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1

Generalized dynamic scaling for quantum critical relaxation in imaginary time.  

PubMed

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. PMID:25375435

Zhang, Shuyi; Yin, Shuai; Zhong, Fan

2014-10-01

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

Scaling the -relaxation time of supercooled fragile organic liquids  

Microsoft Academic Search

It was shown recently [1] that the structural $\\\\alpha $ -relaxation time $\\\\tau $ of supercooled o-terphenyl depends on a single control parameter $\\\\Gamma $ , which is the product of a function of density $E(\\\\rho )$ , by the inverse temperature T -1. We extend this finding to other fragile glassforming liquids using light scattering data. Available experimental results

C. Dreyfus; A. Le Grand; J. Gapinski; W. Steffen; A. Patkowski

2004-01-01

4

Scaling the alpha -relaxation time of supercooled fragile organic liquids  

Microsoft Academic Search

It was shown recently [1] that the structural alpha -relaxation time tau of supercooled o-terphenyl depends on a single control parameter Gamma , which is the product of a function of density E(rho ), by the inverse temperature T -1. We extend this finding to other fragile glassforming liquids using light scattering data. Available experimental results do not allow to

C. Dreyfus; A. Le Grand; J. Gapinski; W. Steffen; A. Patkowski

2004-01-01

5

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

NASA Astrophysics Data System (ADS)

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

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

2012-07-01

6

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

SciTech Connect

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, E-mail: shs3@illinois.edu [Department of Chemistry, University of Illinois at Urbana-Champaign, 600 South Mathews Avenue, Urbana, Illinois 61801 (United States)] [Department of Chemistry, University of Illinois at Urbana-Champaign, 600 South Mathews Avenue, Urbana, Illinois 61801 (United States)

2014-01-21

7

Measurement of magnetic nanoparticle relaxation time  

PubMed Central

Purpose: Nanoparticle relaxation time measurements have many applications including characterizing molecular binding, viscosity, heating, and local matrix stiffness. The methods capable of in vivo application are extremely limited. The hypothesis investigated by the authors was that the relaxation time could be measured quantitatively using magnetic spectroscopy of nanoparticle Brownian motion (MSB). Methods: The MSB signal (1) reflects the nanoparticle rotational Brownian motion, (2) can be measured from very low nanoparticle concentrations, and (3) is a function of the product of the drive frequency and the relaxation time characterizing Brownian motion. To estimate the relaxation time, the MSB signal was measured at several frequencies. The MSB signal for nanoparticles with altered relaxation time is a scaled version of that for reference nanoparticles with a known relaxation time. The scaling factor linking the altered and reference MSB measurements is the same factor linking the altered and reference relaxation times. The method was tested using glycerol solutions of varying viscosities to obtain continuously variable relaxation times. Results: The measured relaxation time increased with increasing viscosity of the solution in which the nanoparticles resided. The MSB estimated relaxation time matched the calculated relaxation times based on viscosity with 2% average error. Conclusions: MSB can be used to monitor the nanoparticle relaxation time quantitatively through a scale space correlation of the MSB signal as a function of frequency. PMID:22559648

Weaver, John B.; Kuehlert, Esra

2012-01-01

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

Inference of multiple earthquake cycle relaxation time scales from irregular geodetic sampling of interseismic deformation  

NASA Astrophysics Data System (ADS)

Characterizing and understanding the earthquake cycle is difficult due to the lack of high-resolution geodetic observations of duration comparable to that of characteristic earthquake recurrence intervals (100-10,000 years). Here we approach this problem by comparing long-term geologic slip rates with geodetically derived fault slip rates sampling only a short fraction (0.001-0.1%) of a complete earthquake cycle along 15 continental strike slip faults. Geodetic observations provide snapshots of surface deformation from different times through the earthquake cycle. The timing of the last earthquake on many of these faults is poorly known, and varies greatly from fault to fault. Assuming that the underlying mechanics of the seismic cycle are similar for many faults, taken as a whole, observations nearby different faults may be interpreted as stochastic samples over a significantly larger fraction of the earthquake cycle than could be obtained from the geodetic record at any one fault alone. As an ensemble, we find that geologic and geodetically inferred slip rates agree well with a linear relation of 0.94±0.05. To simultaneously explain both the ensemble agreement between geologic and geodetic slip rate estimates with observations of rapid postseismic deformation we consider the predictions from simple two-layer earthquake cycle models with both Maxwell and Burgers viscoelastic rheologies. We find that the two-layer Burgers model (with two relaxation timescales) is consistent with observations of deformation throughout the earthquake cycle while the widely used two-layer Maxwell model (single relaxation timescale) is not, suggesting that the earthquake cycle is effectively characterized by rapid postseismic stage and a much more slowly varying interseismic stage.

Meade, B. J.; Klinger, Y.; Hetland, E. A.

2012-12-01

10

Cracking in polymer glasses and evolution at zero stress: Highlighting discrete long time scale relaxations  

E-print Network

Fracture initiation in glassy polymers with no notch is studied together with the evolution at zero stress in the glassy state. Confocal microscopy observations and auto-correlation methods are used to characterize specimens of polymethyl methacrylate (PMMA) loaded at room temperature and subsequently unloaded. The evolution of the morphology and the location of the cracking submitted to elongation rate up to 8% are reported and analyzed during the zero-stress relaxation. The crackling (longitudinal crack, transverse crack and crazes) takes place mainly within a 10micron thickness layer from the surface and does not extend in the bulk. It is shown that the strain field continues to evolve without stress, and that it can be described by an intermittent retraction of the displacement field. Correlatively the number of crazes or of micro-cavities is increasing in the post-loading state at zero-stress relaxation. The timescales involved in the retraction are of the order of several days reporting thus on so far unknown very slow relaxation timescales.

S. Mbarek; P. Baroni; L. Noirez

2014-12-01

11

Relaxation time in disk galaxy simulations.  

NASA Technical Reports Server (NTRS)

An initially stationary and stable axisymmetric disk of stars with a mass spectrum of stars is used to determine the collisional relaxation time. The relaxation time as determined from the rate of energy equipartition was found to be 560 rotation periods for stars with 10 times the mean star mass and was 1700 rotation periods for stars with 0.55 times the mean star mass. These times are in general agreement with theoretical predictions for the relaxation time of the two mass groups. The results show that the model used for the large-scale gravitational N-body calculations is indeed 'collisionless.'

Hohl, F.

1973-01-01

12

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

13

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

14

Dynamic viscosity and material relaxation time during shock loading  

NASA Astrophysics Data System (ADS)

The dynamic viscosity and characteristic relaxation time at various scale-structural levels of deformation of a shock-loaded medium are determined using concepts of multilevel solid-state mechanics. The notion of the quasi-time fractal dimension is introduced and used to calculate the indicated characteristics. Computational-experimental data for the viscosity and relaxation time are given for three materials: M2 copper, AMg6 aluminum base alloy and Armco iron.

Savenkov, G. G.

2010-03-01

15

Structural Relaxation is a Scale-Free Process  

NASA Astrophysics Data System (ADS)

We show that in deeply supercooled liquids, structural relaxation proceeds via the accumulation of Eshelby events, i.e. local rearrangements that create long-ranged and anisotropic stresses in the surrounding medium. Such events must be characterized using tensorial observables and we construct an analytical framework to probe their correlations using local stress data. By analyzing numerical simulations, we then demonstrate that events are power-law correlated in space, with a time-dependent amplitude which peaks at the alpha relaxation time ??. This effect, which becomes stronger near the glass transition, results from the increasingly important role of local stress fluctuations in facilitating relaxation events. Our finding precludes the existence of any length scale beyond which the relaxation process decorrelates.

Lemaître, Anaël

2014-12-01

16

Structural Relaxation is a Scale-Free Process.  

PubMed

We show that in deeply supercooled liquids, structural relaxation proceeds via the accumulation of Eshelby events, i.e. local rearrangements that create long-ranged and anisotropic stresses in the surrounding medium. Such events must be characterized using tensorial observables and we construct an analytical framework to probe their correlations using local stress data. By analyzing numerical simulations, we then demonstrate that events are power-law correlated in space, with a time-dependent amplitude which peaks at the alpha relaxation time ?_{?}. This effect, which becomes stronger near the glass transition, results from the increasingly important role of local stress fluctuations in facilitating relaxation events. Our finding precludes the existence of any length scale beyond which the relaxation process decorrelates. PMID:25541780

Lemaître, Anaël

2014-12-12

17

Well-Posedness and Singular Limit of a Semilinear Hyperbolic Relaxation System with a Two-Scale Discontinuous Relaxation Rate  

NASA Astrophysics Data System (ADS)

Nonlinear hyperbolic systems with relaxations may encounter different scales of relaxation time, which is a prototype multiscale phenomenon that arises in many applications. In such a problem the relaxation time is of O(1) in part of the domain and very small in the remaining domain in which the solution can be approximated by the zero relaxation limit which can be solved numerically much more efficiently. For the Jin-Xin relaxation system in such a two-scale setting, we establish its wellposedness and singular limit as the (smaller) relaxation time goes to zero. The limit is a multiscale coupling problem which couples the original Jin-Xin system on the domain when the relaxation time is O(1) with its relaxation limit in the other domain through interface conditions which can be derived by matched interface layer analysis.As a result, we also establish the well-posedness and regularity (such as boundedness in sup norm with bounded total variation and L 1-contraction) of the coupling problem, thus providing a rigorous mathematical foundation, in the general nonlinear setting, to the multiscale domain decomposition method for this two-scale problem originally proposed in Jin et al. in Math. Comp. 82, 749-779, 2013.

Coquel, Frédéric; Jin, Shi; Liu, Jian-Guo; Wang, Li

2014-08-01

18

Relaxation therapy for insomnia: nighttime and day time effects  

Microsoft Academic Search

We compared day time functioning in college students with and without insomnia and explored changes in day time functioning after progressive relaxation (PR) treatment for insomnia. Students with insomnia (SWI; n=57) were compared to a control group of students not complaining of insomnia (SNI; n=61) on self-reported sleep variables and five questionnaires: Insomnia Impact Scale (IIS), Dysfunctional Beliefs and Attitudes

Melanie K Means; Kenneth L Lichstein; Michael T Epperson; Christopher T Johnson

2000-01-01

19

Scaling of the Structural Relaxation in Supercooled Fragile Liquids and Simulated Liquid Silica  

Microsoft Academic Search

We show that the structural relaxation time in supercooled fragile liquids obeys a scaling law over a large density-temperature domain. The extension of this scaling is also considered in the case of simulated liquid silica.

A. Le Grand; C. Dreyfus; C. Bousquet; R. Pick; J. Gapinski; A. Patkowski; W. Steffen

2008-01-01

20

Spin-Lattice Relaxation Times in 1H NMR Spectroscopy.  

ERIC Educational Resources Information Center

Discussed are the mechanisms of nuclear magnetic relaxation, and applications of relaxation times. The measurement of spin-lattice relaxations is reviewed. It is stressed that sophisticated techniques such as these are becoming more important to the working chemist. (CW)

Wink, Donald J.

1989-01-01

21

Multi-scale times and modes of fast and slow relaxation in solutions with coexisting spherical and cylindrical micelles according to the difference Becker-Döring kinetic equations.  

PubMed

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-Döring 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-Döring kinetic equation. They demonstrated a fair agreement even in the vicinity of the cmc2 where the analytical theory looses formally its applicability. PMID:25134593

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

2014-08-14

22

Multi-scale times and modes of fast and slow relaxation in solutions with coexisting spherical and cylindrical micelles according to the difference Becker-Döring kinetic equations  

NASA Astrophysics Data System (ADS)

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-Döring 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-Döring kinetic equation. They demonstrated a fair agreement even in the vicinity of the cmc2 where the analytical theory looses formally its applicability.

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

2014-08-01

23

Ageing and relaxation times in disordered insulators  

NASA Astrophysics Data System (ADS)

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

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

2012-07-01

24

A detailed test of mode-coupling theory on all time scales: Time domain studies of structural relaxation in a supercooled liquid  

E-print Network

The dynamics of supercooled salol phenyl salicylate was measured in the time domain using optical Kerr effect Schweidler power law, has an almost constant exponent of 0.59 over the entire temperature range studied 247­340 K . Above the MCT Tc T 1.17 Tg , where Tg is the laboratory glass transition temperature for t 1 ps

Fayer, Michael D.

25

Relaxation time measurements by an electronic method.  

NASA Technical Reports Server (NTRS)

Description of a simple electronic system that permits the direct measurement of time constants of decaying signals. The system was used in connection with relaxation experiments on hydrogen and rubidium masers and was found to operate well. The use of a computing counter in the systems gives the possibility of making averages on several experiments and obtaining the standard deviation of the results from the mean. The program for the computing counter is given.

Brousseau, R.; Vanier, J.

1973-01-01

26

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

27

Primary and secondary relaxation time dispersions in fragile supercooled liquids  

Microsoft Academic Search

The relaxation time dispersions of the primary (alpha) and secondary (beta) dielectric relaxations are studied for molecular glass-forming liquids regarding their dependence on structural relaxation time [or lack thereof observed as time-temperature superposition (TTS)], their changes with fragility, and a possible correlation of the values for the alpha and beta processes. Toward more fragile liquids, the width walpha of the

Li-Min Wang; Ranko Richert

2007-01-01

28

Magnetic field dependence of plasma relaxation times  

NASA Technical Reports Server (NTRS)

A previously derived Fokker-Planck collision integral for an electron plasma in a dc magnetic field is examined in the limit in which the Debye length is greater than the thermal gyroradius, which is in turn greater than the mean distance of closest approach. It is demonstrated that the collision integral can be satisfactorily approximated by the classical Landau value (which ignores the presence of a dc magnetic field) if the following replacement is made: In the Coulomb logarithm, the Debye length is replaced by the gyroradius. This induces a fundamental logarithmic dependence on magnetic field in the relaxation times. Numerical comparison of the asymptotic approximations with the previously derived exact results is made, and good agreement is found. The simplification this introduces into the description of collision processes in magnetized plasma is considerable.

Montgomery, D.; Joyce, G.; Turner, L.

1974-01-01

29

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

PubMed Central

To study microsecond processes by relaxation dispersion NMR spectroscopy, low power deposition and short pulses are crucial and encourage the development of experiments that employ 1H Carr?Purcell?Meiboom?Gill (CPMG) pulse trains. Herein, a method is described for the comprehensive study of microsecond to millisecond time scale dynamics of methyl groups in proteins, exploiting their high abundance and favorable relaxation properties. In our approach, protein samples are produced using [1H, 13C]-d-glucose in ?100% D2O, which yields CHD2 methyl groups for alanine, valine, threonine, isoleucine, leucine, and methionine residues with high abundance, in an otherwise largely deuterated background. Methyl groups in such samples can be sequence-specifically assigned to near completion, using 13C TOCSY NMR spectroscopy, as was recently demonstrated (Otten, R.; et al. J. Am. Chem. Soc.2010, 132, 2952?2960). In this Article, NMR pulse schemes are presented to measure 1H CPMG relaxation dispersion profiles for CHD2 methyl groups, in a vein similar to that of backbone relaxation experiments. Because of the high deuteration level of methyl-bearing side chains, artifacts arising from proton scalar coupling during the CPMG pulse train are negligible, with the exception of Ile-?1 and Thr-?2 methyl groups, and a pulse scheme is described to remove the artifacts for those residues. Strong 13C scalar coupling effects, observed for several leucine residues, are removed by alternative biochemical and NMR approaches. The methodology is applied to the transcriptional activator NtrCr, for which an inactive/active state transition was previously measured and the motions in the microsecond time range were estimated through a combination of backbone 15N CPMG dispersion NMR spectroscopy and a collection of experiments to determine the exchange-free component to the transverse relaxation rate. Exchange contributions to the 1H line width were detected for 21 methyl groups, and these probes were found to collectively report on a local structural rearrangement around the phosphorylation site, with a rate constant of (15.5 ± 0.5) × 103 per second (i.e., ?ex = 64.7 ± 1.9 ?s). The affected methyl groups indicate that, already before phosphorylation, a substantial, transient rearrangement takes place between helices 3 and 4 and strands 4 and 5. This conformational equilibrium allows the protein to gain access to the active, signaling state in the absence of covalent modification through a shift in a pre-existing dynamic equilibrium. Moreover, the conformational switching maps exactly to the regions that differ between the solution NMR structures of the fully inactive and active states. These results demonstrate that a cost-effective and quantitative study of protein methyl group dynamics by 1H CPMG relaxation dispersion NMR spectroscopy is possible and can be applied to study functional motions on the microsecond time scale that cannot be accessed by backbone 15N relaxation dispersion NMR. The use of methyl groups as dynamics probes extends such applications also to larger proteins. PMID:21058670

2010-01-01

30

Energy conversion of fully random thermal relaxation times Franois Barriquand  

E-print Network

1 Energy conversion of fully random thermal relaxation times François Barriquand proba5050@hotmail.com ABSTRACT. Thermodynamic random processes in thermal systems are generally associated with one or several relaxation times, the inverse of which are formally homogeneous with energy. Here, we show in a precise way

Paris-Sud XI, Université de

31

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

32

A Mesozoic time scale  

Microsoft Academic Search

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

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

1994-01-01

33

Interactive Geological Time Scale  

NSDL National Science Digital Library

This time scale allows students to select multiple time periods from a list and view them on a highlighted display. It shows the relationship between eon, era, period, sub-period, and epoch and also includes the date in mega-annum (Ma) or millions of years before present. The scale reflects the changes in the Cenozoic Era (Tertiary and Quaternary have been eliminated and the Neogene modified) in the most recent International Stratigraphic Charts.

34

Energy Conversion of Fully Random Thermal Relaxation Times  

E-print Network

Thermodynamic random processes in thermal systems are generally associated with one or several relaxation times, the inverse of which are formally homogeneous with energy. Here, we show in a precise way that the periodic modification of relaxation times during temperature-constant thermodynamic cycles can be thermodynamically beneficiary to the operator. This result holds as long as the operator who adjusts relaxation times does not attempt to control the randomness associated with relaxation times itself as a Maxwell 'demon' would do. Indirectly, our result also shows that thermal randomness appears satisfactorily described within a conventional quantum-statistical framework, and that the attempts advocated notably by Ilya Prigogine to go beyond a Hilbert space description of quantum statistics do not seem justified - at least according to the present state of our knowledge. Fundamental interpretation of randomness, either thermal or quantum mechanical, is briefly discussed.

François Barriquand

2005-07-26

35

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

36

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

37

Scaling between Structural Relaxation and Particle Caging in a Model Colloidal Gel  

E-print Network

In polymers melts and supercooled liquids, the glassy dynamics is characterized by the rattling of monomers or particles in the cage formed by their neighbors. Recently, a direct correlation in such systems, described by a universal scaling form, has been established between the rattling amplitude and the structural relaxation time. In this paper we analyze the glassy dynamics emerging from the formation of a persistent network in a model colloidal gel at very low density. The structural relaxation time of the gel network is compared with the mean squared displacement at short times, corresponding to the localization length associated to the presence of energetic bonds. Interestingly, we find that the same type of scaling as for the dense glassy systems holds. Our findings well elucidate the strong coupling between the cooperative rearrangements of the gel network and the single particle localization in the structure. Our results further indicate that the scaling captures indeed fundamental physical elements of glassy dynamics.

Cristiano De Michele; Emanuela Del Gado; Dino Leporini

2010-09-08

38

Universal divergenceless scaling between structural relaxation and caged dynamics in glass-forming systems.  

PubMed

On approaching the glass transition, the microscopic kinetic unit spends increasing time rattling in the cage of the first neighbors, whereas its average escape time, the structural relaxation time tau(alpha), increases from a few picoseconds up to thousands of seconds. A thorough study of the correlation between tau(alpha) and the rattling amplitude, expressed by the Debye-Waller factor, was carried out. Molecular-dynamics simulations of both a model polymer system and a binary mixture were performed by varying the temperature, the density rho, the potential and the polymer length to consider the structural relaxation as well as both the rotational and the translation diffusion. The present simulations, together with MD studies on other glassformers, evidence the scaling between the structural relaxation and the caged dynamics. An analytic model of the master curve is developed in terms of two characteristic length scales a(2) (1/2) and sigma(a(2) ) (1/2), pertaining to the distance to be covered by the kinetic unit to reach a transition state. The model does not imply tau(alpha) divergences. The comparison with the experiments supports the numerical evidence over a range of relaxation times as wide as about eighteen orders of magnitude. A comparison with other scaling and correlation procedures is presented. In particular, the density scaling of the length scales a(2) (1/2), sigma(a(2) ) (1/2) proportional to rho(-1/3) is shown to be not supported by the present simulations. The study suggests that the equilibrium and the moderately supercooled states of the glassformers possess key information on the huge slowing-down of their relaxation close to the glass transition. The latter, according to the present simulations, exhibits features consistent with the Lindemann melting criterion and the free-volume model. PMID:20001067

Ottochian, A; De Michele, C; Leporini, D

2009-12-14

39

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

SciTech Connect

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

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

1998-12-01

40

Measurement of longitudinal relaxation times for spin-decoupled protons.  

NASA Technical Reports Server (NTRS)

Description of an experimental method for the determination of the longitudinal relaxation time for spin-decoupled protons by a modified version of the saturation recovery technique reported by Van Geet and Hume (1965). The described method should facilitate relaxation studies of chemically shifted protons (or fluorines) and can be applied to more complicated spin systems with the aid of triple resonance and noise-decoupling techniques.

Gerace, M. J.; Kuhlmann, K. F.

1972-01-01

41

Subsecond pore-scale displacement processes and relaxation dynamics in multiphase flow  

NASA Astrophysics Data System (ADS)

recent advances at X-ray microcomputed tomography (?CT) synchrotron beam lines, it is now possible to study pore-scale flow in porous rock under dynamic flow conditions. The collection of four-dimensional data allows for the direct 3-D visualization of fluid-fluid displacement in porous rock as a function of time. However, even state-of-the-art fast-?CT scans require between one and a few seconds to complete and the much faster fluid movement occurring during that time interval is manifested as imaging artifacts in the reconstructed 3-D volume. We present an approach to analyze the 2-D radiograph data collected during fast-?CT to study the pore-scale displacement dynamics on the time scale of 40 ms which is near the intrinsic time scale of individual Haines jumps. We present a methodology to identify the time intervals at which pore-scale displacement events in the observed field of view occur and hence, how reconstruction intervals can be chosen to avoid fluid-movement-induced reconstruction artifacts. We further quantify the size, order, frequency, and location of fluid-fluid displacement at the millisecond time scale. We observe that after a displacement event, the pore-scale fluid distribution relaxes to (quasi-) equilibrium in cascades of pore-scale fluid rearrangements with an average relaxation time for the whole cascade between 0.5 and 2.0 s. These findings help to identify the flow regimes and intrinsic time and length scales relevant to fractional flow. While the focus of the work is in the context of multiphase flow, the approach could be applied to many different ?CT applications where morphological changes occur at a time scale less than that required for collecting a ?CT scan.

Armstrong, Ryan T.; Ott, Holger; Georgiadis, Apostolos; Rücker, Maja; Schwing, Alex; Berg, Steffen

2014-12-01

42

Evaluation of brain edema using magnetic resonance proton relaxation times  

SciTech Connect

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

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

1990-01-01

43

Mindfulness meditation and relaxation training increases time sensitivity.  

PubMed

Two experiments examined the effect of mindfulness meditation and relaxation on time perception using a temporal bisection task. In Experiment 1, the participants performed a temporal task before and after exercises of mindfulness meditation or relaxation. In Experiment 2, the procedure was similar than that used in Experiment 1, except that the participants were trained to mediate or relax every day over a period of several weeks. The results showed that mindfulness meditation exercises increased sensitivity to time and lengthened perceived time. However, this temporal improvement with meditation exercises was primarily observed in the experienced meditators. Our results also showed the experienced meditators were less anxious than the novice participants, and that the sensitivity to time increased when the level of anxiety decreased. Our results were explained by the practice of mindfulness technique that had developed individuals' abilities in devoting more attention resources to temporal information processing. PMID:25460243

Droit-Volet, S; Fanget, M; Dambrun, M

2015-01-01

44

Current fluctuations for totally asymmetric exclusion on the relaxation scale  

NASA Astrophysics Data System (ADS)

The fluctuations of the current for the one-dimensional totally asymmetric exclusion process with L sites are studied in the relaxation regime of times T? {{L}3/2}. Using Bethe ansatz for the periodic system with an evolution conditioned on special initial and final states, the Fourier transform of the probability distribution of the fluctuations is calculated exactly in the thermodynamic limit L\\to ? with finite density of particles. It is found to be equal to a sum over discrete realizations of a scalar field in a linear potential with coupling constant equal to the rescaled time T/{{L}3/2}.

Prolhac, Sylvain

2015-02-01

45

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.

46

Web Geologic Time Scale  

NSDL National Science Digital Library

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

1994-01-01

47

Analysis of White Noise Limits for Stochastic Systems with Two Fast Relaxation Times  

E-print Network

In this paper we present a rigorous asymptotic analysis for stochastic systems with two fast relaxation times. The mathematical model analyzed in this paper consists of a Langevin equation for the particle motion with time-dependent force constructed through an infinite dimensional Gaussian noise process. We study the limit as the particle relaxation time as well as the correlation time of the noise tend to zero and we obtain the limiting equations under appropriate assumptions on the Gaussian noise. We show that the limiting equation depends on the relative magnitude of the two fast time scales of the system. In particular, we prove that in the case where the two relaxation times converge to zero at the same rate there is a drift correction, in addition to the limiting It\\^{o} integral, which is not of Stratonovich type. If, on the other hand, the colored noise is smooth on the scale of particle relaxation then the drift correction is the standard Stratonovich correction. If the noise is rough on this scale then there is no drift correction. Strong (i.e. pathwise) techniques are used for the proof of the convergence theorems.

G. A. Pavliotis; A. M. Stuart

2005-04-16

48

Relaxation times of remanent magnetisation in lunar fines  

NASA Technical Reports Server (NTRS)

On the basis of an analysis of the magnetic parameters, it appears that the bulk of metallic Fe particles in the lunar fines are essentially spherical and have a short remanent relaxation time. These spherical metallic Fe particles could account for the apparently low blocking temperature observed for the unstable components of the natural remanent magnetization detected in the returned lunar samples.

Tsay, F.-D.

1973-01-01

49

Phenomenological Theory of the Translational Relaxation Times in Gases  

NASA Technical Reports Server (NTRS)

The exact solution to the classical equations governing the translational dispersion and absorption of sound in a gas obscures its relaxational character because of its mathematical complexity. The approach taken here is to solve the secular equation by the method of Pade approximants, which even to the relatively low order R(sub 11) yields a remarkably close approximation to the exact solution over a wide range of frequency/pressure (f/P) ratios. As a result, translational relaxation can be formulated in terms of a conventional relaxation process with well-defined relaxation times, relaxation strength, collision numbers, additivity relations, etc. To extend the theory to high values of f/P ratio, a model is proposed to account for the noncontinuum behavior of the transport coefficients (viscosity and thermal conductivity) as the molecular mean free path approaches the acoustical enclosure dimensions. The theoretical dispersion and absorption show good agreement with measurements in argon over the classical and transition regions of f/P, but a discrepancy appears at higher values of f/P, where collective propagating modes, assumed in the theory, give way to single-particle modes, prevailing in the experiments.

Zuckerwar, Allan J.

1999-01-01

50

Relaxed Time Slot Negotiation for Grid Resource Allocation  

NASA Astrophysics Data System (ADS)

Since participants in a computational grid may be independent bodies, some mechanisms are necessary for resolving the differences in their preferences for price and desirable time slots for utilizing/leasing computing resources. Whereas there are mechanisms for supporting price negotiation for grid resource allocation, there is little or no negotiation support for allocating mutually acceptable time slots for grid participants. The contribution of this work is designing a negotiation mechanism for facilitating time slot negotiations between grid participants. In particular, this work adopts a relaxed time slot negotiation protocol designed to enhance the success rate and resource utilization level by allowing some flexibility for making slight adjustments following a tentative agreement for a mutually acceptable time slot. The ideas of the relaxed time slot negotiation are implemented in an agent-based grid testbed, and empirical results of the relaxed time slot negotiation mechanism carried out, (i) a consumer and a provider agent have a mutually satisfying agreement on time slot and price, (ii) consumer agents achieved higher success rates in negotiation, and (iii) provider agents achieved higher utility and resource utilization of overall grid.

Son, Seokho; Sim, Kwang Mong

51

Viscous hydrodynamics relaxation time from AdS/CFT  

E-print Network

We consider an expanding boost-invariant plasma at strong coupling using the AdS/CFT correspondence for N=4 SYM. We determine the relaxation time in second order viscous hydrodynamics and find that it is around thirty times shorter than weak coupling expectations. We find that the nonsingularity of the dual geometry in the string frame necessitates turning on the dilaton which leads to a nonvanishing expectation value for tr F^2 behaving like tau^(-10/3).

Michal P. Heller; Romuald A. Janik

2007-10-12

52

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

53

Aerosol size spectrum analysis using relaxation time measurement  

NASA Technical Reports Server (NTRS)

An experimental method has been developed to measure the dynamic relaxation times of aerosol particles. The particle relaxation time (tau-p) is determined from the ratio of the velocity amplitude of an aerosol particle (v-p) to the velocity amplitude of the medium (u-g) while the aerosol is subjected to acoustic excitation of a known frequency. A differential laser Doppler velocimeter is used to measure v-p, while a microphone is used to measure u-g. From the value of tau-p, the aerodynamic diameter of the particle can be determined if the particle density is known. The method can be applied to real-time in situ measurement of size distribution of an aerosol containing both solid particles and liquid droplets in the range of 0.1-10.0-micron diameters.

Kirsch, K. J.; Mazumder, M. K.

1975-01-01

54

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

55

Relaxation time limits problem for hydrodynamic models in semiconductor science * * Supported by the Chinese Postdoctoral Science Foundation, the Young Scientists Funds of NSF of China (10401019), and the Tsinghua Basic Research Foundation  

Microsoft Academic Search

In this article, two relaxation time limits, namely, the momentum relaxation time limit and the energy relaxation time limit are considered. By the compactness argument, it is obtained that the smooth solutions of the multidimensional nonisentropic Euler–Poisson problem converge to the solutions of an energy transport model or a drift diffusion model, respectively, with respect to different time scales.

Yong Li

2007-01-01

56

Single particle aerodynamic relaxation time analyzer. [for aerosol pollutants  

NASA Technical Reports Server (NTRS)

An instrument employing a laser Doppler velocimeter and a microphone to measure the phase lag of the motion of aerosol particulates relative to the motion of the fluid medium within an acoustic field is described. The relaxation times and aerodynamic diameters of the particles or droplets are determined in real time from the measured values of phase lag; thus, the size analysis is independent of the electrostatic charges and refractive indices of the particulates. The instrument is suitable for analyzing the aerodynamic size spectrum of atmospheric particulate pollutants with aerodynamic diameters ranging from 0.1 to 10.0 microns.

Mazumder, M. K.; Kirsch, K. J.

1977-01-01

57

An electronic time scale in chemistry  

PubMed Central

Ultrafast, subfemtosecond charge migration in small peptides is discussed on the basis of computational studies and compared with the selective bond dissociation after ionization as observed by Schlag and Weinkauf. The reported relaxation could be probed in real time if the removal of an electron could be achieved on the attosecond time scale. Then the mean field seen by an electron would be changing rapidly enough to initiate the migration. Tyrosine-terminated tetrapeptides have a particularly fast charge migration where in <1 fs the charge arrives at the other end. A femtosecond pulse can be used to observe the somewhat slower relaxation induced by correlation between electrons of different spins. A slower relaxation also is indicated when removing a deeper-lying valence electron. When a chromophoric amino acid is at one end of the peptide, the charge can migrate all along the peptide backbone up to the N end, but site-selective ionization is probably easier to detect for tryptophan than for tyrosine. PMID:16636279

Remacle, F.; Levine, R. D.

2006-01-01

58

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

PubMed

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

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

2007-07-01

59

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

60

?-Scale decoupling of the mechanical relaxation and diverging shear wave propagation length scale in triphenylphosphite  

NASA Astrophysics Data System (ADS)

We have performed depolarized impulsive stimulated scattering experiments to observe shear acoustic phonons in supercooled triphenylphosphite (TPP) from ˜10-500 MHz. These measurements, in tandem with previously performed longitudinal and shear measurements, permit further analyses of the relaxation dynamics of TPP within the framework of the mode coupling theory. Our results provide evidence of ? coupling between the shear and longitudinal degrees of freedom up to a decoupling temperature Tc = 231 K. A lower bound length scale of shear wave propagation in liquids verified the exponent predicted by theory in the vicinity of the decoupling temperature.

Torchinsky, Darius H.; Johnson, Jeremy A.; Nelson, Keith A.

2012-05-01

61

A revised relaxation-time spectrum for Fennoscandia  

NASA Astrophysics Data System (ADS)

The Fennoscandian relaxation-time spectrum (RTS), first derived by McConnell (1968), is a classic data set in studies of glacial isostatic adjustment (GIA). We outline a new method for estimating an RTS from a set of strandline data, which is based on a damped least-squares solution for spherical harmonic coefficients associated with the strandline heights. In contrast to the Hankel transform approach outlined by McConnell (1968), the method does not require interpolation or extrapolation of the data, nor does it use the assumption that peripheral deformations are zero. We begin by applying the new approach to a suite of synthetic strandlines. These synthetic calculations quantify the effect on the RTS estimates of the common assumptions of free-decay uplift, an axisymmetric Fennoscandian deformation field, and the uncertainty introduced by limited spatial and temporal sampling of this field. Recently, the accuracy of the Sauramo (1958) strandline data upon which the McConnell (1968) RTS was based has been questioned (Wolf 1996); accordingly, we apply our new approach to a set of more robust strandline data published by Donner (1964, 1969, 1980, 1995) to compute a revised RTS for Fennoscandia. At high harmonic degrees (above 50), our new RTS is characterized by weak constraints, whereas McConnell's (1968) RTS suggests a significant reduction in relaxation times relative to the values at low degrees. This reduction was the basis for McConnell's (1968) inference of an elastic lithosphere. In contrast to this, we conclude that the trend is an artefact of the observational data set he adopted. At lower degrees, McConnell's (1968) relaxation-time estimates lie at the lower end of the range implied by the present analysis. To complete our study, we apply the techniques of linearized Bayesian inference to invert our newly derived RTS for mantle viscosity. We find that the RTS provides an estimate of ~ 5 x 10^20 Pa s for the volumetric mean viscosity in a region extending from the base of the lithosphere to about 550 km depth. Target regions which extend from the transition zone to ~ 1200 km depth are less well constrained; however, the average viscosity from the base of the lithosphere to 1200 km depth is consistent with the classic Haskell (1935) value of 10^21 Pa s for mantle viscosity. Finally, we demonstrate that viscosity models within the class inferred by Mitrovica & Forte (1997) from joint inversions of postglacial relaxation times associated with GIA and mantle convection observables simultaneously fit the revised Fennoscandian RTS.

