These are representative sample records from Science.gov related to your search topic.
For comprehensive and current results, perform a real-time search at Science.gov.
1

Role of relaxation time scale in noisy signal transduction  

E-print Network

Intracellular fluctuations, mainly triggered by gene expression, are an inevitable phenomenon observed in living cells. It influences generation of phenotypic diversity in genetically identical cells. Such variation of cellular components is beneficial in some contexts but detrimental in others. To quantify the fluctuations in a gene product, we undertake an analytical scheme for studying few naturally abundant linear as well as branched chain network motifs. We solve the Langevin equations associated with each motif under the purview of linear noise approximation and quantify Fano factor and mutual information. Both quantifiable expressions exclusively depend on the relaxation time (decay rate constant) and steady state population of the network components. We investigate the effect of relaxation time constraints on Fano factor and mutual information to indentify a time scale domain where a network can recognize the fluctuations associated with the input signal more reliably. We also show how input populatio...

Maity, Alok Kumar; Banik, Suman K

2014-01-01

2

Generalized dynamic scaling for quantum critical relaxation in imaginary time  

NASA Astrophysics Data System (ADS)

We study the imaginary-time relaxation critical dynamics of a quantum system with a vanishing initial correlation length and an arbitrary initial order parameter M0. We find that in quantum critical dynamics, the behavior of M0 under scale transformations deviates from a simple power law, which was proposed for very small M0 previously. A universal characteristic function is then suggested to describe the rescaled initial magnetization, similar to classical critical dynamics. This characteristic function is shown to be able to describe the quantum critical dynamics in both short- and long-time stages of the evolution. The one-dimensional transverse-field Ising model is employed to numerically determine the specific form of the characteristic function. We demonstrate that it is applicable as long as the system is in the vicinity of the quantum critical point. The universality of the characteristic function is confirmed by numerical simulations of models belonging to the same universality class.

Zhang, Shuyi; Yin, Shuai; Zhong, Fan

2014-10-01

3

Huge (but finite) time scales in slow relaxations: beyond simple aging.  

PubMed

Experiments performed in the last years demonstrated slow relaxations and aging in the conductance of a large variety of materials. Here, we present experimental and theoretical results for conductance relaxation and aging for the case-study example of porous silicon. The relaxations are experimentally observed even at room temperature over time scales of hours, and when a strong electric field is applied for a time tw, the ensuing relaxation depends on tw. We derive a theoretical curve and show that all experimental data collapse onto it with a single time scale as a fitting parameter. This time scale is found to be of the order of thousands of seconds at room temperature. The generic theory suggested is not fine-tuned to porous silicon, and thus we believe the results should be universal, and the presented method should be applicable for many other systems manifesting memory and other glassy effects. PMID:22107656

Amir, Ariel; Borini, Stefano; Oreg, Yuval; Imry, Yoseph

2011-10-28

4

Entropy and relaxation time  

E-print Network

This paper discusses the possible relation between entropy and the relaxation time of liquids, in particular glass-forming systems, providing supplementing comments to the paper entitled "A brief critique of the Adam-Gibbs entropy model" by Hecksher et al. [J. Non-Cryst. Solids 325, 624-627 (2009)]. Besides the Adam-Gibbs model, we also briefly discuss Rosenfeld's excess entropy scaling and the 1964 experimental observation by Chang and Bestul of a universal excess entropy at the glass transition.

Jeppe C. Dyre

2014-03-11

5

Dynamic structure factor in liquid cesium on the basis of time-scale invariance of relaxation processes  

Microsoft Academic Search

The dynamic structure factor S(k, ?) in liquid cesium near the melting point at T = 308 K is studied by means of Zwanzig-Mori's memory function formalism. The spectra of S(k, ?) are calculated on the basis of the idea of time-scale invariance of relaxation processes in liquid metals, which appear\\u000a on the fourth relaxation level. The spectra of S(k,

R. M. Yulmetyev; A. V. Mokshin; P. Hänggi; V. Yu. Shurygin

2002-01-01

6

Nonadiabatic dynamics of electron transfer in solution: Explicit and implicit solvent treatments that include multiple relaxation time scales  

NASA Astrophysics Data System (ADS)

The development of efficient theoretical methods for describing electron transfer (ET) reactions in condensed phases is important for a variety of chemical and biological applications. Previously, dynamical dielectric continuum theory was used to derive Langevin equations for a single collective solvent coordinate describing ET in a polar solvent. In this theory, the parameters are directly related to the physical properties of the system and can be determined from experimental data or explicit molecular dynamics simulations. Herein, we combine these Langevin equations with surface hopping nonadiabatic dynamics methods to calculate the rate constants for thermal ET reactions in polar solvents for a wide range of electronic couplings and reaction free energies. Comparison of explicit and implicit solvent calculations illustrates that the mapping from explicit to implicit solvent models is valid even for solvents exhibiting complex relaxation behavior with multiple relaxation time scales and a short-time inertial response. The rate constants calculated for implicit solvent models with a single solvent relaxation time scale corresponding to water, acetonitrile, and methanol agree well with analytical theories in the Golden rule and solvent-controlled regimes, as well as in the intermediate regime. The implicit solvent models with two relaxation time scales are in qualitative agreement with the analytical theories but quantitatively overestimate the rate constants compared to these theories. Analysis of these simulations elucidates the importance of multiple relaxation time scales and the inertial component of the solvent response, as well as potential shortcomings of the analytical theories based on single time scale solvent relaxation models. This implicit solvent approach will enable the simulation of a wide range of ET reactions via the stochastic dynamics of a single collective solvent coordinate with parameters that are relevant to experimentally accessible systems.

Schwerdtfeger, Christine A.; Soudackov, Alexander V.; Hammes-Schiffer, Sharon

2014-01-01

7

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

8

Quantifying millisecond time-scale exchange in proteins by CPMG relaxation dispersion NMR spectroscopy of side-chain carbonyl groups  

Microsoft Academic Search

A new pulse sequence is presented for the measurement of relaxation dispersion profiles quantifying millisecond time-scale\\u000a exchange dynamics of side-chain carbonyl groups in uniformly 13C labeled proteins. The methodology has been tested using the 87-residue colicin E7 immunity protein, Im7, which is known\\u000a to fold via a partially structured low populated intermediate that interconverts with the folded, ground state on

Alexandar L. Hansen; Lewis E. Kay

2011-01-01

9

Asymptotic forms and scaling properties of the relaxation time near threshold points in spinodal-type dynamical phase transitions  

NASA Astrophysics Data System (ADS)

We study critical properties of the relaxation time at a threshold point in switching processes between bistable states under change in external fields. In particular, we investigate the relaxation processes near the spinodal point of the infinitely long-range interaction model (the Husimi-Temperley model) by analyzing the scaling properties of the corresponding Fokker-Planck equation. We also confirm the obtained scaling relations by direct numerical solution of the original master equation, and by kinetic Monte Carlo simulation of the stochastic decay process. In particular, we study the asymptotic forms of the divergence of the relaxation time near the spinodal point and re-examine its scaling properties. We further extend the analysis to transient critical phenomena such as a threshold behavior with diverging switching time under a general external driving perturbation. This models photoexcitation processes in spin-crossover materials. In the ongoing development of nanosize fabrication, such size-dependence of switching processes should be an important issue, and the properties obtained here will be applicable to a wide range of physical processes.

Mori, Takashi; Miyashita, Seiji; Rikvold, Per Arne

2010-01-01

10

Asymptotic forms and scaling properties of the relaxation time near threshold points in spinodal-type dynamical phase transitions.  

PubMed

We study critical properties of the relaxation time at a threshold point in switching processes between bistable states under change in external fields. In particular, we investigate the relaxation processes near the spinodal point of the infinitely long-range interaction model (the Husimi-Temperley model) by analyzing the scaling properties of the corresponding Fokker-Planck equation. We also confirm the obtained scaling relations by direct numerical solution of the original master equation, and by kinetic Monte Carlo simulation of the stochastic decay process. In particular, we study the asymptotic forms of the divergence of the relaxation time near the spinodal point and re-examine its scaling properties. We further extend the analysis to transient critical phenomena such as a threshold behavior with diverging switching time under a general external driving perturbation. This models photoexcitation processes in spin-crossover materials. In the ongoing development of nanosize fabrication, such size-dependence of switching processes should be an important issue, and the properties obtained here will be applicable to a wide range of physical processes. PMID:20365351

Mori, Takashi; Miyashita, Seiji; Rikvold, Per Arne

2010-01-01

11

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

12

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. PMID:19665446

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

2009-01-01

13

Relaxation times estimation in MRI  

NASA Astrophysics Data System (ADS)

Magnetic Resonance Imaging is a very powerful techniques for soft tissue diagnosis. At the present, the clinical evaluation is mainly conducted exploiting the amplitude of the recorded MR image which, in some specific cases, is modified by using contrast enhancements. Nevertheless, spin-lattice (T1) and spin-spin (T2) relaxation times can play an important role in many pathology diagnosis, such as cancer, Alzheimer or Parkinson diseases. Different algorithms for relaxation time estimation have been proposed in literature. In particular, the two most adopted approaches are based on Least Squares (LS) and on Maximum Likelihood (ML) techniques. As the amplitude noise is not zero mean, the first one produces a biased estimator, while the ML is unbiased but at the cost of high computational effort. Recently the attention has been focused on the estimation in the complex, instead of the amplitude, domain. The advantage of working with real and imaginary decomposition of the available data is mainly the possibility of achieving higher quality estimations. Moreover, the zero mean complex noise makes the Least Square estimation unbiased, achieving low computational times. First results of complex domain relaxation times estimation on real datasets are presented. In particular, a patient with an occipital lesion has been imaged on a 3.0T scanner. Globally, the evaluation of relaxation times allow us to establish a more precise topography of biologically active foci, also with respect to contrast enhanced images.

Baselice, Fabio; Caivano, Rocchina; Cammarota, Aldo; Ferraioli, Giampaolo; Pascazio, Vito

2014-03-01

14

Relaxation time dynamics of the toric code in contact with a thermal reservoir: finite-size scaling in a low temperature crossover regime  

E-print Network

We present an analysis of the relaxation dynamics of a finite-size topological qubit in contact with a thermal bath. Using a continuous-time Monte Carlo method, we explicitly compute the low temperature nonequilibrium dynamics of the toric code on finite lattices. In contrast to the size-independent bound predicted for the toric code in the thermodynamic limit, we identify a low temperature crossover regime with non-trivial finite-size and temperature scaling of the relaxation time. We demonstrate how this nontrivial finite-size scaling is governed by the scaling of topologically nontrivial 2D classical random walks. The transition out of this low temperature regime defines a $dynamical$ finite-size crossover temperature which scales inversely with the log of the system size, in agreement with a crossover temperature defined from equilibrium properties. We find that both the finite-size and finite temperature scaling are stronger in the low temperature regime than above the crossover. Since this finite temperature scaling competes with the scaling of the robustness to unitary perturbations, this analysis may elucidate the scaling of memory lifetimess of possible physical realizations of topological qubits.

C. Daniel Freeman; C. M. Herdman; Dylan J Gorman; K. B. Whaley

2014-05-09

15

Scaling between structural relaxation and caged dynamics in Ca_{0.4}K_0.6(NO_{3})_{1.4} and glycerol: free volume, time scales and implications for the pressure-energy correlations  

E-print Network

The scaling of the slow structural relaxation with the fast caged dynamics is evidenced in the molten salt Ca_{0.4}K_{0.6}(NO_{3}$)_{1.4} (CKN) over about thirteen decades of the structural relaxation time. Glycerol caling was analyzed in detail. In glycerol, the short-time mean-square displacement , a measure of the caged dynamics, is contributed by free-volume. It is seen that, in order to evidence the scaling, the observation time of the fast dynamics must be shorter than the time scales of the relaxation processes. Systems with both negligible (like CKN, glycerol and network glassformers) and high (like van der Waals liquids and polymers) pressure-energy correlations exhibit the scaling between the slow relaxation and the fast caged dynamics. According to the available experiments, an isomorph-invariant expression of the master curve of the scaled data is not distinguishable from a simpler not-invariant expression. Instead, the latter grees better with the simulations on a wide class of model polymers.

Alistar Ottochian; Dino Leporini

2011-01-14

16

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

17

The relaxation time spectrum of nearly monodisperse polybutadiene melts  

Microsoft Academic Search

The relaxation behavior of polymers with long linear flexible chains of uniform length has been investigated by means of dynamic mechanical analysis. The relaxation time spectrum (H(?)) follows a scaling relationship with two self-similar regions, one for the entanglement and terminal zone, and a second one for the transition to the glass. This can be described in its most general

M. Baurngaertel; M. E. Rosa; J. Machado; M. Masse; H. H. Winter

1992-01-01

18

Relaxation system based sub-grid scale modelling for large eddy simulation of Burgers' equation  

Microsoft Academic Search

An implicit sub-grid scale model for large eddy simulation is presented by utilising the concept of a relaxation system for one dimensional Burgers' equation in a novel way. The Burgers' equation is solved for three different unsteady flow situations by varying the ratio of relaxation parameter (?) to time step. The coarse mesh results obtained with a relaxation scheme are

Souren Misra; S. V. Raghurama Rao; Manoj Kumar Bobba

2010-01-01

19

Relaxation time of non-conformal plasma  

E-print Network

We study effective relaxation time of viscous hydrodynamics of strongly coupled non-conformal gauge theory plasma using gauge theory/string theory correspondence. We compute leading corrections to the conformal plasma relaxation time from the relevant deformations due to dim-2 and dim-3 operators. We discuss in details the relaxation time tau_eff of N=2^* plasma. For a certain choice of masses this theory undergoes a phase transition with divergent specific heat c_V ~ |1-T_c/T|^(-1/2). Although the bulk viscosity remains finite all the way to the critical temperature, we find that tau_eff diverges near the critical point as tau_eff ~ |1-T_c/T|^(-1/2).

Alex Buchel

2009-08-03

20

Alternate Forms Reliability of the Behavioral Relaxation Scale: Preliminary Results  

ERIC Educational Resources Information Center

Alternate forms reliability of the Behavioral Relaxation Scale (BRS; Poppen,1998), a direct observation measure of relaxed behavior, was examined. A single BRS score, based on long duration observation (5-minute), has been found to be a valid measure of relaxation and is correlated with self-report and some physiological measures. Recently,…

Lundervold, Duane A.; Dunlap, Angel L.

2006-01-01

21

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

22

Multi-scale Times and Modes of Fast and Slow Relaxation in Solutions with Coexisting Spherical and Cylindrical Micelles according to the Difference Becker-Doering Kinetic Equations  

E-print Network

The eigenvalues and eigenvectors of the matrix of coefficients of the linearized kinetic equations applied to aggregation in surfactant solution determine the full spectrum of characteristic times and specific modes of micellar relaxation. The dependence of these relaxation times and modes on the total surfactant concentration has been analyzed for concentrations in the vicinity and well above the second critical micelle concentration (cmc2) for systems with coexisting spherical and cylindrical micelles. The analysis has been done on the basis of a discrete form of the Becker-Doering kinetic equations employing the Smoluchowsky diffusion model for the attachment rates of surfactant monomers to surfactant aggregates with matching the rates for spherical aggregates and the rates for large cylindrical micelles. The equilibrium distribution of surfactant aggregates in solution has been modeled as having one maximum for monomers, another maximum for spherical micelles and wide slowly descending branch for cylindrical micelles. The results of computations have been compared with the analytical ones known in the limiting cases from solutions of the continuous Becker-Doering kinetic equation. They demonstrated a fair agreement even in the vicinity of the cmc2 where the analytical theory looses formally its applicability.

Ilya A. Babintsev; Loran Ts. Adzhemyan; Alexander K. Shchekin

2014-04-15

23

Microscopic Origin of the Shear Relaxation Time in Causal Dissipative Fluid Dynamics  

E-print Network

In this paper we show how to compute the shear relaxation time from an underlying microscopic theory. We prove that the shear relaxation time in Israel-Stewart-type theories is given by the inverse of the pole of the corresponding retarded Green's function, which is nearest to the origin in the complex energy plane. Consequently, the relaxation time in such theories is a microscopic, and not a macroscopic, i.e., fluid-dynamical time scale.

G. S. Denicol; H. Niemi; J. Noronha; D. H. Rischke

2011-03-12

24

Scaling behaviour of relaxation dependencies in metaloxide superconductors  

NASA Technical Reports Server (NTRS)

Superconducting glass state has been investigated in different types of metaloxide ceramics, Y-Ba-Cu-O, Bi-Sr-Ca-Cu-O, Ba-Pb-Bi-O, using the highly sensitive SQUID magnetometer. The analysis of long-time relaxation processes of thermoremanent magnetization m(sup trm) (+) = M(sub o) - Slnt displayed scaling dependence of the decay rate S = -dM/dlnt on quantity of trapped magnetic flux M(sub o): 1gs = 31g M(sub o) - observed universal dependence S is approximately M(sup 3) (sub o) seems to one of the features of superconducting glass state in metaloxide ceramics.

Sidorenko, A. S.; Panaitov, G. I.; Gabovich, A. M.; Moiseev, D. P.; Postnikov, V. M.

1990-01-01

25

Time quantification for Monte Carlo modeling of superparamagnetic relaxation  

NASA Astrophysics Data System (ADS)

Monte Carlo modeling of superparamagnetic kinetics is addressed with regard to quantification of the simulation steps in units of real time. For the classical Néel case (field-free relaxation of the magnetic moment in a single-domain uniaxial particle), a modification of the Nowak-Chantrell-Kennedy formula is proposed enabling the calculations with the variation amplitude of the magnetic moment independent of the particle anisotropy. This relation is obtained from comparison of the Monte Carlo simulated relaxation against the solution of the kinetic equation for the particle magnetic moment. The same idea is applied to a strongly nonequilibrium process: steady re-magnetization of a superparamagnetic particle under an ac field. It is found that in the latter case a linear relationship can be established between the number of simulation steps and the real-time scale (the field period) that holds fairly well in wide frequency and anisotropy parameter intervals.

Melenev, P. V.; Raikher, Yu. L.; Rusakov, V. V.; Perzynski, R.

2012-09-01

26

Validation of NMR relaxation exchange time measurements in porous media.  

PubMed

Two-dimensional T(2)-T(2) NMR relaxation exchange spectroscopy has been applied to model porous media composed of mixtures of nonporous borosilicate and soda lime glass spheres in water. The spheres had a mean diameter of 100 microm, thus providing an approximately constant characteristic pore dimension throughout the structures, while the use of two glass types ensured that water in different pore-space regions had significantly different T(2) relaxation rates. The packed beds were constructed in various ways with controlled glass type domain sizes to rigorously validate a model for region-to-region exchange of water. From the determined exchange times, the corresponding length scales were calculated based on the molecular self-diffusion of water; these agreed to better than +/-25% with the expected domain sizes. Furthermore, exchange distances on the order of the pore size were observed in thoroughly mixed systems. Depending on the relaxation rates present in the sample, this technique can provide estimates of length scales ranging from microns to millimeters. PMID:18154403

Mitchell, J; Griffith, J D; Collins, J H P; Sederman, A J; Gladden, L F; Johns, M L

2007-12-21

27

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.

28

The scaling of the dielectric and electric relaxation in two low molecular weight glass forming liquids  

NASA Astrophysics Data System (ADS)

The scaling of the dielectric and electric relaxation in two low molecular weight glass forming systems (PDE=Phenolphtalein-dimethylether and KDE=Kresolphtalein-di-methylether) is studied in the frequency regime from 10 -3 Hz to 10 9 Hz by use of broadband dielectric spectroscopy. For both the dielectric ?-relaxation and the dc-conductivity the temperature dependence is characterised by a crossover (at a temperature TA) from an Arrhenius to a Vogel-Fulcher-Tammann law. Above TA the dc-conductivity (reflecting translational diffusion of mobile charge carriers) and the ?-relaxation have the same temperature dependence. Below TA a decoupling is found in agreement with recent tracer diffusion experiments (M. Lohfink and H. Sillescu, in: Proc. of the 1st Tohwa University Int. Symp., Fukuoka, Japan, 4-8.11.1991, Am. Inst. Phys. Conf. Series). For the ?-relaxation, the relaxation time distribution shows a pronounced temperature dependence below TA, while it is only weakly varying with temperature above TA.

Stickel, F.; Kremer, F.; Fischer, E. W.

1993-12-01

29

A quantum relaxation-time approximation for finite fermion systems  

E-print Network

We propose a relaxation time approximation for the description of the dynamics of strongly excited fermion systems. Our approach is based on time-dependent density functional theory at the level of the local density approximation. This mean-field picture is augmented by collisional correlations handled in relaxation time approximation which is inspired from the corresponding semi-classical picture. The method involves the estimate of microscopic relaxation rates/times which is presently taken from the well established semi-classical experience. The relaxation time approximation implies evaluation of the instantaneous equilibrium state towards which the dynamical state is progressively driven at the pace of the microscopic relaxation time. As test case, we consider Na clusters of various sizes excited either by a swift ion projectile or by a short and intense laser pulse, driven in various dynamical regimes ranging from linear to strongly non-linear reactions. We observe a strong effect of dissipation on sensi...

Reinhard, P -G

2014-01-01

30

Modeling dependence of creep recovery behavior on relaxation time distribution of ageing colloidal suspensions  

E-print Network

A scaling model is developed to correlate relaxation time distribution of soft glassy materials to ultimate recovery. We propose that in the limit of creep-recovery time smaller than age, time translational invariance can be applied to ageing soft materials. In such limit, multimode linear viscoelastic model with Spriggs relaxation spectrum predicts enhancement in the ultimate recovery with broadening of the relaxation time distribution. We analyze these results in the context of creep-recovery behavior of aqueous suspension of laponite with varying concentration of salt.

Yogesh M. Joshi

2009-02-06

31

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

32

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

33

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

34

Two relaxation time lattice Boltzmann model for rarefied gas flows  

NASA Astrophysics Data System (ADS)

In this paper, the lattice Boltzmann equation (LBE) with two relaxation times (TRT) is implemented in order to study gaseous flow through a long micro/nano-channel. A new relation is introduced for the reflection factor in the bounce-back/specular reflection (BSR) boundary condition based on the analytical solution of the Navier-Stokes equations. The focus of the present study is on comparing TRT with the other LBE models called multiple relaxation times (MRT) and single relaxation time (SRT) in simulation of rarefied gas flows. After a stability analysis for the TRT and SRT models, the numerical results are presented and validated by the analytical solution of the Navier-Stokes equations with slip boundary condition, direct simulation of Monte Carlo (DSMC) and information preservation (IP) method. The effect of various gases on flow behavior is also investigated by using the variable hard sphere (VHS) model through the symmetrical relaxation time.

Esfahani, Javad Abolfazli; Norouzi, Ali

2014-01-01

35

Multiple-Relaxation-Time Lattice Boltzmann Models in 3D  

NASA Technical Reports Server (NTRS)

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 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.

dHumieres, Dominique; Ginzburg, Irina; Krafczyk, Manfred; Lallemand, Pierre; Luo, Li-Shi; Bushnell, Dennis M. (Technical Monitor)

2002-01-01

36

Viscoplasticity and large-scale chain relaxation in glassy-polymeric strain hardening  

E-print Network

A simple theory for glassy polymeric mechanical response which accounts for large scale chain relaxation is presented. It captures the crossover from perfect-plastic response to strong strain hardening as the degree of polymerization $N$ increases, without invoking entanglements. By relating hardening to interactions on the scale of monomers and chain segments, we correctly predict its magnitude. Strain activated relaxation arising from the need to maintain constant chain contour length reduces the $N$ dependence of the characteristic relaxation time by a factor $\\sim \\dot\\epsilon N$ during active deformation at strain rate $\\dot\\epsilon$. This prediction is consistent with results from recent experiments and simulations, and we suggest how it may be further tested experimentally.

Robert S. Hoy; Corey S. O'Hern

2010-04-03

37

ANALYSIS OF A PAIR OF RELAXATION OSCILLATORS WITH TIME DELAYS  

E-print Network

143 APPENDIX B ANALYSIS OF A PAIR OF RELAXATION OSCILLATORS WITH TIME DELAYS For regions II and III the oscillators decreases. In region IV, we find that the time difference between the oscillators decreases only. This region is bounded by , where we use to denote the ini- tial time difference between the two oscillators

Wang, DeLiang "Leon"

38

Nonequilibrium relaxation and aging scaling of the Coulomb and Bose glass  

NASA Astrophysics Data System (ADS)

We employ Monte Carlo simulations to investigate the nonequilibrium relaxation properties of the two- and three-dimensional Coulomb glass with different long-range repulsive interactions. Specifically, we explore the aging scaling laws in the two-time density autocorrelation function. We find that, in the time window and parameter range accessible to us, the scaling exponents are not universal, depending on the filling fraction and temperature: As either the temperature decreases or the filling fraction deviates more from half filling, the exponents reflect markedly slower relaxation kinetics. In comparison with a repulsive Coulomb potential, appropriate for impurity states in strongly disordered semiconductors, we observe that, for logarithmic interactions, the soft pseudogap in the density of states is considerably broader, and the dependence of the scaling exponents on external parameters is much weaker. The latter situation is relevant for flux creep in the disorder-dominated Bose glass phase of type-II superconductors subject to columnar pinning centers.

Shimer, Matthew T.; Täuber, Uwe C.; Pleimling, Michel

2014-09-01

39

Evaluation of brain edema using magnetic resonance proton relaxation times.  

PubMed

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. PMID:2396512

Fu, Y; Tanaka, K; Nishimura, S

1990-01-01

40

Multi-Relaxation Time Lattice Boltzmann Model for Multiphase Flows  

NASA Astrophysics Data System (ADS)

Multi-relaxation time (MRT) for Lattice Boltzmann method is gaining renewed attention among researchers in the field. The advantage of such formulation over the widely popular single-time relaxation version, is twofold: better numerical stability and wider span of physical applications, extending to non-isotropic flows. In this work, the numerical advantages of the MRT model versus single-relaxation time (BGK) operator are quantitatively assessed through direct numerical simulations of droplet formation and capillary wave propagation on interphase boundaries. The results show that by proper tuning of the collision operator, and particularly of the higher-order kinetic modes (ghosts), appreciable improvements in stability limits, of the order of 20%, and viscosity limits, of the order of 80%, can be achieved. Moreover, a theoretical analysis accounting for the reasons behind such stability improvement, is also presented.

Kuzmin, A.; Mohamad, A. A.; Succi, S.

41

RELAXATION OSCILLATORS WITH TIME DELAY COUPLING 4.1 Introduction  

E-print Network

79 CHAPTER 4 RELAXATION OSCILLATORS WITH TIME DELAY COUPLING 4.1 Introduction Thus far we have studied synchronization in networks of locally coupled neurobiolog- ically based oscillator models. One are 1mm apart may have a time delay of approximately 4% of the period of oscillation (assuming 40 Hz

Wang, DeLiang "Leon"

42

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.

43

Relaxation Time of Artificial Periodic Irregularities of the Ionospheric Plasma and Diffusion in the Inhomogeneous Atmosphere  

NASA Astrophysics Data System (ADS)

We consider diffusion of the ionospheric-plasma irregularities as applied to the problem of experimental determination of the lower-ionosphere parameters by artificial periodic irregularities of the electron number density. A rigorous solution to the problem of diffusion of one-dimensional plasma irregularities in a weakly ionized medium, whose diffusion coefficient exponentially decreases with the altitude, is obtained. The Green's function for this problem is found. Three parameters are taken into account in the solution, namely, the size of the region occupied by the irregularities, the size of the irregularities, and a typical spatial scale of the e-fold decrease in the diffusion coefficient. Theoretical relaxation times of the irregularities as functions of these parameters are analyzed. Calculated relaxation times are compared with the times measured in the observation of the artificial periodic irregularities created by the SURA facility. Calculated relaxation times of these irregularities are in good agreement with the observed values.

Grigor'ev, G. I.; Bakhmet'eva, N. V.; Tolmacheva, A. V.; Kalinina, E. E.

2013-09-01

44

A boxcar integrator for pulsed NMR relaxation time measurements  

Microsoft Academic Search

A two-channel analogue boxcar integrator is constructed by using integrated circuits and MOST gates. A ratio of two NMR fee-induction signals can be measured and thus the spin-lattice relaxation time T1 can be obtained without any calculation by comparing output voltages of the channels by the null method.

L. Niemela

1972-01-01

45

Modeling the relaxation time of DNA confined in a nanochannel.  

PubMed

Using a mapping between a Rouse dumbbell model and fine-grained Monte Carlo simulations, we have computed the relaxation time of ?-DNA in a high ionic strength buffer confined in a nanochannel. The relaxation time thus obtained agrees quantitatively with experimental data [Reisner et al., Phys. Rev. Lett. 94, 196101 (2005)] using only a single O(1) fitting parameter to account for the uncertainty in model parameters. In addition to validating our mapping, this agreement supports our previous estimates of the friction coefficient of DNA confined in a nanochannel [Tree et al., Phys. Rev. Lett. 108, 228105 (2012)], which have been difficult to validate due to the lack of direct experimental data. Furthermore, the model calculation shows that as the channel size passes below approximately 100?nm (or roughly the Kuhn length of DNA) there is a dramatic drop in the relaxation time. Inasmuch as the chain friction rises with decreasing channel size, the reduction in the relaxation time can be solely attributed to the sharp decline in the fluctuations of the chain extension. Practically, the low variance in the observed DNA extension in such small channels has important implications for genome mapping. PMID:24309551

Tree, Douglas R; Wang, Yanwei; Dorfman, Kevin D

2013-01-01

46

Scaling and relaxational dynamics near Kondo-destroying quantum critical points  

NASA Astrophysics Data System (ADS)

We study the finite-temperature dynamical scaling in the vicinity of the Kondo-destroying quantum critical points in two quantum impurity models. For the pseudogap Anderson model, we use a combination of renormalization group, continuous time quantum Monte Carlo and large-N techniques to obtain the complete scaling functions of the local susceptibility and single-electron Green's function both in the coherent ( ?>T) and relaxational ( ?relaxation rate is linear in temperature for both quantities. The result for the Green's function is reminiscent of recent experimental findings in the Kondo-destroying quantum critical point of heavy fermion metals [2]. For the Bose-Fermi Kondo model, we report related results derived from the continuous time quantum Monte Carlo and large-N methods. [4pt] [1] M. T. Glossop, S. Kirchner, J. H. Pixley, and Q.Si, ``Critical Kondo destruction in a pseudogap Anderson model: scaling and relaxational dynamics,'' to be published (2009). [0pt] [2] S. Friedemann et al., to be published (2009).

Pixley, Jedediah; Glossop, Matthew; Kirchner, Stefan; Si, Qimiao

2010-03-01

47

Inversion of generalized relaxation time distributions with optimized damping parameter  

NASA Astrophysics Data System (ADS)

Retrieving the Relaxation Time Distribution (RDT), the Grains Size Distribution (GSD) or the Pore Size Distribution (PSD) from low-frequency impedance spectra is a major goal in geophysics. The “Generalized RTD” generalizes parametric models like Cole-Cole and many others, but remains tricky to invert since this inverse problem is ill-posed. We propose to use generalized relaxation basis function (for instance by decomposing the spectra on basis of generalized Cole-Cole relaxation elements instead of the classical Debye basis) and to use the L-curve approach to optimize the damping parameter required to get smooth and realistic inverse solutions. We apply our algorithm to three examples, one synthetic and two real data sets, and the program includes the possibility of converting the RTD into GSD or PSD by choosing the value of the constant connecting the relaxation time to the characteristic polarization size of interest. A high frequencies (typically above 1 kHz), a dielectric term in taken into account in the model. The code is provided as an open Matlab source as a supplementary file associated with this paper.

Florsch, Nicolas; Revil, André; Camerlynck, Christian

2014-10-01

48

Electron-spin relaxation times of chromium(V)  

NASA Astrophysics Data System (ADS)

The electron-spin relaxation times of four Cr(V) complexes have been measured by time-domain methods from 10 to 220 K for T1 and from 80 to 220 K for TM. The magnitudes and temperature dependence of the relaxation times are more similar to those of simple organic radicals than those of transition metals. Specific comparison is made to the relaxation times of nitroxyl radicals. For the nitroxyl radical and three of the Cr(V) complexes, the temperature dependence of the phase memory time, TM, in 1:1 water: glycerol between 80 and 160 K is attributed to the effects of methyl group rotation. The activation energy for the methyl group rotation is 2 kcal/mol for the nitroxyl, 1.5 kcal/mol for a methyl group on the Cr(V) chelate ring, and 1.0 kcal / mol for the methyl of an ethyl group on the Cr(V) chelate ring.

Nakagawa, Kouichi; Candelaria, Matthew B.; Chik, Wilson W. C.; Eaton, Sandra S.; Eaton, Gareth R.

49

Cell water dynamics on multiple time scales.  

PubMed

Water-biomolecule interactions have been extensively studied in dilute solutions, crystals, and rehydrated powders, but none of these model systems may capture the behavior of water in the highly organized intracellular milieu. Because of the experimental difficulty of selectively probing the structure and dynamics of water in intact cells, radically different views about the properties of cell water have proliferated. To resolve this long-standing controversy, we have measured the (2)H spin relaxation rate in living bacteria cultured in D(2)O. The relaxation data, acquired in a wide magnetic field range (0.2 mT-12 T) and analyzed in a model-independent way, reveal water dynamics on a wide range of time scales. Contradicting the view that a substantial fraction of cell water is strongly perturbed, we find that approximately 85% of cell water in Escherichia coli and in the extreme halophile Haloarcula marismortui has bulk-like dynamics. The remaining approximately 15% of cell water interacts directly with biomolecular surfaces and is motionally retarded by a factor 15 +/- 3 on average, corresponding to a rotational correlation time of 27 ps. This dynamic perturbation is three times larger than for small monomeric proteins in solution, a difference we attribute to secluded surface hydration sites in supramolecular assemblies. The relaxation data also show that a small fraction ( approximately 0.1%) of cell water exchanges from buried hydration sites on the microsecond time scale, consistent with the current understanding of protein hydration in solutions and crystals. PMID:18436650

Persson, Erik; Halle, Bertil

2008-04-29

50

Temperature of the magnetic nanoparticle microenvironment: estimation from relaxation times.  

PubMed

Accurate temperature measurements are essential to safe and effective thermal therapies for cancer and other diseases. However, conventional thermometry is challenging so using the heating agents themselves as probes allows for ideal local measurements. Here, we present a new noninvasive method for measuring the temperature of the microenvironment surrounding magnetic nanoparticles from the Brownian relaxation time of nanoparticles. Experimentally, the relaxation time can be determined from the nanoparticle magnetization induced by an alternating magnetic field at various applied frequencies. A previously described method for nanoparticle temperature estimation used a low frequency Langevin function description of magnetic dipoles and varied the excitation field amplitude to estimate the energy state distribution and the corresponding temperature. We show that the new method is more accurate than the previous method at higher applied field frequencies that push the system farther from equilibrium. PMID:24556943

Perreard, I M; Reeves, D B; Zhang, X; Kuehlert, E; Forauer, E R; Weaver, J B

2014-03-01

51

Determining pore length scales and pore surface relaxivity of rock cores by internal magnetic fields modulation at 2 MHz NMR  

NASA Astrophysics Data System (ADS)

Pore length scales and pore surface relaxivities of rock cores with different lithologies were studied on a 2 MHz Rock Core Analyzer. To determine the pore length scales of the rock cores, the high eigenmodes of spin bearing molecules satisfying the diffusion equation were detected with optimized encoding periods in the presence of internal magnetic fields Bin. The results were confirmed using a 64 MHz NMR system, which supports the feasibility of high eigenmode detection at fields as low as 2 MHz. Furthermore, this methodology was combined with relaxometry measurements to a two-dimensional experiment, which provides correlation between pore length and relaxation time. This techniques also yields information on the surface relaxivity of the rock cores. The estimated surface relaxivities were then compared to the results using an independent NMR method.

Liu, Huabing; Nogueira d'Eurydice, Marcel; Obruchkov, Sergei; Galvosas, Petrik

2014-09-01

52

Determining pore length scales and pore surface relaxivity of rock cores by internal magnetic fields modulation at 2MHz NMR.  

PubMed

Pore length scales and pore surface relaxivities of rock cores with different lithologies were studied on a 2MHz Rock Core Analyzer. To determine the pore length scales of the rock cores, the high eigenmodes of spin bearing molecules satisfying the diffusion equation were detected with optimized encoding periods in the presence of internal magnetic fields Bin. The results were confirmed using a 64MHz NMR system, which supports the feasibility of high eigenmode detection at fields as low as 2MHz. Furthermore, this methodology was combined with relaxometry measurements to a two-dimensional experiment, which provides correlation between pore length and relaxation time. This techniques also yields information on the surface relaxivity of the rock cores. The estimated surface relaxivities were then compared to the results using an independent NMR method. PMID:25123539

Liu, Huabing; Nogueira d'Eurydice, Marcel; Obruchkov, Sergei; Galvosas, Petrik

2014-09-01

53

Spin-rotation contribution to the relaxation time of the fluorine nuclei in benzotrifluoride  

E-print Network

to the relaxa- tion time from data on the relaxation time of the hydrogen nuclei in both the pure benzotrifluoride and in a solution of benzotrifluoride and carbon disulfide, since carbon disulfide contains no magnetic dipoles, and since it is assumed...-rotation contribution to the relaxation time, the average moment of inertia, and the correlation time for 13 molecular orientation. In order to separate the various contributions to the relaxation time as outlined above, the relaxation time of the hydrogen nuclei...

Faulk, Robert Hardy

2012-06-07

54

Design of self-refocused pulses under short relaxation times.  

PubMed

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 Bloch equations. These equations are inverted by searching the RF solution space using simulated annealing global optimization technique. A new T2-decay efficient excitation pulse is created (SDETR: single delayed excursion T2 resistive) which is also energy efficient. Inversion pulses which improve the inverted magnetization profile and achieve better suppression of the remaining transverse magnetization are also created even when both T1 and T2 are short. This is achieved, however, on the expense of a more complex B1 shape of larger energy content. PMID:19272823

Issa, Bashar

2009-06-01

55

Vibrational relaxation, dissociation, and dissociation incubation times in norbornene  

SciTech Connect

Shock waves in norbornene (bicyclo [2,2,1] hept-2-ene, C[sub 7]H[sub 10])--krypton mixtures have been examined with the laser-schlieren technique over the very wide range of conditions, 542--1480 K, and 34--416 Torr in 0.5%, 2%, and 4% C[sub 7]H[sub 10]. The experiments exhibit both vibrational relaxation (542--1480 K) and the retro-Diels--Alder dissociation, norbornene[r arrow]1,3-cyclopentadiene+ethylene (869--1480 K). Over 869--1304 K, and for pressures below 140 Torr, both relaxation and dissociation are resolved. These experiments provide the first measurements of unimolecular incubation (induction) times for the dissociation of a large polyatomic molecule. The ratio [ital t][sub [ital i

Kiefer, J.H.; Kumaran, S.S.; Sundaram, S. (Department of Chemical Engineering, University of Illinois at Chicago, Chicago, Illinois 60680 (United States))

1993-09-01

56

Comparison of methods for the calculation of superparamagnetic relaxation times  

NASA Astrophysics Data System (ADS)

A general expression for the correlation time of the decay of the magnetization of an assembly of single-domain noninteracting ferromagnetic particles is given in terms of the inverse of the Fokker-Planck operator. The results of Moro and Nordio [G. Moro and P. L. Nordio, Mol. Phys. 56, 255 (1985)], given in the context of dielectric relaxation, are recovered when the Fokker-Planck operator is axially symmetric. Their result is a particular example of Szabo's calculation of the correlation times of the autocorrelation functions of the Legendre polynomials by means of a generalization of the theory of first-passage times [A. Szabo, J. Chem. Phys. 72, 4620 (1980)]. Likewise, the results of Garanin, Ischenko, and Panina (D. A. Garanin, V. V. Ischenko, and L. V. Panina, Teor. Mat. Fiz. 82, 242 (1990) [Theor. Math. Phys. 82, 169 (1990)]) for the integral relaxation time, i.e., the area under the curve of the normalized decay of the magnetization, are regained in the axially symmetric case where it is possible to integrate the Fokker-Planck equation directly. It is shown by manipulation of Kummer's functions that the exact integral expression for the correlation time for simple uniaxial anisotropy derived by Coffey et al. [W. T. Coffey, D. S. F. Crothers, Yu. P. Kalmykov, E. S. Massawe, and J. T. Waldron. Phys. Rev. E 49, 1869 (1994)] by representing the Fokker-Planck equation as a differential-recurrence relation is identical to the integral relaxation time originally derived by Garanin et al. by direct integration of the Fokker-Planck equation.

Coffey, W. T.; Crothers, D. S. F.

1996-11-01

57

Life-time prediction of a chloroprene rubber (CR) O-ring using intermittent compression stress relaxation (CSR) and time-temperature superposition (TTS) Principle  

Microsoft Academic Search

Intermittent compression stress relaxation (CSR) testing was used to examine the degradation of a large scale chloroprene\\u000a rubber (CR) O-ring, rather than a reduced scale copy, as well as predict its life-time. An intermittent CSR jig was designed\\u000a by considering the O-ring’s environment during use. The testing allowed the observation of the effects of friction, heat loss\\u000a and stress relaxation

Jin Hyok Lee; Jong Woo Bae; Jung Su Kim; Tae Jun Hwang; Sung Doo Park; Sung Han Park; Tae Min Yeo; Wonho Kim; Nam-Ju Jo

2011-01-01

58

Interfacial mobility scale determines the scale of collective motion and relaxation rate in polymer films  

NASA Astrophysics Data System (ADS)

Thin polymer films are ubiquitous in manufacturing and medical applications, and there has been intense interest in how film thickness and substrate interactions influence film dynamics. It is appreciated that a polymer-air interfacial layer with enhanced mobility plays an important role in the observed changes and recent studies suggest that the length scale ? of this interfacial layer is related to film relaxation. In the context of the Adam-Gibbs and random first-order transition models of glass formation, these results provide indirect evidence for a relation between ? and the scale of collective molecular motion. Here we report direct evidence for a proportionality between ? and the average length L of string-like particle displacements in simulations of polymer films supported on substrates with variable interaction strength and rigidity. This relation explicitly links ? to the theoretical scale of cooperatively rearranging regions, offering a promising route to experimentally determine this scale of cooperative motion.

Hanakata, Paul Z.; Douglas, Jack F.; Starr, Francis W.

2014-06-01

59

Diffusion MRI/NMR magnetization equations with relaxation times  

NASA Astrophysics Data System (ADS)

Bloch-Torrey diffusion magnetization equation ignores relaxation effects of magnetization. Relaxation times are important in any diffusion magnetization studies of perfusion in tissues(Brain and heart specially). Bloch-Torrey equation cannot therefore describe diffusion magnetization in a real-life situation where relaxation effects play a key role, characteristics of tissues under examination. This paper describes derivations of two equations for each of the y and z component diffusion NMR/MRI magnetization (separately) in a rotating frame of reference, where rf B1 field is applied along x direction and bias magnetic field(Bo) is along z direction. The two equations are expected to further advance the science & technology of Diffusion MRI(DMRI) and diffusion functional MRI(DFMRI). These two techniques are becoming increasingly important in the study and treatment of neurological disorders, especially for the management of patients with acute stroke. It is rapidly becoming a standard for white matter disorders, as diffusion tensor imaging (DTI) can reveal abnormalities in white matter fibre structure and provide models of brain connectivity.

de, Dilip; Daniel, Simon

2012-10-01

60

Measurements of nuclear thermal relaxation times under conditions of high resolution  

E-print Network

. . . ?0 TABLE OF CONTENTS CHAPTER PAGE V. DATA AND RESULTS (continued) Thermal Relaxation Times of Proton Groups in Pure Organic Liquids.................... 51 Variation of the Relaxation Time with Dilution............ .................. M VI.... Graphical method used to determine the relaxation time T ^ .................... .. . **9 3. Variation of the reciprocal of the thermal relaxation time of the methyl and ring protons of toluene in carbon disulfide. . . . 59 LIST OF TABLES TABLES PAGE 1...

