Traditionally, insurance contracts share risk among a large number of insurees: each contributes a small premium toward a fund that is adequate to cover the large losses that occasionally occur. Participatory processes are needed that extend risk sharing to larger social scales and that reduce adversarial relationships between insurers, insurees, insurance regulators, and governments that intervene or fail to intervene on an ad hoc rather than a contractual basis.

Krantz, D. H.

2010-12-01

299

Time-dependent perturbation theory for vibrational energy relaxation and dephasing in peptides and proteins.  

PubMed

Without invoking the Markov approximation, we derive formulas for vibrational energy relaxation (VER) and dephasing for an anharmonic system oscillator using a time-dependent perturbation theory. The system-bath Hamiltonian contains more than the third order coupling terms since we take a normal mode picture as a zeroth order approximation. When we invoke the Markov approximation, our theory reduces to the Maradudin-Fein formula which is used to describe the VER properties of glass and proteins. When the system anharmonicity and the renormalization effect due to the environment vanishes, our formulas reduce to those derived by and Mikami and Okazaki [J. Chem. Phys. 121, 10052 (2004)] invoking the path-integral influence functional method with the second order cumulant expansion. We apply our formulas to VER of the amide I mode of a small amino-acid like molecule, N-methylacetamide, in heavy water. PMID:16626248

Fujisaki, Hiroshi; Zhang, Yong; Straub, John E

2006-04-14

300

Statistically relaxing to generating partitions for observed time-series data  

NASA Astrophysics Data System (ADS)

We introduce a relaxation algorithm to estimate approximations to generating partitions for observed dynamical time series. Generating partitions preserve dynamical information of a deterministic map in the symbolic representation. Our method optimizes an essential property of a generating partition: avoiding topological degeneracies. We construct an energylike functional and use a nonequilibrium stochastic minimization algorithm to search through configuration space for the best assignment of symbols to observed data. As each observed point may be assigned a symbol, the partitions are not constrained to an arbitrary parametrization. We further show how to select particular generating partition solutions which also code low-order unstable periodic orbits in a given way, hence being able to enumerate through a number of potential generating partition solutions.

Buhl, Michael; Kennel, Matthew B.

2005-04-01

301

Cutoff wave number for shear waves and Maxwell relaxation time in Yukawa liquids.  

PubMed

Because liquids cannot resist shear except over very short distances comparable to the atomic spacing, shear sound waves (i.e., transverse phonons) propagate only for very short wavelengths. A measure of this limit is the cutoff wave number k(c), which is sometimes called the critical wave number. Previously k(c) was determined in molecular dynamics (MD) simulations by obtaining the dispersion relation. Another approach is developed in this paper by identifying the wave number at the onset of a negative peak in the transverse current correlation function. This method is demonstrated using a three-dimensional MD simulation of a Yukawa fluid, which mimics dusty plasmas. In general, k(c) is an indicator of conditions where elastic and dissipative effects are approximately balanced. Additionally, the crossover frequency for the real and imaginary terms of the complex viscosity of a dusty plasma is obtained; this crossover frequency corresponds to the Maxwell relaxation time. PMID:23005223

Goree, J; Donkó, Z; Hartmann, P

2012-06-11

302

Shear viscosities from the Chapman-Enskog and the relaxation time approaches  

NASA Astrophysics Data System (ADS)

The interpretation of the measured elliptic and higher order collective flows in heavy-ion collisions in terms of viscous hydrodynamics depends sensitively on the ratio of shear viscosity to entropy density. Here we perform a quantitative comparison between the results of shear viscosities from the Chapman-Enskog and relaxation time methods for selected test cases with specified elastic differential cross sections: (i) the nonrelativistic, relativistic and ultrarelativistic hard sphere gas with angle and energy independent differential cross section, (ii) the Maxwell gas, (iii) chiral pions, and (iv) massive pions for which the differential elastic cross section is taken from experiments. Our quantitative results (i) reveal that the extent of agreement (or disagreement) depends sensitively on the energy dependence of the differential cross sections employed, and (ii) stress the need to perform quantum molecular dynamical (URQMD) simulations that employ Green-Kubo techniques with similar cross sections to validate the codes employed and to test the accuracy of other methods.

Wiranata, Anton; Prakash, Madappa

2012-05-01

303

Ion-solvent molecule interaction in nonaqueous solutions: Spin-lattice relaxation time of 7 Li  

Microsoft Academic Search

The spin-lattice relaxation time (T1) of7Li+ was measured in solutions of LiCl and LiClO4 in protic (MeOH, EtOH,n-PrOH,i-PrOH,n-BuOH, sec-BuOH, formamide, N-methylformamide) and aprotic (MeCN, acetone, methyl ethyl ketone, propylene carbonate, dimethyl sulfoxide, dimethylformamide, hexamethylphosphotriamide) solvents and in mixtures of H2O-formamide, H2O-N-methylformamide, H2O-N,N-dimethylformamide, H2O-DMSO, H2O-hexamethylphosphotriamide, and formamide-N,N-dimethylformamide at 25°C. The values of (1\\/T1)0 obtained by extrapolation are discussed in terms of

A. I. Mishustin; Yu. M. Kessler

1975-01-01

304

Correlation between the malignant phenotype of virus transformed cells and decreased proton relaxation times  

SciTech Connect

The Nuclear Magnetic Resonance (NMR) properties of normal rat kidney (NRK) cells and their cloned transformed derivatives (CTD), Kirsten sarcoma-(K) and Simian virus 40-(SV) NRK cells were studied. Cells were cultured in DME media containing 10% (v/v) calf serum. After washing, cells were harvested, counted, volume determined and viability established. NMR measurements were made on cell pellets with a permanent magnet system operating at 10 MHz and 37/sup 0/C utilizing a Hahn spin-echo sequence. The proton T/sub 1/ for NRK cells was 1332 +- 78msec (+- 1 SD). In contrast, the T/sub 1/ of both CTD was reduced: T/sub 1/ for SV-NRK cells was 1053 +- 108msec and for K-NRK was 912 +- 53msec. Parallel decreases in T/sub 2/ relaxation times were also found in both CTD in comparison with the NRK cells. Shortened T/sub 1/ and T/sub 2/ values were also found when cells were maintained invarious media during NMR measurements. The results indicate that there is a correlation between the malignant phenotype and the shortened T/sub 1/ and T/sub 2/ values of the SV-NRK and K-NRK cell lines in culture. This relationship was strengthened by the finding that similar results were observed when the cells were maintained in a variety of media during the NMR determinations. The shortened NMR proton relaxation times may be due to the position of the SV-NRK and K-NRK cells in the cell cycle as a significant proportion of the CTD are in the S or M phases of the cell cycle in comparison to NRK cells.

Fletcher, J.W.; Hendershott, L.R.; Fernandez-Pol, J.A.

1984-01-01

305

Basin-scale time reversal communications.  

PubMed

During November 1994, broadband acoustic signals were transmitted from a 75-Hz source to a 20-element, 700-m vertical array at approximately 3250 km range in the eastern North Pacific Ocean as part of the acoustic engineering test (AET) of the acoustic thermometry of ocean climate program [Worcester et al., J. Acoust. Soc. Am. 105, 3185-3201 (1999)]. The AET tomography signal can be treated as a binary-phase shift-keying communication signal with an information rate of 37.5 bitss. With the multipath arrivals spanning 5-8 sec, these data represent an extreme case of intersymbol interference. The AET array data are processed using time reversal combined with frequent channel updates to accommodate channel variations over the 20-min long reception, followed by a single channel decision-feedback equalizer. The almost error-free performance using all 20 array elements demonstrates the feasibility of time reversal communications at basin scale. Further, comparable performance of single receive element communications integrating over multiple transmissions indicates that the ocean provided temporal diversity that is as effective as the spatial diversity provided by the array. PMID:19173408

Song, H C; Kuperman, W A; Hodgkiss, W S

2009-01-01

306

Global exponential stability of delayed BAM network on time scale  

Microsoft Academic Search

Some sufficient conditions are derived to ensure the global exponential stability of delayed bi-directional associative memory (BAM) neural network on time scale, using the time scale calculus theory and the Liapunov functional method. The conditions possess highly important significance and can be easily checked in practice by simple algebraic methods. This is the first time applying the time scale calculus

Anping Chen; Dejun Du

2008-01-01

307

Semi-implicit-linearized multiple-relaxation-time formulation of lattice Boltzmann schemes for mixture modeling  

NASA Astrophysics Data System (ADS)

A lattice Boltzmann model for mixture modeling is developed by applying the multiple-relaxation-time (MRT) approach to the Hamel model, which allows one to derive from a general framework different model equations independently proposed, like the Gross-Krook model and the Sirovich model. By imposing some physical constraints, the MRT lattice-Boltzmann Hamel model reduces to the generalized MRT lattice-Boltzmann Gross-Krook model (involving the local Maxwellian centered on the barycentric velocity), which allows one to tune independently the species diffusivity, the mixture kinematic viscosity, and the mixture bulk viscosity. Reducing the number of moving particles over the total is possible to deal effectively with mass particle ratios far from unity and, for this reason, to model the pressure-driven diffusion. A convenient numerical approach is proposed for solving the developed model, which essentially widens the stability range of conventional schemes in terms of dimensionless relaxation frequencies, by solving explicitly the advection operator together with the nonlinear terms of the collisional operator and solving implicitly the residual linear terms. In this way, the calculations are drastically reduced and the operative matrices can be computed once for all, at the beginning of the calculation (implying moderate additional computational demand). Following this approach, a semi-implicit-linearized backward Euler scheme, ideal for parallel implementations, is proposed. In order to achieve the previous results, the asymptotic analysis, recently suggested for analyzing the macroscopic equations corresponding to lattice-Boltzmann schemes in the low-Mach-number limit, proves to be an effective tool. Some numerical tests are reported for proving the consistency of the proposed method with both the Fick model and Maxwell-Stefan model in the macroscopic limit.

Asinari, Pietro

2006-05-01

308

Origin of abrupt rise in deuteron NMR longitudinal relaxation times of protein methyl groups below 90 K.  

PubMed

In order to examine the origin of the abrupt change in the temperature dependence of (2)H NMR longitudinal relaxation times observed previously for methyl groups of L69 in the hydrophobic core of villin headpiece protein at around 90 K (Vugmeyster et al. J. Am. Chem. Soc. 2010, 132, 4038-4039), we extended the measurements to several other methyl groups in the hydrophobic core. We show that, for all methyl groups, relaxation times experience a dramatic jump several orders of magnitude around this temperature. Theoretical modeling supports the conclusion that the origin of the apparent transition in the relaxation times is due to the existence of the distribution of conformers distinguished by their activation energy for methyl three-site hops. It is also crucial to take into account the differential contribution of individual conformers into overall signal intensity. When a particular conformer approaches the regime at which its three-site hop rate constant is on the order of the quadrupolar coupling interaction constant, the intensity of the signal due to this conformer experiences a sharp drop, thus changing the balance of the contributions of different conformers into the overall signal. As a result, the observed apparent transition in the relaxation rates can be explained without the assumption of an underlying transition in the rate constants. This work in combination with earlier results also shows that the model based on the distribution of conformers explains the relaxation behavior in the entire temperature range between 300 and 70 K. PMID:23627365

Vugmeyster, Liliya; Ostrovsky, Dmitry; Lipton, Andrew S

2013-05-09

309

Relaxation of a shear-induced lamellar phase measured with time-resolved small-angle neutron scattering  

NASA Astrophysics Data System (ADS)

We have measured the relaxation of Couette shear-induced L? lamellar states to their isotropic L3 ``sponge'' equilibrium phases in the cetylpryridinium-hexanol/dextrose-brine system by (cycled) time-resolved small-angle neutron scattering. Although diffusive motions of adjacent membrane sheets may be estimated to bring them into contact with frequencies ~10kHz, we observe structural relaxation times on the order of seconds. This indicates a significant activation energy against the re-establishment of the passages characterizing the convoluted sponge structure.

Porcar, L.; Hamilton, W. A.; Butler, P. D.; Warr, G. G.

2004-07-01

310

Neural Networks-Based Real-Time Determination of the Laser Beam Spatial Profile and Vibrational-to-Translational Relaxation Time Within Pulsed Photoacoustics  

NASA Astrophysics Data System (ADS)

This paper concerns with the possibilities of computational intelligence application for simultaneous determination of the laser beam spatial profile and vibrational-to-translational relaxation time of the polyatomic molecules in gases by pulsed photoacoustics. Results regarding the application of neural computing through the use of feed-forward multilayer perception networks are presented. Feed-forward multilayer perception networks are trained in an offline batch training regime to estimate simultaneously, and in real-time, the laser beam spatial profile (profile shape class) and the vibrational-to-translational relaxation time from given (theoretical) photoacoustic signals. The proposed method significantly shortens the time required for the simultaneous determination of the laser beam spatial profile and relaxation time and has the advantage of accurately calculating the aforementioned quantities.

Luki?, M.; ?ojbaši?, Ž.; Rabasovi?, M. D.; Markushev, D. D.; Todorovi?, D. M.

2013-09-01

311

Detection of crossover time scales in multifractal detrended fluctuation analysis  

NASA Astrophysics Data System (ADS)

Fractal is employed in this paper as a scale-based method for the identification of the scaling behavior of time series. Many spatial and temporal processes exhibiting complex multi(mono)-scaling behaviors are fractals. One of the important concepts in fractals is crossover time scale(s) that separates distinct regimes having different fractal scaling behaviors. A common method is multifractal detrended fluctuation analysis (MF-DFA). The detection of crossover time scale(s) is, however, relatively subjective since it has been made without rigorous statistical procedures and has generally been determined by eye balling or subjective observation. Crossover time scales such determined may be spurious and problematic. It may not reflect the genuine underlying scaling behavior of a time series. The purpose of this paper is to propose a statistical procedure to model complex fractal scaling behaviors and reliably identify the crossover time scales under MF-DFA. The scaling-identification regression model, grounded on a solid statistical foundation, is first proposed to describe multi-scaling behaviors of fractals. Through the regression analysis and statistical inference, we can (1) identify the crossover time scales that cannot be detected by eye-balling observation, (2) determine the number and locations of the genuine crossover time scales, (3) give confidence intervals for the crossover time scales, and (4) establish the statistically significant regression model depicting the underlying scaling behavior of a time series. To substantive our argument, the regression model is applied to analyze the multi-scaling behaviors of avian-influenza outbreaks, water consumption, daily mean temperature, and rainfall of Hong Kong. Through the proposed model, we can have a deeper understanding of fractals in general and a statistical approach to identify multi-scaling behavior under MF-DFA in particular.