Wieczerkowski, Karin; Mitrovica, Jerry X.; Wolf, Detlef

1999-10-01

62

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

63

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

NASA Astrophysics Data System (ADS)

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

Shin, Kaikou; Kuroda, Mitsuru; Natsuyama, Kouichi

64

The time correlation function perspective of NMR relaxation in proteins  

NASA Astrophysics Data System (ADS)

We applied over a decade ago the two-body coupled-rotator slowly relaxing local structure (SRLS) approach to NMR relaxation in proteins. One rotator is the globally moving protein and the other rotator is the locally moving probe (spin-bearing moiety, typically the 15N-1H bond). So far we applied SRLS to 15N-H relaxation from seven different proteins within the scope of the commonly used data-fitting paradigm. Here, we solve the SRLS Smoluchowski equation using typical best-fit parameters as input, to obtain the corresponding generic time correlation functions (TCFs). The following new information is obtained. For actual rhombic local ordering and main ordering axis pointing along C_{i - 1}^? - C_i^?, the measurable TCF is dominated by the (K,K') = (-2,2), (2,2), and (0,2) components (K is the order of the rank 2 local ordering tensor), determined largely by the local motion. Global diffusion axiality affects the analysis significantly when the ratio between the parallel and perpendicular components exceeds approximately 1.5. Local diffusion axiality has a large and intricate effect on the analysis. Mode-coupling becomes important when the ratio between the global and local motional rates falls below 0.01. The traditional method of analysis - model-free (MF) - represents a simple limit of SRLS. The conditions under which the MF and SRLS TCFs are the same are specified. The validity ranges of wobble-in-a-cone and rotation on the surface of a cone as local motions are determined. The evolution of the intricate Smoluchowski operator from the simple diffusion operator for a sphere reorienting in isotropic medium is delineated. This highlights the fact that SRLS is an extension of the established stochastic theories for treating restricted motions. This study lays the groundwork for TCF-based comparison between mesoscopic SRLS and atomistic molecular dynamics.

Shapiro, Yury E.; Meirovitch, Eva

2013-08-01

65

Dependence of Brownian and Néel relaxation times on magnetic field strength  

SciTech Connect

Purpose: In magnetic particle imaging (MPI) and magnetic particle spectroscopy (MPS) the relaxation time of the magnetization in response to externally applied magnetic fields is determined by the Brownian and Néel relaxation mechanisms. Here the authors investigate the dependence of the relaxation times on the magnetic field strength and the implications for MPI and MPS. Methods: The Fokker–Planck equation with Brownian relaxation and the Fokker–Planck equation with Néel relaxation are solved numerically for a time-varying externally applied magnetic field, including a step-function, a sinusoidally varying, and a linearly ramped magnetic field. For magnetic fields that are applied as a step function, an eigenvalue approach is used to directly calculate both the Brownian and Néel relaxation times for a range of magnetic field strengths. For Néel relaxation, the eigenvalue calculations are compared to Brown's high-barrier approximation formula. Results: The relaxation times due to the Brownian or Néel mechanisms depend on the magnitude of the applied magnetic field. In particular, the Néel relaxation time is sensitive to the magnetic field strength, and varies by many orders of magnitude for nanoparticle properties and magnetic field strengths relevant for MPI and MPS. Therefore, the well-known zero-field relaxation times underestimate the actual relaxation times and, in particular, can underestimate the Néel relaxation time by many orders of magnitude. When only Néel relaxation is present—if the particles are embedded in a solid for instance—the authors found that there can be a strong magnetization response to a sinusoidal driving field, even if the period is much less than the zero-field relaxation time. For a ferrofluid in which both Brownian and Néel relaxation are present, only one relaxation mechanism may dominate depending on the magnetic field strength, the driving frequency (or ramp time), and the phase of the magnetization relative to the applied magnetic field. Conclusions: A simple treatment of Néel relaxation using the common zero-field relaxation time overestimates the relaxation time of the magnetization in situations relevant for MPI and MPS. For sinusoidally driven (or ramped) systems, whether or not a particular relaxation mechanism dominates or is even relevant depends on the magnetic field strength, the frequency (or ramp time), and the phase of the magnetization relative to the applied magnetic field.

Deissler, Robert J., E-mail: rjd42@case.edu; Wu, Yong; Martens, Michael A. [Department of Physics, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, Ohio 44106 (United States)] [Department of Physics, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, Ohio 44106 (United States)

2014-01-15

66

Tailoring relaxation time spectrum in soft glassy materials  

NASA Astrophysics Data System (ADS)

Physical properties of out of equilibrium soft materials depend on time as well as deformation history. In this work we propose to transform this major shortcoming into gain by applying controlled deformation field to tailor the rheological properties. We take advantage of the fact that deformation field of a certain magnitude can prevent particles in an aging soft glassy material from occupying energy wells up to a certain depth, thereby populating only the deeper wells. We employ two soft glassy materials with dissimilar microstructures and demonstrate that increase in strength of deformation field while aging leads to narrowing of spectrum of relaxation times. We believe that, in principle, this philosophy can be universally applied to different kinds of glassy materials by changing nature and strength of impetus.

Kaushal, Manish; Joshi, Yogesh M.

2013-07-01

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

Regarding the Néel relaxation time constant in magnetorelaxometry  

NASA Astrophysics Data System (ADS)

Magnetorelaxometry (MRX) is a sensitive measurement technique frequently employed in biomedical applications for imaging magnetic nanoparticles (MNP). In this article, we employ a first principles model to investigate the effects of different iron oxide MNP sample properties on the Néel relaxation time constant ?N in magnetorelaxometry. Using this model, we determined that dipolar interactions start to have an impact on the MRX signal from Fe concentrations of 100 mmol/l and result in a smaller ?N. Additionally, the micromagnetic damping constant, closely related to ?N, was found to be between 0.0005 and 0.002 by comparison to an MRX measurement of iron oxide particles. This is significantly lower compared to the bulk value of 0.07 for this material.

Leliaert, J.; Coene, A.; Crevecoeur, G.; Vansteenkiste, A.; Eberbeck, D.; Wiekhorst, F.; Van Waeyenberge, B.; Dupré, L.

2014-10-01

69

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

SciTech Connect

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

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

2004-03-23

70

The effect of molecular relaxation processes in air on the rise time of sonic booms  

NASA Technical Reports Server (NTRS)

A theory is developed to explain the effect of molecular relaxation processes on the rise time of sonic booms. To determine the rise time of sonic booms, both O2 and N2 relaxation processes must be included. The N2 relaxation process delays the shock pressure reaching the maximum pressure, and the O2 relaxation process causes a shock profile to have a gentle slope. The N2 relaxation controls the lower part of overpressure; the O2 relaxation controls the higher part. The constant rise time curves show that the rise times increase as the overpressures and humidity decrease. The present approach gives longer rise times than those acquired by Bass et al. for given shock overpressures.

Kang, Jongmin; Pierce, Allan D.

1990-01-01

71

An axisymmetric multiple-relaxation-time lattice Boltzmann scheme  

NASA Astrophysics Data System (ADS)

A multiple-relaxation-time (MRT) lattice Boltzmann (LB) scheme developed for axisymmetric flows recovers the complete continuity and Navier-Stokes equations. This scheme follows the strategy of the standard D2Q9 model by using a single particle distribution function and a simple “collision-streaming” updating rule. The extra terms related to axisymmetry in the macroscopic equations are recovered by adding source terms into the LB equation, which are simple and involve no gradients. The compressible effect retained in the Navier-Stokes equations is recovered by introducing a term related to the reversed transformation matrix for MRT collision operator, so as to produce a correct bulk viscosity, making it suitable for compressible flows with high frequency and low Mach number. The validity of the scheme is demonstrated by testing the Hagen-Poiseuille flow and 3D Womersley flow, as well as the standing acoustic waves in a closed cylindrical chamber. The numerical experiments show desirable stability at low viscosities, enabling to simulate a standing ultrasound field in centimeters space.

Xie, Wenjun

2015-01-01

72

Determination of the Thermodynamic Scaling Exponent for Relaxation in Liquids from Static Ambient-Pressure Quantities  

NASA Astrophysics Data System (ADS)

An equation is derived that expresses the thermodynamic scaling exponent, ?, which superposes relaxation times ? and other measures of molecular mobility determined over a range of temperatures and densities, in terms of static physical quantities. The latter are available in the literature or can be measured at ambient pressure. We show for 13 materials, both molecular liquids and polymers, that the calculated ? are equivalent to the scaling exponents obtained directly by superpositioning. The assumptions of the analysis are that the glass transition Tg is isochronal (i.e., ?? is constant at Tg, which is true by definition) and that the pressure derivative of the glass temperature is given by the first Ehrenfest relation. The latter, derived assuming continuity of the entropy at the glass transition, has been corroborated for many glass-forming materials at ambient pressure. However, we find that the Ehrenfest relation breaks down at elevated pressure; this limitation is of no consequence herein, since the appeal of the new equation is its applicability to ambient-pressure data. The ability to determine, from ambient-pressure measurements, the scaling exponent describing the high-pressure dynamics extends the applicability of this approach to a broader range of materials. Since ? is linked to the intermolecular potential, the new equation thus provides ready access to information about the forces between molecules.

Casalini, R.; Roland, C. M.

2014-08-01

73

Relaxation-time measurement via a time-dependent helicity balance model  

SciTech Connect

A time-dependent helicity balance model applied to a spheromak helicity-injection experiment enables the measurement of the relaxation time during the sustainment phase of the spheromak. The experiment, the Helicity Injected Torus with Steady Inductive helicity injection (HIT-SI), studies spheromak formation and sustainment through inductive helicity injection. The model captures the dominant plasma behavior seen during helicity injection in HIT-SI by using an empirical helicity-decay rate, a time-dependent helicity-injection rate, and a composite Taylor state to model both the helicity content of the system and to calculate the resulting spheromak current. During single-injector operations, both the amplitude and the phase of the periodic rise and fall of the toroidal current are predicted by this model, with an exchange of helicity between the injector states and the spheromak state proposed as the causal mechanism. This phenomenon allows for the comparison of the delay between the current rises in the experiment and the numerical model, enabling a measurement of the relaxation time. The measured relaxation time of 4.8 {mu}s {+-} 2.8 {mu}s is shorter than the toroidal Alfven timescale. These results validate Hall MHD calculations of the Geospace Environmental Modeling challenge.

Wrobel, J. S.; Hansen, C. J.; Jarboe, T. R.; Smith, R. J.; Hossack, A. C.; Nelson, B. A.; Marklin, G. J.; Ennis, D. A.; Akcay, C.; Victor, B. S. [Department of Aeronautics and Astronautics, University of Washington, Seattle, Washington 98195 (United States)

2013-01-15

74

Noninvasive Temperature Measurement Using MRI Based on T2 Relaxation Time  

Microsoft Academic Search

Intraoperative temperature measurement using magnetic resonance imaging has shown a great value as a noninvasive method. T2 relaxation time is one of the magnetic resonance imaging (MRI) parameters, theoretically, it is related to temperatures and signal amplitudess. in this paper we tried to find the relationship between temperature and porcine liver's T2 relaxation time by using CPMG sequence under different

Yuhua Peng; Honghong Dong; Xiaoying Tang

2010-01-01

75

Relaxation of the vibrational distribution function in N2 time varying discharges  

E-print Network

L-185 Relaxation of the vibrational distribution function in N2 time varying discharges M dépopulation des bas niveaux. Abstract. 2014 Relaxation of the electron and vibrational distribution functions-discharges. In the discharge the vibrational temperature get bigger with the residence time for t 10-2 s. In the post

Paris-Sud XI, Université de

76

Viscosity and longest relaxation time of semi-dilute polymer solutions. I. Good solvent  

E-print Network

1185 Viscosity and longest relaxation time of semi-dilute polymer solutions. I. Good solvent M expliqués par un modèle de reptation classique. Abstract. 2014 The zero shear viscosity and longest concentration (4 c/c* 70), we find that : 2014 both the relative viscosity ~r and the longest relaxation time TR

Paris-Sud XI, Université de

77

Scaling of transverse nuclear magnetic relaxation due to magnetic nanoparticle aggregation  

PubMed Central

The aggregation of superparamagnetic iron oxide (SPIO) nanoparticles decreases the transverse nuclear magnetic resonance (NMR) relaxation time T2CP of adjacent water molecules measured by a Carr-Purcell-Meiboom-Gill (CPMG) pulse-echo sequence. This effect is commonly used to measure the concentrations of a variety of small molecules. We perform extensive Monte Carlo simulations of water diffusing around SPIO nanoparticle aggregates to determine the relationship between T2CP and details of the aggregate. We find that in the motional averaging regime T2CP scales as a power law with the number N of nanoparticles in an aggregate. The specific scaling is dependent on the fractal dimension d of the aggregates. We find T2CP?N?0.44 for aggregates with d = 2.2, a value typical of diffusion limited aggregation. We also find that in two-nanoparticle systems, T2CP is strongly dependent on the orientation of the two nanoparticles relative to the external magnetic field, which implies that it may be possible to sense the orientation of a two-nanoparticle aggregate. To optimize the sensitivity of SPIO nanoparticle sensors, we propose that it is best to have aggregates with few nanoparticles, close together, measured with long pulse-echo times. PMID:20689678

Brown, Keith A.; Vassiliou, Christophoros C.; Issadore, David; Berezovsky, Jesse; Cima, Michael J.; Westervelt, R. M.

2010-01-01

78

Scaling of transverse nuclear magnetic relaxation due to magnetic nanoparticle aggregation.  

PubMed

The aggregation of superparamagnetic iron oxide (SPIO) nanoparticles decreases the transverse nuclear magnetic resonance (NMR) relaxation time T2CP of adjacent water molecules measured by a Carr-Purcell-Meiboom-Gill (CPMG) pulse-echo sequence. This effect is commonly used to measure the concentrations of a variety of small molecules. We perform extensive Monte Carlo simulations of water diffusing around SPIO nanoparticle aggregates to determine the relationship between T2CP and details of the aggregate. We find that in the motional averaging regime T2CP scales as a power law with the number N of nanoparticles in an aggregate. The specific scaling is dependent on the fractal dimension d of the aggregates. We find T2CP?N-0.44 for aggregates with d = 2.2, a value typical of diffusion limited aggregation. We also find that in two-nanoparticle systems, T2CP is strongly dependent on the orientation of the two nanoparticles relative to the external magnetic field, which implies that it may be possible to sense the orientation of a two-nanoparticle aggregate. To optimize the sensitivity of SPIO nanoparticle sensors, we propose that it is best to have aggregates with few nanoparticles, close together, measured with long pulse-echo times. PMID:20689678

Brown, Keith A; Vassiliou, Christophoros C; Issadore, David; Berezovsky, Jesse; Cima, Michael J; Westervelt, R M

2010-10-01

79

Frequency dependence of MR relaxation times. II. Iron oxides.  

PubMed

The frequency dependence of T1 and T2 was measured for homogeneous suspensions of magnetite and iron oxyhydroxide particles in water with various concentrations of gelatin. The transverse relaxivity showed two types of behavior: (a) For magnetic particles, there was a rapid increase in T2 relaxivity with frequency, followed by a saturation plateau, which accorded with the Langevin magnetization function. From these curves, the magnetic moment of the particle domains was estimated to range from 0.8 to 6.3 x 10(4) Bohr magnetons. (b) For iron oxyhydroxide (ferritin, ferrihydrite, and akaganéite) particles, T2 relaxivity increased linearly with frequency, the slope of the increase characteristic for each particle. T2 relaxivity generally increased with increasing gelatin concentration, corresponding to the measured decrease in the water diffusion coefficient. For iron oxides, homogeneously distributed either as iatrogenic agents or endogenous biominerals, these findings may aid in the interpretation of in vivo relaxivity and the effect on MR imaging. PMID:8347958

Bulte, J W; Vymazal, J; Brooks, R A; Pierpaoli, C; Frank, J A

1993-01-01

80

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

81

Scaling of spin relaxation and angular momentum dissipation in permalloy nanowires  

NASA Astrophysics Data System (ADS)

We study the relationship between the damping (?) and the nonadiabaticity of the spin transport (?) in permalloy nanowires. ? is engineered by Ho doping, and from the characteristics of the current-induced domain-wall velocity, determined by high-resolution x-ray magnetic circular-dichroism photoemission electron microscopy, ? due to spin relaxation is measured. We find that ? scales with ? and conclude that the spin relaxation that leads to nonadiabatic spin torque originates from the same underlying mechanism as the angular momentum dissipation that causes viscous damping.

Moore, T. A.; Kläui, M.; Heyne, L.; Möhrke, P.; Backes, D.; Rhensius, J.; Rüdiger, U.; Heyderman, L. J.; Thiele, J.-U.; Woltersdorf, G.; Back, C. H.; Fraile Rodríguez, A.; Nolting, F.; Mentes, T. O.; Niño, M. Á.; Locatelli, A.; Potenza, A.; Marchetto, H.; Cavill, S.; Dhesi, S. S.

2009-10-01

82

Two typical time scales of the piston effect  

NASA Astrophysics Data System (ADS)

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

Carlès, Pierre; Dadzie, Kokou

2005-06-01

83

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

SciTech Connect

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

Tuncer, Enis [ORNL

2006-01-01

84

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

SciTech Connect

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

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

2006-01-01

85

Spin relaxation time dependence on optical pumping intensity in GaAs:Mn  

SciTech Connect

We analyze the dependence of electron spin relaxation time on optical pumping intensity in a partially compensated acceptor semiconductor GaAs:Mn using analytic solutions for the kinetic equations of the charge carrier concentrations. Our results are applied to previous experimental data of spin-relaxation time vs. excitation power for magnetic concentrations of approximately 10{sup 17}?cm{sup ?3}. The agreement of our analytic solutions with the experimental data supports the mechanism of the earlier-reported atypically long electron-spin relaxation time in the magnetic semiconductor.

Burobina, V. [Department of Physics and Astronomy, University of Utah, 115 South 1400 East, Salt Lake City, Utah 84112-0830 (United States); Binek, Ch. [Department of Physics and Astronomy, Nebraska Center for Materials and Nanoscience, Theodore Jorgensen Hall, 855 North 16th Street, University of Nebraska, P.O. Box 880299, Lincoln, Nebraska 68588-0299 (United States)

2014-04-28

86

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

87

Multi-scales nuclear spin relaxation of liquids in porous media  

NASA Astrophysics Data System (ADS)

The magnetic field dependence of the nuclear spin-lattice relaxation rate 1/T(?) is a rich source of dynamical information for characterizing the molecular dynamics of liquids in confined environments. Varying the magnetic field changes the Larmor frequency ?, and thus the fluctuations to which the nuclear spin relaxation is sensitive. Moreover, this method permits a more complete characterization of the dynamics than the usual measurements as a function of temperature at fixed magnetic field strength, because many common solvent liquids have phase transitions that may alter significantly the character of the dynamics over the temperature range usually studied. Further, the magnetic field dependence of the spin-lattice relaxation rate, 1/T(?), provides a good test of the theories that relate the measurement to the microdynamical behavior of the liquid. This is especially true in spatially confined systems where the effects of reduced dimensionality may force more frequent reencounters of the studied proton spin-bearing molecules with paramagnetic impurities at the pore surfaces that may alter the correlation functions that enter the relaxation equations in a fundamental way. We show by low field NMR relaxation that changing the amount of surface paramagnetic impurities leads to striking different pore-size dependences of the relaxation times T and T of liquids in pores. Here, we focus mainly on high surface area porous materials including calibrated porous silica glasses, granular packings, heterogeneous catalytic materials, cement-based materials and natural porous materials such as clay minerals and rocks. Recent highlights NMR relaxation works are reviewed for these porous materials, like continuous characterization of the evolving microstructure of various cementitious materials and measurement of wettability in reservoir carbonate rocks. Although, the recent applications of 2-dimensional T-T and T-z-store-T correlation experiments for characterization of water exchange in connected micropores of cement pastes are also outlined.

Korb, Jean-Pierre

2010-03-01

88

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

E-print Network

The thermal relaxation time ($\\tau_{\\kappa_{ee}}$) for the degenerate electron plasma has been calculated by incorporating non-Fermi liquid (NFL) corrections both for the thermal conductivity and specific heat capacity. Perturbative results are presented by making expansion in $T/m_D$ with next to leading order corrections (NLO). We see that the NLO NFL corrections further reduce the decrease in relaxation time due to the leading order (LO) correction.

Sreemoyee Sarkar; Abhee K. Dutt-Mazumder

2012-09-24

89

Statistical and scaling behavior of structural relaxation effects in phase-change memory (PCM) devices  

Microsoft Academic Search

The phase-change memory (PCM) technology represents one of the most attractive concepts for next generation data storage. PCM behavior is mainly limited by the structural relaxation (SR) and by the crystallization of an amorphous chalcogenide material: the ternary alloy Ge2Sb2Te5. SR is a local structural-rearrangement at the atomic\\/bonding scale and crystallization is the reaching of a periodic atomic structure. While

Mattia Boniardi; Daniele Ielmini; Simone Lavizzari; Andrea L. Lacaita; Andrea Redaelli; Agostino Pirovano

2009-01-01

90

Well-posedness and singular limit of a semilinear hyperbolic relaxation system with a two-scale discontinuous relaxation rate  

E-print Network

within one problem. One famous example is the space shuttle reentry problem in which the space shuttle relaxation parameter . Here the relaxation rate depends on the space variable x in the following way: (x challenges in PDEs and mathematical physics, a thorough mathematical analysis on the problem under study

Jin, Shi

91

Measurement of orientational relaxation times of OH in a flame using picosecond time-resolved polarization spectroscopy  

NASA Astrophysics Data System (ADS)

Picosecond time-resolved polarization spectroscopy in the ultraviolet has been used to measure relaxation times of the laser-induced optical anisotropy of OH in an atmospheric pressure flame. OH radicals were produced in the post flame gases of a methane/air flame. Transient signals from absorption in theA2?-X2? (0-0) electronic transition were studied by pump-probe experiments using different P- and Q-branch transitions. A theoretical approach has been developed to interpret experimentally observed transient signals in terms of the relaxations of molecular orientation and alignment. The observed effective relaxation times for these flame conditions are of the order of 240-590 ps depending on the rotational state. We found slightly larger values for the relaxation times of molecular orientation than for molecular alignment. These results are relevant to the interpretation and modeling of four-wave mixing spectra.

Dreizler, A.; Tadday, R.; Suvernev, A. A.; Himmelhaus, M.; Dreier, T.; Foggi, P.

1995-06-01

92

Measurement of orientational relaxation times of OH in a flame using picosecond time-resolved polarization spectroscopy  

NASA Astrophysics Data System (ADS)

Picosecond time-resolved polarization spectroscopy in the ultraviolet has been used to measure relaxation times of the laser-induced optical anisotropy of OH in an atmospheric pressure flame. OH radicals were produced in the post flame gases of a methane/air flame. Transient signals from absorption in theA 2?-X 2? (0-0) electronic transition were studied by pump-probe experiments using different P- and Q-branch transitions. A theoretical approach has been developed to interpret experimentally observed transient signals in terms of the relaxations of molecular orientation and alignment. The observed effective relaxation times for these flame conditions are of the order of 240-590 ps depending on the rotational state. We found slightly larger values for the relaxation times of molecular orientation than for molecular alignment. These results are relevant to the interpretation and modeling of four-wave mixing spectra.

Dreizler, A.; Tadday, R.; Suvernev, A. A.; Himmelhaus, M.; Dreier, T.; Foggi, P.

1995-06-01

93

Difference-NMR techniques for selection of components on the basis of relaxation times.  

PubMed

This work describes a numerical methodology to obtain more efficient relaxation filters to selectively retain or remove components based on relaxation times. The procedure uses linear combinations of spectra with various recycle or filter delays to obtain components that are both quantitative and pure. Modulation profiles are calculated assuming exponential relaxation behavior. The method is general and can be applied to a wide range of solution or solid-state NMR experiments including direct-polarization (DP), or filtered cross-polarization (CP) spectra. 13C NMR experiments on isotactic poly(1-butene) and dimethyl sulfone showed the utility of the technique for selectively suppressing peaks. PMID:12762984

Harris, Douglas J; de Azevedo, Eduardo R; Bonagamba, Tito J

2003-05-01

94

Advances in time-scale algorithms  

NASA Technical Reports Server (NTRS)

The term clock is usually used to refer to a device that counts a nearly periodic signal. A group of clocks, called an ensemble, is often used for time keeping in mission critical applications that cannot tolerate loss of time due to the failure of a single clock. The time generated by the ensemble of clocks is called a time scale. The question arises how to combine the times of the individual clocks to form the time scale. One might naively be tempted to suggest the expedient of averaging the times of the individual clocks, but a simple thought experiment demonstrates the inadequacy of this approach. Suppose a time scale is composed of two noiseless clocks having equal and opposite frequencies. The mean time scale has zero frequency. However if either clock fails, the time-scale frequency immediately changes to the frequency of the remaining clock. This performance is generally unacceptable and simple mean time scales are not used. First, previous time-scale developments are reviewed and then some new methods that result in enhanced performance are presented. The historical perspective is based upon several time scales: the AT1 and TA time scales of the National Institute of Standards and Technology (NIST), the A.1(MEAN) time scale of the US Naval observatory (USNO), the TAI time scale of the Bureau International des Poids et Measures (BIPM), and the KAS-1 time scale of the Naval Research laboratory (NRL). The new method was incorporated in the KAS-2 time scale recently developed by Timing Solutions Corporation. The goal is to present time-scale concepts in a nonmathematical form with as few equations as possible. Many other papers and texts discuss the details of the optimal estimation techniques that may be used to implement these concepts.

Stein, S. R.

1993-01-01

95

Time-dependent Jahn-Teller problem: Phonon-induced relaxation through conical intersection  

NASA Astrophysics Data System (ADS)

A theoretical study of time-dependent dynamical Jahn-Teller effect in an impurity center in a solid is presented. We are considering the relaxation of excited states in the E?e-problem through the conical intersection of the potential energy. A strict quantum-mechanical treatment of vibronic interactions with both the main Jahn-Teller active vibration and the nontotally symmetric phonons causing the energy loss is given. The applied method enables us to calculate the time-dependence of the distribution function of the basic configurational coordinate. We have performed a series of numerical calculations allowing us, among other relaxation features, to visualise the details of the relaxation through the conical intersection. In particular, we elucidate how the Slonczewski quantization of the states in the conical intersection affects the relaxation.

Pae, Kaja; Hizhnyakov, Vladimir

2014-12-01

96

Time-dependent Jahn-Teller problem: Phonon-induced relaxation through conical intersection.  

PubMed

A theoretical study of time-dependent dynamical Jahn-Teller effect in an impurity center in a solid is presented. We are considering the relaxation of excited states in the E?e-problem through the conical intersection of the potential energy. A strict quantum-mechanical treatment of vibronic interactions with both the main Jahn-Teller active vibration and the nontotally symmetric phonons causing the energy loss is given. The applied method enables us to calculate the time-dependence of the distribution function of the basic configurational coordinate. We have performed a series of numerical calculations allowing us, among other relaxation features, to visualise the details of the relaxation through the conical intersection. In particular, we elucidate how the Slonczewski quantization of the states in the conical intersection affects the relaxation. PMID:25527925

Pae, Kaja; Hizhnyakov, Vladimir

2014-12-21

97

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

NASA Astrophysics Data System (ADS)

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

Packwood, Daniel M.

2013-02-01

98

Stability of Rasch Scales over Time  

ERIC Educational Resources Information Center

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

Taylor, Catherine S.; Lee, Yoonsun

2010-01-01

99

Relation between the two-body entropy and the relaxation time in supercooled water  

NASA Astrophysics Data System (ADS)

The two-body excess entropy of supercooled water is calculated from the radial distribution functions obtained from computer simulation of the TIP4P model for different densities upon supercooling. This quantity is considered in connection with the relaxation time of the self intermediate scattering function. The relaxation time shows a mode coupling theory (MCT) behavior in the region of mild supercooling and a strong behavior in the deep supercooled region. We find here that the two-body entropy is connected to the relaxation time and shows a logarithmic behavior with an apparent asymptotic divergence at the mode coupling crossover temperature. There is also evidence of a change in behavior of the two-body entropy upon crossing from the fragile (hopping-free) state to the strong (hopping-dominated) state of supercooled water, and the relation that connects the two-body entropy and the relxation time in the MCT region no longer holds.

Gallo, P.; Rovere, M.

2015-01-01

100

Permeability estimation using relaxation time spectra derived from differential evolution inversion  

NASA Astrophysics Data System (ADS)

Permeability is an important indicator for reservoir evaluation, but there is no common model for permeability estimation at present. In this study, we have firstly briefly introduced the principle of time domain-induced polarization, and derived the relationship between relaxation time and pore diameter from the diffusion concentration distribution of pore fluid ions. Then the differential evolution algorithm was used to derive relaxation time spectra from the polarizability decay curve. Finally, a new integrated model with relaxation time spectra, porosity and formation factor was proposed to predict permeability. The results of the numerical simulation declare that the inversion accuracy of the differential evolution algorithm was clearly superior to the traditional singular value decomposition method, and the signal-to-noise ratio had little influence on the differential evolution algorithm. The results of permeability estimation from core samples indicate that the integrated estimation model proposed in this study could improve the accuracy of permeability estimation remarkably.

Liu, Xiaonan; Kong, Li; Zhang, Pu; Zhou, Kaibo

2014-02-01

101

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

102

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

103

Understanding generalized inversions of nuclear magnetic resonance transverse relaxation time in porous media  

NASA Astrophysics Data System (ADS)

The nuclear magnetic resonance transverse relaxation time T2, measured using the Carr-Purcell-Meiboom-Gill (CPMG) experiment, is a powerful method for obtaining unique information on liquids confined in porous media. Furthermore, T2 provides structural information on the porous material itself and has many applications in petrophysics, biophysics, and chemical engineering. Robust interpretation of T2 distributions demands appropriate processing of the measured data since T2 is influenced by diffusion through magnetic field inhomogeneities occurring at the pore scale, caused by the liquid/solid susceptibility contrast. Previously, we introduced a generic model for the diffusion exponent of the form -ant_e^k (where n is the number and te the temporal separation of spin echoes, and a is a composite diffusion parameter) in order to distinguish the influence of relaxation and diffusion in CPMG data. Here, we improve the analysis by introducing an automatic search for the optimum power k that best describes the diffusion behavior. This automated method is more efficient than the manual trial-and-error grid search adopted previously, and avoids variability through subjective judgments of experimentalists. Although our method does not avoid the inherent assumption that the diffusion exponent depends on a single k value, we show through simulation and experiment that it is robust in measurements of heterogeneous systems that violate this assumption. In this way, we obtain quantitative T2 distributions from complicated porous structures and demonstrate the analysis with examples of ceramics used for filtration and catalysis, and limestone of relevance to the construction and petroleum industries.

Mitchell, J.; Chandrasekera, T. C.

2014-12-01

104

Understanding generalized inversions of nuclear magnetic resonance transverse relaxation time in porous media.  

PubMed

The nuclear magnetic resonance transverse relaxation time T2, measured using the Carr-Purcell-Meiboom-Gill (CPMG) experiment, is a powerful method for obtaining unique information on liquids confined in porous media. Furthermore, T2 provides structural information on the porous material itself and has many applications in petrophysics, biophysics, and chemical engineering. Robust interpretation of T2 distributions demands appropriate processing of the measured data since T2 is influenced by diffusion through magnetic field inhomogeneities occurring at the pore scale, caused by the liquid/solid susceptibility contrast. Previously, we introduced a generic model for the diffusion exponent of the form -ante(k) (where n is the number and te the temporal separation of spin echoes, and a is a composite diffusion parameter) in order to distinguish the influence of relaxation and diffusion in CPMG data. Here, we improve the analysis by introducing an automatic search for the optimum power k that best describes the diffusion behavior. This automated method is more efficient than the manual trial-and-error grid search adopted previously, and avoids variability through subjective judgments of experimentalists. Although our method does not avoid the inherent assumption that the diffusion exponent depends on a single k value, we show through simulation and experiment that it is robust in measurements of heterogeneous systems that violate this assumption. In this way, we obtain quantitative T2 distributions from complicated porous structures and demonstrate the analysis with examples of ceramics used for filtration and catalysis, and limestone of relevance to the construction and petroleum industries. PMID:25494741

Mitchell, J; Chandrasekera, T C

2014-12-14

105

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

106

Private and Dynamic Time-Series Data Aggregation with Trust Relaxation  

E-print Network

Private and Dynamic Time-Series Data Aggregation with Trust Relaxation Iraklis Leontiadis, Kaoutar Elkhiyaoui, Refik Molva EURECOM, Sophia Antipolis, France {leontiad,elkhiyao,molva}@eurecom.fr Abstract smart meters. Smart meters can report accurately at specific time intervals energy, gas or water

107

Conductivity and relaxation time of porous silicon using the Kramers-Kronig relation  

NASA Astrophysics Data System (ADS)

To review the dielectric characteristics of porous silicon samples with various porosities, an equivalent circuit including a capacitor and parallel resistance was used. By applying AC voltage with a constant amplitude of 200 mV to the circuit and using impedance measurements of the samples between 10-100 KHz, the variations in the capacitance, dielectric function, refractive index, and resistance for the samples at room temperature and up to 350 °C were studied. The dielectric characteristics of the samples decreased with increasing frequency. In addition, with increasing temperature, the pore diameters increased, and the dielectric characteristics varied. In this paper, we demonstrate that the relaxation time and DC conductivity could be obtained using the Kramers-Kronig function and Hilbert transformation. Our results indicate that the relaxation time and DC conductivity increase with increasing porosity, and with increasing temperature, the relaxation time decreases and the DC conductivity increases.

Dariani, R. S.; Tavakoli, F.

2015-01-01

108

Effect of magnetic relaxation times on electromagnetic pulse shielding  

NASA Astrophysics Data System (ADS)

The penetration of an electromagnetic pulse (EMP) through a ferromagnetic conducting thin film is investigated for the case in which the magnetization of the material has a characteristic time delay tau. Both saturation and hysteresis effects of the magnetization are considered and the susceptibility is defined in the nonlinear region as dM/dh. It is found that the response time tau has a significant effect on the shielding factor with optimum shielding when tau is on the order of twice the rise time of the pulse.

Zayek, Francois; McKnight, Stephen W.; Vittoria, Carmine; Maisch, W.; Stauss, G.