Hildebrandt, Alvin Frank

2013-10-04

61

Relaxation Times of Nano-Colloid Flocculation Induced by Adsorbing and Non-adsorbing Polymers  

E-print Network

Relaxation Times of Nano-Colloid Flocculation Induced by Adsorbing and Non-adsorbing Polymers investigated the relaxation times of the colloid flocculation assisted by the adsorbing and non: relaxation time, flocculation, polymer mediated interaction, nano-colloids. PACS: 82.35.Gh , 82.35.Lr

Ahlers, Guenter

62

Time scales in LISA  

E-print Network

The LISA mission is a space interferometer aiming at the detection of gravitational waves in the [$10^{-4}$,$10^{-1}$] Hz frequency band. In order to reach the gravitational wave detection level, a Time Delay Interferometry (TDI) method must be applied to get rid of (most of) the laser frequency noise and optical bench noise. This TDI analysis is carried out in terms of the coordinate time corresponding to the Barycentric Coordinate Reference System (BCRS), TCB, whereas the data at each of the three LISA stations is recorded in terms of each station proper time. We provide here the required proper time versus BCRS time transformation. We show that the difference in rate of station proper time versus TCB is of the order of $5 10^{-8}$. The difference between station proper times and TCB exhibits an oscillatory trend with a maximum amplitude of about $10^{-3}$ s.

S. Pireaux

2007-03-23

63

Rapid MRI method for mapping the longitudinal relaxation time  

NASA Astrophysics Data System (ADS)

A novel method for mapping the longitudinal relaxation time in a clinically acceptable time is developed based on a recent proposal [J.-J. Hsu, I.J. Lowe, Spin-lattice relaxation and a fast T1-map acquisition method in MRI with transient-state magnetization, J. Magn. Reson. 169 (2004) 270-278] and the speed of the spiral pulse sequence. The method acquires multiple curve-fitting samples with one RF pulse train. It does not require RF pulses of specific flip angles (e.g., 90° or 180°), nor are the long recovery waiting time and the measurement of the magnetization at thermal equilibrium needed. Given the value of the flip angle, the curve fitting is semi-logarithmic and not computationally intensive. On a heterogeneous phantom, the average percentage difference between measurements of the present method and those of an inversion-recovery method is below 2.7%. In mapping the human brain, the present method, for example, can obtain four curve-fitting samples for five 128 × 128 slices in less than 3.2 s and the results are in agreement with other studies in the literature.

Hsu, Jung-Jiin; Glover, Gary H.

2006-07-01

64

Observation of long spin-relaxation times in bilayer graphene at room temperature.  

PubMed

We report on the first systematic study of spin transport in bilayer graphene (BLG) as a function of mobility, minimum conductivity, charge density, and temperature. The spin-relaxation time ?(s) scales inversely with the mobility ? of BLG samples both at room temperature (RT) and at low temperature (LT). This indicates the importance of D'yakonov-Perel' spin scattering in BLG. Spin-relaxation times of up to 2 ns at RT are observed in samples with the lowest mobility. These times are an order of magnitude longer than any values previously reported for single-layer graphene (SLG). We discuss the role of intrinsic and extrinsic factors that could lead to the dominance of D'yakonov-Perel' spin scattering in BLG. In comparison to SLG, significant changes in the carrier density dependence of ?(s) are observed as a function of temperature. PMID:21867039

Yang, T-Y; Balakrishnan, J; Volmer, F; Avsar, A; Jaiswal, M; Samm, J; Ali, S R; Pachoud, A; Zeng, M; Popinciuc, M; Güntherodt, G; Beschoten, B; Özyilmaz, B

2011-07-22

65

Geologic time scale bookmark  

USGS Publications Warehouse

This bookmark, designed for use with U.S. Geological Survey activities at the 2nd USA Science and Engineering Festival (April 26–29, 2012), is adapted from the more detailed Fact Sheet 2010–3059 "Divisions of Geologic Time." The information that it presents is widely sought by educators and students.

U.S. Geological Survey

2012-01-01

66

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

67

Calculation of vibrational relaxation times in multi-component excitable gases  

NASA Astrophysics Data System (ADS)

In the research field of acoustic propagation in excitable gases, one of the most critical parameters is the vibrational relaxation time, which determines the frequency of the acoustic dispersion step or the absorption maximum. In this paper, the vibrational relaxation equations given by Tanczos [J. Chem. Phys. 25, 439 (1956)] have been applied to calculate the vibrational multi-relaxation times in multi-component gases. The eigenvalues of the energy-transition-rate matrix are proven to be the reciprocals of the multi-relaxation times. Comparisons demonstrate that our relaxation frequencies calculated for various gas compositions, including carbon dioxide, methane, chlorine, nitrogen, and oxygen, agree with the experimental data.

Zhang, Ke-Sheng; Ou, Weihua; Jiang, Xueqin; Long, Fei; Hu, Mingzhe

2014-10-01

68

Characteristic relaxation times and their invariance to thermodynamic conditions  

E-print Network

and the forces between molecules. The relaxation behavior also governs to a large extent the physical. Representa- tive data are shown in Fig. 1 for a poly- mer, atactic-polypropylene (aPP),1 and a molecular

Weeks, Eric R.

69

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.

Wenner, Jennifer M.

2011-04-25

70

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

71

Long-time relaxation in pilot-wave theory  

NASA Astrophysics Data System (ADS)

We initiate the study of relaxation to quantum equilibrium over long timescales in pilot-wave theory. We simulate the time evolution of the coarse-grained H-function \\bar{H}(t) for a two-dimensional harmonic oscillator. For a (periodic) wave function that is a superposition of the first 25 energy states we confirm an approximately exponential decay of \\bar{H} over five periods. For a superposition of only the first four energy states we are able to calculate \\bar{H}(t) over 50 periods. We find that, depending on the set of phases in the initial wave function, \\bar{H} can decay to a large nonequilibrium residue exceeding 10% of its initial value or it can become indistinguishable from zero (the equilibrium value). We show that a large residue in \\bar{H} is caused by a tendency for the trajectories to be confined to sub-regions of configuration space for some wave functions, and that this is less likely to occur for larger numbers of energy states (if the initial phases are chosen randomly). Possible cosmological implications are briefly discussed.

Abraham, Eitan; Colin, Samuel; Valentini, Antony

2014-10-01

72

Fundamental studies of stress distributions and stress relaxation in oxide scales on high temperature alloys  

SciTech Connect

The high temperature X-ray diffraction system developed for this program is being used to measure the strains which develop during oxidation. This is being applied to Ni/NiO and Cr/Cr[sub 2]O[sub 3]. Our work suggests tat the oxide and metal crystalline texture, anisotropic elastic modulus and anisotropic thermal expansion can have a pronounced effect on strain state of these systems. Acoustic emission is being used to study oxide scale failure (fracture) during oxidation. AE data from 304 stainless steel are being used to develop a statistical model of fracture process. Strength of metal/scale interface is an important property that has been difficult to quantify. Using Nano-indentation and scratch techniques developed for characterizing thin film interfaces, an effort has begun to measure the fracture toughness of the metal/scale interface. Mathematical modelling of origin and time evolution of growth stresses is an extension and improvement of previous models. The current effort employs a more sophisticated stress analysis and expands the scope to include other stress relaxation process. The interaction between the modeling studies and the X-ray diffraction measurements provides a natural credibility check to both efforts.

Shores, D.A.; Stout, J.H.; Gerberich, W.W.

1992-06-01

73

Time Scales in Evolutionary Dynamics  

Microsoft Academic Search

Evolutionary game theory has traditionally assumed that all individuals in a population interact with each other between reproduction events. We show that eliminating this restriction by explicitly consid- ering the time scales of interaction and selection leads to dramatic changes in the outcome of evolution. Examples include the selection of the inefficient strategy in the Harmony and Stag-Hunt games, and

Carlos P. Roca; Angel Sanchez

2006-01-01

74

A High-Speed Delta-Sigma Modulator with Relaxed DEM Timing Requirement  

E-print Network

presents a high-speed digital feed- forward Delta-Sigma Modulator which relaxes timing requirement accurate transfer functions and highly linear analog-to-digital conversion. However, the performanceA High-Speed Delta-Sigma Modulator with Relaxed DEM Timing Requirement Sunwoo Kwon and Un-Ku Moon

Moon, Un-Ku

75

Determination of the transversal relaxation times in MRI using the FID-modulation method  

NASA Astrophysics Data System (ADS)

Experimental measurements of relaxation time, T2 and T2* were performed in a home-built nuclear magnetic resonance system at 0.5T. The FID-modulation method was employed and results compared with those reported in the literature. This method is intended to use to measure relaxation times of biological specimens.

Nava-Juarez, R. F.; Hernandez, R.; Rodriguez, A. O.

2012-10-01

76

MRI Under Hyperbaric Air and Oxygen: Effects on Local Magnetic Field and Relaxation Times  

E-print Network

,2,3,4,6 * Purpose: Hyperbaric oxygen therapy has shown efficacies in the treatment of a number of diseases. The goal; T2*; relaxation time constants INTRODUCTION Hyperbaric oxygen (HBO) therapy has been used to treatNOTE MRI Under Hyperbaric Air and Oxygen: Effects on Local Magnetic Field and Relaxation Times Eric

Duong, Timothy Q.

77

Dielectric relaxation study of mixtures of alkyl methacrylates and 1-alcohols using time-domain reflectometry  

NASA Astrophysics Data System (ADS)

Dielectric relaxation measurements on alkyl methacrylates (methyl methacrylate, ethyl methacrylate and butyl methacrylate) with 1-alcohols (1-propanol, 1-pentanol, 1-heptanol, 1-octanol and 1-decanol) have been carried out using time-domain reflectometry (TDR) over the frequency range 10?MHz to 20?GHz at 303?K for different concentrations of alcohols. The dielectric parameters, namely the static dielectric constant (?0), the dielectric constant at microwave frequencies (??) and the relaxation time (?) were determined. The Kirkwood correlation factor, which contains information regarding solute-solvent interaction and corresponding structural information, the excess permittivity and the excess inverse relaxation time were also determined. The values of the static dielectric constant and the relaxation time increase with the percentage of alkyl methacrylates in the alcohol, whereas the static dielectric constant decreases and the relaxation time increases with an increase in the alkyl chain length of both the methacrylates and the alcohols.

Sivagurunathan, P.; Dharmalingam, K.; Ramachandran, K.; Prabhakar Undre, B.; Khirade, P. W.; Mehrotra, S. C.

2006-05-01

78

Relaxation-time approximation and relativistic viscous hydrodynamics from kinetic theory  

E-print Network

Using the iterative solution of Boltzmann equation in the relaxation-time approximation, the derivation of a third-order evolution equation for shear stress tensor is presented. To this end we first derive the expression for viscous corrections to the phase-space distribution function, $f(x,p)$, up to second-order in derivative expansion. The expression for $\\delta f(x,p)$ obtained in this method does not lead to violation of the experimentally observed $1/\\sqrt{m_T}$ scaling of the femtoscopic radii, as opposed to the widely used Grad's 14-moment approximation. Subsequently, we present the derivation of a third-order viscous evolution equation and demonstrate the significance of this derivation within one-dimensional scaling expansion. We show that results obtained using third-order evolution equations are in excellent accordance with the exact solution of Boltzmann equation as well as with transport results.

Amaresh Jaiswal

2014-07-03

79

Ageing and relaxation times in disordered insulators , J. Delahaye1  

E-print Network

aluminum films). They manifest themselves as a temporal logarithmic decrease of the conductance after features, involving slow relaxations of the electrical conductance, as well as electrical field effect to liquid He temperature, its electrical conductance is never stable and always decreases logarithmically

Paris-Sud XI, Université de

80

Scales to Measure Four Dimensions of Dispositional Mood: Positive Energy, Tiredness, Negative Activation, and Relaxation  

Microsoft Academic Search

The present study addresses the measurement of trait mood by examining a set of new scales to measure four separate dimensions: positive energy, tiredness, negative arousal, and relaxation. The data were divided into two halves. On the first half of the data, separate exploratory factor analyses were performed for each dimension using 15 items chosen from various sources to represent

Timothy J. Huelsman; Richard C. Nemanick; David C. Munz

1998-01-01

81

Time Scales in Evolutionary Dynamics  

Microsoft Academic Search

Evolutionary game theory has traditionally assumed that all individuals in a\\u000apopulation interact with each other between reproduction events. We show that\\u000aeliminating this restriction by explicitly considering the time scales of\\u000ainteraction and selection leads to dramatic changes in the outcome of\\u000aevolution. Examples include the selection of the inefficient strategy in the\\u000aHarmony and Stag-Hunt games, and the

Carlos P. Roca; Jose A. Cuesta; Angel Sánchez

2006-01-01

82

Timing the ischaemic stroke by 1H-MRI: improved accuracy using absolute relaxation times over signal intensities.  

PubMed

One in four ischaemic stroke patients are ineligible for thrombolytic treatment due to unknown onset time. Quantification of absolute MR relaxation times and signal intensities are potential methods for estimating stroke duration. We compared the accuracy of these approaches and determined whether changes in relaxation times and signal intensities identify the same ischaemic tissue as diffusion MRI. Seven Wistar rats underwent permanent middle cerebral artery occlusion to induce focal ischaemia and were scanned at six time points. The trace of the diffusion tensor (DAV), T1? and T2 were acquired at 4.7?T. Results show relaxation times, and signal intensities of the MR relaxation parameters increase linearly with ischaemia duration (P<0.001). Using T1? and T2 relaxation times, an estimate of 4.5?h after occlusion has an uncertainty of ±12 and ±35?min, respectively, compared with over 50?min for signal intensities. In addition, we present a pixel-by-pixel method that simultaneously estimates stroke onset time and identifies potentially irreversible ischaemic tissue using absolute relaxation times. This method demonstrates signal intensity changes during ischaemia display an ambiguous pattern and highlights the possibility that diffusion MRI overestimates the true extent of irreversible ischaemia. In conclusion, quantification of absolute relaxation times at a single time point enables a more accurate estimation of stroke duration than signal intensities and provides more information about tissue status in ischaemia. PMID:25116145

Rogers, Harriet J; McGarry, Bryony L; Knight, Michael J; Jokivarsi, Kimmo T; Gröhn, Olli H J; Kauppinen, Risto A

2014-10-22

83

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. PMID:23626578

Papo, David

2013-01-01

84

Achieving Flexibility in Direct-Manipulation Programming Environments by Relaxing the Edit-Time Grammar  

E-print Network

Achieving Flexibility in Direct-Manipulation Programming Environments by Relaxing the Edit editing and flexibility, particularly in live development environments. JPie is a graphical programming structure and flexibility. As further illustration of the benefits of a relaxed edit-time grammar, we

Goldman, Kenneth J.

85

Extracting Diffusion Constants from Echo-Time-Dependent PFG NMR Data Using Relaxation-Time Information  

NASA Astrophysics Data System (ADS)

Heterogeneous (bio)systems are often characterized by several water-containing compartments that differ in relaxation time values and diffusion constants. Because of the relatively small differences among these diffusion constants, nonoptimal measuring conditions easily lead to the conclusion that a single diffusion constant suffices to describe the water mobility in a heterogeneous (bio)system. This paper demonstrates that the combination of a T2 measurement and diffusion measurements at various echo times (TE), based on the PFG MSE sequence, enables the accurate determination of diffusion constants which are less than a factor of 2 apart. This new method gives errors of the diffusion constant below 10% when two fractions are present, while the standard approach of a biexponential fit to the diffusion data in identical circumstances gives larger (>25%) errors. On application of this approach to water in apple parenchyma tissue, the diffusion constant of water in the vacuole of the cells ( D = 1.7 × 10 -9 m 2/s) can be distinguished from that of the cytoplasm ( D = 1.0 × 10 -9 m 2/s). Also, for mung bean seedlings, the cell size determined by PFG MSE measurements increased from 65 to 100 ?m when the echo time increased from 150 to 900 ms, demonstrating that the interpretation of PFG SE data used to investigate cell sizes is strongly dependent on the T2 values of the fractions within the sample. Because relaxation times are used to discriminate the diffusion constants, we propose to name this approach diffusion analysis by relaxation- time- separated (DARTS) PFG NMR.

Vandusschoten, D.; Dejager, P. A.; Vanas, H.

86

The length and time scales of water's glass transitions  

NASA Astrophysics Data System (ADS)

Using a general model for the equilibrium dynamics of supercooled liquids, I compute from molecular properties the emergent length and time scales that govern the nonequilibrium relaxation behavior of amorphous ice prepared by rapid cooling. Upon cooling, the liquid water falls out of equilibrium whereby the temperature dependence of its relaxation time is predicted to change from super-Arrhenius to Arrhenius. A consequence of this crossover is that the location of the apparent glass transition temperature depends logarithmically on cooling rate. Accompanying vitrification is the emergence of a dynamical length-scale, the size of which depends on the cooling rate and varies between angstroms and tens of nanometers. While this protocol dependence clarifies a number of previous experimental observations for amorphous ice, the arguments are general and can be extended to other glass forming liquids.

Limmer, David T.

2014-06-01

87

Variable thermal properties and thermal relaxation time in hyperbolic heat conduction  

NASA Technical Reports Server (NTRS)

Numerical solutions were obtained for a finite slab with an applied surface heat flux at one boundary using both the hyperbolic (MacCormack's method) and parabolic (Crank-Nicolson method) heat conduction equations. The effects on the temperature distributions of varying density, specific heat, and thermal relaxation time were calculated. Each of these properties had an effect on the thermal front velocity (in the hyperbolic solution) as well as the temperatures in the medium. In the hyperbolic solutions, as the density or specific heat decreased with temperature, both the temperatures within the medium and the thermal front velocity increased. The value taken for the thermal relaxation time was found to determine the 'hyperbolicity' of the heat conduction model. The use of a time dependent relaxation time allowed for solutions where the thermal energy propagated as a high temperature wave initially, but approached a diffusion process more rapidly than was possible with a constant large relaxation time.

Glass, David E.; Mcrae, D. Scott

1989-01-01

88

Dielectric relaxation time of bulk water at 136-140 K, background loss and crystallization effects  

NASA Astrophysics Data System (ADS)

Dielectric relaxation time, ?, of ultraviscous bulk water has been determined by analyzing its loss tangent, tan?, data, which had been measured on heating the vapor-deposited amorphous solid water and hyperquenched glassy water in our earlier studies. [Johari, Hallbrucker, and Mayer, J. Chem. Phys. 95, 2955 (1991); 97, 5851 (1992)]. As for glasses and liquids generally, the measured tan? of water is the sum of a frequency-independent background loss and a frequency-dependent relaxational loss. A two-frequency method is provided for determining the background loss and used for obtaining the relaxational part of tan?. After considering the structural relaxation and crystal-nuclei growth effects, ? for water has been determined. At 136±1K, it is 2.5±0.6s when a single relaxation time is (untenably) assumed, and 42±14s when a distribution of relaxation times, a characteristic of viscous liquids, is assumed, with Davidson-Cole distribution parameter of 0.75. Structural relaxation time of ˜70s for water at 136K, which was originally estimated from the DSC endotherm [Johari, Hallbrucker, and Mayer, Nature (London) 330, 552 (1987)], has been revised to ˜33s. Temperature dependence of ? could not be determined because ultraviscous water crystallizes too rapidly to cubic ice containing stacking faults and intergranular water. The study demonstrates that water is a liquid over the 136-155K range, thus removing the basis for a recent contention on its state.

Johari, G. P.

2005-04-01

89

Multiple-relaxation-time lattice Boltzmann modeling of incompressible flows in porous media  

E-print Network

In this paper, a two-dimensional eight-velocity (D2Q8) multiple-relaxation-time (MRT) lattice Boltzmann (LB) model is proposed for incompressible porous flows at the representative elementary volume scale based on the Brinkman-Forchheimer-extended Darcy formulation. In the model, the porosity is included into the pressure-based equilibrium moments, and the linear and nonlinear drag forces of the porous media are incorporated into the model by adding a forcing term to the MRT-LB equation in the moment space. Through the Chapman-Enskog analysis, the generalized Navier-Stokes equations can be recovered exactly without artificial compressible errors. Numerical simulations of several typical two-dimensional porous flows are carried out to validate the present MRT-LB model. The numerical results of the present MRT-LB model are in good agreement with the analytical solutions and/or other numerical solutions reported in the literature.

Qing Liu; Ya-Ling He; Chao He

2013-11-28

90

Multiple-relaxation-time lattice Boltzmann model for simulating axisymmetric thermal flows in porous media  

E-print Network

In this paper, a multiple-relaxation-time (MRT) lattice Boltzmann (LB) model is developed for simulating incompressible axisymmetric thermal flows in porous media at the representative elementary volume (REV) scale. In the model, a D2Q9 MRT-LB equation is proposed to solve the flow field in addition to the D2Q5 LB equation for the temperature field. The source terms of the model are simple and contain no velocity and temperature gradient terms. The generalized axisymmetric Navier-Stokes equations for axisymmetric flows in porous media are correctly recovered from the MRT-LB model through the Chapman-Enskog analysis in the moment space. The present model is validated by numerical simulations of several typical axisymmetric thermal problems in porous media. The numerical results agree well with the data reported in the literature, demonstrating the effectiveness and accuracy of the present MRT-LB model for simulating axisymmetric thermal flows in porous media.

Liu, Qing; Li, Qing

2014-01-01

91

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

92

Relaxation time ansatz and shear and bulk viscosities of gluon matter  

SciTech Connect

Shear and bulk viscosity-to-entropy density ratios are calculated for pure gluon matter in a nonequilibrium mean-field quasiparticle approach within the relaxation time approximation. We study how different approximations used in the literature affect the results for the shear and bulk viscosities. Though the results for the shear viscosity turned out to be quite robust, all evaluations of the shear and bulk viscosities obtained in the framework of the relaxation time approximation can be considered only as rough estimations.

Khvorostukhin, A. S. [Joint Institute for Nuclear Research, 141980 Dubna (Russian Federation); Institute of Applied Physics, Moldova Academy of Science, MD-2028 Kishineu (Moldova, Republic of); Toneev, V. D. [Joint Institute for Nuclear Research, 141980 Dubna (Russian Federation); Voskresensky, D. N. [National Research Nuclear University ''MEPhI,'' Kashirskoe sh. 31, Moscow 115409 (Russian Federation); GSI, Helmholtzzentrum fuer Schwerionenforschung GmbH, Planckstrasse 1, DE-64291 Darmstadt (Germany)

2011-09-15

93

The Planck Scale Underpinning for Space Time  

E-print Network

We provide a rationale for the Planck scale being the minimum scale in the universe, as also its specific numerical values. In the process we answer the question of why the Planck scale is $10^{20}$ times the Compton scale of elementary particles. These considerations show how the Planck scale provides an underpinning for space time.

Burra G. Sidharth

2005-09-03

94

The SPORT-NMR Software: A Tool for Determining Relaxation Times in Unresolved NMR Spectra  

NASA Astrophysics Data System (ADS)

A software package which allows the correct determination of individual relaxation times for all the nonequivalent nuclei in poorly resolved NMR spectra is described. The procedure used, based on the fitting of each spectrum in the series recorded in the relaxation experiment, should improve the analysis of relaxation data in terms of quantitative dynamic information, especially in anisotropic phases. Tests on simulated data and experimental examples concerning 1H and 13C T1?measurement in a solid copolymer and 2H T1Zand T1Qmeasurement in a liquid crystal are shown and discussed.

Geppi, Marco; Forte, Claudia

1999-03-01

95

Atomic-scale relaxation dynamics and aging in a metallic glass probed by X-ray photon correlation spectroscopy  

E-print Network

We use X-Ray Photon Correlation Spectroscopy to investigate the structural relaxation process in a metallic glass on the atomic length scale. We report evidence for a dynamical crossover between the supercooled liquid phase and the metastable glassy state, suggesting different origins of the relaxation process across the transition. Furthermore, using different cooling rates we observe a complex hierarchy of dynamic processes characterized by distinct aging regimes. Strong analogies with the aging dynamics of soft glassy materials, such as gels and concentrated colloidal suspensions, point at stress relaxation as a universal mechanism driving the relaxation dynamics of out-of-equilibrium systems.

B. Ruta; Y. Chushkin; G. Monaco; L. Cipelletti; E. Pineda; P. Bruna; V. M. Giordano; M. Gonzalez-Silveira

2012-09-10

96

Relaxation Behavior of Laser-Polarized 129Xe Gas: Size Dependency and Wall Effect of the T 1 Relaxation Time in Glass and Gelatin Bulbs  

Microsoft Academic Search

Size dependency of the relaxation time T1 was measured for laser-polarized 129Xe gas encapsulated in different sized cavities made by glass bulbs or gelatin capsules. The use of laser-polarized gas enhances the sensitivity a great deal, making it possible to measure the longer 129Xe relaxation time in quite a short time. The size dependency is analyzed on the basis of

Hideaki Fujiwara; Atsuomi Kimura; Yasuhiro Yanagawa; Takashi Kamiya; Mineyuki Hattori; Takashi Hiraga

2001-01-01

97

Time and Temperature Dependence of Viscoelastic Stress Relaxation in Gold and Gold Alloy Thin Films  

NASA Astrophysics Data System (ADS)

Radio frequency (RF) switches based on capacitive MicroElectroMechanical System (MEMS) devices have been proposed as replacements for traditional solid-state field effect transistor (FET) devices. However, one of the limitations of the existing capacitive switch designs is long-term reliability. Failure is generally attributed to electrical charging in the capacitor's dielectric layer that creates an attractive electrostatic force between a moving upper capacitor plate (a metal membrane) and the dielectric. This acts as an attractive stiction force between them that may cause the switch to stay permanently in the closed state. The force that is responsible for opening the switch is the elastic restoring force due to stress in the film membrane. If the restoring force decreases over time due to stress relaxation, the tendency for stiction failure behavior will increase. Au films have been shown to exhibit stress relaxation even at room temperature. The stress relaxation observed is a type of viscoelastic behavior that is more significant in thin metal films than in bulk materials. Metal films with a high relaxation resistance would have a lower probability of device failure due to stress relaxation. It has been shown that solid solution and oxide dispersion can strengthen a material without unacceptable decreases in electrical conductivity. In this study, the viscoelastic behavior of Au, AuV solid solution and AuV2O5 dispersion created by DC magnetron sputtering are investigated using the gas pressure bulge testing technique in the temperature range from 20 to 80°C. The effectiveness of the two strengthening approaches is compared with the pure Au in terms of relaxation modulus and 3 hour modulus decay. The time dependent relaxation curves can be fitted very well with a four-term Prony series model. From the temperature dependence of the terms of the series, activation energies have been deduced to identify the possible dominant relaxation mechanism. The measured modulus relaxation of Au films also proves that the films exhibit linear viscoelastic behavior. From this, a linear viscoelastic model is shown to fit very well to experimental steady state stress relaxation data and can predict time dependent stress for complex loading histories including the ability to predict stress-time behavior at other strain rates during loading. Two specific factors that are expected to influence the viscoelastic behavior-degree of alloying and grain size are investigated to explore the influence of V concentration in solid solution and grain size of pure Au. It is found that the normalized modulus of Au films is dependent on both concentration (C) and grain size (D) with proportionalities of C1/3 and D 2, respectively. A quantitative model of the rate-equation for dislocation glide plasticity based on Frost and Ashby is proposed and fitted well with steady state anelastic stress relaxation experimental data. The activation volume and the density of mobile dislocations is determined using repeated stress relaxation tests in order to further understand the viscoelastic relaxation mechanism. A rapid decrease of mobile dislocation density is found at the beginning of relaxation, which correlates well with a large reduction of viscoelastic modulus at the early stage of relaxation. The extracted activation volume and dislocation mobility can be ascribed to mobile dislocation loops with double kinks generated at grain boundaries, consistent with the dislocation mechanism proposed for the low activation energy measured in this study.

Mongkolsuttirat, Kittisun

98

Photoexcitation, relaxation and control of charge carriers in metals through interferometric time-resolved photoemission  

NASA Astrophysics Data System (ADS)

The coherent response of metals to optical excitation is investigated by a newly developed technique, interferometric time-resolved two-photon photoemission spectroscopy.(S. Ogawa, H. Nagano, H. Petek and A. Heberle, Phys. Rev. Lett. 78, 1339 (1997).)(H. Petek, A. P. Heberle, W. Nessler, H. Nagano, S. Kubota, S. Matsunami, N. Moriya and S. Ogawa, Phys. Rev. Lett. 79, 4649 (1997).) Photoexcitation, relaxation, and control of charge carrier distributions are reported for the low index surfaces of copper. Two-photon photoemission (2PP) is excited by an identical pair of pump and probe pulses with a delay defined to a fraction of an optical cycle ( 0.05 fs). Interferometric two-pulse correlation measurements (I2PC), where the 2PP signal at a specific energy and momentum is recorded as a function of the pump probe delay, probe coherent (polarization) and incoherent (population) dynamics of the charge carriers. The time scale for the phase decay (dephasing) of the optically excited wavefunction, as a result of the deformation potential scattering, is deduced from the decay of interference fringes in the I2PC scans. Measurement of optical dephasing on 20 fs time scale in excitation of the occupied s,p-gap surface state on Cu(111) is in good agreement with photoemission linewidth analysis. I2PC also offers an unambiguous way to monitor the decay of the optically created hot-electron population due to e-e scattering and transport into the bulk. Finally, demonstration of long dephasing times in copper suggests a possibility of coherent control of electrons in metals. This is demonstrated with two simple excitation schemes.

Petek, Hrvoje

1998-03-01

99

Thermal Relaxation Time in Chemically Non-equilibrated Quark- Gluon Plasma  

E-print Network

The definition of thermal relaxation time is extended to chemically non-equilibrated quark-gluon plasma and the chemical non-equilibrated thermal relaxation times for partons are calculated using the non-equilibrium Debye mass as the infrared regulator. The dependence of the thermal relaxation time on the fugacity is given and the influence of the chemical non-equilibration is discussed. We find that there are threshold fugacities $\\lambda_g^*$ and $\\lambda_q^*$ for gluons and quarks. For \\lambda_g \\lambda_g^* (\\lambda_q>\\lambda_q^*$), the ratios are almost 1. It is shown that there is also the two-stage equilibration in a chemically non-equilibrated plasma. We also discussed the effect of using the non-equilibrium Deby mass as the infrared cutoff.

Xiao-Fei Zhang; Wei-Qin Chao

1997-07-09

100

A modified multiple-relaxation-time lattice Boltzmann model for convection-diffusion equation  

NASA Astrophysics Data System (ADS)

A modified lattice Boltzmann model with multiple relaxation times (MRT) for the convection-diffusion equation (CDE) is proposed. By modifying the relaxation matrix, as well as choosing the corresponding equilibrium distribution function properly, the present model can recover the CDE with anisotropic diffusion coefficient with no deviation term even when the velocity vector varies generally with space or time through the Chapman-Enskog analysis. This model is firstly validated by simulating the diffusion of a Gaussian hill, which demonstrates it can handle the anisotropic diffusion problem correctly. Then it is adopted to calculate the longitudinal dispersion coefficient of the Taylo-Aris dispersion. Numerical results show that the present model can further reduce the numerical error under the condition of non-zero velocity vector, especially when the dimensionless relaxation time is relatively large.

Huang, Rongzong; Wu, Huiying

2014-10-01

101

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

102

Estimating Mean First Passage Time of Biased Random Walks with Short Relaxation Time on Complex Networks  

PubMed Central

Biased random walk has been studied extensively over the past decade especially in the transport and communication networks communities. The mean first passage time (MFPT) of a biased random walk is an important performance indicator in those domains. While the fundamental matrix approach gives precise solution to MFPT, the computation is expensive and the solution lacks interpretability. Other approaches based on the Mean Field Theory relate MFPT to the node degree alone. However, nodes with the same degree may have very different local weight distribution, which may result in vastly different MFPT. We derive an approximate bound to the MFPT of biased random walk with short relaxation time on complex network where the biases are controlled by arbitrarily assigned node weights. We show that the MFPT of a node in this general case is closely related to not only its node degree, but also its local weight distribution. The MFPTs obtained from computer simulations also agree with the new theoretical analysis. Our result enables fast estimation of MFPT, which is useful especially to differentiate between nodes that have very different local node weight distribution even though they share the same node degrees. PMID:24699325

Lee, Zhuo Qi; Hsu, Wen-Jing; Lin, Miao

2014-01-01

103

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

104

Will Spin-Relaxation Times in Molecular Magnets Permit Quantum Information Processing?  

NASA Astrophysics Data System (ADS)

Using X-band pulsed electron-spin resonance, we report the intrinsic spin-lattice (T1) and phase-coherence (T2) relaxation times in molecular nanomagnets for the first time. In Cr7M heterometallic wheels, with M=Ni and Mn, phase-coherence relaxation is dominated by the coupling of the electron spin to protons within the molecule. In deuterated samples T2 reaches 3?s at low temperatures, which is several orders of magnitude longer than the duration of spin manipulations, satisfying a prerequisite for the deployment of molecular nanomagnets in quantum information applications.

Ardavan, Arzhang; Rival, Olivier; Morton, John J. L.; Blundell, Stephen J.; Tyryshkin, Alexei M.; Timco, Grigore A.; Winpenny, Richard E. P.

2007-02-01

105

The effects of bone on proton NMR relaxation times of surrounding liquids  

NASA Technical Reports Server (NTRS)

Preliminary attempts by our group at UCSF to assess fat content of vertebral marrow in the lumbar spine using relaxation time information demonstrated that the presence of trabecular bone affects relaxation times. The objective of this work was a thorough study of the effects of bone on NMR relaxation characteristics of surrounding liquids. Trabecular bone from autopsy specimens was ground up and sifted into a series of powders with graded densities ranging from 0.3 gm/cc to 0.8 gm/cc. Each powder was placed first in n-saline and then in cottonseed oil. With spectroscopy, spin-lattice relaxation times (T1) and effective spin-spin relaxation times (T2*) were measured for each liquid in each bone powder. As bone density and surface to volume ratio increased, T1 decreased faster for saline than for oil. T2* decreased significantly for both water and oil as the surface to volume ratio increased. It was concluded that effects of water on T1 could be explained by a surface interaction at the bone/liquid interface, which restricted rotational and translational motion of nearby molecules. The T1s of oil were not affected since oil molecules are nonpolar, do not participate in significant intermolecular hydrogen bonding, and therefore would not be expected to interact strongly with the bone surface. Effects on T2* could be explained by local magnetic field inhomogeneities created by discontinuous magnetic susceptibility near the bone surface. These preliminary results suggest that water in contact with trabecular bone in vivo will exhibit shortened relaxation times.

Davis, C. A.; Genant, H. K.; Dunham, J. S.

1986-01-01

106

Fragile-strong fluid crossover and universal relaxation times in a confined hard-disk fluid.  

PubMed

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. PMID:23368134

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

2012-11-30

107

A unified model of hysteresis and long-time relaxation in heterogeneous materials  

NASA Astrophysics Data System (ADS)

A physical model of stress-strain dynamics and long-time relaxation (slow time) in structured media is proposed. The model is based on the analysis of inter-grain contacts and the resulting surface force potential with a barrier. The result is a unified description of the classical acoustic nonlinearity, stress-strain hysteresis, and logarithmic relaxation law for sound velocity (and, hence, for the frequency of nonlinear resonance in samples of structured materials). Estimates of a characteristic volume of interacting contacts give close values for the variety of consolidated materials. For weak (linear) testing waves, the logarithmic relaxation occurs if a classical quadratic nonlinearity is added to the stress-strain relation.

Lebedev, A. V.; Ostrovsky, L. A.

2014-09-01

108

Introduction to the time scale problem  

SciTech Connect

As motivation for the symposium on extended-scale atomistic methods, I briefly discuss the time scale problem that plagues molecular dynamics simulations, some promising recent developments for circumventing the problem, and some remaining challenges.

Voter, A. F.

2002-01-01

109

Relaxation rate and scaling function of the critical system 3-methylpentane-nitroethane-cyclohexane  

NASA Astrophysics Data System (ADS)

The critical system 3-methylpentane-nitroethane-cyclohexane (3-MP-NE-CH) has been investigated and compared to the limiting binary systems 3-MP-NE as well as NE-CH in order to study the degree of renormalization in the critical exponents of the ternary system. The solubility curves of the 3-MP-NE-CH system have been determined at various molar ratios of the nonpolar constituents in order to obtain the plait points as a function of mixture composition. At the col point (the mixture with the lowest transition temperature) and two further plait point compositions shear viscosity, dynamic light scattering, and frequency-dependent ultrasonic attenuation coefficient measurements have been performed as a function of temperature near the critical temperatures. The fluctuation correlation length and the relaxation rate of fluctuations display power law behavior as a function of reduced temperature, with universal critical exponents ?~=0.63 and ?~Z0=1.928, respectively, as characteristic for binary critical mixtures. In conformity with the 3-MP-NE and NE-CH critical mixtures the scaling function in the ultrasonic spectra nicely agrees with the empirical scaling function of the Bhattacharjee-Ferrell dynamic scaling theory. Hence with respect to power laws and scaling the 3-MP-NE-CH system behaves like a quasibinary mixture. The individual amplitudes of the relaxation rate show a minimum at the col point composition, corresponding with a maximum in the background viscosity of the liquids. The amount of the adiabatic coupling constant g, derived from the amplitudes in the ultrasonic spectra, increases monotonously when going from NE-CH (|g|=0.1) to 3-MP-NE (|g|=0.26).

Iwanowski, I.; Mirzaev, S. Z.; Kaatze, U.

2008-08-01

110

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)] [Lawrence Livermore National Laboratory, Livermore, California 94550 (United States)

1995-10-01

111

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

112

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

113

Very short NMR relaxation times of anions in ionic liquids: New pulse sequence to eliminate the acoustic ringing  

NASA Astrophysics Data System (ADS)

NMR relaxation processes of anions were studied in two neat imidazolium-based room temperature ionic liquids (RTILs) 1-decyl-3-methyl-imidazolium bromide- and chloride. The spin-lattice and spin-spin relaxations of 81Br and 35Cl nuclei were found to be extremely fast due to very strong quadrupolar interactions. The determined relaxation rates are comparable with those observed in the solids or in some critical organic solute/water/salt systems. In order to eliminate the acoustic ringing of the probe-head during relaxation times measurements the novel pulse sequence has been devised. It is based on the conventional inversion recovery pulse sequence, however, instead of the last 90° pulse the subsequence of three 90° pulses applied along axes to fulfill the phase cycling condition is used. Using this pulse sequence it was possible to measure T1 for both studied nuclei. The viscosity measurements have been carried out and the rotational correlation times were calculated. The effective 35Cl quadrupolar coupling constant was found to be almost one order lower than that for 81Br, i.e. 1.8 MHz and 16.0 MHz, respectively. Taking into account the facts that the ratio of (Q(35Cl)/Q(81Br))2 ? 0.1 and EFG tensors on the anions are quite similar, analogous structural organizations are expected for both RTILs. The observed T1/T2 (1.27-1.44) ratios were found to be not sufficiently high to confirm the presence of long-living (on the time scale of ?10-8 s) mesoscopic structures or heterogeneities in the studied neat ionic liquids.

Klimavicius, Vytautas; Gdaniec, Zofia; Balevicius, Vytautas

2014-11-01

114

Two-time-scale Wonham filters  

Microsoft Academic Search

This paper is concerned with a two-time-scale approximation of Wonham filters. A main feature is that the underlying hidden Markov chain has a large state space. To reduce computational complexity, we develop two-time-scale approach. Under time scale separation, we divide the state space of the Markov chain into a number of groups such that the chain jumps rapidly within each

Q. Zhang; G. Yin; J. B. Moore

2007-01-01

115

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

116

Time resolved observation of multiple electronic configurations in the electronic relaxation of isolated  

E-print Network

Time resolved observation of multiple electronic configurations in the electronic relaxation from the coupling (essentially non adiabatic) between the electronic configurations of the molecular is a fingerprint of the evolution of its electronic configuration(3, 4). For each #12;traversed electronic state

Boyer, Edmond

117

Time Series Prediction by Genetic Programming with Relaxed Assumptions in Mathematica1  

E-print Network

Time Series Prediction by Genetic Programming with Relaxed Assumptions in Mathematica1 Stuart W. An implementation in Mathematica is illustrated. GP discovery of equations, NN optimization of their parameters optimum, providing point prediction accuracy. 1 Mathematica® 5, © Copyright 1988-2003 Wolfram Research

Fernandez, Thomas

118

Collective friction coefficients in the relaxation time approximation F. A. Ivanyuk  

E-print Network

Collective friction coefficients in the relaxation time approximation F. A. Ivanyuk Institute components of the friction coefficient for various single-particle potentials and have found that the nondiagonal component of the friction coefficient depends generally on the diffuseness of the potential

Pomorski, Krzysztof

119

Relaxation Time Constants and Apparent Diffusion Coefficients of Rat Retina at 7 Tesla  

E-print Network

Relaxation Time Constants and Apparent Diffusion Coefficients of Rat Retina at 7 Tesla Govind Nair* and ADC of the rat eyes were measured at 50 3 50 3 800 lm at 7 Tesla. Profiles of T1, T2, T2* and ADC

Duong, Timothy Q.

120

Scaling Behavior of Hydrologic Time Series  

NASA Astrophysics Data System (ADS)

An important area of research in hydrologic modeling is the issue of scaling of certain deterministic properties at various spatial and temporal scales. The complexity for modeling of most systems is because hydrologic processes scale nonlinearly; that is, the moments (e.g. the mean and variance) obtained at one scale may be significantly different from those obtained at a larger or smaller scale. Improvements in hydrologic modeling that include the tenants of scaling in the relevant processes would be novel, and likely lead to a stronger predictive approach than are currently available. Fractal-based scale invariant approach for analyzing long-term time series data can provide insight into the scaling issue as a quantitative approach for evaluating temporal scale in hydrologic time series. The main objective of this research is to study the effects of deterministic trends, mainly seasonality of hydrologic time series on scaling parameter. Different hydrologic time series (rainfall and runoff) from various locations are investigated. Two hydrologic time series, one with the raw hydrologic time series data and another by removing the seasonality are compared. The comparison of untransformed and deseasonalized data series showed that there is no statistically significant value to deseasonalize the data, although the data series appears to shift toward random scaling after deseasonalization.

Koirala, S. R.

2012-12-01

121

Relaxation dynamics of the toric code in contact with a thermal reservoir: Finite-size scaling in a low-temperature regime  

NASA Astrophysics Data System (ADS)

We present an analysis of the relaxation dynamics of finite-size topological qubits in contact with a thermal bath. Using a continuous-time Monte Carlo method, we explicitly compute the low-temperature nonequilibrium dynamics of the toric code on finite lattices. In contrast to the size-independent bound predicted for the toric code in the thermodynamic limit, we identify a low-temperature regime on finite lattices below a size-dependent crossover temperature with nontrivial finite-size and temperature scaling of the relaxation time. We demonstrate how this nontrivial finite-size scaling is governed by the scaling of topologically nontrivial two-dimensional classical random walks. The transition out of this low-temperature regime defines a dynamical finite-size crossover temperature that scales inversely with the log of the system size, in agreement with a crossover temperature defined from equilibrium properties. We find that both the finite-size and finite-temperature scaling are stronger in the low-temperature regime than above the crossover temperature. Since this finite-temperature scaling competes with the scaling of the robustness to unitary perturbations, this analysis may elucidate the scaling of memory lifetimes of possible physical realizations of topological qubits.

Freeman, C. Daniel; Herdman, C. M.; Gorman, D. J.; Whaley, K. B.