Ge, Erjia; Leung, Yee

2012-05-01

312

Detection of crossover time scales in multifractal detrended fluctuation analysis  

NASA Astrophysics Data System (ADS)

Fractal is employed in this paper as a scale-based method for the identification of the scaling behavior of time series. Many spatial and temporal processes exhibiting complex multi(mono)-scaling behaviors are fractals. One of the important concepts in fractals is crossover time scale(s) that separates distinct regimes having different fractal scaling behaviors. A common method is multifractal detrended fluctuation analysis (MF-DFA). The detection of crossover time scale(s) is, however, relatively subjective since it has been made without rigorous statistical procedures and has generally been determined by eye balling or subjective observation. Crossover time scales such determined may be spurious and problematic. It may not reflect the genuine underlying scaling behavior of a time series. The purpose of this paper is to propose a statistical procedure to model complex fractal scaling behaviors and reliably identify the crossover time scales under MF-DFA. The scaling-identification regression model, grounded on a solid statistical foundation, is first proposed to describe multi-scaling behaviors of fractals. Through the regression analysis and statistical inference, we can (1) identify the crossover time scales that cannot be detected by eye-balling observation, (2) determine the number and locations of the genuine crossover time scales, (3) give confidence intervals for the crossover time scales, and (4) establish the statistically significant regression model depicting the underlying scaling behavior of a time series. To substantive our argument, the regression model is applied to analyze the multi-scaling behaviors of avian-influenza outbreaks, water consumption, daily mean temperature, and rainfall of Hong Kong. Through the proposed model, we can have a deeper understanding of fractals in general and a statistical approach to identify multi-scaling behavior under MF-DFA in particular.

Ge, Erjia; Leung, Yee

2013-04-01

313

Simulation of lid-driven cavity flows by parallel lattice Boltzmann method using multi-relaxation-time scheme  

NASA Astrophysics Data System (ADS)

Two-dimensional near-incompressible steady lid-driven cavity flows (Re = 100-7,500) are simulated using multi-relaxation-time (MRT) model in the parallel lattice Boltzmann BGK Bhatnager-Gross-Krook method (LBGK). Results are compared with those using single-relaxation-time (SRT) model in the LBGK method and previous simulation data using Navier-Stokes equations for the same flow conditions. Effects of variation of relaxation parameters in the MRT model, effects of number of the lattice points, improved computational convergence and reduced spatial oscillations of solution near geometrically singular points in the flow field using LBGK method due to MRT model are highlighted in the study. In summary, lattice Boltzmann method using MRT model introduces much less spatial oscillations near geometrical singular points, which is important for the successful simulation of higher Reynolds number flows.

Wu, J.-S.; Shao, Y.-L.

2004-11-01

314

Atlas-based Investigation of Human Brain Tissue Microstructural Spatial Heterogeneity and Interplay between Transverse Relaxation Time and Radial Diffusivity  

PubMed Central

Microstructural metrics obtained using magnetic resonance imaging (MRI) such as transverse relaxation time and radial diffusivity have been used as in vivo markers of human brain tissue integrity. Considering the sensitivity of these parameters to some common biophysical contributors and their structural and spatial heterogeneity, we hypothesized that strong inter and intra-regional association exist between these variables providing evidence to possible interplay between transverse relaxation time and radial diffusivity. To validate our hypothesis we obtained high resolution anatomical T1-weighted data and fused it with T2-relaxomotry and diffusion tensor imaging (DTI) data on a cohort of healthy adults. The anatomical data were parcellated using FreeSurfer and then coaligned and fused with the T2 and DTI maps. Our data reveal some association between transverse relaxation and radial diffusivity that may help towards the interpretation and modeling of the biophysical contributors to the measured MRI metrics.

Walimuni, Indika S.; Hasan, Khader M.

2011-01-01

315

Fuzzy controller design for passive continuous-time affine T-S fuzzy models with relaxed stability conditions.  

PubMed

In order to design a fuzzy controller for complex nonlinear systems, the work of this paper deals with developing the relaxed stability conditions for continuous-time affine Takagi-Sugeno (T-S) fuzzy models. By applying the passivity theory and Lyapunov theory, the relaxed stability conditions are derived to guarantee the stability and passivity property of closed-loop systems. Based on these relaxed stability conditions, the synthesis of fuzzy controller design problem for passive continuous-time affine T-S fuzzy models can be easily solved via the Optimal Convex Programming Algorithm (OCPA) and Linear Matrix Inequality (LMI) technique. At last, a simulation example for the fuzzy control of a nonlinear synchronous generator system is presented to manifest the applications and effectiveness of proposed fuzzy controller design approach. PMID:19389667

Chang, Wen-Jer; Ku, Cheung-Chieh; Huang, Pei-Hwa; Chang, Wei

2009-04-22

316

Atlas-based investigation of human brain tissue microstructural spatial heterogeneity and interplay between transverse relaxation time and radial diffusivity.  

PubMed

Microstructural metrics obtained using magnetic resonance imaging (MRI) such as transverse relaxation time and radial diffusivity have been used as in vivo markers of human brain tissue integrity. Considering the sensitivity of these parameters to some common biophysical contributors and their structural and spatial heterogeneity, we hypothesized that strong inter and intra-regional associations exist between these variables providing evidence to possible interplay between transverse relaxation time and radial diffusivity. To validate our hypothesis we obtained high resolution anatomical T1-weighted data and fused it with T2-relaxometry and diffusion tensor imaging (DTI) data on a cohort of healthy adults. The anatomical data were parcellated using FreeSurfer and then coaligned and fused with the T2 and DTI maps. Our data reveal some association between transverse relaxation and radial diffusivity that may help toward the interpretation and modeling of the biophysical contributors to the measured MRI metrics. PMID:21658457

Walimuni, Indika S; Hasan, Khader M

2011-05-30

317

Measurement of transverse relaxation times of J-coupled metabolites in the human visual cortex at 4 T  

PubMed Central

Accurate quantification of 1H NMR spectra often requires knowledge of the relaxation times in order to correct for signal losses due to relaxation and saturation. In human brain, T2 values for singlets such as N-acetylaspartate (NAA), creatine, and choline have been reported, but few T2 values are available for J-coupled spin systems. The purpose of the present study was to measure the T2 relaxation times of J-coupled metabolites in the human occipital lobe using the LASER sequence. Spectra were acquired at multiple echo times and were analyzed with an LCModel using basis sets simulated at each echo time. Separate basis spectra were used for resonances of protons belonging to the same molecule but having very different T2 values (e.g. two separate basis spectra were used for the singlet and multiplet signal in NAA). The T2 values for the NAA multiplet (149 ± 12 ms), glutamate (125 ± 10 ms), myo-inositol (139 ± 20 ms) and taurine (196 ± 28 ms) were successfully measured in the human visual cortex at 4 T. These measured T2 relaxation times have enabled the accurate and absolute quantification of cerebral metabolites at longer echo times.

Deelchand, Dinesh Kumar; Henry, Pierre-Gilles; Ugurbil, Kamil; Marjanska, Malgorzata

2011-01-01

318

The differential equations on time scales through impulsive differential equations  

Microsoft Academic Search

In this paper we investigate differential equations on certain time scales with transition conditions (DETC) on the basis of reduction to the impulsive differential equations (IDE). DETC are in some sense more general than dynamic equations on time scales [M. Bohner, A. Peterson, Dynamic equations on time scales, in: An Introduction With Applications, Birkhäuser Boston, Inc., Boston, MA, 2001, p.

M. U. Akhmet; M. Turan

2006-01-01

319

Two-relaxation-time lattice Boltzmann method for the anisotropic dispersive Henry problem  

NASA Astrophysics Data System (ADS)

This study develops a lattice Boltzmann method (LBM) with a two-relaxation-time collision operator (TRT) to cope with anisotropic heterogeneous hydraulic conductivity and anisotropic velocity-dependent hydrodynamic dispersion in the saltwater intrusion problem. The directional-speed-of-sound technique is further developed to address anisotropic hydraulic conductivity and dispersion tensors. Forcing terms are introduced in the LBM to correct numerical errors that arise during the recovery procedure and to describe the sink/source terms in the flow and transport equations. In order to facilitate the LBM implementation, the forcing terms are combined with the equilibrium distribution functions (EDFs) to create pseudo-EDFs. This study performs linear stability analysis and derives LBM stability domains to solve the anisotropic advection-dispersion equation. The stability domains are used to select the time step at which the lattice Boltzmann method provides stable solutions to the numerical examples. The LBM was implemented for the anisotropic dispersive Henry problem with high ratios of longitudinal to transverse dispersivities, and the results compared well to the solutions in the work of Abarca et al. (2007).

Servan-Camas, Borja; Tsai, Frank T.-C.

2010-02-01

320

Picosecond-time-resolved studies of nonradiative relaxation in ruby and alexandrite  

SciTech Connect

Dynamics of the nonradiative transitions between the /sup 4/T/sub 2/ pump band and the /sup 2/E storage level of the Cr/sup 3 +/ ion in ruby and alexandrite crystals is studied using the picosecond excite-and-probe absorption technique. A 527-nm picosecond pulse excites the /sup 4/T/sub 2/ state of the Cr/sup 3 +/ ion, and an infrared picosecond probe pulse monitors the subsequent growth and decay of population in the excited states as a function of pump-probe delay. An upper limit of 7 ps is determined for the nonradiative lifetime of the /sup 4/T/sub 2/ state in ruby. A vibrational relaxation time of 25 ps for the /sup 4/T/sub 2/ band in alexandrite is estimated. The time to attain thermal equilibrium population between the /sup 2/E and /sup 4/T/sub 2/ levels of alexandrite following excitation of /sup 4/T/sub 2/ band is estimated to be approx. 100 ps.

Gayen, S.K.; Wang, W.B.; Petricevic, V.; Alfano, R.R.

1985-01-01

321

Ion-solvent interaction in nonaqueous solutions. II. Spin-lattice relaxation times of 23 Na and 133 Cs  

Microsoft Academic Search

The spin-lattice relaxation time (T1) of23Na was measured in solutions of NaClO4 and (or) NaBr in formamide,N-methylformamide,N,N-dimethylformamide (DMF), MeCN, Me2CO, tetrahydrofuran (THF), and dimethyl sulfoxide (DMSO), and133Cs in a solution of CsCl in formamide. The values of (1\\/T1)0 obtained by extrapolation are discussed in terms of current theories of quadrupolar magnetic relaxation of ionic nuclei. A correlation was found between

Yu. M. Kessler; A. I. Mishustin; A. I. Podkovyrin

1977-01-01

322

Optimizing Flip Angle Selection in Breast MRI for Accurate Extraction and Visualization of T1 Tissue Relaxation Time  

Microsoft Academic Search

Contrast enhanced MRI is a popular diagnostic technique for characterizing angiogenesis and detecting breast cancer. Though conventionally measured relative signal enhancement (RSE) is not linearly proportional to contrast agent concentration, relative enhancement of T1 tissue relaxation time is. Therefore, measurement of T1 using low flip angle acquisitions is essential for characterizing tumors. In this paper, we present a framework to

GEORGIOS KETSETZIS; MICHAEL BRADY

323

Hyaline articular cartilage: relaxation times, pulse-sequence parameters and MR appearance at 1.5 T  

Microsoft Academic Search

In order to optimize the parameters for the best visualization of the internal architecture of the hyaline articular cartilage a study both ex vivo and in vivo was performed. Accurate T1 and T2 relaxation times of articular cartilage were obtained with a particular mixed sequence and then used for the creation of isocontrast intensity graphs. These graphs subsequently allowed in

Stylianos M. Chalkias; Roberto S. Pozzi-Mucelli; Massimo Pozzi-Mucelli; Francesca Frezza; Renata Longo

1994-01-01

324

Time-optimal control of spin 1\\/2 particles in the presence of radiation damping and relaxation  

Microsoft Academic Search

We consider the time-optimal control of an ensemble of uncoupled spin 1\\/2 particles in the presence of relaxation and radiation damping effects, whose dynamics is governed by nonlinear equations generalizing the standard linear Bloch equations. For a single spin, the optimal control strategy can be fully characterized analytically. However, in order to take into account the inhomogeneity of the static

Y. Zhang; M. Lapert; D. Sugny; M. Braun; S. J. Glaser

2011-01-01

325

Determination of Spin-Lattice Relaxation of Time Using (Super 13)C NMR: An Undergraduate Physical Chemistry Laboratory Experiment  

ERIC Educational Resources Information Center

An experiment designed for the physical chemistry laboratory where (super 13)C NMR is applied to determine the spin-lattice relaxation time for carbon atoms in n-hexanol is proposed. It is concluded that students learn the principles and concepts of NMR spectroscopy as well as dynamic NMR experiments.

Gasyna, Zbigniew L.; Jurkiewicz, Antoni

2004-01-01

326

Relationship between atrial function, left ventricular isovolumic relaxation time, and early filling in dual chamber-paced patients  

Microsoft Academic Search

This investigation was performed to study atrial systolic function in response to modification of atrioventricular delay in a sample of 36 patients with a DDD pacemaker implanted for complete atrioventricular block. The relation between atrial systolic performance and diastolic-related parameters was also evaluated. Isovolumic relaxation time, early diastolic peak velocity, late (atrial) diastolic peak velocity, atrial filling fraction, and atrial

Rosario Rossi; Nicola Muia; Maria Grazia Modena

1997-01-01

327

Robustness and Accuracies of Relaxed Clock Methods in Estimating Divergence Times and their Credibility Intervals  

NASA Astrophysics Data System (ADS)

One aspect of the evolutionary history of life is its timeline. Through simulation studies we evaluated the strengths and weaknesses of relaxed molecular clocks in order to improve their performance in empirical data sets.

Battistuzzi, F. U.; Filipski, A.; Hedges, S. B.; Kumar, S.

2010-04-01

328

Time to Talk: 5 Things to Know about Relaxation Techniques for Stress  

MedlinePLUS

... 5 Things To Know About Relaxation Techniques for Stress When you’re under stress, your body reacts by releasing hormones that produce ... vessels narrow (restricting the flow of blood). Occasional stress is a normal coping mechanism. But over the ...

329

Multiple length and time scales of dynamic heterogeneities in model glass-forming liquids: a systematic analysis of multi-point and multi-time correlations.  

PubMed

We report an extensive and systematic investigation of the multi-point and multi-time correlation functions to reveal the spatio-temporal structures of dynamic heterogeneities in glass-forming liquids. Molecular dynamics simulations are carried out for the supercooled states of various prototype models of glass-forming liquids such as binary Kob-Andersen, Wahnstro?m, soft-sphere, and network-forming liquids. While the first three models act as fragile liquids exhibiting super-Arrhenius temperature dependence in their relaxation times, the last is a strong glass-former exhibiting Arrhenius behavior. First, we quantify the length scale of the dynamic heterogeneities utilizing the four-point correlation function. The growth of the dynamic length scale with decreasing temperature is characterized by various scaling relations that are analogous to the critical phenomena. We also examine how the growth of the length scale depends upon the model employed. Second, the four-point correlation function is extended to a three-time correlation function to characterize the temporal structures of the dynamic heterogeneities based on our previous studies [K. Kim and S. Saito, Phys. Rev. E 79, 060501(R) (2009); and J. Chem. Phys. 133, 044511 (2010)]. We provide comprehensive numerical results obtained from the three-time correlation function for the above models. From these calculations, we examine the time scale of the dynamic heterogeneities and determine the associated lifetime in a consistent and systematic way. Our results indicate that the lifetime of the dynamical heterogeneities becomes much longer than the ?-relaxation time determined from a two-point correlation function in fragile liquids. The decoupling between the two time scales is remarkable, particularly in supercooled states, and the time scales differ by more than an order of magnitude in a more fragile liquid. In contrast, the lifetime is shorter than the ?-relaxation time in tetrahedral network-forming strong liquid, even at lower temperatures. PMID:23556757

Kim, Kang; Saito, Shinji

2013-03-28

330

Effects of electric field on the entropy, viscosity, relaxation time, and glass-formation.  