1988-07-01

109

Measurement of a Long Electronic Spin Relaxation Time of Cesium Atoms in Superfluid Helium  

SciTech Connect

The longitudinal electronic spin relaxation time of Cs atoms optically polarized in superfluid helium (He II, 1.5 K) has been measured with special care to cope with a serious decrease in the number of Cs atoms in the observation region. This decrease, mainly caused by helium convection in introducing the atoms into He II by laser sputtering, was significantly reduced using a new atom implantation method. Combined with a careful correction for the number of atoms, we have determined the relaxation time to be 2.24(19) s or longer, roughly twice as long as that in solid He.

Furukawa, T.; Izumi, H.; Shimoda, T. [Department of Physics, Graduate School of Science, Osaka University, Osaka 560-0043 (Japan); Matsuo, Y.; Fukuyama, Y.; Kobayashi, T. [RIKEN, 2-1, Hirosawa, Wako-shi, Saitama 351-0198 (Japan); Hatakeyama, A. [Institute of Physics, Graduate School of Arts and Sciences, University of Tokyo, Komaba, Tokyo 153-8902 (Japan)

2006-03-10

110

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

111

Elongational Flow of Blends of Long and Short Polymers: Effective Stretch Relaxation Time  

NASA Astrophysics Data System (ADS)

We study the onset of chain stretch and emergent extension hardening in the nonlinear rheological response of molten binary blends of long and short polymers. We predict that, upon dilution with short chains, the effective stretch relaxation time of the long chains initially increases in proportion to ?L-? (where ?L is the volume fraction of long chains and ? is the dilution exponent for entanglements). We confirm this behavior experimentally, in a set of experiments that measure both the dilution exponent from linear rheology and the effective stretch relaxation time under extensional flow.

Auhl, Dietmar; Chambon, Pierre; McLeish, Tom C. B.; Read, Daniel J.

2009-09-01

112

Time Domain Optical Studies of Dynamics in Supercooled o-Terphenyl: Comparison to Mode Coupling Theory on Fast and Slow Time Scales  

E-print Network

of temperatures and time scales using optical heterodyne detected optical Kerr effect techniques. A combination times the relaxation data show a temperature independent shape in the temperature regime 361-290 K. When plotted vs temperature, the long time decay constants scaled by a relationship given by MCT fall on a line

Fayer, Michael D.

113

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

114

Long-time relaxation of ion-bombarded silicon studied with the kinetic activation-relaxation technique: Microscopic description of slow aging in a disordered system  

NASA Astrophysics Data System (ADS)

Diffusion and relaxation of defects in bulk systems is a complex process that can only be accessed directly through simulations. We characterize the mechanisms of low-temperature aging in self-implanted crystalline silicon, a model system used extensively to characterize both amorphization and return to equilibrium processes, over 11 orders of magnitudes in time, from 10 ps to 1 s, using a combination of molecular dynamics and kinetic activation-relaxation technique simulations. These simulations allow us to reassess the atomistic mechanisms responsible for structural relaxations and for the overall logarithmic relaxation, a process observed in a large number of disordered systems and observed here over the whole simulation range. This allows us to identify three microscopic regimes, annihilation, aggregation, and reconstruction, in the evolution of defects and to propose atomistic justification for an analytical model of logarithmic relaxation. Furthermore, we show that growing activation barriers and configurational space exploration are kinetically limiting the system to a logarithmic relaxation. Overall, our long-time simulations do not support the amorphous cluster model but point rather to a relaxation driven by elastic interactions between defect complexes of all sizes.

Béland, Laurent Karim; Mousseau, Normand

2013-12-01

115

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

116

Scaling and alpha-helix regulation of protein relaxation in a lipid bilayer.  

PubMed

Protein conformation and orientation in the lipid membrane plays a key role in many cellular processes. Here we use molecular dynamics simulation to investigate the relaxation and C-terminus diffusion of a model helical peptide: beta-amyloid (A?) in a lipid membrane. We observed that after the helical peptide was initially half-embedded in the extracelluar leaflet of phosphatidylcholine (PC) or PC/cholesterol (PC/CHOL) membrane, the C-terminus diffused across the membrane and anchored to PC headgroups of the cytofacial lipid leaflet. In some cases, the membrane insertion domain of the A? was observed to partially unfold. Applying a sigmoidal fit to the process, we found that the characteristic velocity of the C-terminus, as it moved to its anchor site, scaled with ?u (-4/3), where ?u is the fraction of the original helix that was lost during a helix to coil transition. Comparing this scaling with that of bead-spring models of polymer relaxation suggests that the C-terminus velocity is highly regulated by the peptide helical content, but that it is independent of the amino acid type. The A? was stabilized by the attachment of the positive Lys28 side chain to the negative phosphate of PC or 3? oxygen of CHOL in the extracellular lipid leaflet and of the C-terminus to its anchor site in the cytofacial lipid leaflet. PMID:25494768

Qiu, Liming; Buie, Creighton; Cheng, Kwan Hon; Vaughn, Mark W

2014-12-14

117

Scaling and alpha-helix regulation of protein relaxation in a lipid bilayer  

NASA Astrophysics Data System (ADS)

Protein conformation and orientation in the lipid membrane plays a key role in many cellular processes. Here we use molecular dynamics simulation to investigate the relaxation and C-terminus diffusion of a model helical peptide: beta-amyloid (A?) in a lipid membrane. We observed that after the helical peptide was initially half-embedded in the extracelluar leaflet of phosphatidylcholine (PC) or PC/cholesterol (PC/CHOL) membrane, the C-terminus diffused across the membrane and anchored to PC headgroups of the cytofacial lipid leaflet. In some cases, the membrane insertion domain of the A? was observed to partially unfold. Applying a sigmoidal fit to the process, we found that the characteristic velocity of the C-terminus, as it moved to its anchor site, scaled with ?u-4/3, where ?u is the fraction of the original helix that was lost during a helix to coil transition. Comparing this scaling with that of bead-spring models of polymer relaxation suggests that the C-terminus velocity is highly regulated by the peptide helical content, but that it is independent of the amino acid type. The A? was stabilized by the attachment of the positive Lys28 side chain to the negative phosphate of PC or 3? oxygen of CHOL in the extracellular lipid leaflet and of the C-terminus to its anchor site in the cytofacial lipid leaflet.

Qiu, Liming; Buie, Creighton; Cheng, Kwan Hon; Vaughn, Mark W.

2014-12-01

118

? relaxation and low-temperature aging in a Au-based bulk metallic glass: From elastic properties to atomic-scale structure  

NASA Astrophysics Data System (ADS)

The slow ? relaxation is understood to be a universal feature of glassy dynamics. Its presence in bulk metallic glasses (BMGs) is evidence of a broad relaxation time spectrum that extends to deep within the glassy state. Despite the breadth of research devoted to this phenomenon, its microscopic origin is still not fully understood. The low-temperature aging behavior and atomic structural rearrangements of a Au49Cu26.9Si16.3Ag5.5Pd2.3 BMG are investigated in the regime of the slow ? relaxation by employing an ensemble of experimental techniques such as high-intensity synchrotron x-ray scattering, modulated differential scanning calorimetry (MDSC), dynamic mechanical analysis (DMA), impulse excitation, and dilatometry. Evidence of a distinct slow ?-relaxation regime is seen in the form of (1) an excess wing of the DMA loss modulus beginning at ˜50 ?C, (2) a crossover effect of elastic modulus with isothermal aging at 50?C, and (3) a broad, nonreversing and largely irreversible sub-Tg endotherm in the MDSC results. Atomic rearrangements occurring at the onset of the measured slow ?-relaxation temperature regime were found to be confined mainly to the short-range order length scale while no significant atomic rearrangements occur on the length scale of the medium-range order. Furthermore, evidence is presented that suggests the crossover effect in Young's modulus is due to the evolution of chemical short-range order. These results support the emergent picture of a dynamically heterogeneous glassy structure, in which low-temperature relaxation occurs through atomic rearrangements confined mostly to the short-range order length scale.

Evenson, Z.; Naleway, S. E.; Wei, S.; Gross, O.; Kruzic, J. J.; Gallino, I.; Possart, W.; Stommel, M.; Busch, R.

2014-05-01

119

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

E-print Network

We show that a system of hard discs 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 Adams-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 discs, successfully describes the fragile-strong crossover.

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

2012-10-22

120

Longitudinal complex magnetic susceptibility and relaxation times of superparamagnetic particles with triaxial anisotropy  

NASA Astrophysics Data System (ADS)

The longitudinal relaxation time and spectrum of the complex magnetic susceptibility of single domain ferromagnetic particles with triaxial (orthorhombic) anisotropy are calculated by averaging the Gilbert-Langevin equation for the magnetization of an individual particle and by reducing the problem to that of solving a system of linear differential-recurrence relations for the appropriate equilibrium correlation functions. The solution of this system is obtained in terms of matrix continued fractions. It is shown that in contrast to the linear magnetic response of particles with uniaxial anisotropy, there is an inherent geometric dependence of the complex susceptibility and the relaxation time on the damping parameter arising from coupling of longitudinal and transverse relaxation modes. Simple analytic equations, which allow one to understand the qualitative behavior of the system and to accurately predict the spectrum of the longitudinal complex susceptibility in wide ranges of the barrier height and dissipation parameters, are proposed.

Kalmykov, Yuri P.; Ouari, Bachir

2005-03-01

121

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

122

Ageing and relaxation times in disordered insulators , J. Delahaye1  

E-print Network

at extracting "characteristic times" for the glassy systems (granular aluminum, doped indium oxide...). We show aluminum films). They manifest themselves as a temporal logarithmic decrease of the conductance after of the dynamical properties of the system. We stress that the formation of a second field effect anomaly

Paris-Sud XI, Université de

123

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

124

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

PubMed

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. PMID:24938418

Klimavicius, Vytautas; Gdaniec, Zofia; Balevicius, Vytautas

2014-11-11

125

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

126

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

E-print Network

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.

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

2014-12-04

127

Relaxation time of an adsorbing 4He film  

NASA Astrophysics Data System (ADS)

The readsorption of 4He atoms on a constantan heater surface was studied after flash desorption by the heat pulse technique. The replenishment of the desorbed film after the heat pulse was found to be essentially linear with the time between the pulses, reaching saturation at some critical value, trc, which strongly depended on the pressure in the vapor, Pg. With the help of kinetic theory for the flux of atoms striking a surface, the measured value of trc could be calibrated to give Pg. We have verified this formula directly and used it to measure pressures down to 10 -9 Torr.

Sinvani, M.; Goodstein, D.

1983-02-01

128

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

129

Option pricing during post-crash relaxation times  

NASA Astrophysics Data System (ADS)

This paper presents a model for option pricing in markets that experience financial crashes. The stochastic differential equation (SDE) of stock price dynamics is coupled to a post-crash market index. The resultant SDE is shown to have stock price and time dependent volatility. The partial differential equation (PDE) for call prices is derived using risk-neutral pricing. European call prices are then estimated using Monte Carlo and finite difference methods. Results of the model show that call option prices after the crash are systematically less than those predicted by the Black-Scholes model. This is a result of the effect of non-constant volatility of the model that causes a volatility skew.

Dibeh, Ghassan; Harmanani, Haidar M.

2007-07-01

130

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

131

Relaxation Time of a Chiral Quantum R-L Circuit J. Gabelli,1  

E-print Network

Relaxation Time of a Chiral Quantum R-L Circuit J. Gabelli,1 G. Fe`ve,1 T. Kontos,1 J.-M. Berroir,1 by edge states in the quantum Hall regime. The circuit consists of a wide Hall bar (the inductor L) in series with a tunable resistor (R) formed by a quantum point contact. Electron interactions between edges

132

Measured Relaxation Times for the Uniaxial-Anisotropy Spectrum in Nonmagnetostrictive Permalloy Films  

Microsoft Academic Search

The relaxation time ? for realignment of an atomic anisotropy by 90° has been measured for a number of fast processes (?<103 sec) occurring in nonmagnetostrictive Permalloy films. The method of measurement utilizes the magnetoresistance effect and is described in detail elsewhere. For films deposited between 23° and 200°C at 10?6 to 10?5 Torr and measured at the same temperature

D. O. Smith; G. P. Weiss; K. J. Harte

1966-01-01

133

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

Microsoft Academic Search

A compression apparatus for aging experiments on soft rubbers and foams is presented. The sample is compressed between two parallel surfaces and held there for long-time relaxation studies. The specific purpose of the test is twofold: possible exposure of the sample to aggressive environment under compression during aging and measurement of sample modulus without unloading, i.e., while leaving the sample

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

2003-01-01

134

ANALYSIS OF WHITE NOISE LIMITS FOR STOCHASTIC SYSTEMS WITH TWO FAST RELAXATION TIMES  

E-print Network

ANALYSIS OF WHITE NOISE LIMITS FOR STOCHASTIC SYSTEMS WITH TWO FAST RELAXATION TIMES G. A. Key words. white noise limits, Ornstein-Uhlenbeck process, Kraichnan model, Wong­Zakai theorem AMS it is not realistic to model it is as a white noise process. The term colored noise is used for such a noise process

Pavliotis, Grigorios

135

Quantitative Assessment of Image Segmentation Quality by Random Walk Relaxation Times  

E-print Network

Quantitative Assessment of Image Segmentation Quality by Random Walk Relaxation Times Bjoern Andres of Heidelberg, Germany 2 Weizmann Institute of Science, Israel Abstract. The purpose of image segmentation is to partition the pixel grid of an image into connected components termed segments such that (i) each segment

Hamprecht, Fred A.

136

The Kerr constants and relaxation times in the isotropic phase of nematic homologous series  

Microsoft Academic Search

The anisotropy of the refractive index and of the dielectric constant for cyanobiphenyl homologous compounds has been measured. From these results, it is pointed out that the alternation of the Kerr constants and relaxation times with the carbon chain length are due to the variation of the coefficient a of the Landau expansion of the compounds.

R. Yamamoto; S. Ishihara; S. Hayakawa; K. Morimoto

1978-01-01

137

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

E-print Network

to the Relaxation Time for t. he F)uorine Temperature (deRrees centiRrade) (T1FI (T1FDD1 IT1VI SR 1 (seconcls) (seconds) (second. , ) -20 -10 0. 311 0. 319 0 192 0. 166 0. 119 0. 152 0. 331 0. 144 0. 187 10 20 30 40 50 0, 347 0. 360 0. 374 0...

Faulk, Robert Hardy

2012-06-07

138

MRI of bone marrow in the distal radius: in vivo precision of effective transverse relaxation times  

Microsoft Academic Search

The effective transverse relaxation time T2* is influenced by the presence of trabecular bone, and can potentially provide a measure of bone density as well as bone structure. We determined the in vivo precision of T2* in repeated bone marrow measurements. The T2* measurements of the bone marrow of the distal radius were performed twice within 2 weeks in six

Stephan Grampp; Sharmila Majumdar; Michael Jergas; Philipp Lang; Alice Gies; Harry K. Genant

1995-01-01

139

Capacity enhancement of wavelength/time/space asynchronous optical CDMA with relaxed cross-correlation  

NASA Astrophysics Data System (ADS)

The analysis of a three-dimensional (3-D) wavelength/time/space (W-T-S) asynchronous optical CDMA code family is presented considering MAI only under relaxed cross-correlation (?c ? 1). Based on the code performance, it is shown that for code-limited systems (when W and/or T are non-prime), the number of generated codes and hence the supported users can be significantly increased by relaxing the cross-correlation constraint if a slight degradation in code performance can be tolerated.

Singh, Jaswinder

2013-12-01

140

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

141

Isovolumic relaxation time varies predictably with its time constant and aortic and left atrial pressures: implications for the noninvasive evaluation of ventricular relaxation.  

PubMed

The isovolumic relaxation time (IVRT) is an important noninvasive index of left ventricular diastolic function. Despite its widespread use, however, the IVRT has not been related analytically to invasive parameters of ventricular function. Establishing such a relationship would make the IVRT more useful by itself and perhaps allow it to be combined more precisely with other noninvasive parameters of ventricular filling. The purpose of this study was to validate such a quantitative relationship. Assuming isovolumic relaxation to be a monoexponential decay of ventricular pressure (pv) to a zero-pressure asymptote, it was postulated that the time interval from aortic valve closure (when pv = p(o)) until mitral valve opening (when pv = left atrial pressure, pA) would be given analytically by IVRT = tau[log(p(o))-log(pA)], where tau is the time constant of isovolumic relaxation and log is to the base e. To test this hypothesis we analyzed data from six canine experiments in which ventricular preload and afterload were controlled nonpharmacologically. In addition, tau was adjusted with the use of beta-adrenergic blockade and calcium infusion, as well as with hypothermia. In each experiment data were collected before and after the surgical formation of mitral stenosis, performed to permit the study of a wide range of left atrial pressures. High-fidelity left atrial, left ventricular, and aortic root pressures were digitized, the IVRT was measured from the aortic dicrotic notch until the left atrioventricular pressure crossover point, and tau was calculated by nonlinear least-squares regression.(ABSTRACT TRUNCATED AT 250 WORDS) PMID:1442500

Thomas, J D; Flachskampf, F A; Chen, C; Guererro, J L; Picard, M H; Levine, R A; Weyman, A E

1992-11-01

142

Damping dependence of the magnetization relaxation time of single-domain ferromagnetic particles  

NASA Astrophysics Data System (ADS)

The relaxation time of the magnetization of single-domain ferromagnetic particles with cubic and triaxial (i.e., orthorhombic) magnetocrystalline anisotropy is estimated for all dissipation regimes, i.e., very low damping (VLD), intermediate-to-high damping (IHD), and turnover, using the method of Coffey et al. (Adv. Chem. Phys. 117 (2001) 483; Phys. Rev. E 63 (2001) 021102). Their method generalizes the Mel'nikov-Meshkov approach (J. Chem. Phys. 85 (1986) 1018) for bridging the VLD and IHD Kramers' escape rates for mechanical Brownian particles (the Kramers' turnover problem) to the analogous magnetic turnover problem. It is shown that the simple asymptotic formulae for the greatest relaxation time so obtained are in complete agreement with the relaxation time calculated from the infinite hierarchy of linear differential-recurrence equations for the statistical moments. This hierarchy, which governs the relaxation of the magnetization of an individual particle, is derived by averaging the underlying stochastic Landau-Lifshitz-Gilbert equation over its realizations. The exact solution of the system of moment equations is obtained by matrix continued fractions.

Kalmykov, Yuri P.; Coffey, William T.; Ouari, Bachir; Titov, Sergey V.

2005-04-01

143

Relaxation times of the two-phonon processes with spin-flip and spin-conserving in quantum dots  

SciTech Connect

We perform a theoretical investigation on the two-phonon processes of the spin-flip and spin-conserving relaxation in quantum dots in the frame of the Huang-Rhys' lattice relaxation model. We find that the relaxation time of the spin-flip is two orders of magnitude longer than that of the spin-conserving, which is in agreement with previous experimental measurements. Moreover, the opposite variational trends of the relaxation time as a function of the energy separation for two-phonon processes are obtained in different temperature regime. The relaxation times display the oscillatory behaviors at the demarcation point with increasing magnetic field, where the energy separation matches the optical phonon energy and results in the optical phonon resonance. These results are useful in understanding the intraband levels' relaxation in quantum dots and could be helpful in designing photoelectric and spin-memory devices.

Wang, Zi-Wu, E-mail: zwwang@semi.ac.cn [Tianjin Key Laboratory of Low Dimensional Materials Physics and Preparing Technology, Department of Physics, Tianjin University, Tianjin 300072 (China); Liu, Lei [Suzhou Institute of Nano-Tech and Nano-Bionics, CAS, Suzhou 215125 (China); Li, Shu-Shen [Institute of Semiconductor, CAS, Beijing 100083 (China)

2014-04-07

144

Sensitivity of proton NMR relaxation times in a HTPB based polyurethane elastomer to thermo-oxidative aging.  

SciTech Connect

Solid-state {sup 1}H NMR relaxometry studies were conducted on a hydroxy-terminated polybutadiene (HTPB) based polyurethane elastomer thermo-oxidatively aged at 80 C. The {sup 1}H T{sub 1}, T{sub 2}, and T{sub 1{rho}} relaxation times of samples thermally aged for various periods of time were determined as a function of NMR measurement temperature. The response of each measurement was calculated from a best-fit linear function of the relaxation time vs. aging time. It was found that the T{sub 2,H} and T{sub 1{rho},H} relaxation times exhibited the largest response to thermal degradation, whereas T{sub 1,H} showed minimal change. All of the NMR relaxation measurements on solid samples showed significantly less sensitivity to thermal aging than the T{sub 2,H} relaxation times of solvent-swollen samples.

Assink, Roger Alan; Mowery, Daniel Michael; Celina, Mathias Christopher

2004-09-01

145

An MR imaging method for simultaneous measurement of gaseous diffusion constant and longitudinal relaxation time  

Microsoft Academic Search

A magnetic resonance imaging method for simultaneous and accurate determination of gaseous diffusion constant and longitudinal relaxation time is presented. The method is based on direct observation of diffusive motion. Initially, a slice-selective saturation of helium-3 (3He) spins was performed on a 3He\\/O2 phantom (9 atm\\/ 2 atm). A time-delay interval was introduced after saturation, allowing spins to diffuse in

Ivan E. Dimitrov; Sridhar R. Charagundla; Rahim Rizi; Ravinder Reddy; John S. Leigh

1999-01-01

146

Temperature dependence of 1H NMR relaxation time, T2, for intact and neoplastic plant tissues  

NASA Astrophysics Data System (ADS)

Temperature dependences of the spin-spin proton relaxation time, T2, have been shown for normal and tumorous tissues collected from kalus culture Nicotiana tabacum and from the plant Kalanchoe daigremontiana. For neoplastic plant tissues, time T2 was increased compared to that for intact plants, a finding similar to that for animal and human tissues. The temperature dependences obtained were compared to analogous relations observed with animal tissues.

Lewa, Czes?aw J.; Lewa, Maria

147

Measurement of hot electron momentum relaxation times in metals by femtosecond ellipsometry  

NASA Astrophysics Data System (ADS)

Time-resolved ellipsometric measurements were made upon Au, Cu, Ag, Ni, Pd, Ti, Zr, and Hf thin films. Using an elliptically polarized pump beam, the decay of the optically induced polarization of the sample was observed. Characteristic relaxation times are extracted and interpreted in terms of scattering of linear and angular momentum of hot electrons. A systematic variation is observed between different metals that reflects their underlying band structure.

Kruglyak, V. V.; Hicken, R. J.; Ali, M.; Hickey, B. J.; Pym, A. T. G.; Tanner, B. K.

2005-06-01

148

ParaScale: Exploiting Parametric Timing Analysis for Real-Time Schedulers and Dynamic Voltage Scaling  

E-print Network

ParaScale: Exploiting Parametric Timing Analysis for Real-Time Schedulers and Dynamic Voltage for dynamic power conservation by exploiting parametric loop bounds for ParaScale, our intra-task dynamic voltage scaling (DVS) approach. Our results demonstrate that the parametric approach to timing analysis

Mueller, Frank

149

Wavelength dependence of electronic relaxation in isolated adenine using UV femtosecond time-resolved photoelectron spectroscopy.  

PubMed

Electronic relaxation pathways in photoexcited nucleobases have received much theoretical and experimental attention due to their underlying importance to the UV photostability of these biomolecules. Multiple mechanisms with different energetic onsets have been proposed by ab initio calculations yet the majority of experiments to date have only probed the photophysics at a few selected excitation energies. We present femtosecond time-resolved photoelectron spectra (TRPES) of the DNA base adenine in a molecular beam at multiple excitation energies between 4.7-6.2 eV. The two-dimensional TRPES data is fit globally to extract lifetimes and decay associated spectra for unambiguous identification of states participating in the relaxation. Furthermore, the corresponding amplitude ratios are indicative of the relative importance of competing pathways. We adopt the following mechanism for the electronic relaxation of isolated adenine; initially the S(2)(??*) state is populated by all excitation wavelengths and decays quickly within 100 fs. For excitation energies below ?5.2 eV, the S(2)(??*)?S(1)(n?*)?S(0) pathway dominates the deactivation process. The S(1)(n?*)?S(0) lifetime (1032-700 fs) displays a trend toward shorter time constants with increasing excitation energy. On the basis of relative amplitude ratios, an additional relaxation channel is identified at excitation energies above 5.2 eV. PMID:20961159

Evans, Nicholas L; Ullrich, Susanne

2010-10-28

150

Decoupling of the dc conductivity and (alpha-) structural relaxation time in a fragile glass-forming liquid under high pressure  

Microsoft Academic Search

Two relaxation processes, involving dc conductivity and the glass (alpha) structural relaxation, respectively, were measured in the low-molecular-weight glass-forming liquid, bisphenol- A-propoxylate(1 PO\\/phenol)diglycidylether, by dielectric spectroscopy, as a function of temperature and pressure. We focused on the correlation between dc conductivity and the alpha-relaxation time, proving that the fractional Debye-Stokes-Einstein relation is valid for both isobaric and isothermal data. The

Tatiana Psurek; Stella Hensel-Bielowka; Jerzy Ziolo; Marian Paluch

2002-01-01

151

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

152

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

153

Earth accretion dynamics and time-scales  

Microsoft Academic Search

The degree to which efficient mixing of new material, losses of volatiles to space and changes in oxidation characterize the impact-driven growth of Earth-like planets in unclear. These processes affect calculated time-scales and can be studied by parallel modeling of data from different radiogenic isotope systems. The W isotope composition of the silicate Earth yields a model time-scale for accretion

A. N. Halliday

2003-01-01

154

Systolic and diastolic time intervals in pulsus alternans - Significance of alternating isovolumic relaxation  

NASA Technical Reports Server (NTRS)

Systolic and diastolic time intervals in 14 cardiac patients with pulsus alternans revealed significant alternation of preinjection period (PEP), isovolumic contraction time (IVCT), left ventricular ejection time (LVET), ejection time index (ETI), PEP/LVET, and carotid dD/dt with better functional values in the strong beats. Cycle length, duration of electromechanical systole (EMS) and total diastole, i.e., isovolumic relaxation period (IRP) and diastolic filling period (DFP) occurred in 7 out of 8 patients. These diastolic intervals alternated reciprocally such that the IRP of the strong beats encroached upon the DFP of the next (weak) beats.

Spodick, D. H.; Quarry, V. M.; Khan, A. H.

1974-01-01

155

Relationships between induced polarization relaxation time and hydraulic properties of sandstone  

NASA Astrophysics Data System (ADS)

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

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

2010-03-01

156

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

E-print Network

We evaluate the ratio of the shear viscosity to the relaxation time of the shear flux above but near the critical temperature $T_c$ 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, the ratio is evaluated by direct measurements of the Euclidean observables on the lattice. We obtained the ratio with reasonable statistics for the range of temperature $1.3T_c \\lesssim T \\lesssim 4T_c$. We also found that the characteristic speed of the transverse plane wave in gluon media is almost constant, $v \\simeq 0.5$, for $T \\gtrsim 1.5T_c$, which is compatible with the causality in the second order dissipative hydrodynamics.

Yasuhiro Kohno; Masayuki Asakawa; Masakiyo Kitazawa

2011-12-07

157

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

158

Spin-Lattice Relaxation Times of Single Donors and Donor Clusters in Silicon  

NASA Astrophysics Data System (ADS)

An atomistic method of calculating the spin-lattice relaxation times (T1 ) is presented for donors in silicon nanostructures comprising of millions of atoms. The method takes into account the full band structure of silicon including the spin-orbit interaction. The electron-phonon Hamiltonian, and hence, the deformation potential, is directly evaluated from the strain-dependent tight-binding Hamiltonian. The technique is applied to single donors and donor clusters in silicon, and explains the variation of T1 with the number of donors and electrons, as well as donor locations. Without any adjustable parameters, the relaxation rates in a magnetic field for both systems are found to vary as B5 , in excellent quantitative agreement with experimental measurements. The results also show that by engineering electronic wave functions in nanostructures, T1 times can be varied by orders of magnitude.

Hsueh, Yu-Ling; Büch, Holger; Tan, Yaohua; Wang, Yu; Hollenberg, Lloyd C. L.; Klimeck, Gerhard; Simmons, Michelle Y.; Rahman, Rajib

2014-12-01

159

Hybrid multiple-relaxation-time lattice-Boltzmann finite-difference method for axisymmetric multiphase flows  

NASA Astrophysics Data System (ADS)

We propose a hybrid lattice-Boltzmann finite-difference method to simulate axisymmetric multiphase flows. The hydrodynamics is simulated by the lattice-Boltzmann equations with the multiple-relaxation-time (MRT) collision model and suitable forcing terms that account for the interfacial tension and axisymmetric effects. The interface dynamics is captured by the finite-difference solution of the convective Cahn-Hilliard equation. This method is applied to simulate a quiescent drop, an oscillating drop, a drop spreading on a dry surface and a drop accelerated by a constant body force. It is validated through comparisons of the computed results for these problems with analytical solutions or numerical solutions by other different methods. It is shown that the MRT-based method is able to handle more challenging cases than that with the single-relaxation-time collision model for axisymmetric multiphase flows due to its improved stability.

Huang, Jun-Jie; Huang, Haibo; Shu, Chang; Tian Chew, Yong; Wang, Shi-Long

2013-02-01

160

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

161

The time at the subplanckian scale  

E-print Network

With the theory of special relativity, time has been linked with space into a four-dimensional space-time from which a basic question must be asked: can space be really transformed into time and vice-versa? The response is affirmative if time has the same structural topological structure as space at the subplanckian quantum level in such a way that a discrete structural quantum time constitutes the time part of the space-time internal vacuum of every elementary particle. It has thus been shown that a quantum time, quantized algebraically according to a lattice of time quanta, really exists and is emergent in the sense that time quanta can be transformed into space quanta and vice-versa. Furthermore,this quantum time, only relevant at the subplanckian scale, is proved to be in one-to-one correspondence with the absolute and relative clock times.

Christian Pierre

2007-01-22

162

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

163

T2 relaxation time study of iron overload in b-thalassemia  

Microsoft Academic Search

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

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

1998-01-01

164

Viscosity, relaxation time, and dynamics within a model asphalt of larger molecules.  

PubMed

The dynamics properties of a new "next generation" model asphalt system that represents SHRP AAA-1 asphalt using larger molecules than past models is studied using molecular simulation. The system contains 72 molecules distributed over 12 molecule types that range from nonpolar branched alkanes to polar resins and asphaltenes. Molecular weights range from 290 to 890 g/mol. All-atom molecular dynamics simulations conducted at six temperatures from 298.15 to 533.15 K provide a wealth of correlation data. The modified Kohlrausch-Williams-Watts equation was regressed to reorientation time correlation functions and extrapolated to calculate average rotational relaxation times for individual molecules. The rotational relaxation rate of molecules decreased significantly with increasing size and decreasing temperature. Translational self-diffusion coefficients followed an Arrhenius dependence. Similar activation energies of ?42 kJ/mol were found for all 12 molecules in the model system, while diffusion prefactors spanned an order of magnitude. Viscosities calculated directly at 533.15 K and estimated at lower temperatures using the Debye-Stokes-Einstein relationship were consistent with experimental data for asphalts. The product of diffusion coefficient and rotational relaxation time showed only small changes with temperature above 358.15 K, indicating rotation and translation that couple self-consistently with viscosity. At lower temperatures, rotation slowed more than diffusion. PMID:25669400

Li, Derek D; Greenfield, Michael L

2014-01-21

165

Viscosity, relaxation time, and dynamics within a model asphalt of larger molecules  

NASA Astrophysics Data System (ADS)

The dynamics properties of a new "next generation" model asphalt system that represents SHRP AAA-1 asphalt using larger molecules than past models is studied using molecular simulation. The system contains 72 molecules distributed over 12 molecule types that range from nonpolar branched alkanes to polar resins and asphaltenes. Molecular weights range from 290 to 890 g/mol. All-atom molecular dynamics simulations conducted at six temperatures from 298.15 to 533.15 K provide a wealth of correlation data. The modified Kohlrausch-Williams-Watts equation was regressed to reorientation time correlation functions and extrapolated to calculate average rotational relaxation times for individual molecules. The rotational relaxation rate of molecules decreased significantly with increasing size and decreasing temperature. Translational self-diffusion coefficients followed an Arrhenius dependence. Similar activation energies of ˜42 kJ/mol were found for all 12 molecules in the model system, while diffusion prefactors spanned an order of magnitude. Viscosities calculated directly at 533.15 K and estimated at lower temperatures using the Debye-Stokes-Einstein relationship were consistent with experimental data for asphalts. The product of diffusion coefficient and rotational relaxation time showed only small changes with temperature above 358.15 K, indicating rotation and translation that couple self-consistently with viscosity. At lower temperatures, rotation slowed more than diffusion.

Li, Derek D.; Greenfield, Michael L.

2014-01-01

166

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

NASA Astrophysics Data System (ADS)

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

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

2003-11-01

167

Viscosity, relaxation time, and dynamics within a model asphalt of larger molecules  

SciTech Connect

The dynamics properties of a new “next generation” model asphalt system that represents SHRP AAA-1 asphalt using larger molecules than past models is studied using molecular simulation. The system contains 72 molecules distributed over 12 molecule types that range from nonpolar branched alkanes to polar resins and asphaltenes. Molecular weights range from 290 to 890 g/mol. All-atom molecular dynamics simulations conducted at six temperatures from 298.15 to 533.15 K provide a wealth of correlation data. The modified Kohlrausch-Williams-Watts equation was regressed to reorientation time correlation functions and extrapolated to calculate average rotational relaxation times for individual molecules. The rotational relaxation rate of molecules decreased significantly with increasing size and decreasing temperature. Translational self-diffusion coefficients followed an Arrhenius dependence. Similar activation energies of ?42 kJ/mol were found for all 12 molecules in the model system, while diffusion prefactors spanned an order of magnitude. Viscosities calculated directly at 533.15 K and estimated at lower temperatures using the Debye-Stokes-Einstein relationship were consistent with experimental data for asphalts. The product of diffusion coefficient and rotational relaxation time showed only small changes with temperature above 358.15 K, indicating rotation and translation that couple self-consistently with viscosity. At lower temperatures, rotation slowed more than diffusion.

Li, Derek D.; Greenfield, Michael L., E-mail: greenfield@egr.uri.edu [Department of Chemical Engineering, University of Rhode Island, Kingston, Rhode Island 02881 (United States)

2014-01-21

168

Effects of nonsinusoidal character of atomic modulation on NQR spin-lattice relaxation time of incommensurate phases  

Microsoft Academic Search

The present work is an extention of the theoretical calculation developed by Blinc to explain the temperature and frequency dependence of the spin-lattice relaxation time in incommensurate phases. We have evaluated the influence of the nonsinusoidal character of the atomic modulation, in the linear approximation, over the NQR spectra and over the spin-lattice relaxation due to direct and Raman processes.