2014-10-01

122

SYNCHRONY IN RELAXATION OSCILLATORS 3.1 Introduction  

E-print Network

41 CHAPTER 3 SYNCHRONY IN RELAXATION OSCILLATORS 3.1 Introduction The phrase "relaxation oscillations" was coined by van der Pol in 1926 in his analysis of a triode circuit [van der Pol, 1926]. A relaxation oscillator has two distinct time scales; a slow time scale which reflects the charging

Wang, DeLiang "Leon"

123

Scaling exponents estimation from time-scale energy distributions  

Microsoft Academic Search

It is shown using some examples that the problem of estimating the evolution of scaling exponents characterizing locally a self-similar process can be efficiently handled within the general framework of time-scale energy distributions related to the wavelength transform. As is implicit from the structure of the estimators considered, the proposed methodology is dependent on the degree of nonstationarity of such

P. Goncalves; P. Flandrin

1992-01-01

124

On-chip Brownian relaxation measurements of magnetic nanobeads in the time domain  

NASA Astrophysics Data System (ADS)

We present and demonstrate a new method for on-chip Brownian relaxation measurements on magnetic nanobeads in the time domain using magnetoresistive sensors. The beads are being magnetized by the sensor self-field arising from the bias current passed through the sensors and thus no external magnetic fields are needed. First, the method is demonstrated on Brownian relaxation measurements of beads with nominal sizes of 40, 80, 130, and 250 nm. The results are found to compare well to those obtained by an already established measurement technique in the frequency domain. Next, we demonstrate the time and frequency domain methods on Brownian relaxation detection of clustering of streptavidin coated magnetic beads in the presence of different concentrations of biotin-conjugated bovine serum albumin and obtain comparable results. In the time domain, a measurement is carried out in less than 30 s, which is about six times faster than in the frequency domain. This substantial reduction of the measurement time allows for continuous monitoring of the bead dynamics vs. time and opens for time-resolved studies, e.g., of binding kinetics.

Østerberg, Frederik Westergaard; Rizzi, Giovanni; Hansen, Mikkel Fougt

2013-06-01

125

Kalman plus weights: a time scale algorithm  

NASA Technical Reports Server (NTRS)

KPW is a time scale algorithm that combines Kalman filtering with the basic time scale equation (BTSE). A single Kalman filter that estimates all clocks simultaneously is used to generate the BTSE frequency estimates, while the BTSE weights are inversely proportional to the white FM variances of the clocks. Results from simulated clock ensembles are compared to previous simulation results from other algorithms.

Greenhall, C. A.

2001-01-01

126

Parameter extraction for relaxation-time based non-quasi-static MOSFET models  

Microsoft Academic Search

This paper presents a new extraction technique for non-quasi-static (NQS) delay time and gate resistance for relaxation-time-approximation based MOS transistor models. The technique is based on analysis of ydg in strong inversion, as a function of both VGS and frequency, for VDS = 0. An effective delay ?eff is computed from measured data, and a plot of ?eff versus the

Zeqin Zhu; Colin C. McAndrew; Ik-Sung Lim; Gennady Gildenblat

2012-01-01

127

Fundamental studies of stress distributions and stress relaxation in oxide scales on high temperature alloys. Progress report  

SciTech Connect

The high temperature X-ray diffraction system developed for this program is being used to measure the strains which develop during oxidation. This is being applied to Ni/NiO and Cr/Cr{sub 2}O{sub 3}. Our work suggests tat the oxide and metal crystalline texture, anisotropic elastic modulus and anisotropic thermal expansion can have a pronounced effect on strain state of these systems. Acoustic emission is being used to study oxide scale failure (fracture) during oxidation. AE data from 304 stainless steel are being used to develop a statistical model of fracture process. Strength of metal/scale interface is an important property that has been difficult to quantify. Using Nano-indentation and scratch techniques developed for characterizing thin film interfaces, an effort has begun to measure the fracture toughness of the metal/scale interface. Mathematical modelling of origin and time evolution of growth stresses is an extension and improvement of previous models. The current effort employs a more sophisticated stress analysis and expands the scope to include other stress relaxation process. The interaction between the modeling studies and the X-ray diffraction measurements provides a natural credibility check to both efforts.

Shores, D.A.; Stout, J.H.; Gerberich, W.W.

1992-06-01

128

Shear Viscosity Coefficient and Relaxation Time of Causal Dissipative Hydrodynamics in QCD  

SciTech Connect

The shear viscosity coefficient and the corresponding relaxation time for causal dissipative hydrodynamics are calculated based on the microscopic formula proposed in T. Koide and T. Kodama [Phys. Rev. E 78, 051107 (2008)]. Here, the exact formula is transformed into a more compact form and applied to evaluate these transport coefficients in the chiral perturbation theory and perturbative QCD. It is shown that in the leading order calculation, the causal shear viscosity coefficient eta reduces to that of the ordinary Green-Kubo-Nakano formula, and the relaxation time tau{sub p}i is related to eta and pressure P by a simple relationship, tau{sub p}i=eta/P.

Koide, T.; Nakano, E.; Kodama, T. [FIAS, Johann Wolfgang Goethe-Universitaet, Ruth-Moufang Str. 1, 60438, Frankfurt am Main (Germany); Extreme Matter Institute, GSI, Planckstr. 1, D-64291 Darmstadt (Germany); Instituto de Fisica, Universidade Federal do Rio de Janeiro, C. P. 68528, 21945-970, Rio de Janeiro (Brazil)

2009-07-31

129

Application of a time-convolutionless stochastic Schrödinger equation to energy transport and thermal relaxation  

NASA Astrophysics Data System (ADS)

Quantum stochastic methods based on effective wave functions form a framework for investigating the generally non-Markovian dynamics of a quantum-mechanical system coupled to a bath. They promise to be computationally superior to the master-equation approach, which is numerically expensive for large dimensions of the Hilbert space. Here, we numerically investigate the suitability of a known stochastic Schrödinger equation that is local in time to give a description of thermal relaxation and energy transport. This stochastic Schrödinger equation can be solved with a moderate numerical cost, indeed comparable to that of a Markovian system, and reproduces the dynamics of a system evolving according to a general non-Markovian master equation. After verifying that it describes thermal relaxation correctly, we apply it for the first time to the energy transport in a spin chain. We also discuss a portable algorithm for the generation of the coloured noise associated with the numerical solution of the non-Markovian dynamics.

Biele, R.; Timm, C.; D'Agosta, R.

2014-10-01

130

Shear viscosity to relaxation time ratio in SU(3) lattice gauge theory  

NASA Astrophysics Data System (ADS)

We evaluate the ratio of the shear viscosity to the relaxation time of the shear current above but near the critical temperature Tc in SU(3) gauge theory on the lattice. The ratio is related to Kubo's canonical correlation of the energy-momentum tensor in Euclidean space with the relaxation-time approximation and an appropriate regularization. Using this relation, we evaluate the ratio on the lattice in Euclidean space. We obtain the ratio with reasonable statistics for the range of temperature 1.5?T/Tc?4. We find that the characteristic speed of the transverse plane wave propagating in a gluon medium v? is almost constant, v?2?0.5, for T /Tc?1.5, which ensures the causality in this mode in second-order dissipative hydrodynamics.

Kohno, Yasuhiro; Asakawa, Masayuki; Kitazawa, Masakiyo

2014-03-01

131

Excited state dynamics in SO2. I. Bound state relaxation studied by time-resolved photoelectron-photoion coincidence spectroscopy.  

PubMed

The excited state dynamics of isolated sulfur dioxide molecules have been investigated using the time-resolved photoelectron spectroscopy and time-resolved photoelectron-photoion coincidence techniques. Excited state wavepackets were prepared in the spectroscopically complex, electronically mixed (B?)(1)B1/(Ã)(1)A2, Clements manifold following broadband excitation at a range of photon energies between 4.03 eV and 4.28 eV (308 nm and 290 nm, respectively). The resulting wavepacket dynamics were monitored using a multiphoton ionisation probe. The extensive literature associated with the Clements bands has been summarised and a detailed time domain description of the ultrafast relaxation pathways occurring from the optically bright (B?)(1)B1 diabatic state is presented. Signatures of the oscillatory motion on the (B?)(1)B1/(Ã)(1)A2 lower adiabatic surface responsible for the Clements band structure were observed. The recorded spectra also indicate that a component of the excited state wavepacket undergoes intersystem crossing from the Clements manifold to the underlying triplet states on a sub-picosecond time scale. Photoelectron signal growth time constants have been predominantly associated with intersystem crossing to the (c?)(3)B2 state and were measured to vary between 750 and 150 fs over the implemented pump photon energy range. Additionally, pump beam intensity studies were performed. These experiments highlighted parallel relaxation processes that occurred at the one- and two-pump-photon levels of excitation on similar time scales, obscuring the Clements band dynamics when high pump beam intensities were implemented. Hence, the Clements band dynamics may be difficult to disentangle from higher order processes when ultrashort laser pulses and less-differential probe techniques are implemented. PMID:24880274

Wilkinson, Iain; Boguslavskiy, Andrey E; Mikosch, Jochen; Bertrand, Julien B; Wörner, Hans Jakob; Villeneuve, David M; Spanner, Michael; Patchkovskii, Serguei; Stolow, Albert

2014-05-28

132

Excited state dynamics in SO2. I. Bound state relaxation studied by time-resolved photoelectron-photoion coincidence spectroscopy  

NASA Astrophysics Data System (ADS)

The excited state dynamics of isolated sulfur dioxide molecules have been investigated using the time-resolved photoelectron spectroscopy and time-resolved photoelectron-photoion coincidence techniques. Excited state wavepackets were prepared in the spectroscopically complex, electronically mixed ({tildeB})1B1/(Ã)1A2, Clements manifold following broadband excitation at a range of photon energies between 4.03 eV and 4.28 eV (308 nm and 290 nm, respectively). The resulting wavepacket dynamics were monitored using a multiphoton ionisation probe. The extensive literature associated with the Clements bands has been summarised and a detailed time domain description of the ultrafast relaxation pathways occurring from the optically bright ({tildeB})1B1 diabatic state is presented. Signatures of the oscillatory motion on the ({tildeB})1B1/(Ã)1A2 lower adiabatic surface responsible for the Clements band structure were observed. The recorded spectra also indicate that a component of the excited state wavepacket undergoes intersystem crossing from the Clements manifold to the underlying triplet states on a sub-picosecond time scale. Photoelectron signal growth time constants have been predominantly associated with intersystem crossing to the ({tildec})3B2 state and were measured to vary between 750 and 150 fs over the implemented pump photon energy range. Additionally, pump beam intensity studies were performed. These experiments highlighted parallel relaxation processes that occurred at the one- and two-pump-photon levels of excitation on similar time scales, obscuring the Clements band dynamics when high pump beam intensities were implemented. Hence, the Clements band dynamics may be difficult to disentangle from higher order processes when ultrashort laser pulses and less-differential probe techniques are implemented.

Wilkinson, Iain; Boguslavskiy, Andrey E.; Mikosch, Jochen; Bertrand, Julien B.; Wörner, Hans Jakob; Villeneuve, David M.; Spanner, Michael; Patchkovskii, Serguei; Stolow, Albert

2014-05-01

133

A New Time-Scale for Tunneling  

E-print Network

We study the tunneling through an oscillating delta barrier. Using time periodicity of the model, the time-dependent Schr\\"odinger equation is reduced to a simple but infinite matrix equation. Employing Toeplitz matrices methods, the infinite matrix is replaces by a $3\\times 3$ matrix, allowing an analytical solution. Looking at the frequency dependence of the transmissionamplitudes, one observes a new time scale which dominates the tunneling dynamics. This time scale differs from the one previously introduced by B\\"uttiker and Landauer. The relation between these two is discussed.

E. Eisenberg; Y. Ashkenazy

1996-10-25

134

Implicit-correction-based immersed boundary-lattice Boltzmann method with two relaxation times  

NASA Astrophysics Data System (ADS)

In the present paper, we verify the effectiveness of the two-relaxation-time (TRT) collision operator in reducing boundary slip computed by the immersed boundary-lattice Boltzmann method (IB-LBM). In the linear collision operator of the TRT, we decompose the distribution function into symmetric and antisymmetric components and define the relaxation parameters for each part. The Chapman-Enskog expansion indicates that one relaxation time for the symmetric component is related to the kinematic viscosity. Rigorous analysis of the symmetric shear flows reveals that the relaxation time for the antisymmetric part controls the velocity gradient, the boundary velocity, and the boundary slip velocity computed by the IB-LBM. Simulation of the symmetric shear flows, the symmetric Poiseuille flows, and the cylindrical Couette flows indicates that the profiles of the numerical velocity calculated by the TRT collision operator under the IB-LBM framework exactly agree with those of the multirelaxation time (MRT). The TRT is as effective in removing the boundary slip as the MRT. We demonstrate analytically and numerically that the error of the boundary velocity is caused by the smoothing technique using the ? function used in the interpolation method. In the simulation of the flow past a circular cylinder, the IB-LBM based on the implicit correction method with the TRT succeeds in preventing the flow penetration through the solid surface as well as unphysical velocity distortion. The drag coefficient, the wake length, and the separation points calculated by the present IB-LBM agree well with previous studies at Re = 10, 20, and 40.

Seta, Takeshi; Rojas, Roberto; Hayashi, Kosuke; Tomiyama, Akio

2014-02-01

135

Nuclear Spin-Lattice Relaxation Time Due to the Orbital Interaction  

Microsoft Academic Search

In the free electron model the spin-lattice relaxation time {T1}(orb) due to the interaction with the orbital motion of conduction electrons diverges if the nuclear Zeeman energy is neglected. Without neglecting it, {T1}(orb) with the field dependence of a form log(Hext) is derived for high magnetic fields. The divergence which arises for Hext{=}0 is removed by taking into account the

Eijiro Haga; Syozo Maeda

1972-01-01

136

KASSPER analysis of 2.D parametric STAP performance: Further results on time-varying autoregressive “Relaxations  

Microsoft Academic Search

We continue our investigation into the new class of two-dimensional autoregressive relaxed models (ldquorelaxationsrdquo) for space-time adaptive processing (STAP) applications. Previously reported results on the DARPA KASSPER simulated dataset for airborne side-looking radar are now complemented by STAP performance analysis for all range bins and varying antenna-array errors. We discuss the variability of signal-to-interference-plus-noise ratio (SINR) performance associated with the

Yuri I. Abramovich; Muralidhar Rangaswamy; Phillip M. Corbell; Ben A. Johnson; Nicholas K. Spencer

2008-01-01

137

Relaxed heaps  

SciTech Connect

The relaxed heap is a priority queue data structure that achieves the same amortized time bounds as the Fibonacci heap - a sequence of m decrease key and n delete min operations takes time O(m + n log n). A variant of relaxed heaps achieves similar bounds in the worst case - O(1) time for decrease key and O(log n) for delete min. Relaxed heaps give a processor-efficient parallel implementation of Dijkstra's shortest path algorithm, and hence other algorithms in network optimization. A relaxed heap is a type of binomial queue that allows heap order to be violated.

Driscoll, J.R. (Dept. of Mathematics and Computer Science, Dartmouth College, Hanover, NH (US)); Gabow, H.N.; Shrairman, R. (Dept. of Computer Science, Univ. of Colorado, Boulder, CO (US)); Tarjan, R.E. (Computer Science Dept., Princeton Univ., Princeton, NJ (US))

1988-11-01

138

Mouse Activity across Time Scales: Fractal Scenarios  

PubMed Central

In this work we devise a classification of mouse activity patterns based on accelerometer data using Detrended Fluctuation Analysis. We use two characteristic mouse behavioural states as benchmarks in this study: waking in free activity and slow-wave sleep (SWS). In both situations we find roughly the same pattern: for short time intervals we observe high correlation in activity - a typical 1/f complex pattern - while for large time intervals there is anti-correlation. High correlation of short intervals ( to : waking state and to : SWS) is related to highly coordinated muscle activity. In the waking state we associate high correlation both to muscle activity and to mouse stereotyped movements (grooming, waking, etc.). On the other side, the observed anti-correlation over large time scales ( to : waking state and to : SWS) during SWS appears related to a feedback autonomic response. The transition from correlated regime at short scales to an anti-correlated regime at large scales during SWS is given by the respiratory cycle interval, while during the waking state this transition occurs at the time scale corresponding to the duration of the stereotyped mouse movements. Furthermore, we find that the waking state is characterized by longer time scales than SWS and by a softer transition from correlation to anti-correlation. Moreover, this soft transition in the waking state encompass a behavioural time scale window that gives rise to a multifractal pattern. We believe that the observed multifractality in mouse activity is formed by the integration of several stereotyped movements each one with a characteristic time correlation. Finally, we compare scaling properties of body acceleration fluctuation time series during sleep and wake periods for healthy mice. Interestingly, differences between sleep and wake in the scaling exponents are comparable to previous works regarding human heartbeat. Complementarily, the nature of these sleep-wake dynamics could lead to a better understanding of neuroautonomic regulation mechanisms. PMID:25275515

Lima, G. Z. dos Santos; Lobão-Soares, B.; do Nascimento, G. C.; França, Arthur S. C.; Muratori, L.; Ribeiro, S.; Corso, G.

2014-01-01

139

Time resolved observation of multiple electronic configurations in the electronic relaxation of isolated molecules by photoelectron imaging  

Microsoft Academic Search

Femtosecond time resolved photoelectron imaging has been applied to the electronic relaxation of an ethylene-like molecule, tetrakis dimethylamino ethylene, excited to a pipi* valence state. This method has an unprecedented efficiency for the observation of the states traversed by the wavepacket created on the initial state. We infer here that electronic relaxation gains efficiency by the mediation of nearby Rydberg

E. Gloaguen; J. M. Mestdagh; L. Poisson; J. P. Visticot; B. Soep; M. Coroiu; A. Eppink; D. H. Parker

2005-01-01

140

Nonlinear acoustic waves in media with hysteresis and long-time relaxation.  

PubMed

It is known that the media with complex structures (e.g., rocks and ceramics) possess an anomalously strong elastic nonlinearity. Nonlinear acoustic effects are used in a number of important applications, such as seismic waves (earthquakes), non-destructive testing, and contact physics. Two specific features were registered, in most of the experiments: hysteresis in the stress-strain relation and longtime relaxation (slow time). Some physical models, mostly phenomenological, have been suggested to explain these phenomena. However, there are very few works considering the effect of medium hysteresis and relaxation on wave propagation and oscillations in resonators. This presentation is a review of both published and new results in this area. Among the problems discussed are: (1) A brief overview of experiments and models; (2) Analysis of wave propagation in simplified models of media with hysteresis as opposed to the nonlinear waves in media characterized by elastic constants of second and third order; (3) Theory of wave interaction in resonators with hysteresis; (4) Study of waves in media with slow time relaxation; (5) Some data from laboratory and field experiments; (6) Some unsolved issues and the relevant future work will be outlined in conclusion. PMID:25235680

Ostrovsky, Lev A

2014-04-01

141

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

PubMed

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 3T 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 3T; 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. PMID:23941818

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

2013-10-01

142

Assessment of the time constant of relaxation: insights from simulations and hemodynamic measurements  

NASA Technical Reports Server (NTRS)

The objective of this study was to use high-fidelity animal data and numerical simulations to gain more insight into the reliability of the estimated relaxation constant derived from left ventricular pressure decays, assuming a monoexponential model with either a fixed zero or free moving pressure asymptote. Comparison of the experimental data with the results of the simulations demonstrated a trade off between the fixed zero and the free moving asymptote approach. The latter method more closely fits the pressure curves and has the advantage of producing an extra coefficient with potential diagnostic information. On the other hand, this method suffers from larger standard errors on the estimated coefficients. The method with fixed zero asymptote produces values of the time constant of isovolumetric relaxation (tau) within a narrow confidence interval. However, if the pressure curve is actually decaying to a nonzero pressure asymptote, this method results in an inferior fit of the pressure curve and a biased estimation of tau.

De Mey, S.; Thomas, J. D.; Greenberg, N. L.; Vandervoort, P. M.; Verdonck, P. R.

2001-01-01

143

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 CCl 4, 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 CCl 4 compared with the other mixtures.

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

2009-11-01

144

Relaxation and merging flux ropes and 3D effects in the Reconnection Scaling Experiment at LANL  

NASA Astrophysics Data System (ADS)

Magnetic structures are embedded in astrophysical, space, solar and laboratory plasmas. The dynamics and relaxation of these plasmas can involve flows, changes in topology, magnetic reconnection, plasma heating, and dissipation of magnetic energy. This complex behavior is intrinsically three-dimensional (3D). Current-carrying magnetic flux ropes are the fundamental building blocks for many of these cases. At Los Alamos National Laboratory, we have an experimental realization of this model. The Reconnection Scaling Experiment (RSX) is a unique facility that can create multiple current-carrying flux ropes in an MHD experiment. Plasma guns are used to inject magnetic helicity into plasma columns. We show 3D structure with camera views, along with magnetic, electric, and particle probe data. Experiments in the presence of a strong guide magnetic field (Bz/Brcxn>10) show the formation of a current sheet and electron heating during the coalescence of two flux ropes. Computed simulations of the interactions of two current ropes are shown of that predict many of the experimental characteristics. A density wave structure that propagates opposite to the current is measured in the current sheet with wavelength and speed that are consistent with a kinetic Alfven wave. The current channels acquire angular momentum and rotate about each other developing helical structures, both individually and jointly. Parallel pressure gradients (a 3D effect) appear to be an important term in the Ohm's Law.

Intrator, T.; Furno, I.; Light, A.; Madziwa-Nussinov, T.; Lapenta, G.; Ricci, P.; Hemsing, E.

2005-12-01

145

Relaxation of flux ropes and magnetic reconnection in the Reconnection Scaling Experiment at LANL  

NASA Astrophysics Data System (ADS)

Magnetic reconnection and plasma relaxation are studied in the Reconnection Scaling Experiment (RSX) with current carrying plasma columns (magnetic flux ropes). Using plasma guns, multiple flux ropes (B? ? 100 Gauss, L=90 cm, r?3 cm) are generated in a three-dimensional (3D) cylindrical geometry and are observed to evolve dynamically during the injection of magnetic helicity. Detailed evolution of electron density, temperature, plasma potential and magnetic field structures is reconstructed experimentally and visible light emission is captured with a fast-gated, intensified CCD camera to provide insight into the global flux rope dynamics. Experiments with two flux ropes in collisional plasmas and in a strong axial guide field (Bz / B? > 10) suggest that magnetic reconnection plays an important role in the initial stages of flux rope evolution. During the early stages of the applied current drive (t? 20 ? Alfv´ {e}n), the flux ropes are observed to twist, partially coalesce and form a thin current sheet with a scale size comparable to that of the ion sound gyro-radius. Here, non-ideal terms in a generalized Ohm's Law appear to play a significant role in the 3D reconnection process as shown by the presence of a strong axial pressure gradient in the current sheet. In addition, a density perturbation with a structure characteristic of a kinetic Alfvén wave is observed to propagate axially in the current layer, anti-parallel to the induced sheet current. Later in the evolution, when a sufficient amount of helicity is injected into the system, a critical threshold for the kink instability is exceeded and the helical twisting of each individual flux rope can dominate the dynamics of the system. This may prevent the complete coalescence of the flux ropes.

Furno, I.; Intrator, T.; Hemsing, E.; Hsu, S.; Lapenta, G.; Abbate, S.

2004-12-01

146

Relaxation of flux ropes and magnetic reconnection in the Reconnection Scaling Experiment at LANL  

NASA Astrophysics Data System (ADS)

Magnetic reconnection and plasma relaxation are studied in the Reconnection Scaling Experiment (RSX) with current carrying plasma columns (magnetic flux ropes). Using plasma guns, multiple flux ropes (B_pol < 100 Gauss, L=90 cm, r < 3 cm) are generated in a three-dimensional (3D) cylindrical geometry and are observed to evolve dynamically during the injection of magnetic helicity. Detailed evolution of electron density, temperature, plasma potential and magnetic field structures is reconstructed experimentally and visible light emission is captured with a fast-gated, intensified CCD camera to provide insight into the global flux rope dynamics. Experiments with two flux ropes in collisional plasmas and in a strong axial guide field (Bz / B_pol > 10) suggest that magnetic reconnection plays an important role in the initial stages of flux rope evolution. During the early stages of the applied current drive (t < 20?_Alfven), the flux ropes are observed to twist, partially coalesce and form a thin current sheet with a scale size comparable to that of the ion sound gyro-radius. Here, non-ideal terms in a generalized Ohm's Law appear to play a significant role in the 3D reconnection process as shown by the presence of a strong axial pressure gradient in the current sheet. In addition, a density perturbation with a structure characteristic of a kinetic Alfvén wave is observed to propagate axially in the current layer, anti-parallel to the induced sheet current. Later in the evolution, when a sufficient amount of helicity is injected into the system, a critical threshold for the kink instability is exceeded and the helical twisting of each individual flux rope can dominate the dynamics of the system. This may prevent the complete coalescence of the flux ropes.

Furno, Ivo

2004-11-01

147

The Geologic Time Scale in Historical Perspective  

NSDL National Science Digital Library

This brief discussion of the development of the Geologic Time Scale begins with Nicolas Steno in 1669 whose ideas have become known as the principles of original horizontal deposition and superposition. Next are James Hutton in 1795 and Charles Lyell in the early 1800s who supported the principle of uniformitarianism. The work of William Smith and the principle of faunal succession is also noted. The site goes on to explain how and why the scale is divided as it is.

148

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. PMID:23935225

Costabel, Stephan; Yaramanci, Ugur

2013-01-01

149

Brownian motion at short time scales  

E-print Network

Brownian motion has played important roles in many different fields of science since its origin was first explained by Albert Einstein in 1905. Einstein's theory of Brownian motion, however, is only applicable at long time scales. At short time scales, Brownian motion of a suspended particle is not completely random, due to the inertia of the particle and the surrounding fluid. Moreover, the thermal force exerted on a particle suspended in a liquid is not a white noise, but is colored. Recent experimental developments in optical trapping and detection have made this new regime of Brownian motion accessible. This review summarizes related theories and recent experiments on Brownian motion at short time scales, with a focus on the measurement of the instantaneous velocity of a Brownian particle in a gas and the observation of the transition from ballistic to diffusive Brownian motion in a liquid.

Tongcang Li; Mark G. Raizen

2012-11-07

150

Shear and bulk viscosities of the hadron gas within relaxation time approximation and its test  

E-print Network

We concentrate on calculation of the shear and bulk viscosities of the hadron gas. They define its dissipative dynamics and influence its experimentally measurable elliptic flow. Due to difficulty of this calculation the relaxation time approximation (RTA) was used in previous works. As those results have approached the realistic ones, there is a need to find out how accurate the RTA is. For this sake we calculate the viscosities in the RTA using cross sections extracted from the ultrarelativistic quantum molecular dynamics (UrQMD) model and compare them with the same ones calculated without the RTA. This allows us to find the estimates of errors due to the application of RTA in the calculations of the viscosities, which are valid also for other similar models. For instance, in the temperature region $100~MeV \\lesssim T \\lesssim 160~MeV$ at zero chemical potentials the shear viscosity becomes smaller up to $1.57$ times, or up to $1.45$ times if the averaged relaxation time is used. This has important consequences for interpretation of the previously made calculations of the viscosities and some other related calculations. Within the RTA, we also find estimation of the enhancement of the bulk viscosity of the hadron gas because of nonconservation of particle numbers.

O. Moroz

2013-12-22

151

The time scale of evolutionary innovation.  

PubMed

A fundamental question in biology is the following: what is the time scale that is needed for evolutionary innovations? There are many results that characterize single steps in terms of the fixation time of new mutants arising in populations of certain size and structure. But here we ask a different question, which is concerned with the much longer time scale of evolutionary trajectories: how long does it take for a population exploring a fitness landscape to find target sequences that encode new biological functions? Our key variable is the length, L, of the genetic sequence that undergoes adaptation. In computer science there is a crucial distinction between problems that require algorithms which take polynomial or exponential time. The latter are considered to be intractable. Here we develop a theoretical approach that allows us to estimate the time of evolution as function of L. We show that adaptation on many fitness landscapes takes time that is exponential in L, even if there are broad selection gradients and many targets uniformly distributed in sequence space. These negative results lead us to search for specific mechanisms that allow evolution to work on polynomial time scales. We study a regeneration process and show that it enables evolution to work in polynomial time. PMID:25211329

Chatterjee, Krishnendu; Pavlogiannis, Andreas; Adlam, Ben; Nowak, Martin A

2014-09-01

152

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

153

Predicting how nanoconfinement changes the relaxation time of a supercooled liquid  

E-print Network

The properties of nanoconfined fluids can be strikingly different from those of bulk liquids. A basic unanswered question is whether the equilibrium and dynamic consequences of confinement are related to each other in a simple way. We study this question by simulation of a liquid comprising asymmetric dumbbell-shaped molecules, which can be deeply supercooled without crystallizing. We find that the dimensionless structural relaxation times - spanning six decades as a function of temperature, density, and degree of confinement - collapse when plotted versus excess entropy. The data also collapse when plotted versus excess isochoric heat capacity, a behaviour that follows from the existence of isomorphs in the bulk and confined states.

Trond S. Ingebrigtsen; Jeffrey R. Errington; Thomas M. Truskett; Jeppe C. Dyre

2013-11-05

154

The hippocampus, time, and memory across scales.  

PubMed

A wealth of experimental studies with animals have offered insights about how neural networks within the hippocampus support the temporal organization of memories. These studies have revealed the existence of "time cells" that encode moments in time, much as the well-known "place cells" map locations in space. Another line of work inspired by human behavioral studies suggests that episodic memories are mediated by a state of temporal context that changes gradually over long time scales, up to at least a few thousand seconds. In this view, the "mental time travel" hypothesized to support the experience of episodic memory corresponds to a "jump back in time" in which a previous state of temporal context is recovered. We suggest that these 2 sets of findings could be different facets of a representation of temporal history that maintains a record at the last few thousand seconds of experience. The ability to represent long time scales comes at the cost of discarding precise information about when a stimulus was experienced--this uncertainty becomes greater for events further in the past. We review recent computational work that describes a mechanism that could construct such a scale-invariant representation. Taken as a whole, this suggests the hippocampus plays its role in multiple aspects of cognition by representing events embedded in a general spatiotemporal context. The representation of internal time can be useful across nonhippocampal memory systems. PMID:23915126

Howard, Marc W; Eichenbaum, Howard

2013-11-01

155

Time scales in tidal disruption events  

NASA Astrophysics Data System (ADS)

We explore the temporal structure of tidal disruption events pointing out the corresponding transitions in the lightcurves of the thermal accretion disk and of the jet emerging from such events. The hydrodynamic time scale of the disrupted star is the minimal time scale of building up the accretion disk and the jet and it sets a limit on the rise time. This suggest that Swift J1644+57, that shows several flares with a rise time as short as a few hundred seconds could not have arisen from a tidal disruption of a main sequence star whose hydrodynamic time is a few hours. The disrupted object must have been a white dwarf. A second important time scale is the Eddington time in which the accretion rate changes form super to sub Eddington. It is possible that such a transition was observed in the light curve of Swift J2058+05. If correct this provides interesting constraints on the parameters of the system.

Piran, T.; Krolik, J.

2012-12-01

156

Prechirper to relax the timing restrictions for soliton-dragging logic gates  

SciTech Connect

The timing restrictions for soliton-dragging logic gates can be relaxed by asymmetrizing the interaction between the orthogonally polarized control and signal pulses. In particular, by prechirping the signal pulse in a normal group-velocity dispersion fiber, we find experimentally that the timing restriction can be loosened from less than 2 pulse widths to over 3.3 pulse widths. For this passive prechirper arrangement the timing restrictions are loosened at the expense of increased minimum switching energy. Soliton-dragging logic gates with a signal prechirper can provide timing restoration as well as logic-level restoration, so that two inverter gates can be cascaded to implement an ultrafast, all-optical pulse regenerator.

Islam, M.N.; Soccolich, C.E.; Chen, C. (AT T Bell Laboratories, Holmdel, New Jersey 07733 (USA)); Paek, U.; Schroeder, C.M. (Engineering Research Center, Princeton, New Jersey 08540 (USA)); DiGiovanni, D.J.; Simpson, J.R. (AT T Bell Laboratories, Murray Hill, New Jersey 07974 (USA))

1991-04-15

157

Multiple scale dynamics in proteins probed at multiple time scales through fluctuations of NMR chemical shifts.  

PubMed

Fluctuations of NMR resonance frequency shifts and their relation with protein exchanging conformations are usually analyzed in terms of simple two-site jump processes. However, this description is unable to account for the presence of multiple time scale dynamics. In this work, we present an alternative model for the interpretation of the stochastic processes underlying these fluctuations of resonance frequencies. Time correlation functions of (15)N amide chemical shifts computed from molecular dynamics simulations (MD) were analyzed in terms of a transiently fractional diffusion process. The analysis of MD trajectories spanning dramatically different time scales (? 200 ns and 1 ms [ Shaw, D. E.; Science 2010, 330, 341 - 346]) allowed us to show that our model could capture the multiple scale structure of chemical shift fluctuations. Moreover, the predicted exchange contribution Rex to the NMR transverse relaxation rate is in qualitative agreement with experimental results. These observations suggest that the proposed fractional diffusion model may provide significative improvement to the analysis of NMR dispersion experiments. PMID:24628040

Calligari, Paolo; Abergel, Daniel

2014-04-10

158

EDITORIAL: Special issue on time scale algorithms  

Microsoft Academic Search

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

Demetrios Matsakis; Patrizia Tavella

2008-01-01

159

Nuclear magnetic resonance and proton relaxation times in experimental heterotopic heart transplantation  

SciTech Connect

It should be possible to detect heart transplant rejection by nuclear magnetic resonance (NMR) imaging if it induces myocardial T1 and T2 proton relaxation time alterations or both. We studied 20 Lewis rats after a heterotopic heart transplantation. In vitro measurement of T1 and T2 was performed on a Minispec PC20 (Bruker) 3 to 9 days after transplantation. Histologic analysis allowed the quantification of rejection process based on cellular infiltration and myocardiolysis. Water content, a major determinant of relaxation time, was also studied. T1 and T2 were significantly prolonged in heterotopic vs orthotopic hearts (638 +/- 41 msec vs 606 +/- 22 msec for T1, p less than 0.01 and 58.2 +/- 8.4 msec vs 47.4 +/- 1.9 msec for T2, p less than 0.001). Water content was also increased in heterotopic hearts (76.4 +/- 2.3 vs 73.8 +/- 1.0, p less than 0.01). Most importantly, we found close correlations between T1 and especially T2 vs water content, cellular infiltration, and myocardiolysis. We conclude that rejection reaction should be noninvasively detected by NMR imaging, particularly with pulse sequences emphasizing T2.

Eugene, M.; Lechat, P.; Hadjiisky, P.; Teillac, A.; Grosgogeat, Y.; Cabrol, C.

1986-01-01

160

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

161

Unsteady immiscible multiphase flow validation of a multiple-relaxation-time lattice Boltzmann method  

NASA Astrophysics Data System (ADS)

The lattice Boltzmann modeling of immiscible multiphase flows needs to be further validated, especially when density variation occurs between the different flow phases. From this perspective, the goal of this research is to introduce the multiple-relaxation-time operator into a lattice Boltzmann model in order to improve its numerical stability in the presence of large density and viscosity ratios. Essentially, this research shows that the introduction of this operator greatly improves the numerical stability of the approach compared to the original single-relaxation-time collision operator. In many lattice Boltzmann research studies, multiphase lattice Boltzmann methods are validated using a reduced number of test cases, and unsteady flow test cases are frequently omitted before much more complex flow configurations are simulated. In this context, several test cases are proposed to evaluate the behavior of a lattice Boltzmann method for simulating immiscible multiphase flows with high density and viscosity ratios. These are: (1) two-phase Couette flow; (2) three-phase Laplace law; (3) three-phase Zalesak disk; (4) two-phase flow between oscillating plates; (5) two-phase capillary wave; and (6) the two-phase oscillating cylindrical bubble. The first two involve a steady regime, and the remaining four an unsteady regime.

Leclaire, S.; Pellerin, N.; Reggio, M.; Trépanier, J.-Y.

2014-03-01

162

Pressure dependence of structural relaxation time in terms of the Adam-Gibbs model  

NASA Astrophysics Data System (ADS)

A new equation describing the behavior of the structural relaxation time, ?(T,P), as a function of both pressure and temperature, is discussed. This equation has been derived from the Adam-Gibbs theory by writing the configurational entropy, Sc, in terms of the excess thermal heat capacity and of the molar thermal expansion. Consequently, the parameters introduced in the expression are directly related to specific physical properties of the material, such as the thermal expansion coefficient ? and the isothermal bulk modulus K0. At a fixed pressure, for low pressures, the found equation reduces to a Vogel-Fulcher-Tammann equation of ? versus temperature with the fragility parameter independent from pressure. The equation for ?(T,P) was successfully tested directly by fitting the dielectric relaxation time data for two isothermal and one isobaric measurements on diglycidyl ether of bisphenol-A, carried out in previous experiments. The parameters estimated by the best fit were in reasonable agreement with the values determined from the known physical properties of the material. Finally, the expression for the change versus pressure of the temperatures at which the same value of ?max is obtained (e.g., the change versus pressure of the glass transition temperature) agrees with several expressions previously proposed in the literature to provide a phenomenological description of the observed phenomena.

Casalini, R.; Capaccioli, S.; Lucchesi, M.; Rolla, P. A.; Corezzi, S.

2001-03-01

163

EPR linewidth variation, spin relaxation times, and exchange in amorphous hydrogenated carbon  

NASA Astrophysics Data System (ADS)

Electron paramagnetic resonance (EPR) measurements have been made of amorphous hydrogenated carbon (a-C:H) films grown by plasma enhanced chemical vapor deposition (PECVD) with negative self-bias voltages Vb in the approximate range 10-540 V. For Vb<100 V, as the film changes from polymerlike to diamondlike, the changes in linewidth and shape are interpreted in terms of changes to two contributions-one due to dipolar interactions between the unpaired spins and one due to unresolved lines arising from hyperfine interactions with H1. The former yields a Lorentzian line, the latter a Gaussian, and the resultant spectrum has the Voigt shape. The empirical relation ?BGpp (in Gauss)=(0.18+/-0.05)×(at. % H) between the peak-to-peak Gaussian contribution (in Gauss) ?BGpp and the hydrogen content in atomic percentage is obtained. For Vb>100 V the linewidth is shown to be dominated by the dipolar interactions and exchange and it decreases as Vb increases; the change is shown to arise primarily from a change in the exchange interaction. Evidence for this comes from measurements which show that the spin-lattice relaxation time appreciably shortens and the spin-spin relaxation time lengthens as the bias voltage is increased. The magnitude and variation with bias of the linewidth are consistent with the EPR signal originating from the ?-type radicals.

Barklie, R. C.; Collins, M.; Silva, S. R. P.

2000-02-01

164

Phase-field-based multiple-relaxation-time lattice Boltzmann model for incompressible multiphase flows  

NASA Astrophysics Data System (ADS)

In this paper, a phase-field-based multiple-relaxation-time lattice Boltzmann (LB) model is proposed for incompressible multiphase flow systems. In this model, one distribution function is used to solve the Chan-Hilliard equation and the other is adopted to solve the Navier-Stokes equations. Unlike previous phase-field-based LB models, a proper source term is incorporated in the interfacial evolution equation such that the Chan-Hilliard equation can be derived exactly and also a pressure distribution is designed to recover the correct hydrodynamic equations. Furthermore, the pressure and velocity fields can be calculated explicitly. A series of numerical tests, including Zalesak's disk rotation, a single vortex, a deformation field, and a static droplet, have been performed to test the accuracy and stability of the present model. The results show that, compared with the previous models, the present model is more stable and achieves an overall improvement in the accuracy of the capturing interface. In addition, compared to the single-relaxation-time LB model, the present model can effectively reduce the spurious velocity and fluctuation of the kinetic energy. Finally, as an application, the Rayleigh-Taylor instability at high Reynolds numbers is investigated.

Liang, H.; Shi, B. C.; Guo, Z. L.; Chai, Z. H.

2014-05-01

165

Bulk Viscosity and Relaxation Time of Causal Dissipative Relativistic Fluid Dynamics  

E-print Network

The microscopic formulae of the bulk viscosity $\\zeta $ and the corresponding relaxation time $\\tau_{\\Pi}$ in causal dissipative relativistic fluid dynamics are derived by using the projection operator method. In applying these formulae 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 $\\tau_{\\Pi}$ and $\\zeta $ are related as $\\tau_{\\Pi}=\\zeta /[\\beta \\{(1/3-c_{s}^{2})(\\epsilon +P)-2(\\epsilon -3P)/9\\}]$, where $\\epsilon $, $P$ and $c_{s}$ are the energy density, pressure and velocity of sound, respectively. The predicted $\\zeta $ and $% \\tau_{\\Pi}$ 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 the three approaches are consistent with the causality condition.

Xu-Guang Huang; Takeshi Kodama; Tomoi Koide; Dirk H. Rischke

2010-10-21

166

Measurement of myocardial T1 relaxation times in humans with inversion recovery EPI  

NASA Astrophysics Data System (ADS)

Changes in myocardial longitudinal relaxation time (T1) are important for evaluating myocardial blood flow with first-pass contrast-enhanced MRI. Relaxation dynamics for inversion recovery echo planar imaging (IR-EPI) are less complex than partial flip angle, field echo techniques. The goal of this project is to develop and evaluate a robust method for measuring T1 in intact, beating human hearts. IR-EPI was performed on eight asymptomatic volunteers using a 1.5 Tesla MRI system. Imaging parameters were: FOV equals 42.5 cm, phase sampling ratio equals 0.609-0.781, 64 X 112 matrix, TEeff equals 47.8 ms., at least six inversion times, TI, ranging from 72 to 1400 ms, one shot. Four short axis slices were obtained for each TI. Signal intensities were measured for four ROI myocardial segments in each slice and plotted versus TI. T1 measurements were validated using a phantom containing gadolinium contrast at various dilutions. Linear interpolation was used following logarithmic transformation to calculate myocardial T1 based on the determination of the null point. The mean global myocardial T1 value was 811 ms+/- 49.8 ms (mean +/- SD). We conclude that myocardial T1 measurements, specific to each patient, can be measured with good accuracy and reproducibility using IR-EPI.

Pongnapang, Napapong; Clarke, Geoffrey D.; Ozus, Bahadir; Amurao, Maxwell; Lane, Michael J.; Belden, Clifford J.

2001-06-01

167

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

168

Picosecond-Time-Scale Fluctuations of Proteins in Glassy Matrices: The Role of Viscosity  

SciTech Connect

Through elastic neutron scattering we investigated the fast dynamics of lysozyme in hydrated powder form or embedded in glycerol-water and glucose-water matrices. We calculated the relaxational contribution to the mean square displacements of protein hydrogen atoms. We found that the inverse of this quantity is linearly proportional to the logarithm of the viscosity of the solvent glassy matrix. This relationship suggests a close connection between the picosecond-time-scale dynamics of protein side chains and the solvent structural relaxation.

Cornicchi, Elena; Onori, Giuseppe; Paciaroni, Alessandro [Dipartimento di Fisica, Universita di Perugia, INFM-CRS SOFT Unita di Perugia, and Centro per i Materiali Innovativi e Nanostrutturati (CEMIN), Via A. Pascoli, I-06123 Perugia (Italy)

2005-10-07

169

Scaling in the Timing of Extreme Events  

E-print Network

Extreme events can come either from point processes, when the size or energy of the events is above a certain threshold, or from time series, when the intensity of a signal surpasses a threshold value. We are particularly concerned by the time between these extreme events, called respectively waiting time and quiet time. If the thresholds are high enough it is possible to justify the existence of scaling laws for the probability distribution of the times as a function of the threshold value, although the scaling functions are different in each case. For point processes, in addition to the trivial Poisson process, one can obtain double-power-law distributions with no finite mean value. This is justified in the context of renormalization-group transformations, where such distributions arise as limiting distributions after iterations of the transformation. Clear connections with the generalized central limit theorem are established from here. The non-existence of finite moments leads to a semi-parametric scaling...