PubMed

By using the known formalism for the effect of an externally applied electric field, E, on thermodynamics of a dielectric material, we calculated the field-induced configurational entropy factor, ?Sconf (E)/E(2), of 50 dipolar liquids, including those whose static permittivity, ?s, decreases on cooling. The field induced change, ?Sconf (E), is found to be experimentally detectable only when E is on the order of 10(5) V?cm, a value less than the dielectric breakdown field strength of some liquids but in the range of nonlinear dielectric response. We argue that the dielectric response is formally nonlinear already for E > 0, and then show that the difference between the Langevin-function and the extrapolated linear response is < 0.15% for E in the 10(5) V?cm range. Therefore, such high E values may be used to estimate ?Sconf (E). We conclude that (i) for E in the 10(5) V?cm range, ?Sconf (E) is high enough to produce a measurable change in the viscosity and relaxation time of some ultraviscous liquids with prominent dipolar interactions, thereby changing their glass formation temperature, and (ii) application of E would reversibly transform, isothermally, some liquids to glass, and transform some glasses to liquid. Finally, we suggest that the effect of E can be used to determine the merits of the models for non-Arrhenius kinetics. PMID:23614426

Johari, G P

2013-04-21

331

Blood longitudinal (T1) and transverse (T2) relaxation time constants at 11.7 Tesla  

PubMed Central

Object The goal of the study was to determine blood T1 and T2 values as functions of oxygen saturation (Y), temperature (Temp) and hematocrit (Hct) at an ultrahigh MR field (11.7 T) and explore their impacts on physiological measurements, including cerebral blood flow (CBF), blood volume (CBV) and oxygenation determination. Materials and methods T1 and T2 were simultaneously measured. Temperature was adjusted from 25 to 40°C to determine Temp dependence; Hct of 0.17–0.51 to evaluate Hct dependence at 25 and 37°C; and Y of 40–100% to evaluate Y dependence at 25 and 37°C. Comparisons were made with published data obtained at different magnetic field strengths (B0). Results T1 was positively correlated with Temp, independent of Y, and negatively correlated with Hct. T2 was negatively correlated with Temp and Hct, but positively correlated with Y, in a non-linear fashion. T1 increased linearly with B0, whereas T2 decreased exponentially with B0. Conclusion This study reported blood T1 and T2 measurements at 11.7 T for the first time. These blood relaxation data could have implications in numerous functional and physiological MRI studies at 11.7 T.

Qin, Qin; Zhao, Xia; Duong, Timothy Q.

2013-01-01

332

Comparative analysis of encephalization in mammals reveals relaxed constraints on anthropoid primate and cetacean brain scaling.  

PubMed

There is a well-established allometric relationship between brain and body mass in mammals. Deviation of relatively increased brain size from this pattern appears to coincide with enhanced cognitive abilities. To examine whether there is a phylogenetic structure to such episodes of changes in encephalization across mammals, we used phylogenetic techniques to analyse brain mass, body mass and encephalization quotient (EQ) among 630 extant mammalian species. Among all mammals, anthropoid primates and odontocete cetaceans have significantly greater variance in EQ, suggesting that evolutionary constraints that result in a strict correlation between brain and body mass have independently become relaxed. Moreover, ancestral state reconstructions of absolute brain mass, body mass and EQ revealed patterns of increase and decrease in EQ within anthropoid primates and cetaceans. We propose both neutral drift and selective factors may have played a role in the evolution of brain-body allometry. PMID:22435703

Boddy, A M; McGowen, M R; Sherwood, C C; Grossman, L I; Goodman, M; Wildman, D E

2012-03-21

333

Electron relaxation times due to the deformation-potential interaction of electrons with confined acoustic phonons in a free-standing quantum well  

Microsoft Academic Search

The confined acoustic phonons in free-standing quantum wells are considered in detail. The Hamiltonian describing interactions of the confined acoustic phonons with electrons in the approximation of the deformation potential and the corresponding electron transition probability density are derived. They are used to analyze the electron scattering times (inverse scattering rate, momentum relaxation time, and the energy relaxation time) in

N. Bannov; V. Aristov; V. Mitin; M. A. Stroscio

1995-01-01

334

Relaxation-driven binary mergers  

NASA Astrophysics Data System (ADS)

N-body integrations are used to study the merging of two subclusters in the limit where relaxation effects are significant. Relaxation can speed up the orbital decay relative to the prediction of the standard dynamical friction formula, essentially by increasing the density of halo particles. The numerically determined decay time is 4-40 times shorter than the predicted value, and its scaling with the distance between the clumps disagrees with the standard prediction. It is shown that the effect can be explained through a combination of relaxation-induced halo growth and ordinary dynamical friction, and a semianalytic model is presented that accounts for the main features observed in these simulations. This model is used to estimate the minimum number of particles required for relaxation to have a negligible impact on the orbical decay (between 100,000 and 1,000,000). Various measures of the evolution of substructure are described and compared.

Gelato, Sergio; Chernoff, David F.; Wasserman, Ira

1992-01-01

335

Geologic Time Scale 2004 - why, how, and where next!  

Microsoft Academic Search

A Geologic Time Scale (GTS2004) is presented that integrates currently available stratigraphic and geochronologic information. Key features of the new scale are outlined, how it was constructed, and how it can be improved Since Geologic Time Scale 1989 by Harland and his team, many developments have taken place: (1) Stratigraphic standardization through the work of the International Commission on Stratigraphy

Felix Gradstein; James Ogg

2004-01-01

336

Linking Response-Time Parameters onto a Common Scale  

ERIC Educational Resources Information Center

|Although response times on test items are recorded on a natural scale, the scale for some of the parameters in the lognormal response-time model (van der Linden, 2006) is not fixed. As a result, when the model is used to periodically calibrate new items in a testing program, the parameter are not automatically mapped onto a common scale. Several…

van der Linden, Wim J.

2010-01-01

337

Postseismic Relaxation at the Central Nevada Seismic Belt Observed in Vertical GPS Time Series  

NASA Astrophysics Data System (ADS)

Between 1872 and 1954 the Basin and Range province of the western United States experienced six major earthquakes that occurred in a quasi-linear belt known as the Central Nevada Seismic Belt (CNSB). These strike-slip to normal events account for most of the seismic moment release that has occurred in the Basin and Range in historic time. Several studies have noted the possible presence of a contemporary geodetic signal owing to postseismic relaxation from these earthquakes, implying that this signal has persisted for decades after the events. Observations that support the existence of this postseismic signal are: 1) GPS-derived horizontal strain rates that are relatively high compared to the surrounding regions, 2) 3-4 mm/yr vertical upward doming observed with Interferometric Synthetic Aperture Radar (InSAR) that is consistent with models of viscoelastic relaxation of the mantle, 3) possible rapid vertical postseismic motion observed using leveling measurements immediately following the 1954 events, 4) disagreement between geodetically and geologically inferred strain rates that is consistent with elevated contemporary transient strain. Since 2004 the University of Nevada, Reno has operated a semi-continuous GPS network with ~20 km spacing (the Mobile Array of GPS for Nevada Transtension: MAGNET) that complements the spatially less dense Basin and Range Geodetic Network (BARGEN) and Plate Boundary Observatory (PBO) continuously recording networks. MAGNET is ideally deployed to observe the ongoing transient deformation associated with the central Nevada earthquake cycle because it spans the CNSB faults where the predicted postseismic signal is greatest. We analyze the GPS data with the GIPSY/OASIS II software package in precise point positioning and apply regional filtering to remove common mode effects (uniform displacements and/or rotations that are present in all the time series). These common mode signals have a much larger impact on the vertical than on horizontal rates, especially for shorter time series, so accounting for them is essential for studying vertical motions with GPS. The filtered time series enhance our resolution of the relative vertical motion between sites. Our preliminary results based on 2.5-3.3 years of GPS data from MAGNET indeed detect a horizontal gradients in the vertical rates of 3 - 4 mm/yr that is consistent with earlier studies based on InSAR and campaign GPS. We find that the MAGNET sites directly east of Dixie Valley (in the Clan Alpine Range) have the greatest vertical uplift rate, suggesting that the 1954 Dixie Valley earthquake makes a larger contribution to the contemporary uplift than the other earthquakes associated with the CNSB. The largest amplitudes in the vertical signal appear to be limited to the MAGNET sites, highlighting the need for arrays denser than provided by the continuous networks (i.e. PBO and BARGEN) in this region.

Hammond, W. C.; Plag, H.; Blewitt, G.; Kreemer, C.

2007-12-01

338

Time Ephemeris and General Relativistic Scale Factor  

Microsoft Academic Search

Time ephemeris is the location-independent part of the transformation formula relating two time coordinates such as TCB and TCG (Fukushima 2009). It is computed from the corresponding (space) ephemerides providing the relative motion of two spatial coordinate origins such as the motion of geocenter relative to the solar system barycenter. The time ephemerides are inevitably needed in conducting precise four

Toshio Fukushima

2010-01-01

339

Time ephemeris and general relativistic scale factor  

Microsoft Academic Search

Time ephemeris is the location-independent part of the transformation formula relating two time coordinates such as TCB and TCG (Fukushima 1995). It is computed from the corresponding (space) ephemerides providing the relative motion of two spatial coordinate origins such as the motion of geocenter relative to the solar system barycenter. The time ephemerides are inevitably needed in conducting precise four

Toshio Fukushima

2010-01-01

340

Measurement of the relaxation time of hot electrons in laser-solid interaction at relativistic laser intensities  

SciTech Connect

The authors have measured the relaxation time of hot electrons in short pulse laser-solid interactions using a picosecond time-resolved x-ray spectrometer and a time-integrated electron spectrometer. Employing laser intensities of 10{sup 17}, 10{sup 18}, and 10{sup 19} W/cm{sup 2}, they find increased laser coupling to hot electrons as the laser intensity becomes relativistic and thermalization of hot electrons at timescales on the order of 10 ps at all laser intensities. They propose a simple model based on collisional coupling and plasma expansion to describe the rapid relaxation of hot electrons. The agreement between the resulting K{sub {alpha}} time-history from this model with the experiments is best at highest laser intensity and less satisfactory at the two lower laser intensities.

Chen, H; Shepherd, R; Chung, H K; Dyer, G; Faenov, A; Fournier, K B; Hansen, S B; Hunter, J; Kemp, A; Pikuz, T; Ping, Y; Widmann, K; Wilks, S C; Beiersdorfer, P

2006-08-22

341

Binding and relaxation behavior of Coumarin-153 in lecithin-taurocholate mixed micelles: A time resolved fluorescence spectroscopic study  

NASA Astrophysics Data System (ADS)

The microenvironment of the bile salt-lecithin mixed aggregates has been investigated using steady state and picosecond time resolved fluorescence spectroscopy. The steady state spectra show that the polarity of the bile salt is higher compared to lecithin vesicles or the mixed aggregates. We have observed slow solvent relaxation in bile salt micelles and lecithin vesicles. The solvation time is gradually slowed down due to gradual addition of the bile salt in lecithin vesicles. Addition of bile salt leads to the tighter head group packing in lecithin. Thus, mobility of the water molecules becomes slower and consequently the solvation time is also retarded. We have observed bimodal slow rotational relaxation time in all these systems.

Chakrabarty, Debdeep; Chakraborty, Anjan; Seth, Debabrata; Hazra, Partha; Sarkar, Nilmoni

2005-09-01

342

Effects of fatigue and recovery on electromyographic and isometric force- and relaxation-time characteristics of human skeletal muscle  

Microsoft Academic Search

Summary  Effects of fatigue produced by a maintained 60% isometric loading on electromyographic and isometric force-time and relaxation-time characteristics of human skeletal muscle were studied in 21 males accustomed to strength training. Fatigue loading resulted in a slight but not significant change in the maximal integrated EMG of a maximal isometric contraction, and a large decrease (20.4±6.3%, pppppppp

Keijo HÄkkinen; Paavo V. Komi

1986-01-01

343

Magnetic resonance estimation of longitudinal relaxation time (T1) in spoiled gradient echo using an adaptive neural network  

Microsoft Academic Search

Recently, the acquisition of high-resolution T1 maps in a clinically feasible time frame has been demonstrated with Driven Equilibrium Single Pulse Observation of T1 (DESPOT1). DESPOT1 derives the longitudinal relaxation time, T1, from two or more spoiled gradient recalled echo (SPGR) images acquired with a constant TR and different flip angles. In general, T1 can be estimated from two or

H. Bagher-Ebadian; R. Jain; R. Paudyal; S. P. Nejad-Davarani; J. Narang; Q. Jiang; T. Mikkelsen; J. R. Ewing

2011-01-01

344

Magnetic Field and Frequency Dependence of Electron Spin Relaxation Times of the E? Center in Irradiated Vitreous Silica  

Microsoft Academic Search

The electron spin relaxation time, T1, of the E? defect in ?-irradiated vitreous silica, was measured by time-domain EPR and found to be approximately independent of microwave frequency between 1 and 9 GHz and to increase by about 50% at 19.4 GHz. Preliminary results indicate a further increase in T1 at 95 GHz. At each microwave frequency, T1 varies monotonically

B. T. Ghim; S. S. Eaton; G. R. Eaton; R. W. Quine; G. A. Rinard; S. Pfenninger

1995-01-01

345

Relaxation Times and Line Widths of Isotopically-Substituted Nitroxides in Aqueous Solution at X-band  

PubMed Central

Optimization of nitroxides as probes for EPR imaging requires detailed understanding of spectral properties. Spin lattice relaxation times, spin packet line widths, nuclear hyperfine splitting, and overall lineshapes were characterized for six low molecular weight nitroxides in dilute deoxygenated aqueous solution at X-band. The nitroxides included 6-member, unsaturated 5-member, or saturated 5-member rings, most of which were isotopically labeled. The spectra are near the fast tumbling limit with T1 ~ T2 in the range of 0.50 to 1.1 ?s at ambient temperature. Both spin-lattice relaxation T1 and spin-spin relaxation T2 are longer for 15N- than for 14N-nitroxides. The dominant contributions to T1 are modulation of nitrogen hyperfine anisotropy and spin rotation. Dependence of T1 on nitrogen nuclear spin state mI was observed for both 14N and 15N. Unresolved hydrogen/deuterium hyperfine couplings dominate overall line widths. Lineshapes were simulated by including all nuclear hyperfine couplings and spin packet line widths that agreed with values obtained by electron spin echo. Line widths and relaxation times are predicted to be about the same at 250 MHz as at X-band.

Biller, Joshua R.; Meyer, Virginia; Elajaili, Hanan; Rosen, Gerald M.; Kao, Joseph P.Y.; Eaton, Sandra S.; Eatona, Gareth R.

2011-01-01

346

Relaxation times and line widths of isotopically-substituted nitroxides in aqueous solution at X-band.  