Silvina C. Pérez; Clemar Schurrer; Alberto Wolfenson

2001-01-01

169

Long-time stress relaxation of a filled elastomer in vacuum environments  

NASA Technical Reports Server (NTRS)

Samples of a filled elastomeric ablative material were stored at 45 C and 10 to the -6th torr for 7 months. Their tensile stress-relaxation modulus at constant strain was measured throughout the 7 months. Results of the testing are discussed primarily by comparisons of the data to atmospheric-pressure moduli (determined in this work for shorter periods of time) and with moduli predicted from short-time testing. Confirmation of the strengthening effects of vacuum on this composite was obtained. The use of time-temperature superposition techniques as an approximate accelerated testing procedure for this material under these conditions was also verified.

Ward, T. C.

1981-01-01

170

Interactions and magnetic viscosity: Nonmonotonic time variation of the magnetization during relaxation at constant demagnetizing field  

SciTech Connect

We present magnetic relaxation data of PrNdFeB magnets. These data were obtained by measuring the time evolution of the magnetization under constant applied demagnetizing fields. The results corresponding to fields far from the range of the coercive force evidenced a nonmonotonic time variation of the magnetization. We propose that the occurrence of magnetic interactions underlies the observed anomalous behavior. This idea is checked through a micromagnetic simulation of the time evolution of the magnetization of a low field reversed nucleus which is exchange and magnetostically coupled to the main hard phase. {copyright} {ital 1996 American Institute of Physics.}

de Julian, C.; Emura, M.; Cebollada, F.; Gonzalez, J.M. [Departamento de Propiedades Opticas, Magneticas y de Transporte, Instituto de Ciencia de Materiales de Madrid-Consejo Superior de Investigaciones Cientificas, Cantoblanco, 28049 Madrid (Spain)] [Departamento de Propiedades Opticas, Magneticas y de Transporte, Instituto de Ciencia de Materiales de Madrid-Consejo Superior de Investigaciones Cientificas, Cantoblanco, 28049 Madrid (Spain)

1996-12-01

171

Time scale synchronization of chaotic oscillators  

E-print Network

This paper presents the result of the investigation of chaotic oscillator synchronization. A new approach for detecting of synchronized behaviour of chaotic oscillators has been proposed. This approach is based on the analysis of different time scales in the time series generated by the coupled chaotic oscillators. This approach has been applied for the coupled Rossler and Lorenz systems.

Alexander Hramov; Alexey Koronovskii

2006-02-25

172

Multiple short time power laws in the orientational relaxation of nematic liquid crystals.  

PubMed

Relaxation in the nematic liquid crystalline phase is known to be sensitive to its proximity to both isotropic and smectic phases. Recent transient optical Kerr effect (OKE) studies have revealed, rather surprisingly, two temporal power laws at short to intermediate times and also an apparent absence of the expected exponential decay at longer times. In order to understand this unusual dynamics, we have carried out extensive molecular dynamics simulations of transient OKE and related orientational time correlation functions in a system of prolate ellipsoids (with aspect ratio equal to 3). The simulations find two distinct power laws, with a crossover region, in the decay of the orientational time correlation function at short to intermediate times (in the range of a few picoseconds to a few nanoseconds). In addition, the simulation results fail to recover any long time exponential decay component. The system size dependence of the exponents suggests that the first power law may originate from the local orientational density fluctuations (like in a glassy liquid). The origin of the second power law is less clear and may be related to the long range fluctuations (such as smecticlike density fluctuations)--these fluctuations are expected to involve small free energy barriers. In support of the latter, the evidence of pronounced coupling between orientational and spatial densities at intermediate wave numbers is presented. This coupling is usually small in normal isotropic liquids, but it is large in the present case. In addition to slow collective orientational relaxation, the single particle orientational relaxation is also found to exhibit slow dynamics in the nematic phase in the long time. PMID:17115789

Jose, Prasanth P; Bagchi, Biman

2006-11-14

173

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

174

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

PubMed

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

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

2013-05-01

175

The Time Scale of Evolutionary Innovation  

PubMed Central

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, 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 We show that adaptation on many fitness landscapes takes time that is exponential in 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.

2014-01-01

176

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

177

Rheometry-on-a-chip: measuring the relaxation time of a viscoelastic liquid through particle migration in microchannel flows.  

PubMed

A novel method to estimate the relaxation time of viscoelastic fluids, down to milliseconds, is here proposed. The adopted technique is based on the particle migration phenomenon occurring when the suspending viscoelastic fluid flows in microfluidic channels. The method is applied to measure the fluid relaxation times of two water-glycerol polymer solutions in an ample range of concentrations. A remarkable improvement in the accuracy of the measure of the relaxation time is found, as compared with experimental data obtained from shear or elongational experiments available in the literature. Good agreement with available theoretical predictions is also found. The proposed method is reliable, handy and does not need a calibration curve, opening an effective way to measure relaxation times of viscoelastic fluids otherwise not easily detectable by conventional techniques. PMID:25435258

Del Giudice, Francesco; D'Avino, Gaetano; Greco, Francesco; De Santo, Ilaria; Netti, Paolo A; Maffettone, Pier Luca

2014-12-01

178

UNIQUENESS OF DISPLACEMENT-HEAT FLUX AND STRESS-TEMPERATURE PROBLEMS IN THERMOELASTICITY WITH ONE RELAXATION TIME  

Microsoft Academic Search

Two uniqueness theorems of linear thermoelasticity with one relaxation time corresponding to natural initial boundary value problems described in terms of two different pairs of thermoelastic variables: displacement-heat flux and stress-temperature are proved.

Ryszard Wojnar

1985-01-01

179

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

Microsoft Academic Search

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

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

1993-01-01

180

Magnetic Resonance T1 Relaxation Time of Venous Thrombus Is Determined by Iron Processing and Predicts Susceptibility to Lysis  

PubMed Central

Background The magnetic resonance longitudinal relaxation time (T1) changes with thrombus age in humans. In this study, we investigate the possible mechanisms that give rise to the T1 signal in venous thrombi and whether changes in T1 relaxation time are informative of the susceptibility to lysis. Methods and Results Venous thrombosis was induced in the vena cava of BALB/C mice, and temporal changes in T1 relaxation time correlated with thrombus composition. The mean T1 relaxation time of thrombus was shortest at 7days following thrombus induction and returned to that of blood as the thrombus resolved. T1 relaxation time was related to thrombus methemoglobin formation and further processing. Studies in inducible nitric oxide synthase (iNOS?/?)–deficient mice revealed that inducible nitric oxide synthase mediates oxidation of erythrocyte lysis–derived iron to paramagnetic Fe3+, which causes thrombus T1 relaxation time shortening. Studies using chemokine receptor-2–deficient mice (Ccr2?/?) revealed that the return of the T1 signal to that of blood is regulated by removal of Fe3+ by macrophages that accumulate in the thrombus during its resolution. Quantification of T1 relaxation time was a good predictor of successful thrombolysis with a cutoff point of <747 ms having a sensitivity and specificity to predict successful lysis of 83% and 94%, respectively. Conclusions The source of the T1 signal in the thrombus results from the oxidation of iron (released from the lysis of trapped erythrocytes in the thrombus) to its paramagnetic Fe3+ form. Quantification of T1 relaxation time appears to be a good predictor of the success of thrombolysis. PMID:23820077

Modarai, Bijan; Blume, Ulrike; Humphries, Julia; Patel, Ashish S.; Phinikaridou, Alkystis; Evans, Colin E.; Mattock, Katherine; Grover, Steven P.; Ahmad, Anwar; Lyons, Oliver T.; Attia, Rizwan Q.; Renné, Thomas; Premaratne, Sobath; Wiethoff, Andrea J.; Botnar, René M.; Schaeffter, Tobias; Waltham, Matthew; Smith, Alberto

2014-01-01

181

Dynamics of glass-forming liquids. XVIII. Does entropy control structural relaxation times?  

PubMed

We study the dielectric dynamics of viscous glycerol in the presence of a large bias field. Apart from dielectric saturation and polarization anisotropy, we observe that the steady state structural relaxation time is longer by 2.7% in the presence of a 225 kV/cm dc-field relative to the linear response counterpart, equivalent to a field induced glass transition (Tg) shift of +84 mK. This result compares favorably with the 3.0% time constant increase predicted on the basis of a recent report [G. P. Johari, J. Chem. Phys. 138, 154503 (2013)], where the field induced reduction of the configurational entropy translates into slower dynamics by virtue of the Adam-Gibbs relation. Other models of field dependent glass transition temperatures are also discussed. Similar to observations related to the electro-optical Kerr effect, the rise time of the field induced effect is much longer than its collapse when the field is removed again. The orientational relaxation time of the plastic crystal cyclo-octanol is more sensitive to a bias field, showing a 13.5% increase at a field of 150 kV/cm, equivalent to an increase of Tg by 0.58 K. PMID:25637992

Samanta, Subarna; Richert, Ranko

2015-01-28

182

Dynamics of glass-forming liquids. XVIII. Does entropy control structural relaxation times?  

NASA Astrophysics Data System (ADS)

We study the dielectric dynamics of viscous glycerol in the presence of a large bias field. Apart from dielectric saturation and polarization anisotropy, we observe that the steady state structural relaxation time is longer by 2.7% in the presence of a 225 kV/cm dc-field relative to the linear response counterpart, equivalent to a field induced glass transition (Tg) shift of +84 mK. This result compares favorably with the 3.0% time constant increase predicted on the basis of a recent report [G. P. Johari, J. Chem. Phys. 138, 154503 (2013)], where the field induced reduction of the configurational entropy translates into slower dynamics by virtue of the Adam-Gibbs relation. Other models of field dependent glass transition temperatures are also discussed. Similar to observations related to the electro-optical Kerr effect, the rise time of the field induced effect is much longer than its collapse when the field is removed again. The orientational relaxation time of the plastic crystal cyclo-octanol is more sensitive to a bias field, showing a 13.5% increase at a field of 150 kV/cm, equivalent to an increase of Tg by 0.58 K.

Samanta, Subarna; Richert, Ranko

2015-01-01

183

Influence of timing and magnitude of arterial wave reflection on left ventricular relaxation.  

PubMed

The influence of timing and magnitude of arterial wave reflection (WR) on afterload-dependent relaxation was evaluated in patients with a variety of heart diseases (group 1, age < 30 yr; group 2, age > 40 yr) and in dogs. While both femoral arteries were compressed (FC), WR returned just after the dicrotic notch (early diastole) in group 1 but before the dicrotic notch (late systole) in group 2. The time constant of the left ventricular pressure decay (tau) was shortened during FC in group 1, whereas it was prolonged in group 2. In dogs, a constriction of the thoracic aorta induced a late systolic augmentation of WR with a prolongation of tau (cf. group 2), whereas constriction of the lower abdominal aorta induced an early diastolic augmentation of WR with a shortening of tau (cf. group 1). With aortic constriction, coronary flow increased, and there was a close correlation between the peak change in backward aortic pressure and that in coronary flow regardless of the timing of WR. Thus the time at which WR returns during the cardiac cycle may have an important effect on left ventricular relaxation and coronary flow. PMID:11247800

Yano, M; Kohno, M; Kobayashi, S; Obayashi, M; Seki, K; Ohkusa, T; Miura, T; Fujii, T; Matsuzaki, M

2001-04-01

184

Molecular dynamics simulations of proton transverse relaxation times in suspensions of magnetic nanoparticles.  

PubMed

In this work we have analyzed the influence of various factors on the transverse relaxation times T2 of water protons in suspension of magnetic nanoparticles. For that purpose we developed a full molecular dynamics force field which includes the effects of dispersion interactions between magnetic nanoparticles and water molecules, electrostatic interactions between charged nanoparticles and magnetic dipole-dipole and dipole-external field interactions. We also accounted for the magnetization reversal within the nanoparticles body frames due to finite magnetic anisotropy barriers. The force field together with the Langevin dynamics imposed on water molecules and the nanoparticles allowed us to monitor the dephasing of water protons in real time. Thus, we were able to determine the T2 relaxation times including the effects of the adsorption of water on the nanoparticles' surfaces, thermal fluctuations of the orientation of nanoparticles' magnetizations as well as the effects of the core-shell architecture of nanoparticles and their agglomeration into clusters. We found that there exists an optimal cluster size for which T2 is minimized and that the retardation of water molecules motion, due to adsorption on the nanoparticles surfaces, has some effect in the measured T2 times. The typical strengths of the external magnetic fields in MRI are enough to keep the magnetizations fixed along the field direction, however, in the case of low magnetic fields, we observed significant enhancement of T2 due to thermal fluctuations of the orientations of magnetizations. PMID:25313483

Panczyk, Tomasz; Konczak, Lukasz; Zapotoczny, Szczepan; Szabelski, Pawel; Nowakowska, Maria

2015-01-01

185

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

186

Energy and temperature dependence of relaxation time and Wiedemann-Franz law on PbTe  

NASA Astrophysics Data System (ADS)

Recent revival of interest in high-temperature (T) thermoelectrics has made it necessary to understand in detail the T dependence of different transport coefficients, and different processes contributing to this temperature dependence. Since PbTe is a well-studied prototypical high-temperature thermoelectric, we have carried out theoretical studies to analyze how different physical sources contribute to electronic transport coefficients in this system over a wide T and concentration (n) range; 300Krelaxation time approximations. Although the T dependence of the electrical conductivity ? comes from several sources (band structure parameters, chemical potential ? , relaxation time ? ), we find that the T dependence of ? dominates. We fit the T and the energy (?) dependence of the total relaxation time ?tot by a simple function ?˜aT-p/(b+c?r) , where a , b , c , p , and r are T and ? independent parameters but depend on n . Using this function, we find that for concentration range of interest, changing r which governs the energy dependence of scattering does not appreciably affect the T dependence of ? . Electronic thermal conductivities both at constant current J and constant electric field E were calculated using this ? to reexamine the validity of Wiedemann-Franz (WF) law in PbTe, extending the earlier work of Bhandari and Rowe to higher temperatures. We find that using standard WF law to obtain the electronic contribution of the thermal conductivity (?el) usually overestimates this contribution by more than 0.5WK-1m-1 . Therefore the value of the lattice thermal conductivity obtained by subtracting this ?el from the total thermal conductivity is underestimated roughly by the same amount.

Ahmad, Salameh; Mahanti, S. D.

2010-04-01

187

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

PubMed Central

Placental insufficiency is a major cause of fetal growth restriction (FGR) and accumulating evidence indicates several aspects of placental morphology are altered in this condition. MRI provides quantitative indices that may be used in non-invasive assessment of the human placenta, such as relaxation time measurements, T1 and T2. We hypothesised that placental relaxation times relate to alterations in placental tissue morphology and hence may be useful in identifying the changes associated with FGR. We report on the first phase of testing this hypothesis, in a study of women in normal pregnancy. Aims To assess relaxation time measurements in the placenta in normal pregnancy and correlate these with gestational age and stereological analyses of placental morphology following delivery. Methods 30 women underwent MRI examination (1.5 T) between 20 and 41 weeks gestation. Placental T1 and T2 measurements were acquired from a mid-depth placental region, co-localised to a structural scan. Fixed, wax-embedded sections of these placentas collected at delivery were stained with hematoxylin/ eosin and subjected to stereological analysis. Results Placental T1 and T2 show a significant negative correlation with gestation, (Pearson correlation p=0.01, 0.03 respectively). 17 placentas were analysed stereologically. In the group as a whole there was no significant correlation between T1 and T2 and morphological features. However, in a subset of 7 pregnancies scanned within a week of delivery, a significant positive correlation was observed between the fibrin volume density and the ratio of fibrin: villous volume densities and T2 (Spearman correlation p=0.02, 0.03 respectively). Discussion The correlations between placental T1 and T2 and gestation show that these variables are clearly influenced by changes in placental structure. Fibrin might be a key component but further work is needed to fully elucidate the major structural influences on placental T1 and T2. PMID:21978937

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

2013-01-01

188

Stability of graph communities across time scales  

PubMed Central

The complexity of biological, social, and engineering networks makes it desirable to find natural partitions into clusters (or communities) that can provide insight into the structure of the overall system and even act as simplified functional descriptions. Although methods for community detection abound, there is a lack of consensus on how to quantify and rank the quality of partitions. We introduce here the stability of a partition, a measure of its quality as a community structure based on the clustered autocovariance of a dynamic Markov process taking place on the network. Because the stability has an intrinsic dependence on time scales of the graph, it allows us to compare and rank partitions at each time and also to establish the time spans over which partitions are optimal. Hence the Markov time acts effectively as an intrinsic resolution parameter that establishes a hierarchy of increasingly coarser communities. Our dynamical definition provides a unifying framework for several standard partitioning measures: modularity and normalized cut size can be interpreted as one-step time measures, whereas Fiedler’s spectral clustering emerges at long times. We apply our method to characterize the relevance of partitions over time for constructive and real networks, including hierarchical graphs and social networks, and use it to obtain reduced descriptions for atomic-level protein structures over different time scales. PMID:20615936

Delvenne, J.-C.; Yaliraki, S. N.; Barahona, M.

2010-01-01

189

Cartilage and meniscal T2 relaxation time as non-invasive biomarker for knee osteoarthritis and cartilage repair procedures  

PubMed Central

SUMMARY Objective The purpose of this work was to review the current literature on cartilage and meniscal T2 relaxation time. Methods Electronic searches in PubMed were performed to identify relevant studies about T2 relaxation time measurements as non-invasive biomarker for knee osteoarthritis (OA) and cartilage repair procedures. Results Initial osteoarthritic changes include proteoglycan loss, deterioration of the collagen network, and increased water content within the articular cartilage and menisci. T2 relaxation time measurements are affected by these pathophysiological processes. It was demonstrated that cartilage and meniscal T2 relaxation time values were significantly increased in subjects with compared to those without radiographic OA and focal knee lesions, respectively. Subjects with OA risk factors such as overweight/obesity showed significantly greater cartilage T2 values than normal controls. Elevated cartilage and meniscal T2 relaxation times were found in subjects with vs without knee pain. Increased cartilage T2 at baseline predicted morphologic degeneration in the cartilage, meniscus, and bone marrow over 3 years. Furthermore, cartilage repair tissue could be non-invasively assessed by using T2 mapping. Reproducibility errors for T2 measurements were reported to be smaller than the T2 differences in healthy and diseased cartilage indicating that T2 relaxation time may be a reliable discriminatory biomarker. Conclusions Cartilage and meniscal T2 mapping may be suitable as non-invasive biomarker to diagnose early stages of knee OA and to monitor therapy of OA. PMID:23896316

Baum, T.; Joseph, G.B.; Karampinos, D.C.; Jungmann, P.M.; Link, T.M.; Bauer, J.S.

2014-01-01

190

Isovolumic relaxation period as an index of left ventricular relaxation under different afterload conditions--comparison with the time constant of left ventricular pressure decay in the dog.  

PubMed

In order to determine whether isovolumic relaxation period (IRP) reflects left ventricular relaxation under different afterload conditions, 17 anesthetized, open chest dogs were studied, and the left ventricular pressure decay time constant (T) was calculated. In 12 dogs, angiotensin II and nitroprusside were administered, with the heart rate constant at 90 beats/min. Multiple linear regression analysis showed that the aortic dicrotic notch pressure (AoDNP) and T were major determinants of IRP, while left ventricular end-diastolic pressure was a minor determinant. Multiple linear regression analysis, correlating T with IRP and AoDNP, did not further improve the correlation coefficient compared with that between T and IRP. We concluded that correction of the IRP by AoDNP is not necessary to predict T from additional multiple linear regression. The effects of ascending aortic constriction or angiotensin II on IRP were examined in five dogs, after pretreatment with propranolol. Aortic constriction caused a significant decrease in IRP and T, while angiotensin II produced a significant increase in IRP and T. IRP was affected by the change of afterload. However, the IRP and T values were always altered in the same direction. These results demonstrate that IRP is substituted for T and it reflects left ventricular relaxation even in different afterload conditions. We conclude that IRP is a simple parameter easily used to evaluate left ventricular relaxation in clinical situations. PMID:2632821

Ochi, H; Ikuma, I; Toda, H; Shimada, T; Morioka, S; Moriyama, K

1989-12-01

191

Apparent Diffusion Coefficient, Fractional Anisotropy and T2 Relaxation Time Measurement  

Microsoft Academic Search

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

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

2007-01-01

192

Relaxation time of Gauss's continued-fraction map. I. The Hilbert space approach (Koopmanism)  

SciTech Connect

It is shown that U*, the adjoint of Koopman's isometric operator Uf(x) = f(Tx) corresponding to the map Tx = x/sup -1/ (mod 1) of the unit interval, is isomorphic to a symmetric integral operator when restricted to a Hilbert space of holomorphic functions f. This result, also obtained by Babenko in a different setting, allows them to derive new trace formulas. Using generalized Temple's inequalities, they determine the relaxation time of the above system with great accuracy. In contrast to a widespread belief, it appears to be unrelated to the entropy of the map T.

Mayer, D.; Roepstorff, G.

1987-04-01

193

The electron-phonon relaxation time in thin superconducting titanium nitride films  

SciTech Connect

We report on the direct measurement of the electron-phonon relaxation time, ?{sub eph}, in disordered TiN films. Measured values of ?{sub eph} are from 5.5?ns to 88?ns in the 4.2 to 1.7?K temperature range and consistent with a T{sup ?3} temperature dependence. The electronic density of states at the Fermi level N{sub 0} is estimated from measured material parameters. The presented results confirm that thin TiN films are promising candidate-materials for ultrasensitive superconducting detectors.

Kardakova, A., E-mail: kardakova@rplab.ru [Physics Department, Moscow State Pedagogical University, Moscow 119991 (Russian Federation); Moscow Institute of Physics and Technology (State University), Dolgoprudny 141700 (Russian Federation); Finkel, M.; Kovalyuk, V.; An, P. [Physics Department, Moscow State Pedagogical University, Moscow 119991 (Russian Federation)] [Physics Department, Moscow State Pedagogical University, Moscow 119991 (Russian Federation); Morozov, D.; Dunscombe, C.; Mauskopf, P. [School of Physics and Astronomy, Cardiff University, Cardiff CF24 3AA (United Kingdom)] [School of Physics and Astronomy, Cardiff University, Cardiff CF24 3AA (United Kingdom); Tarkhov, M. [National Research Centre, “Kurchatov Institute,” Moscow 123128 (Russian Federation)] [National Research Centre, “Kurchatov Institute,” Moscow 123128 (Russian Federation); Klapwijk, T. M. [Physics Department, Moscow State Pedagogical University, Moscow 119991 (Russian Federation) [Physics Department, Moscow State Pedagogical University, Moscow 119991 (Russian Federation); Kavli Institute of Nanoscience, Delft University of Technology, 2628 CJ Delft (Netherlands); Goltsman, G. [Physics Department, Moscow State Pedagogical University, Moscow 119991 (Russian Federation) [Physics Department, Moscow State Pedagogical University, Moscow 119991 (Russian Federation); National Research University Higher School of Economics, Moscow 101000 (Russian Federation)

2013-12-16

194

Reduction of spectral phonon relaxation times from suspended to supported graphene  

NASA Astrophysics Data System (ADS)

We have performed molecular dynamics simulations with phonon spectral analysis to predict the mode-wise phonon relaxation times (RT) of suspended and supported graphene at room temperature, and the findings are consistent with recent optical measurements. For acoustic phonons, RTs reduce from up to 50 ps to less than 5 ps when graphene is put on silicon dioxide substrate. Similarly, optical phonon RTs reduce by half when supported. Stronger interfacial bonding is found to result in more RT reduction. Our results provide a fundamental understanding at the spectral phonon property level for the observed thermal conductivity reduction in supported graphene.

Qiu, Bo; Ruan, Xiulin

2012-05-01

195

Nuclear magnetic relaxation, correlation time spectrum, and molecular dynamics in a linear polymer  

NASA Astrophysics Data System (ADS)

The pulsed nuclear magnetic resonance (NMR) method at a proton frequency of 25 MHz at temperatures of 22 160°C is used to detect the transverse magnetization decay in polyisoprene rubbers with various molecular masses, to determine the NMR damping time T 2, and to measure spin-lattice relaxation time T 1 and time T 2eff of damping of solid-echo signals under the action of a sequence of MW-4 pulses modified by introducing 180° pulses. The dispersion dependences of T 2eff obtained for each temperature are combined into one using the temperature-frequency equivalence principle. On the basis of the combined dispersion dependence of T 2eff and the data on T 2 and T 1, the correlation time spectrum of molecular movements is constructed. Analysis of the shape of this spectrum shows that the dynamics of polymer molecules can be described in the first approximation by the Doi-Edwards tube-reptation model.

Chernov, V. M.; Krasnopol'Skii, G. S.

2008-08-01

196

A comment on the use of flushing time, residence time, and age as transport time scales  

USGS Publications Warehouse

Applications of transport time scales are pervasive in biological, hydrologic, and geochemical studies yet these times scales are not consistently defined and applied with rigor in the literature. We compare three transport time scales (flushing time, age, and residence time) commonly used to measure the retention of water or scalar quantities transported with water. We identify the underlying assumptions associated with each time scale, describe procedures for computing these time scales in idealized cases, and identify pitfalls when real-world systems deviate from these idealizations. We then apply the time scale definitions to a shallow 378 ha tidal lake to illustrate how deviations between real water bodies and the idealized examples can result from: (1) non-steady flow; (2) spatial variability in bathymetry, circulation, and transport time scales; and (3) tides that introduce complexities not accounted for in the idealized cases. These examples illustrate that no single transport time scale is valid for all time periods, locations, and constituents, and no one time scale describes all transport processes. We encourage aquatic scientists to rigorously define the transport time scale when it is applied, identify the underlying assumptions in the application of that concept, and ask if those assumptions are valid in the application of that approach for computing transport time scales in real systems.

Monsen, N.E.; Cloern, J.E.; Lucas, L.V.; Monismith, S.G.

2002-01-01

197

Multi-scales nuclear spin relaxation of liquids in porous media  

Microsoft Academic Search

The magnetic field dependence of the nuclear spin–lattice relaxation rate 1\\/T1(?0) is a rich source of dynamical information for characterizing the molecular dynamics of liquids in confined environments. Varying the magnetic field changes the Larmor frequency ?0, and thus the fluctuations to which the nuclear spin relaxation is sensitive. Moreover, this method permits a more complete characterization of the dynamics

Jean-Pierre Korb

2010-01-01

198

17O relaxation time and NMR sensitivity of cerebral water and their field dependence.  

PubMed

17O spin relaxation times and sensitivity of detection were measured for natural abundance H(2)(17)O in the rat brain at 4.7 and 9.4 Tesla. The relaxation times were found to be magnetic field independent (T(2) = 3.03 +/- 0.08 ms, T(*)(2) = 1.79 +/- 0.04 ms, and T(1) = 4.47 +/- 0.14 ms at 4.7T (N = 5); T(2) = 3.03 +/- 0.09 ms, T(*)(2) = 1.80 +/- 0.06 ms, and T(1) = 4.84 +/- 0.18 ms at 9.4T (N = 5)), consistent with the concept that the dominant relaxation mechanism is the quadrupolar interaction for this nucleus. The (17)O NMR sensitivity was more than fourfold higher at 9.4T than at 4.7T, for both the rat brain and a sodium chloride solution. With this sensitivity gain, it was possible to obtain localized (17)O spectra with an excellent signal-to-noise ratio (SNR) within 15 s of data acquisition despite the relatively low gyromagnetic ratio of this nucleus. Such a 15-s 2D (17)O-MRS imaging data set obtained for natural abundance H(2)(17)O in the rat brain yielded an SNR greater than 40:1 for a approximately 16 microl voxel. This approach was employed to measure cerebral blood flow using a bolus injection of H(2)(17)O via one internal carotid artery. These results demonstrate the ability of (17)O-MRS imaging to reliably map the H(2)(17)O dynamics in the brain tissue, and its potential for determining tissue blood flow and oxygen consumption rate changes in vivo. Magn Reson Med 45:543-549, 2001. PMID:11283979

Zhu, X H; Merkle, H; Kwag, J H; Ugurbil, K; Chen, W

2001-04-01

199

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

200

Proton NMR transverse relaxation time and membrane stability in wheat leaves exposed to high temperature shock.  

PubMed

Electrolyte leakage from leaves and NMR transverse relaxation time (T2) of leaf water were used to differentiate between heat-tolerant (NIAW 845) and susceptible (HD 2428) wheat (Triticum aestivum L.) cultivars. The leaves were exposed to high temperature shock in the range 30 to 55 degrees C and the damage caused, when evaluated by the two approaches was in close agreement. The critical temperature of injury leading to loss of membrane integrity was lower (39.1 degrees C) for susceptible cultivar, compared to tolerant cultivar (44.2 degrees C). Component analyses of NMR data revealed the existence of two fractions of cellular water in leaf tissues, namely, bound and free bulk water with distinct relaxation times. A dramatic reduction in the proportion of free water and a corresponding increase in bound water was observed in response to increase in temperature. This change in proportion occurred around 38 degrees C and 43 degrees C in HD 2428 and NIAW 845 respectively. The high temperature induced irreversible damage to cellular membrane integrity led to loss of compartmentation of cellular water fractions. The tolerant cultivar maintained its membrane integrity and cell water compartmentation until a temperature of 43 degrees C and susceptible could maintain it only until 38 degrees C. PMID:23923573

Nagarajan, Shantha; Joshi, D K; Anand, Anjali; Verma, A P S; Pathak, P C

2005-04-01

201

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

PubMed

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. PMID:25204376

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

2014-10-01

202

On the nonlinear variation of dc conductivity with dielectric relaxation time  

NASA Astrophysics Data System (ADS)

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

Johari, G. P.; Andersson, Ove

2006-09-01

203

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

204

Divergent Time Scale in Axelrod Model Dynamics  

E-print Network

We study the evolution of the Axelrod model for cultural diversity. We consider a simple version of the model in which each individual is characterized by two features, each of which can assume q possibilities. Within a mean-field description, we find a transition at a critical value q_c between an active state of diversity and a frozen state. For q just below q_c, the density of active links between interaction partners is non-monotonic in time and the asymptotic approach to the steady state is controlled by a time scale that diverges as (q-q_c)^{-1/2}.

Vázquez, F

2006-01-01

205

Dynamical theory of spin noise and relaxation: Prospects for real-time NMR measurements.  

PubMed

Recent developments in theoretical aspects of spin noise and relaxation and their interrelationship reveal a modified spin density, distinct from the density matrix, as the necessary object to describe fluctuations in spin systems. These fluctuations are to be viewed as an intrinsic quantum mechanical property of such systems immersed in random magnetic environments and are observed as "spin noise" in the absence of any radio frequency excitation. With the prospect of ultrafast digitization, the role of spin noise in real-time parameter extraction for (NMR) spin systems, and the advantage over standard techniques, is of essential importance, especially for systems containing a small number of spins. In this article we outline prospects for harnessing the recent dynamical theory in terms of spin-noise measurement, with attention to real-time properties. PMID:25493776

Field, Timothy R

2014-11-01

206

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

207

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

NASA Astrophysics Data System (ADS)

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

Verhulst, Claire; Meneveau, Charles

2011-11-01

208

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

NASA Astrophysics Data System (ADS)

We have performed simulations of the model of infinitely thin rigid rods undergoing rotational and translational diffusion, subject to the restriction that no two rods can cross one another, for various concentrations well into the semidilute regime. We used a modification of the algorithm of Doi et al. [J. Phys. Soc. Jpn. 53, 3000 (1984)], 10.1143/JPSJ.53.3000 that simulates diffusive dynamics using a Monte Carlo method and a nonzero time step. In the limit of zero time step, this algorithm is an exact description of diffusive dynamics subject to the noncrossing restriction. For a wide range of concentrations in the semidilute regime, we report values of the long time rotational diffusion constant of the rods, extrapolated to the limit of zero time step, for various sets of values of the infinite dilution (bare) diffusion constants. These results are compared with the results of a previous simulation of the model by Doi et al. and of previous simulations of rods with finite aspect ratio by Fixman and by Cobb and Butler that had been extrapolated to the limit of infinitely thin rods. The predictions of the Doi-Edwards (DE) scaling law do not hold for this model for the concentrations studied. The simulation data for the model display two deviations from the predictions of the DE theory that have been observed in experimental systems in the semidilute regime, namely, the very slow approach toward DE scaling behavior as the concentration is increased and the large value of the prefactor in the DE scaling law. We present a modified scaling principle for this model that is consistent with the simulation results for a broad range of concentrations in the semidilute regime. The modified scaling principle takes into account two physical effects, which we call "leakage" and "drift," that were found to be important for the transport properties of a simpler model of nonrotating rods on a lattice [Y.-L. S. Tse and H. C. Andersen, J. Chem. Phys. 136, 024904 (2012)], 10.1063/1.3673791.

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

2013-07-01

209

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

210

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

211

Exciton relaxation in PbSe nanorods.  

PubMed

Measurements of the picosecond-time-scale dynamics of photoexcited electrons in PbSe nanorods are reported. The intraband (1? ? 1?) relaxation occurs with a time constant of ~500 fs, which corresponds to a fast energy-relaxation rate of ~0.6 eV/ps. The biexciton lifetime in PbSe nanorods is significantly (3-4 times) longer than the lifetime of PbSe quantum dots with the same energy gap, roughly as expected considering the increased volume. The multiexciton lifetimes of PbSe nanorods scale as expected for a bimolecular recombination mechanism. Implications of the observed relaxations will be discussed. PMID:22861811

Yang, Jun; Hyun, Byung-Ryool; Basile, Anthony J; Wise, Frank W

2012-09-25

212

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

213

Heavy quark collisional energy loss in the quark-gluon plasma including finite relaxation time  

E-print Network

In this paper, we calculate the soft-collisional energy loss of heavy quarks traversing the viscous quark-gluon plasma including the effects of a finite relaxation time $\\tau_\\pi$ on the energy loss. We find that the collisional energy loss depends appreciably on $\\tau_\\pi$ . In particular, for typical values of the viscosity-to-entropy ratio, we show that the energy loss obtained using $\\tau_\\pi$ = 0 can be $\\sim$ 10$\\%$ larger than the one obtained using $\\tau_\\pi$ = 0. Moreover, we find that the energy loss obtained using the kinetic theory expression for $\\tau_\\pi$ is much larger that the one obtained with the $\\tau_\\pi$ derived from the Anti de Sitter/Conformal Field Theory correspondence. Our results may be relevant in the modeling of heavy quark evolution through the quark-gluon plasma.

Mauro Elias; J. Peralta-Ramos; E. Calzetta

2014-04-30

214

Anisotropic anomalous diffusion filtering applied to relaxation time estimation in magnetic resonance imaging.  