Corral, Alvaro

2014-01-01

170

The Effect of Timed Relaxation on Keyboarding Achievement. Research Bulletin No. 46-B.  

ERIC Educational Resources Information Center

Research has shown that relaxation exercises produce physical changes in students. After relaxation exercises, students appear calmer, have reduced levels of anxiety, and are more responsive to instruction. In order to determine if relaxation exercises would improve the rate at which students learn keyboarding, a study was conducted in a South…

Matthews, Doris B.

171

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

172

Transport coefficients for bulk viscous evolution in the relaxation time approximation  

E-print Network

We derive the form of the viscous corrections to the phase-space distribution function due to the bulk viscous pressure and shear stress tensor using the iterative Chapman-Enskog method. We then calculate the transport coefficients necessary for the second-order hydrodynamic evolution of the bulk viscous pressure and the shear stress tensor. We demonstrate that the transport coefficients obtained using the Chapman-Enskog method are different than those obtained previously using the 14-moment approximation for a finite particle mass. Specializing to the case of boost-invariant and transversally homogeneous longitudinal expansion, we show that the transport coefficients obtained using the Chapman-Enskog method result in better agreement with the exact solution of the Boltzmann equation in the relaxation-time approximation compared to results obtained in the 14-moment approximation. Finally, we explicitly confirm that the time evolution of the bulk viscous pressure is significantly affected by its coupling to the shear stress tensor.

Amaresh Jaiswal; Radoslaw Ryblewski; Michael Strickland

2014-07-27

173

Theoretical analysis for measuring the relaxation time between two subvalance bands by using transient incoherent spectroscopy  

NASA Astrophysics Data System (ADS)

A new scheme for studying dynamics process of semiconductor optical amplifier (SOA) in quantum wells structure (QWS) is proposed based on A-type three-level model. When the system is off-resonantly excited by incoherent light beams, the interaction process can be regarded as a coherent Anti-Stokes Raman scattering (CARS). The signal behavior determined by ultrafast process of sub-valance-band (SVB) are analyzed by the transient incoherent spectroscopy based on CARS. If the broad-band light resource as light emitting diode(LED) is utilized in experiment, the time resolution extends femtosecond-resolved. This experiment scheme which is composed of LED ,multimode fiber and the other devices is rather useful to investigate the carrier relaxation time between the two SVl3s.

Hu, Zhenhua; Huang, Dexiu; Gao, Shuzhong

2002-08-01

174

Hydration structure and dynamics in pullulan aqueous solution based on 1H NMR relaxation time  

NASA Astrophysics Data System (ADS)

Dynamic properties of water and polymer chain proton in pullulan/H 2O systems in aqueous solutions and in frozen states were analyzed based on T2 relaxation times in 1H-NMR and DSC. Two relaxing species with different T2 detected in the CPMG pulse sequence were assigned to inert polymer protons with the shorter T2 and to water protons with the longer T2 by using deuterated pullulan solutions in D 2O. It has been proved that hydration water and free water undergoes rapid exchange in pullulan aqueous solutions. In the frozen state at -11°C, protons in ice crystals (T 2˜17 ?s), protons in mobile water ( T2>ms) and inert and labile protons in polymer chains (T 2˜0.1 ms) were distinguished in FID curves measured by using the solid echo pulse sequence. With increase in temperature, the inert protons and the labile protons show different mobility, and the inert protons are separately observable from the labile protons in the Carr-Percell-Meiboom-Gill (CPMG) method at temperatures higher than 0°C and the labile protons become mixed with water protons by rapid chemical exchange. These findings indicate the extremely high flexibility of the pullulan chain in aqueous solution.

Okada, Ryo; Matsukawa, Shingo; Watanabe, Tokuko

2002-01-01

175

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

NASA Astrophysics Data System (ADS)

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.

Zeghib, Nadir; Grucker, Daniel

2001-09-01

176

Understanding long-time vacancy aggregation in iron: A kinetic activation-relaxation technique study  

NASA Astrophysics Data System (ADS)

Vacancy diffusion and clustering processes in body-centered-cubic (bcc) Fe are studied using the kinetic activation-relaxation technique (k-ART), an off-lattice kinetic Monte Carlo method with on-the-fly catalog building capabilities. For monovacancies and divacancies, k-ART recovers previously published results while clustering in a 50-vacancy simulation box agrees with experimental estimates. Applying k-ART to the study of clustering pathways for systems containing from one to six vacancies, we find a rich set of diffusion mechanisms. In particular, we show that the path followed to reach a hexavacancy cluster influences greatly the associated mean-square displacement. Aggregation in a 50-vacancy box also shows a notable dispersion in relaxation time associated with effective barriers varying from 0.84 to 1.1 eV depending on the exact pathway selected. We isolate the effects of long-range elastic interactions between defects by comparing to simulations where those effects are deliberately suppressed. This allows us to demonstrate that in bcc Fe, suppressing long-range interactions mainly influences kinetics in the first 0.3 ms, slowing down quick energy release cascades seen more frequently in full simulations, whereas long-term behavior and final state are not significantly affected.

Brommer, Peter; Béland, Laurent Karim; Joly, Jean-François; Mousseau, Normand

2014-10-01

177

Short-time scale behavior modeling within long-time scale fuel cycle evaluations  

SciTech Connect

Typically, short-time and long-time scales in nuclear energy system behavior are accounted for with entirely separate models. However, long-term changes in system characteristics do affect short-term transients through material variations. This paper presents an approach to consistently account for short-time scales within a nuclear system lifespan. The reported findings and developments are of significant importance for small modular reactors and other nuclear energy systems operating in autonomous modes. It is necessary to simulate the short time-scale kinetic behavior of the reactor as well as the long time-scale dynamics that occur with fuel burnup. The former is modeled using the point kinetics equations, while the latter is modeled by the Bateman equations. (authors)

Johnson, M.; Tsvetkov, P. [Dept. of Nuclear Engineering, Texas A and M Univ., 3133 TAMU, College Station, TX 77843 (United States); Lucas, S. [Idaho National Laboratory, P.O. Box 1625, Idaho Falls, ID 83415 (United States)

2012-07-01

178

Equilibrium distributions and relaxation times in gaslike economic models: An analytical derivation  

NASA Astrophysics Data System (ADS)

A step-by-step procedure to derive analytically the exact dynamical evolution equations of the probability density functions (PDFs) of well-known kinetic wealth exchange economic models is shown. This technique gives a dynamical insight into the evolution of the PDF, for example, allowing the calculation of its relaxation times. Their equilibrium PDFs can also be calculated by finding its stationary solutions. This gives as a result an integro-differential equation, which can be solved analytically in some cases and numerically in others. This should provide some guidance into the type of PDFs that can be derived from particular economic agent exchange rules or, for that matter, any other kinetic model of gases with particular collision physics.

Calbet, Xavier; López, José-Luis; López-Ruiz, Ricardo

2011-03-01

179

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. PMID:22025981

Soroushian, Behrouz; Yang, Xinmai

2011-01-01

180

Reconstructing the Initial Relaxation Time of Young Star Clusters in the Large Magellanic Cloud: The Evolution of Star Clusters  

NASA Astrophysics Data System (ADS)

We reconstruct the initial two-body relaxation time at the half mass radius for a sample of young ? 300 Myr star clusters in the Large Magellanic cloud. We achieve this by simulating star clusters with 12288 to 131072 stars using direct N-body integration. The equations of motion of all stars are calculated with high precision direct N-body simulations which include the effects of the evolution of single stars and binaries. We find that the initial relaxation times of the sample of observed clusters in the Large Magellanic Cloud ranges from about 200 Myr to about 2 Gyr. The reconstructed initial half-mass relaxation times for these clusters have a much narrower distribution than the currently observed distribution, which ranges over more than two orders of magnitude.

Portegies Zwart, S. F.; Chen, H.-C.

2008-06-01

181

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

PubMed

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. PMID:16803072

Asinari, Pietro

2006-05-01

182

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

183

Time scale analysis of ISTTOK probe data  

SciTech Connect

Magnetic and turbulent activity in a tokamak plasma discharge may evolve in a complex trend during the discharge. In the ISTTOK tokamak, characterised by a short 30ms pulse duration, particle confinement of the order 0.3 ms and typical burst-like activity, the analysis of the time scales involved in the plasma activity is even more demanding. In this work, use is made of the Empirical Mode Decomposition (EMD) method as a tool for turbulence and MHD instability analysis obtained with Langmuir and magnetic probes, respectively. The time evolution of the energy content and wavenumber characterisation of fluctuating potential, edge plasma density and perturbed magnetic fields is investigated, with special emphasis on discharges where both limiter and electrode biasing were used to induce local sheared electric fields, thus affecting turbulence and consequently particle confinement.

Coelho, R.; Alves, D.; Silva, C. [Associacao Euratom/IST, Centro de Fusao Nuclear, 1049-001 Lisboa (Portugal)

2008-04-07

184

Convergence of Unilateral Laplace Transforms on Time Scales  

Microsoft Academic Search

A time scale is any closed subset of the real line. Continuous time and discrete time are special cases. The unilateral Laplace\\u000a transform of a signal on a time scale subsumes the continuous-time unilateral Laplace transform, and the discrete-time unilateral\\u000a z-transform as special cases. The regions of convergence (ROCs) time scale Laplace transforms are determined by the time scale’s\\u000a graininess.

John M. Davis; Ian A. Gravagne; Robert J. Marks

2010-01-01

185

Origin of Abrupt Rise in Deuteron NMR Longitudinal Relaxation Times of Protein Methyl Groups Below 90 K  

SciTech Connect

In order to examine the origin of the abrupt change in the temperature dependence of NMR longitudinal relaxation times observed earlier 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), 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 hops 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 300-70 K.

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

2013-05-23

186

Nanosecond Time Scale Motions in Proteins Revealed by High-Resolution NMR Relaxometry  

PubMed Central

Understanding the molecular determinants underlying protein function requires the characterization of both structure and dynamics at atomic resolution. Nuclear relaxation rates allow a precise characterization of protein dynamics at the Larmor frequencies of spins. This usually limits the sampling of motions to a narrow range of frequencies corresponding to high magnetic fields. At lower fields one cannot achieve sufficient sensitivity and resolution in NMR. Here, we use a fast shuttle device where the polarization builds up and the signals are detected at high field, while longitudinal relaxation takes place at low fields 0.5 < B0 < 14.1 T. The sample is propelled over a distance up to 50 cm by a blowgun-like system in about 50 ms. The analysis of nitrogen-15 relaxation in the protein ubiquitin over such a wide range of magnetic fields offers unprecedented insights into molecular dynamics. Some key regions of the protein feature structural fluctuations on nanosecond time scales, which have so far been overlooked in high-field relaxation studies. Nanosecond motions in proteins may have been underestimated by traditional high-field approaches, and slower supra-?c motions that have no effect on relaxation may have been overestimated. High-resolution relaxometry thus opens the way to a quantitative characterization of nanosecond motions in proteins. PMID:24228712

2013-01-01

187

Time Out from Tension: Teaching Young Children How To Relax. Teaching Strategies.  

ERIC Educational Resources Information Center

Discusses how using relaxation and stress reduction activities with individual preschool and elementary school-age children during difficult periods can help them regain control, and how integrating relaxation techniques into everyday activities helps to establish positive behavior patterns to support healthy living. Presents breathing activities…

Scully, Patricia

2003-01-01

188

PSYCHOPHYSIOLOGICAL CHANGES AT THE TIME OF EXAMINATION IN MEDICAL STUDENTS BEFORE AND AFTER THE PRACTICE OF YOGA AND RELAXATION  

PubMed Central

The effect of yoga and relaxation changes in psychophysiological parameters in response to the stress of examination in 75 medical students was studied. Initially five parameters (anxiety level, heart rate, blood pressure, galvanic skin resistance and choice reaction time) were recorded, a month before the examination and on the day of examination. Students were then randomly divided into 3 group of 25 each. One group practiced yoga (Group- Y), and another group practiced relaxation (group-R) regularly for three months. The third group was control group (Group-C). All the parameters were recorded after the changes in anxiety level, heart rate, blood pressure, and galvanic skin resistance in response to stress of examination were significantly attenuated and there was significant improvement in choice reaction time in Group-Y and Group-R as compared to Group-C after yoga and relaxation. PMID:21494440

Malathi, A.; Damodaran, A.; Shah, N.; Krishnamurthy, G.; Namjoshi, P.; Ghodke, S.

1998-01-01

189

Waveform-Relaxation based iterative real-time playback schemes for testing of wide area power system controllers  

Microsoft Academic Search

An alternative to real-time simulation for hardware-in-the-loop testing is proposed. This involves system simulation, not necessarily done in real time, and real-time playback of the simulated output to the controller under test. The time-stamped controller output is stored and subsequently fed as an input to the simulation. This whole process is done iteratively as in the Waveform Relaxation method, till

A. M. Kulkarni; K. Salunkhe; M. C. Chandorkar; S. P. Panda; N. Sankaranarayanan

2010-01-01

190

Structural relaxation dynamics and annealing effects of sodium silicate glass.  

PubMed

Here we report high-precision measurements of structural relaxation dynamics in the glass transition range at the intermediate and short length scale for a strong sodium silicate glass during long annealing times. We evidence for the first time the heterogeneous dynamics at the intermediate range order by probing the acoustic longitudinal frequency in the GHz region by Brillouin light scattering spectroscopy. Or, from in-situ Raman measurements, we show that relaxation is indeed homogeneous at the interatomic length scale. Our results show that the dynamics at the intermediate range order contains two distinct relaxation time scales, a fast and a slow component, differing by about a 10-fold factor below Tg and approaching to one another past the glass transition. The slow relaxation time agrees with the shear relaxation time, proving that Si-O bond breaking constitutes the primary control of structural relaxation at the intermediate range order. PMID:23574051

Naji, Mohamed; Piazza, Francesco; Guimbretière, Guillaume; Canizarès, Aurélien; Vaills, Yann

2013-05-01

191

Interest point detection and scale selection in space-time  

E-print Network

by maximising a scale-normalised space-time Laplacian operator over both spatial scales and temporal scales that the resulting approach is truly scale invariant with respect to both spatial scales and temporal scales of the data in both the spatial and the temporal directions. For example, consider scenes with a person

Lindeberg, Tony

192

Two Distinct Time-Scale Regimes of the Effective Temperature for an Aging Colloidal Glass  

E-print Network

Colloidal dispersions of Laponite platelets are known to age slowly from viscous sols to colloidal glasses. We follow this aging process by monitoring the diffusion of probe particles embedded in the sample via dynamic light scattering. Our results show that the time-dependent diffusion of the probe particles scales with their size. This implies that the fluctuation-dissipation theorem can be generalized for this out-of-equilibrium system by replacing the bath temperature with an effective temperature. Simultaneous dynamic rheological measurements reveal that this effective temperature increases as a function of aging time and frequency. This suggests the existence of two regimes: at probed time scales longer than the characteristic relaxation time of the Laponite dispersion, the system thermalizes with the bath, whereas at shorter time scales, the system is out-of-equilibrium with an effective temperature greater than the bath temperature.

D. R. Strachan; G. C. Kalur; S. R. Raghavan

2005-10-27

193

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

194

Time-resolved resonance Raman study on ultrafast structural relaxation and vibrational cooling of photodissociated carbonmonoxy myoglobin.  

PubMed

A localized small structural change is converted to a higher order conformational change of protein and extends to a mesoscopic scale to induce a physiological function. To understand such features of protein, ultrafast dynamics of myoglobin (Mb) following photolysis of carbon monoxide were investigated. Recent results are summarized here with a stress on structural and vibrational energy relaxation. The core expansion of heme takes place within 2 ps but the out of plane displacement of the heme iron and the accompanying protein conformational change occur in 10 and 100 s of the picosecond regimes, respectively. Unexpectedly, it was found from UV resonance Raman spectra that Trp7 in the N-terminal region and Tyr151 in the C-terminal region undergo appreciable structural changes upon ligand binding-dissociation while Tyr104, Tyr146, and Trp14 do not. Because of the communication between the movements of these surface residues and the heme iron, the rate of spectral change of the iron-histidine (Fe- His) stretching band after CO photodissociation is influenced by the viscosity of solvent. Temporal changes of the anti-Stokes Raman intensity demonstrated immediate generation of vibrationally excited heme upon photodissociation and its decay with a time constant of 1-2 ps. PMID:12012433

Kitagawa, Teizo; Haruta, Nami; Mizutani, Yasuhisa

2002-01-01

195

Temperature Dependence of Relaxation Time in Adam-Gibbs Model of Glass-Forming Liquids: Fluctuation Effects  

NASA Astrophysics Data System (ADS)

We propose a technique that takes into account fluctuations in the number of molecules in a "cooperative rearranging" region in the Adam-Gibbs model of supercooled liquid. The temperature dependence of relaxation time for "cooperative rearrangements" in glass-forming liquids is expressed in terms of experimentally measurably quantities.

Mohanty, Udayan

2008-07-01

196

The time-course of bilateral changes in the reflex excitability of relaxed triceps surae muscle in human hemiparetic spasticity  

Microsoft Academic Search

Short, rapid dorsiflexion of the normal human ankle induces a single, synchronised reflex EMG response in the initially relaxed triceps surae muscle (TS). In subjects in whom hemiparesis is present as a result of a unilateral ischaemic cerebral lesion, a reflex EMG response can be elicited on either side with timing identical to that of the normal response. The magnitude

Alfred F. Thilmann; Stuart J. Fellows

1991-01-01

197

Master equation for the Unruh-DeWitt detector and the universal relaxation time in de Sitter space  

NASA Astrophysics Data System (ADS)

We derive the master equation that completely determines the time evolution of the density matrix of the Unruh-DeWitt detector in an arbitrary background geometry. We apply the equation to reveal a nonequilibrium thermodynamic character of de Sitter space. This generalizes an earlier study on the thermodynamic property of the Bunch-Davies vacuum that an Unruh-DeWitt detector staying in the Poincaré patch and interacting with a scalar field in the Bunch-Davies vacuum behaves as if it is in a thermal bath of finite temperature. In this paper, instead of the Bunch-Davies vacuum, we consider a class of initial states of scalar field, for which the detector behaves as if it is in a medium that is not in thermodynamic equilibrium and that undergoes a relaxation to the equilibrium corresponding to the Bunch-Davies vacuum. We give a prescription for calculating the relaxation times of the nonequilibrium processes. We particularly show that, when the initial state of the scalar field is the instantaneous ground state at a finite past, the relaxation time is always given by a universal value of half the curvature radius of de Sitter space. We expect that the relaxation time gives a nonequilibrium thermodynamic quantity intrinsic to de Sitter space.

Fukuma, Masafumi; Sugishita, Sotaro; Sakatani, Yuho

2014-03-01

198

Microwave dielectric relaxation study of 1Hexanol with 1-propenol mixture by using time domain reflectometry at 300K  

Microsoft Academic Search

Dielectric relaxation measurement of 1-Hexanol (1-HE), 1-Propenol (1-PR) & their complex have been carried out over the entire concentration range using time domain reflectometry technique at 300 K in the frequency range of 10 KHz to 20-GHz. Bilinear calibration method is used to obtain complex permittivity ??*(??) from complex reflection coefficient ??*(??) over the frequency range of 10 MHz to

Anil Tidar; Sayyad Shafiyoddin; Siddharth Kamble; G. M. Dharne; S. S. Patil; P. W. Khirade; S. C. Mehrotra

2009-01-01

199

Longer T2 relaxation time is a marker of hypothalamic gliosis in mice with diet-induced obesity  

PubMed Central

A hallmark of brain injury from infection, vascular, neurodegenerative, and other disorders is the development of gliosis, which can be detected by magnetic resonance imaging (MRI). In rodent models of diet-induced obesity (DIO), high-fat diet (HFD) consumption rapidly induces inflammation and gliosis in energy-regulating regions of the mediobasal hypothalamus (MBH), and recently we reported MRI findings suggestive of MBH gliosis in obese humans. Thus, noninvasive imaging may obviate the need to assess MBH gliosis using histopathological end points, an obvious limitation to human studies. To investigate whether quantitative MRI is a valid tool with which to measure MBH gliosis, we performed analyses, including measurement of T2 relaxation time from high-field MR brain imaging of mice fed HFD and chow-fed controls. Mean bilateral T2 relaxation time was prolonged significantly in the MBH, but not in the thalamus or cortex, of HFD-fed mice compared with chow-fed controls. Histological analysis confirmed evidence of increased astrocytosis and microglial accumulation in the MBH of HFD-fed mice compared with controls, and T2 relaxation times in the right MBH correlated positively with mean intensity of glial fibrillary acidic protein staining (a marker of astrocytes) in HFD-fed animals. Our findings indicate that T2 relaxation time obtained from high-field MRI is a useful noninvasive measurement of HFD-induced gliosis in the mouse hypothalamus with potential for translation to human studies. PMID:23548614

Lee, Donghoon; Thaler, Joshua P.; Berkseth, Kathryn E.; Melhorn, Susan J.; Schwartz, Michael W.

2013-01-01

200

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 ...

201

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

202

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

NASA Astrophysics Data System (ADS)

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, ? S_{conf}^E /E^2, of 50 dipolar liquids, including those whose static permittivity, ?s, decreases on cooling. The field induced change, ? S_{conf}^E, is found to be experimentally detectable only when E is on the order of 105 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 105 V/cm range. Therefore, such high E values may be used to estimate ? S_{conf}^E. We conclude that (i) for E in the 105 V/cm range, ? S_{conf}^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.

Johari, G. P.

2013-04-01

203

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

204

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. PMID:22071580

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

2013-01-01

205

Relaxing the closure assumption in occupancy models: staggered arrival and departure times.  

PubMed

Occupancy statistical models that account for imperfect detection have proved very useful in several areas of ecology, including species distribution and spatial dynamics, disease ecology, and ecological responses to climate change. These models are based on the collection of multiple samples at each of a number of sites within a given season, during which it is assumed the species is either absent or present and available for detection while each sample is taken. However, for some species, individuals are only present or available for detection seasonally. We present a statistical model that relaxes the closure assumption within a season by permitting staggered entry and exit times for the species of interest at each site. Based on simulation, our open model eliminates bias in occupancy estimators and in some cases increases precision. The power to detect the violation of closure is high if detection probability is reasonably high. In addition to providing more robust estimation of occupancy, this model permits comparison of phenology across sites, species, or years, by modeling variation in arrival or departure probabilities. In a comparison of four species of amphibians in Maryland we found that two toad species arrived at breeding sites later in the season than a salamander and frog species, and departed from sites earlier. PMID:23687887

Kendall, William L; Hines, James E; Nichols, James D; Grant, Evan H Campbell

2013-03-01

206

Sensitivity of muscle proton spin-spin relaxation time as an index of muscle activation.  

PubMed

The purpose of this study was to determine the minimum number of contractions that are needed to detect an increase in the muscle proton spin-spin relaxation time (T2) at a given exercise intensity. Five healthy human subjects performed five sets of an exercise that included concentric and eccentric contractions of the elbow-flexor muscles with loads that were 25 or 80% of maximum. With the 80% load, the five sets involved 1, 2, 5, 10, or 20 repetitions of the exercise; with the 25% load the five sets were 2, 5, 10, 20, or 40 repetitions. The upper arm of each subject was imaged before and immediately after each set of the exercise. Spin-echo images (repetition time/echo time = 2,000 ms/30, 60, 90, and 120 ms) were collected using an extremity coil, and T2 values were calculated. The signal intensity was measured from the elbow-flexor and -extensor muscles and from the bone marrow of the humerus. With the 80% load, T2 increased in the short head of the biceps brachii after two repetitions of the elbow exercise and after five repetitions in the brachialis and the long head of the biceps brachii. With the 25% load, T2 became longer after five repetitions of the exercise for the short head of the biceps brachii and after 10 repetitions for the brachialis and the long head of the biceps brachii. T2 varied linearly with the number of contraction repetitions for each of the elbow-flexor muscles at either load (r2 > or = 0.97, P < 0.001).(ABSTRACT TRUNCATED AT 250 WORDS) PMID:7961279

Yue, G; Alexander, A L; Laidlaw, D H; Gmitro, A F; Unger, E C; Enoka, R M

1994-07-01

207

Long Spin Relaxation and Coherence Times of Electrons In Gated Si/SiGe Quantum Dots  

NASA Astrophysics Data System (ADS)

Single electron spin states in semiconductor quantum dots are promising candidate qubits. We report the measurement of 250 ?s relaxation (T1) and coherence (T2) times of electron spins in gated Si/SiGe quantum dots at 350 mK. The experiments used conventional X-band (10 GHz) pulsed electron spin resonance (pESR), on a large area (3.5 x 20 mm^2) dual-gate undoped high mobility Si/SiGe heterostructure sample, which was patterned with 2 x 10^8 quantum dots using e-beam lithography. Dots having 150 nm radii with a 700 nm period are induced in a natural Si quantum well by the gates. The measured T1 and T2 at 350 mK are much longer than those of free 2D electrons, for which we measured T1 to be 10 ?s and T2 to be 6.5 ?s in this gated sample. The results provide direct proof that the effects of a fluctuating Rashba field have been greatly suppressed by confining the electrons in quantum dots. From 0.35 K to 0.8 K, T1 of the electron spins in the quantum dots shows little temperature dependence, while their T2 decreased to about 150 ?s at 0.8 K. The measured 350 mK spin coherence time is 10 times longer than previously reported for any silicon 2D electron-based structures, including electron spins confined in ``natural quantum dots'' formed by potential disorder at the Si/SiO2ootnotetextS. Shankar et al., Phys. Rev. B 82, 195323 (2010) or Si/SiGe interface, where the decoherence appears to be controlled by spin exchange.

He, Jianhua; Tyryshkin, A. M.; Lyon, S. A.; Lee, C.-H.; Huang, S.-H.; Liu, C. W.

2012-02-01

208

Uncertainty, entropy, scaling and hydrological stochastics. 2. Time dependence of hydrological processes and time scaling  

Microsoft Academic Search

The well-established physical and mathematical principle of maximum entropy (ME), is used to explain the distributional and autocorrelation properties of hydrological processes, including the scaling behaviour both in state and in time. In this context, maximum entropy is interpreted as maximum uncertainty. The conditions used for the maximization of entropy are as simple as possible, i.e. that hydrological processes are

DEMETRIS KOUTSOYIANNIS

209

Role of entropy in the thermodynamic evolution of the time scale of molecular dynamics near the glass transition  

E-print Network

In this Letter, we investigate how changes in the system entropy influence the characteristic time scale of the system molecular dynamics near the glass transition. Independently of any model of thermodynamic evolution of the time scale, against some previous suppositions, we show that the system entropy $S$ is not sufficient to govern the time scale defined by structural relaxation time $\\tau $. In the density scaling regime, we argue that the decoupling between $\\tau $ and $S$ is a consequence of different values of the scaling exponents $\\gamma $ and $\\gamma_S $ in the density scaling laws, $\\tau = f(\\rho ^\\gamma /T)$ and $S = h(\\rho ^{\\gamma_S}/T)$, where $\\rho $ and $T$ denote density and temperature, respectively. It implies that the proper relation between $\\tau $ and $S$ requires supplementing with a density factor, $u(\\rho)$, i.e.,$\\tau = g(u(\\rho)w(S))$. This meaningful finding additionally demonstrates that the density scaling idea can be successfully used to separate physically relevant contributions to the time scale of molecular dynamics near the glass transition. As an example, we revise the Avramov entropic model of the dependence $\\tau (T,\\rho)$, giving evidence that its entropic basis has to be extended by the density dependence of the maximal energy barrier for structural relaxation. We also discuss the excess entropy $S_{ex}$, the density scaling of which is found to mimic the density scaling of the total system entropy $S$.

K. Grzybowska; A. Grzybowski; S. Pawlus; J. Pionteck; M. Paluch

2014-06-18

210

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

211

Dynamic Relaxation of Financial Indices  

NASA Astrophysics Data System (ADS)

The dynamic relaxation of the German DAX both before and after a large price-change is investigated. The dynamic behavior is characterized by a power law. At the minutely time scale, the exponent p governing the power-law behavior takes a same value before and after the large price change, while at the daily time scale, it is different. Numerical simulations of an interacting EZ herding model are performed for comparison.

Shen, J.; Zheng, B.; Lin, H.; Qiu, T.

212

Comparison of longitudinal metabolite relaxation times in different regions of the human brain at 1.5 and 3 Tesla  

Microsoft Academic Search

In vivo longitudinal relaxation times of N-acetyl compounds (NA), choline-containing substances (Cho), creatine (Cr), myo- inositol (mI), and tissue water were measured at 1.5 and 3 T using a point-resolved spectroscopy (PRESS) sequence with short echo time (TE). T1 values were determined in six different brain regions: the occipital gray matter (GM), occipital white matter (WM), motor cortex, frontoparietal WM,

Thomas Ethofer; Irina Mader; Uwe Seeger; Gunther Helms; Michael Erb; Wolfgang Grodd; Albert Ludolph; Uwe Klose

2003-01-01

213

A method to diagnose sources of annular mode time scales  

Microsoft Academic Search

Stratospheric annular mode time scales linked to local temperature variationsTropospheric annular mode time scales linked to surface pressure variationsSurface pressure-temperature cross correlations are weak but highly persistent

Lawrence R. Mudryk; Paul J. Kushner

2011-01-01

214

Improving Estimates of Nuclear-Spin Relaxation Time (T1) in Surface-NMR Experiments  

NASA Astrophysics Data System (ADS)

Surface nuclear magnetic resonance (NMR) is a relatively novel and powerful geophysical technique for investigating hydrological characteristics of shallow aquifers from the Earth's surface in a non-invasive way. Large current loops of approximately 100 m diameter laid on the ground transmit electromagnetic pulses into the subsurface. These pulses excite spins of protons in groundwater molecules out of their equilibrium state in the Earth's magnetic field. The spin response is recorded on either coincident or offset surface receiver loops of similar dimension. The amplitudes of the response signals recorded after single-pulse excitation provide estimates of water-content in the shallow subsurface. Another important parameter is the NMR relaxation time T1, from which information on pore structure or even hydraulic conductivity can be inferred under favorable circumstances. T1 data are conventionally acquired using a scheme that involves two sequential pulses of electromagnetic energy, the second of which is phase-shifted by ? relative to the first. We show that common imperfections in the transmitted pulses and variations of the excitation field with distance from the transmitter introduce significant bias in conventional estimates of T1. Here, we propose a novel yet simple modification to the conventional scheme that is theoretically capable of resolving this problem. The proposed scheme comprises a conventional double-pulse sequence followed by an additional double-pulse sequence for which the 2nd pulse is in-phase with the 1st pulse. Subtracting the voltage signals measured during the two double-pulse sequences (i.e., phase cycle) eliminates the bias. This strategy of continuously cycling the phase of the 2nd pulse between ? and 0 in sequential double-pulse experiments and then subtracting the resulting voltages is a promising step towards recording more reliable T1 data under general field conditions.

Walbrecker, Jan O.; Hertrich, Marian; Green, Alan G.

2011-03-01

215

Harsh Corporal Punishment Is Associated With Increased T2 Relaxation Time in Dopamine-Rich Regions  

PubMed Central

Harsh corporal punishment (HCP) was defined as frequent parental administration of corporal punishment (CP) for discipline, with occasional use of objects such as straps, or paddles. CP is linked to increased risk for depression and substance abuse. We examine whether long-term exposure to HCP acts as sub-traumatic stressor that contributes to brain alterations, particularly in dopaminergic pathways, which may mediate their increased vulnerability to drug and alcohol abuse. Nineteen young adults who experienced early HCP but no other forms of maltreatment and twenty-three comparable controls were studied. T2 relaxation time (T2-RT) measurements were performed with an echo planar imaging TE stepping technique and T2 maps were calculated and analyzed voxel-by-voxel to locate regional T2-RT differences between groups. Previous studies indicated that T2-RT provides an indirect index of resting cerebral blood volume. Region of interest (ROI) analyses were also conducted in caudate, putamen, nucleus accumbens, anterior cingulate cortex, dorsolateral prefrontal cortex, thalamus, globus pallidus and cerebellar hemispheres. Voxel-based relaxometry showed that HCP was associated with increased T2-RT in right caudate and putamen. ROI analyses also revealed increased T2-RT in dorsolateral prefrontal cortex, substantia nigra, thalamus and accumbens but not globus pallidus or cerebellum. There were significant associations between T2-RT measures in dopamine target regions and use of drugs and alcohol, and memory performance. Alteration in the paramagnetic or hemodynamic properties of dopaminergic cell body and projection regions were observed in subjects with HCP, and these findings may relate to their increased risk for drug and alcohol abuse. PMID:20600981

Sheu, Yi-Shin; Polcari, Ann; Anderson, Carl M.; Teicher, Martin H.

2010-01-01

216

Determination of the Dipolar Interaction of 23Na in Solution by Triple-Quantum Relaxation Time Measurements  

NASA Astrophysics Data System (ADS)

The measurement of the dipolar interaction of 23Na with hydrogen nuclei in glycerol solution is reported. The method, applied previously to 7Li (U. Eliav and G. Navon, J. Magn. Reson. A123,32 (1996)), is based on the measurement of the triple-quantum relaxation time of 23Na. Several models of motion are discussed. The analysis of the results yielded 1.9 MHz and 12.5 kHz for the quadrupolar and the 23Na- 1H dipolar interaction, respectively. It is shown that under the conditions of long correlation times the triple-quantum relaxation time can be sensitive to dipolar interactions smaller than the quadrupolar interaction by as much as a factor of 5000. This indicates the possibility of measuring interatomic distances for nuclei with sizable quadrupolar moments.

Eliav, Uzi; Navon, Gil

1998-01-01

217

The use of time-resolved X-ray diffraction and sample techniques for studying the muscle structure during relaxation  

NASA Astrophysics Data System (ADS)

The use of the modern time-resolved X-ray diffraction and sample technique has played an important role in studying muscle structures during contraction at various physiological conditions. We represent time-resolved X-ray data on equatorial diffraction and tension response of the frog sartorius muscle during relaxation. The measurements of the time-course of the intensity change of reflections (1,0), (1,1) and the background under them give a possibility to study the effect of potentiation of contraction by repetitive stimulation in fresh and tired muscles. Model calculations of meridional diffraction patterns for various configurations of cross-bridges in the relaxation phase were carried out.

Vazina, A. A.; Gadzhiev, A. M.; Gerasimov, V. S.; Gorbunova, N. P.; Sergienko, P. M.; Korneev, V. N.; Aulchenko, V. M.; Baru, S. E.

1995-02-01

218

Relaxation and short time dynamics of bulk liquids and fluids confined in spherical cavities and slit pores.  

PubMed

The density of states for bulk and confined fluids have been modeled using a recently proposed gamma distribution (Krishnan, S. H.; Ayappa, K. G. J. Chem. Phys. 2004, 121, 3197). The gamma distribution results in a closed form analytical expression for the velocity autocorrelation function and the relaxation time of the fluid. The two parameters of the gamma distribution are related analytically to the second and fourth frequency moments of the fluid using short time expansions. The predictions by the proposed gamma model are compared with the velocity autocorrelation functions obtained using the theory of instantaneous normal modes (INMs) and from molecular dynamics simulations. The model is applied to a bulk soft sphere liquid and fluids confined in a spherical cavity and slit-shaped pores. The gamma model is able to capture the resulting changes in relaxation time due to changes in density and temperature extremely well for both the bulk liquid and confined inhomogeneous fluid situations. In all cases, the predictions by the gamma model are superior to those obtained from the INM theory. In the case of the fluid confined in a slit pore, the loadings were obtained from a grand canonical Monte Carlo simulation where the pore is equilibrated with a bulk fluid. This is similar to a confinement situation in a surface force apparatus. The predicted relaxation times vs pore widths from the gamma model are seen to accurately capture the oscillations due to formation and disruption of layers within the slit pore. PMID:16375288

Krishnan, S H; Ayappa, K G

2005-12-15

219

Pressure dependence of diffusion coefficient and orientational relaxation time for acetonitrile and methanol in water: DRISM/mode-coupling study  

E-print Network

We present results of theoretical description and numerical calculation of the dynamics of molecular liquids based on the Reference Interaction Site Model / Mode-Coupling Theory. They include the temperature-pressure(density) dependence of the translational diffusion coefficients and orientational relaxation times for acetonitrile and methanol in water at infinite dilution. Anomalous behavior, i.e. the increase in mobility with density, is observed for the orientational relaxation time of methanol, while acetonitrile does not show any deviations from the usual. This effect is in qualitative agreement with the recent data of MD simulation and with experimental measurements, which tells us that presented theory is a good candidate to explain such kind of anomalies from the microscopical point of view and with the connection to the structure of the molecules.

Kobryn, A E; Hirata, F

2005-01-01

220

Quantum physical states for describing photonic assisted chemical change: I. Torsional phenomenon at femtosecond time scale  

E-print Network

Femtosecond torsional relaxation processes experimentally detected and recently reported by Clark et al. (Nature Phys. 8,225 (2012)) are theoretically dissected with a Hilbert/Fock quantum physical (QP) framework incorporating entanglement of photon/matter base states overcoming standard semi-classic vibrational descriptions. The quantum analysis of a generic Z/E (cis/trans) isomerization in abstract QP terms shed light to fundamental roles played by photonic spin and excited electronic singlet coupled to triplet states. It is shown that one photon activation cannot elicit femtosecond phenomenon, while a two-photon pulse would do. Estimated time scales for the two-photon case indicate the process to lie between a slower than electronic Franck-Condon-like transition yet faster than (semi-classic) vibration relaxation ones.

O. Tapia

2012-12-20

221

A multiple time scale solution for the Chapman mechanism  

SciTech Connect

The rate equations representing the Chapman mechanism are solved analytically in the Multiple Time Scale Approximation by the exploitation of their stiffness. The widely different time scales of the reactions in the mechanism can be used to disentangle their effects on the solution. The reactions which bring oxygen into equilibrium with ozone are responsible for the overall stiffness, because their time scales are on the extreme ends of time scale spectrum for the reactions comprising the Chapman mechanism. Since catalytic cycles have similar equilibration reactions which may have time scales bordering the time scales of other reactions involving the catalysts, the method of multiple time scales can also be used to cured the stiffness in the rate equations governing these cycles. These analytical solutions may be incorporated into a numerical algorithm to improve its efficiency for the computation of the rate equations governing the chemistry of the atmosphere.

Chang, B.

1994-06-01

222

A Quaternary Geomagnetic Instability Time Scale  

NASA Astrophysics Data System (ADS)

Reversals and excursions of Earth's geomagnetic field create marker horizons that are readily detected in sedimentary and volcanic rocks worldwide. An accurate and precise chronology of these geomagnetic field instabilities is fundamental to understanding several aspects of Quaternary climate, dynamo processes, and surface processes. For example, stratigraphic correlation between marine sediment and polar ice records of climate change across the cryospheres benefits from a highly resolved record of reversals and excursions. The temporal patterns of dynamo behavior may reflect physical interactions between the molten outer core and the solid inner core or lowermost mantle. These interactions may control reversal frequency and shape the weak magnetic fields that arise during successive dynamo instabilities. Moreover, weakening of the axial dipole during reversals and excursions enhances the production of cosmogenic isotopes that are used in sediment and ice core stratigraphy and surface exposure dating. The Geomagnetic Instability Time Scale (GITS) is based on the direct dating of transitional polarity states recorded by lava flows using the 40Ar/39Ar method, in parallel with astrochronologic age models of marine sediments in which O isotope and magnetic records have been obtained. A review of data from Quaternary lava flows and sediments yields a GITS comprising 10 polarity reversals and 27 excursions during the past 2.6 million years. Nine of the ten reversals bounding chrons and subchrons are associated with 40Ar/39Ar ages of transitionally-magnetized lava flows. The tenth, the Guass-Matuyama chron boundary, is tightly bracketed by 40Ar/39Ar dated ash deposits. Of the 27 well-documented excursions, 14 occurred during the Matuyama chron and 13 during the Brunhes chron; 19 have been dated directly using the 40Ar/39Ar method on transitionally-magnetized volcanic rocks and form the backbone of the GITS. Excursions are clearly not the rare phenomena once thought. Rather, during the Quaternary period, they occur nearly three times as often as full polarity reversals. I will address analytical issues, including the size and consistency of system blanks, that have led to the recognition of minor (1%) discrepencies between the 40Ar/39Ar age for a particular reversal or excursion and the best astrochronologic estimates from ODP sediment cores. For example, re-analysis of lava flows from Haleakala volcano, Maui that record in detail the Matuyama-Brunhes polarity reversal have been undertaken with blanks an order of magntitude smaller and more stable than was common a decade ago. Using the modern astrochronologic calibration of 28.201 Ma for the age of the Fish Canyon sanidine standard, results thus far yield an 40Ar/39Ar age of 772 × 11 ka for the reversal that is identical to the most precise and accurate astrochronologic age of 773 × 2 ka for this reversal from ODP cores. Similarly, new dating of sanidine in the Cerro Santa Rosa I rhyolite dome, New Mexico reveals an age of 932 × 5 ka for the excursion it records, in perfect agreement with astrochronologically dated ODP core records. Work underway aims at refining the 40Ar/39Ar ages that underpin the entire GITS by further eliminating the bias between the radioisotopic and astrochronologically determined ages for several reversals and excursions.

Singer, B. S.

2013-12-01

223

Prediction of corn tortilla textural quality using stress relaxation methods  

E-print Network

-relaxation time was chosen to evaluate the speed of stress relaxation. The stronger the flour, the longer the half-relaxation times, while the mixing time showed little influence in the relaxation curves. The stress relaxation behavior of apple pomace...-relaxation time was chosen to evaluate the speed of stress relaxation. The stronger the flour, the longer the half-relaxation times, while the mixing time showed little influence in the relaxation curves. The stress relaxation behavior of apple pomace...

Guo, Zhihong

2012-06-07

224

The Effect of Rotation on Two-Dimensional Problem of a Fiber-Reinforced Thermoelastic with One Relaxation Time  

NASA Astrophysics Data System (ADS)

In this article, the Lord-Shulman (L-S) theory with one relaxation time and coupled theory are applied to study the influence of reinforcement on the total deformation of a rotating thermoelastic half-space and the interaction with each other. The problem of a thermal shock has been solved numerically using normal mode analysis. Numerical results for the temperature, displacement, and thermal stress components are given and illustrated graphically for both L-S and coupled theories.

Othman, Mohamed I. A.; Said, Samia M.

2012-01-01

225

Effects of hydrophobic treatments of stone on pore water studied by continuous distribution analysis of NMR relaxation times.  

PubMed

The effects of protective hydrophobic products applied to porous media such as stone or mortar vary greatly with the product, the porous medium, and the mode of application. Nuclear Magnetic Resonance (NMR) measurements on fluids in the pore spaces of both treated and untreated samples can give information on the contact of the fluid with the internal surfaces, which is affected by all the above factors. Continuous distributions of relaxation times T(1) and T(2) of water in the pores of both synthetic and natural porous media were obtained before and after hydrophobic treatment. The synthetic porous media are ceramic filter materials characterized by narrow distributions of pore dimensions and show that the treatment does not produce large changes in the relaxation times of the water. For three travertine samples most of a long relaxation time component, presumably from the largest pores, remains after treatment, while the amplitude of an intermediate component is greatly reduced. For three pudding-stone samples, treatment leads to a substantial loss from the long component and an even greater loss from the intermediate component. PMID:11445343

Appolonia, L; Borgia, G C; Bortolotti, V; Brown, R J; Fantazzini, P; Rezzaro, G

2001-01-01

226

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 Central

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 is 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

2013-01-01

227

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 (?T(g)). 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 (?T(g)) 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 ?T(g). 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 ?T(g), but the agreement is only qualitative. The comparison plot showed that TAM data are directly proportional to the 1/3 power of ?T(g) data, after correcting for an offset. Nevertheless, the correlation between hGH stability and relaxation time remained qualitatively the same as found with using ?T(g) derived relaxation data, and it was found that the modest extrapolation of TAM data to higher temperatures using ?T(g) 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

2013-10-01

228

Thermal boundary resistance from mode energy relaxation times: Case study of argon-like crystals by molecular dynamics  

NASA Astrophysics Data System (ADS)

We derive the mode spectrum of the thermal boundary resistance between two bodies having a temperature difference ?T. A general expression of the time ? that defines the resistance is derived as the equilibrium autocorrelation of ?T integrated over time. A further decomposition of this autocorrelation yields the resistance spectrum as equal to the mode relaxation time weighted by its energy mean square fluctuation. We then perform molecular dynamics simulations of argon like crystals in equilibrium and nonequilibrium regimes to prove the relevance of our model. This general method allows for deriving the resistance spectrum and therefore can yield key rules to control the exchanged heat flux.