PubMed

Optimization of nitroxides as probes for EPR imaging requires detailed understanding of spectral properties. Spin lattice relaxation times, spin packet line widths, nuclear hyperfine splitting, and overall lineshapes were characterized for six low molecular weight nitroxides in dilute deoxygenated aqueous solution at X-band. The nitroxides included 6-member, unsaturated 5-member, or saturated 5-member rings, most of which were isotopically labeled. The spectra are near the fast tumbling limit with T(1)?T(2) in the range of 0.50-1.1 ?s at ambient temperature. Both spin-lattice relaxation T(1) and spin-spin relaxation T(2) are longer for (15)N- than for (14)N-nitroxides. The dominant contributions to T(1) are modulation of nitrogen hyperfine anisotropy and spin rotation. Dependence of T(1) on nitrogen nuclear spin state m(I) was observed for both (14)N and (15)N. Unresolved hydrogen/deuterium hyperfine couplings dominate overall line widths. Lineshapes were simulated by including all nuclear hyperfine couplings and spin packet line widths that agreed with values obtained by electron spin echo. Line widths and relaxation times are predicted to be about the same at 250 MHz as at X-band. PMID:21843961

Biller, Joshua R; Meyer, Virginia; Elajaili, Hanan; Rosen, Gerald M; Kao, Joseph P Y; Eaton, Sandra S; Eaton, Gareth R

2011-07-29

347

a Study of Water t1 and t2 NMR Relaxation Times in Healthy and Cancer Affected Human Blood Plasma Doped with Hematoporphyrin IX Dye  

Microsoft Academic Search

Human blood plasma water protons relaxation times T1 and T2 in the protein bound water phase restricted motion state have been determined for the native and hematoporphyrin IX (HMP) doped samples at the temperature of 20 °C and H NMR frequency of 80 Mhz. The samples belong to either healthy and myeloma affected patients. The resulting bound water relaxation times

Flaviano Coletta

2001-01-01

348

Relaxation time measurements of bone marrow protons in the calcaneus using a compact MRI system at 0.2 Tesla field strength  

Microsoft Academic Search

Relaxation times (T1 and T2) of the bone marrow protons and trabecular bone volume fraction (TBVF) in the calcaneus were measured for 100 female volunteers using a compact MRI sys- tem at 0.2 T field strength. The speed of sound (SOS) through the calcaneus was measured also for the same subjects using a quantitative ultrasound system. Both relaxation times were

Sadanori Tomiha; Nachiko Iita; Fumi Okada; Shinya Handa; Katsumi Kose

2008-01-01

349

Scale-Limited Activating Sets and Multiperiodicity for Threshold-Linear Networks on Time Scales.  

PubMed

The existing results for multiperiodicity of threshold-linear networks (TLNs) are scale-free on time evolution and hence exhibit some restrictions. Due to the nature of the scale-limited activating set, it is interesting to study the dynamical properties of neurons on time scales. In this paper we analyze and obtain results concerning nondivergence, attractivity, and multiperiodic dynamics of TLNs on time scales. Using the notion of exponential functions on time scales, we obtain results for scale-limited type criteria for boundedness and global attractivity of TLNs. Moreover, by constructing simple algebraic inequalities over scale-limited activating sets, we achieve results regarding multiperiodicity of TLNs. This will show that each scale-limited activating set depends on scale-synchronous self-excitation, and the existence of inactive neurons will slow down convergence of TLNs. At the end of the paper, we perform computer simulations to illustrate the obtained new theories. PMID:23757562

Huang, Zhenkun; Raffoul, Youssef N; Cheng, Chang-Yuan

2013-05-03

350

Evidences of a Common Scaling Under Cooling and Compression for Slow and Fast Relaxations: Relevance of Local Modes for the Glass Transition  

NASA Astrophysics Data System (ADS)

The present study demonstrates, by means of broadband dielectric measurements, that the primary ?- and the secondary Johari-Goldstein (JG) ?-processes are strongly correlated, in contrast with the widespread opinion of statistical independence of these processes. This occurs for different glass-forming systems, over a wide temperature and pressure range. In fact, we found that the ratio of the ?- and ?- relaxation times is invariant when calculated at different combinations of P and T that maintain either the primary or the JG relaxation times constant. The ?-? interdependence is quantitatively confirmed by the clear dynamic scenario of two master curves (one for ?-, one for ?-relaxation) obtained when different isothermal and isobaric data are plotted together versus the reduced variable T g (P)/T, where T g is the glass transition temperature. Additionally, the ?-? mutual dependence is confirmed by the overall superposition of spectra measured at different T-P combinations but with an invariant ?-relaxation time.

Capaccioli, S.; Kessairi, K.; Prevosto, D.; Thayyil, Md. Shahin; Lucchesi, M.; Rolla, P. A.

351

Mechanism of Void Nucleation and Growth in bcc Fe: Atomistic Simulations at Experimental Time Scales  

SciTech Connect

Evolution of small-vacancy clusters in bcc Fe is simulated using a multiscale approach coupling an atomistic activation-relaxation method for sampling transition-state pathways with environment-dependent reaction coordinate calculations and a kinetic Monte Carlo simulation to reach time scales on the order of {approx}10{sup 4} s. Under vacancy-supersaturated condition, di- and trivacancy clusters form and grow by coalescence (Ostwald ripening). For cluster size greater than four we find a transition temperature of 150 deg. C for accelerated cluster growth, as observed in positron annihilation spectroscopy experiments. Implications for the mechanism of stage-IV radiation-damage-recovery kinetics are discussed.

Fan Yue; Kushima, Akihiro; Yip, Sidney; Yildiz, Bilge [Department of Nuclear Science and Engineering, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts, 02139 (United States)

2011-03-25

352

General entanglement scaling laws from time evolution.  

PubMed

We establish a general scaling law for the entanglement of a large class of ground states and dynamically evolving states of quantum spin chains: we show that the geometric entropy of a distinguished block saturates, and hence follows an entanglement-boundary law. These results apply to any ground state of a gapped model resulting from dynamics generated by a local Hamiltonian, as well as, dually, to states that are generated via a sudden quench of an interaction as recently studied in the case of dynamics of quantum phase transitions. We achieve these results by exploiting ideas from quantum information theory and tools provided by Lieb-Robinson bounds. We also show that there exist noncritical fermionic systems and equivalent spin chains with rapidly decaying interactions violating this entanglement-boundary law. Implications for the classical simulatability are outlined. PMID:17155303

Eisert, Jens; Osborne, Tobias J

2006-10-12

353

Relationship between knee kinetics during jumping tasks and knee articular cartilage MRI T1rho and T2 relaxation times  

PubMed Central

Background Articular cartilage of young healthy individuals is dynamic and responsive to loading behaviors. The purpose of this study was to evaluate the relationship of cartilage T1? and T2 relaxation times with loading kinetics during jumping tasks in healthy young individuals. Methods Fourteen healthy subjects underwent: 1) motion analysis while performing a unilateral hopping task and bilateral drop jumping task; and 2) quantitative imaging using a 3 Tesla MRI for T1? and T2 relaxation time analysis. Three dimensional net joint moments and angular impulse was calculated using standard inverse dynamics equations. Average T1? and T2 relaxation times and medial-lateral ratios for each were calculated. Multiple regression was used to identify predictors of cartilage relaxation times. Findings Average knee flexion moment during hopping was observed to best predict overall T1? (R2=.185) and T2 (R2=.154) values. Peak knee adduction moment during a drop jump was the best predictor of the T1? medial-lateral ratio (R2=.220). The T2 medial-lateral ratio was best predicted by average internal rotation moment during the drop jump (R2=.174). Interpretation These data suggest that loads across the knee may affect the biochemistry of the cartilage. In young healthy individuals, higher flexion moments were associated with decreased T1? and T2 values, suggesting a potentially beneficial effect. The medial-to-lateral ratio of T1? and T2 times appears to be related to the frontal and transverse plane joint mechanics. These data offer promising findings of potentially modifiable parameters associated with cartilage composition.

Souza, Richard B.; Fang, Charles; Luke, Anthony; Wu, Samuel; Li, Xiaojuan; Majumdar, Sharmila

2012-01-01

354

Time and scale evolutionary EVD and detection  

Microsoft Academic Search

Optimal detection of a known signal in nonstationary noise requires tracking the eigenvalue decomposition (EVD) of the noise data over time. To take advantage of information in the long-term, as well as short-term, correlation lags we turn to EVD over wavelet subspaces. We develop a multirate EVD updating method over multiresolution subspaces and find maximum detectability nodes on wavelet binary

Nurgun Erdol; Spyros Kyperountas; Branko Petljanski

2001-01-01

355

Measurement of the subnanosecond, nonradiative relaxation time from excited states of Nd sup 3+ in a Nd:YAG crystal  

SciTech Connect

We have time resolved the nonradiative relaxation from the {sup 4}{ital G}{sub 7/2} manifold to the upper laser level (for {Sigma}=1.06 {mu}m) of Nd{sup 3+} in a Nd:YAG crystal. This has been performed by monitoring the onset of gain for the associated {sup 4}{ital F}{sub 3/2}--{sup 4}{ital I}{sub 11/2} transition following excitation of the {sup 4}{ital G}{sub 7/2} pump band by a 40-psec, 0.53-{mu}m pump pulse. The nonradiative relaxation time was found to be 470{plus minus}60 psec at room temperature and no shorter than 400 psec at 440 K.

Cruz, J.; Giuliani, G.; van Driel, H. (Department of Physics, University of Toronto, Toronto, Ontario M5S 1A7, Canada (CA))

1990-03-01

356

Relaxation times of nanoscale deformations on the surface of a polymer thin film near and below the glass transition  

SciTech Connect

We report on measurements of relaxation times of nanometer-sized deformations resulting from the impact of individual energetic ions on poly(methyl methacrylate) surfaces at temperatures close to and below the glass transition T{sub g}. The temporal evolution of the dimensions of the deformations is well described by a stretched exponential function, but with relaxation times {tau}(T) many orders of magnitude smaller than bulk values at the same T. The local T{sub g} was around 86 deg. C, roughly 30 deg. C below the conventional bulk T{sub g}. At the vicinity of the local T{sub g}, {tau}(T) follows the Vogel-Fulcher type of T dependence, but at lower T a transition towards a less steep behavior is seen.

Papaleo, R. M.; Leal, R.; Carreira, W. H.; Barbosa, L. G.; Bello, I.; Bulla, A. [Faculty of Physics, Catholic University of Rio Grande do Sul, Av. Ipiranga 6681, Caixa Postal 1429, 90619-900 Porto Alegre (Brazil); Institute of Physics, Federal University of Rio Grande do Sul, Av. Bento Goncalves 9500, Porto Alegre (Brazil)

2006-09-01

357

The effect of guided relaxation and exercise imagery on self-reported leisure-time exercise behaviors in older adults.  

PubMed

The purpose of this study was to examine the effects of a 6-wk intervention that used guided relaxation and exercise imagery (GREI) to increase self-reported leisure-time exercise behavior among older adults. A total of 93 community-dwelling healthy older adults (age 70.38 ± 8.15 yr, 66 female) were randomly placed in either a placebo control group or an intervention group. The intervention group received instructions to listen to an audio compact disk (CD) containing a GREI program, and the placebo control group received an audio CD that contained 2 relaxation tracks and instructions to listen to music of their choice for 6 wk. Results revealed that listening to a GREI CD for 6 wk significantly increased self-reported leisure-time exercise behaviors (p = .03). Further exploration of GREI and its effects on other psychological variables related to perceived exercise behaviors may substantiate its effectiveness. PMID:21558568

Kim, Bang Hyun; Newton, Roberta A; Sachs, Michael L; Giacobbi, Peter R; Glutting, Joseph J

2011-04-01

358

Space-time correlated two-particle hopping in glassy fluids: Structural relaxation, irreversibility, decoupling, and facilitation  

NASA Astrophysics Data System (ADS)

The microscopic nonlinear Langevin equation (NLE) theory of correlated two-particle dynamics in dense fluids of spherical particles is extended to construct a predictive model of multiple correlated hopping and recaging events of a pair of tagged particles as a function of their initial separation. Modest coarse graining over the liquid structural disorder allows contact to be made with various definitions of irreversible particle motion within the context of a multistate Markov model. The correlated space-time hopping process that underlies structural relaxation can also be analyzed in the context of kinetically constrained models. The dependence of microscopically defined mean persistence and exchange times, their distributions, and relaxation-diffusion decoupling on hard-sphere fluid volume fraction is derived from a model in which irreversible jumps serve as the nucleating persistence event. For a subset of questions, the predictions of the two-particle theory are compared with results from the earlier single-particle NLE approach.

Sussman, Daniel M.; Schweizer, Kenneth S.

2012-06-01

359

Effects of long and short relaxation times of particle interactions in dense and slow granular flows  

SciTech Connect

In this work, dense granular flows are numerically simulated using a discrete element method. The interaction of a pair of colliding particles is modeled as a parallel connection of a linear spring and a linear dashpot. Although the force model for particle interactions is simplistic for many practical problems, a significant amount of meaningful new physics can be extracted from the numerical simulations by studying the behavior of particle interaction time and its probability distribution. For instance, it is found that the probability distribution of particle contact ages is exponential for long-term contacts. The time scale of the exponential decay of the contact age probability is related to the rheological properties of the dense granular medium.

Zhang, D. Z. (Duan Z.); Rauenzahn, Rick M.

2002-01-01

360

Numerical solution of time-dependent nonlinear Schrödinger equations using domain truncation techniques coupled with relaxation scheme  

NASA Astrophysics Data System (ADS)

The aim of this paper is to compare different ways for truncating unbounded domains for solving general nonlinear one- and two-dimensional Schrödinger equations. We propose to analyze Complex Absorbing Potentials, Perfectly Matched Layers and Absorbing Boundary Conditions. The time discretization is made by using a semi-implicit relaxation scheme which avoids any fixed point procedure. The spatial discretization involves finite element methods. We propose some numerical experiments to compare the approaches.

Antoine, X.; Besse, C.; Klein, P.

2011-08-01

361

S-adenosyl-l-methionine: effects on brain bioenergetic status and transverse relaxation time in healthy subjects  

Microsoft Academic Search

BackgroundS-adenosyl-L-methionine is an effective treatment for clinical depression, although the mechanism underlying this effect is unclear. Presently, in vivo phosphorus 31 magnetic resonance spectroscopy and brain transverse relaxometry were employed to test if S-adenosyl-L-methionine supplementation alters brain bioenergetics and\\/or transverse relaxation time in a nondepressed cohort. If these magnetic resonance techniques are sensitive to S-adenosyl-L-methionine induced alterations in neurochemical processes,

Marisa M. Silveri; Aimee M. Parow; Rosemond A. Villafuerte; Karen E. Damico; Jessica Goren; Andrew L. Stoll; Bruce M. Cohen; Perry F. Renshaw

2003-01-01

362

Age-Related Loss of Brain Volume and T2 Relaxation Time in Youth With Type 1 Diabetes  

PubMed Central

OBJECTIVE—2 Childhood-onset type 1 diabetes is associated with neurocognitive deficits, but there is limited evidence to date regarding associated neuroanatomical brain changes and their relationship to illness variables such as age at disease onset. This report examines age-related changes in volume and T2 relaxation time (a fundamental parameter of magnetic resonance imaging that reflects tissue health) across the whole brain. RESEARCH DESIGN AND METHODS— Type 1 diabetes, N = 79 (mean age 20.32 ± 4.24 years), and healthy control participants, N = 50 (mean age 20.53 ± 3.60 years). There were no substantial group differences on socioeconomic status, sex ratio, or intelligence quotient. RESULTS— Regression analyses revealed a negative correlation between age and brain changes, with decreasing gray matter volume and T2 relaxation time with age in multiple brain regions in the type 1 diabetes group. In comparison, the age-related decline in the control group was small. Examination of the interaction of group and age confirmed a group difference (type 1 diabetes vs. control) in the relationship between age and brain volume/T2 relaxation time. CONCLUSIONS— We demonstrated an interaction between age and group in predicting brain volumes and T2 relaxation time such that there was a decline in these outcomes in type 1 diabetic participants that was much less evident in control subjects. Findings suggest the neurodevelopmental pathways of youth with type 1 diabetes have diverged from those of their healthy peers by late adolescence and early adulthood but the explanation for this phenomenon remains to be clarified.