PubMed

Relaxometry mapping is a quantitative modality in magnetic resonance imaging (MRI) widely used in neuroscience studies. Despite its relevance and utility, voxel measurement of relaxation time in relaxometry MRI is compromised by noise that is inherent to MRI modality and acquisition hardware. In order to enhance signal to noise ratio (SNR) and quality of relaxometry mapping we propose application of anisotropic anomalous diffusion (AAD) filter that is consistent with inhomogeneous complex media. Here we evaluated AAD filter in comparison to two usual spatial filters: Gaussian and non local means (NLM) filters applied to real and simulated T2 relaxometry image sequences. The results demonstrate that AAD filter is comparatively more efficient in noise reducing and maintaining the image structural edges. AAD shows to be a robust and reliable spatial filter for brain image relaxometry. PMID:25570842

Senra Filho, Antonio Carlos Da S; Barbosa, Jeam Haroldo O; Salmon, Carlos E G; Murta, Luiz O

2014-08-01

215

Probe Spin-Velocity Dependent New Interactions by Spin Relaxation Times of Polarized $^{3}He$ Gas  

E-print Network

We have studied how to constrain the $\\alpha\\vec{\\sigma}\\cdot\\vec{v}$ type interactions with the relaxation time of spin polarized noble gases in magnetic fields. Using the longest $T_{2}$ measured in the laboratory and the earth as the source, we obtained constraints on three new interactions. We present a new experimental upper bound to the vector-axial-vector($V_{VA}$) type interaction for ranges between $1\\sim10^{8}$m. In combination with the previous result, we set the most stringent experiment limits on $g_{V}g_{A}$ ranging from $\\sim\\mu m$ to $\\sim10^{8}$m. We improve the laboratory limit to the axial-axial-vector($V_{AA}$) type interaction by $\\sim2$ orders or more for distances below $\\sim1$cm. To our best knowledge, we report the first experiment upper limit on torsion induced by the earth on its surface.

Y. Zhang; G. A. Sun; S. M. Peng; C. B. Fu; Hao Guo; B. Q. Liu; H. Yan

2014-12-28

216

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

217

Time scales in nuclear giant resonances  

E-print Network

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

WD Heiss; RG Nazmitdinov; FD Smit

2009-12-18

218

Cratering time scales for the Galilean satellites  

NASA Technical Reports Server (NTRS)

An attempt is made to estimate the present cratering rate for each Galilean satellite within the correct order of magnitude and to extend the cratering rates back into the geologic past on the basis of evidence from the earth-moon system. For collisions with long and short period comets, the magnitudes and size distributions of the comet nuclei, the distribution of their perihelion distances, and the completeness of discovery are addressed. The diameters and masses of cometary nuclei are assessed, as are crater diameters and cratering rates. The dynamical relations between long period and short period comets are discussed, and the population of Jupiter-crossing asteroids is assessed. Estimated present cratering rates on the Galilean satellites are compared and variations of cratering rate with time are considered. Finally, the consistency of derived cratering time scales with the cratering record of the icy Galilean satellites is discussed.

Shoemaker, E. M.; Wolfe, R. F.

1982-01-01

219

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

220

The study of NMR relaxation time spectra multi-exponential inversion based on Lloyd–Max optimal quantization  

NASA Astrophysics Data System (ADS)

The multi-exponential inversion of a NMR relaxation signal plays a key role in core analysis and logging interpretation in the formation of porous media. To find an efficient metod of inverting high-resolution relaxation time spectra rapidly, this paper studies the effect of inversion which is based on the discretization of the original echo in a time domain by using a simulation model. This paper analyzes the ill-condition of discrete equations on the basis of the NMR inversion model and method, determines the appropriate number of discrete echoes and acquires the optimal distribution of discrete echo points by the Lloyd–Max optimal quantization method, in considering the inverse precision and computational complexity comprehensively. The result shows that this method can effectively improve the efficiency of the relaxation time spectra inversion while guaranteeing inversed accuracy.

Li, Xuewei; Kong, Li; Cheng, Jingjing; Wu, Lei

2015-02-01

221

Time-dependent pseudo Jahn-Teller effect: Phonon-mediated long-time nonadiabatic relaxation  

SciTech Connect

Our system under theoretical consideration is an impurity center in a solid. We are considering the time evolution of the center in a quasi-degenerate electronic state. Strict quantum mechanical treatment of non-adiabadicity of the state is used. The phonon continuum is taken into account in addition to the vibration responsible for the main vibronic interaction. To describe the dynamics of the excited state a master equation has been used. The theoretical considerations are illustrated by the calculations of the long-time evolution of vibrations of the center, influenced by the emission of phonons to the bulk.

Vaikjärv, Taavi, E-mail: taavi.vaikjarv@ut.ee; Hizhnyakov, Vladimir [Institute of Physics, University of Tartu, Riia 142, 51014 Tartu (Estonia)] [Institute of Physics, University of Tartu, Riia 142, 51014 Tartu (Estonia)

2014-02-14

222

Nuclear Spin-Lattice Relaxation Times from Continuous Wave NMR Spectroscopy.  

ERIC Educational Resources Information Center

The experiment described, suitable for undergraduate physical chemistry laboratories, illustrates the general principles of relaxation and introduces the nmr concepts of saturation and spin-inversion. (BB)

Wooten, Jan B.; And Others

1979-01-01

223

The climate time scale in the approach to radiative-convective equilibrium  

NASA Astrophysics Data System (ADS)

In this paper, we discuss the importance of the surface boundary condition (fixed versus interactive surface temperature) for the long time scale of approach to Radiative-Convective Equilibrium (RCE). Using a simple linearized two-variable model for surface-atmosphere interaction, we derive an analytic expression for ?C, a long climate relaxation time scale that remains well defined and much longer than either mixing time scale of Tompkins and Craig (1998b), even in the limit that the heat capacity of the surface vanishes. We show that the size of ?C is an intrinsic property of the coupling between the atmosphere and surface, and not a result of the thermal inertia of the surface alone. When the surface heat capacity is low, ?C can be several times longer than expected, due to the effects of moisture on the effective heat capacity of the atmosphere. We also show that the theoretical expression for ?C is a good predictor of best fit exponential relaxation time scales in a single-column model with full physics, across a range of surface temperatures and surface heat capacities.

Cronin, Timothy W.; Emanuel, Kerry A.

2013-12-01

224

Identification of pore type and origin in a Lower Cretaceous carbonate reservoir using NMR T2 relaxation times  

E-print Network

IDENTIFICATION OF PORE TYPE AND ORIGIN IN A LOWER CRETACEOUS CARBONATE RESERVOIR USING NMR T 2 RELAXATION TIMES A Thesis by DOMENICO LODOLA Submitted to the Office of Graduate Studies of Texas A&M University in partial fulfillment... of the requirements for the degree of MASTER OF SCIENCE May 2004 Major Subject: Geology IDENTIFICATION OF PORE TYPE AND ORIGIN IN A LOWER CRETACEOUS CARBONATE RESERVOIR USING NMR T2 RELAXATION TIMES A Thesis by DOMENICO LODOLA Submitted to Texas A&M University...

Lodola, Domenico Domenico

2004-09-30

225

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

PubMed

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

Walimuni, Indika S; Hasan, Khader M

2011-08-15

226

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

PubMed

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

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

2009-07-01

227

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

228

An optimal modification of a Kalman filter for time scales  

NASA Technical Reports Server (NTRS)

The Kalman filter in question, which was implemented in the time scale algorithm TA(NIST), produces time scales with poor short-term stability. A simple modification of the error covariance matrix allows the filter to produce time scales with good stability at all averaging times, as verified by simulations of clock ensembles.

Greenhall, C. A.

2003-01-01

229

Low-temperature dynamics of long-ranged spin-glasses: full hierarchy of relaxation times via real-space renormalization  

NASA Astrophysics Data System (ADS)

We consider the long-ranged Ising spin-glass with random couplings decaying as a power-law of the distance, in the region of parameters where the spin-glass phase exists with a positive droplet exponent. For the Metropolis single-spin-flip dynamics near zero temperature, we construct via real-space renormalization the full hierarchy of relaxation times of the master equation for any given realization of the random couplings. We then analyze the probability distribution of dynamical barriers as a function of the spatial scale. This real-space renormalization procedure represents a simple explicit example of the droplet scaling theory, where the convergence towards local equilibrium on larger and larger scales is governed by a strong hierarchy of activated dynamical processes, with valleys within valleys.

Monthus, Cécile

2014-08-01

230

Basin-scale time reversal communications.  

PubMed

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

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

2009-01-01

231

Relaxed And Multiregion Relaxed  

E-print Network

Relaxed And Multiregion Relaxed Magnetohydrodynamics Robert L. Dewar Plasma Research Laboratory and A.M. Wright, Phys. Plasmas 20, 082103 (2013) #12;Generalization of Taylor Relaxation-consistent dynamics from an RxMHD Lagrangian. · A question for the future is: "Is there a natural helicity transport

Hudson, Stuart

232

Fast method for longitudinal relaxation time and water content mapping of the human brain on a clinical MR scanner  

Microsoft Academic Search

Summary. Background. Longitudinal relaxation time (T 1) map generation from human brain slices renders possible the in vivo follow-up of the changes in T 1 values during the course of several pathologies such as stroke, multiple sclerosis, traumatic brain injury etc. T 1 values can be converted to water contents, thus brain oedema reducing therapy can be non-invasively evaluated. The

F. Kövér; A. Schwarcz; J. Pál; P. Bogner; T. Vajna; G. Vadon; T. Dóczi

2004-01-01

233

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

234

Time-resolved spectroscopy on epitaxial graphene in the infrared spectral range: relaxation dynamics and saturation behavior  

E-print Network

1 Time-resolved spectroscopy on epitaxial graphene in the infrared spectral range: relaxationC, and in the far infrared range for the quasi-intrinsic graphene layers. In addition graphene samples performed in a wide spectral range, namely from the near-infrared

Boyer, Edmond

235

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

ERIC Educational Resources Information Center

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

Gasyna, Zbigniew L.; Jurkiewicz, Antoni

2004-01-01

236

Effect of Long Chain Alcohols on Micellar Relaxation Time and Foaming Properties of Sodium Dodecyl Sulfate Solutions  

Microsoft Academic Search

The effect of long chain alcohols (5 mol% CnOH forn= 8, 10, 12, 14, and 16) on the micellar stability of sodium dodecyl sulfate (SDS) solutions (SDS concentration ranging from 25 to 200 mM) was investigated and related to foaming properties, such as foamability, dynamic and equilibrium surface tension, and surface viscosity. The slow micellar relaxation time ?2, which is

Alexander Patist; Teri Axelberd; Dinesh O. Shah

1998-01-01

237

The effect of a phenomenological relaxation time on the magnetoplasmons in a two-dimensional inhomogeneous electron gas  

Microsoft Academic Search

We investigate the effect of a phenomenological relaxation time on the magnetoplasma excitations of a 2D strip of electrons by using the scheme proposed in a previous paper. Particular attention is put on the lowest frequency mode which exhibits an \\

V. Cataudella; G. Iadonisi

1988-01-01

238

An endohedral single-molecule magnet with long relaxation times: DySc2N@C80.  

PubMed

The magnetism of DySc(2)N@C(80) endofullerene was studied with X-ray magnetic circular dichroism (XMCD) and a magnetometer with a superconducting quantum interference device (SQUID) down to temperatures of 2 K and in fields up to 7 T. XMCD shows hysteresis of the 4f spin and orbital moment in Dy(III) ions. SQUID magnetometry indicates hysteresis below 6 K, while thermal and nonthermal relaxation is observed. Dilution of DySc(2)N@C(80) samples with C(60) increases the zero-field 4f electron relaxation time at 2 K to several hours. PMID:22582902

Westerström, Rasmus; Dreiser, Jan; Piamonteze, Cinthia; Muntwiler, Matthias; Weyeneth, Stephen; Brune, Harald; Rusponi, Stefano; Nolting, Frithjof; Popov, Alexey; Yang, Shangfeng; Dunsch, Lothar; Greber, Thomas

2012-06-20

239

Detection of crossover time scales in multifractal detrended fluctuation analysis  

NASA Astrophysics Data System (ADS)

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

Ge, Erjia; Leung, Yee

2013-04-01

240

Spatial analysis of magnetic resonance T1? and T2 relaxation times improves classification between subjects with and without osteoarthritis  

PubMed Central

Purpose: Studies have shown that functional analysis of knee cartilage based on magnetic resonance (MR) relaxation times is a valuable tool in the understanding of osteoarthritis (OA). In this work, the regional spatial distribution of knee cartilage T1? and T2 relaxation times based on texture and laminar analyses was studied to investigate if they provide additional insight compared to global mean values in the study of OA. Methods: Knee cartilage of 36 subjects, 19 healthy controls and 17 with mild OA, was divided into 16 compartments. T1? and T2 relaxation times were studied with first order statistics, eight texture parameters with four different orientations using gray-level co-occurrence matrices and by subdividing each compartment into two different layers: Deep and superficial. Receiver operating characteristic curve analysis was performed to evaluate the potential of each technique to correctly classify the populations. Results: Although the deep and superficial cartilage layers had in general significantly different T1? and T2 relaxation times, they performed similarly in terms of subject discrimination. The subdivision of lateral and medial femoral compartments into weight-bearing and non-weight-bearing regions did not improve discrimination. Also it was found that the most sensitive region was the patella and that T1? discriminated better than T2. The most important finding was that with respect to global mean values, laminar and texture analyses improved subject discrimination. Conclusions: Results of this study suggest that spatially assessing MR images of the knee cartilage relaxation times using laminar and texture analyses could lead to better and probably earlier identification of cartilage matrix abnormalities in subjects with OA. PMID:19810478

Carballido-Gamio, Julio; Stahl, Robert; Blumenkrantz, Gabrielle; Romero, Adan; Majumdar, Sharmila; Link, Thomas M.

2009-01-01

241

Radial Transport of Large-scale Magnetic Fields in Accretion Disks. II. Relaxation to Steady States  

NASA Astrophysics Data System (ADS)

We study the time evolution of a large-scale magnetic flux threading an accretion disk. The induction equation of the mean poloidal field is solved under the standard viscous disk model. Magnetic flux evolution is controlled by two timescales: one is the timescale of the inward advection of the magnetic flux, ?adv. This is induced by the dragging of the flux by the accreting gas. The other is the outward diffusion timescale of the magnetic flux ?dif. We consider diffusion due to the Ohmic resistivity. These timescales can be significantly different from the disk viscous timescale ?disk. The behaviors of the magnetic flux evolution are quite different depending on the magnitude relationship of the timescales ?adv, ?dif, and ?disk. The most interesting phenomena occur when ?adv Lt ?dif, ?disk. In such a case, the magnetic flux distribution approaches a quasi-steady profile much faster than the viscous evolution of the gas disk, and the magnetic flux has also been tightly bundled to the inner part of the disk. In the inner part, although the poloidal magnetic field becomes much stronger than the interstellar magnetic field, the field strength is limited to the maximum value that is analytically given by our previous work. We also find a condition for the initial large magnetic flux, which is a fossil of the magnetic field dragging during the early phase of star formation that survives for a duration in which significant gas disk evolution proceeds.

Takeuchi, Taku; Okuzumi, Satoshi

2014-12-01

242

Relaxing the closure assumption in single-season occupancy models: staggered arrival and departure times  

USGS Publications Warehouse

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.

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

2013-01-01

243

Tighten after Relax: Minimax-Optimal Sparse PCA in Polynomial Time  

PubMed Central

We provide statistical and computational analysis of sparse Principal Component Analysis (PCA) in high dimensions. The sparse PCA problem is highly nonconvex in nature. Consequently, though its global solution attains the optimal statistical rate of convergence, such solution is computationally intractable to obtain. Meanwhile, although its convex relaxations are tractable to compute, they yield estimators with suboptimal statistical rates of convergence. On the other hand, existing nonconvex optimization procedures, such as greedy methods, lack statistical guarantees. In this paper, we propose a two-stage sparse PCA procedure that attains the optimal principal subspace estimator in polynomial time. The main stage employs a novel algorithm named sparse orthogonal iteration pursuit, which iteratively solves the underlying nonconvex problem. However, our analysis shows that this algorithm only has desired computational and statistical guarantees within a restricted region, namely the basin of attraction. To obtain the desired initial estimator that falls into this region, we solve a convex formulation of sparse PCA with early stopping. Under an integrated analytic framework, we simultaneously characterize the computational and statistical performance of this two-stage procedure. Computationally, our procedure converges at the rate of 1?t within the initialization stage, and at a geometric rate within the main stage. Statistically, the final principal subspace estimator achieves the minimax-optimal statistical rate of convergence with respect to the sparsity level s*, dimension d and sample size n. Our procedure motivates a general paradigm of tackling nonconvex statistical learning problems with provable statistical guarantees.

Wang, Zhaoran; Lu, Huanran; Liu, Han

2014-01-01

244

Phylogeography Takes a Relaxed Random Walk in Continuous Space and Time  

PubMed Central

Research aimed at understanding the geographic context of evolutionary histories is burgeoning across biological disciplines. Recent endeavors attempt to interpret contemporaneous genetic variation in the light of increasingly detailed geographical and environmental observations. Such interest has promoted the development of phylogeographic inference techniques that explicitly aim to integrate such heterogeneous data. One promising development involves reconstructing phylogeographic history on a continuous landscape. Here, we present a Bayesian statistical approach to infer continuous phylogeographic diffusion using random walk models while simultaneously reconstructing the evolutionary history in time from molecular sequence data. Moreover, by accommodating branch-specific variation in dispersal rates, we relax the most restrictive assumption of the standard Brownian diffusion process and demonstrate increased statistical efficiency in spatial reconstructions of overdispersed random walks by analyzing both simulated and real viral genetic data. We further illustrate how drawing inference about summary statistics from a fully specified stochastic process over both sequence evolution and spatial movement reveals important characteristics of a rabies epidemic. Together with recent advances in discrete phylogeographic inference, the continuous model developments furnish a flexible statistical framework for biogeographical reconstructions that is easily expanded upon to accommodate various landscape genetic features. PMID:20203288

Lemey, Philippe; Rambaut, Andrew; Welch, John J.; Suchard, Marc A.

2010-01-01

245

Phylogeography takes a relaxed random walk in continuous space and time.  

PubMed

Research aimed at understanding the geographic context of evolutionary histories is burgeoning across biological disciplines. Recent endeavors attempt to interpret contemporaneous genetic variation in the light of increasingly detailed geographical and environmental observations. Such interest has promoted the development of phylogeographic inference techniques that explicitly aim to integrate such heterogeneous data. One promising development involves reconstructing phylogeographic history on a continuous landscape. Here, we present a Bayesian statistical approach to infer continuous phylogeographic diffusion using random walk models while simultaneously reconstructing the evolutionary history in time from molecular sequence data. Moreover, by accommodating branch-specific variation in dispersal rates, we relax the most restrictive assumption of the standard Brownian diffusion process and demonstrate increased statistical efficiency in spatial reconstructions of overdispersed random walks by analyzing both simulated and real viral genetic data. We further illustrate how drawing inference about summary statistics from a fully specified stochastic process over both sequence evolution and spatial movement reveals important characteristics of a rabies epidemic. Together with recent advances in discrete phylogeographic inference, the continuous model developments furnish a flexible statistical framework for biogeographical reconstructions that is easily expanded upon to accommodate various landscape genetic features. PMID:20203288

Lemey, Philippe; Rambaut, Andrew; Welch, John J; Suchard, Marc A

2010-08-01

246

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

247

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

248

Vibrational Energy Relaxation of "Tailored" Hemes in Myoglobin Following Ligand Photolysis Supports Energy Funneling Mechanism of Heme "Cooling"  

E-print Network

Vibrational Energy Relaxation of "Tailored" Hemes in Myoglobin Following Ligand Photolysis Supports or dissociation, heme proteins undergo vibrational energy relaxation (VER). Understanding the time scales and mechanisms of vibrational energy transfer is an essential component of a complete understanding

Straub, John E.

249

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

NASA Astrophysics Data System (ADS)

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

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

2005-09-01

250

Fluctuation and relaxation properties of pulled fronts: A scenario for nonstandard kardar-parisi-zhang scaling  

PubMed

We argue that while fluctuating fronts propagating into an unstable state should be in the standard Kardar-Parisi-Zhang (KPZ) universality class when they are pushed, they should not when they are pulled: The 1/t velocity relaxation of deterministic pulled fronts makes it unlikely that the KPZ equation is their proper effective long-wavelength low-frequency theory. Simulations in 2D confirm the proposed scenario, and yield exponents beta approximately 0.29+/-0.01, zeta approximately 0.40+/-0.02 for fluctuating pulled fronts, instead of the (1+1)D KPZ values beta = 1/3, zeta = 1/2. Our value of beta is consistent with an earlier result of Riordan et al., and with a recent conjecture that the exponents are the (2+1)D KPZ values. PMID:11030949

Tripathy; van Saarloos W

2000-10-23

251

Atomic Scale Strain Relaxation in Axial Semiconductor III-V Nanowire Heterostructures.  

PubMed

Combination of mismatched materials in semiconductor nanowire heterostructures offers a freedom of bandstructure engineering that is impossible in standard planar epitaxy. Nevertheless, the presence of strain and structural defects directly control the optoelectronic properties of these nanomaterials. Understanding with atomic accuracy how mismatched heterostructures release or accommodate strain, therefore, is highly desirable. By using atomic resolution high angle annular dark field scanning transmission electron microscopy combined with geometrical phase analyses and computer simulations, we are able to establish the relaxation mechanisms (including both elastic and plastic deformations) to release the mismatch strain in axial nanowire heterostructures. Formation of misfit dislocations, diffusion of atomic species, polarity transfer, and induced structural transformations are studied with atomic resolution at the intermediate ternary interfaces. Two nanowire heterostructure systems with promising applications (InAs/InSb and GaAs/GaSb) have been selected as key examples. PMID:25330094

de la Mata, María; Magén, César; Caroff, Philippe; Arbiol, Jordi

2014-11-12

252

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

NASA Astrophysics Data System (ADS)

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

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

2007-12-01

253

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

254

MRI of bone marrow in the distal radius: in vivo precision of effective transverse relaxation times  

NASA Technical Reports Server (NTRS)

The effective transverse relaxation time T2* is influenced by the presence of trabecular bone, and can potentially provide a measure of bone density as well as bone structure. We determined the in vivo precision of T2* in repeated bone marrow measurements. The T2* measurements of the bone marrow of the distal radius were performed twice within 2 weeks in six healthy young volunteers using a modified water-presaturated 3D Gradient-Recalled Acquisition at Steady State (GRASS) sequence with TE 7, 10, 12, 20, and 30; TR 67; flip angle (FA) 90 degrees. An axial volume covering a length of 5.6 cm in the distal radius was measured. Regions of interest (ROIs) were determined manually and consisted of the entire trabecular bone cross-section extending proximally from the radial subchondral endplate. Reproducibility of T2* and area measurements was expressed as the absolute precision error (standard deviation [SD] in ms or mm2) or as the relative precision error (SD/mean x 100, or coefficient of variation [CV] in %) between the two-point measurements. Short-term precision of T2* and area measurements varied depending on section thickness and location of the ROI in the distal radius. Absolute precision errors for T2* times were between 1.3 and 2.9 ms (relative precision errors 3.8-9.5 %) and for area measurements between 20 and 55 mm2 (relative precision errors 5.1-16.4%). This MR technique for quantitative assessment of trabecular bone density showed reasonable reproducibility in vivo and is a promising future tool for the assessment of osteoporosis.

Grampp, S.; Majumdar, S.; Jergas, M.; Lang, P.; Gies, A.; Genant, H. K.

1995-01-01

255

Ab Initio Time-Domain Study of Phonon-Assisted Relaxation of Charge Carriers in a PbSe Quantum Dot  

E-print Network

of inorganic semiconductors, known as artificial atoms or quantum dots (QD), exhibit a variety of uniqueAb Initio Time-Domain Study of Phonon-Assisted Relaxation of Charge Carriers in a PbSe Quantum Dot The phonon-induced relaxation dynamics of charge carriers in a PbSe quantum dot is studied for the first time

256

Solution of the multivalley Boltzmann transport equations in Si and GaAs based on the time scales of hydrodynamic equations  

NASA Astrophysics Data System (ADS)

The previously developed hydrokinetic transport theory is used to arrive at a multivalley transport model for the electron distribution function evolving at the energy relaxation scale. The hydrokinetic distribution described by hydrodynamic parameters, including the density, mean energy, and average velocity, is introduced to approximate the kinetic distribution. The developed multivalley hydrokinetic model, together with the Monte Carlo method, is applied to study nonequilibrium energy and momentum distribution functions of electrons in n-type Si <100> and GaAs. It is shown that the hydrokinetic concept can be used to characterize extreme nonequilibrium phenomena of the distribution and transport parameters in terms of the relaxation scales of hydrodynamic parameters. The study suggests that evolution of the distribution is strongly influenced by energy relaxation. It is also found that in ultrafast transient situations the influence of velocity relaxation on the distribution function is more pronounced if the ratio ?? /?m is larger, where ?? and ?m are energy and momentum relaxation times, respectively. In general, similar influences of energy and momentum dependences also show in the relaxation times. In Si at room temperature, the ratio is near or below 10 at low or medium field, and the distribution, which is subjected to a rapid change in field, weakly depends on the velocity relaxation. In the ? valley of GaAs, although the ratio is not larger than that in Si, effects of velocity relaxation are considerably stronger due to much more pronounced velocity overshoot. The hydrokinetic distribution at the energy relaxation scale therefore provides a good description for electrons in Si in extreme nonequilibrium situations, but not in GaAs during the strong overshoot/undershoot interval. In the L valleys the ratio is much larger than 10 at low or medium fields. Consequently, The L-valley distribution function subjected to a drastically increasing field from a low value is also strongly influenced by velocity relaxation even though no overshoot is observed.

Cheng, Ming-C.; Chennupati, Rambabu; Wen, Ying

1995-10-01

257

Fast and simultaneous measurement of longitudinal and transverse NMR relaxation times in a single continuous wave free precession experiment.  

PubMed

The purpose of this communication is to describe a method for rapid and simultaneous determination of longitudinal (T1) and transversel (T2) relaxation times, based on a single continuous wave free precession (CWFP) experiment which employs RF pulses with a pi/2 flip angle. We analyze several examples, involving nuclei such as 1H, 31P, and 19F, where good agreement with T1 and T2 measurements obtained by traditional methods is apparent. We also compare with the more time-consuming steady-state free precession (SSFP) method of Kronenbitter and Schwenk where several experiments are needed to determine the optimum flip angle. The role of an inhomogeneous magnetic field on the observed decays and its effect upon the accuracy of relaxation times obtained by these methods is examined by comparing numerical simulations with experimental data. Possible sources of error and conditions to minimize its effects are described. PMID:15705510

Venâncio, Tiago; Engelsberg, Mario; Azeredo, Rodrigo B V; Alem, Neif E R; Colnago, Luiz A

2005-03-01

258

Surface vibrational relaxation of N2 studied by infrared titration with time resolved Quantum Cascade Laser diagnostics  

NASA Astrophysics Data System (ADS)

Relaxation of vibrationally excited nitrogen molecules on reactor walls is the most efficient N2(v) loss mechanism in laboratory plasmas at pressures up to few tens of mbars. In the present study a new method for determination of the de-excitation probability ?N2 of vibrationally excited N2 on different surfaces has been developed. A short dc discharge pulse was applied to a mixture containing 0.05-1% of CO2, N2O or CO in N2 at 1.3 mbar. Due to a very efficient vibrational coupling between N2(v) and CO2 (N2O, CO), the vibrational excitation of these titrating molecules is an image of the vibrational excitation of N2. In the afterglow, the vibrational relaxation was monitored in-situ using quantum cascade laser absorption spectroscopy. The measurements were performed in a single discharge pulse without signal accumulation. Experimental results were interpreted in terms of a numerical model of non-equilibrium vibrational kinetics. The value of ?N2 was determined from the best agreement between the measured and calculated relaxation times. Using new technique the relaxation probability of N2(v) was measured for SiO2, TiO2, Al2O3, Pyrex and anodized aluminum.

Marinov, D.; Guaitella, O.; Rousseau, A.; Lopatik, D.; Hübner, M.; Röpcke, J.; Ionikh, Yu

2012-10-01

259

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

260

Invariance of conductivity relaxation under pressure and temperature variations at constant conductivity relaxation time in 0.4 Ca (N O3)2-0.6 KN O3  

NASA Astrophysics Data System (ADS)

The article reports the dependence of the conductivity relaxation on temperature T and pressure P in the canonical ionic glass former 0.4 Ca (N O3)2-0.6 KN O3(CKN ) . At constant conductivity relaxation time ??, the entire conductivity relaxation spectra obtained at widely different combinations of T and P superpose almost perfectly, and thus it is the ion-ion interaction but not thermodynamics that determines the frequency dispersion. Moreover, on vitrifying CKN by either elevating P or decreasing T, changes of P or T dependence of ?? at the glass transition pressure Pg and temperature Tg are observed to occur at the same value, i.e., ??(Pg) =??(Tg) , indicating that the relation between ?? and the structural relaxation time ?? is also independent of P and T.

Wojnarowska, Z.; Ngai, K. L.; Paluch, M.

2014-12-01

261

Trabecular Bone Structure and Spatial Differences in Articular Cartilage MR Relaxation Times in Individuals with Posterior Horn Medial Meniscal Tears  

PubMed Central

Objective To analyze knee trabecular bone structure and spatial cartilage T1? and T2 relaxation times using 3-T MRI in subjects with and without tears of posterior horn of medial meniscus (PHMM). Design 3-T MRI from 59 subjects (> 18 years), were used to evaluate PHMM tears based on modified WORMS scoring; and to calculate apparent trabecular bone - volume over total bone volume fraction (app. BV/TV), number (app. Tb.N), separation (app. Tb.Sp) and thickness (app. Tb.Th) for overall femur/tibia and medial/lateral femur/tibia; and relaxation times for deep and superficial layers of articular cartilage. A repeated measures analysis using GEE was performed to compare trabecular bone and cartilage relaxation time parameters between people with (n = 35) and without (n= 24) PHMM tears, while adjusting for age and knee OA presence. Results Subjects with PHMM tears had lower app. BV./TV and app. Tb.N, and greater app. Tb.Th, and app. Tb.Sp. They also had higher T1? times in the deep cartilage layer for lateral tibia and medial femur and higher T2 relaxation times for the deep cartilage layer across all compartments. Conclusions PHMM tears are associated with differences in underlying trabecular bone and deep layer of cartilage. Overload of subchondral bone can lead to its sclerosis and stress shielding of trabecular bone leading to the resorptive changes observed in this study. The results underline the importance of interactions of trabecular bone and cartilage in the pathogenesis of knee OA in people with PHMM tears. PMID:23047010

Kumar, Deepak; Schooler, Joseph; Zuo, Jin; McCulloch, Charles E.; Nardo, Lorenzo; Link, Thomas M.; Li, Xiaojuan; Majumdar, Sharmila

2012-01-01

262

Effect of the off-diagonal Onsager rate coefficient on the relaxation times in a spin-1 Ising system  

NASA Astrophysics Data System (ADS)

As a continuation of our previously published works, we used the lowest approximation of the cluster variation method that is identical to the mean-field approximation and linearized equations of motions which are obtained by the Onsager reciprocity theorem to study the effect of the off-diagonal Onsager rate coefficient ( ?) on the relaxation times ?1 and ?2 near the critical point of the spin-1 Ising system. The temperature variations of the relaxation times have been studied for different values of the kinetic coefficient ( ?) which couples the dipolar and quadrupolar order currents in the system. Below and above the critical temperature ( TC), a maximum of ?2 is observed according to the values of off-diagonal coefficient ( ?).

Keskin, Mustafa; Erdem, R?za

2002-05-01

263

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

SciTech Connect

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

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

2006-09-01

264

Dislocation-mediated relaxation in nanograined columnar palladium films revealed by on-chip time-resolved HRTEM testing.  

PubMed

The high-rate sensitivity of nanostructured metallic materials demonstrated in the recent literature is related to the predominance of thermally activated deformation mechanisms favoured by a large density of internal interfaces. Here we report time-resolved high-resolution electron transmission microscopy creep tests on thin nanograined films using on-chip nanomechanical testing. Tests are performed on palladium, which exhibited unexpectedly large creep rates at room temperature. Despite the small 30-nm grain size, relaxation is found to be mediated by dislocation mechanisms. The dislocations interact with the growth nanotwins present in the grains, leading to a loss of coherency of twin boundaries. The density of stored dislocations first increases with applied deformation, and then decreases with time to drive additional deformation while no grain boundary mechanism is observed. This fast relaxation constitutes a key issue in the development of various micro- and nanotechnologies such as palladium membranes for hydrogen applications. PMID:25557273

Colla, M-S; Amin-Ahmadi, B; Idrissi, H; Malet, L; Godet, S; Raskin, J-P; Schryvers, D; Pardoen, T

2015-01-01

265

Dislocation-mediated relaxation in nanograined columnar palladium films revealed by on-chip time-resolved HRTEM testing  

NASA Astrophysics Data System (ADS)

The high-rate sensitivity of nanostructured metallic materials demonstrated in the recent literature is related to the predominance of thermally activated deformation mechanisms favoured by a large density of internal interfaces. Here we report time-resolved high-resolution electron transmission microscopy creep tests on thin nanograined films using on-chip nanomechanical testing. Tests are performed on palladium, which exhibited unexpectedly large creep rates at room temperature. Despite the small 30-nm grain size, relaxation is found to be mediated by dislocation mechanisms. The dislocations interact with the growth nanotwins present in the grains, leading to a loss of coherency of twin boundaries. The density of stored dislocations first increases with applied deformation, and then decreases with time to drive additional deformation while no grain boundary mechanism is observed. This fast relaxation constitutes a key issue in the development of various micro- and nanotechnologies such as palladium membranes for hydrogen applications.

Colla, M.-S.; Amin-Ahmadi, B.; Idrissi, H.; Malet, L.; Godet, S.; Raskin, J.-P.; Schryvers, D.; Pardoen, T.

2015-01-01

266

Temperature-dependent chemical shift and relaxation times of (23)Na in Na(4)HTm[DOTP].  