Rajabpour, Ali; Volz, Sebastian

2010-11-01

229

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

230

Mechanical relaxation times as indicators of stickiness in skim milk–maltodextrin solids systems  

Microsoft Academic Search

Thermal and water plasticization and glass transition of amorphous components often result in changes in physico-chemical properties of food solids including stickiness and component crystallization. The glass transition temperatures (Tg) of skim milk–maltodextrin solids systems were measured by differential scanning calorimetry (DSC) and a sticky point test was used to determine the sticky-point temperatures (SPT). The mechanical ?-relaxation around glass

Nattiga Silalai; Yrjö H. Roos

2011-01-01

231

Distributions of transverse relaxation times for soft-solids measured in strongly inhomogeneous magnetic fields.  

PubMed

The single-sided NMR-MOUSE sensor that operates in highly inhomogeneous magnetic fields is used to record a CPMG (1)H transverse relaxation decay by CPMG echo trains for a series of cross-linked natural rubber samples. Effective transverse relaxation rates 1/T(2,short) and 1/T(2,long) were determined by a bi-exponential fit. A linear dependence of transverse relaxation rates on cross-link density is observed for medium to large values of cross-link density. As an alternative to multi-exponential fits the possibility to analyze the dynamics of soft polymer network in terms of multi-exponential decays via the inverse Laplace transformation was studied. The transient regime and the effect of the T(1)/T(2) ratio in inhomogeneous static and radiofrequency magnetic fields on the CPMG decays were studied numerically using a dedicated C++ program to simulate the temporal and spatial dependence of the CPMG response. A correction factor T(2)/T(2,eff) is derived as a function of the T(1)/T(2) ratio from numerical simulations and compared with earlier results from two different well logging devices. High-resolution T(1)-T(2) correlations maps are obtained by two-dimensional Laplace inversion of CPMG detected saturation recovery curves. The T(1)-T(2) experimental correlations maps were corrected for the T(1)/T(2) effect using the derived T(2)/T(2,eff) correction factor. PMID:19083248

Chelcea, R I; Fechete, R; Culea, E; Demco, D E; Blümich, B

2009-02-01

232

Distributions of transverse relaxation times for soft-solids measured in strongly inhomogeneous magnetic fields  

NASA Astrophysics Data System (ADS)

The single-sided NMR-MOUSE sensor that operates in highly inhomogeneous magnetic fields is used to record a CPMG 1H transverse relaxation decay by CPMG echo trains for a series of cross-linked natural rubber samples. Effective transverse relaxation rates 1/ T2,short and 1/ T2,long were determined by a bi-exponential fit. A linear dependence of transverse relaxation rates on cross-link density is observed for medium to large values of cross-link density. As an alternative to multi-exponential fits the possibility to analyze the dynamics of soft polymer network in terms of multi-exponential decays via the inverse Laplace transformation was studied. The transient regime and the effect of the T1/ T2 ratio in inhomogeneous static and radiofrequency magnetic fields on the CPMG decays were studied numerically using a dedicated C++ program to simulate the temporal and spatial dependence of the CPMG response. A correction factor T2/ T2,eff is derived as a function of the T1/ T2 ratio from numerical simulations and compared with earlier results from two different well logging devices. High-resolution T1- T2 correlations maps are obtained by two-dimensional Laplace inversion of CPMG detected saturation recovery curves. The T1- T2 experimental correlations maps were corrected for the T1/ T2 effect using the derived T2/ T2,eff correction factor.

Chelcea, R. I.; Fechete, R.; Culea, E.; Demco, D. E.; Blümich, B.

2009-02-01

233

Scale-Time Kernels and Models  

Microsoft Academic Search

Receptive eld sensitivity proles of visual front-end cells in the LGN and V1 area in intact animals can be measured with increas- ing accuracy, both in the spatial and temporal domain. This urges the need for mathematical models. Scale-space theory, as a theory of (mul- tiscale) apertures as operators on observed data, is concerned with the mathematical modeling of front-end

Bart M. Ter Haar Romeny; Luc Florack; Mads Nielsen

2001-01-01

234

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

235

Surface-NMR measurements of the longitudinal relaxation time T1 in a homogeneous sandy aquifer in Skive, Denmark  

NASA Astrophysics Data System (ADS)

Efficient groundwater management requires reliable means of characterizing shallow groundwater aquifers. One key parameter in this respect is hydraulic conductivity. Surface nuclear magnetic resonance (NMR) is a geophysical exploration technique that can potentially provide this type of information in a noninvasive, cost-effective way. The technique is based on measuring the precession of nuclear spins of protons in groundwater molecules. It involves large loop antennas deployed on Earth's surface to generate electromagnetic pulses tuned to specifically excite and detect groundwater proton spins. Naturally, the excited state of spins is transitory - once excited, spins relax back to their equilibrium state. This relaxation process is strongly influenced by the spin environment, which, in the case of groundwater, is defined by the aquifer. By employing empirical relations, changes in relaxation behavior can be used to identify changes in aquifer hydraulic conductivity, making the NMR relaxation signal a very important piece of information. Particularly, efforts are made to record the longitudinal relaxation parameter T1, because it is known from laboratory studies that it often reliably correlates with hydraulic conductivity, even in the presence of magnetic species. In surface NMR, T1 data are collected by recording the NMR signal amplitude following two sequential excitation pulses as a function of the delay time ? between the two pulses. In conventional acquisition, the two pulses have a mutual phase shift of ?. Based on theoretical arguments it was recently shown that T1 times acquired according to this conventional surface-NMR scheme are systematically biased. It was proposed that the bias can be minimized by cycling the phase of the two pulses between ? and zero in subsequent double-pulse experiments, and subtracting the resulting signal amplitudes (phase-cycled pseudosaturation recovery scheme, pcPSR). We present the first surface-NMR T1 data set recorded employing the pcPSR scheme and compare it to conventional T1 data. For our feasibility study we have chosen a site in Skive, Denmark, that features excellent signal/noise conditions, allowing us to collect high quality data in reasonable survey time. In addition, proximate boreholes and TEM measurements suggest a relatively homogeneous aquifer extending from 5 to more than 25m below surface. We may therefore expect roughly constant T1 relaxation times throughout the shallow aquifer, providing us a simple framework for our comparative study. We used a 50x50m surface-NMR loop and employed 16 pulse moments selected to spatially cover the shallow aquifer region. For each pulse moment, we recorded surface-NMR T1 data densely sampled at 14 delay times ? between 250 and 4'000 ms. On this high-quality data set we demonstrate that the pcPSR acquisition approach yields to a good degree homogeneous T1 relaxation times, whereas the conventional approach leads to variations in T1 that could be misinterpreted in terms of changes of aquifer characteristics. Thereby we provide first empirical evidence for the superiority of the pcPSR scheme for surface NMR T1 acquisition.

Walbrecker, J.; Behroozmand, A.

2011-12-01

236

Observation time scale, free-energy landscapes, and molecular symmetry  

E-print Network

Observation time scale, free-energy landscapes, and molecular symmetry David J. Walesa,1 and Peter structures that interconvert on a given time scale are lumped together, the corresponding free-energy surface that are connected by free-energy barriers below a certain threshold. We illustrate this time dependence for some

Salamon, Peter

237

Relaxation properties in classical diamagnetism Relaxation properties in classical diamagnetism  

E-print Network

Relaxation properties in classical diamagnetism Relaxation properties in classical diamagnetism A either to equilibrium or to a diamagnetic (presumably metastable) state. The analogy with the relaxation diamagnetism, billiards, relaxation time, metastability It is well known since the time of the disserta- tion

Carati, Andrea

238

Time\\/scale-adjusted dyadic wavelet packet bases  

Microsoft Academic Search

This paper generalizes the dyadic wavelet packet bases (DWP), developed by Coifman and Wickerhauser, to time\\/scale-adjusted DWP bases. These generalized DWP bases provide more flexibility in matching the time-scale characteristics of the input signal. Development of these generalized bases is achieved by combining the previously defined time-invariant DWP bases of Pesquet, Krim, Carfantan, and Proakis with a generalized scale sampling.

Stephen P. del Marco

1996-01-01

239

A Real-Time Framework for Video Time and Pitch Scale Modification  

Microsoft Academic Search

A framework is presented which addresses the issues related to the real-time implementation of synchronized video and audio time-scale and pitch-scale modification algorithms. It allows for seamless real-time transition between continually varying, independent time-scale and pitch-scale parameters arising as a result of manual or automatic intervention. We illuminate the problems which arise in a real-time context as well as provide

Ivan Damnjanovic; Dan Barry; David Dorran; Joshua D. Reiss

2010-01-01

240

Local-time effect on small space-time scale  

E-print Network

The paper presents an investigation of local-time effect - one of the manifestations of macroscopic fluctuations phenomena. Was shown the existence of the named effect for longitudinal distance between locations of measurements up to 500 meters. Also a structure of intervals distribution in neighborhood of local-time peak was studied and splitting of the peak was found out. Obtained results lead to conclusion about sharp anisotropy of space-time.

V. A. Panchelyuga; V. A. Kolombet; M. S. Panchelyuga; S. E. Shnoll

2006-10-18

241

Estimating the apparent transverse relaxation time (R2*) from images with different contrasts (ESTATICS) reduces motion artifacts  

PubMed Central

Relaxation rates provide important information about tissue microstructure. Multi-parameter mapping (MPM) estimates multiple relaxation parameters from multi-echo FLASH acquisitions with different basic contrasts, i.e., proton density (PD), T1 or magnetization transfer (MT) weighting. Motion can particularly affect maps of the apparent transverse relaxation rate R2*, which are derived from the signal of PD-weighted images acquired at different echo times. To address the motion artifacts, we introduce ESTATICS, which robustly estimates R2* from images even when acquired with different basic contrasts. ESTATICS extends the fitted signal model to account for inherent contrast differences in the PDw, T1w and MTw images. The fit was implemented as a conventional ordinary least squares optimization and as a robust fit with a small or large confidence interval. These three different implementations of ESTATICS were tested on data affected by severe motion artifacts and data with no prominent motion artifacts as determined by visual assessment or fast optical motion tracking. ESTATICS improved the quality of the R2* maps and reduced the coefficient of variation for both types of data—with average reductions of 30% when severe motion artifacts were present. ESTATICS can be applied to any protocol comprised of multiple 2D/3D multi-echo FLASH acquisitions as used in the general research and clinical setting.

Weiskopf, Nikolaus; Callaghan, Martina F.; Josephs, Oliver; Lutti, Antoine; Mohammadi, Siawoosh

2014-01-01

242

General Entanglement Scaling Laws from Time Evolution  

NASA Astrophysics Data System (ADS)

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.

Eisert, Jens; Osborne, Tobias J.

2006-10-01

243

Modeling orbital changes on tectonic time scales  

NASA Technical Reports Server (NTRS)

Geologic time series indicate significant 100 ka and 400 ka pre-Pleistocene climate fluctuations, prior to the time of such fluctuations in Pleistocene ice sheets. The origin of these fluctuations must therefore depend on phenomena other than the ice sheets. In a previous set of experiments, we tested the sensitivity of an energy balance model to orbital insolation forcing, specifically focusing on the filtering effect of the Earth's geography. We found that in equatorial areas, the twice-yearly passage of the sun across the equator interacts with the precession index to generate 100 ka and 400 ka power in our modeled time series. The effect is proportional to the magnitude of land in equatorial regions. We suggest that such changes may reflect monsoonal variations in the real climate system, and the subsequent wind and weathering changes may transfer some of this signal to the marine record. A comparison with observed fluctuations of Triassic lake levels is quite favorable. A number of problems remain to be studied or clarified: (1) the EBM experiments need to be followed up by a limited number of GCM experiments; (2) the sensitivity to secular changes in orbital forcing needs to be examined; (3) the possible modifying role of sedimentary processes on geologic time series warrants considerably more study; (4) the effect of tectonic changes on Earth's rotation rate needs to be studied; and (5) astronomers need to make explicit which of their predictions are robust and geologists and astronomers have to agree on which of the predictions are most testable in the geologic record.

Crowley, Thomas J.

1992-01-01

244

Measurements of spin-lattice relaxation times, T1, in Na2O-MgO-SiO2 glasses doped with MnO.  

PubMed

Silicate glasses without paramagnetic components show 29Si relaxation times, T1, in the order of minutes. Because of these T1 values, unacceptably long instrument times are needed to obtain satisfactory' signal-to-noise ratios. Therefore, all samples were doped with MnO when microstructures of electrode glasses were investigated. Small amounts of paramagnetic ions in the glass reduce the relaxation time but do not affect the electrode properties. In any case when the distribution of manganese ions is homogeneous, the relaxation rates are proportional to the MnO content. The spin-lattice relaxation times of the different Qn species are similar within error limits. The best spectra were obtained using 0.1 mol% MnO. PMID:7583067

Scholz, K; Thomas, B

1995-07-01

245

Improved phase vocoder time-scale modification of audio  

Microsoft Academic Search

The phase vocoder is a well established tool for time scaling and pitch shifting speech and audio signals via modification of their short-time Fourier transforms (STFTs). In contrast to time-domain time-scaling and pitch-shifting techniques, the phase vocoder is generally considered to yield high quality results, especially for large modification factors and\\/or polyphonic signals. However, the phase vocoder is also known

Jean Laroche; Mark Dolson

1999-01-01

246

Relaxed dispersion requirement in the generation of chirped RF signals based on frequency-to-time mapping  

NASA Astrophysics Data System (ADS)

Photonic generation of chirped RF signal based on frequency-to-time mapping (FTM) is investigated in this paper. A new criterion on system parameters (dispersion amounts and pulse duration) for the generation of well-shaped linearly chirped signals is given, which is proved to be less restrictive than the currently known conditions. Therefore, requirement on the dispersion amount can be relaxed, which is highly desired in practical implementation of the FTM-based system. Theoretical results are presented, the correctness of which is verified by numerical and experimental results. The reported theory is a good guidance in designing the photonic system for the generation of chirped signals based on FTM.

Xu, Yuxiao; Shi, Zhiguo; Chi, Hao; Jin, Xiaofeng; Zheng, Shilie; Zhang, Xianmin

2014-11-01

247

MRI T2 RELAXATION TIME EVALUATION OF WRIST CARTILAGE WITH SCAPHOLUNATE LIGAMENT INJURY IN THE PRE-OPERATIVE AND POST-OPERATIVE STATE  

E-print Network

MRI T2 RELAXATION TIME EVALUATION OF WRIST CARTILAGE WITH SCAPHOLUNATE LIGAMENT INJURY IN THE PRE-OPERATIVE AND POST- OPERATIVE STATE By Dannica Leigh Sturgeon Submitted to the graduate degree program in Mechanical Engineering and the Graduate... thesis: MRI T2 RELAXATION TIME EVALUATION OF WRIST CARTILAGE WITH SCAPHOLUNATE LIGAMENT INJURY IN THE PRE-OPERATIVE AND POST- OPERATIVE STATE ________________________________ Co-Chairperson: Dr. Kenneth J. Fischer...

Sturgeon, Dannica Leigh

2011-04-27

248

Spatial distribution and relationship of T1rho and T2 relaxation times in knee cartilage with osteoarthritis.  

PubMed

T(1rho) and T(2) relaxation time constants have been proposed to probe biochemical changes in osteoarthritic cartilage. This study aimed to evaluate the spatial correlation and distribution of T(1rho) and T(2) values in osteoarthritic cartilage. Ten patients with osteoarthritis (OA) and 10 controls were studied at 3T. The spatial correlation of T(1rho) and T(2) values was investigated using Z-scores. The spatial variation of T(1rho) and T(2) values in patellar cartilage was studied in different cartilage layers. The distribution of these relaxation time constants was measured using texture analysis parameters based on gray-level co-occurrence matrices (GLCM). The mean Z-scores for T(1rho) and T(2) values were significantly higher in OA patients vs. controls (P < 0.05). Regional correlation coefficients of T(1rho) and T(2) Z-scores showed a large range in both controls and OA patients (0.2-0.7). OA patients had significantly greater GLCM contrast and entropy of T(1rho) values than controls (P < 0.05). In summary, T(1rho) and T(2) values are not only increased but are also more heterogeneous in osteoarthritic cartilage. T(1rho) and T(2) values show different spatial distributions and may provide complementary information regarding cartilage degeneration in OA. PMID:19319904

Li, Xiaojuan; Pai, Alex; Blumenkrantz, Gabrielle; Carballido-Gamio, Julio; Link, Thomas; Ma, Benjamin; Ries, Michael; Majumdar, Sharmila

2009-06-01

249

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

250

Using bio-functionalized magnetic nanoparticles and dynamic nuclear magnetic resonance to characterize the time-dependent spin-spin relaxation time for sensitive bio-detection.  

PubMed

In this work, we report the use of bio-functionalized magnetic nanoparticles (BMNs) and dynamic magnetic resonance (DMR) to characterize the time-dependent spin-spin relaxation time for sensitive bio-detection. The biomarkers are the human C-reactive protein (CRP) while the BMNs are the anti-CRP bound onto dextran-coated Fe3O4 particles labeled as Fe3O4-antiCRP. It was found the time-dependent spin-spin relaxation time, T2, of protons decreases as time evolves. Additionally, the ?T2 of of protons in BMNs increases as the concentration of CRP increases. We attribute these to the formation of the magnetic clusters that deteriorate the field homogeneity of nearby protons. A sensitivity better than 0.1 ?g/mL for assaying CRP is achieved, which is much higher than that required by the clinical criteria (0.5 mg/dL). The present MR-detection platform shows promise for further use in detecting tumors, viruses, and proteins. PMID:25397920

Liao, Shu-Hsien; Chen, Kuen-Lin; Wang, Chun-Min; Chieh, Jen-Jie; Horng, Herng-Er; Wang, Li-Min; Wu, C H; Yang, Hong-Chang

2014-01-01

251

Water Peak Suppression: Time-Frequency vs TimeScale Approach  

Microsoft Academic Search

Wavelets are the most popular time-scale analysis tool. A well-known application of wavelets in nuclear magnetic resonance spectroscopy is water peak extraction\\/suppression. However, spectroscopists are more familiar with frequency than scale. So, from a spectroscopist point of view, a time-scale analysis tool (i.e., wavelets) is not natural and a time-frequency approach would be much more satisfactory. We explain a time-frequency

Jean-Pierre Antoine; Alain Coron; Jean-Marie Dereppe

2000-01-01

252

Liquidity Spillover in International Stock Markets through Distinct Time Scales  

PubMed Central

This paper identifies liquidity spillovers through different time scales based on a wavelet multiscaling method. We decompose daily data from U.S., British, Brazilian and Hong Kong stock markets indices in order to calculate the scale correlation between their illiquidities. The sample is divided in order to consider non-crisis, sub-prime crisis and Eurozone crisis. We find that there are changes in correlations of distinct scales and different periods. Association in finest scales is smaller than in coarse scales. There is a rise on associations in periods of crisis. In frequencies, there is predominance for significant distinctions involving the coarsest scale, while for crises periods there is predominance for distinctions on the finest scale. PMID:24465918

Righi, Marcelo Brutti; Vieira, Kelmara Mendes

2014-01-01

253

Liquidity spillover in international stock markets through distinct time scales.  

PubMed

This paper identifies liquidity spillovers through different time scales based on a wavelet multiscaling method. We decompose daily data from U.S., British, Brazilian and Hong Kong stock markets indices in order to calculate the scale correlation between their illiquidities. The sample is divided in order to consider non-crisis, sub-prime crisis and Eurozone crisis. We find that there are changes in correlations of distinct scales and different periods. Association in finest scales is smaller than in coarse scales. There is a rise on associations in periods of crisis. In frequencies, there is predominance for significant distinctions involving the coarsest scale, while for crises periods there is predominance for distinctions on the finest scale. PMID:24465918

Righi, Marcelo Brutti; Vieira, Kelmara Mendes

2014-01-01

254

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

255

Resonant relaxation in electroweak baryogenesis  

NASA Astrophysics Data System (ADS)

We compute the leading, chiral charge-changing relaxation term in the quantum transport equations that govern electroweak baryogenesis using the closed time path formulation of nonequilibrium quantum field theory. We show that the relaxation transport coefficients may be resonantly enhanced under appropriate conditions on electroweak model parameters and that such enhancements can mitigate the impact of similar enhancements in the CP-violating source terms. We also develop a power counting in the time and energy scales entering electroweak baryogenesis and include effects through second order in ratios ? of the small and large scales. We illustrate the implications of the resonantly enhanced O(?2) terms using the Minimal Supersymmetric Standard Model, focusing on the interplay between the requirements of baryogenesis and constraints obtained from collider studies, precision electroweak data, and electric dipole moment searches.

Lee, Christopher; Cirigliano, Vincenzo; Ramsey-Musolf, Michael J.

2005-04-01

256

Anomalous diffusion and power-law relaxation of the time averaged mean squared displacement in worm-like micellar solutions  

NASA Astrophysics Data System (ADS)

We report the results of single tracer particle tracking by optical tweezers and video microscopy in micellar solutions. From careful analysis in terms of different stochastic models, we show that the polystyrene tracer beads of size 0.52-2.5 ?m after short-time normal diffusion turn over to perform anomalous diffusion of the form ? t? with ? ? 0.3. This free anomalous diffusion is ergodic and consistent with a description in terms of the generalized Langevin equation with a power-law memory kernel. With optical tweezers tracking, we unveil a power-law relaxation over several decades in time to the thermal plateau value under the confinement of the harmonic tweezer potential, as predicted previously (Phys. Rev. E 85 021147 (2012)). After the subdiffusive motion in the millisecond range, the motion becomes faster and turns either back to normal Brownian diffusion or to even faster superdiffusion, depending on the size of the tracer beads.

Jeon, Jae-Hyung; Leijnse, Natascha; Oddershede, Lene B.; Metzler, Ralf

2013-04-01

257

Simple models and time scales in the dynamo effect  

Microsoft Academic Search

The dynamo effect has been studied for 50 years, starting from the simple homopolar dynamo of Bullard. Numerical calculations on simple models, such as the crossed dynamos of Rikitake, display large oscillations and brutal reversals. The present Note puts emphasis on time scales. One scale ?1, purely electromagnetic, describes inductive decay (the frequency at which the skin depth is the

Philippe Nozières

2008-01-01

258

EXPLOITING MULTIPLE TIME SCALE PROPERTIES FOR FAST SIMULATION ALGORITHMS  

Microsoft Academic Search

Adaptive step size algorithms are presented making use of the muliple time scale character of power systems. The pa- per analyzes methods using multiple step sizes simultane- ously (multirate methods) and methods adapting the inte- gration step size in time. The resulting algorithm covers transients of all time ranges, from electromagnetic to elec- tromechanical phenomena.

Markus Poller; Martin Schmieg

259

Multiple-relaxation-time lattice Boltzmann method for study of two-lid-driven cavity flow solution multiplicity  

NASA Astrophysics Data System (ADS)

As a fundamental subject in fluid mechanics, sophisticated cavity flow patterns due to the movement of multi-lids have been routinely analyzed by the computational fluid dynamics community. Unlike those reported computational studies that were conducted using more conventional numerical methods, this paper features employing the multiple-relaxation-time (MRT) lattice Boltzmann method (LBM) to numerically investigate the two-dimensional cavity flows generated by the movements of two adjacent lids. The obtained MRT-LBM results reveal a number of important bifurcation flow features, such as the symmetry and steadiness of cavity flows at low Reynolds numbers, the multiplicity of stable cavity flow patterns when the Reynolds number exceeds its first critical value, as well as the periodicity of the cavity flow after the second critical Reynolds number is reached. Detailed flow characteristics are reported that include the critical Reynolds numbers, the locations of the vortex centers, and the values of stream function at the vortex centers. Through systematic comparison against the simulation results obtained elsewhere by using the lattice Bhatnagar-Gross-Krook model and other numerical schemes, not only does the MRT-LBM approach exhibit fairly satisfactory accuracy, but also demonstrates its remarkable flexibility that renders the adjustment of its multiple relaxation factors fully manageable and, thus, particularly accommodates the need of effectively investigating the multiplicity of flow patterns with complex behaviors.

Guo, Xixiong; Zhong, Chengwen; Zhuo, Congshan; Cao, Jun

2014-04-01

260

Modes and emergent time scales of embayed beach dynamics  

NASA Astrophysics Data System (ADS)

In this study, we use a simple numerical model (the Coastline Evolution Model) to explore alongshore transport-driven shoreline dynamics within generalized embayed beaches (neglecting cross-shore effects). Using principal component analysis (PCA), we identify two primary orthogonal modes of shoreline behavior that describe shoreline variation about its unchanging mean position: the rotation mode, which has been previously identified and describes changes in the mean shoreline orientation, and a newly identified breathing mode, which represents changes in shoreline curvature. Wavelet analysis of the PCA mode time series reveals characteristic time scales of these modes (typically years to decades) that emerge within even a statistically constant white-noise wave climate (without changes in external forcing), suggesting that these time scales can arise from internal system dynamics. The time scales of both modes increase linearly with shoreface depth, suggesting that the embayed beach sediment transport dynamics exhibit a diffusive scaling.

Ratliff, Katherine M.; Murray, A. Brad

2014-10-01

261

A variable resolution radio-frequency spectrometer employing time scaling  

Microsoft Academic Search

The effective resolution of a constant resolution filter spectrometer is varied by employing a time-scaling stage between data acquisition and spectral computation. For low-input data rates multiplexing can be introduced to analyze several signals simultaneously.

J. L. Yen; S. KITAOKA; Komukai Toshiba-cho; H. IIZUKA

1970-01-01

262

Distinguishing Förster Resonance Energy Transfer and solvent-mediated charge-transfer relaxation dynamics in a zinc(II) indicator: a femtosecond time-resolved transient absorption spectroscopic study.  

PubMed

A bifluorophoric molecule (1) capable of intramolecular Förster Resonance Energy Transfer (FRET) is reported. The emission intensity of the FRET acceptor in 1 depends on the molar absorptivity of the donor, which is a function of zinc(II) complexation. The FRET dynamics of [Zn(1)](ClO4)2 is characterized by femtosecond time-resolved transient absorption spectroscopy. The solvent-mediated relaxation of the charge-transfer (CT) state of the isolated donor and the FRET process of the donor–acceptor conjugate are on similar time scales (40–50 ps in CH3CN), but distinguishable by the opposite solvent polarity dependency. As the solvent polarity increases, the efficiency of Columbic-based FRET is reduced, whereas CT relaxation is accelerated. In addition to revealing a method to distinguish CT and FRET dynamics, this work provides a photophysical foundation for developing indicators based on the FRET strategy. PMID:24504046

Sreenath, Kesavapillai; Yi, Chongyue; Knappenberger, Kenneth L; Zhu, Lei

2014-03-21

263

Kibble-Zurek mechanism and finite-time scaling  

NASA Astrophysics Data System (ADS)

The Kibble-Zurek (KZ) mechanism has been applied to a variety of systems ranging from low-temperature Bose-Einstein condensations to grand unification scales in particle physics and cosmology and from classical phase transitions to quantum phase transitions. Here, we show that finite-time scaling (FTS) provides a detailed improved understanding of the mechanism. In particular, the finite time scale, which is introduced by the external driving (or quenching) and results in FTS, is the origin of the division of the adiabatic regimes from the impulse regime in the KZ mechanism. The origin of the KZ scaling for the defect density, generated during the driving through a critical point, is not that the correlation length ceases growing in the nonadiabatic impulse regime, but rather, is that it is taken over by the effective finite length scale corresponding to the finite time scale. We also show that FTS accounts well for and improves the scaling ansatz proposed recently by Liu, Polkovnikov, and Sandvik, [Phys. Rev. B 89, 054307 (2014), 10.1103/PhysRevB.89.054307]. Further, we show that their universal power-law scaling form applies only to some observables in cooling but not to heating. Even in cooling, it is invalid either when an appropriate external field is present. However, this finite-time-finite-size scaling calls for caution in application of FTS. Detailed scaling behaviors of the FTS and finite-size scaling, along with their crossover, are explicitly demonstrated, with the dynamic critical exponent z being estimated for two- and three-dimensional Ising models under the usual Metropolis dynamics. These values of z are found to give rise to better data collapses than the extant values do in most cases but take on different values in heating and cooling in both two- and three-dimensional spaces.

Huang, Yingyi; Yin, Shuai; Feng, Baoquan; Zhong, Fan

2014-10-01

264

Diffusion Time-Scale of Porous Pressure-Sensitive Paint  

NASA Technical Reports Server (NTRS)

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

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

2001-01-01

265

Two-Time-Scale Approximation for Wonham Filters  

Microsoft Academic Search

Abstract—This paper is concerned with approximation of Wonham filters. A focal point is that the underlying hidden Markov chain has a large state space. To reduce computational complexity, a two-time-scale approach is developed. Under time scale separation, the state space of the underlying Markov chain is divided into a number of groups such that the chain jumps rapidly within each

Qing Zhang; Gang George Yin; Johb B. Moore

2007-01-01

266

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

267

Time scale for point-defect equilibration in nanostructures  

SciTech Connect

Molecular dynamics simulations of high-temperature annealing are performed on nanostructured materials enabling direct observation of vacancy emission from planar defects (i.e., grain boundaries and free surfaces) to populate the initially vacancy-free grain interiors on a subnanosecond time scale. We demonstrate a universal time-length scale correlation that governs these re-equilibration processes, suggesting that nanostructures are particularly stable against perturbations in their point-defect concentrations, caused for example by particle irradiation or temperature fluctuations.

Millett, Paul C.; Wolf, Dieter; Desai, Tapan [Materials Science Department, Idaho National Laboratory, Idaho Falls, Idaho 83415 (United States); Yamakov, Vesselin [National Institute of Aerospace, Hampton, Virginia 23693 (United States)

2008-10-20

268

Time Scales of Observation and Ontological Levels of Reality  

Microsoft Academic Search

My goal is to conceive how the reality would look like for hypothetical creatures that supposedly perceive on time scales\\u000a much faster or much slower than that of us humans. To attain the goal, I propose modelling in two steps. At step one, we have\\u000a to single out a unified parameter that sets time scale of perception. Changing substantially the

Alexey Alyushin

2010-01-01

269

Signatures of discrete scale invariance in Dst time series  

NASA Astrophysics Data System (ADS)

Self-similar systems are characterized by continuous scale invariance and, in response, the existence of power laws. However, a significant number of systems exhibits discrete scale invariance (DSI) which in turn leads to log-periodic corrections to scaling that decorate the pure power law. Here, we present the results of a search of log-periodic corrections to scaling in the squares of Dst index increments which are taken as proxies of the energy dissipation rate in the magnetosphere. We show that Dst time series exhibit DSI and discuss the consequence of this feature, as well as the possible implications of Dst DSI on space weather forecasting efforts.

Balasis, Georgios; Papadimitriou, Constantinos; Daglis, Ioannis A.; Anastasiadis, Anastasios; Athanasopoulou, Labrini; Eftaxias, Konstantinos

2011-07-01

270

Phenomenology of scale-dependent space-time dimension  

E-print Network

Loop-mediated processes characterized by dynamical scale M indirectly measure space-time dimension d at this scale. Assuming the latter to be scale-dependent d=d(L) and taking as examples B-oscillations and muon (g-2) experimental results we address the question about constraints put by this data on 4-d(L). It is shown that sensitivity is lost for 1/L around 350 GeV, and any value of d(L) between 2 and 5 at this scale is compatible with the data.

V. I. Shevchenko

2009-03-03

271

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

272

On the time scale of energy transport in the sun  

NASA Astrophysics Data System (ADS)

It is pointed out that the time scale of energy transport in the Sun is the Kelvin Helmholtz time scale, of order 3×107 years, roughly 100 times longer than the photon-diffusion time estimated by Mitalas and Sills (1992). The difference corresponds to a factor U gas/U rad, the ratio of thermal energy density to radiation energy density. Thus the heat transport, even when mediated by photons, is slowed down by the large heat capacity of the star. A numerical example calculation is presented.

Stix, Michael

2003-01-01

273

Physical activity and spatial differences in medial knee t1rho and t2 relaxation times in knee osteoarthritis.  

PubMed

Study Design Cross-sectional. Objectives To investigate the association between knee loading- related osteoarthritis (OA) risk factors (obesity, malalignment, and physical activity) and medial knee laminar (superficial and deep) T1rho and T2 relaxation times. Background The interaction of various modifiable loading-related knee risk factors and cartilage health in knee OA is currently not well known. Methods Participants with and without knee OA (n = 151) underwent magnetic resonance imaging at 3 T for superficial and deep cartilage T1rho and T2 magnetic resonance relaxation times in the medial femur (MF) and medial tibia (MT). Other variables included radiographic Kellgren-Lawrence (KL) grade, alignment, pain and symptoms using the Knee injury and Osteoarthritis Outcome Score, and physical activity using the International Physical Activity Questionnaire (IPAQ). Individuals with a KL grade of 4 were excluded. Group differences were calculated using 1-way analysis of variance, adjusting for age and body mass index. Linear regression models were created with age, sex, body mass index, alignment, KL grade, and the IPAQ scores to predict the laminar T1rho and T2 times. Results Total IPAQ scores were the only significant predictors among the loading-related variables for superficial MF T1rho (P = .005), deep MT T1rho (P = .026), and superficial MF T2 (P = .049). Additionally, the KL grade predicted the superficial MF T1rho (P = .023) and deep MT T1rho (P = .022). Conclusion Higher physical activity levels and worse radiographic severity of knee OA, but not obesity or alignment, were associated with worse cartilage composition. J Orthop Sports Phys Ther 2014;44(12):964-972. Epub 29 October 2014. doi:10.2519/jospt.2014.5523. PMID:25353261

Kumar, Deepak; Souza, Richard B; Singh, Justin; Calixto, Nathaniel E; Nardo, Lorenzo; Link, Thomas M; Li, Xiaojuan; Majumdar, Sharmila

2014-12-01

274

Simple models and time scales in the dynamo effect  

NASA Astrophysics Data System (ADS)

The dynamo effect has been studied for 50 years, starting from the simple homopolar dynamo of Bullard. Numerical calculations on simple models, such as the crossed dynamos of Rikitake, display large oscillations and brutal reversals. The present Note puts emphasis on time scales. One scale ?, purely electromagnetic, describes inductive decay (the frequency at which the skin depth is the size of the system), the other ? is magnetohydrodynamic, controlling the exchanges of kinetic and magnetic energies. Usually ???: a clear separation of time scales makes the physics much more transparent. We show why sharp reversals must be expected, starting either from the slow or from the fast time scale. Such a comparison clarifies the issue. To cite this article: P. Nozières, C. R. Physique 9 (2008).

Nozières, Philippe

2008-09-01

275

Time scale construction from multiple sources of information (Invited)  

NASA Astrophysics Data System (ADS)

Geological age estimates are provided by diverse chronometers, such as radiometric measurements, astrochronology, and the spacing of magnetic anomalies recorded on mid-ocean ridges by seafloor spreading. These age estimates are affected by errors that can be systematic (e.g., biased radiometric dates due to imperfect assumptions) or random (e.g., imprecise recording of astronomical cycles in sedimentary records). Whereas systematic errors can be reduced by improvements in technique and calibration, uncertainties due to random errors will always be present and need to be dealt with. A Bayesian framework can be used to construct an integrated time scale that is based on several uncertain sources of information. In this framework, each piece of data and the final time scale have an associated probability distribution that describes their uncertainty. The key calculation is to determine the uncertainty in the time scale from the uncertain data that constrain it. In practice, this calculation can be performed by Monte Carlo sampling. In Markov chain Monte Carlo algorithms, the time scale is iteratively perturbed and the perturbed time scale is accepted or rejected depending on how closely it fits the data. The final result is a large ensemble of possible time scales that are consistent with all the uncertain data; while the average of this ensemble defines a 'best' time scale, the ensemble variability quantifies the time scale uncertainty. An example of this approach is the M-sequence (Late Jurassic-Early Cretaceous, ~160-120 Ma) MHTC12 geomagnetic polarity time scale (GPTS) of Malinverno et al. (2012, J. Geophys. Res., B06104, doi:10.1029/2012JB009260). Previous GPTSs were constructed by interpolating between dated marine magnetic anomalies while assuming constant or smoothly varying spreading rates. These GPTSs were typically based on magnetic lineations from one or a few selected spreading centers, and an undesirable result is that they imply larger spreading rate fluctuations on other ridges. On the other hand, the Monte Carlo algorithm used in MHTC12 makes it easy to sample GPTSs that result in small spreading rate variations over multiple spreading centers (in the Western Pacific, North Atlantic, and Indian Ocean NW of Australia). MHTC12 also accounts for the duration of five polarity chrons estimated from floating astrochronologies (CM0r through CM3r). A Bayesian framework and Monte Carlo sampling offer a useful strategy to construct time scales that incorporate different types of chronological information, have a quantified uncertainty, and can be easily updated with additional data that may become available in the future.

Malinverno, A.

2013-12-01

276

Evidence for non-diverging time-scales in glass-forming liquids  

NASA Astrophysics Data System (ADS)

One perceived important signature of the ``ideal'' glass transition and of the complex fluid nature of glass-forming liquids remains the apparent divergence of the dynamics at temperatures above zero Kelvin. Recently, however, this perception has been increasingly challenged both through experiments and in new theories of the dynamics of glass forming systems. In this presentation we summarize some of the prior evidence suggesting that time scales actually do not diverge in glasses that are aged into equilibrium, perhaps 15 K below the conventional glass transition temperature Tg. We then show new results from an extremely densified glass, 20 Ma old Jamaican amber, in which we were able to obtain the upper bound to the relaxation times through a step-wise temperature scan in which the stress relaxation response of the amber was measured both below and above the fictive temperature TF. We find that in the case of the upper bound responses at TTF, there is a strong deviation of the response from the Super-Arrhenius Vogel-Fulcher behavior and this persists to the fictive temperature which is some 33.8 K below Tg. The results are compared to the parabolic model of Chandler and co-workers and we find the model to be consistent with our results if the value of Tx in the model is taken to be the calorimetric glass transition temperature. The significance of the results will be discussed.

McKenna, Gregory

2013-03-01

277

Interpretations of the real time scattering experiment for polystyrene melts during stress relaxation  

E-print Network

L-593 Interpretations of the real time scattering experiment for polystyrene melts during stressR(q) of the single chain, in amorphous polystyrene (Mw = 650 000) in the submolecular range for different durations data are now available for the time dependence ofthe static coil form factors StR(q) for polystyrene

Paris-Sud XI, Université de

278

Electron-ion relaxation time dependent signal enhancement in ultrafast double-pulse laser-induced breakdown spectroscopy  

SciTech Connect

We investigated the emission properties of collinear double-pulse compared to single-pulse ultrafast laser induced breakdown spectroscopy. Our results showed that the significant signal enhancement noticed in the double pulse scheme is strongly correlated to the characteristic electron-ion relaxation time and hence to the inter-pulse delays. Spectroscopic excitation temperature analysis showed that the improvement in signal enhancement is caused by the delayed pulse efficient reheating of the pre-plume. The signal enhancement is also found to be related to the upper excitation energy of the selected lines, i.e., more enhancement noticed for lines originating from higher excitation energy levels, indicating reheating is the major mechanism behind the signal improvement.

Harilal, S. S.; Diwakar, P. K.; Hassanein, A. [Center for Materials Under Extreme Environment, School of Nuclear Engineering, Purdue University, West Lafayette, Indiana 47907 (United States)] [Center for Materials Under Extreme Environment, School of Nuclear Engineering, Purdue University, West Lafayette, Indiana 47907 (United States)

2013-07-22

279

Measurement of solute proton spin-lattice relaxation times in water using the 1,3,3,1 sequence.  

PubMed

1H NMR spin-lattice relaxation times (T1) of the N-CH3 proton resonances of phosphocreatine (PCr) and creatine (Cr) in water solutions were obtained using the 1,3,3,1 pulse sequence. These T1 values were equivalent to those obtained in D2O and water using either the conventional inversion-recovery experiment or the 1,3,3,1 pulse sequence. Thus, the 1,3,3,1 sequence of proton NMR can provide an independent means along with phosphorous NMR for assess PCr and for the study of the creatine kinase reaction (PCr + ADP in equilibrium ATP + Cr) in aqueous solutions and perhaps in biological preparations. PMID:3029535

Sankar, S S; Molé, P A; Coulson, R L

1986-12-01

280

Following the relaxation dynamics of photoexcited aniline in the 273-266 nm region using time-resolved photoelectron imaging  

NASA Astrophysics Data System (ADS)

Time-resolved photoelectron imaging was used to investigate the relaxation dynamics of electronically excited aniline in the gas-phase following ultraviolet irradiation in the 273-266 nm region. We find that at all wavelengths studied, excitation is predominantly to the long-lived (>1 ns) S1(??*) state, which exhibits ultrafast intramolecular vibrational redistribution on a <1 ps timescale. At excitation wavelengths centred on resonant transitions in the aniline absorption spectrum that have previously been assigned to the higher lying S2(3s/??*) state, we also see clear evidence of this state playing a role in the dynamics. However, we see no indication of any non-adiabatic coupling between the S1(??*) and S2(3s/??*) states over the range of excitation wavelengths studied.

Thompson, James O. F.; Livingstone, Ruth A.; Townsend, Dave

2013-07-01

281

Numerical analysis of relaxation times of multiple quantum coherences in the system with a large number of spins  

NASA Astrophysics Data System (ADS)

We study the decay of multiple quantum (MQ) NMR coherences in systems with the large number of equivalent spins. As being created on the preparation period of the MQ NMR experiment, they decay due to the dipole-dipole interactions (DDI) on the evolution period of this experiment. It is shown that the relaxation time decreases with the increase in MQ coherence order (according to the known results) and in the number of spins. We also consider the modified preparation period of the MQ NMR experiment [G. A. Alvarez and D. Suter, Phys. Rev. Lett. 104, 230403 (2010)] concatenating the short evolution periods under the secular DDI Hamiltonian (the perturbation) with the evolution period under the nonsecular averaged two-spin/two-quantum Hamiltonian. The influence of the perturbation on the decoherence rate is investigated for the systems consisting of 200-600 equivalent spins.

Doronin, S. I.; Fel'Dman, E. B.; Zenchuk, A. I.

2011-01-01

282

Spin-echo methods for the determination of 31P transverse relaxation times of the ATP NMR signals in vivo.  

PubMed

31P magnetic resonance spectroscopy (MRS) examinations of the calf muscles of healthy volunteers were performed to determine T2 of the coupled ATP signals by use of the Hahn spin-echo and the frequency-selective spin-echo method. Additional measurements with the J-coupling refocused double echo are presented. The most reliable determination of T2 relaxation times is possible with the frequency-selective spin echo. The other methods yield substantially wrong results. Theoretical explanations are given how J-coupling and pulse-angle deviations affect the signals and therefore the T2 determinations. The calculations for a weakly coupled homonuclear AX spin system are shown because they demonstrate most of the relevant facts. In addition, some important results for a homonuclear AMX spin system, which the ATP is considered to be, are given. PMID:8295499

Straubinger, K; Jung, W I; Bunse, M; Lutz, O; Küper, K; Dietze, G

1994-01-01

283

Measurement of solute proton spin-lattice relaxation times in water using the 1,3,3,1 sequence  

SciTech Connect

/sup 1/H NMR spin-lattice relaxation times (T1) of the N-CH3 proton resonances of phosphocreatine (PCr) and creatine (Cr) in water solutions were obtained using the 1,3,3,1 pulse sequence. These T1 values were equivalent to those obtained in D/sub 2/O and water using either the conventional inversion-recovery experiment or the 1,3,3,1 pulse sequence. Thus, the 1,3,3,1 sequence of proton NMR can provide an independent means along with phosphorous NMR for assess PCr and for the study of the creatine kinase reaction (PCr + ADP in equilibrium ATP + Cr) in aqueous solutions and perhaps in biological preparations.

