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1

Truncation of scales by time relaxation  

NASA Astrophysics Data System (ADS)

We study a time relaxation regularization of flow problems proposed and tested extensively by Stolz and Adams. The aim of the relaxation term is to drive the unresolved fluctuations in a computational simulation to zero exponentially fast by an appropriate and often problem dependent choice of its coefficient; this relaxation term is thus intermediate between a tunable numerical stabilization and a continuum modeling term. Our aim herein is to understand how this term, by itself, acts to truncate solution scales and to use this understanding to give insight into parameter selection.

Layton, William; Neda, Monika

2007-01-01

2

Relaxation Processes and Time Scale Transformation.  

National Technical Information Service (NTIS)

Stochastic processes with a special class of non-stationary transition rates (NSTR) that can be related to stationary rates (STR) by time scale transformations are considered. Calculations are carried out on the time scale on which the process has STR and...

S. Teitler, A. K. Rajagopal, K. L. Ngai

1982-01-01

3

Time relaxation of ac susceptibility on very short time scales  

Microsoft Academic Search

We present an experimental method enabling measurements of time dependence of ac susceptibility down to 1 ms after a steplike change of the applied dc magnetic field. An analog-digital converter has been used to collect the transient of the current, signaling the change of the dc magnetic field. The time window for investigation of magnetic time relaxation phenomena, as studied

Ivica Zivkovic; Ðuro Drobac; Mladen Prester

2005-01-01

4

Time scales and pathways of vibrational energy relaxation in liquid CHBr3 and CDBr3  

NASA Astrophysics Data System (ADS)

Molecular dynamics simulations are used in conjunction with Landau-Teller, fluctuating Landau-Teller, and time-dependent perturbation theories to investigate energy flow out of various vibrational states of liquid CHBr3 and CDBr3. The CH stretch overtone is found to relax with a time scale of about 1 ps compared to the 50 ps rate for the fundamental. The relaxation pathways and rates for the CD stretch decay in CDBr3 are computed in order to understand the changes arising from deuteration. While the computed relaxation rate agrees well with experiments, the pathway is found to be more complex than anticipated. In addition to the above channels for CH(D) stretch relaxation that involve only the hindered translations and rotations of the solvent, routes involving off-resonant and resonant excitations of solvent vibrational modes are also examined. Finally, the decay of energy from low frequency states to near-lying solute states and solvent vibrations are studied.

Ramesh, Sai G.; Sibert, Edwin L.

2006-12-01

5

Coupled relaxations at the protein-water interface in the picosecond time scale  

PubMed Central

The spectral behaviour of a protein and its hydration water has been investigated through neutron scattering. The availability of both hydrogenated and perdeuterated samples of maltose-binding protein (MBP) allowed us to directly measure with great accuracy the signal from the protein and the hydration water alone. Both the spectra of the MBP and its hydration water show two distinct relaxations, a behaviour that is reminiscent of glassy systems. The two components have been described using a phenomenological model that includes two Cole–Davidson functions. In MBP and its hydration water, the two relaxations take place with similar average characteristic times of approximately 10 and 0.2 ps. The common time scales of these relaxations suggest that they may be a preferential route to couple the dynamics of the water hydrogen-bond network around the protein surface with that of protein fluctuations.

Paciaroni, A.; Cornicchi, E.; Marconi, M.; Orecchini, A.; Petrillo, C.; Haertlein, M.; Moulin, M.; Sacchetti, F.

2009-01-01

6

An exact expression for the transverse nuclear magnetic resonance relaxation of a dynamic scale invariant polymer chain governed by a single relaxation time  

Microsoft Academic Search

An exact analytic calculation of the transverse nuclear magnetic resonance (NMR) relaxation function, due to dipolar interactions, is presented for a polymer chain considered at the scale invariant level of description. The calculation is possible for the particular case where the dynamics of the bond vectors are governed by a single relaxation time. This exact result is used to check

M. G. Brereton

1991-01-01

7

Time-resolved magnetic relaxation of a nanomagnet on subnanosecond time scales  

NASA Astrophysics Data System (ADS)

We present a two-current-pulse temporal correlation experiment to study the intrinsic subnanosecond nonequilibrium magnetic dynamics of a nanomagnet during and following a pulse excitation. This method is applied to a model spin-transfer system, a spin-valve nanopillar with perpendicular magnetic anisotropy. Two pulses separated by a short delay (<500 ps) are shown to lead to the same switching probability as a single pulse with a duration that depends on the delay. This demonstrates a remarkable symmetry between magnetic excitation and relaxation and provides a direct measurement of the magnetic relaxation time. The results are consistent with a simple finite-temperature Fokker-Planck macrospin model of the dynamics, suggesting more coherent magnetization dynamics in this short-time nonequilibrium limit than near equilibrium.

Liu, H.; Bedau, D.; Sun, J. Z.; Mangin, S.; Fullerton, E. E.; Katine, J. A.; Kent, A. D.

2012-06-01

8

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

NASA Astrophysics Data System (ADS)

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

Mishra, S. K.; Srinivasan, J.

2010-10-01

9

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

NASA Astrophysics Data System (ADS)

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

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

2014-01-01

10

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

NASA Astrophysics Data System (ADS)

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

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

2012-01-01

11

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

PubMed

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

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

2010-01-01

12

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

NASA Astrophysics Data System (ADS)

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

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

2010-01-01

13

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

14

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

PubMed Central

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

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

2009-01-01

15

Dynamics of short-time-scale energy relaxation of optical excitations due to electron-electron scattering in the presence of arbitrary disorder  

Microsoft Academic Search

A nonequilibrium occupation distribution relaxes towards the Fermi-Dirac distribution due to electron-electron scattering even in finite Fermi systems. The dynamic evolution of this thermalization process assumed to result from an optical excitation is investigated numerically by solving a Boltzmann equation for the carrier populations using a one-dimensional disordered system. We focus on the short-time-scale behavior. The logarithmically long time scale

Imre Varga; Peter Thomas; Torsten Meier; Stephan W. Koch

2003-01-01

16

Relationship between thermodynamic parameter and thermodynamic scaling parameter for orientational relaxation time for flip-flop motion of nematic liquid crystals  

NASA Astrophysics Data System (ADS)

Thermodynamic parameter ? and thermodynamic scaling parameter ? for low-frequency relaxation time, which characterize flip-flop motion in a nematic phase, were verified by molecular dynamics simulation with a simple potential based on the Maier-Saupe theory. The parameter ?, which is the slope of the logarithm for temperature and volume, was evaluated under various conditions at a wide range of temperatures, pressures, and volumes. To simulate thermodynamic scaling so that experimental data at isobaric, isothermal, and isochoric conditions can be rescaled onto a master curve with the parameters for some liquid crystal (LC) compounds, the relaxation time was evaluated from the first-rank orientational correlation function in the simulations, and thermodynamic scaling was verified with the simple potential representing small clusters. A possibility of an equivalence relationship between ? and ? determined from the relaxation time in the simulation was assessed with available data from the experiments and simulations. In addition, an argument was proposed for the discrepancy between ? and ? for some LCs in experiments: the discrepancy arises from disagreement of the value of the order parameter P2 rather than the constancy of relaxation time ?1* on pressure.

Satoh, Katsuhiko

2013-03-01

17

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

18

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

NASA Astrophysics Data System (ADS)

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

Pasko, V. P.

2009-12-01

19

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

20

Probing relaxation times in graphene quantum dots  

NASA Astrophysics Data System (ADS)

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

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

2013-04-01

21

Probing relaxation times in graphene quantum dots  

PubMed Central

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

Volk, Christian; Neumann, Christoph; Kazarski, Sebastian; Fringes, Stefan; Engels, Stephan; Haupt, Federica; Muller, Andre; Stampfer, Christoph

2013-01-01

22

Serpentine channels: micro-rheometers for fluid relaxation times.  

PubMed

We propose a novel device capable of measuring relaxation times of viscoelastic fluids as small as 1 ms. In contrast to most rheometers, which by their very nature are concerned with producing viscometric or nearly-viscometric flows, here we make use of an elastic instability that occurs in the flow of viscoelastic fluids with curved streamlines. To calibrate the rheometer we combine simple scaling arguments with relaxation times obtained from first normal-stress difference data measured in a classical shear rheometer. As an additional check we also compare these relaxation times to those obtained from Zimm theory and good agreement is observed. Once calibrated, we show how the serpentine rheometer can be used to access smaller polymer concentrations and lower solvent viscosities where classical measurements become difficult or impossible to use due to inertial and/or resolution limitations. In the absence of calibration, the serpentine channel can still be a very useful comparative or index device. PMID:24253108

Zilz, Josephine; Schäfer, Christof; Wagner, Christian; Poole, Robert J; Alves, Manuel A; Lindner, Anke

2014-01-21

23

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

NASA Astrophysics Data System (ADS)

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

Uneyama, Takashi; Akimoto, Takuma; Miyaguchi, Tomoshige

2012-09-01

24

Conformational relaxation of ?-conjugated polymer radical anion on picosecond scale  

NASA Astrophysics Data System (ADS)

We report the conformational relaxation of poly[bis(p-n-butylphenyl)silane] (PBPS) radical anion measured by near-ultraviolet-enhanced picosecond pulse radiolysis in tetrahydrofuran solutions. The peak shift and increase in optical density of the transient photoabsorption spectra were investigated by kinetic analysis including reactions of PBPS with solvated/presolvated electrons, peak extraction protocol, and diffusion theory, demonstrating the correspondence in the rate constant (5+/-1×102 ps) between the peak shift and increase in oscillator strength. The results were examined by density functional theory and molecular dynamics simulations, where the modeled oligosilane radical anion shows more planner conformation relative to its neutral state and a relaxation time of 8 ps. The difference of the time scale is discussed from the viewpoints of actual experimental factors. To the best of our knowledge, this is the first report on the direct observation of the conformational dynamics of rodlike ?-conjugated polymer: PBPS radical anion.

Ohnishi, Yuko; Saeki, Akinori; Seki, Shu; Tagawa, Seiichi

2009-05-01

25

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

26

Estimation of spin-echo relaxation time  

NASA Astrophysics Data System (ADS)

In spin-echo-based EPR oximetry, traditional methods to estimate the T2 relaxation time, which encodes the oxygen concentration of the sample, include fitting an exponential to the peaks or the integrated areas of multiple noisy echoes. These methods are suboptimal and result in a loss of estimation precision for a given acquisition time. Here, we present the maximum likelihood estimate (MLE) of T2 from spin-echo data. The MLE provides, for the data considered, approximately 3-fold time savings over echo-integration and more than 40-fold time savings over peak-picking. A one-dimensional line search results in simple computation of the MLE. It is observed that, perhaps counter-intuitively, prior knowledge of the lineshape does not yield additional reduction of estimation error variance at practical noise levels. The result also illuminates the near optimal performance of T2 estimation via principal components calculated by a singular value decomposition. The proposed method is illustrated by application to simulated and experimental EPR data.

Golub, F.; Potter, L. C.; Ash, J. N.; Blank, A.; Ahmad, R.

2013-12-01

27

Geological Time Scale  

NSDL National Science Digital Library

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

28

Validation of NMR relaxation exchange time measurements in porous media.  

PubMed

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

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

2007-12-21

29

Thermal relaxation times: an outdated concept in photothermal treatments.  

PubMed

Thermal relaxation times were introduced into modern skin-laser science with the inception of selective photothermolysis. As a result, laser pulsewidths were determined according to the thermal relaxation times of the tissue targets. The Arrhenius Damage Integral shows that this approach is incorrect. The important parameter is the time required to induce irreversible protein denaturation within the target. This time is determined by the tissue's intrinsic structure, not its physical dimensions. This report explains why thermal relaxation times should not be considered when treating many skin conditions with lasers or IPL systems. PMID:24085595

Murphy, M J; Torstensson, P A

2014-05-01

30

Analysis of anelastic relaxations controlled by a spectrum of relaxation times  

SciTech Connect

Anelastic studies, although they have provided an important method for investigating the mobility of point defects in solids, have often been difficult to analyze when a continuous spectra of relaxation times controls the anelastic response. This paper describes a new method for obtaining accurate estimates of relaxation time spectra by direct analysis (without prior assumptions) of the data using a nonlinear regression method. Applications to internal friction and anelastic creep results are described with emphasis upon the internal friction technique. 5 references.

Cost, J.R.

1983-01-01

31

A NOTE ON UNIQUENESS IN THERMOELASTICITY WITH ONE RELAXATION TIME  

Microsoft Academic Search

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

Józef Ignaczak

1982-01-01

32

GSA Geologic Time Scale  

NSDL National Science Digital Library

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

1999-01-01

33

Fluctuating Relaxation Times in Glass-forming Liquids  

NASA Astrophysics Data System (ADS)

The presence of fluctuating local relaxation times, ?(r,t) has been used for some time as a conceptual tool to describe dynamical heterogeneities Ediger-arpc-2000. Here we report on a new method for determining the local phase field, ?(r,t)?T?dt'?(r,t') from snapshots r(ti)i=1...M of the positions of the particles in a system, and we apply it to extract ?(r,t) from simulations of glass forming models. By studying how the phase field depends on the number of snapshots, we find that it is a well defined quantity. By studying fluctuations of the phase field, we find that they describe heterogeneities well at long distance scales. We also determine how the stretching exponent ? depends on the coarse graining volume, in order to test the hypothesis that relaxation in small regions is exponential and it only becomes non-exponential when considering large regions of the system. [4pt] [1] M. D. Ediger, 2000 Annu. Rev. Phys. Chem. 51 99

Mavimbela, Gcina A.; Castillo, Horacio E.; Parsaeian, Azita

2012-02-01

34

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

35

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.

36

Irreversibility time scale.  

PubMed

Entropy creation rate is introduced for a system interacting with thermostats (i.e., for a system subject to internal conservative forces interacting with "external" thermostats via conservative forces) and a fluctuation theorem for it is proved. As an application, a time scale is introduced, to be interpreted as the time over which irreversibility becomes manifest in a process leading from an initial to a final stationary state of a mechanical system in a general nonequilibrium context. The time scale is evaluated in a few examples, including the classical Joule-Thompson process (gas expansion in a vacuum). PMID:16822023

Gallavotti, G

2006-06-01

37

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

38

Proton-nuclear magnetic resonance relaxation times in brain edema  

SciTech Connect

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

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

1990-01-01

39

Phenomenological theory of structural relaxation based on a thermorheologically complex relaxation time distribution  

NASA Astrophysics Data System (ADS)

The aim of this work is to explore the consequences on the kinetics of structural relaxation of considering a glass-forming system to consist of a series of small but macroscopic relaxing regions that evolve independently from each other towards equilibrium in the glassy state. The result of this assumption is a thermorheologically complex model. In this approach each relaxing zone has been assumed to follow the Scherer-Hodge model for structural relaxation (with the small modification of taking a linear dependence of configurational heat capacity with temperature). The model thus developed contains four fitting parameters. A least-squares search routine has been used to find the set of model parameters that fit simultaneously four DSC thermograms in PVAc after different thermal histories. The computer-simulated curves are compared with those obtained with Scherer-Hodge model and the model proposed by Gómez and Monleón. The evolution of the relaxation times during cooling or heating scans and also during isothermal annealing below the glass transition has been analysed. It has been shown that the relaxation times distribution narrows in the glassy state with respect to equilibrium. Isothermal annealing causes this distribution to broaden during the process to finally attain in equilibrium the shape defined at temperatures above Tg.

Andreozzi, L.; Faetti, M.; Salmerã³n Sanchez, M.; Gã³mez Ribelles, J. L.

2008-09-01

40

Relaxation time and elasticity during polymerization with DER 332  

NASA Astrophysics Data System (ADS)

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

Venkateshan, K.; Johari, G. P.

2006-10-01

41

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

42

Direct Spectrum-Analysis Method for Obtaining the Relaxation-Time Spectrum from Relaxation-Response Data: Amorphous Metals.  

National Technical Information Service (NTIS)

A method is described for determining without prior assumptions the distribution of relaxation times from the experimental relaxation response curve for a system approaching equilibrium by a single-step process following first-order kinetics. By analysis ...

J. R. Cost

1982-01-01

43

Some evidence of scaling behavior in the relaxation dynamics of aqueous polymer solutions.  

PubMed

The structural relaxation behavior of aqueous solution of poly(ethylene glycol) and methoxy-capped poly(ethylene glycol), both of mean molecular mass 400 g/mol, is investigated by Brillouin scattering experiments. In both cases non-Debye relaxation processes have been detected, proceeding on the picosecond time scale. The average values of the detected relaxation time distributions fail to follow the simple Arrhenius behavior. The temperature evolution of the relaxation time is adequately fitted using the phenomenological Vogel-Fulcher-Tamman (VFT) model. In spite of the different temperature and concentration dependences observed for the two kinds of systems, with the exception of the highest samples concentrations, a unique scaling behavior has been found for the real and imaginary parts of the loss modulus plotted as a function of the reduced inverse temperature, T(0)/T, T(0) being the VFT arrest temperature. The presence of a unique scaling law in aqueous solutions of polymers characterized by different end groups suggests the establishment of similar hydrogen-bonded local structures. Within this scenario, water acts as a stabilizer and plays the main role bridging neighboring polymer chains. The possible physical interpretation of the obtained fit parameters is discussed, and the results are compared with other literature findings. PMID:20055360

Pochylski, M; Aliotta, F; Ponterio, R C; Saija, F; Gapi?ski, J

2010-02-01

44

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

45

Calculation of nanocolloidal liquid time scales by molecular dynamics simulations  

NASA Astrophysics Data System (ADS)

Molecular dynamics, MD, simulations have been used to calculate the translational and rotational relaxation dynamics of model atomistically rough spherical nanocolloidal particles in solution at infinite dilution by immersing a single Lennard-Jones cluster in a molecularly discrete solvent. Key time scales characterizing colloidal particle dynamical relaxation were computed from time correlation functions. For translational motion these were ? v, the colloidal velocity relaxation time, ?f, the hydrodynamic relaxation time and the time scale for significant particle displacement, ?d. We show that ?v ? ?f when the relative mass density of the colloidal particle divided by the bulk density of the solvent is ca. ?*=20, in agreement with theoretical predictions. Preliminary evidence from the velocity autocorrelation functions, VACF, of the nanocolloidal particle also supports the theoretical treatments that the transition from the Liouville to Fokker-Planck description (evident by exponential decay in the VACF) is determined by both the colloidal particle mass and size. We calculated the relaxation times for angular velocity relaxation, ?? and reorientation, ?u and found them to scale reasonably well with the relaxation time for the free rotor, for size dependence but not so well for mass dependence. The angular velocity correlation function of 13 atom clusters departed from Langevin (exponential) relaxation also for ?*< 20. The rotational self-diffusion coefficient was also non-classical in this range.