PubMed

We describe the characterization of a (23)Na temperature-dependent chemical shift and relaxation rates in the complex, Na(4)HTm[DOTP]. This is the first characterization of a (23)Na temperature-dependent chemical shift in a nonmetallic sample. The (23)Na temperature-dependent chemical shift coefficient is approximately -0. 5 PPM/ degrees C for both an aqueous solution and a 6% agarose gel of this compound. This is 50 times the magnitude of the temperature-dependent chemical shift coefficient of water protons. The relaxation times, T(1), T(2f), and T(2s) increased by 0.1, 0.01, and 0.05 ms/ degrees C, respectively. Applications of these unique properties for designing an MRI technique for monitoring heat deposition in tissue and tissue phantoms are discussed. PMID:10698662

Shapiro, E M; Borthakur, A; Bansal, N; Leigh, J S; Reddy, R

2000-03-01

267

Temperature-Dependent Chemical Shift and Relaxation Times of 23Na in Na 4HTm[DOTP  

NASA Astrophysics Data System (ADS)

We describe the characterization of a 23Na temperature-dependent chemical shift and relaxation rates in the complex, Na 4HTm[DOTP]. This is the first characterization of a 23Na temperature-dependent chemical shift in a nonmetallic sample. The 23Na temperature-dependent chemical shift coefficient is ˜-0.5 PPM/°C for both an aqueous solution and a 6% agarose gel of this compound. This is 50 times the magnitude of the temperature-dependent chemical shift coefficient of water protons. The relaxation times, T1, T2f, and T2s increased by 0.1, 0.01, and 0.05 ms/°C, respectively. Applications of these unique properties for designing an MRI technique for monitoring heat deposition in tissue and tissue phantoms are discussed.

Shapiro, Erik M.; Borthakur, Arijitt; Bansal, Navin; Leigh, John S.; Reddy, Ravinder

2000-03-01

268

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

269

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

NASA Astrophysics Data System (ADS)

Evolution of small-vacancy clusters in bcc Fe is simulated using a multiscale approach coupling an atomistic activation-relaxation method for sampling transition-state pathways with environment-dependent reaction coordinate calculations and a kinetic Monte Carlo simulation to reach time scales on the order of ˜104s. Under vacancy-supersaturated condition, di- and trivacancy clusters form and grow by coalescence (Ostwald ripening). For cluster size greater than four we find a transition temperature of 150°C for accelerated cluster growth, as observed in positron annihilation spectroscopy experiments. Implications for the mechanism of stage-IV radiation-damage-recovery kinetics are discussed.

Fan, Yue; Kushima, Akihiro; Yip, Sidney; Yildiz, Bilge

2011-03-01

270

Quantitative model for the interecho time dependence of the CPMG relaxation rate in iron-rich gray matter  

Microsoft Academic Search

A quantitative model is proposed for computing the dependence on the interecho time of the NMR relaxation rate in iron-rich gray matter obtained with a Carr-Purcell-Meiboom-Gill sequence. The model consists of representing oligodendrocytes as identical magnetic spheres arranged in a spatially random pattern, and in approximating water diffusion as isotropic and unrestricted. Pre- dictions of the model are calculated numerically

J. H. Jensen; R. Chandra; H. Yu

2001-01-01

271

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

Microsoft Academic Search

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

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

2003-01-01

272

Lattice Relaxation Effect Associated with Core Holes in Ionic Crystals Studied by Time-Resolved Luminescence Spectroscopy  

NASA Astrophysics Data System (ADS)

Auger-decay-free core luminescence in RbF, CsF, CsCl, CsBr and BaF2 has been studied under monochromatic vacuum ultraviolet light excitation using a time-resolved technique. Luminescence spectra associated with core holes are carefully separated from those originating in the valence-band excitation. Based on the spectral shape and energy range of the luminescence bands, a lattice relaxation effect following the core hole creation is discussed.

Matsumoto, Tamao; Kan'no, Ken-ichi; Itoh, Minoru; Ohno, Nobuhito

1996-05-01

273

Effect of Compression on the Relationship between Viscosity and Dielectric Relaxation Time in Hydrogen-Bonded Primary Alcohols  

NASA Astrophysics Data System (ADS)

High pressure viscosity and dielectric measurements were carried out on two monohydroxy alcohols, 2-ethyl-1-hexanol and 5-methyl-2-hexanol, at room temperature. Analysis of the dielectric relaxation times versus viscosity revealed the breakdown of the Einstein-Debye relation above some characteristic pressure. The failure of the Einstein-Debye relation is a manifestation of pressure induced changes of supramolecular hydrogen bonded structures which occur in these liquids.

Pawlus, S.; Klotz, S.; Paluch, M.

2013-04-01

274

Multiple conformational states of the hammerhead ribozyme, broad time range of relaxation and topology of dynamics  

Microsoft Academic Search

The dynamics of a hammerhead ribozyme was analyzed by measurements of fluorescence-detected temperature jump relaxation. The ribozyme was substituted at different positions by 2-aminopurine (2-AP) as fluorescence indicator; these substitutions do not inhibit catalysis. The general shape of relaxa- tion curves reported from different positions of the ribozyme is very similar: af ast decrease of fluorescence, mainly due to physical

Marcus Menger; Fritz Eckstein; Dietmar Porschke

2000-01-01

275

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

276

Effects of nonsinusoidal character of atomic modulation on NQR spin-lattice relaxation time of incommensurate phases  

SciTech Connect

The present work is an extention of the theoretical calculation developed by Blinc to explain the temperature and frequency dependence of the spin-lattice relaxation time in incommensurate phases. We have evaluated the influence of the nonsinusoidal character of the atomic modulation, in the linear approximation, over the NQR spectra and over the spin-lattice relaxation due to direct and Raman processes. It is shown that the peak with lower intensity in the NQR spectra always has a larger T{sub 1} and viceversa. The results have been applied to bis(4-chlorophenyl)sulfone T{sub 1} and line-shape data. The temperature and frequency dependence of T{sub 1} are well reproduced if Raman processes are considered.

Perez, Silvina C.; Schurrer, Clemar; Wolfenson, Alberto

2001-06-01

277

Polarized Alkali-Metal Vapor with Minute-Long Transverse Spin-Relaxation Time  

SciTech Connect

We demonstrate lifetimes of Zeeman populations and coherences in excess of 60 sec in alkali-metal vapor cells with inner walls coated with an alkene material. This represents 2 orders of magnitude improvement over the best paraffin coatings. We explore the temperature dependence of cells coated with this material and investigate spin-exchange relaxation-free magnetometry in a room-temperature environment, a regime previously inaccessible with conventional coating materials.

Balabas, M. V. [S. I. Vavilov State Optical Institute, St. Petersburg, 199034 (Russian Federation); Karaulanov, T.; Ledbetter, M. P. [Department of Physics, University of California at Berkeley, Berkeley, California 94720-7300 (United States); Budker, D. [Department of Physics, University of California at Berkeley, Berkeley, California 94720-7300 (United States); Nuclear Science Division, Lawrence Berkeley National Laboratory, Berkeley California 94720 (United States)

2010-08-13

278

Longitudinal relaxation oscillations induced by HOMs  

SciTech Connect

Taking advantage of the vastly different time scales of the problem, a simple analytical model of HOM induced relaxation oscillations has been developed. First a continuous approximation of the impulsive discrete forces is made. Then only the components of the force with the synchrotron frequency are retained to describe the slowly varying amplitude and frequency of the relaxation oscillation. A two particle version of this model reproduces the main characteristics of the system.

Sebek, J.; Limborg, C. [SSRL/SLAC, Stanford, California 94309 (United States)

1999-12-03

279

A molecular time-scale for eukaryote evolution recalibrated with the continuous microfossil record  

PubMed Central

Recent attempts to establish a molecular time-scale of eukaryote evolution failed to provide a congruent view on the timing of the origin and early diversification of eukaryotes. The major discrepancies in molecular time estimates are related to questions concerning the calibration of the tree. To limit these uncertainties, we used here as a source of calibration points the rich and continuous microfossil record of dinoflagellates, diatoms and coccolithophorids. We calibrated a small-subunit ribosomal RNA tree of eukaryotes with four maximum and 22 minimum time constraints. Using these multiple calibration points in a Bayesian relaxed molecular clock framework, we inferred that the early radiation of eukaryotes occurred near the Mesoproterozoic–Neoproterozoic boundary, about 1100 million years ago. Our results indicate that most Proterozoic fossils of possible eukaryotic origin cannot be confidently assigned to extant lineages and should therefore not be used as calibration points in molecular dating. PMID:16822745

Berney, Cédric; Pawlowski, Jan

2006-01-01

280

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

281

Scaling behavior of the alpha relaxation in fragile glass-forming liquids under conditions of high compression  

Microsoft Academic Search

The effect of pressure variation on dynamics of alpha relaxation process in poly[(phenyl glycidyl ether)-co-formaldehyde] has been investigated both under isothermal (T=293 K) and isobaric (P=0.1, 60, 120, 180, and 240 MPa) conditions using broad band dielectric spectroscopy (10-2 to 106 Hz). The alpha relaxation is analyzed by means of the Havriliak-Negami relaxation function which has two shape parameters (alpha

Marian Paluch; Stella Hensel-Bielówka; Jerzy Ziolo

2000-01-01

282

Ion-Beam Sculpting Time Scales Derek Stein,1  

E-print Network

Ion-Beam Sculpting Time Scales Derek Stein,1 Jiali Li,2 and Jene A. Golovchenko1,2 1 Division) A study of ion sculpting dynamics in SiO2 and SiN using periodically pulsed ion beams reveals material nanoscale matter transport can occur over second long time scales after the ion beam has been extinguished

Li, Jiali

283

Estimating ventilation time scales using overturning stream functions  

E-print Network

Estimating ventilation time scales using overturning stream functions Bijoy Thompson & Jonas for estimating ventilation time scales from overturning stream functions is proposed. The stream function may describing an ide- alized semi-enclosed ocean basin ventilated through a narrow strait over a sill

Döös, Kristofer

284

Variability of global lightning activity on the ENSO time scale  

Microsoft Academic Search

Global lightning activity has been studied on the ENSO (El Niño Southern Oscillation) time scale based on recordings of the Earth's Schumann resonances at Nagycenk (NCK), Hungary as well as observations from the OTD (Optical Transient Detector) and the LIS (Lightning Imaging Sensor) satellites in space. Both the intensity and position of lightning activity vary on the ENSO time scale.

G. Sátori; E. Williams; I. Lemperger

2009-01-01

285

LINK BETWEEN COSMIC RAYS AND CLOUDS ON DIFFERENT TIME SCALES  

E-print Network

LINK BETWEEN COSMIC RAYS AND CLOUDS ON DIFFERENT TIME SCALES ILYA G. USOSKIN and GENNADY A is related to a link between the cosmic ray flux and cloudiness. Here we review evidences relating terrestrial climate variability to changes of cosmic ray flux in the Earth's vicinity on different time scales

Usoskin, Ilya G.

286

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. PMID:25309307

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

2014-01-01

287

Acceleration time scale in an ultrarelativistic shock  

E-print Network

The acceleration mechanism at ultrarelativistic shocks is investigated using the Monte Carlo simulations. We apply a method of discrete small amplitude particle momentum scattering to reproduce highly anisotropic conditions at the shock and carefully describe the acceleration mechanism. The obtained acceleration times equal $1.0 r_{g}/c$ if the spectral index reach the value of 2.2, independent of physical conditions in the shock. Some other parameters of the acceleration process are also provided.

Janusz Bednarz

2000-05-10

288

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

289

Probing Photosynthesis on a Picosecond Time Scale  

PubMed Central

Fluorescent emission kinetics of isolated spinach chloroplasts have been observed at room temperature with an instrument resolution time of 10 ps using a frequency doubled, mode-locked Nd:glass laser and an optical Kerr gate. At 685 nm two maxima are apparent in the time dependency of the fluorescence; the first occurs at 15 ps and the second at 90 ps after the flash. The intervening minimum occurs at about 50 ps. On the basis of theoretical models, lifetimes of the components associated with the two peaks and spectra (in escarole chloroplasts), the fluorescence associated with the first peak is interpreted as originating from Photosystem I (PSI) (risetime ?10 ps, lifetime ?10 ps) and the second peak from Photosystem II (PSII) (lifetime, 210 ps in spinach chloroplasts and 320 ps in escarole chloroplasts). The fact that there are two fluorescing components with a quantum yield ratio ?0.048 explains the previous discrepancy between the quantum yield of fluorescence measured in chloroplasts directly and that calculated from the lifetime of PSII. The 90 ps delay in the peak of PSII fluorescence is probably explained by energy transfer between accessory pigments such as carotenoids and Chl a. Energy spillover between PSI and PSII is not apparent during the time of observation. The results of this work support the view that the transfer of excitation energy to the trap complex in both photosystems occurs by means of a molecular excitation mechanism of intermediate coupling strength. Although triplet states are not of major importance in energy transfer to PSII traps, the possibility that they are involved in PSI photochemistry has not been eliminated. PMID:4830466

Seibert, Michael; Alfano, Robert R.

1974-01-01

290

Acceleration time scale at ultrarelativistic shock waves  

E-print Network

The first-order cosmic ray acceleration at ultrarelativistic shocks is investigated using the Monte Carlo method. We apply a method of discrete particle momentum scattering as a model of particle pitch angle diffusion to reproduce highly anisotropic conditions at the shock wave. Shocks with Lorentz factors $\\gamma$ up to 320 and varying magnetic field inclinations $\\psi$ are considered. Values of diffusion coefficients upstream in the point where energy spectral indices stabilize to the limit 2.2 were calculated. The obtained acceleration time does not depend on shock conditions.

J. Bednarz

1998-08-26

291

Tracking Temperature-Dependent Relaxation Times of Ferritin Nanomagnets with a Wideband Quantum Spectrometer  

NASA Astrophysics Data System (ADS)

We demonstrate the tracking of the spin dynamics of ensemble and individual magnetic ferritin proteins from cryogenic up to room temperature using the nitrogen-vacancy color center in diamond as a magnetic sensor. We employ different detection protocols to probe the influence of the ferritin nanomagnets on the longitudinal and transverse relaxation of the nitrogen-vacancy center, which enables magnetic sensing over a wide frequency range from Hz to GHz. The temperature dependence of the observed spectral features can be well understood by the thermally induced magnetization reversals of the ferritin and enables the determination of the anisotropy barrier of single ferritin molecules.

Schäfer-Nolte, Eike; Schlipf, Lukas; Ternes, Markus; Reinhard, Friedemann; Kern, Klaus; Wrachtrup, Jörg

2014-11-01

292

Allometric scaling and maximum efficiency in physiological eigen time  

PubMed Central

General optimization results from physics indicate that maximum efficiency of a process, in the sense of minimum overall entropy production, is achieved when the rate of entropy production is constant over time, however not in ordinary clock time but on an, in general varying, “eigen timescale, intrinsic to the system. We identify the eigen time of a biological system with “physiological time,” which generally scales with the 1/4 power of body mass, M1/4, over a vast range of species. Since it is equally well established that metabolic rate scales as M3/4, it follows that organisms produce entropy at the same intrinsic rate, fulfilling a necessary condition for maximum efficiency, and are all, furthermore, equally efficient on the physiological eigen time scale. PMID:11959910

Andresen, Bjarne; Shiner, J. S.; Uehlinger, Dominik E.

2002-01-01

293

Structural and microscopic relaxations in a colloidal glass.  

PubMed

The aging dynamics of a colloidal glass has been studied by multiangle dynamic light scattering, neutron spin echo, X-ray photon correlation spectroscopy and molecular dynamics simulations. The two relaxation processes, microscopic (fast) and structural (slow), have been investigated in an unprecedentedly wide range of time and length scales covering both ergodic and nonergodic regimes. The microscopic relaxation time remains diffusive at all length scales across the glass transition scaling with wavevector Q as Q(-2). The length-scale dependence of structural relaxation time changes from diffusive, characterized by a Q(-2)-dependence in the early stages of aging, to a Q(-1)-dependence in the full aging regime which marks a discontinuous hopping dynamics. Both regimes are associated with a stretched behaviour of the correlation functions. We expect these findings to provide a general description of both relaxations across the glass transition. PMID:25406421

Augusto de Melo Marques, Flavio; Angelini, Roberta; Zaccarelli, Emanuela; Farago, Bela; Ruta, Beatrice; Ruocco, Giancarlo; Ruzicka, Barbara

2014-12-17

294

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

295

Continuum traffic model with the consideration of two delay time scales  

NASA Astrophysics Data System (ADS)

This paper presents a continuum traffic model. The derivation of this model is based upon the assumption that the stream velocity u reaches the equilibrium velocity ue within the relaxation time T, while the equilibrium velocity ue is adjusted to be attained through the driver’s reaction time tr. It is also assumed that the former delay time scale is greater than the latter. A motion equation with nonconstant propagation velocity of a disturbance in traffic flow is derived that can reflect the anisotropy of disturbance propagation in real traffic, unlike some other higher-order continuum models. It indicates that in our model the undesirable “wrong-way travel” phenomenon and gaslike behavior have been eliminated. The formation and diffusion of traffic shock can be better simulated.

Xue, Yu; Dai, Shi-Qiang

2003-12-01

296

Multiple-Relaxation-Time Lattice Boltzmann Approach to Compressible Flows with Flexible Specific-Heat Ratio and Prandtl Number  

E-print Network

A new multiple-relaxation-time lattice Boltzmann scheme for compressible flows with arbitrary specific heat ratio and Prandtl number is presented. In the new scheme, which is based on a two-dimensional 16-discrete-velocity model, the moment space and the corresponding transformation matrix are constructed according to the seven-moment relations associated with the local equilibrium distribution function. In the continuum limit, the model recovers the compressible Navier-Stokes equations with flexible specific-heat ratio and Prandtl number. Numerical experiments show that compressible flows with strong shocks can be simulated by the present model up to Mach numbers $Ma \\sim 5$.

Feng Chen; Aiguo Xu; Guangcai Zhang; Yingjun Li; Sauro Succi

2010-04-30

297

Spin relaxation and linear-in-electric-field frequency shift in an arbitrary, time-independent magnetic field  

SciTech Connect

A method is presented to calculate the spin relaxation times T{sub 1}, T{sub 2} due to a nonuniform magnetic field, and the linear-in-electric-field precession frequency shift {delta}{omega}{sub E} when an electric field is present, in the diffusion approximation for spins confined to a rectangular cell. It is found that the rectangular cell geometry admits of a general result for T{sub 1}, T{sub 2}, and {delta}{omega}{sub E} in terms of the spatial cosine-transform components of the magnetic field.

Clayton, Steven Michael [Los Alamos National Laboratory

2010-12-03

298

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

299

On time scale invariance of random walks in confined space.  

PubMed

Animal movement is often modelled on an individual level using simulated random walks. In such applications it is preferable that the properties of these random walks remain consistent when the choice of time is changed (time scale invariance). While this property is well understood in unbounded space, it has not been studied in detail for random walks in a confined domain. In this work we undertake an investigation of time scale invariance of the drift and diffusion rates of Brownian random walks subject to one of four simple boundary conditions. We find that time scale invariance is lost when the boundary condition is non-conservative, that is when movement (or individuals) is discarded due to boundary encounters. Where possible analytical results are used to describe the limits of the time scaling process, numerical results are then used to characterise the intermediate behaviour. PMID:25481837

Bearup, Daniel; Petrovskii, Sergei

2015-02-21

300

Time Scaling of Chaotic Systems: Application to Secure Communications  

E-print Network

The paper deals with time-scaling transformations of dynamical systems. Such scaling functions operate a change of coordinates on the time axis of the system trajectories preserving its phase portrait. Exploiting this property, a chaos encryption technique to transmit a binary signal through an analog channel is proposed. The scheme is based on a suitable time-scaling function which plays the role of a private key. The encoded transmitted signal is proved to resist known decryption attacks offering a secure and reliable communication.

Donatello Materassi; Michele Basso

2007-10-23

301

Learning Across Time Scales: Science, Policy, Management, and Communication  

NASA Astrophysics Data System (ADS)

This presentation will draw together common themes raised in the session and discuss lessons learned across time scales and their implications for managers and policy makers concerned with both climate change and variability. Session themes will be examined in the context of the upcoming World Summit on Sustainable Development (WSSD) and considered as opportunities for linking climate change policy discussions with lessons learned from the study of adaptation on seasonal to interannual time scales. The presentation will raise questions about future research directions, discuss recommendations for promoting learning across time scales, and explore options for better communicating the links between climate change and variability.

Stewart, M. M.

2002-05-01

302

Asymmetry of Information Flow Between Volatilities Across Time Scales  

E-print Network

Asymmetry of Information Flow Between Volatilities Across Time Scales Ramazan Gen¸cay Faruk Sel horizon is most likely followed by low volatility states at shorter time horizons. On the other hand, a high volatility state at long time horizons does not necessarily imply a high volatility state

Whitcher, Brandon

303

Real-Time Communication for Large Scale Distributed Control Systems  

Microsoft Academic Search

Because of their scale, complexity and requirement of ex- pandability, Large Scale Distributed Control Systems (LSDCS) are usu- ally created in a multistep integration process. To succeed, it has to be governed by well-defined information architecture, appropriate commu- nication infrastructure and the supervisory role of the time notion taken into consideration from the very beginning of the design stage. Mutual

Mariusz Postol

304

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

305

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

306

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

307

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

NASA Astrophysics Data System (ADS)

We report an extensive and systematic investigation of the multi-point and multi-time correlation functions to reveal the spatio-temporal structures of dynamic heterogeneities in glass-forming liquids. Molecular dynamics simulations are carried out for the supercooled states of various prototype models of glass-forming liquids such as binary Kob-Andersen, Wahnström, soft-sphere, and network-forming liquids. While the first three models act as fragile liquids exhibiting super-Arrhenius temperature dependence in their relaxation times, the last is a strong glass-former exhibiting Arrhenius behavior. First, we quantify the length scale of the dynamic heterogeneities utilizing the four-point correlation function. The growth of the dynamic length scale with decreasing temperature is characterized by various scaling relations that are analogous to the critical phenomena. We also examine how the growth of the length scale depends upon the model employed. Second, the four-point correlation function is extended to a three-time correlation function to characterize the temporal structures of the dynamic heterogeneities based on our previous studies [K. Kim and S. Saito, Phys. Rev. E 79, 060501-R (2009), 10.1103/PhysRevE.79.060501; K. Kim and S. Saito, J. Chem. Phys. 133, 044511 (2010), 10.1063/1.3464331]. We provide comprehensive numerical results obtained from the three-time correlation function for the above models. From these calculations, we examine the time scale of the dynamic heterogeneities and determine the associated lifetime in a consistent and systematic way. Our results indicate that the lifetime of the dynamical heterogeneities becomes much longer than the ?-relaxation time determined from a two-point correlation function in fragile liquids. The decoupling between the two time scales is remarkable, particularly in supercooled states, and the time scales differ by more than an order of magnitude in a more fragile liquid. In contrast, the lifetime is shorter than the ?-relaxation time in tetrahedral network-forming strong liquid, even at lower temperatures.

Kim, Kang; Saito, Shinji

2013-03-01

308

Time-Domain Ab Initio Simulation of Electron and Hole Relaxation Dynamics in a Single-Wall Semiconducting Carbon Nanotube  

E-print Network

tube-tube and tube- matrix interactions provide additional decay channels. The relaxation is faster) and high-frequency longitudinal optical (LO) G phonons in the charge carrier relaxation has been detected

309

Contrast at high field: relaxation times, magnetization transfer and phase in the rat brain at 16.4 T.  

PubMed

As field strength increases, the magnetic resonance imaging contrast parameters like relaxation times, magnetization transfer or image phase change, causing variations in contrast and signal-to-noise ratio. To obtain reliable data for these parameters at 16.4 T, high-resolution measurements of the relaxation times T(1), T(2) and T(2)*, as well as of the magnetization transfer ratio and the local frequency in the rat brain were performed. Tissue-specific values were obtained for up to 17 brain structures to assess image contrast. The measured parameters were compared to those found at different field strengths to estimate contrast and signal behavior at increasing field. T(1) values were relatively long with (2272 ± 113) ms in cortex and (2073 ± 97) ms in white matter, but did not show a tendency to converge, leading to an almost linear increase in signal-to-noise ratio and still growing contrast-to-noise ratio. T(2) was short with (25 ± 2) ms in cortex and (20 ± 1) ms in white matter. Magnetization transfer effects increase by around 25% compared to published 4.7 T data, which leads to improved contrast. The image phase, as novel and high-field specific contrast mechanism, is shown to obtain good contrast in deep brain regions with increasing signal-to-noise ratio up to high field strengths. PMID:21671265

Pohmann, Rolf; Shajan, G; Balla, D Z

2011-12-01

310

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

311

Relaxation processes in a turbulent compressible magnetofluid  

NASA Technical Reports Server (NTRS)

The compressible extensions of time asymptotic relaxation states of incompressible two-dimensional magnetohydrodynamic turbulence are studied. A polytropic equation of state is used with viscous and resistive dissipation. The incompressible case is known to allow three distinct time asymptotic types of behavior: magnetic energy dominated relaxation, kinetic energy dominated relaxation, and cross helicity dominated relaxation. At low Mach numbers the incompressible scenario is reproducible from the compressible simulations, and compressibility plays only a secondary role. At moderate, but still subsonic, Mach numbers the distinct incompressible processes are still recognizable, but strong compressibility features dominate the high-wave-number regime of several simulations. In particular, the magnetic and kinetic energy dominated simulations display regions of strong acoustic turbulence near the dissipation scale.

Ghosh, S.; Matthaeus, W. H.

1990-01-01

312

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

313

Vorticity statistics and the time scales of turbulent strain.  

PubMed

Time scales of turbulent strain activity, denoted as the strain persistence times of first and second order, are obtained from time-dependent expectation values and correlation functions of Lagrangian rate-of-strain eigenvalues taken in particularly defined statistical ensembles. Taking into account direct numerical simulation data, our approach relies on heuristic closure hypotheses which allow us to establish a connection between the statistics of vorticity and strain. It turns out that softly divergent prefactors correct the usual "1/s" strain time-scale estimate of standard turbulence phenomenology, in a way which is consistent with the phenomenon of vorticity intermittency. PMID:23944547

Moriconi, L; Pereira, R M

2013-07-01

314

Using Bio-Functionalized Magnetic Nanoparticles and Dynamic Nuclear Magnetic Resonance to Characterize the Time-Dependent Spin-Spin Relaxation Time for Sensitive Bio-Detection  

PubMed Central

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

315

Vibrational population relaxation of carbon monoxide in the heme pocket of photolyzed carbonmonoxy myoglobin: Comparison of time-resolved mid-IR absorbance experiments and molecular dynamics simulations  

PubMed Central

The vibrational energy relaxation of carbon monoxide in the heme pocket of sperm whale myoglobin was studied by using molecular dynamics simulation and normal mode analysis methods. Molecular dynamics trajectories of solvated myoglobin were run at 300 K for both the ?- and ?-tautomers of the distal His-64. Vibrational population relaxation times of 335 ± 115 ps for the ?-tautomer and 640 ± 185 ps for the ?-tautomer were estimated by using the Landau–Teller model. Normal mode analysis was used to identify those protein residues that act as the primary “doorway” modes in the vibrational relaxation of the oscillator. Although the CO relaxation rates in both the ?- and ?-tautomers are similar in magnitude, the simulations predict that the vibrational relaxation of the CO is faster in the ?-tautomer with the distal His playing an important role in the energy relaxation mechanism. Time-resolved mid-IR absorbance measurements were performed on photolyzed carbonmonoxy hemoglobin (Hb13CO). From these measurements, a T1 time of 600 ± 150 ps was determined. The simulation and experimental estimates are compared and discussed. PMID:10588704

Sagnella, Diane E.; Straub, John E.; Jackson, Timothy A.; Lim, Manho; Anfinrud, Philip A.

1999-01-01

316

Universal scaling function in discrete time asymmetric exclusion processes  

NASA Astrophysics Data System (ADS)

In the universality class of the one dimensional Kardar-Parisi-Zhang surface growth, Derrida and Lebowitz conjectured the universality of not only the scaling exponents, but of an entire scaling function. Since Derrida and Lebowitz' original publication this universality has been verified for a variety of continuous time systems in the KPZ universality class. We study the Derrida-Lebowitz scaling function for multi-particle versions of the discrete time Asymmetric Exclusion Process. We find that in this discrete time system the Derrida-Lebowitz scaling function not only properly characterizes the large system size limit, but even accurately describes surprisingly small systems. These results have immediate applications in searching biological sequence databases.

Chia, Nicholas; Bundschuh, Ralf

2005-03-01

317

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

318

Concentration regimes of biopolymers xanthan, tara, and clairana, comparing dynamic light scattering and distribution of relaxation time.  

PubMed

The aim of this work was to evaluate the utilization of analysis of the distribution of relaxation time (DRT) using a dynamic light back-scattering technique as alternative method for the determination of the concentration regimes in aqueous solutions of biopolymers (xanthan, clairana and tara gums) by an analysis of the overlap (c*) and aggregation (c**) concentrations. The diffusion coefficients were obtained over a range of concentrations for each biopolymer using two methods. The first method analysed the behaviour of the diffusion coefficient as a function of the concentration of the gum solution. This method is based on the analysis of the diffusion coefficient versus the concentration curve. Using the slope of the curves, it was possible to determine the c* and c** for xanthan and tara gum. However, it was not possible to determine the concentration regimes for clairana using this method. The second method was based on an analysis of the DRTs, which showed different numbers of relaxation modes. It was observed that the concentrations at which the number of modes changed corresponded to the c* and c**. Thus, the DRT technique provided an alternative method for the determination of the critical concentrations of biopolymers. PMID:23671627

Oliveira, Patrícia D; Michel, Ricardo C; McBride, Alan J A; Moreira, Angelita S; Lomba, Rosana F T; Vendruscolo, Claire T

2013-01-01

319

Concentration Regimes of Biopolymers Xanthan, Tara, and Clairana, Comparing Dynamic Light Scattering and Distribution of Relaxation Time  

PubMed Central

The aim of this work was to evaluate the utilization of analysis of the distribution of relaxation time (DRT) using a dynamic light back-scattering technique as alternative method for the determination of the concentration regimes in aqueous solutions of biopolymers (xanthan, clairana and tara gums) by an analysis of the overlap (c*) and aggregation (c**) concentrations. The diffusion coefficients were obtained over a range of concentrations for each biopolymer using two methods. The first method analysed the behaviour of the diffusion coefficient as a function of the concentration of the gum solution. This method is based on the analysis of the diffusion coefficient versus the concentration curve. Using the slope of the curves, it was possible to determine the c* and c** for xanthan and tara gum. However, it was not possible to determine the concentration regimes for clairana using this method. The second method was based on an analysis of the DRTs, which showed different numbers of relaxation modes. It was observed that the concentrations at which the number of modes changed corresponded to the c* and c**. Thus, the DRT technique provided an alternative method for the determination of the critical concentrations of biopolymers. PMID:23671627

Oliveira, Patrícia D.; Michel, Ricardo C.; McBride, Alan J. A.; Moreira, Angelita S.; Lomba, Rosana F. T.; Vendruscolo, Claire T.

2013-01-01

320

The biology of time across different scales Dean V Buonomano  

E-print Network

that span from microseconds to days. In contrast to the technologies devised by humans to keep track of time individuals and society as a whole,the ability to precisely track and tell time is critical across scales positioning systems to the tracking of our yearly trip around the sun. In-between these extremes we track

Buonomano, Dean

321

Estimating ventilation time scales using overturning stream functions  

E-print Network

Estimating ventilation time scales using overturning stream functions Bijoy Thompson & Jonas 2014 # Springer-Verlag Berlin Heidelberg 2014 Abstract A simple method for estimating ventilation time-enclosed ocean basin ventilated through a narrow strait over a sill, and the result is compared to age estimates

Döös, Kristofer

322

Atomic Time Scales for the 21st Century  

NASA Astrophysics Data System (ADS)

The International Bureau of Weights and Measures, in coordination with international organizations and national institutes, maintains and disseminates Coordinated Universal Time (UTC). Other timescales exist for different purposes. This article describes the state-of-the-art in the elaboration of these time scales.

Arias, E. F.

2014-06-01

323

Parametric Timing Analysis and Its Application to Dynamic Voltage Scaling  

E-print Network

25 Parametric Timing Analysis and Its Application to Dynamic Voltage Scaling SIBIN MOHAN and FRANK (WCETs) to determine if tasks meet deadlines. Static timing analysis derives bounds on WCETs but requires statically known loop bounds. This work removes the constraint on known loop bounds through parametric

Whalley, David

324

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

325

Thermodynamics Constrains Allometric Scaling of Optimal Development Time in Insects  

PubMed Central

Development time is a critical life-history trait that has profound effects on organism fitness and on population growth rates. For ectotherms, development time is strongly influenced by temperature and is predicted to scale with body mass to the quarter power based on 1) the ontogenetic growth model of the metabolic theory of ecology which describes a bioenergetic balance between tissue maintenance and growth given the scaling relationship between metabolism and body size, and 2) numerous studies, primarily of vertebrate endotherms, that largely support this prediction. However, few studies have investigated the allometry of development time among invertebrates, including insects. Abundant data on development of diverse insects provides an ideal opportunity to better understand the scaling of development time in this ecologically and economically important group. Insects develop more quickly at warmer temperatures until reaching a minimum development time at some optimal temperature, after which development slows. We evaluated the allometry of insect development time by compiling estimates of minimum development time and optimal developmental temperature for 361 insect species from 16 orders with body mass varying over nearly 6 orders of magnitude. Allometric scaling exponents varied with the statistical approach: standardized major axis regression supported the predicted quarter-power scaling relationship, but ordinary and phylogenetic generalized least squares did not. Regardless of the statistical approach, body size alone explained less than 28% of the variation in development time. Models that also included optimal temperature explained over 50% of the variation in development time. Warm-adapted insects developed more quickly, regardless of body size, supporting the “hotter is better” hypothesis that posits that ectotherms have a limited ability to evolutionarily compensate for the depressing effects of low temperatures on rates of biological processes. The remaining unexplained variation in development time likely reflects additional ecological and evolutionary differences among insect species. PMID:24391935

Dillon, Michael E.; Frazier, Melanie R.

2013-01-01

326

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

327

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

PubMed Central

When structures that interconvert on a given time scale are lumped together, the corresponding free-energy surface becomes a function of the observation time. This view is equivalent to grouping structures that are connected by free-energy barriers below a certain threshold. We illustrate this time dependence for some benchmark systems, namely atomic clusters and alanine dipeptide, highlighting the connections to broken ergodicity, local equilibrium, and “feasible” symmetry operations of the molecular Hamiltonian. PMID:24374625

Wales, David J.; Salamon, Peter

2014-01-01

328

Magnetic relaxation in dipolar magnetic nanoparticle clusters  

NASA Astrophysics Data System (ADS)

Understanding the role of dipolar interactions on thermal relaxation in magnetic nanoparticle (MNP) systems is of fundamental importance in magnetic recording, for optimizing the hysteresis heating contribution in the hyperthermia cancer treatment in biomedicine, or for biological and chemical sensing, for example. In this talk, we discuss our related efforts to quantify the influence of dipolar interactions on thermal relaxation in small clusters of MNPs. Setting up the master equation and solving the associated eigenvalue problem, we identify the observable relaxation time scale spectra for various types of MNP clusters, and demonstrate qualitatively different spectral characteristics depending on the point group of symmetries of the particle arrangement within the cluster -- being solely a dipolar interaction effect. Our findings provide insight into open questions related to magnetic relaxation in bulk MNP systems, and may prove to be also of practical relevance, e.g., for improving robustness of methodologies in biological and chemical sensing.