Sankar, S.S.; Mole, P.A.; Coulson, R.L.

1986-12-01

284

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

NASA Astrophysics Data System (ADS)

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 HYDRUS code where the TRT schemes behave more robustly for small diffusion coefficients and sharp infiltration profiles. The focus is on the stability and efficiency of two transport schemes. The first scheme conventionally prescribes C for diffusive flux equilibrium variable while conserving ?C. The second scheme prescribes ?C for both variables, expecting to retain the stable parameter areas and velocity amplitudes recently predicted by linear von Neumann stability analysis. We show that the first scheme reduces the stable diffusion range, e.g. from ?-/ d to ??-/ d for simplest velocity sets, but it also modifies the linearized numerical diffusion, from - ?-U?U? to - ??-U?U?, giving rise to possible enhancement of stable velocity U2, max by a factor 1/ ?. This analysis indicates that the first scheme is most efficient for infiltration into dry soil. When the product ?+?- is kept constant, we find a good agreement between the attainable velocity and our predictions providing that ?- does not exceed ?5. Otherwise, approaching two opposite stability limits, ?+ ? 0 when ?- ? ? , the stable velocity amplitude drastically falls for the two transport TRT schemes. At the same time, their BGK submodels ?+ = ?- may keep the optimal stability for diffusion-dominant problems but their boundary and bulk approximations are completely destroyed. The analysis presented here may serve as a starting point for construction of the suitable equilibrium transformations, based on the analytical stability argument and a proper parameter choice.

Hammou, H.; Ginzburg, I.; Boulerhcha, M.

2011-06-01

285

Age related reduction of T1rho and T2 magnetic resonance relaxation times of lumbar intervertebral disc  

PubMed Central

This report aims to study the age related T1rho and T2 relaxation time changes in lumbar intervertebral disc. Lumbar sagittal magnetic resonance imaging (MRI) was performed with a 3 Tesla scanner in 52 subjects. With a spin-lock frequency of 500 Hz, T1rho was measured using a rotary echo spin-lock pulse embedded in a 3D balanced fast field echo sequence. A multi-echo turbo spin echo sequence was used for T2 mapping. Regions-of-interest were drawn over the T1rho and T2 maps, including nucleus pulposus and annulus fibrosus. For L1/2-L4/5 discs, results showed the age associated reduction of T1rho of nucleus pulposus had a of slope of –1.06, the reduction of T2 of nucleus pulposus had a slope of –1.47, the reduction of T1rho of annulus fibrosus had a slope of –0.25, and the reduction of T2 of annulus fibrosus had a slope of –0.18, with all the slopes significantly non-zero. In nucleus pulposus the slope of T2 was slightly steeper than that of T1rho (P=0.085), while in annulus fibrosus the slope of T1rho was slightly steeper than that of T2 (P=0.31). We conclude that significant age related reduction of T1rho and T2 magnetic resonance relaxation times of lumbar intervertebral disc was observed, however, the relative performances of T1rho vs. T2 were broadly similar.

Griffith, James F.; Leung, Jason C. S.; Yuan, Jing

2014-01-01

286

Multiple-time scales analysis of physiological time series under neural control  

NASA Technical Reports Server (NTRS)

We discuss multiple-time scale properties of neurophysiological control mechanisms, using heart rate and gait regulation as model systems. We find that scaling exponents can be used as prognostic indicators. Furthermore, detection of more subtle degradation of scaling properties may provide a novel early warning system in subjects with a variety of pathologies including those at high risk of sudden death.

Peng, C. K.; Hausdorff, J. M.; Havlin, S.; Mietus, J. E.; Stanley, H. E.; Goldberger, A. L.

1998-01-01

287

NMR Relaxation and Petrophysical Properties  

NASA Astrophysics Data System (ADS)

NMR relaxation is routinely used in the field of geosciences to give basic petrophysical properties such as porosity, pore size distribution, saturation etc. In this tutorial, we focus on the pore size distribution deduced from NMR. We recall the basic principle used in the interpretation of the NMR signal and compare the results with other standard petrophysical techniques such as mercury pore size distribution, BET specific surface measurements, thin section visualizations. The NMR pore size distribution is a unique information available on water saturated porous media and can give similar results as MICP in certain situations. The scaling of NMR relaxation time distribution (s) into pore sizes (?m) requires the knowledge of the surface relaxivity (?m/s) and we recommend using specific surface measurements as an independent determination of solid surface areas. With usual surface relaxivities, the NMR technique can explore length-scales starting from nano-meters and ending around 100 ?m. Finally, we will introduce briefly recent techniques sensitive to the pore to pore diffusional exchange, providing new information on the connectivity of the pore network, but showing another possibility of discrepancy in the determination of pore size distribution with standard techniques.

Fleury, Marc

2011-03-01

288

Music Visualization by Means of Comb Filter and Relaxation Time According to Human Perception  

Microsoft Academic Search

\\u000a The visualization of an audio signal’s time structure is the primary step for every rhythm synchronizer system. To achieve\\u000a this, principle components of the musical signal beats as strength, tempo and onset time must be detected. A filter bank of\\u000a 180 different comb filters (from 60 bpm to 240 bpm) is convolved with different styles of musical signal to visualize

Mahdieh Poostchi; Iman Kamkar; Javad Mohebbi

289

Dielectric long time relaxation of domains walls in PbZrTiO3 thin films  

NASA Astrophysics Data System (ADS)

Ferroelectric materials subjected to a DC electric field have their dielectric permittivity which decreases with time. This is connected to the reorganization of the domain walls to achieve a more stable configuration. We propose here to study the domain walls motion when the material is subjected to an electrical field. We use the hyperbolic law (generalized Rayleigh law) for contributions related to the walls. This allows to clearly identifying the domain walls as responsible for the time decay of the permittivity.

Borderon, Caroline; Renoud, Raphaël; Ragheb, Mostafa; Gundel, Hartmut W.

2014-02-01

290

Planck Scale Physics, Pregeometry and the Notion of Time  

E-print Network

Recent progress in quantum gravity and string theory has raised interest among scientists to whether or not nature behaves discretely at the Planck scale. There are two attitudes twoards this discretenes i.e. top-down and bottom-up approach. We have followed up the bottom-up approach. Here we have tried to describe how macroscopic space-time or its underlying mesoscopic substratum emerges from a more fundamental concept. The very concept of space-time, causality may not be valid beyond Planck scale. We have introduced the concept of generalised time within the framework of Sheaf Cohomology where the physical time emrges around and above Planck scale. The possible physical amd metaphysical implications are discussed.

S. Roy

2003-11-04

291

Imaging of relaxation times and microwave field strength in a microfabricated vapor cell  

NASA Astrophysics Data System (ADS)

We present a characterization technique for atomic vapor cells, combining time-domain measurements with absorption imaging to obtain spatially resolved information on decay times, atomic diffusion, and coherent dynamics. The technique is used to characterize a 5-mm-diameter, 2-mm-thick microfabricated Rb vapor cell, with N2 buffer gas, placed inside a microwave cavity. Time-domain Franzen and Ramsey measurements are used to produce high-resolution images of the population (T1) and coherence (T2) lifetimes in the cell, while Rabi measurements yield images of the ?-, ?, and ?+ components of the applied microwave magnetic field. For a cell temperature of 90?C, the T1 times across the cell center are found to be a roughly uniform 265?s, while the T2 times peak at around 350?s. We observe a “skin” of reduced T1 and T2 times around the edge of the cell due to the depolarization of Rb after collisions with the silicon cell walls. Our observations suggest that these collisions are far from being 100% depolarizing, consistent with earlier observations made with Na and glass walls. Images of the microwave magnetic field reveal regions of optimal field homogeneity, and thus coherence. Our technique is useful for vapor cell characterization in atomic clocks, atomic sensors, and quantum information experiments.

Horsley, Andrew; Du, Guan-Xiang; Pellaton, Matthieu; Affolderbach, Christoph; Mileti, Gaetano; Treutlein, Philipp

2013-12-01

292

Multiple time scales from hard local constraints: Glassiness without disorder  

NASA Astrophysics Data System (ADS)

While multiple time scales generally arise in the dynamics of disordered systems, we find multiple time scales in the absence of disorder in a simple model with hard local constraints. The dynamics of the model, which consists of local collective rearrangements of various scales, is not determined by the smallest scale but by a length l* that grows at low energies. In real space we find a hierarchy of fast and slow regions: Each slow region is geometrically insulated from all faster degrees of freedom, which are localized in fast pockets below percolation thresholds. A tentative analogy with structural glasses is given, which attributes the slowing down of the dynamics to the growing size of mobile elementary excitations, rather than to the size of some domains.

Cépas, O.

2014-08-01

293

Deviations from uniform power law scaling in nonstationary time series  

NASA Technical Reports Server (NTRS)

A classic problem in physics is the analysis of highly nonstationary time series that typically exhibit long-range correlations. Here we test the hypothesis that the scaling properties of the dynamics of healthy physiological systems are more stable than those of pathological systems by studying beat-to-beat fluctuations in the human heart rate. We develop techniques based on the Fano factor and Allan factor functions, as well as on detrended fluctuation analysis, for quantifying deviations from uniform power-law scaling in nonstationary time series. By analyzing extremely long data sets of up to N = 10(5) beats for 11 healthy subjects, we find that the fluctuations in the heart rate scale approximately uniformly over several temporal orders of magnitude. By contrast, we find that in data sets of comparable length for 14 subjects with heart disease, the fluctuations grow erratically, indicating a loss of scaling stability.

Viswanathan, G. M.; Peng, C. K.; Stanley, H. E.; Goldberger, A. L.

1997-01-01

294

Real-time observation of anisotropic strain relaxation by three-dimensional reciprocal space mapping during InGaAs/GaAs (001) growth  

SciTech Connect

Real-time three-dimensional reciprocal space mapping (3D-RSM) measurement during In{sub 0.12}Ga{sub 0.88}As/GaAs(001) molecular beam epitaxial growth has been performed to investigate anisotropy in relaxation processes along [110] and [110] directions caused by alpha and beta misfit dislocations (MDs). Anisotropies, strain relaxation, and crystal quality in both directions were simultaneously evaluated via the position and broadness of 022 diffraction in 3D-RSM. In the small-thickness region, strain relaxation caused by alpha-MDs is higher than that caused by beta-MDs, and therefore crystal quality along [110] is worse than that along [110]. Rapid relaxation along both [110] and [110] directions occurs at almost the same thickness. After rapid relaxation, anisotropy in strain relaxation gradually decreases, whereas crystal quality along [110] direction, presumably due to beta-MDs, becomes better that along [110] direction and the ratio does not decay with thickness.

Suzuki, Hidetoshi; Sasaki, Takuo; Sai, Akihisa; Ohshita, Yoshio; Kamiya, Itaru; Yamaguchi, Masafumi [Toyota Technological Institute, 2-12-1 Hisakata, Tempaku, Nagoya 468-8511 (Japan); Takahasi, Masamitu; Fujikawa, Seiji [Synchrotron Radiation Research Center, Japan Atomic Energy Agency, Hyogo 679-5148 (Japan)

2010-07-26

295

Common scaling patterns in intertrade times of U. S. stocks  

NASA Astrophysics Data System (ADS)

We analyze the sequence of time intervals between consecutive stock trades of thirty companies representing eight sectors of the U.S. economy over a period of 4 yrs. For all companies we find that: (i) the probability density function of intertrade times may be fit by a Weibull distribution, (ii) when appropriately rescaled the probability densities of all companies collapse onto a single curve implying a universal functional form, (iii) the intertrade times exhibit power-law correlated behavior within a trading day and a consistently greater degree of correlation over larger time scales, in agreement with the correlation behavior of the absolute price returns for the corresponding company, and (iv) the magnitude series of intertrade time increments is characterized by long-range power-law correlations suggesting the presence of nonlinear features in the trading dynamics, while the sign series is anticorrelated at small scales. Our results suggest that independent of industry sector, market capitalization and average level of trading activity, the series of intertrade times exhibit possibly universal scaling patterns, which may relate to a common mechanism underlying the trading dynamics of diverse companies. Further, our observation of long-range power-law correlations and a parallel with the crossover in the scaling of absolute price returns for each individual stock, support the hypothesis that the dynamics of transaction times may play a role in the process of price formation.

Ivanov, Plamen Ch.; Yuen, Ainslie; Podobnik, Boris; Lee, Youngki

2004-05-01

296

Grueneisen Relaxation Photoacoustic Microscopy  

NASA Astrophysics Data System (ADS)

The temperature-dependent property of the Grueneisen parameter has been employed in photoacoustic imaging mainly to measure tissue temperature. Here we explore this property using a different approach and develop Grueneisen relaxation photoacoustic microscopy (GR-PAM), a technique that images nonradiative absorption with confocal optical resolution. GR-PAM sequentially delivers two identical laser pulses with a microsecond-scale time delay. The first laser pulse generates a photoacoustic signal and thermally tags the in-focus absorbers. When the second laser pulse excites the tagged absorbers within the thermal relaxation time, a photoacoustic signal stronger than the first one is produced, owing to the temperature dependence of the Grueneisen parameter. GR-PAM detects the amplitude difference between the two colocated photoacoustic signals, confocally imaging the nonradiative absorption. We greatly improved axial resolution from 45 ?m to 2.3 ?m and, at the same time, slightly improved lateral resolution from 0.63 ?m to 0.41 ?m. In addition, the optical sectioning capability facilitates the measurement of the absolute absorption coefficient without fluence calibration.

Wang, Lidai; Zhang, Chi; Wang, Lihong V.

2014-10-01

297

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

298

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

299

Systematic differences between lean and obese adolescents in brain spin-lattice relaxation time, a quantitative study  

PubMed Central

Background and Purpose Emerging evidence suggests that obese adolescents show changes in brain structure compared to lean adolescents. In addition, obesity impacts body development during adolescence. We tested a hypothesis that spin-lattice relaxation time T1, a marker of brain maturation, can show brain differences associated with obesity. Materials and Methods Adolescents similar in gender, family income, and school grade were recruited using strict entry criteria. We measured brain T1 in 48 obese and 31 lean adolescents by quantitative magnetic resonance imaging at 1.5T. We combined MPRAGE and inversion recovery sequences with normalization to standard space and automated skull stripping to obtain T1 maps with a symmetric voxel volume of 1 mm3. Results Gender, income, triglycerides, total cholesterol, and fasting glucose did not differ between groups, but obese adolescents had significantly lower HDL, higher LDL, and higher fasting insulin levels than lean adolescents. Intracranial vault volume did not differ between groups, but obese adolescents had smaller intracranial vault-adjusted brain parenchymal volumes. Obese adolescents had 4 clusters (>100 contiguous voxels) of T1 relaxation that were significantly different (p<0.005) from lean adolescents. Three of these clusters had longer T1 in obese adolescents (in the orbitofrontal and parietal regions), and 1 cluster had shorter T1, compared to lean adolescents. Conclusion Our results suggest that obesity may have a significant impact on brain development, especially in the frontal and parietal lobes. It is unclear if these changes persist into adulthood or whether they indicate that obese subjects follow a different developmental trajectory during adolescence. PMID:21960489

Cazettes, Fanny; Tsui, Wai H; Johnson, Glyn; Steen, R. Grant; Convit, Antonio

2011-01-01

300

Dynamic correlations and heterogeneity in the primary and secondary relaxations of a model molecular liquid  

NASA Astrophysics Data System (ADS)

Molecular dynamics simulations were carried out on a series of Lennard-Jones binary mixtures of rigid, asymmetric, dumbbell-shaped molecules. Below an onset temperature, the rotational and translational dynamics split into the slow structural ? relaxation and a higher-frequency Johari-Goldstein ? relaxation. Both processes are dynamically heterogeneous, having broad distributions of relaxation times. However, only the ? relaxation shows strong dynamic correlations; correlations at the ? time scale are weak, in particular for molecules having shorter bonds. Despite the close connection between the two processes, we find no correlation between the ? and ? relaxation times of individual molecules; that is, a molecule exhibiting slow ? motion does not necessarily undergo slow ? dynamics and likewise for fast molecules. However, the single-molecule ? relaxation times do correlate with both the ? and ? relaxation strengths.

Fragiadakis, D.; Roland, C. M.

2014-05-01

301

Uniqueness and reciprocal theorems in linear micropolar electro-magnetic thermoelasticity with two relaxation times  

NASA Astrophysics Data System (ADS)

A general model for the linear micropolar electro-magnetic thermoelastic continuum based on the hyperbolic heat equation, which is physically more relevant than the classical thermoelasticity theory in analyzing problems involving very short intervals of time and/or very high heat fluxes, is introduced. An integral identity that involves two admissible processes at different instants is established. Uniqueness theorem is proved, with no definiteness assumption on the elastic constitutive coefficients and no restrictions on the electro-elastic coupling moduli, magneto-elastic coupling moduli, and thermal coupling coefficients other than symmetry conditions. The reciprocity theorem is derived, without the use of Laplace transforms. The integral representation formula is obtained in case instantaneous concentrated, time-continuous or time-harmonic loads are applied. The Maysel’s, Somigliana’s and Green’s formulas are derived. The mixed boundary value problem is considered and a system of five singular Fredholm integral equations is obtained. The results for dynamic classical coupled theory can be easy deduced from the given general model formulated for the temperature-rate dependent thermoelasticity.

El-Karamany, Ahmed S.; Ezzat, Magdy A.

2009-03-01

302

Improving the Geologic Time Scale (Jean Baptiste Lamarck Medal Lecture)  

NASA Astrophysics Data System (ADS)

The Geologic Time Scale (GTS) provides the framework for the physical, chemical and biological processes on Earth. The time scale is the tool "par excellence" of the geological trade, and insight in its construction, strength, and limitations enhances its function and its utility. Earth scientists should understand how time scales are constructed and its myriad of physical and abstract data are calibrated, rather than merely using ages plucked from a convenient chart or card. Calibration to linear time of the succession of events recorded in the rocks on Earth has three components: (1) the standard stratigraphic divisions and their correlation in the global rock record, (2) the means of measuring linear time or elapsed durations from the rock record, and (3) the methods of effectively joining the two scales, the stratigraphic one and the linear one. Under the auspices of the International Commission on Stratigraphy (ICS), the international stratigraphic divisions and their correlative events are now largely standardized, especially using the GSSP (Global Stratigraphic Section and Point) concept. The means of measuring linear time or elapsed durations from the rock record are objectives in the EARTH TIME and GTS NEXT projects, that also are educating a new generation of GTS dedicated scientists. The U/Pb, Ar/Ar and orbital tuning methods are intercalibrated, and external error analysis improved. Existing Ar/Ar ages become almost 0.5% older, and U/Pb ages stratigraphically more realistic. The new Os/Re method has potential for directly dating more GSSP's and its correlative events. Such may reduce scaling uncertainty between the sedimentary levels of an age date and that of a stage boundary. Since 1981, six successive Phanerozoic GTS have been published, each new one achieving higher resolution and more users. The next GTS is scheduled for 2011/2012, with over 50 specialists taking part. New chapters include an expanded planetary time scale, sequence stratigraphy, Osmium, Carbon and Oxygen stratigraphy, the Cryogenian period, history of the plants, hominid prehistory, and last but not least the Anthropocene. The Cambrian Period is radically improved with 10 standard stages and detailed trilobite biochronology. Ordovician now has a stable international stages and graptolites scale. The integration of a refined 100 and 400 ka sedimentary cycles scale and a truly high-resolution U/Pb ages scale for the Mississippian is a major step towards the global Carboniferous GTS. The Devonian GTS leaves to be desired with lack of firm definitions for its upper boundary, and the long Emsian stage; it also lacks age dates. Its stages scaling is disputed. The Rhaetian and Norian stages in the Triassic and the Berriasian stage in the Cretaceous urgently require lower boundary definitions, and also boundary age dates. The single ~400 ka eccentricity component is very stable and can extend orbital tuning from the Cenozoic well into the Mesozoic portion of the GTS. Jurassic and Cretaceous now have long orbitally tuned segments. A completely astronomical-tuned Geological Time Scale (AGTS) for the Cenozoic is within reach showing unprecedented accuracy, precision and resolution. Burdigalian in the Miocene, and Lutetian, Bartonian and Priabonian stages in the Eocene still require formal definition. The K/T boundary will become about 0.5 ± 0.1 Ma older. After 25 years of research and authorship in the GTS it behoves me to especially thank my colleagues James Ogg, Frits Agterberg, John McArthur and Roger Cooper for longstanding collaboration. As a final note I urge construction of more regional time scales(like developed ‘down under') calibrated to the standard global GTS, to scale regional rock units.

Gradstein, Felix M.

2010-05-01

303

NMR T1 relaxation time measurements and calculations with translational and rotational components for liquid electrolytes containing LiBF4 and propylene carbonate.  

PubMed

Longitudinal relaxation (T1) measurements of (19)F, (7)Li, and (1)H in propylene carbonate/LiBF4 liquid electrolytes are reported. Comparison of T1 values with those for the transverse relaxation time (T2) confirm that the measurements are in the high temperature (low correlation time) limit of the T1 minimum. Using data from pulsed field gradient measurements of self-diffusion coefficients and measurements of solution viscosity measured elsewhere, it is concluded that although in general there are contributions to T1 from both translational and rotational motions. For the lithium ions, this is mainly translational, and for the fluorine ions mainly rotational. PMID:24320385

Richardson, P M; Voice, A M; Ward, I M

2013-12-01

304

A time scale for electrical screening in pulsed gas discharges  

NASA Astrophysics Data System (ADS)

The Maxwell time is a typical time scale for the screening of an electric field in a medium with a given conductivity. We introduce a generalization of the Maxwell time that is valid for gas discharges: the ionization screening time, that takes the growth of the conductivity due to impact ionization into account. We present an analytic estimate for this time scale, assuming a planar geometry, and evaluate its accuracy by comparing with one- and three-dimensional numerical simulations. We investigate the minimum plasma density required to prevent the growth of streamers with local field enhancement, and we discuss the effects of photoionization and electron detachment on ionization screening. Our results can help to understand the development of pulsed discharges, for example nanosecond pulsed discharges at atmospheric pressure or halo discharges in the lower ionosphere.

Teunissen, Jannis; Sun, Anbang; Ebert, Ute

2014-09-01

305

A time scale for electrical screening in pulsed gas discharges  

E-print Network

The Maxwell time is a typical time scale for the screening of an electric field in a medium with a given conductivity. We introduce a generalization of the Maxwell time that is valid for gas discharges: the \\emph{ionization screening time}, that takes the growth of the conductivity due to impact ionization into account. We present an analytic estimate for this time scale, assuming a planar geometry, and evaluate its accuracy by comparing with numerical simulations in 1D and 3D. We investigate the minimum plasma density required to prevent the growth of streamers with local field enhancement, and we discuss the effects of photoionization and electron detachment on ionization screening. Our results are especially relevant for the description of nanosecond pulsed discharges.

Teunissen, Jannis; Ebert, Ute

2014-01-01

306

Time-dependent entropy evolution in microscopic and macroscopic electromagnetic relaxation  

SciTech Connect

This paper is a study of entropy and its evolution in the time and frequency domains upon application of electromagnetic fields to materials. An understanding of entropy and its evolution in electromagnetic interactions bridges the boundaries between electromagnetism and thermodynamics. The approach used here is a Liouville-based statistical-mechanical theory. I show that the microscopic entropy is reversible and the macroscopic entropy satisfies an H theorem. The spectral entropy development can be very useful for studying the frequency response of materials. Using a projection-operator based nonequilibrium entropy, different equations are derived for the entropy and entropy production and are applied to the polarization, magnetization, and macroscopic fields. I begin by proving an exact H theorem for the entropy, progress to application of time-dependent entropy in electromagnetics, and then apply the theory to relevant applications in electromagnetics. The paper concludes with a discussion of the relationship of the frequency-domain form of the entropy to the permittivity, permeability, and impedance.

Baker-Jarvis, James [National Institute of Standards and Technology, Electromagnetics Division, MS 818.01, Boulder, Colorado 80305 (United States)

2005-12-15

307

Transport coefficients for bulk viscous evolution in the relaxation time approximation  

E-print Network

We derive the form of the viscous corrections to the phase-space distribution function due to bulk viscous pressure and shear stress using the iterative Chapman-Enskog method. We then calculate the transport coefficients necessary for the second-order hydrodynamic evolution of the bulk viscous pressure and the shear stress tensor. We demonstrate that the transport coefficients obtained using the Chapman-Enskog method are different than those obtained previously using 14-moment approximation for finite particle mass. Specializing to the case of boost-invariant and transversally homogeneous longitudinal expansion, we show that the transport coefficients obtained using the Chapman-Enskog method result in better agreement with the exact solution of the Boltzmann equation compared to results obtained in the 14-moment approximation. Finally, we explicitly confirm that the time evolution of the bulk viscous pressure is significantly affected by its coupling to the shear stress tensor.

Jaiswal, Amaresh; Strickland, Michael

2014-01-01

308

Appropriate time scales for nonlinear analyses of deterministic jump systems  

NASA Astrophysics Data System (ADS)

In the real world, there are many phenomena that are derived from deterministic systems but which fluctuate with nonuniform time intervals. This paper discusses the appropriate time scales that can be applied to such systems to analyze their properties. The financial markets are an example of such systems wherein price movements fluctuate with nonuniform time intervals. However, it is common to apply uniform time scales such as 1-min data and 1-h data to study price movements. This paper examines the validity of such time scales by using surrogate data tests to ascertain whether the deterministic properties of the original system can be identified from uniform sampled data. The results show that uniform time samplings are often inappropriate for nonlinear analyses. However, for other systems such as neural spikes and Internet traffic packets, which produce similar outputs, uniform time samplings are quite effective in extracting the system properties. Nevertheless, uniform samplings often generate overlapping data, which can cause false rejections of surrogate data tests.

Suzuki, Tomoya

2011-06-01

309

T2 relaxation time measurements are limited in monitoring progression, once advanced cartilage defects at the knee occur  

PubMed Central

Purpose To study the natural evolution of cartilage T2 relaxation times in knees with various extents of morphological cartilage abnormalities, assessed with 3T MRI from the Osteoarthritis Initiative. Materials and Methods Right knee MRIs of 245, 45–60 year old individuals without radiographic OA were included. Cartilage was segmented and T2 maps were generated in five compartments (patella, medial and lateral femoral condyle, medial and lateral tibia) at baseline and two-year follow-up. We examined the association of T2 values and two-year change of T2 values with various Whole-Organ MR Imaging Scores (WORMS). Statistical analysis was performed with ANOVA and Students t-tests. Results Higher baseline T2 was associated with more severe cartilage defects at baseline and subsequent cartilage loss (P<0.001). However, longitudinal T2 change was inversely associated with both baseline (P=0.038) and follow-up (P=0.002) severity of cartilage defects. Knees that developed new cartilage defects had smaller increases in T2 than subjects without defects (P=0.045). Individuals with higher baseline T2 showed smaller T2 increases over time (P<0.001). Conclusion An inverse correlation of longitudinal T2 changes versus baseline T2 values and morphological cartilage abnormalities suggests that once morphological cartilage defects occur, T2 values may be limited for evaluating further cartilage degradation. PMID:24038491

Jungmann, P.M.; Kraus, M.S.; Nardo, L.; Liebl, H.; Alizai, H.; Joseph, G.B.; Liu, F.; Lynch, J.; McCulloch, C.E.; Nevitt, M.C.; Link, T.M.

2014-01-01

310

Time Scale Calculus - a new perspectives for synthetic seismogram calculations  

NASA Astrophysics Data System (ADS)

Synthetic, numerically generated seismograms are one of the key factors of any interpretation of recorded seismic data. At the early stage of development, calculation of full seismic waveforms was impossible due to a limited computational resource so we were forced to used only some selected characteristics of seismic waves relatively easy for numerical calculations like first arrival times, maximum amplitude, approximate source spectra, to name a few. Continues development of computational resources as well as progress in numerical techniques has opened possibilities of generation the full, 3-component seismograms incorporating many physically important elements like wave attenuation, anisotropy or randomness of the media. Although achieved results are impressive we still need new numerical methods to tackle existing problems with the synthetic seismogram generation. In this contribution we present a novel approach to discretization of the wave equation which brings together continues and discrete numerical analysis of the seismic waves. The foundations of this new technique, called Time Scale Calculus, have been formulated by Hilger in late eighties and is very dynamically developing. The Time scale calculus, due to its universality seems to have a great potential when practical applications are considered. Thus we have decided to bring the Time Scale calculus concept closer to geophysical, or more precisely to seismological applications. This presentation is intend as a basic introduction to the time scales calculus considered from seismological point of view. We shortly present and discuss the possibility of using the Time Scales (TS) technique for solving the simplest acoustic 2D wave equation keeping in mind its particular applications for mining induced seismicity.

Waskiewicz, Kamil; Debski, Wojciech

2013-04-01

311

A pseudo-Bertrand distribution for time-scale analysis  

Microsoft Academic Search

Using the pseudo-Wigner time-frequency distribution as a guide, we derive two new time-scale representations: the pseudo-Bertrand and the smoothed pseudo-Bertrand distributions. Unlike the Bertrand distribution, these representations support efficient online operation at the same computational cost as the continuous wavelet transform. Moreover, they take advantage of the affine smoothing inherent in the sliding structure of their implementation to suppress cumbersome

P. Goncalves; R. G. Baraniuk

1996-01-01

312

NMR relaxation times and quadrupole coupling constants in [M(CO) 6] (M ? Cr, Mo, W) and [V(CO) 6] -. Transition-metal quadrupole moments. 17O relaxation times and bonding  

NASA Astrophysics Data System (ADS)

Spin-lattice relaxation times have been measured for the 53Cr, 51V, and 17O nuclei in [M(CO) 6] complexes (M ? Cr 0, W 0, V -). The T1 values and derived quadrupole coupling constants (QCC) for the transition metals in [Cr(CO) 6] and [V(CO) 6] - are 267 ms, 0.356 MHz and 3.31 s, 0.326 MHz, respectively. Together with T1 values and QCCs previously reported for [ 95,97Mo(CO) 6], and the quadrupole moment value of Q = 0.17 barns (B) for 97Mo, a self-consistent set of quadrupole moment values of 0.041 ( 53Cr), 0.015 ( 95Mo), and 0.037 ( 51V) B is derived. These values are supported by those calculated from the literature T1 values of the corresponding tetrahedral oxoanions, validating the underlying assumption of uniform electric field gradients in isosymmetric, isoelectronic series. The QCCs obtained from the 17O T1's are 2.11, 2.20, 2.09, and 1.19 MHz for the Cr, Mo, W, and V - hexacarbonyls, respectively. These values indicate d?- p? back bonding ability is constant for the Group VI B metals, but substantially increases with decreasing metal oxidation state for the [V(CO) 6] - complex.

Brownlee, Robert T. C.; Shehan, B. Philip

313

Simulations of Bingham plastic flows with the multiple-relaxation-time lattice Boltzmann model  

NASA Astrophysics Data System (ADS)

Fresh cement mortar is a type of workable paste, which can be well approximated as a Bingham plastic and whose flow behavior is of major concern in engineering. In this paper, Papanastasiou's model for Bingham fluids is solved by using the multiplerelaxation-time lattice Boltzmann model (MRT-LB). Analysis of the stress growth exponent m in Bingham fluid flow simulations shows that Papanastasiou's model provides a good approximation of realistic Bingham plastics for values of m > 108. For lower values of m, Papanastasiou's model is valid for fluids between Bingham and Newtonian fluids. The MRT-LB model is validated by two benchmark problems: 2D steady Poiseuille flows and lid-driven cavity flows. Comparing the numerical results of the velocity distributions with corresponding analytical solutions shows that the MRT-LB model is appropriate for studying Bingham fluids while also providing better numerical stability. We further apply the MRT-LB model to simulate flow through a sudden expansion channel and the flow surrounding a round particle. Besides the rich flow structures obtained in this work, the dynamics fluid force on the round particle is calculated. Results show that both the Reynolds number Re and the Bingham number Bn affect the drag coefficients C D , and a drag coefficient with Re and Bn being taken into account is proposed. The relationship of Bn and the ratio of unyielded zone thickness to particle diameter is also analyzed. Finally, the Bingham fluid flowing around a set of randomly dispersed particles is simulated to obtain the apparent viscosity and velocity fields. These results help simulation of fresh concrete flowing in porous media.

Chen, SongGui; Sun, QiCheng; Jin, Feng; Liu, JianGuo

2014-03-01

314

Simulations of Bingham plastic flows with the multiple-relaxation-time lattice Boltzmann model  

NASA Astrophysics Data System (ADS)

Fresh cement mortar is a type of workable paste, which can be well approximated as a Bingham plastic and whose flow behavior is of major concern in engineering. In this paper, Papanastasiou's model for Bingham fluids is solved by using the multiplerelaxation-time lattice Boltzmann model (MRT-LB). Analysis of the stress growth exponent m in Bingham fluid flow simulations shows that Papanastasiou's model provides a good approximation of realistic Bingham plastics for values of m > 108. For lower values of m, Papanastasiou's model is valid for fluids between Bingham and Newtonian fluids. The MRT-LB model is validated by two benchmark problems: 2D steady Poiseuille flows and lid-driven cavity flows. Comparing the numerical results of the velocity distributions with corresponding analytical solutions shows that the MRT-LB model is appropriate for studying Bingham fluids while also providing better numerical stability. We further apply the MRT-LB model to simulate flow through a sudden expansion channel and the flow surrounding a round particle. Besides the rich flow structures obtained in this work, the dynamics fluid force on the round particle is calculated. Results show that both the Reynolds number Re and the Bingham number Bn affect the drag coefficients C D , and a drag coefficient with Re and Bn being taken into account is proposed. The relationship of Bn and the ratio of unyielded zone thickness to particle diameter is also analyzed. Finally, the Bingham fluid flowing around a set of randomly dispersed particles is simulated to obtain the apparent viscosity and velocity fields. These results help simulation of fresh concrete flowing in porous media.

Chen, SongGui; Sun, QiCheng; Jin, Feng; Liu, JianGuo

2014-01-01

315

Food Expenditure, Food Preparation Time and Household Economies of Scale  

Microsoft Academic Search

This paper is concerned with the effect of household size on the allocation of household money and time to food consumption. A broad literature has examined household economies of scale. Since food is a private good, it might be expected that larger households, which could economize on shared goods such as housing, would spend more per equivalent household member on

Victoria Vernon

2004-01-01

316

Scaling Task Management in Space and Time: Reducing User Overhead  

E-print Network

on some tasks for days or even months. It is well known that such tasks typically involve severalScaling Task Management in Space and Time: Reducing User Overhead in Ubiquitous at Carnegie Mellon University were supported in part by the Portuguese Ministry of Science and Technology

317

Scaling Task Management in Space and Time: Reducing User Overhead  

E-print Network

expand their computer-supported tasks across multiple locations, and they may work on some tasks for daysScaling Task Management in Space and Time: Reducing User Overhead in Ubiquitous at Carnegie Mellon University were supported in part by the Portuguese Ministry of Science and Technology

318

Speech Compensation for Time-Scale-Modified Auditory Feedback  

ERIC Educational Resources Information Center

Purpose: The purpose of this study was to examine speech compensation in response to time-scale-modified auditory feedback during the transition of the semivowel for a target utterance of /ija/. Method: Each utterance session consisted of 10 control trials in the normal feedback condition followed by 20 perturbed trials in the modified auditory…

Ogane, Rintaro; Honda, Masaaki

2014-01-01

319

Measuring Change over Time with a Rasch Rating Scale Model.  

ERIC Educational Resources Information Center

When measures are taken on the same individual over time, it is difficult to determine whether observed differences are the result of changes in the person or changes in other facets of the measurement situation (e.g. interpretation of items or use of rating scale). This paper describes a method for disentangling changes in persons from changes in…

Wolfe, Edward W.; Chiu, Chris W. T.

320

GNSS observations of deep convective time scales in the Amazon  

NASA Astrophysics Data System (ADS)

In the tropics, understanding the shallow-to-deep transition and organization of convection on the mesoscale is made difficult due the paucity of long-term high spatial/temporal resolution data. In this paper, data from the world's first long-term equatorial Global Navigational Satellite System meteorological station in Manaus (Central Amazon) is used to create a new metric, a water vapor convergence time scale, to characterize the temporal evolution of deep convection over a tropical continental region. From 3.5 years of data, 320 convective events were analyzed using a compositing analysis. Results reveal two characteristic time scales of water vapor convergence; an 8 h time scale of weak convergence and 4 h timescale of intense water vapor convergence associated with the shallow-to-deep convection transition. The 4 h shallow-to-deep transition time scale is particularly robust, regardless of convective intensity, seasonality, or nocturnal versus daytime convection. This new result provides a useful metric for both high resolution and global climate models to replicate.

Adams, D. K.; Gutman, Seth I.; Holub, Kirk L.; Pereira, Dulcineide S.

2013-06-01

321

Behavioral Programming, Decentralized Control, and Multiple Time Scales  

E-print Network

Behavioral Programming, Decentralized Control, and Multiple Time Scales David Harel, Assaf Marron, Guy Wiener Weizmann Institute of Science {first name.last name}@weizmann.ac.il Gera Weiss Ben Gurion University of the Negev geraw@cs.bgu.ac.il Abstract Behavioral programming is a recently proposed approach

Weiss, Gera

322

Separation of time scales in the HCA model for sand  

NASA Astrophysics Data System (ADS)

Separation of time scales is used in a high cycle accumulation (HCA) model for sand. An important difficulty of the model is the limited applicability of the Miner's rule to multiaxial cyclic loadings applied simultaneously or in a combination with monotonic loading. Another problem is the lack of simplified objective HCA formulas for geotechnical settlement problems. Possible solutions of these problems are discussed.

Niemunis, Andrzej; Wichtmann, Torsten

2014-10-01

323

Time Flies When You're Learning About Scale!  

NSDL National Science Digital Library

Not many students would forget to say "Dinosaurs!" if you mention the Jurassic period, yet the word scale only conjures up ideas of measuring objects. Most students automatically think of measuring mass, volume, or distance, and not necessarily time. In t

Taylor, Amy R.; Jones, M. G.; Falvo, Michael R.

2009-04-01

324

Replenish and Relax: Explaining Logarithmic Annealing in Ion-Implanted c-Si  

NASA Astrophysics Data System (ADS)

We study ion-damaged crystalline silicon by combining nanocalorimetric experiments with an off-lattice kinetic Monte Carlo simulation to identify the atomistic mechanisms responsible for the structural relaxation over long time scales. We relate the logarithmic relaxation, observed in a number of disordered systems, with heat-release measurements. The microscopic mechanism associated with this logarithmic relaxation can be described as a two-step replenish and relax process. As the system relaxes, it reaches deeper energy states with logarithmically growing barriers that need to be unlocked to replenish the heat-releasing events leading to lower-energy configurations.

Béland, Laurent Karim; Anahory, Yonathan; Smeets, Dries; Guihard, Matthieu; Brommer, Peter; Joly, Jean-François; Pothier, Jean-Christophe; Lewis, Laurent J.; Mousseau, Normand; Schiettekatte, François

2013-09-01

325

Stellar differential rotation and coronal time-scales  

NASA Astrophysics Data System (ADS)

We investigate the time-scales of evolution of stellar coronae in response to surface differential rotation and diffusion. To quantify this, we study both the formation time and lifetime of a magnetic flux rope in a decaying bipolar active region. We apply a magnetic flux transport model to prescribe the evolution of the stellar photospheric field, and use this to drive the evolution of the coronal magnetic field via a magnetofrictional technique. Increasing the differential rotation (i.e. decreasing the equator-pole lap time) decreases the flux rope formation time. We find that the formation time is dependent upon the lap time and the surface diffusion time-scale through the relation ?_Form ? ?{?_Lap?_Diff}. In contrast, the lifetimes of flux ropes are proportional to the lap time (?Life??Lap). With this, flux ropes on stars with a differential rotation of more than eight times the solar value have a lifetime of less than 2 d. As a consequence, we propose that features such as solar-like quiescent prominences may not be easily observable on such stars, as the lifetimes of the flux ropes which host the cool plasma are very short. We conclude that such high differential rotation stars may have very dynamical coronae.

Gibb, G. P. S.; Jardine, M. M.; Mackay, D. H.

2014-10-01

326

Relaxation properties in classical diamagnetism.  

PubMed

It is an old result of Bohr that, according to classical statistical mechanics, at equilibrium a system of electrons in a static magnetic field presents no magnetization. Thus a magnetization can occur only in an out of equilibrium state, such as that produced through the Foucault currents when a magnetic field is switched on. It was suggested by Bohr that, after the establishment of such a nonequilibrium state, the system of electrons would quickly relax back to equilibrium. In the present paper, we study numerically the relaxation to equilibrium in a modified Bohr model, which is mathematically equivalent to a billiard with obstacles, immersed in a magnetic field that is adiabatically switched on. We show that it is not guaranteed that equilibrium is attained within the typical time scales of microscopic dynamics. Depending on the values of the parameters, one has a relaxation either to equilibrium or to a diamagnetic (presumably metastable) state. The analogy with the relaxation properties in the Fermi Pasta Ulam problem is also pointed out. PMID:21721776

Carati, A; Benfenati, F; Galgani, L

2011-06-01

327

Evolution of Bulk Scale Factor in Warped Space-time  

E-print Network

In this work the role of extra dimensions in the accelerated universe through the scenario of higher-dimensional Friedmann-Robertson-Walker (FRW) cosmology has been studied. For this purpose, we first consider warped space-time in the standard flat brane scenario as the modified form of Robertson-Walker (RW) metric in five-dimension (5D) space-time and then the variation of the bulk scale factor (warp factor), with respect to both space-like and time-like extra dimensions is obtained. Finally, it is shown that both of two types of extra dimensions are important in this scenario and also the bulk scale factor plays two different roles.

M. Mohsenzadeh; E. Yusofi

2012-02-22

328

New techniques for cartilage magnetic resonance imaging relaxation time analysis: texture analysis of flattened cartilage and localized intra- and inter-subject comparisons.  

PubMed

MR relaxation time measurements of knee cartilage have shown potential to characterize knee osteoarthritis (OA). In this work, techniques that allow localized intra- and inter-subject comparisons of cartilage relaxation times, as well as cartilage flattening for texture analysis parallel and perpendicular to the natural cartilage layers, are presented. The localized comparisons are based on the registration of bone structures and the assignment of relaxation time feature vectors to each point in the bone-cartilage interface. Cartilage flattening was accomplished with Bezier splines and warping, and texture analysis was performed with second-order texture measures using gray-level co-occurrence matrices (GLCM). In a cohort of five normal subjects the performance and reproducibility of the techniques were evaluated using T1rho maps of femoral knee cartilage. The feasibility of creating a mean cartilage relaxation time map is also presented. Successful localized intra- and inter-subject T1rho comparisons were obtained with reproducibility similar to that reported in the literature for regional T2. Improvement of the reproducibility of GLCM features was obtained by flattening the T1rho maps. The results indicate that the presented techniques have potential in longitudinal and population studies of knee OA at different stages of the disease. PMID:18506807

Carballido-Gamio, Julio; Link, Thomas M; Majumdar, Sharmila

2008-06-01

329

A robust method for calculating geometric mean times from multiexponential relaxation data, using only a few data points and only a few elementary operations.  