Pell, Gaby S.; Lin, Ashleigh; Wellard, R. Mark; Werther, George A.; Cameron, Fergus J.; Finch, Sue J.; Papoutsis, Jennifer; Northam, Elisabeth A.

2012-01-01

363

Effect of a spectrum of relaxation times on the capillary thinning of a filament of elastic liquid  

Microsoft Academic Search

The capillary thinning of a filament of viscoelastic liquid, which is the basis of a microrheometer, is analyzed in terms of a multi-mode FENE fluid. After a short time of viscous adjustment, the stress becomes dominated by the elastic contribution and the strain-rate takes on a value equal to two-thirds the rate at which the stress would relax at fixed

V. M. Entov; E. J. Hinch

1997-01-01

364

The free volume interpretation of the dependence of viscosities and viscoelastic relaxation times on concentration, pressure, and tensile strain  

Microsoft Academic Search

Summary  The free volume interpretation of the dependence of relaxation times and viscosities on temperature can be extended to their\\u000a dependence on concentration, pressure, and tensile strain. The coefficient which in theWilliams\\/Landel\\/Ferry equation represents the thermal expansion of the relative free volume has the following analogs, respectively: for concentration\\u000a dependence, a constant closely related to the fractional free volume of the

John D. Ferry; Robert A. Stratton

1960-01-01

365

Optimal Stability of Advection-Diffusion Lattice Boltzmann Models with Two Relaxation Times for Positive\\/Negative Equilibrium  

Microsoft Academic Search

Despite the growing popularity of Lattice Boltzmann schemes for describing multi-dimensional flow and transport governed by\\u000a non-linear (anisotropic) advection-diffusion equations, there are very few analytical results on their stability, even for\\u000a the isotropic linear equation. In this paper, the optimal two-relaxation-time (OTRT) model is defined, along with necessary and sufficient (easy to use) von Neumann stability conditions for a very

Irina Ginzburg; Dominique d’Humières; Alexander Kuzmin

2010-01-01

366

Relaxation times and line widths of isotopically-substituted nitroxides in aqueous solution at X-band  

Microsoft Academic Search

Optimization of nitroxides as probes for EPR imaging requires detailed understanding of spectral properties. Spin lattice relaxation times, spin packet line widths, nuclear hyperfine splitting, and overall lineshapes were characterized for six low molecular weight nitroxides in dilute deoxygenated aqueous solution at X-band. The nitroxides included 6-member, unsaturated 5-member, or saturated 5-member rings, most of which were isotopically labeled. The

Joshua R. Biller; Virginia Meyer; Hanan Elajaili; Gerald M. Rosen; Joseph P. Y. Kao; Sandra S. Eaton; Gareth R. Eaton

2011-01-01

367

Li chemisorption on Ru(001): LDA theory of the coverage dependence of the spin lattice relaxation time  

Microsoft Academic Search

The chemisorption of alkali atoms on metals still remains a challenging topic after almost sixty years of study. Recently, a novel type of experiment, beta-decay NMR, was developed and applied to investigate Li atoms chemisorbed on a Ru(001) surface( H. J. Jänsch et al., Phys.Rev.Lett. 25, 120 (1995)). Such measurements of the spin lattice relaxation time provide information about the

W. Mannstadt; A. J. Freeman

1997-01-01

368

High-frequency dielectric relaxation of liquid crystals: THz time-domain spectroscopy of liquid crystal colloids  

Microsoft Academic Search

Terahertz time-domain spectroscopy has been used to study the dielectric relaxation of pure 4' n-pentyl 4 cyanobiphenyl (5CB) liquid crystal (LC) and its mixtures with 10 mum SiO2 particles in the frequency range 0.2 2 THz. For the pure sample, we find that spatial inhomogeneities consisting of oriented domains, comparable in size to our probe area (~1 mm2), cause a

Masahito Oh-E; Hiroshi Yokoyama; Mattijs Koeberg; Euan Hendry; Mischa Bonn

2006-01-01

369

Shortening of hippocampal spin-spin relaxation time in probable Alzheimer's disease: a 1H magnetic resonance spectroscopy study  

Microsoft Academic Search

We quantified the differential effects of the spin-spin relaxation times (T2) of tissue water and cerebral spinal fluid in order to examine hippocampal T2 changes as a non-invasive bio-marker of Alzheimer's disease (AD). We measured T2 in the right hippocampus of ten patients fulfilling the NINCDS-ADRDA criteria for AD and 40 healthy adult volunteers using localized proton magnetic resonance spectroscopy.

Andreana P. Haley; Jack Knight-Scott; Kathleen L. Fuchs; Virginia I. Simnad; Carol A. Manning

2004-01-01

370

Measurement of electron spin-lattice relaxation times in radical doped butanol samples at 1 K using the NEDOR method  

NASA Astrophysics Data System (ADS)

The electron spin-lattice relaxation time (T1e) of TEMPO- and trityl-doped butanol samples at 2.5 T and temperatures between 0.95 K and 2.17 K was studied by pulsed nuclear magnetic resonance (NMR) using the nuclear-electron double resonance (NEDOR) method. This method is based on the idea to measure the NMR lineshift produced by the local field of paramagnetic impurities, whose polarization can be manipulated. This is of technical advantage as measurements can be performed under conditions typically used for the dynamic nuclear polarization (DNP) process - in our case 2.5 T and temperatures around 1 K - where a direct measurement on the electronic spins would be far more complicated to perform.As T1e is a crucial parameter determining the overall efficiency of DNP, the effect of the radical type, its spin concentration, the temperature and the oxygen content on T1e has been investigated.For radical concentrations as used in DNP (several 1019 spins/cm3) the relaxation rate (T1e-1) has shown a linear dependence on the paramagnetic electron concentration for both radicals investigated. Experiments with perdeuterated and ordinary butanol have given no indication for any influence of the host materials isotopes. The measured temperature dependence has shown an exponential characteristic. It is further observed that the oxygen content in the butanol samples has a considerable effect on the electron relaxation time and thus influences the nuclear relaxation time and polarization rate during the DNP.The experiments also show a variation in the NMR linewidth, leading to comparable time constants as determined by the lineshift. NEDOR measurements were also performed on irradiated, crystal grains of 6LiD. These samples exhibited a linewidth behavior similar to that of the cylindrically shaped butanol samples.

Hess, C.; Herick, J.; Berlin, A.; Meyer, W.; Reicherz, G.

2012-12-01

371

Effect of Compression on the Relationship between Viscosity and Dielectric Relaxation Time in Hydrogen-Bonded Primary Alcohols  

NASA Astrophysics Data System (ADS)

High pressure viscosity and dielectric measurements were carried out on two monohydroxy alcohols, 2-ethyl-1-hexanol and 5-methyl-2-hexanol, at room temperature. Analysis of the dielectric relaxation times versus viscosity revealed the breakdown of the Einstein-Debye relation above some characteristic pressure. The failure of the Einstein-Debye relation is a manifestation of pressure induced changes of supramolecular hydrogen bonded structures which occur in these liquids.

Pawlus, S.; Klotz, S.; Paluch, M.

2013-04-01

372

Value of T1 and T2 relaxation times from echoplanar MR imaging in the characterization of focal hepatic lesions  

Microsoft Academic Search

OBJECTIVE. The purpose of this study was to determine the value of echoplanar imaging in characterizing focal hepatic lesions on the basis of image-derived T1 and T2 relaxation times. SUBJECTS AND METHODS. Forty-six proven hepatic lesions were analyzed: 24 solid (21 metastases, three primary liver tumors) and 22 nonsolid (11 hemangiomas and 11 cysts). Mean lesion size (maximal length) was

MA Goldberg; PF Hahn; S Saini; M. S. Cohen; P Reimer; TJ Brady; PR Mueller

1993-01-01

373

The temperature and polymerization effects on the relaxation time and conductivity, and the evolution of the localized motions  

Microsoft Academic Search

To examine the manner in which molecular dynamics of a polymerizing liquid (stoichiometric amounts of 4,4'-diaminodicyclohexylamine and diglycidyl ether of bisphenol-A) evolves during thermal cycling from its (molecular) vitreous state to its fully polymerized vitreous state, calorimetry, and dielectric spectrometry were performed simultaneously in real time. The half-width of the relaxation spectrum of the liquid was relatively narrow and became

E. Tombari; G. Salvetti; G. P. Johari

2000-01-01

374

Characterization of dynamics in complex lyophilized formulations: I. Comparison of relaxation times measured by isothermal calorimetry with data estimated from the width of the glass transition temperature region.  

PubMed

The purposes of this study are to characterize the relaxation dynamics in complex freeze dried formulations and to investigate the quantitative relationship between the structural relaxation time as measured by thermal activity monitor (TAM) and that estimated from the width of the glass transition temperature (?Tg). The latter method has advantages over TAM because it is simple and quick. As part of this objective, we evaluate the accuracy in estimating relaxation time data at higher temperatures (50°C and 60°C) from TAM data at lower temperature (40°C) and glass transition region width (?Tg) data obtained by differential scanning calorimetry. Formulations studied here were hydroxyethyl starch (HES)-disaccharide, HES-polyol, and HES-disaccharide-polyol at various ratios. We also re-examine, using TAM derived relaxation times, the correlation between protein stability (human growth hormone, hGH) and relaxation times explored in a previous report, which employed relaxation time data obtained from ?Tg. Results show that most of the freeze dried formulations exist in single amorphous phase, and structural relaxation times were successfully measured for these systems. We find a reasonably good correlation between TAM measured relaxation times and corresponding data obtained from estimates based on ?Tg, but the agreement is only qualitative. The comparison plot showed that TAM data are directly proportional to the 1/3 power of ?Tg data, after correcting for an offset. Nevertheless, the correlation between hGH stability and relaxation time remained qualitatively the same as found with using ?Tg derived relaxation data, and it was found that the modest extrapolation of TAM data to higher temperatures using ?Tg method and TAM data at 40°C resulted in quantitative agreement with TAM measurements made at 50°C and 60°C, provided the TAM experiment temperature, is well below the Tg of the sample. PMID:23608636

Chieng, Norman; Mizuno, Masayasu; Pikal, Michael

2013-04-20

375

Image Denoising Using Similarities in the TimeScale Plane  

Microsoft Academic Search

This paper presents a de-noising method that recognizes similarities in the image through the time scale behaviour of wavelet\\u000a coefficients. Wavelet details are represented as linear combination of predefined atoms whose center of mass traces trajectories\\u000a in the time scale plane (from fine to coarse scale). These trajectories are the solution of a proper ordinary differential\\u000a equation and characterize atoms

Vittoria Bruni; Domenico Vitulano

2008-01-01

376

Preliminary evaluation of time scales based on hydrogen masers  

Microsoft Academic Search

Two experimental time scales based on ensembles of hydrogen masers were generated and compared with a variety of other references both internal and external to NIST. The masers all had some type of active cavity control to reduce frequency drift due to cavity changes, The first experimental time scale, TA2M, was generated over the interval from MJD 49050 to 49190

Marc A. Weiss; Fred L. Walls

1996-01-01

377

SiGe:C HBT transit time analysis based on hydrodynamic modeling using doping, composition and strained dependent SiGe:C carriers mobility and relaxation time  

Microsoft Academic Search

We present an original method for the detailed evaluation of different device region contributions to the whole SiGe:C heterojunction bipolar transistor transit time in the frame of modeling studies. This method is based on AC analysis with structures of several base widths. The two-dimensional hydrodynamic solver relies on analytical models of electron and hole mobilities, and of energy relaxation times,

E. Ramirez-Garcia; M. Michaillat; F. Aniel; N. Zerounian; M. Enciso-Aguilar; D. Rideau

2011-01-01

378

Investigation of doped calcium aluminosilicate glass: A coupling between thermal-expansion and thermal-diffusion models for assessment of nonradiative relaxation time and characteristic diffusion time  

Microsoft Academic Search

This paper discusses the use of photoacoustic models to obtain the nonradiative relaxation time (?) and characteristic diffusion time (??) for a sample showing visible absorption bands from fluorescent ion-doped low-silica calcium aluminosilicate glass. Two models allowing phase shift analyses, the thermal-expansion and thermal-diffusion models, are briefly reviewed. These models have limitations when the photoacoustic signal depends on both factors,

N. E. Souza Filho; A. C. Nogueira; J. H. Rohling; M. L. Baesso; A. N. Medina; A. P. L. Siqueira; J. A. Sampaio; H. Vargas; A. C. Bento

2009-01-01

379

Investigation of doped calcium aluminosilicate glass: A coupling between thermal-expansion and thermal-diffusion models for assessment of nonradiative relaxation time and characteristic diffusion time  

Microsoft Academic Search

This paper discusses the use of photoacoustic models to obtain the nonradiative relaxation time (tau) and characteristic diffusion time (taubeta) for a sample showing visible absorption bands from fluorescent ion-doped low-silica calcium aluminosilicate glass. Two models allowing phase shift analyses, the thermal-expansion and thermal-diffusion models, are briefly reviewed. These models have limitations when the photoacoustic signal depends on both factors,

N. E. Souza Filho; A. C. Nogueira; J. H. Rohling; M. L. Baesso; A. N. Medina; A. P. L. Siqueira; J. A. Sampaio; H. Vargas; A. C. Bento

2009-01-01

380

Scaling the Martian Walls of Time  

NASA Astrophysics Data System (ADS)

On Earth, when scientists want to investigate planetary history they take a core sample, with deeper fragments corresponding to older materials. In essence, descending through sedimentary layers is like going back in time. But creating a robot capable of taking samples more than a few meters below the planetary surface is still beyond the current available technology. The cliffhanger idea takes advantage of the natural surface features of Mars to explore the history of the planet without digging. So interesting and difficult questions can be answered not with the brute force of a drill, but with creative mission design. Penn State University HEDS-UP team has designed a novel Mars mission approach. A main Lander with a Rover and a Cliffhanger will land near cliffs of Valles Mariners. Especially design cannon (gas, guided munitions or rocket) will deploy a long rope into the canyon. The rover will carry the cliffhanger to the edge of Valles Marineris following the rope, attach the cliffhanger to the rope. The Cliffhanger will then climb a 2 km down the rope and will allow the team to study sedimentary layers of rock on the side of the cliff. Samples and high-resolution images will be taken and delivered to the Lander for further investigation (optical multispectral imaging microscope, spectrometry) and sending the results to Earth. The robot has been designed to have the capability for locomotion at any angle (including somewhat uphill slopes) but maximum effective After the mission of rope-climbing is completed, the Rover am Lander will embark on another long-term mission to provide meteorological and geological data over a long period of time (long-term Mars Observatory), and perform acoustic and seismic experiments on the surface of Mars in preparation for human arrival.