Hovorka, Ondrej; Barker, Joe; Chantrell, Roy; Friedman, Gary

2013-03-01

329

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

330

Laterally localizing potential as a tool for controlling the electron spin relaxation time in GaAs quantum wells  

SciTech Connect

The coherent spin dynamics of electrons localized in a plane of GaAs quantum wells is studied experimentally by the application of an electrically controlled potential. The localizing potential is produced with the use of a metal gate with submicrometer windows deposited onto the sample surface. The photoinduced spin Kerr effect is used to study the electron spin lifetime as a function of the temperature, applied bias, and magnetic field for gates with different sets of windows. It is shown that, with an electrically controlled laterally localizing potential, it is possible to gradually change the electron spin lifetime from several hundreds of picoseconds to several tens of nanoseconds. The dependence of the electron spin relaxation time on the sizes of the lateral localization region is in good qualitative agreement with theoretical prediction.

Larionov, A. V., E-mail: larionov@issp.ac.ru [Russian Academy of Sciences, Institute of Solid State Physics (Russian Federation); Il’in, A. I. [Russian Academy of Sciences, Institute of Microelectronics Technology and High-Purity Materials (Russian Federation)

2013-12-15

331

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

E-print Network

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 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 MQ NMR experiment (G.A.Alvarez, D.Suter, PRL {\\bf 104}, 230403 (2010)) concatenating the short evolution periods under the secular DDI Hamiltonian (the perturbation) with the evolution period under the non-secular 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.

S. I. Doronin; E. B. Fel'dman; A. I. Zenchuk

2010-12-30

332

Relaxation of an unstable state in parametrically excited cold atoms.  

PubMed

We investigate the scaling behavior of the relaxation process for an unstable state near a subcritical Hopf bifurcation point. When the parametric modulation is applied to a magneto-optical trap, the atomic cloud becomes unstable and decays to the dynamic bistable states. Near the subcritical Hopf bifurcation point, we experimentally show that the relaxation process exhibits the scaling behavior; the relaxation time shows a scaling exponent of -1.002 (±0.024). We also present the passage time distribution for the statistical interpretation of the escape process associated with the relaxation of the unstable state. We compare the experimental results to the numerical and analytic results, demonstrating the good agreement between them. PMID:22060485

Moon, Geol; Kim, Yonghee; Heo, Myoung-Sun; Park, Jina; Yum, Dahyun; Lee, Wanhee; Noh, Heung-Ryoul; Jhe, Wonho

2011-09-01

333

Variable Time Scale Rainfall Disaggregation Using Artificial Neural Networks  

NASA Astrophysics Data System (ADS)

Variability of precipitation is the primary factor driving land surface hydrological processes. In order to accurately understand many land surface hydrological processes such as infiltration and Hortonian runoff, an accurate and fine time scale description of precipitation is necessary. In many cases, this is neither time nor cost effective. An alternative to maintaining fine time scale networks of rain gauges is to disaggregate records from gauges with coarser time steps. This research developed disaggregation methods for converting daily rainfall records into hourly records and hourly records into fifteen-minute records using artificial neural networks (ANNs). Artificial neural networks have been successfully utilized in the past in many different areas of natural science including climate change, seismology, and groundwater remediation. More recently, ANNs have been developed to disaggregate hourly rainfall records into fifteen-minute records. This study extends prior research in the use of ANNs by examining their performance when disaggregating into a range of time scales. The performances of the ANNs developed to account for seasonal variability of rainfall in west-central Florida were compared to those of the ANNs that did not account for seasonal variability of rainfall. Network architecture for each feed-forward, backpropagation ANN was developed and optimized. The performances of the final ANNs were compared to determine if the fractal structure of rainfall was conserved across the two time scales studied.

Rokicki, R.; Nachabe, M.

2001-12-01

334

Grueneisen relaxation photoacoustic microscopy  

PubMed Central

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 non-radiative absorption with confocal optical resolution. GR-PAM sequentially delivers two identical laser pulses with a micro-second-scale time delay. The first laser pulse generates a photoacoustic signal and thermally tags the in-focus absorbers. Owing to the temperature dependence of the Grueneisen parameter, when the second laser pulse excites the tagged absorbers within the thermal relaxation time, a photoacoustic signal stronger than the first one is produced. GR-PAM detects the amplitude difference between the two co-located photoacoustic signals, confocally imaging the non-radiative absorption. We greatly improved axial resolution from 45 µm to 2.3 µm and at the same time slightly improved lateral resolution from 0.63 µm to 0.41 µm. In addition, the optical sectioning capability facilitates the measurement of the absolute absorption coefficient without fluence calibration. PMID:25379919

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

2014-01-01

335

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

336

Evaluation of Scaling Invariance Embedded in Short Time Series  

PubMed Central

Scaling invariance of time series has been making great contributions in diverse research fields. But how to evaluate scaling exponent from a real-world series is still an open problem. Finite length of time series may induce unacceptable fluctuation and bias to statistical quantities and consequent invalidation of currently used standard methods. In this paper a new concept called correlation-dependent balanced estimation of diffusion entropy is developed to evaluate scale-invariance in very short time series with length . Calculations with specified Hurst exponent values of show that by using the standard central moving average de-trending procedure this method can evaluate the scaling exponents for short time series with ignorable bias () and sharp confidential interval (standard deviation ). Considering the stride series from ten volunteers along an approximate oval path of a specified length, we observe that though the averages and deviations of scaling exponents are close, their evolutionary behaviors display rich patterns. It has potential use in analyzing physiological signals, detecting early warning signals, and so on. As an emphasis, the our core contribution is that by means of the proposed method one can estimate precisely shannon entropy from limited records. PMID:25549356

Pan, Xue; Hou, Lei; Stephen, Mutua; Yang, Huijie; Zhu, Chenping

2014-01-01

337

Evaluation of scaling invariance embedded in short time series.  

PubMed

Scaling invariance of time series has been making great contributions in diverse research fields. But how to evaluate scaling exponent from a real-world series is still an open problem. Finite length of time series may induce unacceptable fluctuation and bias to statistical quantities and consequent invalidation of currently used standard methods. In this paper a new concept called correlation-dependent balanced estimation of diffusion entropy is developed to evaluate scale-invariance in very short time series with length [Formula: see text]. Calculations with specified Hurst exponent values of [Formula: see text] show that by using the standard central moving average de-trending procedure this method can evaluate the scaling exponents for short time series with ignorable bias ([Formula: see text]) and sharp confidential interval (standard deviation [Formula: see text]). Considering the stride series from ten volunteers along an approximate oval path of a specified length, we observe that though the averages and deviations of scaling exponents are close, their evolutionary behaviors display rich patterns. It has potential use in analyzing physiological signals, detecting early warning signals, and so on. As an emphasis, the our core contribution is that by means of the proposed method one can estimate precisely shannon entropy from limited records. PMID:25549356

Pan, Xue; Hou, Lei; Stephen, Mutua; Yang, Huijie; Zhu, Chenping

2014-01-01

338

Time scales for molecule formation by ion-molecule reactions  

NASA Technical Reports Server (NTRS)

Analytical solutions are obtained for nonlinear differential equations governing the time-dependence of molecular abundances in interstellar clouds. Three gas-phase reaction schemes are considered separately for the regions where each dominates. The particular case of CO, and closely related members of the Oh and CH families of molecules, is studied for given values of temperature, density, and the radiation field. Nonlinear effects and couplings with particular ions are found to be important. The time scales for CO formation range from 100,000 to a few million years, depending on the chemistry and regime. The time required for essentially complete conversion of C(+) to CO in the region where the H3(+) chemistry dominates is several million years. Because this time is longer than or comparable to dynamical time scales for dense interstellar clouds, steady-state abundances may not be observed in such clouds.

Langer, W. D.; Glassgold, A. E.

1976-01-01

339

Relativistic fireballs - Energy conversion and time-scales  

NASA Technical Reports Server (NTRS)

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

Rees, M. J.; Meszaros, P.

1992-01-01

340

Dynamics symmetries of Hamiltonian system on time scales  

SciTech Connect

In this paper, the dynamics symmetries of Hamiltonian system on time scales are studied. We study the symmetries and quantities based on the calculation of variation and Lie transformation group. Particular focus lies in: the Noether symmetry leads to the Noether conserved quantity and the Lie symmetry leads to the Noether conserved quantity if the infinitesimal transformations satisfy the structure equation. As the new application of result, at end of the article, we give a simple example of Noether symmetry and Lie symmetry on time scales.

Peng, Keke, E-mail: pengkeke88@126.com; Luo, Yiping, E-mail: zjstulyp@126.com [Department of Physics, Zhejiang Sci-Tech University, Hangzhou 310018 (China)] [Department of Physics, Zhejiang Sci-Tech University, Hangzhou 310018 (China)

2014-04-15

341

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

342

TIME DELAY AND MOTION ESTIMATORS BASED ON DIGITAL FAST TIME-SCALING OF RANDOM SIGNALS  

Microsoft Academic Search

The estimation of time-delay and time-scaling is required in many signal processing applications. A parabolic approximation was recently suggested for fine estimation of time delay from sampled signals. The method directly extends to scaling estimation by a parallel multi-rate sampling of the analog received signal. Such rescaling can be implemented by digital techniques and two efficient algorithms are here devised

Gaetano Giunta

343

THEORETICAL REVIEW The Hippocampus, Time, and Memory Across Scales  

PubMed Central

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

2014-01-01

344

Effective masses, relaxation times, and carrier mobilities in some chloride intercalants of graphite  

NASA Technical Reports Server (NTRS)

The effective masses, carrier scattering times and carrier mobilities have been measured in selected graphite intercalation compounds using the Shubnikov-de Haas effect at a series of temperatures between 4 and 50 K. Effective masses are less than or equal to 0.1 of the free-electron mass, scattering times are about 10 to the -13th/s and carrier mobilities are on the order of 10,000 sq cm/V s.

Woollam, J. A.; Haugland, E.; Dowell, M. B.; Underhill, C.

1981-01-01

345

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

346

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

NASA Astrophysics Data System (ADS)

Longitudinal relaxation (T1) measurements of 19F, 7Li, and 1H 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.

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

2013-12-01

347

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

348

Comparative responsiveness of Parkinson's disease scales to change over time.  

PubMed

The objective of the study is to examine the comparative responsiveness of outcome measures to assess progression over time in Parkinson's disease (PD). One hundred twenty-eight patients participating in a clinic-based naturalistic study of PD were assessed with the Hoehn and Yahr, UPDRS, MMSE, PDQ-39, PDQL, EQ-5D, and BDI scales at baseline and at 1 year. In addition, 82 patients in a community-based study of patients with PD who had completed self-rated Schwab and England, PDQ-39, EQ-5D, and BDI scales at baseline, were sent the same questionnaires at 1 and 4 years. Responsiveness was assessed using t-tests, standardised effect size, and standardised response mean. In both samples, the Hr-QoL measures were less responsive to change over time than the impairment and disability scales (Hoehn and Yahr, UPDRS, Schwab and England scales). In addition, in the clinic-based sample, Hoehn and Yahr and UPDRS ADL scale ("on") were more responsive to progression over time than UPDRS motor part and ADL part ("off"). Hr-QoL measures are less responsive to change over time than measures of impairment and disability. Although this suggests that these measures are less accurate in detecting subtle changes, it may also indicate that the multifactorial subjective assessment of Hr-QoL adapts to changes over time. Global assessment of overall impairment and disability (which incorporates motor and nonmotor features of PD), however, appeared relatively responsive to change over time in patients in a naturalistic setting. PMID:19199355

Schrag, Anette; Spottke, Annika; Quinn, Niall Patrick; Dodel, Richard

2009-04-30

349

Multi-scale Template Reconstruction of ABL Time Series  

NASA Astrophysics Data System (ADS)

It has been shown previously that a large fraction of instantaneous turbulent time series of 1-D velocity in an atmospheric boundary layer(ABL) can be reconstructed using a set of templates taken from samples of laboratory-scale wall turbulence (Hommema and Adrian [1]). A new analysis is presented in which the 3-D velocity time series from NCAR's HATS (Horizontal Array Turbulence Study) experiment is matched with templates from laboratory-scale flows using wavelet transforms. The template amplitude, temporal scale and temporal location is varied to produce the maximum correlation coefficient. Efficient templates generally take the form of segments through hairpin vortex packets. [1] Hommema S.E., and Adrian R.J.,"Similarity of apparently random structures in the outer region of wall turbulence", Exp. Fluids, 33, 5--12 (2002).

Balakumar, B. J.; Adrian, R. J.

2003-11-01

350

Quantitative assessment of regional peak myocardial acceleration during isovolumic contraction and relaxation times by tissue Doppler imaging  

PubMed Central

Objective: To examine regional wall acceleration and its relation to relaxation. Study design: 8 sheep were examined by tissue Doppler ultrasound imaging (VingMed Vivid FiVe) in apical four chamber views to evaluate the left ventricular wall divided into six segments and the mitral annulus in two segments. Peak myocardial acceleration during isovolumic periods (pIVA) derived from tissue Doppler echocardiography was analysed during isovolumic contraction (ICT) and relaxation times (IRT) in each segment. Interventions: After scanning at baseline, haemodynamic status was changed by administration of blood, dobutamine, and metoprolol. Changes of pIVA during IRT and ICT were compared over the four haemodynamic conditions in parallel with their peak positive and negative dP/dt measured with a high frequency manometer tipped catheter. Results: pIVA of the basal lateral segment during ICT correlated most strongly with peak positive dP/dt (r ?=? 0.96, p < 0.0001) and there was good correlation between pIVA of the mitral valve annulus in the septum during IRT and peak negative dP/dt (r ?=? 0.80, p < 0.0001). pIVA differed significantly between the four haemodynamic conditions during ICT in all segments (p < 0.05); pIVA during IRT did not differ significantly between the four conditions. Conclusions: pIVA of the basal lateral wall during ICT correlated most strongly with peak positive dP/dt, and pIVA of the septal mitral valve annulus during IRT correlated well with peak negative dP/dt. PMID:15894787

Hashimoto, I; Li, X-K; Hejmadi Bhat, A; Jones, M; Sahn, D J

2005-01-01

351

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

352

Gott Time Machines, BTZ Black Hole Formation, and Choptuik Scaling  

E-print Network

We study the formation of BTZ black holes by the collision of point particles. It is shown that the Gott time machine, originally constructed for the case of vanishing cosmological constant, provides a precise mechanism for black hole formation. As a result, one obtains an exact analytic understanding of the Choptuik scaling.

Danny Birmingham; Siddhartha Sen

1999-08-23

353

Multiple time scale numerical methods for the inverted pendulum problem  

E-print Network

Multiple time scale numerical methods for the inverted pendulum problem Richard Sharp1, Yen (HMM) [1]. We apply the methods to compute the averaged path of the inverted pendulum under a highly and thus compute the average path of the inverted pendulum. 1 Introduction The focus of this paper

Tsai, Yen-Hsi Richard

354

MULTIPLE TIME SCALE NUMERICAL METHODS FOR THE INVERTED PENDULUM PROBLEM  

E-print Network

MULTIPLE TIME SCALE NUMERICAL METHODS FOR THE INVERTED PENDULUM PROBLEM RICHARD SHARP, YEN-HSI TSAI multiscale methods (HMM) [1]. We apply the methods to compute the averaged path of the inverted pendulum approximate the averaged equation and thus compute the average path of the inverted pendulum. 1. INTRODUCTION

Soatto, Stefano

355

Multiple time-scale power system dynamic simulation  

Microsoft Academic Search

A new program, EXSTAB (extended time-scale stability) has been developed for representing a wide variety of power system performance problems, from transient stability through long-term dynamics and voltage instability. The capability of the program includes multiple execution modes and automatic step size selection to address conflicting goals of accuracy and efficiency. The modeling includes a broad range of apparatus to

A. Kurita; H. Okubo; K. Oki; S. Agematsu; D. B. Klapper; N. W. Miller; J. J. Sanchez-Gasca; K. A. Wirgau; T. D. Younkins

1993-01-01

356

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

357

Loss rates and time scales for sodium at Mercury  

NASA Astrophysics Data System (ADS)

The time scales and loss rates for sodium in the exosphere of Mercury are studied here. Sodium comes from release processes occurring at the planetary surface; the amount of surface sodium that is available for release (mostly through thermal- or photon-stimulated desorption) is limited. Loss processes deplete the surface concentration of sodium, which is continuously refilled by diffusion from the interior of regolith grains or by chemical sputtering. Ejected sodium particles may either escape the gravity, also aided by the radiation pressure acceleration, or be photoionized, or fall back onto the surface. Falling particles may either stick to the surface or bounce. A Monte Carlo model, simulating all these processes, is used to obtain the exosphere densities, the global loss rates at different true anomaly angles, and typical time scales for small-term variations, taking into account planet's orbit and rotation speed. Assuming an impulsive event, which causes the enhancement of sodium in the exosphere, the model gives the time scales for the exosphere to recover to a steady-state condition. It is found that time scales go from one or two hour (close to perihelion) to half day (close to aphelion). The escape probability ranges from 20% at perihelion and aphelion up to 40% at true anomaly angles of about 60° and 300°.

Mura, Alessandro

2012-04-01

358

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.

359

Modeling of streamflow processes at different time scales  

Microsoft Academic Search

The analysis and modeling of streamflow processes has attracted the attention of water resources specialists for several decades. A number of models have been suggested in the past for representing seasonal and annual streamflow processes. The topic addressed in this paper centers around the compatibility of stochastic models of streamflow at different time scales. More specifically, given a model for

Paolo Bartolini; Jose D. Salas

1993-01-01

360

The time-scale of escape from star clusters  

Microsoft Academic Search

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

T. Fukushige; D. C. Heggie

2000-01-01

361

Dynamical masses, time-scales, and evolution of star clusters  

E-print Network

This review discusses (i) dynamical methods for determining the masses of Galactic and extragalactic star clusters, (ii) dynamical processes and their time-scales for the evolution of clusters, including evaporation, mass segregation, core collapse, tidal shocks, dynamical friction and merging. These processes lead to significant evolution of globular cluster systems after their formation.

Ortwin Gerhard

2000-07-18

362

Over-relaxation applied to the MacCormack finite-difference scheme. [to reduce computing time in flow equation solution  

NASA Technical Reports Server (NTRS)

An over-relaxation procedure is applied to the MacCormack finite-difference scheme in order to reduce the computation time required to obtain a steady-state solution. The implementation of this acceleration procedure to an existing computer program using the regular MacCormack method is extremely simple and does not require additional storage. The over-relaxation procedure does not alter the steady-state solution, which is second-order accurate. The method is first applied to Burgers' equation. A stability condition and an expression for the increase in the rate of convergence are derived. The method is then applied to the calculation of the hypersonic viscous flow over a flat plate, using the complete Navier-Stokes equations, and the inviscid flow over a wedge. Reductions in computing time by factors of 3 and 1.5, respectively, are obtained by over-relaxation.

Desideri, J.-A.; Tannehill, J. C.

1977-01-01

363

Isotope ratio of Cl NQR spin-lattice relaxation times in 1D hydrogen-bonding system of tetramethylpyrazine-chloranilic acid at high temperatures  

NASA Astrophysics Data System (ADS)

The temperature dependences of spin-lattice relaxation time T 1 of 35Cl and 37Cl NQR were studied for the co-crystal of tetramethylpyrazine (TMP) with chloranilic acid (H2ca), TMP-H2ca, in which one-dimensional hydrogen bonding is formed by alternate arrangement of TMP and H2ca. The isotope ratio 37Cl T 1 / 35Cl T 1 was determined to be 1.0 ± 0.1 above ca. 290 K where a steep decrease of spin-lattice relaxation time T 1 with increasing temperature was observed. In this temperature range it is suggested that the relaxation is originated from the slow fluctuation of electric field gradient (EFG). Beside EFG fluctuation due to the external-charge-density fluctuation, the small angle reorientation of the quantization axis triggered by a proton transfer motion between N...H-O and N-H...O hydrogen bonding states is proposed.

Asaji, Tetsuo

2013-05-01

364

Shear Relaxations of Confined Liquids.  

NASA Astrophysics Data System (ADS)

Ultrathin (<40 A) films of octamethylcyclotetrasiloxane (OMCTS), hexadecane, and dodecane were subjected to linear and non-linear oscillatory shear between flat plates. Shearing frequencies of 0.1 to 800 s^{-1} were applied at pressures from zero to 0.8 MPa using a surface rheometer only recently developed. In most cases the plates were atomically smooth mica surfaces; the role of surface interactions was examined by replacing these with alkyl chain monolayers. OMCTS and hexadecane were examined at a temperature about 5 Celsius degrees above their melting points and tended to solidify. Newtonian plateaus having enormous viscosities were observed at low shear rates. The onset of shear thinning implied relaxation times of about 0.1 s in the linear structure of the confined liquids. Large activation volumes (~80 nm ^3) suggested that shear involved large-scale collective motion. Dodecane was studied at a much higher temperature relative to its melting point and showed no signs of impending solidification though it exhibited well-defined regions of Newtonian response and power law shear thinning. When treated with molecular sieves before use, dodecane had relaxation times which were short (0.02 s) compared to hexadecane, but still exhibited large-scale collective motion. When treated with silica gel, an unexplained long -time relaxation (10 s) was seen in the Newtonian viscosity of dodecane. The relaxation time of the linear structure, 0.005 s was very small, and the storage modulus was unresolvable. The small activation volume (7nm^3) indicated a much lower level of collective motion. The activation volume remained small when dodecane was confined between tightly bound, low energy, alkyl monolayers. At low strains the storage and loss moduli became very large (>10^4 Pa), probably due to interactions with flaws in the monolayers. Dramatic signs of wall slip were observed at large strains even at low pressures.

Carson, George Amos, Jr.

365

Asymmetry of charge relaxation times in quantum dots: The influence of degeneracy  

NASA Astrophysics Data System (ADS)

Using time-resolved transconductance spectroscopy, we study the tunneling dynamics between a two-dimensional electron gas (2DEG) and self-assembled quantum dots (QDs), embedded in a field-effect transistor structure. We find that the tunneling of electrons from the 2DEG into the QDs is governed by a different time constant than the reverse process, i.e., tunneling from the QDs to the 2DEG. This asymmetry is a clear signature of Coulomb interaction and makes it possible to determine the degeneracy of the quantum-dot orbitals even when the individual states cannot be resolved energetically because of inhomogeneous broadening. Our experimental data can be qualitatively explained within a master-equation approach.

Beckel, A.; Kurzmann, A.; Geller, M.; Ludwig, A.; Wieck, A. D.; König, J.; Lorke, A.

2014-05-01

366

Relaxation processes in an epoxy resin studied by time-resolved optical Kerr effect  

Microsoft Academic Search

The dynamics of the epoxy resin phenyl glycidyl ether, a fragile glass-forming liquid, is investigated in the liquid and supercooled phases by time-resolved optical Kerr effect experiment with an heterodyne detection technique. We tested the mode-coupling theory and found that the predicted dynamic scenario allows to reproduce properly the measured signal, for t>1 ps, in the whole temperature interval investigated.

D. Prevosto; P. Bartolini; R. Torre; M. Ricci; A. Taschin; S. Capaccioli; M. Lucchesi; P. Rolla

2002-01-01

367

Angular size and emission time scales of relativistic fireballs  

E-print Network

The detection of delayed X-ray, optical and radio emission, ``afterglow,'' associated with gamma-ray bursts (GRBs) is consistent with models, where the bursts are produced by relativistic expanding blast waves, driven by expanding fireballs at cosmological distances. In particular, the time scales over which radiation is observed at different wave bands agree with model predictions. It had recently been claimed that the commonly used relation between observation time t and blast wave radius r, t=r/2\\gamma^{2}c where \\gamma(r) is the fluid Lorentz factor, should be replaced with t=r/16\\gamma^{2}c due to blast wave deceleration. Applying the suggested deceleration modification would make it difficult to reconcile observed time scales with model predictions. It would also imply an apparent source size which is too large to allow attributing observed radio variability to diffractive scintillation. We present a detailed analysis of the implications of the relativistic hydrodynamics of expanding blast waves to the observed afterglow. We find that modifications due to shock deceleration are small, therefore allowing for both the observed afterglow time scales and for diffractive scintillation. We show that at time t the fireball appears on the sky as a narrow ring of radius h=r/\\gamma and width 0.1h, where r and t are related by t=r/2\\gamma^{2}c.

Eli Waxman

1997-09-18

368

Relaxation properties in classical diamagnetism  

NASA Astrophysics Data System (ADS)

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.

Carati, A.; Benfenati, F.; Galgani, L.

2011-06-01

369

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

370

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

371

The Importance of Rotational Time-scales in Accretion Variability  

NASA Astrophysics Data System (ADS)

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

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

2013-07-01

372

Probing Fission Time Scales with Neutrons and GDR Gamma Rays  

SciTech Connect

The time scales for nuclear fission have been explored using both pre-and postfission neutrons and GDR gamma rays. Four systems were investigated: 133-MeV 16O + 176Yb and 208Pb and 104-MeV 4He + 188Os and 209Bi. Fission fragments were measured in coincidence with PPACs. The neutrons were detected using eight detectors from the DEMON array, while gamma rays were measured using the US BaF2 array. The pre-and postfission gamma rays were determined using moving source fits parallel and perpendicular to the fission fragment emission directions. The time scales for fission for the neutrons were determined using the neutron clock technique. The gamma-ray data were fitted using a statistical model calculation based on the code CASCADE. The results of the fits from both data types were used to extract nuclear friction coefficients, ?, and fission time scales. The ? values ranged from 7 to 20, while the fission times were (31-105) 10?21 s. From Yadernaya Fizika, Vol. 66, No. 6, 2003, pp. 1199-1203.

Schmitt, R. P. [Texas A& M University; Botting, Tye [Texas A& M University; Chubarian, G G [Texas A& M University; Wolf, K [Texas A& M University; Hurst, B J [Texas A& M University; Jabs, H [Texas A& M University; Hamelin, M [Texas A& M University; Bacak, A [Texas A& M University; Oganessian, Yuri Ts. [FLNR-JINR, Russia; Itkis, M. G. [FLNR-JINR, Russia; Kozulin, E M [FLNR-JINR, Russia; Kondratiev, N. A. [FLNR-JINR, Russia; Salamatin, V S [FLNR-JINR, Russia; Pokrovsky, I V [FLNR-JINR, Russia; Hanappe, F [Universite Libre de Bruxelles, Brussels, Belgium; de Goes Brennand, E. [Universite Libre de Bruxelles, Brussels, Belgium; Huck, A [CRN, Strasbourg, France; Stuttge, L [CRN, Strasbourg, France; Liatard, E [CRN, Strasbourg, France; Beene, James R [ORNL; Varner Jr, Robert L [ORNL; Halbert, Melvyn L [ORNL; Gan, Ning [ORNL

2003-06-01

373

Reconstructions of solar irradiance on centennial time scales  

NASA Astrophysics Data System (ADS)

Solar irradiance is the main external source of energy to Earth's climate system. The record of direct measurements covering less than 40 years is too short to study solar influence on Earth's climate, which calls for reconstructions of solar irradiance into the past with the help of appropriate models. An obvious requirement to a competitive model is its ability to reproduce observed irradiance changes, and a successful example of such a model is presented by the SATIRE family of models. As most state-of-the-art models, SATIRE assumes that irradiance changes on time scales longer than approximately a day are caused by the evolving distribution of dark and bright magnetic features on the solar surface. The surface coverage by such features as a function of time is derived from solar observations. The choice of these depends on the time scale in question. Most accurate is the version of the model that employs full-disc spatially-resolved solar magnetograms and reproduces over 90% of the measured irradiance variation, including the overall decreasing trend in the total solar irradiance over the last four cycles. Since such magnetograms are only available for about four decades, reconstructions on time scales of centuries have to rely on disc-integrated proxies of solar magnetic activity, such as sunspot areas and numbers. Employing a surface flux transport model and sunspot observations as input, we have being able to produce synthetic magnetograms since 1700. This improves the temporal resolution of the irradiance reconstructions on centennial time scales. The most critical aspect of such reconstructions remains the uncertainty in the magnitude of the secular change.

Krivova, Natalie; Solanki, Sami K.; Dasi Espuig, Maria; Leng Yeo, Kok

374

Sublinear scaling for time-dependent stochastic density functional theory.  

PubMed

A stochastic approach to time-dependent density functional theory 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 first 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 infinite, 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 using real-space grids and find that the overall scaling of the algorithm is sublinear with computational time and memory. PMID:25612688

Gao, Yi; Neuhauser, Daniel; Baer, Roi; Rabani, Eran

2015-01-21

375

Nonlogarithmic magnetization relaxation at the initial time intervals and magnetic field dependence of the flux creep rate in Bi2Sr2Ca(sub I)Cu2Ox single crystals  

NASA Technical Reports Server (NTRS)

At the initial time intervals, preceding the thermally activated flux creep regime, fast nonlogarithmic relaxation is found. The fully magnetic moment Pm(t) relaxation curve is shown. The magnetic measurements were made using SQUID-magnetometer. Two different relaxation regimes exist. The nonlogarithmic relaxation for the initial time intervals may be related to the viscous Abrikosov vortices flow with j is greater than j(sub c) for high enough temperature T and magnetic field induction B. This assumption correlates with Pm(t) measurements. The characteristic time t(sub O) separating two different relaxation regimes decreases as temperature and magnetic field are lowered. The logarithmic magnetization relaxation curves Pm(t) for fixed temperature and different external magnetic field inductions B are given. The relaxation rate dependence on magnetic field, R(B) = dPm(B, T sub O)/d(1nt) has a sharp maximum which is similar to that found for R(T) temperature dependences. The maximum shifts to lower fields as temperature goes up. The observed sharp maximum is related to a topological transition in shielding critical current distribution and, consequently, in Abrikosov vortices density. The nonlogarithmic magnetization relaxation for the initial time intervals is found. This fast relaxation has almost an exponentional character. The sharp relaxation rate R(B) maximum is observed. This maximum corresponds to a topological transition in Abrikosov vortices distribution.

Moshchalcov, V. V.; Zhukov, A. A.; Kuznetzov, V. D.; Metlushko, V. V.; Leonyuk, L. I.

1990-01-01

376

Time scale of diffusion in molecular and cellular biology  

NASA Astrophysics Data System (ADS)

Diffusion is the driver of critical biological processes in cellular and molecular biology. The diverse temporal scales of cellular function are determined by vastly diverse spatial scales in most biophysical processes. The latter are due, among others, to small binding sites inside or on the cell membrane or to narrow passages between large cellular compartments. The great disparity in scales is at the root of the difficulty in quantifying cell function from molecular dynamics and from simulations. The coarse-grained time scale of cellular function is determined from molecular diffusion by the mean first passage time of molecular Brownian motion to a small targets or through narrow passages. The narrow escape theory (NET) concerns this issue. The NET is ubiquitous in molecular and cellular biology and is manifested, among others, in chemical reactions, in the calculation of the effective diffusion coefficient of receptors diffusing on a neuronal cell membrane strewn with obstacles, in the quantification of the early steps of viral trafficking, in the regulation of diffusion between the mother and daughter cells during cell division, and many other cases. Brownian trajectories can represent the motion of a molecule, a protein, an ion in solution, a receptor in a cell or on its membrane, and many other biochemical processes. The small target can represent a binding site or an ionic channel, a hidden active site embedded in a complex protein structure, a receptor for a neurotransmitter on the membrane of a neuron, and so on. The mean time to attach to a receptor or activator determines diffusion fluxes that are key regulators of cell function. This review describes physical models of various subcellular microdomains, in which the NET coarse-grains the molecular scale to a higher cellular-level, thus clarifying the role of cell geometry in determining subcellular function.

Holcman, D.; Schuss, Z.

2014-05-01

377

Spatially resolved measurements of mean spin-spin relaxation time constants  

NASA Astrophysics Data System (ADS)

Magnetic Resonance measurements of the T2 distribution have become very common and they are a powerful way to probe microporous fluid bearing solids. While the structure of the T2 distribution, and changes in the structure, are often very informative, it is common to reduce the T2 distribution to a mean numeric quantity in order to provide a quantitative interpretation of the distribution. Magnetic Resonance Imaging measurements of the T2 distribution have recently been introduced, but they are time consuming, especially for 2 and 3 spatial dimensions. In this paper we explore a direct MRI measurement of the arithmetic mean of 1/T2, characterizing the distribution by using the initial slope of the spatially resolved T2 decay in a CPMG prepared Centric Scan SPRITE experiment. The methodology is explored with a test phantom sample and realistic petroleum reservoir core plug samples. The arithmetic mean of 1/T2 is related to the harmonic mean of T2. The mean obtained from the early decay is explored through measurements of uniform saturated core plug samples and by comparison to other means determined from the complete T2 distribution. Complementary data were obtained using SE-SPI T2 distribution MRI measurements. The utility of the arithmetic mean 1/T2 is explored through measurements of centrifuged core plug samples where the T2 distribution varies spatially. The harmonic mean T2 obtained from the early decay was employed to estimate the irreducible water saturation for core plug samples.

Nechifor, Ruben Emanuel; Romanenko, Konstantin; Marica, Florea; Balcom, Bruce J.

2014-02-01

378

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

SciTech Connect

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; Liang, WanZhen; Zhao, Yi, E-mail: yizhao@xmu.edu.cn [State Key Laboratory of Physical Chemistry of Solid Surfaces, Collaborative Innovation Center of Chemistry for Energy Materials, Fujian Provincial Key Lab of Theoretical and Computational Chemistry, and Department of Chemistry, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005 (China); Zhong, Xinxin [State Key Laboratory of Physical Chemistry of Solid Surfaces, Collaborative Innovation Center of Chemistry for Energy Materials, Fujian Provincial Key Lab of Theoretical and Computational Chemistry, and Department of Chemistry, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005 (China); Institute of Theoretical and Computational Chemistry, College of Chemistry and Molecular Engineering, Beijing National Laboratory for Molecular Sciences, Peking University, Beijing 100871 (China)

2014-06-07

379

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

380

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

381

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

382

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

383

Investigation of doped calcium aluminosilicate glass: A coupling between thermal-expansion and thermal-diffusion models for assessment of nonradiative relaxation time and characteristic diffusion time  

NASA Astrophysics Data System (ADS)

This paper discusses the use of photoacoustic models to obtain the nonradiative relaxation time (?) and characteristic diffusion time (??) for a sample showing visible absorption bands from fluorescent ion-doped low-silica calcium aluminosilicate glass. Two models allowing phase shift analyses, the thermal-expansion and thermal-diffusion models, are briefly reviewed. These models have limitations when the photoacoustic signal depends on both factors, in a coupling mechanism. An alternative model is proposed to take both thermal expansion and thermal diffusion into account with a single temperature solution for the heat-coupled differential equation. This model is simulated for absorbing samples near the thermally thick region. The model is applied to Eu-V codoped glass showing intermediate signal dependence from ?-1.0 to ?-3/2. The nonradiative time and characteristic diffusion time are derived with 33

Souza Filho, N. E.; Nogueira, A. C.; Rohling, J. H.; Baesso, M. L.; Medina, A. N.; Siqueira, A. P. L.; Sampaio, J. A.; Vargas, H.; Bento, A. C.