Heyes, D. M.; Bra?ka, A. C.

46

Effects of Stress and Relaxation on Time Perception.  

National Technical Information Service (NTIS)

Changes in time perception during and following experiences of stress and relaxation are commonly reported, but little is known about the direction and nature of any time perception changes. In this experimental study, men and women ages 18 to 79 were ran...

B. R. Chavez

2003-01-01

47

Scale interactions of turbulence subjected to a straining relaxation destraining cycle  

NASA Astrophysics Data System (ADS)

The response of turbulence subjected to planar straining and de-straining is studied experimentally, and the impact of the applied distortions on the energy transfer across different length scales is quantified. The data are obtained using planar particle image velocimetry (PIV) in a water tank, in which high-Reynolds-number turbulence with very low mean velocity is generated by an array of spinning grids. Planar straining and de-straining mean flows are produced by pushing and pulling a rectangular piston towards, and away from, the bottom wall of the tank. The data are processed to yield the time evolution of Reynolds stresses, anisotropy tensors, turbulence kinetic energy production, and mean subgrid-scale (SGS) dissipation rate at various scales. During straining, the production rises rapidly. After the relaxation period the small-scale SGS stresses recover isotropy, but the Reynolds stresses still display significant anisotropy. Thus when destraining is applied, a strong negative production (mean backscatter) occurs, i.e. the turbulence returns kinetic energy to the mean flow. The SGS dissipation displays similar behaviour at large filter scales, but the mean backscatter gradually disappears with decreasing filter scales. Energy spectra are compared to predictions of rapid distortion theory (RDT). Good agreement is found for the initial response but, as expected for the time-scale ratios of the experiment, turbulence relaxation causes discrepancies between measurements and RDT at later times.

Chen, Jun; Meneveau, Charles; Katz, Joseph

2006-09-01

48

Anomalous Pressure Dependence of Dipolar Relaxation Times in Rare Earth Doped Lead Fluoride.  

National Technical Information Service (NTIS)

Electrical relaxation measurements at high pressures have been carried out on lead fluoride doped with lanthanum and cerium. A single, strong relaxation peak is observed and the relaxation time decreases with pressure. This is contrary to the behavior exh...

J. J. Fontanella M. C. Wintersgill D. R. Figueroa A. V. Chadwick C. G. Andeen

1984-01-01

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

Cell water dynamics on multiple time scales  

PubMed Central

Water–biomolecule interactions have been extensively studied in dilute solutions, crystals, and rehydrated powders, but none of these model systems may capture the behavior of water in the highly organized intracellular milieu. Because of the experimental difficulty of selectively probing the structure and dynamics of water in intact cells, radically different views about the properties of cell water have proliferated. To resolve this long-standing controversy, we have measured the 2H spin relaxation rate in living bacteria cultured in D2O. The relaxation data, acquired in a wide magnetic field range (0.2 mT–12 T) and analyzed in a model-independent way, reveal water dynamics on a wide range of time scales. Contradicting the view that a substantial fraction of cell water is strongly perturbed, we find that ?85% of cell water in Escherichia coli and in the extreme halophile Haloarcula marismortui has bulk-like dynamics. The remaining ?15% of cell water interacts directly with biomolecular surfaces and is motionally retarded by a factor 15 ± 3 on average, corresponding to a rotational correlation time of 27 ps. This dynamic perturbation is three times larger than for small monomeric proteins in solution, a difference we attribute to secluded surface hydration sites in supramolecular assemblies. The relaxation data also show that a small fraction (?0.1%) of cell water exchanges from buried hydration sites on the microsecond time scale, consistent with the current understanding of protein hydration in solutions and crystals.

Persson, Erik; Halle, Bertil

2008-01-01

51

Hamiltonian Systems on Time Scales  

Microsoft Academic Search

Linear and nonlinear Hamiltonian systems are studied on time scales T. We unify symplectic flow properties of discrete and continuous Hamiltonian systems. A chain rule which unifies discrete and continuous settings is presented for our so-called alpha derivatives on generalized time scales. This chain rule allows transformation of linear Hamiltonian systems on time scales under simultaneous change of independent and

Calvin D. Ahlbrandt; Martin Bohner; Jerry Ridenhour

2000-01-01

52

Calculation of the relaxation times for an inhomogeneous ESR line  

Microsoft Academic Search

A method for separately determining the longitudinal, T1, and transverse, T2, relaxation times from the saturation curve of an inhomogeneously broadened slow-passage ESR absorption line is presented. It imposes no restriction on the relative values of the spin packet (Lorentzian) and Gaussian widths conforming with the overall inhomogeneous width. It gives a simple way of calculating T2=2\\/(spin-packet width) through the

R. Zamorano-Ulloa; H. Flores-Llamas; H. Yee-Madeira

1992-01-01

53

MR T2 Relaxation Time Measurements for Cartilage and Menisci  

Microsoft Academic Search

\\u000a Magnetic Resonance Imaging (MRI) can be used not only for morphologic but also for quantitative assessment of knee cartilage.\\u000a Quantitative T1rho and T2 relaxation time measurements and dGEMRIC (delayed Gadolinium enhanced MRI of the cartilage) have\\u000a emerged as potential cartilage biomarkers to assess early degenerative disease. This chapter focuses on the T2-technique and\\u000a clinical applications of hyaline cartilage and meniscal

Thomas Baum; Thomas M. Link; Bernard J. Dardzinski

54

Comparison of methods for the calculation of superparamagnetic relaxation times  

NASA Astrophysics Data System (ADS)

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

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

1996-11-01

55

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

56

One-dimensional thermal shock problem with two relaxation times  

SciTech Connect

The theory of generalized thermoelasticity with two relaxation times is used to solve a boundary value problem of an isotropic elastic half-space with its plane boundary either held rigidly fixed or stress-free and subjected to a sudden temperature increase. An approximate small-time solution is obtained by using the Laplace transform method. Numerical values of displacement, stress, and temperature are obtained and displayed graphically. Two discontinuities in both the displacement and temperature functions and that the stress has infinite discontinuities at these two wave fronts were noted. 22 refs.

Dhaliwal, R.S.; Rokne, J.G. (Calgary Univ. (Canada))

1989-01-01

57

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

PubMed

Thin polymer films are ubiquitous in manufacturing and medical applications, and there has been intense interest in how film thickness and substrate interactions influence film dynamics. It is appreciated that a polymer-air interfacial layer with enhanced mobility plays an important role in the observed changes and recent studies suggest that the length scale ? of this interfacial layer is related to film relaxation. In the context of the Adam-Gibbs and random first-order transition models of glass formation, these results provide indirect evidence for a relation between ? and the scale of collective molecular motion. Here we report direct evidence for a proportionality between ? and the average length L of string-like particle displacements in simulations of polymer films supported on substrates with variable interaction strength and rigidity. This relation explicitly links ? to the theoretical scale of cooperatively rearranging regions, offering a promising route to experimentally determine this scale of cooperative motion. PMID:24932594

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

2014-01-01

58

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.

Remacle, F.; Levine, R. D.

2006-01-01

59

Short-time scaling behavior of growing interfaces  

Microsoft Academic Search

The short-time evolution of a growing interface is studied within the framework of the dynamic renormalization-group approach for the Kadar-Parisi-Zhang (KPZ) equation and for an idealized continuum model of molecular-beam epitaxy. The scaling behavior of response and correlation functions is reminiscent of the ``initial slip'' behavior found in purely dissipative critical relaxation (model A) and critical relaxation with conserved order

Michael Krech; Fachbereich Physik

1997-01-01

60

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

61

Dependence on chain length of NMR relaxation times in mixtures of alkanes  

NASA Astrophysics Data System (ADS)

Many naturally occurring fluids, such as crude oils, consist of a very large number of components. It is often of interest to determine the composition of the fluids in situ. Diffusion coefficients and nuclear magnetic resonance (NMR) relaxation times can be measured in situ and depend on the size of the molecules. It has been shown [D. E. Freed et al., Phys. Rev. Lett. 94, 067602 (2005)] that the diffusion coefficient of each component in a mixture of alkanes follows a scaling law in the chain length of that molecule and in the mean chain length of the mixture, and these relations were used to determine the chain length distribution of crude oils from NMR diffusion measurements. In this paper, the behavior of NMR relaxation times in mixtures of chain molecules is addressed. The author explains why one would expect scaling laws for the transverse and longitudinal relaxation times of mixtures of short chain molecules and mixtures of alkanes, in particular. It is shown how the power law dependence on the chain length can be calculated from the scaling laws for the translational diffusion coefficients. The author fits the literature data for NMR relaxation in binary mixtures of alkanes and finds that its dependence on chain length agrees with the theory. Lastly, it is shown how the scaling laws in the chain length and the mean chain length can be used to determine the chain length distribution in crude oils that are high in saturates. A good fit is obtained between the NMR-derived chain length distributions and the ones from gas chromatography.

Freed, Denise E.

2007-05-01

62

Effective rotational correlation times of proteins from NMR relaxation interference  

NASA Astrophysics Data System (ADS)

Knowledge of the effective rotational correlation times, ?c, for the modulation of anisotropic spin-spin interactions in macromolecules subject to Brownian motion in solution is of key interest for the practice of NMR spectroscopy in structural biology. The value of ?c enables an estimate of the NMR spin relaxation rates, and indicates possible aggregation of the macromolecular species. This paper reports a novel NMR pulse scheme, [ 15N, 1H]-TRACT, which is based on transverse relaxation-optimized spectroscopy and permits to determine ?c for 15N- 1H bonds without interference from dipole-dipole coupling of the amide proton with remote protons. [ 15N, 1H]-TRACT is highly efficient since only a series of one-dimensional NMR spectra need to be recorded. Its use is suggested for a quick estimate of the rotational correlation time, to monitor sample quality and to determine optimal parameters for complex multidimensional NMR experiments. Practical applications are illustrated with the 110 kDa 7,8-dihydroneopterin aldolase from Staphylococcus aureus, the uniformly 15N-labeled Escherichia coli outer membrane protein X (OmpX) in 60 kDa mixed OmpX/DHPC micelles with approximately 90 molecules of unlabeled 1,2-dihexanoyl- sn-glycero-3-phosphocholine (DHPC), and the 16 kDa pheromone-binding protein from Bombyx mori, which cover a wide range of correlation times.

Lee, Donghan; Hilty, Christian; Wider, Gerhard; Wüthrich, Kurt

2006-01-01

63

Rapid MRI method for mapping the longitudinal relaxation time  

NASA Astrophysics Data System (ADS)

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

Hsu, Jung-Jiin; Glover, Gary H.

2006-07-01

64

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

PubMed

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 T(c) = 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. PMID:22583251

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

2012-05-01

65

?-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

66

Long time stress relaxation of a triblock copolymer with asymmetric composition  

Microsoft Academic Search

The long-time stress relaxation was examined for poly(styrene)-poly(ethylene- co-butylene)-polystyrene triblock copolymer with asymmetric composition in the microphase separated state. Stress relaxation data from a parallel plate rheometer were extended to very long times by using a newly built compression instrument. Three properties were measured, the relaxation time spectrum, the equilibrium modulus, and the instantaneous modulus. Relaxation experiments over several months

Prashant Mandare; Roland Horst; H. Henning. Winter

2005-01-01

67

Fractional relaxation and the time-temperature superposition principle  

Microsoft Academic Search

Relaxation processes in complex systems like polymers or other viscoelastic materials can be described by equations containing fractional differential or integral operators. In order to give a physical motivation for fractional order equations, the fractional relaxation is discussed in the framework of statistical mechanics. We show that fractional relaxation represents a special type of a non-Markovian process. Assuming a separation

W. G. Glöckle; T. F. Nonnenmacher

1994-01-01

68

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 Ci-1?-Ci?, 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

69

The time correlation function perspective of NMR relaxation in proteins.  

PubMed

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 (15)N-(1)H bond). So far we applied SRLS to (15)N-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. PMID:24006974

Shapiro, Yury E; Meirovitch, Eva

2013-08-28

70

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

71

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

PubMed

The elastic models of the glass transition relate the increasing solidity of the glassforming systems with the huge slowing down of the structural relaxation and the viscous flow. The solidity is quantified in terms of the instantaneous shear modulus G(?), i.e., the immediate response to a step change in the strain. By molecular-dynamics simulations of a model polymer system, one shows the virtual absence of correlations between the instantaneous elasticity and the structural relaxation. Instead, a well-defined scaling is evidenced by considering the elastic response observed at intermediate times after the initial fast stress relaxation. The scaling regime ranges from sluggish states with virtually pure elastic response on the picosecond time scale up to high-mobility states where fast restructuring events are more apparent. PMID:22299854

Puosi, F; Leporini, D

2012-01-28

72

Time dependent parallel viscosity and relaxation rate of poloidal rotation in the banana regime  

SciTech Connect

Time dependent ion parallel viscous force in the banana regime with arbitrary inverse aspect ratio [epsilon] is calculated using the eigenfunction approach. The flux surface averaged viscosity is then used to study the relaxation process of the poloidal rotation which leads to oscillatory relaxation behavior. The relaxation rate [nu][sub [ital p

Hsu, C.T.; Shaing, K.C.; Gormley, R. (Plasma Fusion Center, Massachusetts Institute of Technology, 167 Albany Street, NW16-260, Cambridge, Massachusetts 02139 (United States))

1994-01-01

73

Numerical decomposition of a complex thermostimulated depolarization current spectrum in single time relaxation peaks  

Microsoft Academic Search

We have proposed a numerical method for the decomposition of an experimental thermally stimulated depolarization current (TSDC) curve into a sum of elementary spectra obeying the Debye law (a single relaxation time). This method allows one to solve the case of two close overlapping relaxations as well as the case of a distributed relaxation. It consists of fitting the rightmost

F. Faubert; M. Sanchez

1998-01-01

74

Multiple-relaxation-time lattice Boltzmann scheme for homogeneous mixture flows with external force  

NASA Astrophysics Data System (ADS)

A lattice Boltzmann scheme is developed for homogeneous mixture modeling, based on the multiple-relaxation-time (MRT) formulation, which fully recovers the Maxwell-Stefan diffusion model in the continuum limit with (a) external force and (b) tunable Schmidt number. The theoretical basis of the proposed MRT formulation is a recently proposed Bhatnagar-Gross-Krook-type kinetic model for gas mixtures [Andries , J. Stat. Phys. 106, 993 (2002)] and it substantially extends the applicability of a scheme already proposed by the same author, which used only one relaxation parameter. The recovered equations at the macroscopic level are derived by an innovative expansion technique, based on the Grad moment system. Some numerical simulations are reported for the solvent test case with external force, aiming to find the numerical ranges for the transport coefficients that ensure acceptable accuracies. The numerical results reduce the theoretical expectations, which are based on a strong separation among the characteristic scales.

Asinari, Pietro

2008-05-01

75

Multiple-relaxation-time lattice Boltzmann scheme for homogeneous mixture flows with external force.  

PubMed

A lattice Boltzmann scheme is developed for homogeneous mixture modeling, based on the multiple-relaxation-time (MRT) formulation, which fully recovers the Maxwell-Stefan diffusion model in the continuum limit with (a) external force and (b) tunable Schmidt number. The theoretical basis of the proposed MRT formulation is a recently proposed Bhatnagar-Gross-Krook-type kinetic model for gas mixtures [Andries, J. Stat. Phys. 106, 993 (2002)] and it substantially extends the applicability of a scheme already proposed by the same author, which used only one relaxation parameter. The recovered equations at the macroscopic level are derived by an innovative expansion technique, based on the Grad moment system. Some numerical simulations are reported for the solvent test case with external force, aiming to find the numerical ranges for the transport coefficients that ensure acceptable accuracies. The numerical results reduce the theoretical expectations, which are based on a strong separation among the characteristic scales. PMID:18643194

Asinari, Pietro

2008-05-01

76

Dynamical robustness of biological networks with hierarchical distribution of time scales  

Microsoft Academic Search

We propose the concepts of distributed robustness and r-robustness, well adapted to functional genetics. Then we discuss the robustness of the relaxation time using a chemical reaction description of genetic and signalling networks. First, we obtain the following result for linear networks: for large multiscale systems with hierarchical distribution of time scales the variance of the inverse relaxation time (as

A. N. Gorban; O. Radulescu

2007-01-01

77

Scaling between relaxation, transport and caged dynamics in a binary mixture on a per-component basis.  