PubMed

A method is presented to compute values of geometric mean time Tg that uses only a few data points equispaced in the logarithm of time (or equispaced in time and weighted by 1/t) and a few elementary operations for the computation. The method has been tested on a large number of synthetic relaxation data and on actual NMR relaxation measurements in porous samples, using as few as four points (including the two points needed to normalize the relaxation for decay from 1.0 to 0) on each relaxation curve. This computation of the geometric-mean rate very adequately matches the synthetic data and the results of multiexponential inversion of many (or only a few) data points from NMR measurements. When many computations are needed in short times, as for voxel-by-voxel computations in magnetic resonance imaging (MRI) or for depth-by-depth computation in nuclear magnetism logging (NML) of oilwells, a very quickly computed estimate of Tg should be useful. PMID:8970103

Borgia, G C; Bortolotti, V; Brown, R J; Fantazzini, P

1996-01-01

330

P3.11 ESTIMATION OF THE INTEGRAL TIME SCALE WITH TIME SERIES MODELS  

Microsoft Academic Search

Climate- and regional models solve the dynamics of the atmosphere with a resolution ? of 10 km or more. They use parameterizations to incorporate the effects of turbu- lence in the atmospheric boundary layer (ABL). Fluxes, entrainment and dissipation are associated with charac- teristic time-scales T. They are often constructed from characteristic length scales L for these quantities (tem- perature,

Stijn de Waele; Arjan van Dijk; Piet Broersen; Peter Duynkerke

331

Energy relaxation and separation of a hot electron-hole pair in organic aggregates from a time-dependent wavepacket diffusion method  

NASA Astrophysics Data System (ADS)

The time-dependent wavepacket diffusive method [X. Zhong and Y. Zhao, J. Chem. Phys. 138, 014111 (2013)] is extended to investigate the energy relaxation and separation of a hot electron-hole pair in organic aggregates with incorporation of Coulomb interaction and electron-phonon coupling. The pair initial condition generated by laser pulse is represented by a Gaussian wavepacket with a central momentum. The results reveal that the hot electron energy relaxation is very well described by two rate processes with the fast rate much larger than the slow one, consistent with experimental observations, and an efficient electron-hole separation is accomplished accompanying the fast energy relaxation. Furthermore, although the extra energy indeed helps the separation by overcoming the Coulomb interaction, the width of initial wavepacket is much sensitive to the separation efficiency and the narrower wavepacket generates the more separated charges. This behavior may be useful to understand the experimental controversy of the hot carrier effect on charge separation.

Han, Lu; Zhong, Xinxin; Liang, WanZhen; Zhao, Yi

2014-06-01

332

Shear Viscosity of a strongly interacting system: Green-Kubo vs. Chapman-Enskog and Relaxation Time Approximation  

E-print Network

The shear viscosity $\\eta$ has been calculated by using the Green-Kubo relation in the framework of a partonic transport approach solved at cascade level. We compare the numerical results for $\\eta$ obtained from the Green-Kubo correlator with the analytical formulas in both the Relaxation Time Approximation (RTA) and the Chapman-Enskog approximation (CE). We investigate and emphasize the differences between the isotropic and anisotropic cross sections and between the massless and massive particles. We show that in the range of temperature explored in a Heavy Ion collision and for pQCD-like cross section the RTA significantly underestimates the viscosity by about a factor of 2-3, while a good agreement is found between the CE approximation and Gree-Kubo relation already at first order of approximation. The agreement with the CE approximation supplies an analytical formula that allows to develop kinetic transport theory at fixed shear viscosity to entropy density ratio, $\\eta/s$. This open the possibility to explore dissipative non-equilibrium evolution of the distribution functions vs T-dependent $\\eta/s$ and particle momenta in the dynamics of the Quark-Gluon Plasma created in ultra-relativistic heavy-ion collisions.

S. Plumari; A. Puglisi; F. Scardina; V. Greco

2012-08-02

333

Sublinear scaling for time-dependent stochastic density functional theory  

E-print Network

A stochastic approach to time-dependent density functional theory (TDDFT) is developed for computing the absorption cross section and the random phase approximation (RPA) correlation energy. The core idea of the approach involves time-propagation of a small set of stochastic orbitals which are fi?rst projected on the occupied space and then propagated in time according to the time-dependent Kohn-Sham equations. The evolving electron density is exactly represented when the number of random orbitals is in?finite, but even a small number (? 16) of such orbitals is enough to obtain meaningful results for absorption spectrum and the RPA correlation energy per electron. We implement the approach for silicon nanocrystals (NCs) using real-space grids and ?find that the overall scaling of the algorithm is sublinear with computational time and memory.

Gao, Yi; Baer, Roi; Rabani, Eran

2014-01-01

334

Reduction of nonautonomous population dynamics models with two time scales.  

PubMed

The purpose of this work is reviewing some reduction results to deal with systems of nonautonomous ordinary differential equations with two time scales. They could be included among the so-called approximate aggregation methods. The existence of different time scales in a system, together with some long-term features, are used to build up a simpler system governed by a lesser number of state variables. The asymptotic behavior of the latter system is then used to describe the asymptotic behaviour of the former one. The reduction results are stated in two particular but important cases: periodic systems and asymptotically autonomous systems. The reduction results are illustrated with the help of simple spatial SIS epidemic models including either periodic or asymptotically autonomous terms. PMID:24838547

Marvá, Marcos; Bravo de la Parra, Rafael

2014-09-01

335

A study of Venus rotation at short time scale  

NASA Astrophysics Data System (ADS)

Venus which can be considered as the twin sister of the Earth in view of its global characteristics (size, density) has been the subject of many investigations to understand its slow retrograde rotation (243d) and its rather small obliquity (2°.63). Many of these studies concern the evolution of Venus rotation at very long time scales. Here we present a complete model of Venus precession and nutation based on Hamiltonian formalism for short times scales. We apply a theoretical framework already used by Kinoshita (1977) for the rigid Earth. After calculating the effects due to the gravitational tide exerted by the Sun, we also evaluate the indirect planetary effects due to the perturbation of the planets. We compare our results with those obtained by Souchay et al. (1999) on the Earth. At last we present the prospect for future studies among which are the polhody, the effects of the atmosphere and of the core-mantle interaction.

Cottereau, L.; Souchay, J.

2009-12-01

336

TimeScale Feature Extractions for Emotional Speech Characterization  

Microsoft Academic Search

Abstract,Emotional,speech,characterization,is,an important issue for the understanding,of interaction. This article discusses the time-scale analysis problem in feature extraction for emotional speech processing. We describe a computational,framework,for combining,segmental,and supra-segmental features for emotional,speech detection. The statistical fusion is based on the estimation of local a posteriori class probabilities and the overall decision employs,weighting factors directly related to the duration of the individual speech

Mohamed Chetouani; Ammar Mahdhaoui; Fabien Ringeval

2009-01-01

337

Solar Irradiance Variations on Active Region Time Scales  

NASA Technical Reports Server (NTRS)

The variations of the total solar irradiance is an important tool for studying the Sun, thanks to the development of very precise sensors such as the ACRIM instrument on board the Solar Maximum Mission. The largest variations of the total irradiance occur on time scales of a few days are caused by solar active regions, especially sunspots. Efforts were made to describe the active region effects on total and spectral irradiance.

Labonte, B. J. (editor); Chapman, G. A. (editor); Hudson, H. S. (editor); Willson, R. C. (editor)

1984-01-01

338

Rejuvenation in scale-free optics and enhanced diffraction cancellation life-time.  

PubMed

We demonstrate rejuvenation in scale-free optical propagation. The phenomenon is caused by the non-ergodic relaxation of the dipolar glass that mediates the photorefractive nonlinearity in compositionally-disordered lithium-enriched potassium-tantalate-niobate (KTN:Li). We implement rejuvenation to halt aging in the dipolar glass and extend the duration of beam diffraction cancellation. PMID:23187594

Parravicini, J; Conti, C; Agranat, A J; DelRe, E

2012-11-19

339

Scale dependence of the directional relationships between coupled time series  

NASA Astrophysics Data System (ADS)

Using the cross-correlation of the wavelet transformation, we propose a general method of studying the scale dependence of the direction of coupling for coupled time series. The method is first demonstrated by applying it to coupled van der Pol forced oscillators and coupled nonlinear stochastic equations. We then apply the method to the analysis of the log-return time series of the stock values of the IBM and General Electric (GE) companies. Our analysis indicates that, on average, IBM stocks react earlier to possible common sector price movements than those of GE.

Shirazi, Amir Hossein; Aghamohammadi, Cina; Anvari, Mehrnaz; Bahraminasab, Alireza; Rahimi Tabar, M. Reza; Peinke, Joachim; Sahimi, Muhammad; Marsili, Matteo

2013-02-01

340

Scaling Brain Size, Keeping Timing: Evolutionary Preservation of Brain Rhythms  

PubMed Central

Despite the several-thousand-fold increase of brain volume during the course of mammalian evolution, the hierarchy of brain oscillations remains remarkably preserved, allowing for multiple-time-scale communication within and across neuronal networks at approximately the same speed, irrespective of brain size. Deployment of large-diameter axons of long-range neurons could be a key factor in the preserved time management in growing brains. We discuss the consequences of such preserved network constellation in mental disease, drug discovery, and interventional therapies. PMID:24183025

Buzsáki, György; Logothetis, Nikos; Singer, Wolf

2014-01-01

341

Measurement of wall relaxation times of polarized Helium-3 in bulk liquid Helium-4 for the neutron electric dipole moment experiment  

NASA Astrophysics Data System (ADS)

The Neutron Electric Dipole Moment (nEDM) experiment that will take place at the Spallation Neutron Source (SNS) in Oak Ridge, Tennessee will measure the electric dipole moment (EDM) of the neutron with a precision of order 10-28 e-cm, utilizing spin-polarized 3He in bulk liquid 4He to detect neutron precession in a 10 mG magnetic field and 50 kV/cm electric field. Since depolarized 3He will produce a background, relaxation of the polarized 3He, characterized by the probability of depolarization per bounce, Pd, was measured for materials that will be in contact with polarized 3He. Depolarization probabilities were determined from measurements of the longitudinal relaxation time of polarized 3He in bulk liquid 4He inside an acrylic cell coated with the wavelength shifter deuterated tetraphenyl butadiene (d-TPB), which will be used to coat the nEDM measurement cell. Relaxation measurements were also performed while rods, made from plumbing material Torlon and valve bellows material BeCu, were present in the cell. The BeCu was coated with Pyralin resin prior to relaxation measurements, while relaxation measurements were performed both before and after the Torlon rod was coated with Pyralin resin. The depolarization probabilities were found to be Pd-TPBd <1.32x10-7 PBareTorlon d=1.01+/-0.08 x10-6 PCoatedTorlon d=2.5+/-0.1 x10-7 PCoatedBeCu d=7.9+/-0.3 x10-7 The relaxation rates extrapolated from the observed values of Pd for d-TPB, coated Torlon, and coated BeCu in the nEDM apparatus were found to be consistent with design goals.

Yoder, Jacob

342

Two-time-scale population evolution on a singular landscape  

NASA Astrophysics Data System (ADS)

Under the effect of strong genetic drift, it is highly probable to observe gene fixation or gene loss in a population, shown by singular peaks on a potential landscape. The genetic drift-induced noise gives rise to two-time-scale diffusion dynamics on the bipeaked landscape. We find that the logarithmically divergent (singular) peaks do not necessarily imply infinite escape times or biological fixations by iterating the Wright-Fisher model and approximating the average escape time. Our analytical results under weak mutation and weak selection extend Kramers's escape time formula to models with B (Beta) function-like equilibrium distributions and overcome constraints in previous methods. The constructed landscape provides a coherent description for the bistable system, supports the quantitative analysis of bipeaked dynamics, and generates mathematical insights for understanding the boundary behaviors of the diffusion model.

Xu, Song; Jiao, Shuyun; Jiang, Pengyao; Ao, Ping

2014-01-01

343

5nsec Dead time multichannel scaling system for Mössbauer spectrometer  

NASA Astrophysics Data System (ADS)

A PC programmable and fast multichannel scaling module has been designed to use a commercial Mössbauer spectrometer. This module is based on a 10 single chip 8 bits microcomputer (MC6805) and on a 35 fast ALU, which allows a high performance and low cost system. The module can operate in a stand-alone mode. Data analysis are performed in real time display, on XT/AT IBM PC or compatibles. The channels are ranged between 256 and 4096, the maximum number of counts is 232-1 per channel, the dwell time is 3 ?sec and the dead time between channels is 5 nsec. A friendly software display the real time spectrum and offers menues with different options at each state.

Verrastro, C.; Trombetta, G.; Pita, A.; Saragovi, C.; Duhalde, S.

1991-11-01

344

Scale and time dependence of serial correlations in word-length time series of written texts  

NASA Astrophysics Data System (ADS)

This work considered the quantitative analysis of large written texts. To this end, the text was converted into a time series by taking the sequence of word lengths. The detrended fluctuation analysis (DFA) was used for characterizing long-range serial correlations of the time series. To this end, the DFA was implemented within a rolling window framework for estimating the variations of correlations, quantified in terms of the scaling exponent, strength along the text. Also, a filtering derivative was used to compute the dependence of the scaling exponent relative to the scale. The analysis was applied to three famous English-written literary narrations; namely, Alice in Wonderland (by Lewis Carrol), Dracula (by Bram Stoker) and Sense and Sensibility (by Jane Austen). The results showed that high correlations appear for scales of about 50-200 words, suggesting that at these scales the text contains the stronger coherence. The scaling exponent was not constant along the text, showing important variations with apparent cyclical behavior. An interesting coincidence between the scaling exponent variations and changes in narrative units (e.g., chapters) was found. This suggests that the scaling exponent obtained from the DFA is able to detect changes in narration structure as expressed by the usage of words of different lengths.

Rodriguez, E.; Aguilar-Cornejo, M.; Femat, R.; Alvarez-Ramirez, J.

2014-11-01

345

Stress Relaxation in Aging Soft Colloidal Glasses  

E-print Network

We investigate the stress relaxation behavior on the application of step strains to aging aqueous suspensions of the synthetic clay Laponite. The stress exhibits a two-step decay, from which the slow relaxation modes are extracted as functions of the sample ages and applied step strain deformations. Interestingly, the slow time scales that we estimate show a dramatic enhancement with increasing strain amplitudes. We argue that the system ends up exploring the deeper sections of its energy landscape following the application of the step strain.

Ranjini Bandyopadhyay; P. Harsha Mohan; Yogesh M. Joshi

2009-05-05

346

Time scaling with efficient time-propagation techniques for atoms and molecules in pulsed radiation fields  

SciTech Connect

We present an ab initio approach to solving the time-dependent Schroedinger equation to treat electron- and photon-impact multiple ionization of atoms or molecules. It combines the already known time-scaled coordinate method with a high-order time propagator based on a predictor-corrector scheme. In order to exploit in an optimal way the main advantage of the time-scaled coordinate method, namely, that the scaled wave packet stays confined and evolves smoothly toward a stationary state, of which the squared modulus is directly proportional to the electron energy spectra in each ionization channel, we show that the scaled bound states should be subtracted from the total scaled wave packet. In addition, our detailed investigations suggest that multiresolution techniques like, for instance, wavelets are the most appropriate ones to represent the scaled wave packet spatially. The approach is illustrated in the case of the interaction of a one-dimensional model atom as well as atomic hydrogen with a strong oscillating field.

Hamido, Aliou; Frapiccini, Ana Laura; Piraux, Bernard [Institute of Condensed Matter and Nanosciences, Universite Catholique de Louvain, Batiment de Hemptinne, 2, chemin du cyclotron, B-1348 Louvain-la Neuve (Belgium); Eiglsperger, Johannes [Institut fuer Theoretische Physik, Universitaet Regensburg, D-93040 Regensburg (Germany); Physik Departement, Technische Universitaet Muenchen, D-85747 Garching (Germany); Madronero, Javier [Physik Departement, Technische Universitaet Muenchen, D-85747 Garching (Germany); Mota-Furtado, Francisca; O'Mahony, Patrick [Department of Mathematics, Royal Holloway, University of London, Egham, TW20 0EX Surrey (United Kingdom)

2011-07-15

347

Correlated and uncorrelated heart rate fluctuations during relaxing visualization  

NASA Astrophysics Data System (ADS)

The heart rate variability (HRV) of healthy subjects practicing relaxing visualization is studied by use of three multiscale analysis techniques: the detrended fluctuation analysis (DFA), the entropy in natural time (ENT) and the average wavelet (AWC) coefficient. The scaling exponent of normal interbeat interval increments exhibits characteristics of the presence of long-range correlations. During relaxing visualization the HRV dynamics change in the sense that two new features emerge independent of each other: a respiration-induced periodicity that often dominates the HRV at short scales (<40 interbeat intervals) and the decrease of the scaling exponent at longer scales (40-512 interbeat intervals). In certain cases, the scaling exponent during relaxing visualization indicates the breakdown of long-range correlations. These characteristics have been previously seen in the HRV dynamics during non-REM sleep.

Papasimakis, N.; Pallikari, F.

2010-05-01

348

Terrestrial Waters and Sea Level Variations on Interannual Time Scale  

NASA Technical Reports Server (NTRS)

On decadal to multi-decadal time scales, thermal expansion of sea waters and land ice loss are the main contributors to sea level variations. However, modification of the terrestrial water cycle due to climate variability and direct anthropogenic forcing may also affect sea level. For the past decades, variations in land water storage and corresponding effects on sea level cannot be directly estimated from observations because these are almost non-existent at global continental scale. However, global hydrological models developed for atmospheric and climatic studies can be used for estimating total water storage. For the recent years (since mid-2002), terrestrial water storage change can be directly estimated from observations of the GRACE space gravimetry mission. In this study, we analyse the interannual variability of total land water storage, and investigate its contribution to mean sea level variability at interannual time scale. We consider three different periods that, each, depend on data availability: (1) GRACE era (2003-2009), (2) 1993-2003 and (3) 1955-1995. For the GRACE era (period 1), change in land water storage is estimated using different GRACE products over the 33 largest river basins worldwide. For periods 2 and 3, we use outputs from the ISBA-TRIP (Interactions between Soil, Biosphere, and Atmosphere-Total Runoff Integrating Pathways) global hydrological model. For each time span, we compare change in land water storage (expressed in sea level equivalent) to observed mean sea level, either from satellite altimetry (periods 1 and 2) or tide gauge records (period 3). For each data set and each time span, a trend has been removed as we focus on the interannual variability. We show that whatever the period considered, interannual variability of the mean sea level is essentially explained by interannual fluctuations in land water storage, with the largest contributions arising from tropical river basins.

Llovel, W.; Becker, M.; Cazenave, A.; Jevrejeva, S.; Alkama, R.; Decharme, B.; Douville, H.; Ablain, M.; Beckley, B.

2011-01-01

349

Structural relaxation and self-repair behavior in nano-scaled Zr-Cu metallic glass under cyclic loading: Molecular-dynamics simulations  

SciTech Connect

Bulk metallic glasses are generally regarded as highly brittle materials at room temperature, with deformation localized within a few principal shear bands. In this simulation work, it is demonstrated that when the Zr-Cu metallic glass is in a small size-scale, it can deform under cyclic loading in a semi-homogeneous manner without the occurrence of pronounced mature shear bands. Instead, the plastic deformation in simulated samples proceeds via the network-like shear-transition zones (STZs) by the reversible and irreversible structure-relaxations during cyclic loading. Dynamic recovery and reversible/irreversible structure rearrangements occur in the current model, along with annihilation/creation of excessive free volumes. This behavior would in-turn retard the damage growth of metallic glass. Current studies can help to understand the structural relaxation mechanism in metallic glass under loading. The results also imply that the brittle bulk metallic glasses can become ductile with the sample size being reduced. The application of metallic glasses in the form of thin film or nano pieces in micro-electro-mechanical systems (MEMS) could be promising.

Lo, Y. C. [National Sun Yat-Sen University, Taiwan; Chou, H. S. [National Sun Yat-Sen University, Taiwan; Cheng, Y. T. [National Sun Yat-Sen University, Taiwan; Huang, J. C. [National Sun Yat-Sen University, Taiwan; Morris, James R [ORNL; Liaw, Peter K [University of Tennessee, Knoxville (UTK)

2010-01-01

350

Slow Relaxations and Aging in the Electron Glass  

NASA Astrophysics Data System (ADS)

Glassy systems are ubiquitous in nature. They are characterized by slow relaxations to equilibrium without a typical time scale, aging, and memory effects. Understanding this has been a long-standing problem in physics. We study the aging of the electron glass, a system showing remarkable slow relaxations of the conductance. We find that the appropriate broad distribution of relaxation rates leads to a universal relaxation of the form log?(1+tw/t) for the common aging protocol, where tw is the length of time the perturbation driving the system out of equilibrium was on, and t the time of measurement. These results agree well with several experiments performed on different glassy systems, and examining different physical observables, for times ranging from seconds to several hours. The suggested theoretical framework appears to offer a paradigm for aging in a broad class of glassy materials.

Amir, Ariel; Oreg, Yuval; Imry, Yoseph

2009-09-01

351

Many roads to synchrony: Natural time scales and their algorithms  

NASA Astrophysics Data System (ADS)

We consider two important time scales—the Markov and cryptic orders—that monitor how an observer synchronizes to a finitary stochastic process. We show how to compute these orders exactly and that they are most efficiently calculated from the ?-machine, a process's minimal unifilar model. Surprisingly, though the Markov order is a basic concept from stochastic process theory, it is not a probabilistic property of a process. Rather, it is a topological property and, moreover, it is not computable from any finite-state model other than the ?-machine. Via an exhaustive survey, we close by demonstrating that infinite Markov and infinite cryptic orders are a dominant feature in the space of finite-memory processes. We draw out the roles played in statistical mechanical spin systems by these two complementary length scales.

James, Ryan G.; Mahoney, John R.; Ellison, Christopher J.; Crutchfield, James P.

2014-04-01

352

Holographic Brownian motion and time scales in strongly coupled plasmas  

NASA Astrophysics Data System (ADS)

We study Brownian motion of a heavy quark in field theory plasma in the AdS/CFT setup and discuss the time scales characterizing the interaction between the Brownian particle and plasma constituents. Based on a simple kinetic theory, we first argue that the mean-free-path time is related to the connected 4-point function of the random force felt by the Brownian particle. Then, by holographically computing the 4-point function and regularizing the IR divergence appearing in the computation, we write down a general formula for the mean-free-path time, and apply it to the STU black hole which corresponds to plasma charged under three U(1)R-charges. The result indicates that the Brownian particle collides with many plasma constituents simultaneously.

Atmaja, Ardian Nata; de Boer, Jan; Shigemori, Masaki

2014-03-01

353

Study on vibrational relaxation dynamics of phenol-water complex by picosecond time-resolved IR-UV pump-probe spectroscopy in a supersonic molecular beam  

NASA Astrophysics Data System (ADS)

A comparative study of vibrational energy relaxation (VER) between the monohydrated complexes of phenol-d0 and phenol-d1 is investigated in a supersonic molecular beam. The direct time-resolved measurement of energy redistribution from the phenolic OH/OD stretching mode of the phenol-d0-H2O/phenol-d1-D2O is performed by picosecond IR-UV pump-probe spectroscopy. Two complexes follow the same relaxation process that begins with the intramolecular vibrational energy redistribution (IVR) and the intermolecular vibrational energy redistribution (IVR), which is followed by the vibrational predissociation (VP). The difference in the relaxation lifetimes between them is discussed by anharmonic force field and RRKM calculations. Anharmonic analysis implies that intra- (IVR) and intermolecular (IVR) relaxations occur in parallel in the complexes. The RRKM-predicted dissociation (VP) lifetimes show qualitative agreement with the observed results, suggesting that VP takes place after the statistical energy distribution in the complexes.

Miyazaki, Yasunori; Inokuchi, Yoshiya; Ebata, Takayuki; Petkovi?, Milena

2013-06-01

354

Relation between Direct Observation of Relaxation and Self-Reported Mindfulness and Relaxation States  

ERIC Educational Resources Information Center

Forty-four individuals, 18-47 (MN 21.8, SD 5.63) years of age, took part in a study examining the magnitude and direction of the relationship between self-report and direct observation measures of relaxation and mindfulness. The Behavioral Relaxation Scale (BRS), a valid direct observation measure of relaxation, was used to assess relaxed behavior…

Hites, Lacey S.; Lundervold, Duane A.

2013-01-01

355

Scaling in a Continuous Time Model for Biological Aging  

NASA Astrophysics Data System (ADS)

In this paper, we consider a generalization to the asexual version of Penna model for biological aging, where we take a continuous time limit. The genotype associated to each individual is an interval of real numbers over which Dirac ?-functions are defined, representing genetically programmed diseases to be switched on at defined ages of the individual life. We discuss two different continuous limits for the evolution equation and two different mutation protocols, to be implemented during reproduction. Exact stationary solutions are obtained and scaling properties are discussed.

de Almeida, R. M. C.; Thomas, G. L.

356

Rotating-frame spin-lattice relaxation time imaging by radio-frequency field gradients: visualization of strained crosslinked natural rubbers  

NASA Astrophysics Data System (ADS)

NMR imaging by radio-frequency field gradients ( B1 gradients) is especially convenient for heterogeneous samples and/or in the case of relatively short transverse relaxation times. The method has been combined with the application of two spin-lock periods of different duration so as to produce rotating-frame spin-lattice relaxation time ( T1 ?) images. In the case of natural rubber samples with different crosslink densities, such images are not only characteristic of the crosslink density but also reveal the way in which the material has been stressed. The strained parts can be visualized either directly or through histograms showing the T1 ? distribution over the whole sample.

Chaumette, H.; Grandclaude, D.; Canet, D.

2003-08-01

357

NMR T{sub 1} relaxation time measurements and calculations with translational and rotational components for liquid electrolytes containing LiBF{sub 4} and propylene carbonate  

SciTech Connect

Longitudinal relaxation (T{sub 1}) measurements of {sup 19}F, {sup 7}Li, and {sup 1}H in propylene carbonate/LiBF{sub 4} liquid electrolytes are reported. Comparison of T{sub 1} values with those for the transverse relaxation time (T{sub 2}) confirm that the measurements are in the high temperature (low correlation time) limit of the T{sub 1} minimum. Using data from pulsed field gradient measurements of self-diffusion coefficients and measurements of solution viscosity measured elsewhere, it is concluded that although in general there are contributions to T{sub 1} from both translational and rotational motions. For the lithium ions, this is mainly translational, and for the fluorine ions mainly rotational.

Richardson, P. M., E-mail: phy5pmr@leeds.ac.uk; Voice, A. M., E-mail: a.m.voice@leeds.ac.uk; Ward, I. M., E-mail: i.m.ward@leeds.ac.uk [Soft Matter Physics, School of Physics and Astronomy, University of Leeds, Leeds LS2 9JT (United Kingdom)

2013-12-07

358

Relaxation time and impurity effects on linear and nonlinear refractive index changes in (In,Ga)N-GaN spherical QD  

NASA Astrophysics Data System (ADS)

By means of a combination of Quantum Genetic Algorithm and Hartree-Fock-Roothaan method, the changes in linear, third-order nonlinear and total refractive index associated with intra-conduction band transition are investigated with and without shallow-donor impurity in wurtzite (In,Ga)N-GaN spherical quantum dot. For both cases with and without impurity, the calculation is performed within the framework of single band effective-mass and parabolic band approximations. Impurity's position and relaxation time effects are investigated. It is found that the modulation of the refractive index changes, suitable for good performance optical modulators and various infra-red optical device applications can be easily obtained by tailoring the relaxation time and the position of the impurity.

El Ghazi, Haddou; Jorio, Anouar

2014-10-01

359

Electromagnetism, Optics, Acoustics, Heat Transfer, Classical Mechanics, and Fluid Dynamics Multiple-Relaxation-Time Lattice Boltzmann Approach to Richtmyer---Meshkov Instability  

Microsoft Academic Search

The aims of the present paper are twofold. At first, we further study the Multiple-Relaxation-Time (MRT) Lattice Boltzmann (LB) model proposed in [Europhys. Lett. 90 (2010) 54003]. We discuss the reason why the Gram---Schmidt orthogonalization procedure is not needed in the construction of transformation matrix M; point out a reason why the Kataoka---Tsutahara model [Phys. Rev. E 69 (2004) 035701

Feng Chen; Ai-Guo Xu; Guang-Cai Zhang; Ying-Jun Li

2011-01-01

360

Quantitative T2* (T2 Star) Relaxation Times Predict Site Specific Proteoglycan Content and Residual Mechanics of the Intervertebral Disc Throughout Degeneration  

PubMed Central

Degeneration alters the biochemical composition of the disc, affecting the mechanical integrity leading to spinal instability. Quantitative T2* MRI probes water mobility within the macromolecular network, a potentially more sensitive assessment of disc health. We determined the relationship between T2* relaxation time and proteoglycan content, collagen content, and compressive mechanics throughout the degenerative spectrum. Eighteen human cadaveric lumbar (L4–L5) discs were imaged using T2* MRI. The T2* relaxation time at five locations (nucleous pulposus or NP, anterior annulus fibrosis or AF, posterior AF, inner AF, and outer AF) was correlated with sulfated-glycosaminoglycan (s-GAG) content, hydroxyproline content, and residual stress and strain at each location. T2* relaxation times were significantly correlated with s-GAG contents in all test locations and were particularly strong in the NP (r = 0.944; p < 0.001) and inner AF (r = 0.782; p < 0.001). T2* relaxation times were also significantly correlated with both residual stresses and excised strains in the NP (r = 0.857; p < 0.001: r = 0.816; p < 0.001), inner AF (r = 0.535; p = 0.022: r = 0.516; p = 0.028), and outer AF (r = 0.668; p = 0.002: r = 0.458; p = 0.041). These strong correlations highlight T2* MRI’s ability to predict the biochemical and mechanical health of the disc. T2* MRI assessment of disc health is a clinically viable tool showing promise as a biomarker for distinguishing degenerative changes. PMID:24788830

Ellingson, Arin M.; Nagel, Tina M.; Polly, David W.; Ellermann, Jutta; Nuckley, David J.

2014-01-01

361

Estimating ventilation time scales using overturning stream functions  

NASA Astrophysics Data System (ADS)

A simple method for estimating ventilation time scales from overturning stream functions is proposed. The stream function may be computed using either geometric coordinates or a generalized vertical coordinate, such as potential density (salinity in our study). The method is tested with a three-dimensional circulation model describing an idealized semi-enclosed ocean basin ventilated through a narrow strait over a sill, and the result is compared to age estimates obtained from a passive numerical age tracer. The best result is obtained when using the stream function in salinity coordinates. In this case, the reservoir-averaged advection time obtained from the overturning stream function in salinity coordinates agrees rather well with the mean age of the age tracer, and the corresponding maximum ages agree very well.

Thompson, Bijoy; Nycander, Jonas; Nilsson, Johan; Jakobsson, Martin; Döös, Kristofer

2014-06-01

362

Infrasonic Observations of Thunderstorms at High Latitudes: Time Scales  

NASA Astrophysics Data System (ADS)

The present work summarizes some results of infrasonic observations of thunderstorms recorded in the Northern Scandinavia by the Swedish-Finnish Infrasound Network (SIN). A lightning in the atmosphere is a source of cylindrical shock waves. When the distance from the source increases, more and more energy is transferred into the low-frequency range through the same mechanism as for shock waves from supersonic aircraft. Frequently, semi-regular sequences of lightning with similar orientation and nearly constant repetition frequency are observed. For that reason the spectrum of time delays between individual strokes is studied. It has been found that the apparent random occurrence of strokes seems be a result of superposition of several processes with slowly varying time scales.

Liszka, L. J.

2008-12-01

363

Coupling among Electroencephalogram Gamma Signals on a Short Time Scale  

PubMed Central

An important goal in neuroscience is to identify instances when EEG signals are coupled. We employ a method to measure the coupling strength between gamma signals (40–100?Hz) on a short time scale as the maximum cross-correlation over a range of time lags within a sliding variable-width window. Instances of coupling states among several signals are also identified, using a mixed multivariate beta distribution to model coupling strength across multiple gamma signals with reference to a common base signal. We first apply our variable-window method to simulated signals and compare its performance to a fixed-window approach. We then focus on gamma signals recorded in two regions of the rat hippocampus. Our results indicate that this may be a useful method for mapping coupling patterns among signals in EEG datasets. PMID:20811477

McAssey, Michael P.; Hsieh, Fushing; Smith, Anne C.

2010-01-01

364

Exact dynamical coarse-graining without time-scale separation  

NASA Astrophysics Data System (ADS)

A family of collective variables is proposed to perform exact dynamical coarse-graining even in systems without time scale separation. More precisely, it is shown that these variables are not slow in general, yet satisfy an overdamped Langevin equation that statistically preserves the sequence in which any regions in collective variable space are visited and permits to calculate exactly the mean first passage times from any such region to another. The role of the free energy and diffusion coefficient in this overdamped Langevin equation is discussed, along with the way they transform under any change of variable in collective variable space. These results apply both to systems with and without inertia, and they can be generalized to using several collective variables simultaneously. The view they offer on what makes collective variables and reaction coordinates optimal breaks from the standard notion that good collective variable must be slow variable, and it suggests new ways to interpret data from molecular dynamics simulations and experiments.

Lu, Jianfeng; Vanden-Eijnden, Eric

2014-07-01

365

Nonlinear Dynamics of Extended Hydrologic Systems over long time scales  

NASA Astrophysics Data System (ADS)

We often view our knowledge of hydrology and hence of nature as intransient, at least over the time scales over which we study processes we wish to predict and understand. Over the last few decades, this assumption has come under question, largely because of the vocal expression of a changing climate, but also the recurrent demonstration of significant land use change, both of which significantly affect the boundary conditions for terrestrial hydrology that is our forte. Most recently, the concepts of hydromorphology and social hydrology have entered the discussion, and the notion that climate and hydrology influence human action, which in turn shapes hydrology, is being recognized. Finally, as a field, we seem to be coming to the conclusion that the hydrologic system is an open system, whose boundaries evolve in time, and that the hydrologic system, at many scales, has a profound effect on the systems that drive it -- whether they be the ecological and climatic systems, or the social system. What a mess! Complexity! Unpredictability! At a certain level of abstraction, one can consider the evolution of these coupled systems with nonlinear feedbacks and ask what types of questions are relevant in terms of such a coupled evolution? What are their implications at the planetary scale? What are their implications for a subsistence farmer in an arid landscape who may under external influence achieve a new transient hydro-ecological equilibrium? What are the implications for the economy and power of nations? In this talk, I will try to raise some of these questions and also provide some examples with very simple dynamical systems that suggest ways of thinking about some practical issues of feedback across climate, hydrology and human behavior.

Lall, Upmanu

2014-05-01

366

Multiple-time-scale motion in molecularly linked nanoparticle arrays.  

PubMed

We explore the transport of electrons between electrodes that encase a two-dimensional array of metallic quantum dots linked by molecular bridges (such as ?,? alkaline dithiols). Because the molecules can move at finite temperatures, the entire transport structure comprising the quantum dots and the molecules is in dynamical motion while the charge is being transported. There are then several physical processes (physical excursions of molecules and quantum dots, electronic migration, ordinary vibrations), all of which influence electronic transport. Each can occur on a different time scale. It is therefore not appropriate to use standard approaches to this sort of electron transfer problem. Instead, we present a treatment in which three different theoretical approaches-kinetic Monte Carlo, classical molecular dynamics, and quantum transport-are all employed. In certain limits, some of the dynamical effects are unimportant. But in general, the transport seems to follow a sort of dynamic bond percolation picture, an approach originally introduced as formal models and later applied to polymer electrolytes. Different rate-determining steps occur in different limits. This approach offers a powerful scheme for dealing with multiple time scale transport problems, as will exist in many situations with several pathways through molecular arrays or even individual molecules that are dynamically disordered. PMID:23199199

George, Christopher; Szleifer, Igal; Ratner, Mark

2013-01-22

367

White matter and lesion T1 relaxation times increase in parallel and correlate with disability in multiple sclerosis.  

PubMed

Previous studies have established the clinical relevance of hypointense lesions ("black holes") on T1-weighted MRI as a surrogate marker for pathological change [36]. In contrast to measuring the volume of "black holes", the direct measurement of T1 values allows an objective assessment of the changes contributing to hypointensity both in the focal lesions and in the normal appearing white matter (NAWM). The aims of this study were first, to determine the relationship between T1 values in the NAWM and in discrete lesions, second, to test the relationship between white matter T1 changes and measures of disability and third, to determine whether pathology leading to T1 change occurred in thalamic grey matter of patients with multiple sclerosis. 24 patients with clinically definite multiple sclerosis (13 with relapsing-remitting multiple sclerosis and 11 with secondary progressive multiple sclerosis) and 11 controls participated. White matter T1 histograms and mean T1 values for the thalamus were generated from whole brain T1 relaxation time maps measured using a novel echo-planar imaging based MRI sequence at 3Tesla. Tissue segmentation based on T2- and T1-weighted images allowed independent study of changes in lesions and NAWM. White matter T1 histograms from the patient group showed a reduced peak height and a shift towards higher T1 values (p = 0.028) relative to controls. The mean thalamic T1 was greater for secondary progressive patients than for healthy controls (p = 0.03). Mean white matter T1 values correlated significantly with disability (r = 0.48, p = 0.02). The mean T1 value in the T1-hypointense lesions correlated strongly with the mean T1 value in the NAWM (r = 0.80, p < 0.001). No significant relationship was found between mean white matter T1 value and cerebral volume (r = -0.23, p = 0.31). The T1 measurements extend previous observations suggesting that changes in the NAWM occur in parallel with pathology in lesions of MS. T1 measurements of either the total or NAWM therefore may provide a potentially observer- and scanner- independent marker of pathology relevant to disability in MS. PMID:12242554

Parry, A; Clare, S; Jenkinson, M; Smith, S; Palace, J; Matthews, P M

2002-09-01

368

1H relaxation enhancement induced by nanoparticles in solutions: Influence of magnetic properties and diffusion  

NASA Astrophysics Data System (ADS)

Magnetic nanoparticles that induce nuclear relaxation are the most promising materials to enhance the sensitivity in Magnetic Resonance Imaging. In order to provide a comprehensive understanding of the magnetic field dependence of the relaxation enhancement in solutions, Nuclear Magnetic Resonance 1H spin-lattice relaxation for decalin and toluene solutions of various Fe2O3 nanoparticles was investigated. The relaxation experiments were performed in a frequency range of 10 kHz-20 MHz by applying Field Cycling method, and in the temperature range of 257-298 K, using nanoparticles differing in size and shape: spherical - 5 nm diameter, cubic - 6.5 nm diameter, and cubic - 9 nm diameter. The relaxation dispersion data were interpreted in terms of a theory of nuclear relaxation induced by magnetic crystals in solution. The approach was tested with respect to its applicability depending on the magnetic characteristics of the nanocrystals and the time-scale of translational diffusion of the solvent. The role of Curie relaxation and the contributions to the overall 1H spin-lattice relaxation associated with the electronic spin-lattice and spin-spin relaxation was thoroughly discussed. It was demonstrated that the approach leads to consistent results providing information on the magnetic (electronic) properties of the nanocrystals, i.e., effective electron spin and relaxation times. In addition, features of the 1H spin-lattice relaxation resulting from the electronic properties of the crystals and the solvent diffusion were explained.

Kruk, D.; Korpa?a, A.; Taheri, S. Mehdizadeh; Koz?owski, A.; Förster, S.; Rössler, E. A.

2014-05-01

369

CPMG relaxation dispersion.  

PubMed

NMR relaxation is sensitive to molecular and internal motion of proteins. (15)N longitudinal relaxation rate (R 1), transverse relaxation rate (R 2), and {(1)H}-(15)N Nuclear Overhauser Effect (NOE) experiments are often performed to globally elucidate protein dynamics, primarily on the sub-nanosecond timescale. In contrast, constant relaxation time R 2 dispersion experiments are applied to characterize protein equilibrium conformations that interconvert on the millisecond timescale. Information on local conformational equilibria of proteins provides important insights about protein energy landscapes and is useful to interpret molecular recognition mechanisms as well. Here, we describe a protocol for performing (15)N Carr-Purcell-Meiboom-Gill (CPMG) R 2 dispersion measurements in solution, including protein preparation, step-by-step experimental parameter settings, and the first step of data analysis. PMID:24061914

Ishima, Rieko

2014-01-01

370

Relaxation and phase space singularities in time series of human magnetoencephalograms can serve as an indicator of the photosensitive epilepsy  

E-print Network

To analyze the crucial role of the fluctuation and relaxational effects in the human brain functioning we have studied a some statistical quantifiers that support the informational characteristics of neuromagnetic responses of magnetoencephalographic (MEG) signals. The signals to a flickering stimulus of different color combinations has been obtained from a group of control subjects which is contrasted with those for a patient with photosensitive epilepsy (PSE). We have revealed that the existence of the specific stratification of the phase clouds and the concomitant relaxation singularities of the corresponding nonequilibrium processes of chaotic behavior of the signals in the separate areas for a patient most likely shows the pronounced zones responsible the appearance of PSE.

Yulmetyev, R M; Hänggi, P; Khusaenova, E V; Shimojo, S; Yulmetyeva, D G

2006-01-01

371

Critical time scales for advection-diffusion-reaction processes  

NASA Astrophysics Data System (ADS)

The concept of local accumulation time (LAT) was introduced by Berezhkovskii and co-workers to give a finite measure of the time required for the transient solution of a reaction-diffusion equation to approach the steady-state solution [A. M. Berezhkovskii, C. Sample, and S. Y. Shvartsman, Biophys. J.BIOJAU0006-349510.1016/j.bpj.2010.07.045 99, L59 (2010); A. M. Berezhkovskii, C. Sample, and S. Y. Shvartsman, Phys. Rev. EPLEEE81539-375510.1103/PhysRevE.83.051906 83, 051906 (2011)]. Such a measure is referred to as a critical time. Here, we show that LAT is, in fact, identical to the concept of mean action time (MAT) that was first introduced by McNabb [A. McNabb and G. C. Wake, IMA J. Appl. Math.IJAMDM0272-496010.1093/imamat/47.2.193 47, 193 (1991)]. Although McNabb's initial argument was motivated by considering the mean particle lifetime (MPLT) for a linear death process, he applied the ideas to study diffusion. We extend the work of these authors by deriving expressions for the MAT for a general one-dimensional linear advection-diffusion-reaction problem. Using a combination of continuum and discrete approaches, we show that MAT and MPLT are equivalent for certain uniform-to-uniform transitions; these results provide a practical interpretation for MAT by directly linking the stochastic microscopic processes to a meaningful macroscopic time scale. We find that for more general transitions, the equivalence between MAT and MPLT does not hold. Unlike other critical time definitions, we show that it is possible to evaluate the MAT without solving the underlying partial differential equation (pde). This makes MAT a simple and attractive quantity for practical situations. Finally, our work explores the accuracy of certain approximations derived using MAT, showing that useful approximations for nonlinear kinetic processes can be obtained, again without treating the governing pde directly.

Ellery, Adam J.; Simpson, Matthew J.; McCue, Scott W.; Baker, Ruth E.