Thornton, Nikki; Yagloski, Joseph; Fledderman, Joe; OMarr, Gregg; Weber, Ben; Carlins, Chris; Krishna, Shubh; Sloan, Kevin; Merriman, Taite; Borowski, David

2000-01-01

381

Time scales of tunneling decay of a localized state  

SciTech Connect

Motivated by recent time-domain experiments on ultrafast atom ionization, we analyze the transients and time scales that characterize, aside from the relatively long lifetime, the decay of a localized state by tunneling. While the tunneling starts immediately, some time is required for the outgoing flux to develop. This short-term behavior depends strongly on the initial state. For the initial state, tightly localized so that the initial transients are dominated by over-the-barrier motion, the time scale for flux propagation through the barrier is close to the Buettiker-Landauer traversal time. Then a quasistationary, slow-decay process follows, which sets ideal conditions for observing diffraction in time at longer times and distances. To define operationally a tunneling time at the barrier edge, we extrapolate backward the propagation of the wave packet that escaped from the potential. This extrapolated time is considerably longer than the time scale of the flux and density buildup at the barrier edge.

Ban, Yue; Muga, J. G. [Department of Physical Chemistry, Universidad del Pais Vasco UPV-EHU, E-48080 Bilbao (Spain); Sherman, E. Ya. [Department of Physical Chemistry, Universidad del Pais Vasco UPV-EHU, E-48080 Bilbao (Spain); IKERBASQUE, Basque Foundation for Science, E-48011 Bilbao (Spain); Buettiker, M. [Departement de Physique Theorique, Universite de Geneve, CH-1211 Geneve 4 (Switzerland)

2010-12-15

382

Extended frequency range measurements for determining the Kneser-type acoustic relaxation time.  

PubMed

In the present paper, the authors discuss studies carried out for many years dealing particularly with two compounds: benzene and carbon disulphide and compare them with the results obtained by numerous acoustics researchers. These compounds are typical liquids in which acoustic Kneser-type relaxation occurs, caused by an irreversible vibrational and translational (VT) transition. Since magnitudes describing the relaxation process were diverse in many papers, we have undertaken an attempt to clarify these differences and to indicate how to avoid errors resulting from instrumental imperfections and the disregard of the considerable measurement errors when investigating velocity dispersion in the hypersonic (GHz) range. The results of these researches changed the interpretation of previous papers. PMID:11106005

Linde, B B; Lezhnev, N B

2000-11-01

383

Effect of an applied magnetic field on the relaxation time of single-chain magnets  

Microsoft Academic Search

Single-chain magnets (SCMs) are one-dimensional systems in which the relaxation of the magnetization becomes very slow at low temperature. This singular behavior is due to the vicinity of the critical point located at vanishing temperature (T=0) and applied magnetic field (H=0) . In order to optimize the properties of these nano-objects, detailed studies of the observed critical behavior are necessary.

Claude Coulon; Rodolphe Clérac; Wolfgang Wernsdorfer; Thierry Colin; Ayumi Saitoh; Natsuko Motokawa; Hitoshi Miyasaka

2007-01-01

384

Time Scales for Achieving Astronomical Consensus  

NASA Astrophysics Data System (ADS)

The history of science can be recounted in many ways: by addressing the work of one person or school; by starting with the ancients and working chronologically up to the present; by focusing on a particular century; or by tracing a particular important idea as far back and forward as it can be found. The present discussion does none of these. Rather, it adopts the ordering of a standard introductory astronomy textbook, from the solar system via stars and galaxies, to the universe as a whole, and in each regime picks out a few issues that were controversial or wrongly decided for a long time. For each, I attempt to identify a duration of the period of uncertainty or error and some of the causes of the confusion. This is surely not an original idea, though I am not aware of having encountered it elsewhere, and it is not one that is likely to appeal to most 21st century historians of science, for whom the question "Who first got it right?" is not necessarily an important, or even appropriate, one. Some of the stories have been told as historical introductions to conferences and are here summarized and brought up to date. Others I had not previously addressed.

Trimble, Virginia

385

Relaxation dynamics in a Fe7 nanomagnet  

NASA Astrophysics Data System (ADS)

We investigate the phonon-induced relaxation dynamics in the Fe7 magnetic molecule, which is made of two Fe3+ triangles bridged together by a central Fe3+ ion. The competition between different antiferromagnetic exchange interactions leads to a low-spin ground state multiplet with a complex pattern of low-lying excited levels. We theoretically investigate the decay of the time correlation function of molecular observables, such as the cluster magnetization, due to the spin-phonon interaction. We find that more than one time contributes to the decay of the molecular magnetization. The relaxation dynamics is probed by measurements of the nuclear spin-lattice relaxation rate 1/T1. The interpretation of these measurements allows the determination of the magnetoelastic coupling strength and to set the scale factor of the relaxation dynamics time scales. In our theoretical interpretation of 1/T1 data we also take into account the wipeout effect at low temperatures.

Garlatti, E.; Carretta, S.; Santini, P.; Amoretti, G.; Mariani, M.; Lascialfari, A.; Sanna, S.; Mason, K.; Chang, J.; Tasker, P.; Brechin, E. K.

2013-02-01

386

Thermal Time Scales in a Color Glass Condensate  

NASA Astrophysics Data System (ADS)

In a model of relativistic heavy ion collisions wherein the unconfined quark-gluon plasma is condensed into glass, we derive the Vogel-Fulcher-Tammann cooling law. This law is well known to hold true in condensed matter glasses. The high energy plasma is initially created in a very hot negative temperature state and cools down to the Hagedorn glass temperature at an ever decreasing rate. The cooling rate is largely determined by the QCD string tension derived from hadronic Regge trajectories. The ultimately slow relaxation time is characteristic of a color glass condensate.

Parihar, Vivek; Widom, Allan; Srivastava, Yogi

2006-04-01

387

Thermal time scales in a color glass condensate  

NASA Astrophysics Data System (ADS)

In a model of relativistic heavy-ion collisions wherein the unconfined quark-gluon plasma is condensed into glass, we derive the Vogel-Fulcher-Tammann cooling law. This law is well known to hold true in condensed matter glasses. The high-energy plasma is initially created in a very hot negative temperature state and cools down to the Hagedorn glass temperature at an ever decreasing rate. The cooling rate is largely determined by the QCD string tension derived from hadronic Regge trajectories. The ultimately slow relaxation time is a defining characteristic of a color glass condensate.

Parihar, V.; Widom, A.; Srivastava, Y. N.

2006-01-01

388

In vivo relaxation time measurements on a murine tumor model--prolongation of T1 after photodynamic therapy.  

PubMed

RIF tumors implanted on mice feet were investigated for changes in relaxation times (T1 and T2) after photodynamic therapy (PDT). Photodynamic therapy was performed using Photofrin II as the photosensitizer and laser light at 630 nm. A home-built proton solenoid coil in the balanced configuration was used to accommodate the tumors, and the relaxation times were measured before, immediately after, and up to several hours after therapy. Several control experiments were performed untreated tumors, tumors treated with Photofrin II alone, or tumors treated with laser light alone. Significant increases in T1s of water protons were observed after PDT treatment. In all experiments, 31P spectra were recorded before and after the therapy to study the tumor status and to confirm the onset of PDT. These studies show significant prolongation of T1s after the PDT treatment. The spin-spin relaxation measurements, on the other hand, did not show such prolongation in T2 values after PDT treatment. PMID:7739367

Liu, Y H; Hawk, R M; Ramaprasad, S

1995-01-01

389

Pump-and-probe measurements of the nuclear spin relaxation time in a two-subband electron system  

NASA Astrophysics Data System (ADS)

Nuclear spin relaxation measurements are emerging as an effective tool to study the low-frequency spin dynamics of two-dimensional electrons in quantum Hall systems. We present such a measurement in a two-dimensional electron system consisting of two filled subbands. A recently developed pump-and-probe technique [1] was used to obtain the nuclear spin relaxation time in a region where the two sets of Landau levels, corresponding to the two subbands, were nearly degenerate. The pump-and-probe technique allowed us to measure the relaxation time over a much broader range of magnetic fields and electron densities than that in an earlier nuclear magnetic resonance study [2]. An array of interesting observations will be reported,including phase space and temperature dependence study. The project is supported by the NSF under Grant No. DMR-0804794. [4pt] [1] N. Kumada, K. Muraki, and Y. Hirayama, Science 313, 329 (2006). [0pt] [2] X. C. Zhang, G. D. Scott and H. W. Jiang, Phys. Rev. Lett. 98,246802 (2007).

Pan, Hong; Jiang, Hongwen

2010-03-01

390

Causality across rainfall time scales revealed by continuous wavelet transforms  

NASA Astrophysics Data System (ADS)

Rainfall variability occurs over a wide range of time scales owing to processes initiated by cloud microphysics and sustained by atmospheric circulation. A central topic in rainfall research is to determine whether rainfall variability at a given scale is caused by dynamics acting at some other scales. Random multiplicative cascades (RMCs) are standard approaches for describing rainfall variability across such a wide range of time scales. Their popularity stems from their ability to reproduce rainfall self-similarity and long-range correlations as well as intermittency buildup at finer scales. However, standard RMCs only predict instantaneous flow of variance (energy or activity) from large to fine scales and cannot account for scale-wise causal relationships. Such relationships reveal themselves through noninstantaneous cascade mechanisms, namely, large-scale events influencing finer-scale events at later times (i.e., forward causal cascade) or conversely (inverse causal cascade). The presence of causal cascade signatures within the rainfall process is explored here using both continuous wavelet decomposition (CWT) and scale-by-scale causality measures such as cross-scale correlation and linearized transfer entropy. The causality hypothesis is further tested against results from toy models, surrogate data, and a scalar turbulence time series (water vapor) to ensure that rainfall causality is not an artifact of the estimation method or resulting from the redundancy in CWT. The analysis demonstrates the presence of causal cascades (mainly forward) in rainfall series when sampled at fine temporal resolutions (seconds). These causal relationships tend to vanish when rainfall is aggregated at coarser time scales (hours and longer).

Molini, Annalisa; Katul, Gabriel G.; Porporato, Amilcare

2010-07-01

391

Time-resolved infrared absorption studies of the solvent-dependent vibrational relaxation dynamics of chlorine dioxide  

NASA Astrophysics Data System (ADS)

We report a series of time-resolved infrared absorption studies on chlorine dioxide (OClO) dissolved in H2O, D2O, and acetonitrile. Following the photoexcitation at 401 nm, the evolution in optical density for frequencies corresponding to asymmetric stretch of OClO is measured with a time resolution of 120+/-50 fs. The experimentally determined optical-density evolution is compared with theoretical models of OClO vibrational relaxation derived from collisional models as well as classical molecular-dynamics (MD) studies. The vibrational relaxation rates in D2O are reduced by a factor of 3 relative to H2O consistent with the predictions of MD. This difference reflects modification of the frequency-dependent solvent-solute coupling accompanying isotopic substitution of the solvent. Also, the geminate-recombination quantum yield for the primary photofragments resulting in the reformation of ground-state OClO is reduced in D2O relative to H2O. It is proposed that this reduction reflects enhancement of the dissociation rate accompanying vibrational excitation along the asymmetric-stretch coordinate. In contrast to H2O and D2O, the vibrational-relaxation dynamics in acetonitrile are not well described by the theoretical models. Reproduction of the optical-density evolution in acetonitrile requires significant modification of the frequency-dependent solvent-solute coupling derived from MD. It is proposed that this modification reflects vibrational-energy transfer from the asymmetric stretch of OClO to the methyl rock of acetonitrile. In total, the results presented here provide a detailed description of the solvent-dependent geminate-recombination and vibrational-relaxation dynamics of OClO in solution.

Bolinger, Joshua C.; Bixby, Teresa J.; Reid, Philip J.

2005-08-01

392

Effects of Off-Resonance Irradiation, Cross-Relaxation, and Chemical Exchange on Steady-State Magnetization and Effective Spin-Lattice Relaxation Times  

NASA Astrophysics Data System (ADS)

In the presence of an off-resonance radiofrequency field, recovery of longitudinal magnetization to a steady state is not purely monoexponential. Under reasonable conditions with zero initial magnetization, recovery is nearly exponential and an effective relaxation rate constant R1eff = 1/T1eff can be obtained. Exact and approximate formulas for R1eff and steady-state magnetization are derived from the Bloch equations for spins undergoing cross-relaxation and chemical exchange between two sites in the presence of an off-resonance radiofrequency field. The relaxation formulas require that the magnetization of one spin is constant, but not necessarily zero, while the other spin relaxes. Extension to three sites with one radiofrequency field is explained. The special cases of off-resonance effects alone and with cross-relaxation or chemical exchange, cross-relaxation alone, and chemical exchange alone are compared. The inaccuracy in saturation transfer measurements of exchange rate constants by published formulas is discussed for the creatine kinase reaction.

Kingsley, Peter B.; Monahan, W. Gordon

2000-04-01

393

Scaled CMOS MEMS for real-time infrared scene generation  

NASA Astrophysics Data System (ADS)

CMOS/MEMS is used as a technique to create infrared emitters. A commercial CMOS process is used that, with a post-processing silicon etch, creates thermally isolated, electronically addressable polysilicon resistors suitable for infrared scene generation. Previous efforts have focused on 2.0 micron CMOS processes which require large suspended structures in order to accommodate the design rules. This work has successfully used a 1.2 micron commercial process with a post-processing silicon etch to scale down the emitter structure to 40 X 40 microns. This allows higher density arrays, and together with using the high value poly resistor available in the 1.2 micrometer process, allows lower current operation, significantly relaxing the design constraints previously encountered. A 128 X 128 design was fabricated in this process and is characterized using a microradiometer. A silicon-on-insulator thermal pixel array design with a further reduction in emitter dimensions is also presented.

Offord, Bruce W.; Marlin, H. Ronald; Bates, Richard L.; Perkins, Gordon C.; Hutchens, Chris; Huang, Derek

2000-07-01

394

Exact solutions of triple-order time-fractional differential equations for anomalous relaxation and diffusion I: The accelerating case  

NASA Astrophysics Data System (ADS)

In recent years the interest around the study of anomalous relaxation and diffusion processes is increased due to their importance in several natural phenomena. Moreover, a further generalization has been developed by introducing time-fractional differentiation of distributed order which ranges between 0 and 1. We refer to accelerating processes when the driving power law has a changing-in-time exponent whose modulus tends from less than 1 to 1, and to decelerating processes when such an exponent modulus decreases in time moving away from the linear behaviour. Accelerating processes are modelled by a time-fractional derivative in the Riemann–Liouville sense, while decelerating processes by a time-fractional derivative in the Caputo sense. Here the focus is on the accelerating case while the decelerating one is considered in the companion paper. After a short reminder about the derivation of the fundamental solution for a general distribution of time-derivative orders, we consider in detail the triple-order case for both accelerating relaxation and accelerating diffusion processes and the exact results are derived in terms of an infinite series of H-functions. The method adopted is new and it makes use of certain properties of the generalized Mittag-Leffler function and the H-function, moreover it provides an elegant generalization of the method introduced by Langlands (2006) [T.A.M. Langlands, Physica A 367 (2006) 136] to study the double-order case of accelerating diffusion processes.