PubMed

The universal scaling between the average slow relaxation/transport and the average picosecond rattling motion inside the cage of the first neighbors has been evidenced in a variety of numerical simulations and experiments. Here, we first show that the scaling does not need information concerning the arbitrarily-defined glass transition region and relies on a single characteristic length scale a(2)(1/2) which is determined even far from that region. This prompts the definition of a novel reduced rattling amplitude (1/2) which has been investigated by extensive molecular-dynamics simulations addressing the slow relaxation, the diffusivity, and the fast cage-dynamics of both components of an atomic binary mixture. States with different potential, density, and temperature are considered. It is found that if two states exhibit coinciding incoherent van Hove function on the picosecond timescale, the coincidence is observed at long times too, including the large-distance exponential decay--a signature of heterogeneous dynamics--observed when the relaxation is slow. A major result of the present study is that the correlation plot between the diffusivity of the two components of the binary mixtures and their respective reduced rattling amplitude collapse on the same master curve. This holds true also for the structural relaxation of the two components and the unique master curve coincides with the one of the average scaling. It is shown that the breakdown of the Stokes-Einstein law exhibited by the distinct atomic species of the mixture and the monomers of a chain in a polymer melt is predicted at the same reduced rattling amplitude. Finally, we evidence that the well-known temperature/density thermodynamic scaling of the transport and the relaxation of the mixture is still valid on the picosecond timescale of the rattling motion inside the cage. This provides a link between the fast dynamics and the thermodynamic scaling of the slow dynamics. PMID:23556783

Puosi, F; De Michele, C; Leporini, D

2013-03-28

78

Scaling between relaxation, transport and caged dynamics in a binary mixture on a per-component basis  

NASA Astrophysics Data System (ADS)

The universal scaling between the average slow relaxation/transport and the average picosecond rattling motion inside the cage of the first neighbors has been evidenced in a variety of numerical simulations and experiments. Here, we first show that the scaling does not need information concerning the arbitrarily-defined glass transition region and relies on a single characteristic length scale a21/2 which is determined even far from that region. This prompts the definition of a novel reduced rattling amplitude ?1/2 which has been investigated by extensive molecular-dynamics simulations addressing the slow relaxation, the diffusivity, and the fast cage-dynamics of both components of an atomic binary mixture. States with different potential, density, and temperature are considered. It is found that if two states exhibit coinciding incoherent van Hove function on the picosecond timescale, the coincidence is observed at long times too, including the large-distance exponential decay--a signature of heterogeneous dynamics--observed when the relaxation is slow. A major result of the present study is that the correlation plot between the diffusivity of the two components of the binary mixtures and their respective reduced rattling amplitude collapse on the same master curve. This holds true also for the structural relaxation of the two components and the unique master curve coincides with the one of the average scaling. It is shown that the breakdown of the Stokes-Einstein law exhibited by the distinct atomic species of the mixture and the monomers of a chain in a polymer melt is predicted at the same reduced rattling amplitude. Finally, we evidence that the well-known temperature/density thermodynamic scaling of the transport and the relaxation of the mixture is still valid on the picosecond timescale of the rattling motion inside the cage. This provides a link between the fast dynamics and the thermodynamic scaling of the slow dynamics.

Puosi, F.; De Michele, C.; Leporini, D.

2013-03-01

79

Deep Time: The Geologic Time Scale  

NSDL National Science Digital Library

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

2007-01-01

80

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

81

A Geologic Time Scale 2004  

NASA Astrophysics Data System (ADS)

This may be the most straightforward book review imaginable to write. Just buy this book and use it! You will not regret it.Verlyn Klinkenborg's 23 August 2005 editorial in the New York Times (“Grasping the depth of time as a first step in understanding evolution”) serves as a most timely way begin a review of A Geologic Time Scale 2004 (GTS2004). Klinkenborg writes, “One of the most powerful limits to the human imagination is our inability to grasp, in a truly intuitive way the depths of terrestrial and cosmological time.”

Geissman, John W.

82

Time-resolved X-ray measurements of energy relaxation in ultrafast laser excited semiconductors  

NASA Astrophysics Data System (ADS)

In semiconductors, the properties and dynamics of photoexcited carriers and subsequent energy relaxation through lattice vibrations are quite complex and occur on a variety of time scales. Typically the transient dynamics involving transitions of electrons from lower energy states to higher ones upon photoexcitation take place almost instantaneously. The electrons eventually recombine with holes while losing most of their kinetic energy to the lattice through various routes at different time scales. The lattice relaxation processes, especially at high photoexcitation levels, have been subjected to numerous experimental and theoretical investigations during past decades. Time-resolved X-ray diffraction (TRXD) method provides a novel tool for studying these dynamics because X-rays have short wavelength, long material penetration depth and relatively strong interaction with core electrons. In my work, femtosecond laser pulses excite electrons in opaque materials, and subsequent carrier relaxation process and coherent/incoherent lattice dynamics are investigated using TRXD. My thesis covers quantitative detail of the generation and propagation of ultrafast laser induces acoustic strain waves in bulk semiconductor materials as well as at the heterostructure interface. In particular propagation of strain waves, which are comprised of broadband low wave vector phonons, is studied in an AlGaAs/GaAs multilayer structure. The spatial and temporal profiles of the acoustic waves at varying photoexcitation density are characterized. We are able to distinguish thermal from carrier-induced strain and measure the free-carrier absorption cross-section. The approximation that impulsively generated acoustic waves are uniaxial is found to break down. The research also demonstrates a novel approach to explore laser induced acoustic phonon dynamics at high wavevector, near the Brillouin zone-boundary, the details of which are inaccessible to optical pump-probe methods. Throughout this thesis, the validity and limits of our theoretical model of high frequency acoustic phonon generation are examined. Toward the end, theoretical and experimental challenges are addressed and possible solutions are presented.

Lee, Soo Heyong

83

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

84

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

85

Instantaneous scale and the short-time scale transform  

Microsoft Academic Search

The concept of instantaneous scale, ci, is developed and it is shown that it is given by ci=tØ'(t) where Ø'( t) is the derivative of the phase of the signal. Formulas for average scale, scale bandwidth, and scale group delay are obtained. The scale transform, the short time scale transform, the analytic scale signal, and other related concepts are defined

LEON COHEN

1992-01-01

86

The Concise Geologic Time Scale  

NASA Astrophysics Data System (ADS)

This concise handbook presents a summary of Earth's history over the past 4.5 billion years as well as a brief overview of contemporaneous events on the Moon, Mars and Venus. The authors have been at the forefront of chronostratigraphic research and initiatives to create an international geologic time scale for many years, and the charts in this book present the most up to date, international standard, as ratified by the International Commission on Stratigraphy and the International Union of Geological Sciences. This book is an essential reference for all geoscientists, including researchers, students, and petroleum and mining professionals. The presentation is non-technical and illustrated with numerous colour charts, maps and photographs. The book also includes a detachable laminated card of the complete time scale for use as a handy reference in the office, laboratory or field.

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

87

a Comparison of Single-Time Relaxation Lattice Boltzmann Schemes with Enhanced Stability  

Microsoft Academic Search

In the recent years the entropic version of the lattice Boltzmann method (ELB) has made proof of significantly enhanced numerical stability as compared to the standard single-time relaxation form of the lattice Boltzmann equation. In this paper, we compare ELB with a more empirical procedure, based on the idea of modifying the value of the relaxation time in such a

Francesca Tosi; Stefano Ubertini; Sauro Succi; Hudong Chen; Ilya V. Karlin

2006-01-01

88

Time scales in cognitive neuroscience  

PubMed Central

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

Papo, David

2013-01-01

89

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

SciTech Connect

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

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

2007-03-15

90

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

National Technical Information Service (NTIS)

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

W. M. Nevins

1995-01-01

91

Multiple Time Scale Decomposition of Discrete Time Markov Chains,  

National Technical Information Service (NTIS)

The multiple time scale decomposition of discrete time, finite state Markov chains is addressed. In previous works, the behavior of a continuous time Markov chain is approximated using a fast time scale, epsilon-independent, continuous time process, and a...

J. R. Rohlicek, A. S. Willsky

1988-01-01

92

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

MedlinePLUS

Time to Talk Tips 5 Things To Know About Relaxation Techniques for Stress When you’re under ... About Complementary Health Approaches for Quitting Smoking More Time To Talk Tip Sheets Home Home Page Contact ...

93

A model of acoustic absorption in fluids based on a continuous distribution of relaxation times  

Microsoft Academic Search

This work extends the quasi-equilibrium relaxation theory of sound absorption in liquids to the case of continuous distribution of relaxation times. Such extension is needed when absorption mechanisms are not confined to the action of viscosity and heat conduction, but are mainly due to the excitation of a large number of internal molecular degrees of freedom. In this case the

G. Vilensky; G. ter Haar; N. Saffari

94

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

NASA Astrophysics Data System (ADS)

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

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

95

Genetic Programming for Multi-Time-Scale Modeling: First Results  

NASA Astrophysics Data System (ADS)

A bottleneck for effective multi-time-scale modeling of alloys is the computation of jump frequencies (or potential energy, PE, surface). We explore the use of genetic programming (GP)---a genetic algorithm that evolves computer programs---to create a local mapping of the jump frequency for any possible chemical or defect configuration that avoids explicit calculation of the entirety of the PE surface. We use a simple genetic program to perform symbolic regression of activation energies as a function of local configuration. To exemplify the ideas, we use (un)relaxed 2-D FCC Leonard-Jones A_xB_1-x alloy exhibiting phase segregation that includes a vacancy point defect. We show that the GP predicts activations energies within 0.5% for the relaxed case using only ˜3% of the total configuration space. These initial results hold promise to scale kinetics simulations, via kinetic Monte Carlo, by ˜9 orders in time over molecular dynamics.

Sastry, Kumara; Johnson, D. D.; Goldberg, D. E.

2003-03-01

96

The length and time scales of water's glass transitions.  

PubMed

Using a general model for the equilibrium dynamics of supercooled liquids, I compute from molecular properties the emergent length and time scales that govern the nonequilibrium relaxation behavior of amorphous ice prepared by rapid cooling. Upon cooling, the liquid water falls out of equilibrium whereby the temperature dependence of its relaxation time is predicted to change from super-Arrhenius to Arrhenius. A consequence of this crossover is that the location of the apparent glass transition temperature depends logarithmically on cooling rate. Accompanying vitrification is the emergence of a dynamical length-scale, the size of which depends on the cooling rate and varies between angstroms and tens of nanometers. While this protocol dependence clarifies a number of previous experimental observations for amorphous ice, the arguments are general and can be extended to other glass forming liquids. PMID:24908028

Limmer, David T

2014-06-01

97

Time scales, their users, and leap seconds  

Microsoft Academic Search

Numerous time scales exist to address specific user requirements. Accurate dynamical time scales (barycentric, geocentric and terrestrial) have been developed based on the theory of relativity. A family of time scales has been developed based on the rotation of the Earth that includes Universal Time (specifically UT1), which serves as the traditional astronomical basis of civil time. International Atomic Time

P. Kenneth Seidelmann; John H. Seago

2011-01-01

98

Erratum: Short-time scaling behavior of growing interfaces  

Microsoft Academic Search

The short-time evolution of a growing interface is studied analytically and numerically for the Kadar-Parisi-Zhang (KPZ) universality class. The scaling behavior of response and correlation functions is reminiscent of the ``initial slip'' behavior found in purely dissipative critical relaxation (model A). Unlike model A the initial slip exponent for the KPZ equation can be expressed by the dynamical exponent z.

Michael Krech

1997-01-01

99

Understanding the viscoelastic behavior of collagen matrices through relaxation time distribution spectrum.  

PubMed

This study aims to provide understanding of the macroscopic viscoelastic behavior of collagen matrices through studying the relaxation time distribution spectrum obtained from stress relaxation tests. Hydrated collagen gel and dehydrated collagen thin film was exploited as two different hydration levels of collagen matrices. Genipin solution was used to induce crosslinking in collagen matrices. Biaxial stress relaxation tests were performed to characterize the viscoelastic behavior of collagen matrices. The rate of stress relaxation of both hydrated and dehydrated collagen matrices shows a linear initial stress level dependency. Increased crosslinking reduces viscosity in collagen gel, but the effect is negligible for thin film. Relaxation time distribution spectrum was obtained from the stress relaxation data by inverse Laplace transform. For most of the collagen matrices, three peaks at the short (0.3s ~1 s), medium (3s ~90 s), and long relaxation time (> 200 s) were observed in the continuous spectrum, which likely corresponds to relaxation mechanisms involve fiber, inter-fibril, and fibril sliding. Splitting of the middle peak was observed at higher initial stress levels suggesting increased structural heterogeneity at the fibril level with mechanical loading. The intensity of the long-term peaks increases with higher initial stress levels indicating the engagement of collagen fibrils at higher levels of tissue strain. PMID:23628869

Xu, Bin; Li, Haiyue; Zhang, Yanhang

2013-01-01

100

Understanding the viscoelastic behavior of collagen matrices through relaxation time distribution spectrum  

PubMed Central

This study aims to provide understanding of the macroscopic viscoelastic behavior of collagen matrices through studying the relaxation time distribution spectrum obtained from stress relaxation tests. Hydrated collagen gel and dehydrated collagen thin film was exploited as two different hydration levels of collagen matrices. Genipin solution was used to induce crosslinking in collagen matrices. Biaxial stress relaxation tests were performed to characterize the viscoelastic behavior of collagen matrices. The rate of stress relaxation of both hydrated and dehydrated collagen matrices shows a linear initial stress level dependency. Increased crosslinking reduces viscosity in collagen gel, but the effect is negligible for thin film. Relaxation time distribution spectrum was obtained from the stress relaxation data by inverse Laplace transform. For most of the collagen matrices, three peaks at the short (0.3s ~1 s), medium (3s ~90 s), and long relaxation time (> 200 s) were observed in the continuous spectrum, which likely corresponds to relaxation mechanisms involve fiber, inter-fibril, and fibril sliding. Splitting of the middle peak was observed at higher initial stress levels suggesting increased structural heterogeneity at the fibril level with mechanical loading. The intensity of the long-term peaks increases with higher initial stress levels indicating the engagement of collagen fibrils at higher levels of tissue strain.

Xu, Bin; Li, Haiyue; Zhang, Yanhang

2013-01-01

101

Competition between surface relaxation and ballistic deposition models in scale-free networks  

NASA Astrophysics Data System (ADS)

In this paper we study the scaling behavior of the fluctuations in the steady state WS with the system size N for a surface growth process given by the competition between the surface relaxation (SRM) and the ballistic deposition (BD) models on degree uncorrelated scale-free (SF) networks, characterized by a degree distribution P(k) ˜ k-?, where k is the degree of a node. It is known that the fluctuations of the SRM model above the critical dimension (dc = 2) scale logarithmically with N on Euclidean lattices. However, Pastore y Piontti et al. (Phys. Rev. E, 76 (2007) 046117) found that the fluctuations of the SRM model in SF networks scale logarithmically with N for ? < 3 and as a constant for ? ? 3. In this letter we found that for a pure ballistic deposition model on SF networks WS scales as a power law with an exponent that depends on ?. On the other hand when both processes are in competition, we find that there is a continuous crossover between a SRM behavior and a power law behavior due to the BD model that depends on the occurrence probability of each process and the system size. Interestingly, we find that a relaxation process contaminated by any small contribution of ballistic deposition will behave, for increasing system sizes, as a pure ballistic one. Our findings could be relevant when surface relaxation mechanisms are used to synchronize processes that evolve on top of complex networks.

La Rocca, C. E.; Macri, P. A.; Braunstein, L. A.

2013-01-01

102

Time scales in the approach to equilibrium of macroscopic quantum systems.  

PubMed

We prove two theorems concerning the time evolution in general isolated quantum systems. The theorems are relevant to the issue of the time scale in the approach to equilibrium. The first theorem shows that there can be pathological situations in which the relaxation takes an extraordinarily long time, while the second theorem shows that one can always choose an equilibrium subspace, the relaxation to which requires only a short time for any initial state. PMID:24138227

Goldstein, Sheldon; Hara, Takashi; Tasaki, Hal

2013-10-01

103

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

NASA Astrophysics Data System (ADS)

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

Li, Jingliang; Zhao, Kongshuang; Liu, Chunyan

2013-04-01

104

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

NASA Astrophysics Data System (ADS)

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 1017 cm-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.; Binek, Ch.

2014-04-01

105

Ba-ferrite particles for magnetic liquids with enhanced Neel relaxation time and loss investigations  

NASA Astrophysics Data System (ADS)

Nanometer-scale particles are interesting because of their unique magnetic properties. Barium ferrite with particle sizes ? 10 nm behave superparamagnetically and show at bigger sizes the transition to single domain behaviour. Beside the particle size, the anisotropy energy K_1\\cdot V, and thus the Neel relaxation time, depends also on the amount of doping. The glass crystallisation method was used for preparation of different Ba-ferrites. Ferrofluids have been prepared using Isopar^{circledR} M or dodecane as a carrier liquid. Magnetic parameters were obtained by VSM, hysteresis losses (specific loss power) of ferrite powders by a hysteresometer at 50 Hz. Magnetic core sizes were calculated from hysteresis loops. SANS curves of a ferrofluid reveal single magnetic particles and aggregated magnetic particles with an incomplete organic shell. Figs 3, Refs 9.

Muller, R.; Hiergeist, R.; Gawalek, W.; Hoell, A.

2003-03-01

106

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

NASA Astrophysics Data System (ADS)

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

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

2001-10-01

107

Optimization of CPMG sequences to measure NMR transverse relaxation time T2 in borehole applications  

NASA Astrophysics Data System (ADS)

Nuclear Magnetic Resonance (NMR) can provide key information such as porosity and permeability for hydrological characterization of geological material. In particular the NMR transverse relaxation time T2 is used to estimate permeability since it reflects a pore-size dependent relaxation process. The measurement sequence (CPMG) usually consists of several thousands of electromagnetic pulses to densely record the relaxation process and to avoid relaxation processes that are due to diffusion. These pulses are equidistantly spaced by a time constant tE. In NMR borehole applications the use of CPMG sequences for measuring the transverse relaxation time T2 is limited due to requirements on energy consumption. For measuring T2, it is state-of-the-art to conduct at least two sequences with different echo spacings (tE) for recording fast and slow relaxing processes that correspond to different pore-sizes. We focus on conducting only a single CPMG sequence and reducing the amount of energy while obtaining both slow and fast decaying components and minimizing the influence of relaxation due to diffusion. Therefore, we tested the usage of CPMG sequences with an increasing tE and a decreasing number of pulses. A synthetic study as well as laboratory measurements on samples of glass beads and granulate material of different grain size spectra were conducted to evaluate the effects of an increasing tE. We show that T2 distributions are broadened if the number of pulses is decreasing and the mean grain size is increasing, which is mostly an effect of a significantly shortened acquisition time. The shift of T2 distributions to small decay times as a function of tE and the mean grain size distribution is observed. We found that it is possible to conduct CPMG sequences with an increased tE. According to the acquisition time and increasing influence of relaxation due to diffusion, the sequence parameters need to be chosen carefully to avoid misinterpretations.

Ronczka, M.; Müller-Petke, M.

2012-11-01

108

Feedback systems and multiple time-scales  

NASA Technical Reports Server (NTRS)

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

Silva-Madriz, R.

1986-01-01

109

The recovery of dipolar relaxation times from fluorescence decays as a tool to probe local dynamics in single tryptophan proteins.  