2009-11-01

384

Backpropagation and ordered derivatives in the time scales calculus.  

PubMed

Backpropagation is the most widely used neural network learning technique. It is based on the mathematical notion of an ordered derivative. In this paper, we present a formulation of ordered derivatives and the backpropagation training algorithm using the important emerging area of mathematics known as the time scales calculus. This calculus, with its potential for application to a wide variety of inter-disciplinary problems, is becoming a key area of mathematics. It is capable of unifying continuous and discrete analysis within one coherent theoretical framework. Using this calculus, we present here a generalization of backpropagation which is appropriate for cases beyond the specifically continuous or discrete. We develop a new multivariate chain rule of this calculus, define ordered derivatives on time scales, prove a key theorem about them, and derive the backpropagation weight update equations for a feedforward multilayer neural network architecture. By drawing together the time scales calculus and the area of neural network learning, we present the first connection of two major fields of research. PMID:20615808

Seiffertt, John; Wunsch, Donald C

2010-08-01

385

HIV-1 dynamics at different time scales under antiretroviral therapy.  

PubMed

We exploit a model that considers three compartments: blood plasma (BP), lymphoid tissue-interstitial spaces (LT-IS), and follicular dendritic cells (FDC), for the HIV-1 dynamics under the application of highly active antiretroviral therapy (HAART) which allowed us to unravel distinct viral dynamics occurring in short- (2 days), middle- (21 days), and long-term (183 days) time scales. The different time scales are determined by the viral clearance rate, the ratio of productively infected CD4(+) T cells to chronically infected cells, and the dissociation rate of HIV-1 complexes from FDC. This generates a scenario in which, after an initial transient stage, the viral BP dynamics decouples and becomes governed by the lymphoid tissue (LT) dynamics; in a later stage, a new decoupling occurs in which the LT-IS dynamics is slaved to that of the FDC dynamics. We observed an initial increase in the viremia after HAART in a patient who did not receive protease inhibitors (PI). By means of the above-mentioned model we were able to highlight the relevant parameters which need to be estimated at three different time scales after HAART. PMID:16005903

García, José A; Soto-Ramírez, Luis E; Cocho, Germinal; Govezensky, Tzipe; José, Marco V

2006-01-01

386

Modeling of streamflow processes at different time scales  

NASA Astrophysics Data System (ADS)

The analysis and modeling of streamflow processes has attracted the attention of water resources specialists for several decades. A number of models have been suggested in the past for representing seasonal and annual streamflow processes. The topic addressed in this paper centers around the compatibility of stochastic models of streamflow at different time scales. More specifically, given a model for monthly flows, the models for the processes obtained by aggregation, i.e., models for bimonthly, quarterly, etc., time scales, are derived. Likewise, parameter space and covariance properties of such derived processes as well as the relationship of such properties of different time scales are given. These concepts are applied to modeling streamflow of the Niger River. The developments are restricted to the family of periodic autoregressive moving average (PARMA) processes. For instance, it was found that monthly flows based on the PARMA(2, 1) process leads to PARMA(2, 2) bimonthly flows and stationary ARMA(2, 2) annual flows. Furthermore, applications to modeling the Niger River flows suggest that one can reproduce the seasonal and annual second-order statistics without using disaggregation if PARMA models are used for modeling the seasonal flows.

Bartolini, Paolo; Salas, Jose D.

1993-08-01

387

Scaling brain size, keeping timing: evolutionary preservation of brain rhythms.  

PubMed

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

2013-10-30

388

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

389

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

390

A methodological bias toward overestimation of molecular evolutionary time scales.  

PubMed

There is presently a conflict between fossil- and molecular-based evolutionary time scales. Molecular approaches for dating the branches of the tree of life frequently lead to substantially deeper times of divergence than those inferred by paleontologists. The discrepancy between molecular and fossil estimates persists despite the booming growth of sequence data sets, which increasingly feeds the interpretation that molecular estimates are older than stratigraphic dates because of deficiencies in the fossil record. Here we show that molecular time estimates suffer from a methodological handicap, namely that they are asymmetrically bounded random variables, constrained by a nonelastic boundary at the lower end, but not at the higher end of the distribution. This introduces a bias toward an overestimation of time since divergence, which becomes greater as the length of the molecular sequence and the rate of evolution decrease. PMID:12060757

Rodriguez-Trelles, Francisco; Tarrio, Rosa; Ayala, Francisco J

2002-06-11

391

Transposition and Time-Scale Invariant Geometric Music Retrieval  

NASA Astrophysics Data System (ADS)

This paper considers how to adapt geometric algorithms, developed for content-based music retrieval of symbolically encoded music, to be robust against time deformations required by real-world applications. In this setting, music is represented by sets of points in plane. A matching, pertinent to the application, involves two such sets of points and invariances under translations and time scalings. We give an algorithm for finding exact occurrences, under such a setting, of a given query point set, of size m, within a database point set, of size n, with running time O(mn 2logn); partial occurrences are found in O(m 2 n 2logn) time. The algorithms resemble the sweepline algorithm introduced in [1].

Lemström, Kjell

392

Scaling in non-stationary time series. (I)  

NASA Astrophysics Data System (ADS)

Most data processing techniques, applied to biomedical and sociological time series, are only valid for random fluctuations that are stationary in time. Unfortunately, these data are often non-stationary and the use of techniques of analysis resting on the stationary assumption can produce a wrong information on the scaling, and so on the complexity of the process under study. Herein, we test and compare two techniques for removing the non-stationary influences from computer generated time series, consisting of the superposition of a slow signal and a random fluctuation. The former is based on the method of wavelet decomposition, and the latter is a proposal of this paper, denoted by us as step detrending technique. We focus our attention on two cases, when the slow signal is a periodic function mimicking the influence of seasons, and when it is an aperiodic signal mimicking the influence of a population change (increase or decrease). For the purpose of computational simplicity the random fluctuation is taken to be uncorrelated. However, the detrending techniques here illustrated work also in the case when the random component is correlated. This expectation is fully confirmed by the sociological applications made in the companion paper. We also illustrate a new procedure to assess the existence of a genuine scaling, based on the adoption of diffusion entropy, multiscaling analysis and the direct assessment of scaling. Using artificial sequences, we show that the joint use of all these techniques yield the detection of the real scaling, and that this is independent of the technique used to detrend the original signal.

Ignaccolo, M.; Allegrini, P.; Grigolini, P.; Hamilton, P.; West, B. J.

2004-05-01

393

Membrane fluidity profiles as deduced by saturation-recovery EPR measurements of spin-lattice relaxation times of spin labels  

NASA Astrophysics Data System (ADS)

There are no easily obtainable EPR spectral parameters for lipid spin labels that describe profiles of membrane fluidity. The order parameter, which is most often used as a measure of membrane fluidity, describes the amplitude of wobbling motion of alkyl chains relative to the membrane normal and does not contain explicitly time or velocity. Thus, this parameter can be considered as nondynamic. The spin-lattice relaxation rate ( T1-1) obtained from saturation-recovery EPR measurements of lipid spin labels in deoxygenated samples depends primarily on the rotational correlation time of the nitroxide moiety within the lipid bilayer. Thus, T1-1 can be used as a convenient quantitative measure of membrane fluidity that reflects local membrane dynamics. T1-1 profiles obtained for 1-palmitoyl-2-( n-doxylstearoyl)phosphatidylcholine ( n-PC) spin labels in dimyristoylphosphatidylcholine (DMPC) membranes with and without 50 mol% cholesterol are presented in parallel with profiles of the rotational diffusion coefficient, R?, obtained from simulation of EPR spectra using Freed's model. These profiles are compared with profiles of the order parameter obtained directly from EPR spectra and with profiles of the order parameter obtained from simulation of EPR spectra. It is shown that T1-1 and R? profiles reveal changes in membrane fluidity that depend on the motional properties of the lipid alkyl chain. We find that cholesterol has a rigidifying effect only to the depth occupied by the rigid steroid ring structure and a fluidizing effect at deeper locations. These effects cannot be differentiated by profiles of the order parameter. All profiles in this study were obtained at X-band (9.5 GHz).

Mainali, Laxman; Feix, Jimmy B.; Hyde, James S.; Subczynski, Witold K.

2011-10-01

394

A Hierarchy of Time-Scales and the Brain  

PubMed Central

In this paper, we suggest that cortical anatomy recapitulates the temporal hierarchy that is inherent in the dynamics of environmental states. Many aspects of brain function can be understood in terms of a hierarchy of temporal scales at which representations of the environment evolve. The lowest level of this hierarchy corresponds to fast fluctuations associated with sensory processing, whereas the highest levels encode slow contextual changes in the environment, under which faster representations unfold. First, we describe a mathematical model that exploits the temporal structure of fast sensory input to track the slower trajectories of their underlying causes. This model of sensory encoding or perceptual inference establishes a proof of concept that slowly changing neuronal states can encode the paths or trajectories of faster sensory states. We then review empirical evidence that suggests that a temporal hierarchy is recapitulated in the macroscopic organization of the cortex. This anatomic-temporal hierarchy provides a comprehensive framework for understanding cortical function: the specific time-scale that engages a cortical area can be inferred by its location along a rostro-caudal gradient, which reflects the anatomical distance from primary sensory areas. This is most evident in the prefrontal cortex, where complex functions can be explained as operations on representations of the environment that change slowly. The framework provides predictions about, and principled constraints on, cortical structure–function relationships, which can be tested by manipulating the time-scales of sensory input. PMID:19008936

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

2008-01-01

395

Computational Modeling of Semiconductor Dynamics at Femtosecond Time Scales  

NASA Technical Reports Server (NTRS)

The main objective of the Joint-Research Interchange NCC2-5149 was to develop computer codes for accurate simulation of femtosecond pulse propagation in semiconductor lasers and semiconductor amplifiers [I]. The code should take into account all relevant processes such as the interband and intraband carrier relaxation mechanisms and the many-body effects arising from the Coulomb interaction among charge carriers [2]. This objective was fully accomplished. We made use of a previously developed algorithm developed at NASA Ames [3]-[5]. The new algorithm was tested on several problems of practical importance. One such problem was related to the amplification of femtosecond optical pulses in semiconductors. These results were presented in several international conferences over a period of three years. With the help of a postdoctoral fellow, we also investigated the origin of instabilities that can lead to the formation of femtosecond pulses in different kinds of lasers. We analyzed the occurrence of absolute instabilities in lasers that contain a dispersive host material with third-order nonlinearities. Starting from the Maxwell-Bloch equations, we derived general multimode equations to distinguish between convective and absolute instabilities. We find that both self-phase modulation and intensity-dependent absorption can dramatically affect the absolute stability of such lasers. In particular, the self-pulsing threshold (the so-called second laser threshold) can occur at few times the first laser threshold even in good-cavity lasers for which no self-pulsing occurs in the absence of intensity-dependent absorption. These results were presented in an international conference and published in the form of two papers.

Agrawal, Govind P.; Goorjian, Peter M.

1998-01-01

396

Optimal Control Modification for Time-Scale Separated Systems  

NASA Technical Reports Server (NTRS)

Recently a new optimal control modification has been introduced that can achieve robust adaptation with a large adaptive gain without incurring high-frequency oscillations as with the standard model-reference adaptive control. This modification is based on an optimal control formulation to minimize the L2 norm of the tracking error. The optimal control modification adaptive law results in a stable adaptation in the presence of a large adaptive gain. This study examines the optimal control modification adaptive law in the context of a system with a time scale separation resulting from a fast plant with a slow actuator. A singular perturbation analysis is performed to derive a modification to the adaptive law by transforming the original system into a reduced-order system in slow time. A model matching conditions in the transformed time coordinate results in an increase in the actuator command that effectively compensate for the slow actuator dynamics. Simulations demonstrate effectiveness of the method.

Nguyen, Nhan T.

2012-01-01

397

Defining a trend for time series using the intrinsic time-scale decomposition  

NASA Astrophysics Data System (ADS)

We propose criteria that define a trend for time series with inherent multi-scale features. We call this trend the tendency of a time series. The tendency is defined empirically by a set of criteria and captures the large-scale temporal variability of the original signal as well as the most frequent events in its histogram. Among other properties, the tendency has a variance no larger than that of the original signal; the histogram of the difference between the original signal and the tendency is as symmetric as possible; and with reduced complexity, the tendency captures essential features of the signal. To find the tendency we first use the intrinsic time-scale decomposition (ITD) of the signal, introduced in 2007 by Frei and Osorio, to produce a set of candidate tendencies. We then apply the criteria to each of the candidates to single out the one that best agrees with them. While the criteria for the tendency are independent of the signal decomposition scheme, it is found that the ITD is a simple and stable methodology, well suited for multi-scale signals. The ITD is a relatively new decomposition and little is known about its outcomes. In this study we take the first steps towards a probabilistic model of the ITD analysis of random time series. This analysis yields details concerning the universality and scaling properties of the components of the decomposition.

Restrepo, Juan M.; Venkataramani, Shankar; Comeau, Darin; Flaschka, Hermann

2014-08-01

398

A Technique for Determining Relaxation Times by Free-Flight Tests of Low-Fineness-Ratio Cones; with Experimental Results for Air at Equilibrium Temperatures up to 3440 K  

NASA Technical Reports Server (NTRS)

This report describes a technique which combines theory and experiments for determining relaxation times in gases. The technique is based on the measurement of shapes of the bow shock waves of low-fineness-ratio cones fired from high-velocity guns. The theory presented in the report provides a means by which shadowgraph data showing the bow waves can be analyzed so as to furnish effective relaxation times. Relaxation times in air were obtained by this technique and the results have been compared with values estimated from shock tube measurements in pure oxygen and nitrogen. The tests were made at velocities ranging from 4600 to 12,000 feet per second corresponding to equilibrium temperatures from 35900 R (19900 K) to 6200 R (34400 K), under which conditions, at all but the highest temperatures, the effective relaxation times were determined primarily by the relaxation time for oxygen and nitrogen vibrations.

Stephenson, Jack D.

1960-01-01

399

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

400

Time scales in the context of general relativity.  

PubMed

Towards 1967, the accuracy of caesium frequency standards reached such a level that the relativistic effect could not be ignored anymore. Corrections began to be applied for the gravitational frequency shift and for distant time comparisons. However, these corrections were not applied to an explicit theoretical framework. Only in 1991 did the International Astronomical Union provide metrics (then improved in 2000) for a definition of space-time coordinates in reference systems centred at the barycentre of the Solar System and at the centre of mass of the Earth. In these systems, the temporal coordinates (coordinate times) can be realized on the basis of one of them, the International Atomic Time (TAI), which is itself a realized time scale. The definition and the role of TAI in this context will be recalled. There remain controversies regarding the name to be given to the unit of coordinate times and to other quantities appearing in the theory. However, the idea that astrometry and celestial mechanics should adopt the usual metrological rules is progressing, together with the use of the International System of Units, among astronomers. PMID:21930569

Guinot, Bernard

2011-10-28

401

Ti diffusion in quartz inclusions: implications for metamorphic time scales  

NASA Astrophysics Data System (ADS)

Quartz inclusions in garnet from samples collected from the staurolite zone in central New England are zoned in cathodoluminescence (CL). The CL intensity is interpreted to be a proxy for Ti concentration and the zoning attributed to Ti diffusion into the quartz grains driven by Ti exchange between quartz and enclosing garnet as a function of changing temperature. The CL zoning has been interpreted using a numerical diffusion model to constrain the time scales over which the diffusion has occurred. Temperature-time histories are sensitive to the presumed peak temperature but not to other model parameters. The total time of the metamorphic heating and cooling cycle from around 450 °C to the peak temperature (550-600 °C) back to 450 °C is surprisingly short and encompasses only 0.2-2 million years for peak temperatures of 600-550 °C. The metamorphism was accompanied by large-scale nappe and dome formation, and it is suggested that this occurred as a consequence of in-sequence thrusting resulting in a mid-crustal ductile duplex structure.

Spear, Frank S.; Ashley, Kyle T.; Webb, Laura E.; Thomas, Jay B.

2012-12-01

402

The role of time scales in extrinsic noise propagation  

NASA Astrophysics Data System (ADS)

Cell-to cell variability in the number of proteins has been studied extensively experimentally. There are many sources of this stochastic variability or noise that can be classified as intrinsic, due to the stochasticity of chemical reactions and extrinsic, due to environmental differences. The different stages in the production of proteins in response to a stimulus, the signaling cascade before transcription, transcription, and translation are characterized by different time scales. We analyze how these time scales determine the effect of the reactions at each stage on different sources of noise. For example, even if intrinsic noise dominates the fluctuations in mRNA number, for typical degradation rates, extrinsic noise can dominate corresponding protein number fluctuations. Such results are important in determining the importance of intrinsic noise at earlier stages of a genetic network on the products of subsequent stages. We examine cases in which the dynamics of the extrinsic noise can lead to differences from cases in which extrinsic noise arises from static (in time) cell-to-cell variations. We will interpret the experiments of Pedraza et al*. in the light of these results. *J. M. Pedraza et al, Science 25 March 2005:Vol. 307. no. 5717, pp. 1965 - 1969.

Iyer-Biswas, Srividya; Pedraza, Juan Manuel; Jayaprakash, C.

2009-03-01

403

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

404

Granular impact dynamics: Fluctuations at short time-scales  

NASA Astrophysics Data System (ADS)

Several recent studies on granular impact have used a macroscopic force law which describes the slow (mean) dynamics. However, these force-law models must be modified to capture large fluctuations at short time-scales. Here, we discuss granular impact experiments using photoelastic particles, where high-speed video captures both the intruder dynamics and the local granular force response. We show how to systematically separate the fluctuations from the mean dynamics. We also show that these fluctuations are multiplicative with the mean force, and otherwise decoupled from the dynamics. These observations are instructive in connecting to microscopic processes which generate the fluctuations.

Clark, Abram H.; Kondic, Lou; Behringer, R. P.

2013-06-01

405

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

SciTech Connect

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 {sup 1}H spin-lattice relaxation for decalin and toluene solutions of various Fe{sub 2}O{sub 3} 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 {sup 1}H 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 {sup 1}H spin-lattice relaxation resulting from the electronic properties of the crystals and the solvent diffusion were explained.

Kruk, D., E-mail: danuta.kruk@matman.uwm.edu.pl [Faculty of Mathematics and Computer Science, University of Warmia and Mazury in Olsztyn, S?oneczna 54, 10-710 Olsztyn (Poland); Experimentalphysik II, Universität Bayreuth, 95440 Bayreuth (Germany); Korpa?a, A. [Department of Biophysics, Jagiellonian University Medical College, ?azarza 16, 31-530 Kraków (Poland) [Department of Biophysics, Jagiellonian University Medical College, ?azarza 16, 31-530 Kraków (Poland); Institute of Physics, Jagiellonian University, Reymonta 4, 30-059 Kraków (Poland); Taheri, S. Mehdizadeh; Förster, S. [Department of Physical Chemistry I, Universität Bayreuth, 95440 Bayreuth (Germany)] [Department of Physical Chemistry I, Universität Bayreuth, 95440 Bayreuth (Germany); Koz?owski, A. [NU-MED Group Inc., Center of Radiotherapy and Improvements in Elbl?g, Królewiecka 146, 82-300 Elbl?g (Poland)] [NU-MED Group Inc., Center of Radiotherapy and Improvements in Elbl?g, Królewiecka 146, 82-300 Elbl?g (Poland); Rössler, E. A. [Experimentalphysik II, Universität Bayreuth, 95440 Bayreuth (Germany)] [Experimentalphysik II, Universität Bayreuth, 95440 Bayreuth (Germany)

2014-05-07

406

Metabolic Risk Factors are associated with Cartilage Degradation assessed by T2 Relaxation Time at the Knee  

PubMed Central

Objective To evaluate the association of metabolic risk factors with severity and two-year progression of early degenerative cartilage changes at the knee, measured with T2 relaxation times in middle-aged subjects from the Osteoarthritis Initiative. Methods Cartilage segmentation and T2 map generation was performed in 3T knee MR images from 403, 45 – 60 year old subjects without radiographic osteoarthritis (OA). The influence of risk factors on baseline and longitudinal progression of T2 was analyzed using linear regression, adjusting for age, gender and other OA risk factors. Results Four metabolic risk factors (i) high abdominal circumference (P<0.001), (ii) hypertension (P=0.040), (iii) high fat consumption (P=0.019) and (iv) self-reported diabetes (P=0.012) were individually associated with higher baseline T2. When the four metabolic risk factors were considered in a multivariate regression model, higher T2 remained significantly associated with abdominal circumference (P<0.001) and diabetes (P=0.031) and there was a trend for high fat consumption (P=0.096). Of individual risk factors, only diabetes remained associated with higher baseline T2 after adjustment for BMI. After adjustment for BMI, baseline T2 increased in dose-reponse fashion with the number of metabolic risk factors present (P=0.032 for linear trend), and subjects with ?3 metabolic factors (versus <3) had significantly higher baseline T2 (mean difference, 1.2ms; lower 95% confidence interval (CI), 0.3ms; upper 95% CI, 2.1ms; P=0.011). Metabolic risk factors were not significantly associated with increases in T2 during follow-up. Conclusion Metabolic risk factors are associated with higher T2, suggesting that increased cartilage degeneration may be caused by modifiable metabolic disorders. PMID:23926027

Jungmann, Pia M.; Kraus, Mareen S.; Alizai, Hamza; Nardo, Lorenzo; Baum, Thomas; Nevitt, Michael C.; McCulloch, Chuck E.; Joseph, Gabby B.; Lynch, John A.; Link, Thomas M.

2014-01-01

407

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

408

Polymorphism in ferroic functional elements. Bridging length and time scales  

NASA Astrophysics Data System (ADS)

The present study describes an approach for the scale-bridging modeling of ferroic materials as functional elements in micro- and nanoelectronic devices. Ferroic materials are characterized by temperature-dependent complex ordering phenomena of the internal magnetic, electronic, and structural degrees of freedom with several involved length and time scales. Hence, the modelling of such compounds is not straightforward, but relies on a combination of electronic-structure-based methods like ab-initio and density-functional schemes with classical particle-based approaches given by Monte-Carlo simulations with Ising, lattice-gas, or Heisenberg Hamiltonians, which incorporate material-specific parameters both from theory and experiment. The interplay of those methods is demonstrated for device concepts based on electroceramic materials like ferroelectrics and multiferroics, whose functionality is closely related with their propensity towards structural and magnetic polymorphism. In the present case, such scale-bridging techniques are employed to aid the development of an organic field effect transistor on a ferroelectric substrate generated by the self-assembly of field-sensitive molecules on the surfaces of ferroic oxides. Electronic-structure-based methods yield the microscopic properties of the oxide, the surface, the molecules, and the respective interactions. They are combined with classical particle-based methods on a scale-hopping basis. This combination allows to study the morphology evolution during the self-assembly of larger adsorbate arrays on the (defective) oxide surface and to investigate the interplay of low-temperature magnetic ordering phenomena with the ferroelectric functionality at higher temperatures in multiferroic oxides like the hexagonal manganites. The combination of density-functional data with classical continuum modelling also yielded a model Hamiltonian for the quick determination of the properties of a gate structure based on bio-functionalized carbon nanotubes.

Gemming, S.; Luschtinetz, R.; Chaplygin, I.; Seifert, G.; Loppacher, C.; Eng, L. M.; Kunze, T.; Olbrich, C.

2007-10-01

409

Quantifying catchment-scale mixing and its effect on time-varying travel time distributions  

NASA Astrophysics Data System (ADS)

Travel time distributions are often used to characterize catchment discharge behavior, catchment vulnerability to pollution and pollutant loads from catchments to downstream waters. However, these distributions vary with time because they are a function of rainfall and evapotranspiration. It is important to account for these variations when the time scale of interest is smaller than the typical time-scale over which average travel time distributions can be derived. Recent studies have suggested that subsurface mixing controls how rainfall and evapotranspiration affect the variability in travel time distributions of discharge. To quantify this relation between subsurface mixing and dynamics of travel time distributions, we propose a new transformation of travel time that yields transformed travel time distributions, which we call Storage Outflow Probability (STOP) functions. STOP functions quantify the probability for water parcels in storage to leave a catchment via discharge or evapotranspiration. We show that this is equal to quantifying mixing within a catchment. Compared to the similar Age function introduced by Botter et al. (2011), we show that STOP functions are more constant in time, have a clearer physical meaning and are easier to parameterize. Catchment-scale STOP functions can be approximated by a two-parameter beta distribution. One parameter quantifies the catchment preference for discharging young water; the other parameter quantifies the preference for discharging old water from storage. Because of this simple parameterization, the STOP function is an innovative tool to explore the effects of catchment mixing behavior, seasonality and climate change on travel time distributions and the related catchment vulnerability to pollution spreading.

van der Velde, Y.; Torfs, P. J. J. F.; van der Zee, S. E. A. T. M.; Uijlenhoet, R.

2012-06-01

410

Complex Processes from Dynamical Architectures with Time-Scale Hierarchy  

PubMed Central

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

Perdikis, Dionysios; Huys, Raoul; Jirsa, Viktor

2011-01-01

411

Variability of global lightning activity on the ENSO time scale  

NASA Astrophysics Data System (ADS)

Global lightning activity has been studied on the ENSO (El Niño Southern Oscillation) time scale based on recordings of the Earth's Schumann resonances at Nagycenk (NCK), Hungary as well as observations from the OTD (Optical Transient Detector) and the LIS (Lightning Imaging Sensor) satellites in space. Both the intensity and position of lightning activity vary on the ENSO time scale. The magnitude of the global variation in lightning flash rate is ~10% from La Niña to El Niño. In general, more lightning is observed in the tropical-extratropical land regions during warm, El Niño episodes, especially in Southeast Asia. Although oceanic lightning activity is a minor contributor to global lightning, an opposite behavior is observed in the Pacific and other oceanic regions. More lightning is present during cold, La Niña conditions than during the warm, El Niño episodes. The annual distribution of global lightning is slightly offset from the equator into the Northern Hemisphere due to the north-south asymmetry of the land/ocean area ratio. Schumann resonance intensity variations suggest a southward (equator-ward) shift and satellite observations support this and show in addition an eastward shift in the global position during warm, El Niño episodes. The greatest lightning contrast between warm El Niño and cold La Niña episodes has been identified at the latitudes of descending dry air in the Hadley circulation.

Sátori, G.; Williams, E.; Lemperger, I.

2009-02-01

412

Reusable Launch Vehicle Control In Multiple Time Scale Sliding Modes  

NASA Technical Reports Server (NTRS)

A reusable launch vehicle control problem during ascent is addressed via multiple-time scaled continuous sliding mode control. The proposed sliding mode controller utilizes a two-loop structure and provides robust, de-coupled tracking of both orientation angle command profiles and angular rate command profiles in the presence of bounded external disturbances and plant uncertainties. Sliding mode control causes the angular rate and orientation angle tracking error dynamics to be constrained to linear, de-coupled, homogeneous, and vector valued differential equations with desired eigenvalues placement. Overall stability of a two-loop control system is addressed. An optimal control allocation algorithm is designed that allocates torque commands into end-effector deflection commands, which are executed by the actuators. The dual-time scale sliding mode controller was designed for the X-33 technology demonstration sub-orbital launch vehicle in the launch mode. Simulation results show that the designed controller provides robust, accurate, de-coupled tracking of the orientation angle command profiles in presence of external disturbances and vehicle inertia uncertainties. This is a significant advancement in performance over that achieved with linear, gain scheduled control systems currently being used for launch vehicles.

Shtessel, Yuri; Hall, Charles; Jackson, Mark

2000-01-01

413

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

414

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

415

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

416

Quantitative T2* (T2 star) relaxation times predict site specific proteoglycan content and residual mechanics of the intervertebral disc throughout degeneration.  

PubMed

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?relaxation times were also significantly correlated with both residual stresses and excised strains in the NP (r?=?0.857; p?

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

2014-08-01

417

Frequency Dependence of Electron Spin Relaxation Times in Aqueous Solution for a Nitronyl Nitroxide Radical and Per-deuterated-Tempone between 250 MHz and 34 GHz  

PubMed Central

Electron spin relaxation times of perdeuterated tempone (PDT) 1 and of a nitronyl nitroxide 2-(4-carboxy-phenyl)-4,4,5,5-tetramethylimidazoline-3-oxide-1-oxyl) 2 in aqueous solution at room temperature were measured by 2-pulse electron spin echo (T2) or 3-pulse inversion recovery (T1) in the frequency range of 250 MHz to 34 GHz. At 9 GHz values of T1 measured by long-pulse saturation recovery were in good agreement with values determined by inversion recovery. Below 9 GHz for 1 and below 1.5 GHz for 2, T1~ T2, as expected in the fast tumbling regime. At higher frequencies T2 was shorter than T1 due to incomplete motional averaging of g and A anisotropy. The frequency dependence of 1/T1 is modeled as the sum of spin rotation, modulation of g and A-anisotropy, and a thermally-activated process that has maximum contribution at about 1.5 GHz. The spin lattice relaxation times for the nitronyl nitroxide were longer than for PDT by a factor of about 2 at 34 GHz, decreasing to about a factor of 1.5 at 250 MHz. The rotational correlation times, ?R are calculated to be 9 ps for 1 and about 25 ps for 2. The longer spin lattice relaxation times for 2 than for 1 at 9 and 34 GHz are due predominantly to smaller contributions from spin rotation that arise from slower tumbling. The smaller nitrogen hyperfine couplings for the nitronyl 2 than for 1 decrease the contribution to relaxation due to modulation of A anisotropy. However, at lower frequencies the slower tumbling of 2 results in a larger value of ??R (? is the resonance frequency) and larger values of the spectral density function, which enhances the contribution from modulation of anisotropic interactions for 2 to a greater extent than for 1. PMID:23123770

Biller, Joshua R.; Meyer, Virginia M.; Elajaili, Hanan; Rosen, Gerald M.; Eaton, Sandra S.; Eaton, Gareth R.

2012-01-01

418

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

419

Hydration of surfactant-modified and PEGylated cationic cholesterol-based liposomes and corresponding lipoplexes by monitoring a fluorescent probe and the dielectric relaxation time.  

PubMed

For the optimization of plasmid DNA (pDNA)-cationic lipid complexes and lipoplex delivery, proper indexes of the physicochemical properties of lipoplexes are required. In general, the characteristics of lipoplexes are defined by particle size and zeta-potential at various mixing ratios of cationic liposomes and pDNA. In this study, we characterized the hydration level of surfactant-modified and PEGylated cationic cholesterol-based (OH-Chol) liposomes and their lipoplexes by monitoring both the fluorescent probe laurdan and the dielectric relaxation time. Fluorescence measurement using laurdan detected hydration of the headgroup of lipids in surfactant-modified liposomes and PEGylated DOTAP-liposomes, but hardly any fluorescence was detected in PEGylated OH-Chol-liposomes because the PEG layers may extend and cover the fluorescent maker. On the other hand, the measurement of dielectric relaxation time of water molecules revealed total hydration, including hydration of the PEG layer and the headgroup of cationic lipids. Furthermore, we found an inverse correlation between hydration level and cellular uptake of PEGylated lipoplexes (R=0.946). This finding indicated that the dielectric relaxation time of water molecules provides an important indicator of hydration of liposome and lipoplexes along with the fluorescence intensity of laurdan. PMID:22348874

Maitani, Yoshie; Nakamura, Ayako; Tanaka, Takumi; Aso, Yukio

2012-05-10

420

Fast two-phonon relaxation process between the Landau levels of graphene on different polar substrates  

NASA Astrophysics Data System (ADS)

Within the frame of Huang-Rhys's lattice relaxation model, we theoretically investigate the carrier relaxation mediated by two-phonon processes, which consists in polar surface optical phonon and longitudinal acoustic phonon emission between the Landau levels of graphene on different polar substrates. This two-phonon relaxation process is very fast within the picosecond scale and may seriously hinder the carrier multiplication based on effective Auger processes. Moreover, the polarizability of the polar substrate plays an important role in determining the relaxation time. These results could be helpful in designing graphene-based photoelectric and photodetector devices.

Wang, Zi-Wu; Liu, Lei; Li, Zhi-Qing

2014-11-01

421

Modelling Time and Length Scales of Scour Around a Pipeline  

NASA Astrophysics Data System (ADS)

The scour and burial of submarine objects is an area of interest for engineers, oceanographers and military personnel. Given the limited availability of field observations, there exists a need to accurately describe the hydrodynamics and sediment response around an obstacle using numerical models. In this presentation, we will compare observations of submarine pipeline scour with model predictions. The research presented here uses the computational fluid dynamics (CFD) model FLOW-3D. FLOW-3D, developed by Flow Science in Santa Fe, NM, is a 3-dimensional finite-difference model that solves the Navier-Stokes and continuity equations. Using the Volume of Fluid (VOF) technique, FLOW-3D is able to resolve fluid-fluid and fluid-air interfaces. The FAVOR technique allows for complex geometry to be resolved with rectangular grids. FLOW-3D uses a bulk transport method to describe sediment transport and feedback to the hydrodynamic solver is accomplished by morphology evolution and fluid viscosity due to sediment suspension. Previous investigations by the authors have shown FLOW-3D to well-predict the hydrodynamics around five static scoured bed profiles and a stationary pipeline (``Modelling of Flow Around a Cylinder Over a Scoured Bed,'' submit to Journal of Waterway, Port, Coastal, and Ocean Engineering). Following experiments performed by Mao (1986, Dissertation, Technical University of Denmark), we will be performing model-data comparisons of length and time scales for scour around a pipeline. Preliminary investigations with LES and k-? closure schemes have shown that the model predicts shorter time scales in scour hole development than that observed by Mao. Predicted time and length scales of scour hole development are shown to be a function of turbulence closure scheme, grain size, and hydrodynamic forcing. Subsequent investigations consider variable wave-current flow regimes and object burial. This investigation will allow us to identify different regimes for the scour process based on dimensionless parameters such as the Reynolds number, the Keulegan-Carpenter number, and the sediment mobility number. This research is sponsored by the Office of Naval Research - Mine Burial Program.

Smith, H. D.; Foster, D. L.

2002-12-01

422