Saxena, Ram K.; Pagnini, Gianni

2011-02-01

395

Ultra-Slow Dielectric Relaxation Process in Polyols  

NASA Astrophysics Data System (ADS)

Dielectric relaxation processes with relaxation times larger than that for the structural ? process are reported for glycerol, xylitol, sorbitol and their mixtures for the first time. Appearance of this ultra-slow process depends on cooling rate. More rapid cooling gives larger dielectric relaxation strength. However, relaxation time is not affected by cooling rate and shows non-Arrhenius temperature dependence with correlation to the ? process. It can be considered that non-equilibrium dynamic structure causes the ultra-slow process. Scale of such structure would be much larger than that of the region for the cooperative molecular orientations for the ? process.

Yomogida, Yoshiki; Minoguchi, Ayumi; Nozaki, Ryusuke

2004-04-01

396

FDTD Modeling of Biological Tissues Cole–Cole Dispersion for 0.5–30 GHz Using Relaxation Time Distribution Samples—Novel and Improved Implementations  

Microsoft Academic Search

In this paper, novel finite-difference time-domain implementations of the Cole-Cole dispersion model for biological tissues, from 0.5 to 30 GHz, based on the sampling of the distribution of relaxation time, and the convolution integral formulation, are provided and verified. Moreover, shortcomings of the original relaxation time sampling implementation, with polarization formulation, were identified, and the improved polarization implementation is provided

Mohammad-Reza Tofighi

2009-01-01

397

Learning Across Time Scales: Science, Policy, Management, and Communication  

NASA Astrophysics Data System (ADS)

This presentation will draw together common themes raised in the session and discuss lessons learned across time scales and their implications for managers and policy makers concerned with both climate change and variability. Session themes will be examined in the context of the upcoming World Summit on Sustainable Development (WSSD) and considered as opportunities for linking climate change policy discussions with lessons learned from the study of adaptation on seasonal to interannual time scales. The presentation will raise questions about future research directions, discuss recommendations for promoting learning across time scales, and explore options for better communicating the links between climate change and variability.

Stewart, M. M.

2002-05-01

398

Relaxation Dynamics in Heme Proteins.  

NASA Astrophysics Data System (ADS)

A protein molecule possesses many conformational substates that are likely arranged in a hierarchy consisting of a number of tiers. A hierarchical organization of conformational substates is expected to give rise to a multitude of nonequilibrium relaxation phenomena. If the temperature is lowered, transitions between substates of higher tiers are frozen out, and relaxation processes characteristic of lower tiers will dominate the observational time scale. This thesis addresses the following questions: (i) What is the energy landscape of a protein? How does the landscape depend on the environment such as pH and viscosity, and how can it be connected to specific structural parts? (ii) What relaxation phenomena can be observed in a protein? Which are protein specific, and which occur in other proteins? How does the environment influence relaxations? (iii) What functional form best describes relaxation functions? (iv) Can we connect the motions to specific structural parts of the protein molecule, and are these motions important for the function of the protein?. To this purpose, relaxation processes after a pressure change are studied in carbonmonoxy (CO) heme proteins (myoglobin-CO, substrate-bound and substrate-free cytochrome P450cam-CO, chloroperoxidase-CO, horseradish peroxidase -CO) between 150 K and 250 K using FTIR spectroscopy to monitor the CO bound to the heme iron. Two types of p -relaxation experiments are performed: p-release (200 to ~eq40 MPa) and p-jump (~eq40 to 200 MPa) experiments. Most of the relaxations fall into one of three groups and are characterized by (i) nonexponential time dependence and non-Arrhenius temperature dependence (FIM1( nu), FIM1(Gamma)); (ii) exponential time dependence and non-Arrhenius temperature dependence (FIM0(A_{i}to A_{j})); exponential time dependence and Arrhenius temperature dependence (FIMX( nu)). The influence of pH is studied in myoglobin-CO and shown to have a strong influence on the substate population of the highest tier, tier 0, but not on the relaxation rates. Two different viscosities in myoglobin-CO are compared. The dependence of relaxations on the thermodynamic history of a sample is shown. For substrate-free P450cam-CO, relaxations after a p-jump are observed far above the glass transition of the protein-solvent system.

Scholl, Reinhard Wilhelm

399

The impact of mergers on relaxed X-ray clusters - II. Effects on global X-ray and Sunyaev-Zel'dovich properties and their scaling relations  

NASA Astrophysics Data System (ADS)

We use the suite of simulations presented by Poole et al. to examine global X-ray and Sunyaev-Zel'dovich (SZ) observables for systems of merging relaxed X-ray clusters. The time evolution of our merging systems' X-ray luminosities, temperatures, total mass measures, SZ central Compton parameters and integrated SZ fluxes are presented and the resulting impact on their scaling relations examined. In all cases, and for all parameters, we observe a common time evolution: two rapid transient increases during first and second pericentric passage, with interceding values near or below their initial levels. This is in good qualitative agreement with previous idealized merger simulations, although we find several important differences related to the inclusion of radiative cooling in our simulations. These trends translate into a generic evolution in the scaling-relation planes as well: a rapid transient roughly along the mass scaling relations, a subsequent slow drift across the scatter until virialization, followed by a slow evolution along and up the mass scaling relations as cooling recovers in the cluster cores. However, this drift is not sufficient to account for the observed scatter in the scaling relations. We also study the effects of mergers on several theoretical temperature measures of the intracluster medium: emission-weighted measures (Tew), the spectroscopic-like measure (Tsl) proposed by Mazzotta et al. and plasma model fits to the integrated spectrum of the system (Tspec). We find that Tsl tracks Tspec for the entire duration of our mergers, illustrating that it remains a good tool for observational comparison even for highly disturbed systems. Furthermore, the transient temperature increases produced during first and second pericentric passage are 15-40 per cent larger for Tew than for Tsl or Tspec. This suggests that the effects of transient temperature increases on ?8 and ?M derived by Randall et al. are over estimated. Lastly, we examine the X-ray SZ proxy proposed by Kravtsov, Vikhlinin & Nagai (2006) and find that the tight mass scaling relation they predict remains secure through the entire duration of a merger event, independent of projection effects.

Poole, Gregory B.; Babul, Arif; McCarthy, Ian G.; Fardal, Mark A.; Bildfell, C. J.; Quinn, Thomas; Mahdavi, Andisheh

2007-09-01

400

Dominant time scale for brittle fragmentation of vesicular magma by decompression  

NASA Astrophysics Data System (ADS)

Brittle fragmentation was examined in a vesicular material analogous to magma, in this case, maltose syrup with bubbles. All the key time scales for magma fragmentation are controlled in the experiment using a rapid decompression facility. It was found that the onset of fragmentation can be well characterized using the Maxwell relaxation time ? r and the decompression time ?t dec, in the case where sufficiently large stress is generated in the material. As the ratio ?t dec/? r increases from less than unity to over fifty, the response of the specimen changes from brittle fragmentation to ductile expansion without fragmentation. During the transition, the specimen exhibits small ductile deformation before the onset of fragmentation. The transition occurs even though the stress at the bubble wall is the same. The results suggest that ?t dec/? r is the controlling parameter not only for the onset of, but also for the variation of magma fragmentation by decompression.

Kameda, Masaharu; Kuribara, Hideaki; Ichihara, Mie

2008-07-01

401

Real-Time Communication for Large Scale Distributed Control Systems  

Microsoft Academic Search

Because of their scale, complexity and requirement of ex- pandability, Large Scale Distributed Control Systems (LSDCS) are usu- ally created in a multistep integration process. To succeed, it has to be governed by well-defined information architecture, appropriate commu- nication infrastructure and the supervisory role of the time notion taken into consideration from the very beginning of the design stage. Mutual

Mariusz Postol

402

Assessment of the two relaxation time Lattice-Boltzmann scheme to simulate Stokes flow in porous media  

NASA Astrophysics Data System (ADS)

The recent advances in 3-D imaging of porous structures have generated a tremendous interest in the simulation of complex single and two-phase flows. Lattice-Boltzmann (LB) schemes present a powerful tool to solve the flow field directly from the binarized 3-D images. However, as viscosity often plays an important role, the LB scheme should correctly treat viscosity effects. This is the case using a LB scheme with two relaxation times (TRT) unlike the broadly used, the single-relaxation rate, BGK, where the velocity of the modeled fluid does not vary as the inverse of the viscosity applying the bounce-back (no-slip) boundary rule. The aim of this work is to apply the LB-TRT approach to different types of porous media (straight channels, 2-D model porous media, sandstone) to solve for the flow field and to evaluate the approach in terms of parameter dependence, error and convergence time on the basis of permeability. We show that the variation of permeability with the free relaxation parameter ? of the TRT scheme depends on the heterogeneity of the sample and on the numerical resolution. The convergence time depends on the applied viscosity and the parameter standing for the speed of sound, thus the computation time can be reduced by choosing appropriate values of those parameters. Two approaches to calculate permeability (Darcy's law and viscous energy dissipation) are proposed and investigated. We recommend to use Darcy's law, as dependence on ? is less important. Periodic (in the presence of a driving body force) and pressure boundary conditions are evaluated in terms of the results.

Talon, L.; Bauer, D.; Gland, N.; Youssef, S.; Auradou, H.; Ginzburg, I.

2012-04-01

403

Optimal multi-scale patterns in time series streams  

Microsoft Academic Search

We introduce a method to discover optimal local patterns, which concisely describe the main trends in a time series. Our approach examines the time series at multiple time scales (i.e., window sizes) and efficiently discovers the key patterns in each. We also introduce a criterion to select the best window sizes, which most concisely capture the key oscillatory as well

Spiros Papadimitriou; Philip S. Yu

2006-01-01

404

Optimal dynamic voltage scaling for wireless sensor nodes with real-time constraints  

NASA Astrophysics Data System (ADS)

Sensors are increasingly embedded in manufacturing systems and wirelessly networked to monitor and manage operations ranging from process and inventory control to tracking equipment and even post-manufacturing product monitoring. In building such sensor networks, a critical issue is the limited and hard to replenish energy in the devices involved. Dynamic voltage scaling is a technique that controls the operating voltage of a processor to provide desired performance while conserving energy and prolonging the overall network's lifetime. We consider such power-limited devices processing time-critical tasks which are non-preemptive, aperiodic and have uncertain arrival times. We treat voltage scaling as a dynamic optimization problem whose objective is to minimize energy consumption subject to hard or soft real-time execution constraints. In the case of hard constraints, we build on prior work (which engages a voltage scaling controller at task completion times) by developing an intra-task controller that acts at all arrival times of incoming tasks. We show that this optimization problem can be decomposed into two simpler ones whose solution leads to an algorithm that does not actually require solving any nonlinear programming problems. In the case of soft constraints, this decomposition must be partly relaxed, but it still leads to a scalable (linear in the number of tasks) algorithm. Simulation results are provided to illustrate performance improvements in systems with intra-task controllers compared to uncontrolled systems or those using inter-task control.

Cassandras, Christos G.; Zhuang, Shixin

2005-11-01

405

Carbon-14 time scale extended: comparison of chronologies.  

PubMed

Thermal diffusion isotopic enrichment of carbon-14 has extended the radiocarbon dating range to about 75,000 years ago. Twenty-eight samples obtained up to June 1976, mainly from northwest Europe, were dated. Consideration of the basic assumptions of carbon-14 dating and of the sources of contamination indicates that the ages are generally reliable. Together with the pollen analytic and stratigraphic the dates yield a more detailed radiocarbon time scale for climatic variations in northwest Europe, showing three early glacial interstades. The radiocarbon time scale agrees with the Camp Century chronology and with the thorium-230 ages of corals representing high sea level stands on New Guinea. Ther is a discrepancy between the radiocarbon time scale and the deep-sea chronology, which may be due to correlation errors. With a modified interpretation of the correlation, all four time scales agree within the estimated experimental uncertainties of the dating techniques used. PMID:17847309

Grootes, P M

1978-04-01

406

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

407

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

408

Large Deviations for Two-Time-Scale Diffusions, with Delays  

SciTech Connect

We consider the problem of large deviations for a two-time-scale reflected diffusion process, possibly with delays in the dynamical terms. The Dupuis-Ellis weak convergence approach is used. It is perhaps the most intuitive and simplest for the problems of concern. The results have applications to the problem of approximating optimal controls for two-time-scale systems via use of the averaged equation.

Kushner, Harold J., E-mail: hjk@dam.brown.ed [Brown University, Applied Math (United States)

2010-12-15

409

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

410

Characteristic Time Scales of Characteristic Magmatic Processes and Systems  

NASA Astrophysics Data System (ADS)

Every specific magmatic process, regardless of spatial scale, has an associated characteristic time scale. Time scales associated with crystals alone are rates of growth, dissolution, settling, aggregation, annealing, and nucleation, among others. At the other extreme are the time scales associated with the dynamics of the entire magmatic system. These can be separated into two groups: those associated with system genetics (e.g., the production and transport of magma, establishment of the magmatic system) and those due to physical characteristics of the established system (e.g., wall rock failure, solidification front propagation and instability, porous flow). The detailed geometry of a specific magmatic system is particularly important to appreciate; although generic systems are useful, care must be taken to make model systems as absolutely realistic as possible. Fuzzy models produce fuzzy science. Knowledge of specific time scales is not necessarily useful or meaningful unless the hierarchical context of the time scales for a realistic magmatic system is appreciated. The age of a specific phenocryst or ensemble of phenocrysts, as determined from isotopic or CSD studies, is not meaningful unless something can be ascertained of the provenance of the crystals. For example, crystal size multiplied by growth rate gives a meaningful crystal age only if it is from a part of the system that has experienced semi-monotonic cooling prior to chilling; crystals entrained from a long-standing cumulate bed that were mechanically sorted in ascending magma may not reveal this history. Ragged old crystals rolling about in the system for untold numbers of flushing times record specious process times, telling more about the noise in the system than the life of typical, first generation crystallization processes. The most helpful process-related time scales are those that are known well and that bound or define the temporal style of the system. Perhaps the most valuable of these times comes from the observed durations and rates of volcanism. There can be little doubt that the temporal styles of volcanism are the same as those of magmatism in general. Volcano repose times, periodicity, eruptive fluxes, acoustic emission structures, lava volumes, longevity, etc. must also be characteristic of pluton-dominated systems. We must therefore give up some classical concepts (e.g., instantaneous injection of crystal-free magma as an initial condition) for any plutonic/chambered system and move towards an integrated concept of magmatism. Among the host of process-related time scales, probably the three most fundamental of any magmatic system are (1) the time scale associated with crystal nucleation (J) and growth (G) (tx}=C{1(G3 J)-{1}/4; Zieg & Marsh, J. Pet. 02') along with the associated scales for mean crystal size (L) and population (N), (2) the time scale associated with conductive cooling controlled by a local length scale (d) (tc}=C{2 d2/K; K is thermal diffusivity), and (3) the time scale associated with intra-crystal diffusion (td}=C{3 L2/D; D is chemical diffusivity). It is the subtle, clever, and insightful application of time scales, dovetailed with realistic system geometry and attention paid to the analogous time scales of volcanism, that promises to reveal the true dynamic integration of magmatic systems.