PubMed

The dipolar relaxation process induced by the excitation of the single tryptophan residue of four proteins (staphylococcal nuclease, ribonuclease-T1, phosphofructokinase, and superoxide dismutase) has been studied by dynamic fluorescence measurements. A new algorithm taking into account the relaxation effect has been applied to the fluorescence decay function obtained by phase-shift and demodulation data. This approach only requires that fluorescence be collected through the whole emission spectrum, avoiding the time-consuming determination of the data at different emission wavelengths, as usual with time-resolved emission spectroscopy. The results nicely match those reported in the literature for staphylococcal nuclease and ribonuclease-T1, demonstrating the validity of the model. Furthermore, this new methodology provides an alternative explanation for the complex decay of phosphofructokinase and human superoxide dismutase suggesting the presence of a relaxation process even in proteins that lack a lifetime-dependent spectral shift. These findings may have important implications on the analysis of small-scale protein dynamics, since dielectric relaxation directly probes a local structural change around the excited state of tryptophan. PMID:12941297

Mei, Giampiero; Di Venere, Almerinda; De Matteis, Fabio; Rosato, Nicola

2003-09-15

110

The effects of proteins on the proton N.M.R. transverse relaxation time of water  

NASA Astrophysics Data System (ADS)

The changes in water proton transverse relaxation behaviour induced by aggregation of Bovine serum albumin are explained in terms of the simple molecular processes of diffusion and chemical exchange without recourse to invoking changes in 'bound' water or the 'state' of water in the system. It is proposed that the main effect of aggregation is to reduce the protein proton transverse relaxation time because dipole-dipole interactions between protein protons are no longer as efficiently averaged by rotational motions, this in turn causes a reduction in water proton transverse relaxation time since water protons are in fast chemical exchange with protein protons. Diffusive exchange between water molecules then spatially averages the water proton signal to an extent that depends on the morphology of the aggregate-water system. The diffusive averaging process can give rise to multi-exponential relaxation.

Hills, B. P.; Takacs, S. F.; Belton, P. S.

111

Relaxation time of the order parameter in a high-temperature superconductor  

NASA Astrophysics Data System (ADS)

Femtosecond time-resolved measurements on the high-Tc superconductor Tl2Ba2Ca2-Cu3O10 are presented. At temperatures below Tc, a relaxation process is observed which is distinct from the equilibrium of hot carriers in the normal state. The results demonstrate an increasing relaxation rate as the superconducting gap opens. This is consistent with the behavior of conventional metallic superconductors.

Eesley, G. L.; Heremans, J.; Meyer, M. S.; Doll, G. L.; Liou, S. H.

1990-12-01

112

The relaxation-time limit in the quantum hydrodynamic equations for semiconductors  

Microsoft Academic Search

The relaxation-time limit from the quantum hydrodynamic model to the quantum drift–diffusion equations in R3 is shown for solutions which are small perturbations of the steady state. The quantum hydrodynamic equations consist of the isentropic Euler equations for the particle density and current density including the quantum Bohm potential and a momentum relaxation term. The momentum equation is highly nonlinear

Ansgar Jüngel; Hai-Liang Li; Akitaka Matsumura

2006-01-01

113

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

Microsoft Academic Search

Dynamic properties of water and polymer chain proton in pullulan\\/H2O systems in aqueous solutions and in frozen states were analyzed based on T2 relaxation times in 1H-NMR and DSC. Two relaxing species with different T2 detected in the CPMG pulse sequence were assigned to inert polymer protons with the shorter T2 and to water protons with the longer T2 by

Ryo Okada; Shingo Matsukawa; Tokuko Watanabe

2002-01-01

114

Rotational relaxation times of individual compounds within simulations of molecular asphalt models  

NASA Astrophysics Data System (ADS)

The dynamical properties of a complex system incorporate contributions from the diverse components from which it is constituted. To study this relationship in a multicomponent system, relaxation times based on rotation autocorrelation functions in molecular dynamics simulations were analyzed for molecules in two sets of unmodified and polymer-modified model asphalt/bitumen systems over 298-473 K. The model asphalt systems were proposed previously to approximate the chemical and mechanical properties of real asphalts. Relaxations were modeled using a modified Kaulrausch-Williams-Watts function and were based on the third Legendre polynomial of normal vector time correlation functions for aromatic species (asphaltene, polar aromatic, naphthene aromatic). Both the end-to-end vector and the longest axis eigenvector of the radius of gyration matrix were used for time correlation functions of chain molecules (C22, polystyrene). Decreases in temperature induced large increases in relaxation time consistent with the Vogel-Fulcher-Tammann equation. The presence of a polymer slowed the decay of each correlation function to some extent. The product of relaxation time and diffusion coefficient revealed qualitative differences between larger and smaller molecules in the same system. These relaxation mechanisms remained coupled for small molecules, while the larger asphaltene and polymer molecules revealed significant slowdowns in rotation compared to translational diffusion at lower temperatures. Smaller values of the stretched exponential parameter ? for asphaltenes compared to smaller molecules suggested a broader range of relaxation times and were consistent with this distinction. Difficulties in converging polymer chain relaxation times are discussed in terms of fluctuations in the magnitude and orientation of the end-to-end vector and chain axis eigenvector. Viscosity results suggested by the Debye-Stokes-Einstein relationship are consistent with trends shown in the literature for true bitumen systems.

Zhang, Liqun; Greenfield, Michael L.

2010-05-01

115

Time scales, their users, and leap seconds  

NASA Astrophysics Data System (ADS)

Numerous time scales exist to address specific user requirements. Accurate dynamical time scales (barycentric, geocentric and terrestrial) have been developed based on the theory of relativity. A family of time scales has been developed based on the rotation of the Earth that includes Universal Time (specifically UT1), which serves as the traditional astronomical basis of civil time. International Atomic Time (TAI) is also maintained as a fundamental time scale based on the output of atomic frequency standards. Coordinated Universal Time (UTC) is an atomic scale for worldwide civil timekeeping, referenced to TAI, but with epoch adjustments via so-called leap seconds to remain within one second of UT1. A review of the development of the time scales, the status of the leap-second issue, and user considerations and perspectives are discussed. A description of some more recent applications for time usage is included.

Seidelmann, P. Kenneth; Seago, John H.

2011-08-01

116

Time-dependent reduction of acetylcholine-induced relaxation in aortic rings of cholestatic rats.  

PubMed

Changes in vascular responsiveness are the basis for some of the cardiovascular complications in cholestasis. Since the duration of cholestasis is important in determining the degree of the complications, we investigated the time-course dependent evolution of vascular relaxation responsiveness in the aortic rings of cholestatic rats. Acetylcholine-induced endothelium-dependent relaxation was investigated in the isolated aortic rings of unoperated, sham-operated and two-, five-, seven- and fourteen-day bile-duct ligated rats. There was a significant reduction in acetylcholine-induced relaxation of the aortic rings by the second day after the bile-duct ligation operation, compared to those of unoperated and sham-operated groups, but more reduction still occurs in 5- and 7-day bile-duct ligated groups, reaching a plateau by the seventh day. The relaxation response to sodium nitroprusside in the aortic rings of the unoperated and the 7-day bile-duct ligated rats did not differ, implying the intact smooth muscle component of the relaxation pathway. L-NAME ( N(omega)-nitro-L-arginine methyl ester), a nitric oxide (NO) synthase inhibitor, attenuated the acetylcholine-induced relaxation in both groups (unoperated and bile-duct ligated), while L-arginine prevents this inhibitory effect. Indomethacin potentiated the acetylcholine-induced relaxation in the aortic rings of the bile-duct ligated rats while it has no effect on unoperated controls, providing evidence for the possible role of vasoconstrictor prostanoids in cholestasis-induced reduction in acetylcholine-induced relaxation. These results state that the reduced acetylcholine-induced relaxation in the cholestatic aortic rings during the first week, when no portal hypertension was reported to be present, may be due to the decreased acetylcholine-induced NO release from endothelium or increased NO inactivation. PMID:11735360

Rastegar, H; Jorjani, M; Roushanzamir, F; Ahmadiani, A; Namiranian, K; Dehpour, A R

2001-12-01

117

T2 relaxation time analysis in patients with multiple sclerosis: correlation with magnetization transfer ratio.  

PubMed

The aim of the current study was to perform T2 relaxation time measurements in multiple sclerosis (MS) patients and correlate them with magnetization transfer ratio (MTR) measurements, in order to investigate in more detail the various histopathological changes that occur in lesions and normal-appearing white matter (NAWM). A total number of 291 measurements of MTR and T2 relaxation times were performed in 13 MS patients and 10 age-matched healthy volunteers. Measurements concerned MS plaques (105), NAWM (80), and "dirty" white matter (DWM; 30), evenly divided between the MS patients, and normal white matter (NWM; 76) in the healthy volunteers. Biexponential T2 relaxation-time analysis was performed, and also possible linearity between MTR and mean T2 relaxation times was evaluated using linear regression analysis in all subgroups. Biexponential relaxation was more pronounced in "black-hole" lesions (16.6%) and homogeneous enhancing plaques (10%), whereas DWM, NAWM, and mildly hypointense lesions presented biexponential behavior with a lower frequency(6.6, 5, and 3.1%, respectively). Non-enhancing isointense lesions and normal white matter did not reveal any biexponential behavior. Linear regression analysis between monoexponential T2 relaxation time and MTR measurements demonstrated excellent correlation for DWM( r=-0.78, p<0.0001), very good correlation for black-hole lesions( r=-0.71, p=0.002), good correlation for isointense lesions( r=-0.60, p=0.005), moderate correlation for mildly hypointense lesions( r=-0.34, p=0.007), and non-significant correlation for homogeneous enhancing plaques, NAWM, and NWM. Biexponential T2 relaxation-time behavior is seen in only very few lesions (mainly on plaques with high degree of demyelination and axonal loss). A strong correlation between MTR and monoexponential T2 values was found in regions where either inflammation or demyelination predominates; however, when both pathological conditions coexist, this linear relationship is lost. PMID:14600774

Papanikolaou, Nickolas; Papadaki, Eufrosini; Karampekios, Spyros; Spilioti, Martha; Maris, Thomas; Prassopoulos, Panos; Gourtsoyiannis, Nicholas

2004-01-01

118

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

119

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

120

Constraints on Formation History of Large Scale Lunar Topography from Observed Admittance: Viscous Relaxation with Lunar Thermal History  

Microsoft Academic Search

The scale- and age-dependence of topographic relaxation of a cooling viscoelastic sphere indicates that the 5000- km-scale (dichotomy scale) topography of the Moon should be external origin and formed later than 100 m.y. from the lunar formation.

K. Ojima; Y. Abe

1999-01-01

121

Time constants in thermal laser medicine: II. Distributions of time constants and thermal relaxation of tissue.  

PubMed

The thermal response of a semi-infinite medium in air, irradiated by laser light in a cylindrical geometry, cannot accurately be approximately by single radial and axial time constants for heat conduction. This report presents an analytical analysis of hear conduction where the thermal response is expressed in terms of distributions over radial and axial time constants. The source term for heat production is written as the product of a Gaussian shaped radial term and an exponentially shaped axial term. The two terms are expanded in integrals over eigenfunctions of the radial and axial parts of the Laplace heat conduction operator. The result is a double integral over the coupled distributions of the two time constants to compute the temperature rise as a function of time and of axial and radial positions. The distribution of axial time constants is a homogeneous slowly decreasing function of spatial frequency (v) indicating that one single axial time constant cannot reasonably characterize axial heat conduction. The distribution of radial time constants is a function centred around a distinguished maximum in the spatial frequency (lambda) close to the single radial time constant value used previously. This suggests that one radial time constant to characterize radial heat conduction may be a useful concept. Special cases have been evaluated analytically, such as short and long irradiation times, axial or radial heat conduction (shallow or deep penetrating laser beams) and, especially, thermal relaxation (cooling) of the tissue. For shallow penetrating laser beams the asymptotic cooling rate is confirmed to be proportional to [(t)0.5-(t-tL)0.5] which approaches 1/t0.5 for t > tL, where t is the time and tL is the laser pulse duration. For deep penetrating beams this is proportional to 1/(t-tL). For intermediate penetration, i.e. penetration depths about equal to spot size diameters, this is proportional to 1/(t-tL)1.5. The double integral has been evaluated numerically and the results have been compared with the various approximations available including the new results and the single time constant model. The present analysis completes our previous work, presents a closed-form formulation for the non-ablative thermal response of laser irradiated tissue and provides insight into the practical value of using time constants for representing heat conduction effects, in particular for the rate of cooling of the tissue surface. PMID:8858726

van Gemert, M J; Lucassen, G W; Welch, A J

1996-08-01

122

Introduction to the time scale problem  

SciTech Connect

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

Voter, A. F.

2002-01-01

123

Data matching of building polygons at multiple map scales improved by contextual information and relaxation  

NASA Astrophysics Data System (ADS)

The aim of matching spatial data at different map scales is to find corresponding objects at different levels of detail (LODs) that represent the same real-world phenomena. This is a prerequisite for integrating, evaluating and updating spatial data collected and maintained at various scales. However, matching spatial data is not straightforward due to the ambiguities caused by problems like many-to-many correspondence, non-systematic displacement and different LODs between data sets. This paper proposes an approach to matching areal objects (e.g. buildings) based on relaxation labeling techniques widely applied in pattern recognition and computer vision. The underlying idea is to utilize contextual information (quantified by compatibility coefficient) in an iterative process, where the ambiguities are reduced until a consistent matching is achieved. This paper describes (1) a domain-specific extension to previous relaxation schemes and (2) a new compatibility coefficient that exploits relative relationships between areal object pairs in spatial data. Our approach were validated through extensive experiments using building data sets at 1:10k and 1:50k as an example. Our contextual approach showed superior performance against a non-contextual approach in general and especially in ambiguous situations. The proposed approach can also be applied to matching other areal features and/or for a different scale range.

Zhang, Xiang; Ai, Tinghua; Stoter, Jantien; Zhao, Xi

2014-06-01

124

Correlation of carrier localization with relaxation time distribution and electrical conductivity relaxation in silver-nanoparticle-embedded moderately doped polypyrrole nanostructures  

NASA Astrophysics Data System (ADS)

The electrical conductivity relaxation in moderately doped polypyrrole and its nanocomposites reinforced with different proportion of silver nanoparticles was investigated in both frequency and time domain. An analytical distribution function of relaxation times is constructed from the results obtained in the frequency domain formalism and is used to evaluate the Kohlrausch-Williams-Watts (KWW) type decay function in the time domain. The thermal evolution of different relaxation parameters was analyzed. The temperature-dependent dc electrical conductivity, estimated from the average conductivity relaxation time is observed to depend strongly on the nanoparticle loading and follows Mott three-dimensional variable range hopping (VRH) conduction mechanism. The extent of charge carrier localization calculated from the VRH mechanism is well correlated to the evidences obtained from the structural characterizations of different nanostructured samples.

Biswas, Swarup; Dutta, Bula; Bhattacharya, Subhratanu

2014-02-01

125

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

Microsoft Academic Search

This paper attempts to establish the dynamics of a microscopic model for a continuous-time random walk. The waiting-time distribution Q(t) is derived from the time-dependent perturbation theory of quantum mechanics for the walker's motion coupled with the media. The walker's motion includes the hopping of a localized particle and a spin (or dipole) flip. The medium is modeled as a

Fu-Sui Liu; Wen Chao

1989-01-01

126

Time-dependent deformation of the eastern flank of Mt. Etna: After-slip or viscoelastic relaxation?  

Microsoft Academic Search

Major results of post-intrusive GPS monitoring of the 5 months encompassing and following the onset of 2002–03 Mt. Etna eruption are presented and discussed here. The overall ground deformation pattern is characterized by a time-dependent relaxation function. We evaluated two different parametrizations of relaxation functions, each one linked to a different relaxation process: i) viscoelastic relaxation and ii) after-slip mechanism. The

M. Palano; S. Gresta; G. Puglisi

2009-01-01

127

Direct measurement of transverse relaxation time of intermolecular multiple quantum coherences in NMR  

NASA Astrophysics Data System (ADS)

A one-dimensional NMR method is presented for measuring the transverse relaxation time, T2,n, of intermolecular multiple quantum coherences (IMQCs) of coherence order n in highly polarized spin systems. The pulse sequence proposed in this paper effectively suppresses the effects of radiation damping, molecular diffusion, inhomogeneity of magnetic field and variations of dipolar correlation distance, all of which may affect quantitation of T2,n. This pulse sequence can be used to measure not only IMQC transverse relaxation time T2,n(n>1) quickly and directly, but also the conventional transverse relaxation time. Experimental results demonstrate that the quantitative relationship between T2,n(n?1) and T2 is T2,n?T2/n. These results will be helpful for understanding the fundamental properties and mechanisms of IMQCs.

Zheng, Shao-kuan; Chen, Zhong; Chen, Zhi-wei; Zhong, Jian-hui

2001-06-01

128

Relaxation Times, Residual Sizes and Limit Temperatures for Ni+Ni HIC  

NASA Astrophysics Data System (ADS)

LATINO Molecular Dynamics semiclassical Model has been used to simulate heavy ion collisions. All correlations are included and Internucleonic forces are replicated via a binary Pandharipande potential. Fragments are detected with an Early Cluster Recognition Algorithm. Temperature is obtained applying Kinetic Theory to Participant Region. Limit Temperature decreases as the residual size increases, in agreement with previous experimental analyses. Event by event trajectories in phase diagram confirm this tendency. Thermal relaxation time is increased as the residual size increases, indicating more deformation energy. A shorter relaxation time for small residual sizes suggests energy is spent on hot fragment production. Therefore, fragmentation process is determined by relaxation times and residual sizes. Computations were carried out at UAM Supercomputing Lab and UT-El Paso facilities. Authors acknowledge financial support from NSF through PHYS-96-00038 grant, Universidad de Buenos Aires (EX-070, Grant No. TW98, CONICET Grant No. PIP 4436/96) and hospitality from IF-UNAM.

Barranon, Armando; Lopez, Jorge A.; Dorso, Claudio O.

2003-03-01

129

Changes in Postnatal Contraction and Half-Relaxation Times of the Canine Pectineus Muscle.  

National Technical Information Service (NTIS)

Isometric contraction and half-relaxation times of pectineus muscles were recorded in mongrel dogs 1 to 144 days of age. Contraction time decreased from 127 msec. one day after birth to 71 msec. during the first 16 days of life and remained relatively con...

G. H. Cardinet G. L. Tunell M. R. Fedde

1971-01-01

130

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.