2012-04-01

372

Bilateral Laplace Transforms on Time Scales: Convergence, Convolution, and the Characterization of Stationary Stochastic Time Series  

Microsoft Academic Search

The convergence of Laplace transforms on time scales is generalized to the bilateral case. The bilateral Laplace transform\\u000a of a signal on a time scale subsumes the continuous time bilateral Laplace transform, and the discrete time bilateral z-transform as special cases. As in the unilateral case, the regions of convergence (ROCs) time scale Laplace transforms are\\u000a determined by the time

John M. Davis; Ian A. Gravagne; Robert J. Marks II

2010-01-01

373

The Effects of Changing Water Content, Relaxation Times, and Tissue Contrast on Tissue Segmentation and Measures of Cortical Anatomy in MR Images  

PubMed Central

Water content is the dominant chemical compound in the brain and it is the primary determinant of tissue contrast in magnetic resonance (MR) images. Water content varies greatly between individuals, and it changes dramatically over time from birth through senescence of the human life span. We hypothesize that the effects that individual- and age-related variations in water content have on contrast of the brain in MR images also has important, systematic effects on in vivo, MRI-based measures of regional brain volumes. We also hypothesize that changes in water content and tissue contrast across time may account for age-related changes in regional volumes, and that differences in water content or tissue contrast across differing neuropsychiatric diagnoses may account for differences in regional volumes across diagnostic groups. We demonstrate in several complementary ways that subtle variations in water content across age and tissue compartments alter tissue contrast, and that changing tissue contrast in turn alters measures of the thickness and volume of the cortical mantle: (1) We derive analytic relations describing how age-related changes in tissue relaxation times produce age-related changes in tissue gray-scale intensity values and tissue contrast; (2) We vary tissue contrast in computer-generated images to assess its effects on tissue segmentation and volumes of gray matter and white matter; and (3) We use real-world imaging data from adults with either Schizophrenia or Bipolar Disorder and age- and sex-matched healthy adults to assess the ways in which variations in tissue contrast across diagnoses affects group differences in tissue segmentation and associated volumes. We conclude that in vivo MRI-based morphological measures of the brain, including regional volumes and measures of cortical thickness, are a product of, or at least are confounded by, differences in tissue contrast across individuals, ages, and diagnostic groups, and that differences in tissue contrast in turn likely derive from corresponding differences in water content of the brain across individuals, ages, and diagnostic groups. PMID:24055410

Bansal, Ravi; Hao, Xuejun; Liu, Feng; Xu, Dongrong; Liu, Jun; Peterson, Bradley S.

2013-01-01

374

Reid Roundabout Theorem for Symplectic Dynamic Systems on Time Scales  

SciTech Connect

The principal aim of this paper is to state and prove the so-called Reid roundabout theorem for the symplectic dynamic system (S) z{sup {delta}}= cal S {sub t}z on an arbitrary time scale Bbb T , so that the well known case of differential linear Hamiltonian systems (Bbb T = Bbb R ) and the recently developed case of discrete symplectic systems (Bbb T = Bbb Z ) are unified. We list conditions which are equivalent to the positivity of the quadratic functional associated with (S), e.g. disconjugacy (in terms of no focal points of a conjoined basis) of (S), no generalized zeros for vector solutions of (S), and the existence of a solution to the corresponding Riccati matrix equation. A certain normality assumption is employed. The result requires treatment of the quadratic functionals both with general and separated boundary conditions.

Hilscher, R. [Department of Mathematics, Masaryk University Brno, Janackovo nam. 2a, CZ-66295 Brno (Czech Republic)], E-mail: houska@math.muni.cz

2001-07-01

375

Large-scale structure of time evolving citation networks  

NASA Astrophysics Data System (ADS)

In this paper we examine a number of methods for probing and understanding the large-scale structure of networks that evolve over time. We focus in particular on citation networks, networks of references between documents such as papers, patents, or court cases. We describe three different methods of analysis, one based on an expectation-maximization algorithm, one based on modularity optimization, and one based on eigenvector centrality. Using the network of citations between opinions of the United States Supreme Court as an example, we demonstrate how each of these methods can reveal significant structural divisions in the network and how, ultimately, the combination of all three can help us develop a coherent overall picture of the network's shape.

Leicht, E. A.; Clarkson, G.; Shedden, K.; Newman, M. E. J.

2007-09-01

376

Large-scale structure of time evolving citation networks  

E-print Network

In this paper we examine a number of methods for probing and understanding the large-scale structure of networks that evolve over time. We focus in particular on citation networks, networks of references between documents such as papers, patents, or court cases. We describe three different methods of analysis, one based on an expectation-maximization algorithm, one based on modularity optimization, and one based on eigenvector centrality. Using the network of citations between opinions of the United States Supreme Court as an example, we demonstrate how each of these methods can reveal significant structural divisions in the network, and how, ultimately, the combination of all three can help us develop a coherent overall picture of the network's shape.

Leicht, E A; Shedden, Kerby; Newman, M E J

2007-01-01

377

Control of Systems With Slow Actuators Using Time Scale Separation  

NASA Technical Reports Server (NTRS)

This paper addresses the problem of controlling a nonlinear plant with a slow actuator using singular perturbation method. For the known plant-actuator cascaded system the proposed scheme achieves tracking of a given reference model with considerably less control demand than would otherwise result when using conventional design techniques. This is the consequence of excluding the small parameter from the actuator dynamics via time scale separation. The resulting tracking error is within the order of this small parameter. For the unknown system the adaptive counterpart is developed based on the prediction model, which is driven towards the reference model by the control design. It is proven that the prediction model tracks the reference model with an error proportional to the small parameter, while the prediction error converges to zero. The resulting closed-loop system with all prediction models and adaptive laws remains stable. The benefits of the approach are demonstrated in simulation studies and compared to conventional control approaches.

Stepanyan, Vehram; Nguyen, Nhan

2009-01-01

378

1. Geologic time scale 2. Local stratigraphic column ( Cambrian Flathead -f , Cambrian Wolsey -w , Cambrian  

E-print Network

for each period of geologic time (e.g. Cambrian ­ west to east transgression; Late Jurassic ­ widespread that you know the geologic time scale, at least to the period level. Knowing the time scale is essential

Polly, David

379

Oligomerization of a retroviral matrix protein is facilitated by backbone flexibility on nanosecond time scale.  

PubMed

The oligomerization capacity of the retroviral matrix protein is an important feature that affects assembly of immature virions and their interaction with cellular membrane. A combination of NMR relaxation measurements and advanced analysis of molecular dynamics simulation trajectory provided an unprecedentedly detailed insight into internal mobility of matrix proteins of the Mason-Pfizer monkey virus. Strong evidence have been obtained that the oligomerization capacity of the wild-type matrix protein is closely related to the enhanced dynamics of several parts of its backbone on a nanosecond time scale. Increased flexibility has been observed for two regions: the loop between ?-helices ?2 and ?3 and the C-terminal half of ?-helix ?3 which accommodate amino acid residues that form the oligomerization interface. On the other hand, matrix mutant R55F that has changed structure and does not exhibit any specific oligomerization in solution was found considerably more rigid. Our results document that conformational selection mechanism together with induced fit and favorable structural preorganization play an important role in the control of the oligomerization process. PMID:21366213

Srb, Pavel; Vlach, Ji?í; Prchal, Jan; Grocký, Marián; Ruml, Tomáš; Lang, Jan; Hrabal, Richard

2011-03-24

380

Homogenization of historical time series on a subdaily scale  

NASA Astrophysics Data System (ADS)

Homogeneous long-term climatological time series provide useful information on climate back to the preindustrial era. High temporal resolution of climate data is desirable to address trends and variability in the mean climate and in climatic extremes. For Switzerland, three long (~250 yrs) historical time series (Basel, Geneva, Gr. St. Bernhard) that were hitherto available in the form of monthly means only have recently been digitized (in cooperation with MeteoSwiss) on a subdaily scale. The digitized time series contain subdaily data (varies from 2-5 daily measurements) on temperature, precipitation/snow height, pressure and humidity, as subdaily descriptions on wind direction, wind speeds and cloud cover. Long-term climatological records often contain inhomogeneities due to non climatic changes such as station relocations, changes in instrumentation and instrument exposure, changes in observing schedules/practices and environmental changes in the proximity of the observation site. Those disturbances can distort or hide the true climatic signal and could seriously affect the correct assessment and analysis of climate trends, variability and climatic extremes. It is therefore crucial to detect and eliminate artificial shifts and trends, to the extent possible, in the climate data prior to its application. Detailed information of the station history and instruments (metadata) can be of fundamental importance in the process of homogenization in order to support the determination of the exact time of inhomogeneities and the interpretation of statistical test results. While similar methods can be used for the detection of inhomogeneities in subdaily or monthly mean data, quite different correction methods can be chosen. The wealth of information in a high temporal resolution allows more physics-based correction methods. For instance, a detected radiation error in temperature can be corrected with an error model that incorporates radiation and ventilation terms using the subdaily information on cloud cover and wind from the station. The basic approach will be demonstrated.

Kocen, Renate; Brönnimann, Stefan; Breda, Leila; Spadin, Reto; Begert, Michael; Füllemann, Christine

2010-05-01

381

Structural studies of melting on the picosecond time scale.  

PubMed

Ultrafast structural studies of laser-induced melting have demonstrated that the solid-liquid phase transition can take place on a picosecond time scale in a variety of materials. Experimental studies using ångström wavelength X-rays from the sub-picosecond pulse source at Stanford (now retired) on non-thermal melting of semi-conductors, such as indium antimonide, employed the decay of a single Bragg-peak to measure the time component of the phase transition. These materials were found to start melting within one picosecond after the laser pulse. Recent computer simulations have described the thermal melting of ice induced by an infrared laser pulse. Here it was shown that melting can happen within a few picoseconds, somewhat slower than non-thermal melting in semi-conductors. These computer simulations are compatible with spectroscopy experiments on ice-melting, demonstrating that simulations form a very powerful complement to experiments targeting the process of phase-transitions. Here we present an overview of recent experimental and theoretical studies of melting, as well as new simulations of ice-melting where the effect of the size of the crystal on scattering is studied. Based on simulations of a near-macroscopic crystal, we predict the decay of the most intense Bragg peaks of ice following heating by laser pulse, by modeling the scattering from the melting sample in the simulations. PMID:18972022

Spoel, David van der; Maia, Filipe R N C; Caleman, Carl

2008-11-14

382

Gyrokinetic Particle Simulation of Microturbulence in Transport Time Scale  

NASA Astrophysics Data System (ADS)

Recent investigations on Alfven waves in gyrokinetic plasmas and their relationship with those in the MHD theory have enabled us to extend the gyrokinetic particle simulation techniques into the kinetic-MHD regime when the finite-Larmor radius effects are important and the time step restrictions imposed by compressional Alfven waves are not desirable.[1,2] Some of the numerical schemes have already been devised based on their thermodynamic properties.[1,2] Here, we propose to use gyrokinetic particle simulation to study microturbulence in transport time scale. The procedures involve the use of finite-? microturbulence simulation as well as the use of transport coefficients in the steady state for predicting density,temperature and parallel current profile changes, along with the use of perpendicular current information for the establishment of equilibrium magnetic structure. Details will be given. [1] W. W. Lee and H. Qin, Phys. Plasmas, to appear (August 2003). [2] W. W. Lee, J. L. V. Lewandowski, T. S. Hahm, and Z. Lin, Phys. Plasmas 8, 4435 (2001).

Lee, W. W.

2003-10-01

383

Use of a Walk Through Time to Facilitate Student Understandings of the Geological Time Scale  

NASA Astrophysics Data System (ADS)

Students often have difficulties in appreciating just how old the earth and the universe are. While they can simply memorize a number, they really do not understand just how big that number really is, in comparison with other, more familiar student referents like the length of a human lifetime or how long it takes to eat a pizza. (See, e.g., R.D. Trend 2001, J. Research in Science Teaching 38(2): 191-221) Students, and members of the general public, also display such well-known misconceptions as the "Flintstone chronology" of believing that human beings and dinosaurs walked the earth at the same time. (In the classic American cartoon "The Flintstones," human beings used dinosaurs as draft animals. As scientists we know this is fiction, but not all members of the public understand that.) In an interdisciplinary undergraduate college class that dealt with astronomy, cosmology, and biological evolution, I used a familiar activity to try to improve student understanding of the concept of time's vastness. Students walked through a pre-determined 600-step path which provided a spatial analogy to the geological time scale. They stopped at various points and engaged in some pre-determined discussions and debates. This activity is as old as the hills, but reports of its effectiveness or lack thereof are quite scarce. This paper demonstrates that this activity was effective for a general-audience, college student population in the U.S. The growth of student understandings of the geological time scale was significant as a result of this activity. Students did develop an understanding of time's vastness and were able to articulate this understanding in various ways. This growth was monitored through keeping track of several exam questions and through pre- and post- analysis of student writings. In the pre-writings, students often stated that they had "no idea" about how to illustrate the size of the geological time scale to someone else. While some post-time walk responses simply restated what was done in the walk through time, some students were able to develop their own ways of conceptualizing the vastness of the geological time scale. A variety of findings from student understandings will be presented. This work has been supported in part by the Distinguished Scholars Program of the National Science Foundation (DUE-0308557).

Shipman, H. L.

2004-12-01

384

The Effects of Suggestibility on Relaxation.  

ERIC Educational Resources Information Center

Selected undergraduates (N=32) on the basis of Creative Imagination Scale scores and randomly assigned high and low suggestibility subjects to progressive relaxation (PR) and suggestions of relaxation (SR) training modes. Results revealed a significant pre-post relaxation effect, and main efffects for both suggestibility and training mode. (NRB)

Rickard, Henry C.; And Others

1985-01-01

385

Identical temperature dependence of the time scales of several linear-response functions of two glass-forming liquids  

E-print Network

The frequency-dependent dielectric constant, shear and adiabatic bulk moduli, longitudinal thermal expansion coefficient, and longitudinal specific heat have been measured for two van der Waals glass-forming liquids, tetramethyl-tetraphenyl-trisiloxane (DC704) and 5-polyphenyl-4-ether. Within the experimental uncertainties the loss-peak frequencies of the measured response functions have identical temperature dependence over a range of temperatures, for which the Maxwell relaxation time varies more than nine orders of magnitude. The time scales are ordered from fastest to slowest as follows: Shear modulus, adiabatic bulk modulus, dielectric constant, longitudinal thermal expansion coefficient, longitudinal specific heat. The ordering is discussed in light of the recent conjecture that van der Waals liquids are strongly correlating, i.e., approximate single-parameter liquids.

Bo Jakobsen; Tina Hecksher; Kristine Niss; Tage Christensen; Niels Boye Olsen; Jeppe C. Dyre

2011-06-01

386

Communication: Identical temperature dependence of the time scales of several linear-response functions of two glass-forming liquids.  

PubMed

The frequency-dependent dielectric constant, shear and adiabatic bulk moduli, longitudinal thermal expansion coefficient, and longitudinal specific heat have been measured for two van der Waals glass-forming liquids, tetramethyl-tetraphenyl-trisiloxane (DC704) and 5-polyphenyl-4-ether. Within the experimental uncertainties the loss-peak frequencies of the measured response functions have identical temperature dependence over a range of temperatures, for which the Maxwell relaxation time varies more than nine orders of magnitude. The time scales are ordered from fastest to slowest as follows: Shear modulus, adiabatic bulk modulus, dielectric constant, longitudinal thermal expansion coefficient, and longitudinal specific heat. The ordering is discussed in light of the recent conjecture that van der Waals liquids are strongly correlating, i.e., approximate single-parameter liquids. PMID:22380025

Jakobsen, Bo; Hecksher, Tina; Christensen, Tage; Olsen, Niels Boye; Dyre, Jeppe C; Niss, Kristine

2012-02-28

387

Nanosecond Relaxation Dynamics of Hydrated Proteins: Water versus protein contributions  

SciTech Connect

We have studied picosecond to nanosecond dynamics of hydrated protein powders using dielectric spectroscopy and molecular dynamics (MD) simulations. Our analysis of hydrogen-atom single particle dynamics from MD simulations focused on main ( main tens of picoseconds) and slow ( slow nanosecond) relaxation processes that were observed in dielectric spectra of similar hydrated protein samples. Traditionally, the interpretation of these processes observed in dielectric spectra has been ascribed to the relaxation behavior of hydration water tightly bounded to a protein and not to protein atoms. Detailed analysis of the MD simulations and comparison to dielectric data indicate that the observed relaxation process in the nanosecond time range of hydrated protein spectra is mainly due to protein atoms. The relaxation processes involve the entire structure of protein including atoms in the protein backbone, side chains, and turns. Both surface and buried protein atoms contribute to the slow processes; however, surface atoms demonstrate slightly faster relaxation dynamics. Analysis of the water molecule residence and dipolar relaxation correlation behavior indicates that the hydration water relaxes at much shorter time scales.

Khodadadi, S [University of Akron; Curtis, J. E. [National Institute of Standards and Technology (NIST), Gaithersburg, MD; Sokolov, Alexei P [ORNL

2011-01-01

388

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

SciTech Connect

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

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

1999-09-13

389

Timescale invariance of relaxation processes of density fluctuation in slow neutron scattering in liquid cesium  

Microsoft Academic Search

The realization of the idea of time-scale invariance for relaxation processes in liquids has been performed by the memory functions formalism. The best agreement with experimental data for the dynamic structure factor S(k,omega) of liquid cesium near melting point in the range of wave vectors (0.4 Å-1<=k<=2.55 Å-1) is found with the assumption of concurrence of relaxation scales for memory

R. M. Yulmetyev; A. V. Mokshin; P. Hänggi; V. Yu. Shurygin

2001-01-01

390

Evaluating the uncertainty of predicting future climate time series at the hourly time scale  

NASA Astrophysics Data System (ADS)

A stochastic downscaling methodology is developed to generate hourly, point-scale time series for several meteorological variables, such as precipitation, cloud cover, shortwave radiation, air temperature, relative humidity, wind speed, and atmospheric pressure. The methodology uses multi-model General Circulation Model (GCM) realizations and an hourly weather generator, AWE-GEN. Probabilistic descriptions of factors of change (a measure of climate change with respect to historic conditions) are computed for several climate statistics and different aggregation times using a Bayesian approach that weights the individual GCM contributions. The Monte Carlo method is applied to sample the factors of change from their respective distributions thereby permitting the generation of time series in an ensemble fashion, which reflects the uncertainty of climate projections of future as well as the uncertainty of the downscaling procedure. Applications of the methodology and probabilistic expressions of certainty in reproducing future climates for the periods, 2000 - 2009, 2046 - 2065 and 2081 - 2100, using the 1962 - 1992 period as the baseline, are discussed for the location of Firenze (Italy). The climate predictions for the period of 2000 - 2009 are tested against observations permitting to assess the reliability and uncertainties of the methodology in reproducing statistics of meteorological variables at different time scales.

Caporali, E.; Fatichi, S.; Ivanov, V. Y.

2011-12-01

391

Existence results for time scale boundary value problem  

NASA Astrophysics Data System (ADS)

In this paper, we establish some existence results for positive solutions to a class of singular boundary value problem on time scale by using the Krasnosel'skii fixed point theorem. Two examples are presented as applications. The conditions we used in this paper are different from those in [D.R. Anderson, Eigenvalue intervals for a two-point boundary value problem on a measure chain, J. Comput. Appl. Math. 141 (2002) 57-64; C.J. Chyan, J. Henderson, Eigenvalues problems for nonlinear differential equations on a measure chain, J. Math. Anal. Appl. 245 (2000) 547-559; L.H. Erbe, A. Peterson Positive solutions for nonlinear differential equation on a measure chain, Math. Comput. Modelling 32 (2000) 571-585; L.H. Erbe, H.Y. Wang, On the existence of positive solutions of ordinary differential equations, Proc. Amer. Math. Soc. 120 (1994) 743-748; J. Henderson, H.Y. Wang, Positive solutions for nonlinear eigenvalue problems, J. Math. Anal. Appl. 208 (1997) 252-259; C.H. Hong, C.C. Yeh, Positive solutions for eigenvalue problems on a measure chain, Nonlinear Anal. 51 (2002) 499-507; W.C. Lian; W.F. Wong; C.C. Yeh, On the existence of positive solutions of nonlinear differential equations, Proc. Amer. Math. Soc. 124 (1996) 1117-1126; J. Liang, T.J. Xiao, Z.C. Hao, Positive solutions of singular differential equations on measure chain, Comput. Math. Appl. 49 (2005) 651-663].

Hao, Zhao-Cai; Liang, Jin; Xiao, Ti-Jun

2006-12-01

392

Scale relativity and fractal space-time: Applications to quantum physics, cosmology and chaotic systems  

Microsoft Academic Search

The theory of scale relativity is a new approach to the problem of the origin of fundamental scales and of scaling laws in physics, that consists of generalizing Einstein's principle of relativity (up to now applied to motion laws) to scale transformations. Namely, we redefine space-time resolutions as characterizing the state of scale of the reference system and require that

L. Nottale

1996-01-01

393

Collisionless relaxation in gravitational systems: From violent relaxation to gravothermal collapse  

NASA Astrophysics Data System (ADS)

Theory and simulations are used to study collisionless relaxation of a gravitational N -body system. It is shown that when the initial one-particle distribution function satisfies the virial condition—potential energy is minus twice the kinetic energy—the system quickly relaxes to a metastable state described quantitatively by the Lynden-Bell distribution with a cutoff. If the initial distribution function does not meet the virial requirement, the system undergoes violent oscillations, resulting in a partial evaporation of mass. The leftover particles phase-separate into a core-halo structure. The theory presented allows us to quantitatively predict the amount and the distribution of mass left in the central core, without any adjustable parameters. On a longer time scale ?G˜N , collisionless relaxation leads to a gravothermal collapse.

Levin, Yan; Pakter, Renato; Rizzato, Felipe B.

2008-08-01

394

A Group Simulation of the Development of the Geologic Time Scale.  

ERIC Educational Resources Information Center

Explains how to demonstrate to students that the relative dating of rock layers is redundant. Uses two column diagrams to simulate stratigraphic sequences from two different geological time scales and asks students to complete the time scale. (YDS)

Bennington, J. Bret

2000-01-01

395

Modulated heterodyne light scattering set-up for measuring long relaxation time at small and wide angle  

SciTech Connect

We present a simple, compact, and versatile experimental setup working in the heterodyne detection mode with modulation of the reference beam. The system is implemented with a collection optics based on a unimodal optical fiber coupler. This choice allows the heterodyne to be used in a wide range of scattering angles, even for very small ones, without losing the optical beating. The apparatus can be successfully used to study translational diffusive dynamics of dispersed particles at scattering angles smaller than 5 Degree-Sign and it is suitable for exploring slow relaxation processes in sub-Hertz frequency domain, for example, in glass-forming systems. It is also possible to measure the electrophoretic mobility by applying an electric field into a charged particles solution.

Leone, Nancy; Villari, Valentina; Micali, Norberto [CNR-Istituto per i Processi Chimico-Fisici, V.le F. Stagno D'Alcontres 37, 98158 Messina (Italy)

2012-08-15

396

Resolving the Impact of Biological Processes on DNAPL Transport in Unsaturated Porous Media through Nuclear Magnetic Resonance Relaxation Time Measurements  

SciTech Connect

This research leads to a better understanding of how physical and biological properties of porous media influence water and dense non-aqueous phase liquid (DNAPL) distribution under saturated and unsaturated conditions. This project exploits the capability of low-field nuclear magnetic resonance (NMR) proton relaxation decay-rate measurements for determining environmental properties affecting DNAPL solvent flow in the subsurface, including determining if DNAPL exist in water-wet or solvent-wet environments, the pore-size distribution of the soils containing DNAPLs, and the impact of biological processes on their transport mechanisms in porous media. Knowledge of the in-situ flow properties and pore distributions of organic contaminants are critical to understanding where and when these fluids will enter subsurface aquifers.

Hertzog, Russel; Geesey, Gill G.

2004-06-01

397

Single-relaxation-time lattice Boltzmann scheme for advection-diffusion problems with large diffusion-coefficient heterogeneities and high-advection transport  

NASA Astrophysics Data System (ADS)

The paper presents an approach that extends the flexibility of the standard lattice Boltzmann single relaxation time scheme in terms of spatial variation of dissipative terms (e.g., diffusion coefficient) and stability for high Péclet mass transfer problems. Spatial variability of diffusion coefficient in SRT is typically accommodated through the variation of relaxation time during the collision step. This method is effective but cannot deal with large diffusion coefficient variations, which can span over several orders of magnitude in some natural systems. The approach explores an alternative way of dealing with large diffusion coefficient variations in advection-diffusion transport systems by introducing so-called diffusion velocity. The diffusion velocity is essentially an additional convective term that replaces variations in diffusion coefficients vis-à-vis a chosen reference diffusion coefficient which defines the simulation time step. Special attention is paid to the main idea behind the diffusion velocity formulation and its implementation into the lattice Boltzmann framework. Finally, the performance, stability, and accuracy of the diffusion velocity formulation are discussed via several advection-diffusion transport benchmark examples. These examples demonstrate improved stability and flexibility of the proposed scheme with marginal consequences on the numerical performance.

Perko, Janez; Patel, Ravi A.

2014-05-01

398

Dynamics of Sulfonated Polystyrene Ionomers by Dielectric Relaxation Spectroscopy  

NASA Astrophysics Data System (ADS)

Broadband dielectric spectroscopy was used to investigate the dynamics of sulfonated polystyrene (SPS) ionomers, in both the acid and neutralized form. This study seeks to elucidate the role of counter ion type (Zn, Na, and Cs), degree of sulfonation (9 and 6%), and ion cluster morphology on the relaxation phenomena of SPS. Degree of neutralization and ion type have been found to significantly impact the breadth and time scale of the segmental relaxation process. High temperature relaxation processes, tentatively proposed to arise from Maxwell-Wagner-Sillars interfacial polarization and a hydrogen bonding relaxation, have also been identified. Bands in the sulfonate stretching region of FTIR spectra reveal information about ion coordination in the local aggregate environment. A combination of scanning transmission electron microscopy imaging and X-ray scattering confirmed the presence of homogeneously distributed, nearly monodisperse spherical ionic aggregates in the polymer matrix.

Castagna, Alicia; Wang, Wenqin; Winey, Karen; Runt, James

2010-03-01

399

Viscoelastic and poroelastic relaxations of polymer-loaded gels  

NASA Astrophysics Data System (ADS)

Gel layers are prevalent in many applications including water purification, fuel cells, tissue engineering and drug delivery. In these materials, their performance is closely linked to controlling transport of solutes such as solvent or polymer. Thus, understanding the critical time- and length-scale that regulate solute transport will enable development of membrane materials with the desired performance. In this contribution, we present the Poroelastic Indentation Relaxation (PRI) approach in quantifying the viscoelastic and poroelastic relaxations of geometrically-confined hydrogel layers. We demonstrate this indentation-based measurement approach in characterizing several materials properties including diffusion coefficient, shear modulus, and average pore dimensions of the hydrogel independent of the extent of geometric confinement. Additionally, we present a relaxation model that accounts for the viscoelastic and poroelastic contributions to the total relaxation process. Finally, we show that the PRI approach can quantify diffusion of solvent and polymer solution in a single test simply by changing the extent of deformation.

Chan, Edwin; Deeyaa, Blessing; Johnson, Peter; Stafford, Christopher

2012-02-01

400

Studying the Dynamics of Problem Behavior across Multiple Time Scales: Prospects and Challenges.  

ERIC Educational Resources Information Center

As a commentary on the Special Issue, this paper discusses recent advances in the study of change across several time scales. It points out the importance of specifying time scales and putative patterns of change when characterizing problem behavior over developmental time scales. Methods for studying risk and protective mechanisms through…

Howe, George W.

2004-01-01

401

Collisional Time Scales in the Kuiper Disk and Their Implications  

NASA Technical Reports Server (NTRS)

We explore the rate of collisions among bodies in the present-day Kuiper Disk as a function of the total mass and population size structure of the disk. We find that collisional evolution is an important evolutionary process in the disk as a whole, and indeed, that it is likely the dominant evolutionary process beyond approx. 42 AU, where dynamical instability time scales exceed the age of the solar system. Two key findings we report from this modeling work are: that unless the disk's population structure is sharply truncated for radii smaller than approx. 1-2 km, collisions between comets and smaller debris are occurring so frequently in the disk, and with high enough velocities, that the small body (i.e., KM-class object) population in the disk has probably developed into a collisional cascade, thereby implying that the Kuiper Disk comets may not all be primordial, and that the rate of collisions of smaller bodies with larger 100 less R less 400 km objects (like 1992QB(sub 1) and its cohorts) is so low that there appears to be a dilemma in explaining how QB(sub 1)s could have grown by binary accretion in the disk as we know it. Given these findings, it appears that either the present-day paradigm for the formation of Kuiper Disk is failed in some fundamental respect, or that the present-day disk is no longer representative of the ancient structure from which it evolved. This in turn suggests the intriguing possibility that the present-day Kuiper Disk evolved through a more erosional stage reminiscent of the disks around the stars Beta Pictorus, alpha PsA, and alpha Lyr.

Stern, S. Alan

1995-01-01

402

Speed of Markovian relaxation toward the ground state  

SciTech Connect

For sufficiently low reservoir temperatures, it is known that open quantum systems subject to decoherent interactions with the reservoir relax toward their ground state in the weak coupling limit. Within the framework of quantum master equations, this is formalized by the Born-Markov-secular (BMS) approximation, where one obtains the system Gibbs state with the reservoir temperature as a stationary state. When the solution to some problem is encoded in the (isolated) ground state of a system Hamiltonian, decoherence can therefore be exploited for computation. The computational complexity is then given by the scaling of the relaxation time with the system size n. We study the relaxation behavior for local and nonlocal Hamiltonians that are coupled dissipatively with local and nonlocal operators to a bosonic bath in thermal equilibrium. We find that relaxation is generally more efficient when coherences of the density matrix in the system energy eigenbasis are taken into account. In addition, the relaxation speed strongly depends on the matrix elements of the coupling operators between initial state and ground state. We show that Dicke superradiance is a special case of our relaxation models and can thus be understood as a coherence-assisted relaxation speedup.

Vogl, Malte; Schaller, Gernot; Brandes, Tobias [Institut fuer Theoretische Physik, Technische Universitaet Berlin, Hardenbergstr. 36, D-10623 Berlin (Germany)

2010-01-15

403

Noise in relaxation oscillators  

Microsoft Academic Search

Relaxation oscillator noise may be described by a single, normalized equation which allows its timing jitter to be predicted. The value of this equation lies in its linearization of the nonlinear regenerative waveforms of the oscillator, and also suggests those circuit topologies promising low jitter. This theory is presently confirmed through experimental measurement of practical oscillators, as well as through

A. A. Abidi; R. G. Meyer

1983-01-01

404

Time-resolved and time-scale adaptive measures of spike train synchrony.  

PubMed

A wide variety of approaches to estimate the degree of synchrony between two or more spike trains have been proposed. One of the most recent methods is the ISI-distance which extracts information from the interspike intervals (ISIs) by evaluating the ratio of the instantaneous firing rates. In contrast to most previously proposed measures it is parameter free and time-scale independent. However, it is not well suited to track changes in synchrony that are based on spike coincidences. Here we propose the SPIKE-distance, a complementary measure which is sensitive to spike coincidences but still shares the fundamental advantages of the ISI-distance. In particular, it is easy to visualize in a time-resolved manner and can be extended to a method that is also applicable to larger sets of spike trains. We show the merit of the SPIKE-distance using both simulated and real data. PMID:21129402

Kreuz, Thomas; Chicharro, Daniel; Greschner, Martin; Andrzejak, Ralph G

2011-01-30

405

Solid-State NMR of 1-Propyltetrazole Complexes of Iron(II) and Zinc(II). 1. 1H Spin-Lattice Relaxation Time  

NASA Astrophysics Data System (ADS)

Proton spin-lattice relaxation times were measured between 2.2 K and room temperature in [Zn(ptz) 6](BF 4) 2(ptz = 1- n-propyl-1 H-tetrazole) and in the spin-crossover complex [Fe(ptz) 6](BF 4) 2. Three different types of intramolecular motion of the propyl group are suggested in [Zn(ptz) 6](BF 4) 2, namely tunneling and classical rotation of methyl groups and rotation of methylene groups. Correlation times and activation energies are calculated for tunneling rotation of the CH 3group and for the classical (hindered) rotations of -CH 3and -CH 2-CH 3as reorientations over a three-well asymmetrical potential. In [Fe(ptz) 6](BF 4) 2the mechanism for the paramagnetic relaxation is found to be of the rapid-diffusion type according to the theory of Lowe and Tse, and the intramolecular motions are suggested to be the same as for the zinc complex.

Bokor, Mónika; Marek, Tamás; Tompa, Kálmán

406

A multiple-relaxation-time lattice-boltzmann model for bacterial chemotaxis: effects of initial concentration, diffusion, and hydrodynamic dispersion on traveling bacterial bands.  

PubMed

Bacterial chemotaxis can enhance the bioremediation of contaminants in aqueous and subsurface environments if the contaminant is a chemoattractant that the bacteria degrade. The process can be promoted by traveling bands of chemotactic bacteria that form due to metabolism-generated gradients in chemoattractant concentration. We developed a multiple-relaxation-time (MRT) lattice-Boltzmann method (LBM) to model chemotaxis, because LBMs are well suited to model reactive transport in the complex geometries that are typical for subsurface porous media. This MRT-LBM can attain a better numerical stability than its corresponding single-relaxation-time LBM. We performed simulations to investigate the effects of substrate diffusion, initial bacterial concentration, and hydrodynamic dispersion on the formation, shape, and propagation of bacterial bands. Band formation requires a sufficiently high initial number of bacteria and a small substrate diffusion coefficient. Uniform flow does not affect the bands while shear flow does. Bacterial bands can move both upstream and downstream when the flow velocity is small. However, the bands disappear once the velocity becomes too large due to hydrodynamic dispersion. Generally bands can only be observed if the dimensionless ratio between the chemotactic sensitivity coefficient and the effective diffusion coefficient of the bacteria exceeds a critical value, that is, when the biased movement due to chemotaxis overcomes the diffusion-like movement due to the random motility and hydrodynamic dispersion. PMID:25223537

Yan, Zhifeng; Hilpert, Markus

2014-10-01

407

Real time density functional simulations of quantum scale conductance  

E-print Network

We study electronic conductance through single molecules by subjecting a molecular junction to a time dependent potential and propagating the electronic state in real time using time-dependent density functional theory ...

Evans, Jeremy Scott

2009-01-01

408

Vitrification in a wide cooling rate range: The relations between cooling rate, relaxation time, transition width, and fragility.  

PubMed

The cooling rate dependence of the thermal glass transition of polystyrene (PS) is measured in a range between 0.2 K/min (0.003 K/s) and 4000 K/s using conventional differential scanning calorimetry (DSC) and Fast Scanning Calorimetry (Flash DSC 1). The cooling rate dependence of the thermal glass transition can be described in an analogy to the frequency dependence of the dynamic glass transition. The relation between cooling rate, ?c, and frequency, ?, is usually described by the Frenkel-Kobeko-Reiner-(FKR) hypothesis ?c/? = C, where C is a constant. We have introduced a new property to describe the kinetics of the vitrification process; the vitrification function, ?. This function is the ratio between the width of the thermal and dynamic glass transition. The validity of the FKR hypothesis is analyzed by two independent methods, the analysis of the activation diagram using the Vogel-Fulcher-Tammann-Hesse equation and the analysis of the temperature dependence of the transition width. We derived a relation for the FKR-constant, which indicates the validity range of the FKR hypotheses. This hypothesis is valid if the logarithmic width of the vitrified and the non-vitrified relaxation spectrum is temperature invariant. This condition is fulfilled for polystyrene in the measured cooling rate range. Furthermore we discuss the relation between the vitrification function, the transition width, the FKR constant, and the fragility. PMID:25399160

Schawe, Jürgen E K

2014-11-14

409

Viscous relaxation times of the core and mantle of Mars from observations of tidal decay of the orbit of Phobos  

NASA Astrophysics Data System (ADS)

The orbit of Phobos exhibits an along-track acceleration, which suggests energy dissipation in the Mars-Phobos system. We hypothesize that the inferred dissipation occurs within Mars. We explore the response of a layered, incompressible Maxwell viscoelastic Mars to tidal forcing by Phobos using normal mode relaxation theory. Our results elucidate the general behavior of a tidally forced viscoelastic body, and have implications for the viscoelastic structure of Mars. We find the real and imaginary part of the degree-two tidal Love number for Mars to be 0.168 and -9.32x10 -4 respectively. Models which satisfy these and other constraints have either: a fluid core with radius 2040 km and density 5410 kg/m 3; or an elastic inner core with radius 1200 km and density 6700 kg/m 3, along with a fluid outer core with thickness 850 km and density 4850 kg/m3. These findings support previous hypotheses that Mars has at least a fluid outer core.

Pithawala, Taronish M.

410

A simple scaling for the minimum instability time-scale of two widely spaced planets  

NASA Astrophysics Data System (ADS)

Long-term instability in multiplanet exosystems is a crucial consideration when confirming putative candidates, analysing exoplanet populations, constraining the age of exosystems and identifying the sources of white dwarf pollution. Two planets that are Hill stable are separated by a wide-enough distance to ensure that they will never collide. However, Hill-stable planetary systems may eventually manifest Lagrange instability when the outer planet escapes or the inner planet collides with the star. We show empirically that for two nearly coplanar Hill-stable planets with eccentricities less than about 0.3, instability can manifest itself only after a time corresponding to x initial orbits of the inner planet, where log10x ˜ 5.2[?/(MJupiter/M?)]-0.18 and ? is the planet-star mass ratio. This relation applies to any type of equal-mass secondaries, and suggests that two low-eccentricity Hill-stable terrestrial-mass or smaller mass planets should be Lagrange stable throughout the main-sequence lifetime of any white dwarf progenitor. However, Hill-stable giant planets are not guaranteed to be Lagrange stable, particularly within a few tens of per cent beyond the critical Hill separation. Our scaling represents a useful `rule of thumb' for planetary population syntheses or individual systems for which performing detailed long-term integrations is unfeasible.

Veras, Dimitri; Mustill, Alexander J.

2013-07-01

411

Local scale invariance as dynamical space-time symmetry in phase-ordering kinetics  

E-print Network

The scaling of the spatio-temporal response of coarsening systems is studied through simulations of the 2D and 3D Ising model with Glauber dynamics. The scaling functions agree with the prediction of local scale invariance, extending dynamical scaling to a space-time dynamical symmetry.

Malte Henkel; Michel Pleimling

2003-02-24

412

Reaching extended length scales and time scales in atomistic simulations via spatially parallel temperature-accelerated dynamics  

Microsoft Academic Search

We present a method for performing parallel temperature-accelerated dynamics TAD simulations over extended length scales. In our method, a two-dimensional spatial decomposition is used along with the recently proposed semirigorous synchronous sublattice algorithm of Shim and Amar Phys. Rev. B 71, 125432 2005. The scaling behavior of the simulation time as a function of system size is studied and compared

Yunsic Shim; Jacques G. Amar; B. P. Uberuaga; A. F. Voter

2007-01-01

413

Reaching extended length scales and time scales in atomistic simulations via spatially parallel temperature-accelerated dynamics  

Microsoft Academic Search

We present a method for performing parallel temperature-accelerated dynamics (TAD) simulations over extended length scales. In our method, a two-dimensional spatial decomposition is used along with the recently proposed semirigorous synchronous sublattice algorithm of Shim and Amar [Phys. Rev. B 71, 125432 (2005)]. The scaling behavior of the simulation time as a function of system size is studied and compared

Yunsic Shim; Jacques G. Amar; B. P. Uberuaga; A. F. Voter

2007-01-01

414

Measurements of the methane relaxation times for application to the infrared emission models of the upper atmospheres of outer planets and Titan  

NASA Technical Reports Server (NTRS)

The 7.8 micrometer emission from the nu(sub 4) band of methane (CH4) is a regularly observed feature in the stratosphere of all the giant planets and Titan. On Jupiter, enhancements in this emission are associated with the infrared hot spots in the auroral zone. Attempts to model this phenomenon in particular, and to understand the role of methane in general, have been hampered in part by a lack of adequate laboratory measurements of the collisional relaxation times for the nu(sub 3) and nu(sub 4) levels over the appropriate temperature range. To provide this needed data, a series of laboratory experiments were initiated. In the experimental arrangement the nu(sub3) band of methane is pumped at 3.3 micrometers using a pulsed infrared source (Nd:YAG/dye laser system equipped with a wave-length extender). The radiative lifetime of the nu(sub 3) level (approximately 37 ms) is much shorter than the nu(sub 4) lifetime (approximately 390 ms); however, a rapid V-V energy transfer rate ensures that the nu(sub 4) level is substantially populated. The photoacoustic technique is used to acquire relaxation rate information. The experiments are performed using a low-temperature, low-pressure cell. Experimental apparatus and technique are described. In addition some of the experimental difficulties associated with making these measurements are discussed and some preliminary results are presented.

Halthore, Rangasayi N.; Caldwell, John J.; Allen, John E., Jr.; Burt, Jim A.; Yang, Kuanghua; Delaney, Paul

1990-01-01

415

Critical aging of Ising ferromagnets relaxing from an ordered state  

E-print Network

We investigate the nonequilibrium behavior of the d-dimensional Ising model with purely dissipative dynamics during its critical relaxation from a magnetized initial configuration. The universal scaling forms of the two-time response and correlation functions of the magnetization are derived within the field-theoretical approach and the associated scaling functions and fluctuation-dissipation ratio are computed up to first order in the epsilon-expansion. Aging behavior is clearly displayed during the critical relaxation. These results are confirmed by Monte Carlo simulations of the two-dimensional Ising model with Glauber dynamics. The crossover to the case of relaxation from a disordered state is discussed and the crossover function for the fluctuation-dissipation ratio is computed within the Gaussian approximation.

Pasquale Calabrese; Andrea Gambassi; Florent Krzakala

2006-04-18

416

A POLYNOMIAL-TIME AFFINE-SCALING METHOD FOR ...  

E-print Network

We develop a natural variant of Dikin's affine-scaling method, first for semidefinite ... displayed for a Klee-Minty cube that given ? > 0, by beginning at a particular interior point .... In section 3 we are thus led to bring duality into the picture, even

2014-10-22

417

The biology of time across different scales Dean V Buonomano  

E-print Network

of large networks of neurons--lack the digital precision of modern clocks. Second, the features required a traffic light will change,or control the circadian fluctuations in sleep-wake cycles. The mechanisms oscillations, such as our sleep-wake cycle. In-between these extremes temporal processing occurs on the scale

Buonomano, Dean

418

Multiple Time Scales And Canards In A Chemical Oscillator  

Microsoft Academic Search

. We present a geometric singular perturbation analysis of a chemicaloscillator. Although the studied three-dimensional model is rather simple its dynamicsare quite complex. In the original scaling the problem has a folded critical manifold whichadditionally becomes tangent to the fast fibers in a region relevant to the dynamics.Thus normal hyperbolicity of the critical manifold is lost in two regions. The

Alexandra Milik Peter Szmolyan

1998-01-01

419

Scaling up dynamic time warping for datamining applications  

Microsoft Academic Search

There has been much recent interest in adapting data mining algorithms to time series databases. Most of these algorithms need to compare time series. Typically some variation of Euclidean distance is used. However, as we demonstrate in this paper, Euclidean distance can be an extremely brittle distance measure. Dynamic time warping (DTW) has been suggested as a technique to allow

Eamonn J. Keogh; Michael J. Pazzani

2000-01-01

420

Dynamical characterization of residual and non-native structures in a partially folded protein by (15)N NMR relaxation using a model based on a distribution of correlation times.  

PubMed

A spectral density model based on a truncated lorentzian distribution of correlation times is used to analyze the nanosecond time-scale dynamics of the partially unfolded domain 2 of annexin I from its (15)N NMR relaxation parameters measured at three magnetic field strengths. The use of a distribution of correlation times enables the characterization of the dynamical features of the NH bonds of the protein in terms of heterogeneity of dynamical states in the nanosecond range. The variation along the sequence of the two dynamical parameters introduced, namely the center and the width of the distribution, points out the different types of residual secondary structures present in the D2 domain. Moreover, it allows a physically sensible interpretation of the dynamical behavior of the different residual helices and of the non-native structures. Also, a striking correspondence is found between the parameters obtained using an extended Lipari and Szabo model and the parameters obtained using the distribution of correlation times. This result led us to propose a specific interpretation of the model-free order parameter for internal motions in the nanosecond range in the case of unfolded states. PMID:11910038

Ochsenbein, Françoise; Neumann, Jean-Michel; Guittet, Eric; van Heijenoort, Carine

2002-04-01