Marsh, B. D.

2004-05-01

411

Spin relaxation and linear-in-electric-field frequency shift in an arbitrary, time-independent magnetic field  

SciTech Connect

A method is presented to calculate the spin relaxation times T{sub 1}, T{sub 2} due to a nonuniform magnetic field, and the linear-in-electric-field precession frequency shift {delta}{omega}{sub E} when an electric field is present, in the diffusion approximation for spins confined to a rectangular cell. It is found that the rectangular cell geometry admits of a general result for T{sub 1}, T{sub 2}, and {delta}{omega}{sub E} in terms of the spatial cosine-transform components of the magnetic field.

Clayton, Steven Michael [Los Alamos National Laboratory

2010-12-03

412

Comparison betweenTime Relaxed Monte Carlo Method and Majorant Frequency Scheme methods for the space homogeneous Boltzmann equation  

NASA Astrophysics Data System (ADS)

Recently a new class of schemes, called Time Relaxed Monte Carlo (TRMC) has been introduced for the numerical solution of the Boltzmann equation of gas dynamics. The motivation is to propose a systematic framework to derive Monte Carlo methods effective near the fluid dynamic regime. Before the methods can be accepted as alternative tools to other methods, they have to show that they are able to reproduce results obtainable by well established reliable methods. In this paper a detailed comparison is performed between TRMC methods and the Majorant Frequency Scheme in the case of the space-homogeneous Boltzmann equation. In particular, the effect of finite number of particles is considered.

Russo, G.; Pareschi, L.; Trazzi, S.; Shevyrin, A.; Bondar, Ye.; Ivanov, M.

2005-05-01

413

Experimental investigation of the longitudinal relaxation time of electronic polarization of the ground state of potassium atoms in a cell with an antirelaxation coating on the walls  

Microsoft Academic Search

We report the results of an experimental investigation of the longitudinal relaxation time T\\u000a 1 of the electronic polarization of the ground state of potassium atoms in cells with an antirelaxation coating on the walls.\\u000a Investigations were performed for a number of cells at temperature T=24C. The maximum recorded relaxation times ? are 3.6, 4.3, and 5.2 s for cells

M. V. Balabas; M. I. Karuzin; A. S. Pazgalev

1999-01-01

414

Determination of T 1? values for head and neck tissues at 0.1 T: a comparison to T 1 and T 2 relaxation times  

Microsoft Academic Search

In order to optimize head and neck magnetic resonance (MR) imaging with the spin-lock (SL) technique, the T1? relaxation times for normal tissues were determined. Furthermore, T1? was compared to T1 and T2 relaxation times. Ten healthy volunteers were studied with a 0.1 T clinical MR imager. T1? values were determined by first measuring the tissue signal intensities with different

Antti T Markkola; Hannu J Aronen; Usama Abo Ramadan; Juha T Halavaara; Jukka I Tanttu; Raimo E Sepponen

1998-01-01

415

Universal pattern for the distribution of relaxation times in the isotropic phase of liquid crystalline n-cyanobiphenyls.  

PubMed

A universal pattern emerging from the analysis of the distribution of relaxation times in the isotropic phase of liquid crystalline n-alkylcyanobiphenyls (nCB) from 4CB to 14CB is presented. The increase of the length of nCB molecules causes the high-frequency (short-time) branch of the primary relaxation loss curve to approach the form epsilon(f>fpeak) approximately omega(-n), with n-->1/2 in frequency (omega=2pif) or approximately sqrt[t] in time on cooling toward the isotropic-mesophase "clearing" phase-transition temperature (TC). Recently, such behavior was suggested as a hypothetical universal pattern for diverse glass forming organic liquids on approaching the glass temperature [A. I. Nielsen, T. Christensen, B. Jakobsen, K. Niss, N. B. Olsen, R. Richert, and J. C. Dyre, J. Chem. Phys. 130, 154508 (2009)]. The isotropic phase of rodlike liquid crystalline compounds is considered to be an important experimental model system for studying glassy dynamics since it constitutes a link with the model fluid of hard ellipsoids of revolution. PMID:19658715

Drozd-Rzoska, Aleksandra

2009-07-14

416

Le Chatelier's principle with multiple relaxation channels  

NASA Astrophysics Data System (ADS)

Le Chatelier's principle is discussed within the constrained variational approach to thermodynamics. The formulation is general enough to encompass systems not in thermal (or chemical) equilibrium. Particular attention is given to systems with multiple constraints which can be relaxed. The moderation of the initial perturbation increases as additional constraints are removed. This result is studied in particular when the (coupled) relaxation channels have widely different time scales. A series of inequalities is derived which describes the successive moderation as each successive relaxation channel opens up. These inequalities are interpreted within the metric-geometry representation of thermodynamics.

Gilmore, R.; Levine, R. D.

1986-05-01

417

Wavelet analysis and scaling properties of time series  

Microsoft Academic Search

We propose a wavelet based method for the characterization of the scaling behavior of nonstationary time series. It makes use of the built-in ability of the wavelets for capturing the trends in a data set, in variable window sizes. Discrete wavelets from the Daubechies family are used to illustrate the efficacy of this procedure. After studying binomial multifractal time series

P. Manimaran; Prasanta K. Panigrahi; Jitendra C. Parikh

2005-01-01

418

Evidence of dynamic scaling in space-time rainfall  

Microsoft Academic Search

As in any evolving process, including rainfall, variability in space and time are not independent of each other but depend in a way particular to the process at hand. Understanding and quantifying the space-time dependences in a process over a range of scales is not always easy because these dependences may be hidden under complex patterns with pronounced statistical variability

V. Venugopal; Efi Foufoula-Georgiou; Victor Sapozhnikov

1999-01-01

419

SNO+ Liquid Scintillator Characterization: Timing, Quenching, and Energy Scale  

NASA Astrophysics Data System (ADS)

This contribution describes laboratory measurements designed to investigate the optical properties of linear alkybenzene (LAB). Presented here is the measurement of the scintillation light timing profiles due to alpha and beta-particle excitation, the calculation of alpha/beta discrimination capability based on these timing distributions, and the investigation of electron energy scale.

O'Sullivan, E.; Wan Chan Tseung, H. S.; Tolich, N.; O'Keeffe, H. M.; Chen, M.

2012-08-01

420

Physical Process Time and Space Scales Related to River Restoration  

Microsoft Academic Search

River restoration studies need to consider stream dynamics, evolution, rates of adjustment, and relative effects of various human disturbances. The history of stream channel adjustment typically needs to be investigated over a time scale of decades to centuries to include the time before human disturbance. An investigation of historical change will help with understanding the processes of physical change, how

T. Randle; J. Boutry

2005-01-01

421

PREDICTIVE ADAPTIVE FEEDFORWARD CONTROL OF A TIME SCALED SOLAR PLANT  

Microsoft Academic Search

This paper concerns the control of a solar energy collector field using predictive feedforward adaptive control techniques based on multiple identifiers. The ACUREX field used in these work is described by a partial differential equation (PDE). The plant is characterized by: non linearity, fast accessible disturbances and time varying dynamics. The dynamic dependency on flow is overcome by time-scaling. The

R. N. Silva; J. M. Lemos

422

Nanosecond relaxation in polymer electrolyte nanocomposites  

NASA Astrophysics Data System (ADS)

We present recent results on the dynamics and relaxation of nanocomposite polymer electrolytes. We have measured the relaxation on the 10-100 nsec time scale in PEO-LiClO_4-based nanocomposites using quasielastic neutron scattering (QENS). Complementary information on the conductivity have been derived on the same samples. Our results show that, on the time scale of the QENS measurements -- 0.01 to 0.1 ns --- the addition of ceramic nanoparticles has no significant effect on the dynamics of the polymer electrolyte while the confinement in porous materials such as Vycor and synthetic hectorite clays induces a spectacular slowing down of the dynamics.

Marie-Louise, Saboungi; Price, David L.; Smith, Luis J.; Zanotti, Jean-Marc; Armand, Michel

2004-03-01

423

Surface field measurements of scale models in the time domain  

Microsoft Academic Search

Time-domain measurement have been performed of the surface densities of current and charge induced on scale models when illuminated by a transient electromagnetic pulse in order to provide test points to validate numerical models. three bodies--a cylinder, a crossed-cylinder, and a 1:100 scale model 747 aircraft were used in the experiments. Responses were measured for objects in a simulated free

H. S. Cabayan

1981-01-01

424

A scale model of multivariate rainfall time series  

Microsoft Academic Search

A multivariate time-series model that uses a factor-analytic approach is shown to provide an effective description of both monthly and annual rainfall in south Florida. In the case of monthly rainfall, the scale model shows that deviations from monthly means are caused primarily by large-scale phenomena that have temporal structure. These sort of phenomena are not accounted for by using

David A. Chin

1995-01-01

425

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

426

Physics in space-time with scale-dependent metrics  

NASA Astrophysics Data System (ADS)

We construct three-dimensional space R?3 with the scale-dependent metric and the corresponding Minkowski space-time M?,?4 with the scale-dependent fractal (DH) and spectral (DS) dimensions. The local derivatives based on scale-dependent metrics are defined and differential vector calculus in R?3 is developed. We state that M?,?4 provides a unified phenomenological framework for dimensional flow observed in quite different models of quantum gravity. Nevertheless, the main attention is focused on the special case of flat space-time M1/3,14 with the scale-dependent Cantor-dust-like distribution of admissible states, such that DH increases from DH=2 on the scale ??0 to DH=4 in the infrared limit ??0, where ?0 is the characteristic length (e.g. the Planck length, or characteristic size of multi-fractal features in heterogeneous medium), whereas DS?4 in all scales. Possible applications of approach based on the scale-dependent metric to systems of different nature are briefly discussed.

Balankin, Alexander S.

2013-10-01

427

Note: Extraction of hydrogen bond thermodynamic properties of water from dielectric constant and relaxation time data  

NASA Astrophysics Data System (ADS)

We recently proposed a theory [Suresh, J. Chem. Phys. 113, 9727 (2000)], based on the principles of statistical mechanics, for describing the temperature variation of static dielectric constant of water and the average number of H-bonds per molecule in the liquid phase. The theoretical model contains three parameters; two of them pertain to the energy and entropy changes accompanying bond-formation, and the third (??) represents the dielectric constant at a frequency that is sufficiently low for atomic and electronic polarization, but sufficiently high for intermolecular relaxation processes involving the movement of permanent dipole moments to be inoperative. In the absence of a consensus in the literature for the value of V? to be used in dielectric constant calculations, it was arbitrarily set to a commonly accepted value of 1.77 (corresponding to refractive index of 1.33). Values for H-bond parameters were then estimated by best fitting model calculations to experimental data for dielectric constant across temperatures ranging from melting to the critical point of water. It is the purpose of the present Note to eliminate the ambiguity on the choice of V? and propose refined values for the H-bond parameters.

Rastogi, Abhishek; Yadav, Siddharth; Suresh, S. J.

2011-08-01

428

Quarkonia and heavy-quark relaxation times in the quark-gluon plasma  

SciTech Connect

A thermodynamic T-matrix approach for elastic two-body interactions is employed to calculate spectral functions of open and hidden heavy-quark systems in the quark-gluon plasma. This enables the evaluation of quarkonium bound-state properties and heavy-quark diffusion on a common basis and thus to obtain mutual constraints. The two-body interaction kernel is approximated within a potential picture for spacelike momentum transfers. An effective field-theoretical model combining color-Coulomb and confining terms is implemented with relativistic corrections and for different color channels. Four pertinent model parameters, characterizing the coupling strengths and screening, are adjusted to reproduce the color-average heavy-quark free energy as computed in thermal lattice QCD. The approach is tested against vacuum spectroscopy in the open (D, B) and hidden ({Psi} and {Upsilon}) flavor sectors, as well as in the high-energy limit of elastic perturbative QCD scattering. Theoretical uncertainties in the static reduction scheme of the four-dimensional Bethe-Salpeter equation are elucidated. The quarkonium spectral functions are used to calculate Euclidean correlators which are discussed in light of lattice QCD results, while heavy-quark relaxation rates and diffusion coefficients are extracted utilizing a Fokker-Planck equation.

Riek, F.; Rapp, R. [Cyclotron Institute, Texas A and M University, College Station, Texas 77843-3366 (United States)

2010-09-15

429

Quarkonia and heavy-quark relaxation times in the quark-gluon plasma  

NASA Astrophysics Data System (ADS)

A thermodynamic T-matrix approach for elastic two-body interactions is employed to calculate spectral functions of open and hidden heavy-quark systems in the quark-gluon plasma. This enables the evaluation of quarkonium bound-state properties and heavy-quark diffusion on a common basis and thus to obtain mutual constraints. The two-body interaction kernel is approximated within a potential picture for spacelike momentum transfers. An effective field-theoretical model combining color-Coulomb and confining terms is implemented with relativistic corrections and for different color channels. Four pertinent model parameters, characterizing the coupling strengths and screening, are adjusted to reproduce the color-average heavy-quark free energy as computed in thermal lattice QCD. The approach is tested against vacuum spectroscopy in the open (D, B) and hidden (? and ?) flavor sectors, as well as in the high-energy limit of elastic perturbative QCD scattering. Theoretical uncertainties in the static reduction scheme of the four-dimensional Bethe-Salpeter equation are elucidated. The quarkonium spectral functions are used to calculate Euclidean correlators which are discussed in light of lattice QCD results, while heavy-quark relaxation rates and diffusion coefficients are extracted utilizing a Fokker-Planck equation.

Riek, F.; Rapp, R.

2010-09-01

430

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

431

LASER APPLICATIONS AND OTHER TOPICS IN QUANTUM ELECTRONICS: Study of relaxation times of polymethine dyes used for passive mode locking of solid-state lasers emitting between 750 and 850 nm  

Microsoft Academic Search

The relaxation times tau of the bleached states of polymethine dyes absorbing light in the 750 --- 850-nm are determined by the direct pump --- probe method. The effect of the dye structure and the solvent type on the relaxation time is discussed. The role of different intra- and intermolecular interactions in the relaxation of excited electronic states of the

R. Grigonis; Nadezhda A. Derevyanko; Aleksandr A. Ishchenko; V. A. Sirutkaitis

2001-01-01

432

Investigating the Geologic Time Scale: Creating posters to Display Trends in Geologic Time  

NSDL National Science Digital Library

This observational inquiry activity involving careful descriptions of rocks and fossil including age will be used to create a scalar accurate geologic time scale. Students will observe and learn that the geologic time scale was created based on changes in fossil, rock, and atmospheric changes.

Atkins, Kim