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

2014-01-01

131

Multiple time scale based reduction scheme for nonlinear chemical dynamics  

NASA Astrophysics Data System (ADS)

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

Das, D.; Ray, D. S.

2013-07-01

132

Investigation of microenvironmental factors influencing the longitudinal relaxation times of drugs and other compounds.  

PubMed

The aim of this study was to investigate the microenvironmental factors likely to influence the longitudinal relaxation time of MR visible drugs or compounds in vivo at 1.5 T. The relative influence that viscosity, albumin and paramagnetic contrast agent concentrations have on the observed longitudinal relaxation times of three 19F MR detectable drugs and compounds have been investigated. Our data show that for 5-fluorouracil, flucloxacillin and tetrafluorosuccinic acid-containing phantoms, the presence of albumin at normal physiological concentrations will have relaxation effects of the same order of magnitude as that of a commonly clinically administered contrast agent, gadolinium diethylenetriamine pentaacetic acid. The contribution of viscosity is shown, in the examples studied here, to be of minor importance, contributing less than 6.5% to the observed relaxation effects. It is also demonstrated that in the presence of competitive binding of other ligands for common binding sites on albumin, the 19F longitudinal relaxation time of 5-fluorouracil can increase by up to 340% from its value in the absence of the competing ligand. The relevance of the findings to in vivo studies is discussed. PMID:15288138

Dzik-Jurasz, A S K; Leach, M O; Rowland, I J

2004-09-01

133

Establishment of a Brazilian Atomic Time Scale.  

National Technical Information Service (NTIS)

The Atomic Time Scale at the Time Service Division of the National Observatory in Rio de Janeiro (ONRJ) has been carried out by commercial cesium clocks. The UTC(ONRJ) time scale based on a single commercial cesium clock selected from the ensemble of cloc...

R. Jose de Carvalho

2006-01-01

134

Some applications of the Lagrange identity in thermoelasticity with one relaxation time  

SciTech Connect

Consideration is given to the uniqueness and continuous data dependence questions appropriate to the fundamental initial/boundary-value problems in thermoelasticity with one relaxation time. On the basis of the Lagrange identity, results are obtained for bounded domains as well as for exterior unbounded domains, without definiteness conditions on the thermoelastic coefficients other than the positiveness of the product between the thermal conductivity and the relaxation time. The applicability of the Lagrange identity in order to obtain some reciprocal theorems is outlined. 24 references.

Chirita, S.

1988-01-01

135

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

136

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

NASA Astrophysics Data System (ADS)

The shear viscosity coefficient and the corresponding relaxation time for causal dissipative hydrodynamics are calculated based on the microscopic formula proposed in T. Koide and T. Kodama [Phys. Rev. EPLEEE81539-3755 78, 051107 (2008)10.1103/PhysRevE.78.051107]. Here, the exact formula is transformed into a more compact form and applied to evaluate these transport coefficients in the chiral perturbation theory and perturbative QCD. It is shown that in the leading order calculation, the causal shear viscosity coefficient ? reduces to that of the ordinary Green-Kubo-Nakano formula, and the relaxation time ?? is related to ? and pressure P by a simple relationship, ??=?/P.

Koide, T.; Nakano, E.; Kodama, T.

2009-07-01

137

Deconvolution analysis to determine relaxation time spectra of internal friction peaks  

SciTech Connect

A new method for analysis of an internal friction vs temperature peak to obtain an approximation of the spectrum of relaxation time responsible for the peak is described. This method, referred to as direct spectrum analysis (DSA), is shown to provide an accurate estimate of the distribution of relaxation times. The method is validated for various spectra, and it is shown that: (1) It provides approximations to known input spectra which replicate the position, amplitude, width and shape with good accuracy (typically 10%). (2) It does not yield approximations which have false spectral peaks.

Cost, J.R.

1985-01-01

138

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

139

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

140

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

141

Only through perturbation can relaxation times be estimated.  

PubMed

Estimation of model parameters is as important as model building, but is often neglected in model studies. Here we show that despite the existence of well known results on parameter estimation in a simple homogenous Ornstein-Uhlenbeck process, in most practical situations the methods suffer greatly from finite sample sizes and especially the estimator of the time constant of the system is degraded. Therefore an alternative solution is of paramount importance. We present such a solution based on perturbation of the system, observing trajectories far from equilibrium. The results are illustrated on computer experiments based on applications in neuroscience and pharmacokinetics, which show a striking improvement of the quality of estimation. The results are important for judicious designs of experiments to obtain maximal information from each data point, especially when samples are expensive or difficult to obtain. PMID:23214727

Ditlevsen, Susanne; Lansky, Petr

2012-11-01

142

Only through perturbation can relaxation times be estimated  

NASA Astrophysics Data System (ADS)

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

Ditlevsen, Susanne; Lansky, Petr

2012-11-01

143

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

PubMed

We show that a system of hard disks confined to a narrow channel exhibits a fragile-strong fluid crossover located at the maximum of the isobaric heat capacity and that the relaxation times for different channel widths fall onto a single master curve when rescaled by the relaxation times and temperatures of the crossover. Calculations of the configurational entropy and the inherent structure equation of state find that the crossover is related to properties of the jamming landscape for the model but that the Adam-Gibbs relation does not predict the relaxation behavior. We also show that a facilitated dynamics description of the system, where kinetically excited regions are identified with local packing arrangements of the disks, successfully describes the fragile-strong crossover. PMID:23368134

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

2012-11-30

144

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

145

Effective time-reversal symmetry breaking in the spin relaxation in a graphene quantum dot  

NASA Astrophysics Data System (ADS)

We study the relaxation of a single electron spin in a circular gate-tunable quantum dot in gapped graphene [1]. Direct coupling of the spin to out-of-plane phonons via the intrinsic spin-orbit coupling leads to a lowered relaxation time T1 at intermediate B-fields. At low fields, T1 increases as B-2 due to the suppression of the phonon density of states at long wavelengths in a finite system. We also find that Rashba spin-orbit induced admixture of opposite spin states in combination with the emission of in-plane phonons provides various further relaxation channels via deformation potential and bond-length change. In the absence of valley mixing, spin relaxation takes place within each valley separately and thus time-reversal symmetry is effectively broken, thus inhibiting the van Vleck cancellation at B=0 known from GaAs quantum dots. Both the absence of the van Vleck cancellation as well as the out-of-plane phonons lead to a behavior of the spin relaxation rate at low magnetic and intermediate fields which is markedly different from the known results for GaAs. At high fields there is a crossover to T1B-2 or B-4.[4pt] [1] P. R. Struck and G. Burkard, Phys. Rev. B 82, 125401 (2010).

Struck, Philipp; Burkard, Guido

2011-03-01

146

Multi-scale freeform surface texture filtering using a mesh relaxation scheme  

NASA Astrophysics Data System (ADS)

Surface filtering algorithms using Fourier, Gaussian, wavelets, etc, are well-established for simple Euclidean geometries. However, these filtration techniques cannot be applied to today's complex freeform surfaces, which have non-Euclidean geometries, without distortion of the results. This paper proposes a new multi-scale filtering algorithm for freeform surfaces that are represented by triangular meshes based on a mesh relaxation scheme. The proposed algorithm is capable of decomposing a freeform surface into different scales and separating surface roughness, waviness and form from each other, as will be demonstrated throughout the paper. Results of applying the proposed algorithm to computer-generated as well as real surfaces are represented and compared with a lifting wavelet filtering algorithm.

(Jane Jiang, Xiangqian; Abdul-Rahman, Hussein S.; Scott, Paul J.

2013-11-01

147

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

PubMed

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

Mamontov, Eugene

2013-08-15

148

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

NASA Astrophysics Data System (ADS)

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

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

2008-08-01

149

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 (81)Br and (35)Cl 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 (35)Cl quadrupolar coupling constant was found to be almost one order lower than that for (81)Br, i.e. 1.8MHz and 16.0MHz, respectively. Taking into account the facts that the ratio of (Q((35)Cl)/Q((81)Br))(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

150

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

151

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

NASA Astrophysics Data System (ADS)

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

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

2010-03-01

152

Multiple time scale methods in tokamak magnetohydrodynamics  

SciTech Connect

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

Jardin, S.C.

1984-01-01

153

Dynamic equations on time scales: a survey  

Microsoft Academic Search

The study of dynamic equations on time scales, which goes back to its founder Stefan Hilger (1988), is an area of mathematics that has recently received a lot of attention. It has been created in order to unify the study of differential and difference equations. In this paper we give an introduction to the time scales calculus. We also present

Ravi Agarwal; Martin Bohner; Donal O'Regan; Allan Peterson

2002-01-01

154

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

155

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

Microsoft Academic Search

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

M. Chahid; M. Benhamou

2000-01-01

156

Vibrational Relaxation Times of a Number of Polyatomic Gases Derived from Measurements of Acoustic Absorption  

Microsoft Academic Search

The authors have described in a previous paper a method for deriving the acoustic absorption coefficient of gases from measurements of the decay time of a cylindrical resonator containing the gas in question. This technique has been applied to determine the relaxational contribution to the absorption at frequencies well below the dispersion region for a number of gases. The information

P. D. Edmonds; J. Lamb

1958-01-01

157

Self?Organization of Amphiphilic Copolymers into Nanoparticles: Study by H NMR Longitudinal Relaxation Time  

Microsoft Academic Search

The aggregation and nanoparticle formation of a novel amphiphilic polymer 1 based on polyethylene glycol has been studied by H NMR longitudinal relaxation time (T1). The T1 of proton NMR, which may be associated with the mobility of molecular chains showed different trends when the amphiphilic polymer was dissolved in aqueous and organic solvents. It was observed that the T1

Rajesh Kumar; Virinder S. Parmar; Jayant Kumar; Lynne A. Samuelson; Arthur C. Watterson

2004-01-01

158

Application of continuous time random walks to dielectric relaxation with age-dependent transition rates  

Microsoft Academic Search

It is shown that the continuous time random walk (CTRW) method provides a simple and natural way of treating problems with age-dependent transition rates (ADTRs) that arise in many theories of non-exponential dielectric relaxation. In particular, ADTRs are especially suitable for analysing systems in which after any transition from one state to another there is initially an increased probability of

V. Halpern

1995-01-01

159

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

Microsoft Academic Search

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

Hany H. Sherief

1993-01-01

160

Relaxation-time approximations to the Boltzmann equation for electron transport in bulk silicon  

NASA Astrophysics Data System (ADS)

Relaxation-time approximations of the collisional operator of the Boltzmann transport equation are used for simulating carrier transport in silicon semiconductors. Solutions of these kinetic models are obtained through the use of exact-integral representations in the stationary and homogeneous regime. Some properties of these solutions have been discussed and their validity have been assessed by Monte Carlo simulations in bulk silicon.

Muscato, Orazio

2003-01-01

161

Analysis of a complex TSDC peak using single time relaxation peaks  

Microsoft Academic Search

In this paper the authors propose a method for the decomposition of an experimental TSDC curve into a sum of elementary peaks, every one being characterized by a single relaxation time and a unique activation energy. The model is used for analysis of the TSDC spectrum for polyethylene terephthalate

R. M. Neagu; C. Botez; E. R. Neagu

1999-01-01

162

Shock tube - New experimental results on the electron density and the relaxation time  

Microsoft Academic Search

The electron density and relaxation times in a shock tube were monitored for a shock wave propagating through xenon at a pressure of 200 Pa. Spectrophotometry and interferometry provided the electron density maxima as a function of the Mach number of the wave. The densities were less than predicted with the Rankine-Hugoniot relation. A comparison of the spectroscopic and interferometric

P. Maillot; S. Rasset; C. Thenard

1984-01-01

163

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

NASA Astrophysics Data System (ADS)

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

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

2008-11-01

164

Measurement of the spin-lattice relaxation time in the NQR of light nuclei  

SciTech Connect

This work proposed a method for increasing the signal/noise ratio in NQR by preliminary magnetization of the sample in a constant magnetic field B/sub 0/ and it subsequent adiabatic demagnetization. The proposed method for the measurement of spin-lattice relaxation times is verified experimentally with a number of compounds. The results agree well with published data.

Anferov, V.P.; Anferova, S.V.; Grechishkin, V.S.; Sinyavskii, N.Ya.

1988-01-01

165

Accelerated Relaxation of Sensitive Nuclei for Enhancement of Signal-to-Noise with Time  

NASA Astrophysics Data System (ADS)

A pulse sequence is proposed that accelerates the relaxation of sensitive nuclei through inverse polarization transfer from insensitive nuclei that have been subject to NOE during their detection: the sequence is designed to replace normal intersequence relaxation delays. Typically, for the observation of { 1H}- 13C, the 13C relaxes during data acquisition and is enhanced by NOE from decoupled 1H's. After data acquisition the 13C polarization can be transferred to 1H in order to step-jump accelerate the relaxation of 1H and hence provide 1H polarization more rapidly for transfer to 13C during the next repetition of polarization-transfer sequences. It is suggested that the sequence (SNARE) can advantageously replace the relaxation delays in many common sequences. The benefits of so doing are illustrated using PENDANT and DEPT for 13C investigations. Conditions for the implementation of SNARE are proposed, and it is demonstrated that there is a range of spectral-acquisition parameters of practical interest for which the method can be beneficial. Experimental time savings in achieving a chosen S/ Ntypically exceed 30%.

Homer, John; Perry, Michael C.; Palfreyman, Stuart A.

1997-03-01

166

Enhanced spin-relaxation time due to electron-electron scattering in semiconductor quantum wells  

NASA Astrophysics Data System (ADS)

We present a detailed experimental and theoretical analysis of the spin dynamics of two-dimensional electron gases (2DEGs) in a series of n -doped GaAs/AlxGa1-xAs quantum wells. Picosecond-resolution polarized pump-probe reflection techniques were applied in order to study in detail the temperature, concentration, and quantum-well-width dependencies of the spin relaxation rate of a small photoexcited electron population. A rapid enhancement of the spin lifetime with temperature up to a maximum near the Fermi temperature of the 2DEG was demonstrated experimentally. These observations are consistent with the D’yakonov-Perel’ spin-relaxation mechanism controlled by electron-electron collisions. The experimental results and theoretical predictions for the spin relaxation times are in good quantitative agreement.

Leyland, W. J. H.; John, G. H.; Harley, R. T.; Glazov, M. M.; Ivchenko, E. L.; Ritchie, D. A.; Farrer, I.; Shields, A. J.; Henini, M.

2007-04-01

167

? 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

168

Effect of finite relaxation time on modeling neutral transport in hydrogen plasma  

NASA Astrophysics Data System (ADS)

In low-temperature hydrogen plasma, the effect of neutral transport on the relative population of excited-level neutrals has been investigated. In particular, the validity of the quasi-steady-state approximation of collisional radiative model for a neutral transport simulation of detached divertor plasma is discussed. The relaxation times of the population density are compared with the residence time in detached plasma by solving the time-dependent zero-dimensional rate equations. It is shown that the relaxation times of the population density are comparable with the residence time (10-6-10-5 s) for vibrationally excited hydrogen molecules, which means that the transport of vibrationally excited molecules strongly affects the spatial distributions of their densities and reaction rates for ion conversion and dissociative attachment. The one-dimensional Monte Carlo calculation results support these transport effects. It is important to follow the traces of each vibrationally excited molecule separately.

Miyamoto, K.; Ishii, Y.; Hatayama, A.

2003-01-01

169

Influence of left ventricular relaxation on the pressure half time of aortic regurgitation  

PubMed Central

BACKGROUND—The severity of aortic regurgitation can be estimated using pressure half time (PHT) of the aortic regurgitation flow velocity, but the correlation between regurgitant fraction and PHT is weak.?AIM—To test the hypothesis that the association between PHT and regurgitant fraction is substantially influenced by left ventricular relaxation.?METHODS—In 63 patients with aortic regurgitation, subdivided into a group without (n = 22) and a group with (n = 41) left ventricular hypertrophy, regurgitant fraction was calculated using the difference between right and left ventricular cardiac outputs. Left ventricular relaxation was assessed using the early to late diastolic Doppler tissue velocity ratio of the mitral annulus (E/ADTI), the E/A ratio of mitral inflow (E/AM), and the E deceleration time (E-DT). Left ventricular hypertrophy was assessed using the M mode derived left ventricular mass index.?RESULTS—The overall correlation between regurgitant fraction and PHT was weak (r = 0.36, p < 0.005). In patients without left ventricular hypertrophy, there was a significant correlation between regurgitant fraction and PHT (r = 0.62, p < 0.005), but not in patients with left ventricular hypertrophy. In patients with a left ventricular relaxation abnormality (defined as E/ADTI< 1, E/AM< age corrected lower limit, E-DT ? 220 ms), no associations between regurgitant fraction and PHT were found, whereas in patients without left ventricular relaxation abnormalities, the regurgitant fraction to PHT relations were significant (normal E/AM: r = 0.57, p = 0.02; E-DT< 220 ms: r = 0.50, p < 0.001; E/ADTI < 1: r = 0.57, p = 0.02).?CONCLUSIONS—Only normal left ventricular relaxation allows a significant decay of PHT with increasing aortic regurgitation severity. In abnormal relaxation, which is usually present in left ventricular hypertrophy, wide variation in prolonged backward left ventricular filling may cause dissociation between the regurgitant fraction and PHT. Thus the PHT method should only be used in the absence of left ventricular relaxation abnormalities.???Keywords: aortic regurgitation; left ventricular relaxation; pressure half time

de Marchi, S F; Windecker, S; Aeschbacher, B; Seiler, C

1999-01-01

170

Analysing Forced Oscillators with Multiple Time Scales  

Microsoft Academic Search

We present a novel formulation, called the WaMPDE, for solving systems with forced autonomous components. An important feature of the WaMPDE is its ability to capture frequency modulation (FM) in a natural and compact man- ner. This is made possible by a key new concept: that of warped time, related to normal time through separate time scales. Using warped time,

Onuttom Narayan; Jaijeet S. Roychowdhury

1999-01-01

171

Metaphor for the geologic time scale  

NSDL National Science Digital Library

This assignment serves as an introduction to the geologic time scale and to help students visualize the long time intervals between major events in Earth's history. The assignment encourages students to choose a metaphor for geologic time, research major events throughout Earth' history, and calculate how much (cumulative) of their metaphor each time interval represents.

Thompson, Cara

172

A relaxation time study of molecular motion in trimethylolpropane triacrylate and trimethylolpropane trimethacrylate  

NASA Astrophysics Data System (ADS)

Proton NMR relaxation times, T1, T2, and T1?, have been measured as a function of temperature in trimethylolpropane triacryla (TMPTA) and trimethylolpropane trimethacrylate (TMPTMA). The results for TMPTA and TMPTMA are very similar. Low temperature T1 minima have been obtained due to methyl group reorientation, and high temperature T1 and T1? minima have been obtained due to whole-molecule reorientation. T2 decreases continuously from the T1 and T1? values at high temperat to rigid lattice values at low temperatures. Nearly all of the relaxation time measurements could be analyzed in terms of a Cole-Davidson (CD) distribution of correlation times. The whole-molecule reorientation was described in terms of a cutoff correlation time with a temperature-dependent activation energy. The CD distribution fails to accurately describe the measured T1? dispersion below the high temperature T1? minimum in TMPTMA.

Harrell, J. W.; Ahuja, S. J.

1989-11-01

173

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

NASA Astrophysics Data System (ADS)

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

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

2013-06-01

174

Finite-time relaxation of the solution of a nonlinear pseudoparabolic equation  

Microsoft Academic Search

A model equation is considered that describes the relaxation of an initial perturbation in a crystalline semiconductor in\\u000a the case when its electrical conductivity depends nonlocally on the field. For certain initial parameters, the effect of finite-time\\u000a “cooling” is proved to occur. For other parameters, the first term of the long-time asymptotics is found and the remainder\\u000a of the asymptotic

M. O. Korpusov; A. G. Sveshnikov

2011-01-01

175

Waveform relaxation synthesis of time-domain characteristic model of loaded microstrip from FDTD simulation  

Microsoft Academic Search

From the finite-difference time-domain (FDTD) simulation of response voltages and currents of a microstrip terminated by a step-pulse excitation voltage source and a resistor load, the time-domain characteristic model (TDCM) of the microstrip is synthesized by use of the waveform relaxation method, which is based on the iteration and deconvolution techniques. As an example, the extracted model is applied to

Qing-Xin Chu; Fung-Yuel Chang

1997-01-01

176

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

177

Breaking of Ergodicity and Long Relaxation Times in Systems with Long-Range Interactions  

Microsoft Academic Search

The thermodynamic and dynamical properties of an Ising model with both short-range and long-range, mean-field-like, interactions are studied within the microcanonical ensemble. It is found that the relaxation time of thermodynamically unstable states diverges logarithmically with system size. This is in contrast with the case of short-range interactions where this time is finite. Moreover, at sufficiently low energies, gaps in

D. Mukamel; S. Ruffo; N. Schreiber

2005-01-01

178

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

179

Application of scaling theory to vibrational relaxation in linear anharmonic triatomic molecules  

SciTech Connect

The energy-corrected-sudden (ECS) scaling theory is extended to vibrational relaxation in the collisions of anharmonic linear triatomic molecules with atoms. Application is made to the collisions of He atoms with /sup 12/C /sup 16/O/sub 2/, /sup 14/C /sup 16/O/sub 2/, and /sup 12/C /sup 18/O/sub 2/. By combining the rate constants for the (01/sup 1/0 ..-->.. 00/sup 0/0) transitions, calculated using the vibrational close-coupling rotational infinite-order-sudden (VCC-IOS) method, with the ECS scaling theory, we predict rate constants for the transitions (10/sup 0/0 ..-->.. 01/sup 1/0), (02/sup 2/0 ..-->.. 01/sup 1/0) and (02/sup 0/0 ..-->.. 01/sup 1/0). These agree very well with the rate constants computed directly using the VCC-IOS technique. This comparison presents a particularly severe test of the accuracy of the ECS scaling theory for anharmonic polyatomics since Fermi resonance effects are large for the 10/sup 0/0 and 02/sup 0/0 levels in CO/sub 2/.

Clary, D.C.; DePristo, A.E.

1983-09-01

180

Optimal configuration for relaxation times estimation in complex spin echo imaging.  

PubMed

Many pathologies can be identified by evaluating differences raised in the physical parameters of involved tissues. In a Magnetic Resonance Imaging (MRI) framework, spin-lattice T1 and spin-spin T2 relaxation time parameters play a major role in such an identification. In this manuscript, a theoretical study related to the evaluation of the achievable performances in the estimation of relaxation times in MRI is proposed. After a discussion about the considered acquisition model, an analysis on the ideal imaging acquisition parameters in the case of spin echo sequences, i.e., echo and repetition times, is conducted. In particular, the aim of the manuscript consists in providing an empirical rule for optimal imaging parameter identification with respect to the tissues under investigation. Theoretical results are validated on different datasets in order to show the effectiveness of the presented study and of the proposed methodology. PMID:24476682

Baselice, Fabio; Ferraioli, Giampaolo; Grassia, Alessandro; Pascazio, Vito

2014-01-01

181

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

NASA Astrophysics Data System (ADS)

Time-dependent isothermal dielectric measurements were carried out deeply in the glassy state on two very important saccharides: sucrose and trehalose. In both compounds two prominent secondary relaxation processes were identified. The faster one is an inherent feature of the whole family of carbohydrates. The slower one can also be detected in oligo- and polysaccharides. It was shown earlier that the ? process is the Johari-Goldstein (JG) relaxation coupled to motions of the glycosidic linkage, while the ? relaxation originates from motions of the exocyclic hydroxymethyl unit. Recently, it was shown that the JG relaxation process can be used to determine structural relaxation times in the glassy state [R. Casalini and C. M. Roland, Phys. Rev. Lett.PRLTAO0031-900710.1103/PhysRevLett.102.035701 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. SolidsJNCSBJ0022-309310.1016/j.jnoncrysol.2010.07.067 357, 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.; Kaminska, E.; Paluch, M.

2011-06-01

182

Surface NMR measurement of proton relaxation times in medium to coarse-grained sand aquifer.  

PubMed

A surface NMR investigation of groundwater in the geomagnetic field is under study. To detect the surface NMR a wire loop with a diameter of about 100 m, being an antenna for both an exciting field source and the NMR signal receiver, is laid out on the ground. A sinusoidal current pulse with a rectangular envelope is passed through the loop to excite the NMR signal. The carrier frequency of the oscillating current in this pulse is equal to the Larmor frequency of protons in the Earth's magnetic field. The current amplitude is changed up to 200 amps and the pulse duration is fixed and is equal to 40 ms. The exciting pulse is followed by an induction emf signal caused by the Larmor nuclear precession in geomagnetic field. The relaxation times T1, T2, and T2* were measured by the surface NMR for both groundwater in medium to coarse-grained sand at borehole and for bulk water under the ice surface of frozen lake. To determine T1, a longitudinal interference in experiments with repeated pulses was measured. A sequence with equal period between equal excitation pulses was used. The relaxation times T1, T2, measured for bulk water under the ice of the Ob reservoir were 1.0 s and 0.7 s, respectively. To estimate an influence of dissolved oxygen T1 of the same water at the same temperature was measured by lab NMR with and without pumping of oxygen. The relaxation time T1 measured for water in the medium to coarse-grained sand is 0.65 s. The relaxation time T2 estimated by spin echo sequence is found to be equal to 0.15 s. The relaxation time T2* is found to be about 80 ms. This result contradicts published earlier phenomenological correlation between relaxation time T2* and grain size of water-bearing rock. This could be as a result of unsound approach based on grain size or influence of paramagnetic impurities. PMID:8970122

Shushakov, O A

1996-01-01

183

A Morphological Time-Scale for Rivers.  

National Technical Information Service (NTIS)

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

M. Devries

1975-01-01

184

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

NASA Astrophysics Data System (ADS)

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

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

2004-09-01

185

Rate variation and estimation of divergence times using strict and relaxed clocks  

PubMed Central

Background Understanding causes of biological diversity may be greatly enhanced by knowledge of divergence times. Strict and relaxed clock models are used in Bayesian estimation of divergence times. We examined whether: i) strict clock models are generally more appropriate in shallow phylogenies where rate variation is expected to be low, ii) the likelihood ratio test of the clock (LRT) reliably informs which model is appropriate for dating divergence times. Strict and relaxed models were used to analyse sequences simulated under different levels of rate variation. Published shallow phylogenies (Black bass, Primate-sucking lice, Podarcis lizards, Gallotiinae lizards, and Caprinae mammals) were also analysed to determine natural levels of rate variation relative to the performance of the different models. Results Strict clock analyses performed well on data simulated under the independent rates model when the standard deviation of log rate on branches, ?, was low (?0.1), but were inappropriate when ?>0.1 (95% of rates fall within 0.0082-0.0121 subs/site/Ma when ? = 0.1, for a mean rate of 0.01). The independent rates relaxed clock model performed well at all levels of rate variation, although posterior intervals on times were significantly wider than for the strict clock. The strict clock is therefore superior when rate variation is low. The performance of a correlated rates relaxed clock model was similar to the strict clock. Increased numbers of independent loci led to slightly narrower posteriors under the relaxed clock while older root ages provided proportionately narrower posteriors. The LRT had low power for ? = 0.01-0.1, but high power for ? = 0.5-2.0. Posterior means of ?2 were useful for assessing rate variation in published datasets. Estimates of natural levels of rate variation ranged from 0.05-3.38 for different partitions. Differences in divergence times between relaxed and strict clock analyses were greater in two datasets with higher ?2 for one or more partitions, supporting the simulation results. Conclusions The strict clock can be superior for trees with shallow roots because of low levels of rate variation between branches. The LRT allows robust assessment of suitability of the clock model as does examination of posteriors on ?2.

2011-01-01

186

Effect of gadolinium-DTPA on the magnetic relaxation times of normal and infarcted myocardium. [Dogs  

SciTech Connect

Acute myocardial infarctions were produced in 11 dogs by ligation of the left anterior descending coronary artery. Twenty-four hours after ligation Gd-DTPA was injected intravenously, followed by cardiectomy either 90 seconds (3 dogs) or 5 minutes (5 dogs) later. The remaining 3 dogs had cardiectomy without injection of Gd-DTPA at 24 hours after coronary occlusion. The 3 dogs that did not receive Gd-DTPA had longer T1 and T2 relaxation times in infarcted myocardium than in normal myocardium. The T1 and T2 relaxation times of normal myocardium at 90 seconds postinjection of Gd-DTPA were significantly shorter than those of the normal myocardium of animals that did not receive Gd-DTPA. At five minutes postinjection, significantly greater T1 shortening was exhibited in the infarcted myocardium compared with adjacent normal myocardium in the dogs injected with Gd-DTPA. Thus, Gd-DTPA has differential and time-varying effects on relaxation times of normal and infarcted myocardium.

Wesbey, G.E.; Higgins, C.B.; McNamara, M.T.; Engelstad, B.L.; Lipton, M.J.; Sievers, R.; Ehman, R.L.; Lovin, J.; Brasch, R.C.

1984-10-01

187

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

PubMed

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

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

2014-05-28

188

Bulk viscosity and relaxation time of causal dissipative relativistic fluid dynamics  

NASA Astrophysics Data System (ADS)

The microscopic formulas of the bulk viscosity ? and the corresponding relaxation time ?? 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 ?? and ? are related as ??=?/[?{(1/3-cs2)(?+P)-2(?-3P)/9}], where ?, P, and cs are the energy density, pressure, and velocity of sound, respectively. The predicted ? and ?? 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, Xu-Guang; Kodama, Takeshi; Koide, Tomoi; Rischke, Dirk H.

2011-02-01

189

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

SciTech Connect

This report summarizes a three-year study of stresses arising in the oxide scale and underlying metal during high temperature oxidation and of scale cracking. In-situ XRD was developed to measure strains during oxidation over 1000{degrees}C on pure metals. Acoustic emission was used to observe scale fracture during isothermal oxidation and cooling, and statistical analysis was used to infer mechanical aspects of cracking. A microscratch technique was used to measure the fracture toughness of scale/metal interface. A theoretical model was evaluated for the development and relaxation of stresses in scale and metal substrate during oxidation.

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

1993-06-01

190

Spin-Lattice Relaxation-Time Measurements of Trivalent Iron in Single-Crystal Calcite  

Microsoft Academic Search

The spin-lattice relaxation time for the M=-12-->12 transition of trivalent iron in single-crystal calcite has been measured at X band by pulse recovery from 1.4 to 45 K and by spectral line broadening from 40 to 195 K. The resulting transition-probability data are well described by the sum of a direct-process term and a Raman-process term, the latter having a

S. A. Marshall; S. V. Nistor; R. A. Serway

1972-01-01

191

Oxygen-induced changes in longitudinal relaxation times in skeletal muscle  

Microsoft Academic Search

The objective was to measure the effect of 100% oxygen inhalation on T1 relaxation times in skeletal muscle. Healthy volunteers were scanned using three different MRI protocols while breathing medical air and 100% oxygen. Measurements of T1 were made from regions of interest (ROIs) within various skeletal muscle groups. Dynamic data of subjects breathing a sequence of air–oxygen–air allowed the

Deirdre M. McGrath; Josephine H. Naish; James P. B. O'Connor; Charles E. Hutchinson; John C. Waterton; Chris J. Taylor; Geoffrey J. M. Parker

2008-01-01

192

Simulation of Silicon Nanowire Transistors Using Boltzmann Transport Equation Under Relaxation Time Approximation  

Microsoft Academic Search

An efficient approach for the simulation of electronic transport in nanoscale transistors is presented based on the multi-subband Boltzmann transport equation under the relaxation time approximation, which takes into account the effects of quantum confinement and quasi-ballistic transport. This approach is applied to the study of electronic transport in circular gate-all-around silicon nanowire transistors. Comparison with the nonequilibrium Green's function

Seonghoon Jin; Ting-Wei Tang; Massimo V. Fischetti

2008-01-01

193

Nuclear spin-lattice relaxation times of metallic antimony at low temperatures  

Microsoft Academic Search

We have used pulsed Nuclear Quadrupole Resonance (NQR) techniques to measure the nuclear spin-lattice relaxation times in antimony at low temperatures. High quality echoes with strong signal\\/noise ratios were only observed for finely powdered samples of high purity (99.9999%). The samples were carefully annealed and diluted with fine silica to below the percolation limit to minimize RF heating. The powder

E. B. Genio; J. Xu; T. Lang; G. G. Ihas; N. S. Sullivan

1995-01-01

194

Time-dependent damage accumulation under stress relaxation testing of bovine trabecular bone  

Microsoft Academic Search

Time-dependent loading of trabecular bone consists of both cyclic and sustained static loads. Numerous studies have investigated the effects of fatigue and creep loading on the apparent and damage behavior of bone; however, microdamage formation in trabecular bone under stress relaxation tests has not been characterized. Bovine trabecular bone specimens (1.5–3 years old) were loaded in uniaxial compression to 0.9%

Srinidhi Nagaraja; Mario D. Ball; Robert E. Guldberg

2007-01-01

195

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

PubMed Central

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

Soroushian, Behrouz; Yang, Xinmai

2011-01-01

196

Relaxed clocks and inferences of heterogeneous patterns of nucleotide substitution and divergence time estimates across whales and dolphins (Mammalia: Cetacea).  

PubMed

Various nucleotide substitution models have been developed to accommodate among lineage rate heterogeneity, thereby relaxing the assumptions of the strict molecular clock. Recently developed "uncorrelated relaxed clock" and "random local clock" (RLC) models allow decoupling of nucleotide substitution rates between descendant lineages and are thus predicted to perform better in the presence of lineage-specific rate heterogeneity. However, it is uncertain how these models perform in the presence of punctuated shifts in substitution rate, especially between closely related clades. Using cetaceans (whales and dolphins) as a case study, we test the performance of these two substitution models in estimating both molecular rates and divergence times in the presence of substantial lineage-specific rate heterogeneity. Our RLC analyses of whole mitochondrial genome alignments find evidence for up to ten clade-specific nucleotide substitution rate shifts in cetaceans. We provide evidence that in the uncorrelated relaxed clock framework, a punctuated shift in the rate of molecular evolution within a subclade results in posterior rate estimates that are either misled or intermediate between the disparate rate classes present in baleen and toothed whales. Using simulations, we demonstrate abrupt changes in rate isolated to one or a few lineages in the phylogeny can mislead rate and age estimation, even when the node of interest is calibrated. We further demonstrate how increasing prior age uncertainty can bias rate and age estimates, even while the 95% highest posterior density around age estimates decreases; in other words, increased precision for an inaccurate estimate. We interpret the use of external calibrations in divergence time studies in light of these results, suggesting that rate shifts at deep time scales may mislead inferences of absolute molecular rates and ages. PMID:21926070

Dornburg, Alex; Brandley, Matthew C; McGowen, Michael R; Near, Thomas J

2012-02-01

197

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

198

Deducting the temperature dependence of the structural relaxation time in equilibrium far below the nominal Tg by aging the decoupled conductivity relaxation to equilibrium  

NASA Astrophysics Data System (ADS)

Using broadband dielectric spectroscopy we investigate the changes in the conductivity relaxation times ?? observed during the physical aging of the protic ionic conductor carvedilol dihydrogen phosphate (CP). Due to the large decoupling of ion diffusion from host molecule reorientation, the ion conductivity relaxation time ??(Tage,tage) can be directly measured at temperatures Tage below Tg for exceedingly long aging times tage till ??(Tage,tage) has reached the equilibrium value ?_? ^{eq} ( {T_{age} } ). The dependence of ??(Tage,tage) on tage is well described by the stretched exponential function, ?_? ( {T_{age},t_{age} } ) = Aexp[ { - ( {{t_{age} }/{?_{age ( {T_{age} } )}}} )^? } ] + ?_? ^{eq} ( {T_{age} } ), where ? is a constant and ?age(Tage) can be taken as the structural ?-relaxation time of the equilibrium liquid at T = Tage. The value of ?_? ^{eq} ( {T_{age} } ) obtained after 63 days long annealing of CP, deviates from the Vogel-Fulcher-Tammann-Hesse (VFTH?) dependence of ??(T) determined from data taken above Tg and extrapolated down to Tage. Concurrently, ?age(Tage) also deviates from the Vogel-Fulcher-Tammann-Hesse (VFTH?) dependence. The results help to answer the longstanding question of whether the VFTH dependence of ??(T) as well as the structural ?-relaxation time ??(T) holds or not in the equilibrium liquid state far below Tg.

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

2014-05-01

199

Deducting the temperature dependence of the structural relaxation time in equilibrium far below the nominal Tg by aging the decoupled conductivity relaxation to equilibrium.  

PubMed

Using broadband dielectric spectroscopy we investigate the changes in the conductivity relaxation times ?? observed during the physical aging of the protic ionic conductor carvedilol dihydrogen phosphate (CP). Due to the large decoupling of ion diffusion from host molecule reorientation, the ion conductivity relaxation time ??(Tage,tage) can be directly measured at temperatures Tage below Tg for exceedingly long aging times tage till ??(Tage,tage) has reached the equilibrium value [Formula: see text]. The dependence of ??(Tage,tage) on tage is well described by the stretched exponential function, [Formula: see text], where ? is a constant and ?age(Tage) can be taken as the structural ?-relaxation time of the equilibrium liquid at T = Tage. The value of [Formula: see text] obtained after 63 days long annealing of CP, deviates from the Vogel-Fulcher-Tammann-Hesse (VFTH?) dependence of ??(T) determined from data taken above Tg and extrapolated down to Tage. Concurrently, ?age(Tage) also deviates from the Vogel-Fulcher-Tammann-Hesse (VFTH?) dependence. The results help to answer the longstanding question of whether the VFTH dependence of ??(T) as well as the structural ?-relaxation time ??(T) holds or not in the equilibrium liquid state far below Tg. PMID:24811641

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

2014-05-01

200

Long term stability of atomic time scales  

NASA Astrophysics Data System (ADS)

International Atomic Time TAI gets its stability from some 400 atomic clocks worldwide that generate the free atomic scale EA L and its accuracy from a small number of primary frequency standards (PFS) which frequency measurements are used to steer the EAL frequency. Because TAI is computed in "real - time" (every month) and has operational constraints, it is not optimal and the BIPM computes in deferred time another time scale TT(BIPM), which is based on a weighted average of the evaluations of TAI frequency by the PFS. We show that a point has been reached where the stability of atomic time scales, the accuracy of primary frequency standards, and the capabilities of frequency transfer are approximately at a similar level, in the low 10 - 16 in relative frequency. The goal is now to reach and surpass 1x10 - 16 and the three fields are in various stages of advancement towards this aim. We review the stability and accuracy recently achieved by frequency standards, focusing on primary frequency standards on one hand, and on new secondary realizations e.g. based on optical transitions on the other hand. We study how these performances can translate to the performance of atomic time scales, and the possible implications of the availability of new high - accuracy frequency standards operating on a regular basis. Finally we show how time transfer is trying to keep up with the progresses of frequency standards. Time transfer is presently the limiting factor at short averaging time (e.g. 1 - 2 weeks) but it should not be limiting the long term stability of atomic time scales, which is the main need of many applications in astronomy.

Petit, Gérard; Arias, Elisa Felicitas

2012-08-01

201

Time scales of turbulent relative dispersion.  

PubMed

Tracers in a turbulent flow separate according to the celebrated t3/2 Richardson-Obukhov law, which is usually explained by a scale-dependent effective diffusivity. Here, supported by state-of-the-art numerics, we revisit this argument. The Lagrangian correlation time of velocity differences increases too quickly for validating this approach, but acceleration differences decorrelate on dissipative time scales. Phenomenological arguments are used to relate the behavior of separations to that of a "local energy dissipation," defined as the average ratio between the cube of the longitudinal velocity difference and the distance between the two tracers. This quantity is shown to stabilize on short time scales and this results in an asymptotic diffusion ?t1/2 of velocity differences. The time of convergence to this regime is shown to be that of deviations from Batchelor's initial ballistic regime, given by a scale-dependent energy dissipation time rather than the usual turnover time. It is finally demonstrated that the fluid flow intermittency should not affect this long-time behavior of the relative motion. PMID:23214642

Bitane, Rehab; Homann, Holger; Bec, Jérémie

2012-10-01

202

Length and Time Scales in Continental Drift  

NASA Astrophysics Data System (ADS)

Nonlinear feedback between continents and the mantle through thermal blanketing has long been surmised as a mechanism for continental drift and Wilson cycles. Paleomagnetism provides ample evidence for large scale (10,000 km) continental motion on time scales of several hundred million years, indicative of large scale mantle circulation. While much has been learned about the interactions between continents and mantle flow from analog and numerical modeling studies in two and three dimensions, a rigorous sensitivity study on the effects of continents in high resolution 3D spherical mantle convection models has yet to be pursued. As a result, a quantitative understanding of the scales of continental motion as they relate to relevant fluid dynamic processes is lacking. Here we focus on the effect of continental size. Continents covering 30% of the surface are representative of a supercontinent such as Pangea, smaller continents (10% of Earth's surface) are representative of present day Asia, and still smaller continents (3% of Earth's surface) are similar to present day Antarctica. These continents are introduced into simple end-member mantle flow regimes characterized by combinations of bottom or internal heating and uniform or layered mantle viscosity. We find that large scale mantle structure, and correspondingly the large scale displacement of continents, depends not only on mantle heating mode and radial viscosity structure, but also on continental size. Supercontinents promote heterogeneity on the largest scales (spherical harmonic degree one), especially when combined with strong bottom heating and a high viscosity lower mantle. Degree one heterogeneities in turn drive cyclical continental motion, with continents moving from the hot to the cold hemisphere on time scales of several hundred million years. Smaller continents are unable to initiate degree one convection. As a result, their motion is governed by shorter length and time scales. We apply these insights toward understanding the motion of several continents to study the aggregation and dispersal of continental groups.

Phillips, B. R.; Bunge, H.

2003-12-01

203

The Geologic Time Scale in Historical Perspective  

NSDL National Science Digital Library

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

204

Time-scale segmentation of respiratory sounds.  

PubMed

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

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

1998-06-01

205

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

206

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

PubMed

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

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

2012-06-15

207

Scaling physiological pharmacokinetic models by physiological time  

SciTech Connect

This paper shows that a multicompartment physiological pharmacokinetic model, used to account for inhalation exposure to volatile chlorohydrocarbons in mammalian species, can be made species-independent if chronological time is re-expressed in terms of physiological time. Physiological time is defined as chronological time divided by species body weight to the 1/4 power. We demonstrate the usefulness of this time scaling of the multicompartment physiological pharmacokinetic model by using it to model the inhalation of the volatile chlorinated hydrocarbon tetrachloroethylene in mice, rats, and humans. 8 refs., 2 figs.

Ward, R.C.; Travis, C.C.

1987-01-01

208

Time-resolved torsional relaxation of spider draglines by an optical technique.  

PubMed

The sensitivity of the torsional pendulum demonstrates the self-shape-memory effect in different types of spider draglines. Here we report the time-resolved noncovalent bonds recovery in the protein structure. The torsional dynamics of such multilevel structure governed by reversible interactions are described in the frame of a nested model. Measurement of three different relaxation times confirms the existence of three energy storage levels in such two protein spidroin systems. Torsion opens the way to further investigations towards unraveling the tiny torque effects in biological molecules. PMID:17501459

Emile, O; Le Floch, A; Vollrath, F

2007-04-20

209

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

NASA Astrophysics Data System (ADS)

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

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

2009-11-01

210

Mechanical relaxation and the notion of time-dependent extent of ergodicity during the glass transition.  

PubMed

A postulate that ergodicity and entropy continuously decrease to zero on cooling a liquid to a glassy state was used to support the view that glass has no residual entropy, and the features of mechanical relaxation spectra were cited as proof for the decrease. We investigate whether such spectra and the relaxation isochrones can serve as the proof. We find that an increase in the real component of elastic moduli with an increase in spectral frequency does not indicate continuous loss of ergodicity and entropy, and the spectra do not confirm isothermal glass transition or loss of entropy. Variation in ergodicity and entropy with the spectral frequency has untenable consequences for both thermodynamics and molecular dynamics and implies that, despite a broad distribution of its relaxation times, an equilibrium liquid can be considered as always ergodic. Perturbation from equilibrium used to obtain a spectrum does not have the effect of dynamic freezing and unfreezing, and Maxwell-Voigt models for the mechanical response function have neither the characteristic irreversibility of liquid-glass transition nor are commutable to ergodicity or entropy. PMID:21928991

Johari, G P

2011-08-01

211

Direct observation of strain relaxation in iron layers on W(110) by time-resolved STM  

NASA Astrophysics Data System (ADS)

Time-resolved, in-situ-applied STM has been used to study the epitaxial growth of iron on W(110) at room temperature. By this way, sequences of STM images show directly the atomistics of the growth process on the surface. The first layer of iron on W(110) grows pseudomorphically without a preferred growth direction. Beginning with the second layer, the islands grow anisotropically with preferred growth in the [001]-direction. The generation of an ordered two-dimensional dislocation network starts at a coverage of 1.4 pseudomorphic monolayers to relax the misfit of 9.4%. A direct correlation of the creation of misfit dislocations in the second layer and the nucleation of the third-layer islands was found. Together with the onset of strain relaxation, the growth mode abruptly changes from layer-by-layer to statistical growth. A quantitative statistical analysis of the data allows to exactly determine the onset of relaxation, the vertical location of the dislocation lines, and the lateral extension of an island that is necessary to induce the formation of dislocations.

Jensen, C.; Reshöft, K.; Köhler, U.

1996-03-01

212

Relationship between Structural and Stress Relaxation in a Block-Copolymer Melt  

NASA Astrophysics Data System (ADS)

The relationship between structural relaxation on molecular length scales and macroscopic stress relaxation was explored in a disordered block-copolymer melt. Experiments show that the structural relaxation time, measured by x-ray photon correlation spectroscopy is larger than the terminal stress relaxation time, measured by rheology, by factors as large as 100. We demonstrate that the structural relaxation data are dominated by the diffusion of intact micelles while the stress relaxation data are dominated by contributions due to disordered concentration fluctuations.

Patel, Amish J.; Narayanan, Suresh; Sandy, Alec; Mochrie, Simon G. J.; Garetz, Bruce A.; Watanabe, Hiroshi; Balsara, Nitash P.

2006-06-01

213

NMR relaxation times in the human brain at 3.0 tesla.  

PubMed

Relaxation time measurements at 3.0 T are reported for both gray and white matter in normal human brain. Measurements were made using a 3.0 T Bruker Biospec magnetic resonance imaging (MRI) scanner in normal adults with no clinical evidence of neurological disease. Nineteen subjects, 8 female and 11 male, were studied for T1 and T2 measurements, and 7 males were studied for T2. Measurements were made using a saturation recovery method for T1, a multiple spin-echo experiment for T2, and a fast low-angle shot (FLASH) sequence with 14 different echo times for T2. Results of the measurements are summarized as follows. Average T1 values measured for gray matter and white matter were 1331 and 832 msec, respectively. Average T2 values measured for gray matter and white matter were 80 and 110 msec, respectively. The average T2 values for occipital and frontal gray matter were 41.6 and 51.8 msec, respectively. Average T2 values for occipital and frontal white matter were 48.4 and 44.7 msec, respectively. ANOVA tests of the measurements revealed that for both gray and white matter there were no significant differences in T1 from one location in the brain to another. T2 in occipital gray matter was significantly higher (0.0001 < P < .0375) than the rest of the gray matter, while T2 in frontal white matter was significantly lower (P < 0.0001). Statistical analysis of cerebral hemispheric differences in relaxation time measurements showed no significant differences in T1 values from the left hemisphere compared with the right, except in insular gray matter, where this difference was significant at P = 0.0320. No significant difference in T2 values existed between the left and right cerebral hemispheres. Significant differences were apparent between male and female relaxation time measurements in brain. PMID:10232510

Wansapura, J P; Holland, S K; Dunn, R S; Ball, W S

1999-04-01

214

Time-domain ab initio study of charge relaxation and recombination in dye-sensitized TiO2.  

PubMed

In order to investigate the electron dynamics at the alizarin/I2-/TiO2 interface this study uses a novel state-of-the-art quantum-classical approach that combines time-dependent density functional theory with surface hopping in the Kohn-Sham basis. Representing the dye-sensitized semiconductor Grätzel cell with the I-/I3- mediator, the system addresses the problems of an organic/inorganic, molecule/bulk interface that are commonly encountered in molecular electronics, photovoltaics, and photoelectrochemistry. The processes studied include the relaxation of the injected electron inside the TiO2 conduction band (CB), the back electron transfer (ET) from TiO2 to alizarin, the ET from the surface to the electrolyte, and the regeneration of the neutral chromophore by ET from the electrolyte to alizarin. Developing a theoretical understanding of these processes is crucial for improving solar cell design and optimizing photovoltaic current and voltage. The simulations carried out for the entire system that contains many electronic states reproduce the experimental time scales and provide detailed insights into the ET dynamics. In particular, they demonstrate the differences between the optimized geometric and electronic structure of the system at 0 K and the experimentally relevant structure at ambient temperature. The relaxation of the injected electron inside the TiO2 CB, which affects the solar cell voltage, is shown to occur on a 100 fs time scale and occurs simultaneously with the electron delocalization into the semiconductor bulk. The transfer of the electron trapped at the surface to the ground state of alizarin proceeds on a 1 ps time scale and is facilitated by vibrational modes localized on alizarin. If the electrolyte mediator is capable of approaching the semiconductor surface, it can form a stable complex and short-circuit the cell by accepting the photoexcited electron on a subpicosecond time scale. The ET from TiO2 to both alizarin and the electrolyte diminishes the solar cell current. Finally, the simulations show that the electrolyte can efficiently regenerate the neutral chromophore. This is true even though the two species do not form a chemical bond and, therefore, the electronic coupling between them is weaker than in the TiO2-chromophore and TiO2-electrolyte donor-acceptor pairs. The chromophore-electrolyte coupling can occur both directly through space and indirectly through bonding to the semiconductor surface. The ET events involving the electrolyte are promoted primarily by the electrolyte vibrational modes. PMID:17579405

Duncan, Walter R; Craig, Colleen F; Prezhdo, Oleg V

2007-07-11

215

Time-scaling in irreversible thermodynamics  

Microsoft Academic Search

We consider linear dynamical systems with motions characterized by two different time-scales. In practice the dynamical matrix in the phenomenological equations of motion often exhibits a strong coupling of the slow and fast variables. It is shown on the basis of the Onsager symmetry relations that a simple transformation of variables leads to a weak coupling. After the transformation one

U. Geigenmüller; B. U. Felderhof; U. M. Titulaer

1983-01-01

216

ISOTOPIC DATING AND THE GEOLOGIC TIME SCALE  

Microsoft Academic Search

The intensive research on isotopic methods of age determination at a ; number of laboratories has produced new methods, advances in experimental ; techniques, and many additional measurements. These developments are reviewed ; with particular reference to the effect of the new age determinations on the ; geologic time scale. The age of the planet now appears to be about

Kulp

1955-01-01

217

Water mobility in poly(ethylene glycol)-, poly(vinylpyrrolidone)-, and gelatin-water systems, as indicated by dielectric relaxation time, spin-lattice relaxation time, and water activity.  

PubMed

The mobility of water molecules present in poly(ethylene glycol) (PEG)-, poly(vinylpyrrolidone) (PVP)-, and gelatin-water systems was determined by dielectric relaxation and 17O NMR spectroscopy. Water activity was also measured. Dielectric relaxation spectra indicate that all the polymer systems studied contained water exhibiting a dispersion at a frequency > 10(9) Hz; in other words, water with high mobility close to that of bulk water. The dielectric relaxation time of the highly mobile water increased as polymer concentration increased. The PVP- and gelatin-water systems also contained water exhibiting a dispersion at a frequency < 10(9) Hz, which can be considered to be "bound water" with a restricted mobility because of its association with polymer molecules. Dielectric relaxation spectroscopy was used to determine water mobility separately for the populations of highly mobile water and bound water, whereas NMR relaxation spectroscopy was used to determine the average mobility of both populations. The spin-lattice relaxation time of water in these polymer-water systems showed a deviation from the isotropic two-state model. Dielectric relaxation data indicate that this deviation can be ascribed to variations in the relaxation time of highly mobile water caused by a change in polymer concentration. The dielectric relaxation time of highly mobile water in the gelatin system did not change with a change in polymer concentration to the extent that it did in the PEG and PVP systems. This result is consistent with a slight change in water activity of the gelatin system with increasing polymer concentration.(ABSTRACT TRUNCATED AT 250 WORDS) PMID:8537884

Yoshioka, S; Aso, Y; Otsuka, T; Kojima, S

1995-09-01

218

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

NASA Astrophysics Data System (ADS)

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

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

2013-02-01

219

Postmortem MRI of human brain hemispheres: T2 relaxation times during formaldehyde fixation.  

PubMed

Unlike in vivo imaging, postmortem MRI allows for invasive examination of the tissue specimen immediately after the MR scan. However, natural tissue decomposition and chemical fixation cause the postmortem tissue's MRI properties to be different from those found in vivo. Moreover, these properties change as postmortem fixation time elapses. The goal of this study was to characterize the T(2) relaxation changes that occur over time in cadaveric human brain hemispheres during fixation. Five hemispheres immersed in formaldehyde solution were scanned on a weekly basis for 3 months postmortem, and once again at 6 months postmortem. The T(2) relaxation times were measured throughout the hemispheres. Over time, T(2) values near the edges of the hemispheres decreased rapidly after death, while T(2) values of deep tissue decreased more slowly. This difference is likely due to the relatively large distance from the hemisphere surface, and other barriers limiting diffusion of formaldehyde molecules to deep tissues. In addition, T(2) values in deep tissue did not continuously decay to a plateau, but instead reached a minimum and then increased to a plateau. This final increase may be due to the effects of prolonged tissue decomposition, a hypothesis that is supported by numerical simulations of the fixation process. PMID:19189294

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

2009-04-01

220

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

PubMed Central

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

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

2009-01-01

221

Sodium relaxation times in the knee joint in vivo at 7T.  

PubMed

The sodium concentration correlates directly with the concentration of proteoglycans (PG) in cartilage, the loss of which is an early signature of osteoarthritis (OA). As a result, quantitative sodium MRI is a promising technique for assessing the degradation of articular cartilage in patients with OA. Sodium relaxation times can also provide information on the degradation of cartilage: it has already been shown on bovine cartilage that T(1) and T2long are longer and T2short shorter when the PG concentration decreases. In this study, sodium T(1), T2*short and T2*long relaxation maps were measured in vivo at 7 T on 8 healthy volunteers and in 4 different regions of the cartilage in the knee joint. The patellar, femoro-tibial medial, lateral, and femoral condyle cartilage have an average T(1)~20 ms, but different T2*short (from 0.5 ms to 1.4 ms) and T2*long (from 11.4 ms to 14.8 ms). Statistically significant differences in T(1), T2*short and T2*long were observed between the different regions in cartilage (p < 10(- 5)). Statistical differences in T(1) were also observed between male and female data (p < 10(- 5)). These relaxation times measurements can further be applied as correction factors for sodium concentration maps in vivo and can also be useful as complementary information to quantitative sodium MRI in the quest for detecting early OA. These measurements were done on low resolution sodium images in order to acquire sufficient quality data for fitting (5 images for T(1) and 9 images for T2*) while keeping the total time of acquisition of the data reasonable for the volunteer's comfort (1 h 15 min). PMID:21853493

Madelin, Guillaume; Jerschow, Alexej; Regatte, Ravinder R

2012-04-01

222

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

223

Enthalpy space analysis of the evolution of the primary relaxation time in ultraslowing systems  

NASA Astrophysics Data System (ADS)

For decades the Vogel-Fulcher-Tammann equation has dominated the description of dynamics of the non-Arrhenius behavior in glass forming systems. Recently, this dominance has been questioned. Hecksher et al. [Nat. Phys. 4, 737 (2008)], Elmatad et al. [J. Phys. Chem. B 113, 5563 (2009)], and Mauro et al. [Proc. Natl. Acad. Sci. U.S.A. 106, 19780 (2009)] indicated superiority of several equations showing no divergence at a finite (nonzero) temperature. This paper shows distortion-sensitive and derivative based empirical analysis of the validity of leading equations for portraying the previtreous evolution of primary relaxation time.

Martinez Garcia, J. C.; Tamarit, J. Ll.; Rzoska, S. J.

2011-01-01

224

Predicting How Nanoconfinement Changes the Relaxation Time of a Supercooled Liquid  

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

225

Quantitative validation of the Boltzmann transport equation phonon thermal conductivity model under the single-mode relaxation time approximation  

Microsoft Academic Search

The phonon thermal conductivity of the Lennard-Jones argon face-centered cubic crystal is predicted between temperatures of 20 K and 80 K using the Boltzmann transport equation under the single-mode relaxation time approximation. The temperature and frequency dependencies of the phonon dispersion and phonon relaxation times are obtained from lattice-dynamics calculations based on the results of molecular-dynamics simulations. No fitting parameters

A. J. McGaughey; M. Kaviany

2004-01-01

226

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.

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.; Renne, Thomas; Premaratne, Sobath; Wiethoff, Andrea J.; Botnar, Rene M.; Schaeffter, Tobias; Waltham, Matthew; Smith, Alberto

2014-01-01

227

Relaxation and dissipation in time-dependent current-density functional theory  

NASA Astrophysics Data System (ADS)

In a typical relaxation problem a many-particle system evolves from an initial excited state under the action of its own hamiltonian plus a ``thermal bath", until equilibrium (or the ground-state at T=0) is reached. Due to the presence of the thermal bath the time evolution of the system is not unitary, and an initially pure state will evolve into a statistical mixture of states. Here we show that the time-dependent current density functional theory^1 allows a hamiltonian description of the relaxation process, whereby the quantum state of the system undergoes a unitary time evolution without becoming entangled with a thermal bath. The essential feature that causes the system to eventually settle into a stationary state of the ground-state Kohn-Sham hamiltonian is the presence of an effective electric field, which is determined by the instantaneous values of the current and the density. Our theory is consistent with recent numerical results by Wijewardane and Ullrich^ 2.1. G. Vignale, C. A. Ullrich, and S. Conti, PRL 79, 4878 (1997)2. H. O. Wijewardane and C. A. Ullrich, cond-mat/0411157

D'Agosta, Roberto

2005-03-01

228

Long component time constant of 23Na T*2 relaxation in healthy human brain.  

PubMed

Signal intensity in 23Na images is altered in pathologic conditions such as ischemia and may provide information regarding tissue viability complementary to MR diffusion and perfusion imaging. However, the multicomponent transverse relaxation of 23Na (spin 3/2) complicates the determination of tissue sodium concentration from 23Na images with nonzero echo-time. The purpose of this study was to measure the long component time constant of tissue sodium T*2 relaxation in the healthy human brain at 4 T. Multiecho gradient-echo 23Na images (10 echo-times ranging from 3.8-68.7 ms) were acquired in five healthy human volunteers. T*2 was quantified on a pixel-by-pixel basis using a nonnegative least squares fitting routine using 100 equally spaced bins between 0.5-99.5 ms and parametric maps were produced representing components between 0.5-3, 3.1-50, 50.1-98, and 98.1-99.5 ms. The long T*2 component of tissue sodium (average +/- standard deviation) varied between cortex (occipital = 22.0 +/- 2.4 ms), white matter (parietal = 18.2 +/- 1.9 ms), and subcortical gray matter (thalamus = 16.9 +/- 2.4 ms). These results demonstrate considerable regional variability and establish a foundation for future characterization of 23Na T*2 in conditions such as cerebral ischemia and cancer. PMID:15282825

Bartha, Robert; Menon, Ravi S

2004-08-01

229

Accuracy metrics for judging time scale algorithms  

NASA Technical Reports Server (NTRS)

Time scales have been constructed in different ways to meet the many demands placed upon them for time accuracy, frequency accuracy, long-term stability, and robustness. Usually, no single time scale is optimum for all purposes. In the context of the impending availability of high-accuracy intermittently-operated cesium fountains, we reconsider the question of evaluating the accuracy of time scales which use an algorithm to span interruptions of the primary standard. We consider a broad class of calibration algorithms that can be evaluated and compared quantitatively for their accuracy in the presence of frequency drift and a full noise model (a mixture of white PM, flicker PM, white FM, flicker FM, and random walk FM noise). We present the analytic techniques for computing the standard uncertainty for the full noise model and this class of calibration algorithms. The simplest algorithm is evaluated to find the average-frequency uncertainty arising from the noise of the cesium fountain's local oscillator and from the noise of a hydrogen maser transfer-standard. This algorithm and known noise sources are shown to permit interlaboratory frequency transfer with a standard uncertainty of less than 10(exp -15) for periods of 30-100 days.

Douglas, R. J.; Boulanger, J.-S.; Jacques, C.

1994-01-01

230

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

231

Relating Measurements of Decaying Postseismic Surface Deformation to Viscoelastic Relaxation: This is no Time for Elsasser Time  

NASA Astrophysics Data System (ADS)

Techniques for measuring displacements of the Earth's surface have recently advanced to the point where the time-dependence of postseismic deformation (as well as its spatial patterns) can be characterized for large earthquakes. Given the availability of such data (and the promise of increasingly detailed measurements from future earthquakes), describing differences in early postseismic deformation from different rheological profiles of the lithosphere is no longer just a theoretical exercise. If postseismic deformation is due to stress relaxation in a viscoelastic crust or upper mantle layer below an effectively elastic upper crust of known thickness, the viscoelastic layer thickness and viscosity (? ) may be determined independently using temporally detailed displacement observations (i.e., continuous GPS) from one or more locations. A related strategy of modeling postseismic displacements over a single time interval at several measurement points is currently used to estimate these parameters independently (e.g. Pollitz, 2001). For models of an earthquake in an elastic layer of known thickness overlying a viscoelastic halfspace, ? /G (Maxwell time, or Tm) is the rate-controlling parameter. In a given location relative to the fault, displacements produced by models with various Maxwell times may all be represented with one curve, provided displacement is plotted against time/Tm. The time-depence of postseismic surface deformation even for this simple model is complicated, but the same complicated response occurs for models with identical Maxwell times. This is not so for earthquake models incorporating viscoelastic layers, however: thicker viscoelastic layers yield faster postseismic velocities early in the earthquake cycle than thinner layers with the same Maxwell time (e.g. Pollitz, 1997; Cohen, 1984). Elsasser time (proportional to ? /w, where w is viscoelastic layer thickness) is often posited as a reasonable rate-governing parameter for layered viscoelastic models because it has been proven to control time-dependent evolution of surface displacements in some cases (e.g., screw dislocation models for geometries in which variation of horizontal shear stress in the relaxing layer may be ignored, Rice, 1980). For near-field postseismic deformation following strike-slip earthquakes, however, thin viscoelastic layers yield faster postseismic velocities early in the earthquake cycle than thicker layers with the same Elsasser time (the opposite holds in some far-field locations). This means that for models with the same elastic plate thickness, ? and w may be independently identified (theoretically) by modeling time-dependent surface displacement data from a single point. Such monitoring sites must be chosen carefully. If the observation point is adjacent to the rupture, relaxing layers with identical Maxwell times tend to produce similar time-dependent displacements. These data can provide an estimate of viscosity but not layer thickness. Models with the same Elsasser time can yield similar, time-dependent displacements in the far-field; data from these locations can constrain only ? /w. I will present some descriptions of how ideal monitoring locations depend on model geometry, and will address how well displacement data from various locations relative to an earthquake rupture can bracket the width and viscosity of a relaxing layer. I will also show that for a range of reasonable lithosphere viscosity profiles, detailed displacement data from most locations between a few kilometers and 1-2 rupture lengths from the fault can contribute toward independent estimates of ? and w.

Hearn, E. H.

2001-12-01

232

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

PubMed

Relaxation rates in NMR are usually measured by intensity modulation as a function of a relaxation delay during which the relaxation mechanism of interest is effective. Other mechanisms are often suppressed during the relaxation delay by pulse sequences which eliminate their effects, or cancel their effects when two data sets with appropriate combinations of relaxation rate effects are added. Cross-correlated relaxation (CCR) involving dipole-dipole and CSA interactions differ from auto-correlated relaxation (ACR) in that the signs of contributions can be changed by inverting the state of one spin involved in the dipole-dipole interaction. This property has been exploited previously using CPMG sequences to refocus CCR while ACR evolves. Here we report a new pulse scheme that instead eliminates intensity modulation by ACR and thus allows direct measurement of CCR. The sequence uses a constant time relaxation period for which the contribution of ACR does not change. An inversion pulse is applied at various points in the sequence to effect a decay that depends on CCR only. A 2-D experiment is also described in which chemical shift evolution in the indirect dimension can share the same constant period. This improves sensitivity by avoiding the addition of a separate indirect dimension acquisition time. We illustrate the measurement of residue specific CCR rates on the non-myristoylated yeast ARF1 protein and compare the results to those obtained following the conventional method of measuring the decay rates of the slow and fast-relaxing (15)N doublets. The performances of the two methods are also quantitatively evaluated by simulation. The analysis shows that the shared constant-time CCR (SCT-CCR) method significantly improves sensitivity. PMID:18406649

Liu, Yizhou; Prestegard, James H

2008-07-01

233

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

NASA Astrophysics Data System (ADS)

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

Liu, Yizhou; Prestegard, James H.

2008-07-01

234

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

235

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

236

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

237

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

238

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

PubMed

A new equation describing the behavior of the structural relaxation time, tau(T,P), as a function of both pressure and temperature, is discussed. This equation has been derived from the Adam-Gibbs theory by writing the configurational entropy, S(c), in terms of the excess thermal heat capacity and of the molar thermal expansion. Consequently, the parameters introduced in the expression are directly related to specific physical properties of the material, such as the thermal expansion coefficient alpha and the isothermal bulk modulus K0. At a fixed pressure, for low pressures, the found equation reduces to a Vogel-Fulcher-Tammann equation of tau versus temperature with the fragility parameter independent from pressure. The equation for tau(T,P) was successfully tested directly by fitting the dielectric relaxation time data for two isothermal and one isobaric measurements on diglycidyl ether of bisphenol-A, carried out in previous experiments. The parameters estimated by the best fit were in reasonable agreement with the values determined from the known physical properties of the material. Finally, the expression for the change versus pressure of the temperatures at which the same value of tau(max) is obtained (e.g., the change versus pressure of the glass transition temperature) agrees with several expressions previously proposed in the literature to provide a phenomenological description of the observed phenomena. PMID:11308642

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

2001-03-01

239

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

NASA Astrophysics Data System (ADS)

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

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

2001-03-01

240

The relationship between radiation-induced chemical processes and transverse relaxation times in polymer gel dosimeters.  

PubMed

The effects of ionizing radiation in different compositions of polymer gel dosimeters are investigated using FT-Raman spectroscopy and NMR T2 relaxation times. The dosimeters are manufactured from different concentrations of comonomers (acrylamide and N,N'-methylene-bis-acrylamide) dispersed in different concentrations of an aqueous gelatin matrix. Results are analysed using a model of fast exchange of magnetization between three proton pools. The fraction of protons in each pool is determined using the known chemical composition of the dosimeter and FT-Raman spectroscopy. Based on these results, the physical and chemical processes in interplay in the dosimeters are examined in view of their effect on the changes in T2. The precipitation of growing macroradicals and the scavenging of free radicals by gelatin are used to explain the rate of polymerization. The model describes the changes in T2 as a function of the absorbed dose up to 50 Gy for the different compositions. This is expected to aid the theoretical design of new, more efficient dosimeters, since it was demonstrated that the optimum dosimeter (i.e, with the lowest dose resolution) must have a range of relaxation times which match the range of T2 values which can be determined with the lowest uncertainty using an MRI scanner. PMID:11324951

Lepage, M; Whittaker, A K; Rintoul, L; Bäck, S A; Baldock, C

2001-04-01

241

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

SciTech Connect

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

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

2012-07-01

242

Relative Geologic Time and the Geologic Time Scale  

NSDL National Science Digital Library

Students are given a short introduction to fossils, strata, Steno's law of superposition, and the development of the geologic time scale from initial description of systems, through the realization that fossils could be used to correlate between systems, to the assembly of the modern geologic time scale. Then, each student in the course is given a sheet of paper with a simple stratigraphic column and associated fossils representing a geologic system on one side and a short description of the location and history of discovery of the system on the other. On a large wall, students then assemble four geologic columns from their systems representing mainland Europe, Great Britain, the Eastern U.S. and the Western U.S. using the fossils illustrated on their sheets to correlate systems. The instructor guides this process by placing the first system on the wall and by providing some narration as the columns take shape. Europe and Great Britain are assembled first, one sheet at a time, providing when completed the framework of the modern geologic time scale. Once this is up on the wall, the remaining students can assemble the other two columns in minutes using fossils to correlate between American and European systems. A temporal gap in the Grand Canyon sequence provides an opportunity to discuss the incompleteness of the rock record in any one place and a system composed of igneous and metamorphic rocks with no fossils is used to point out the difference between radiometric (absolute) and biostratigraphic (relative) dating.

Bennington, Bret

243

Thermally induced vibrations of piezo-thermo-viscoelastic composite beam with relaxation times and system response  

Microsoft Academic Search

Purpose – The purpose of this paper is to present numerical studies on thermally induced vibrations of piezo-thermo-viscoelastic composite beam subjected to a transient thermal load using coupled finite element method. Design\\/methodology\\/approach – The thermal relaxation and viscoelastic relaxations are taken into consideration to obtain the system response. The concept of “memory load” along with the thermal relaxation is accounted

Sharnappa; N. Ganesan; Raju Sethuraman

2010-01-01

244

Towards a quaternary time scale*1  

NASA Astrophysics Data System (ADS)

Nine first-appearance datums (FADs), twenty-three last-appearance datums (LADs), and three other micropaleontological datums are related to the magnetic-reversal, oxygen-isotope, and calcite-dissolution/coarse-fraction time scales to provide a preliminary basis for subdivision of the Quaternary in deep-sea sediments. The magnetic-reversal, oxygen-isotope, and calcite-dissolution/coarse-fraction scales have been correlated by determination on the same core materials, and absolute dates applied by {40K}/{40Ar} or 14C dating of materials in known positions on one or another of these scales. FADS and LADs have been determined in cores for which either a magnetic-reversal, oxygen-isotope, or calcite-dissolution/coarse-fraction scale has also been available. Altogether 3 FADs and 5 LADs based on diatoms, 4 FADs and 5 LADs based on calcareous nannoplankton, 1 FAD and 8 LADs based on radiolarians, 1 FAD and 5 LADs based on planktonic foraminifers, 2 acme datums, and 1 ratio reversal datum have been determined, and absolute dates inferred by interpolation from known dates on the reference time scales. Some of the FADs and LADs apply or are synchronous only over limited areas of the oceans; others appear to be synchronous throughout the oceans. The base of the Quaternary is set at the top of the Olduvai event at 1.7 my. Four FADs, twelve LADs, two acme datums, and one ratio reversal datum occur above the base of the Quaternary at an average rate of about 1 per 100,000 yr. Five FADs and twelve LADs are recognized in the 0.8-my interval between the top of the Olduvai event and the Gauss/Matuyama Boundary at 2.5 my at an average incidence of about 1 per 50,000 yr.

Berggren, W. A.; Burckle, L. H.; Cita, M. B.; Cooke, H. B. S.; Funnell, B. M.; Gartner, S.; Hays, J. D.; Kennett, J. P.; Opdyke, N. D.; Pastouret, L.; Shackleton, N. J.; Takayanagi, Y.

1980-05-01

245

South Atlantic Spreading Velocities and Time Scales  

NASA Astrophysics Data System (ADS)

Plate reconstructions based on hierarchical spherical rotations have been around for many years. For the breakup of Pangea and Gondwana, these reconstructions are based on two major sources: magnetic isochrons and geological evidence for the onset of rifting and the tightness of the fit between continents. These reconstructions imply spreading velocities and it is the changes in velocities that can be used to probe questions of the forces moving plates around. In order to calculate the velocities correctly though, the importance of the choice of geologic time scale is often ignored. In this talk, we focus on the South Atlantic and calculate the spreading velocity errors implied by the choice of time scale for three major epochs: the Cenozoic and Late Mesozoic, the Cretaceous Quiet Zone and the Late Cretaceous to the Early Jurassic. In addition, we report the spreading velocities implied through these phases by various available magnetic isochron-derived reconstructions and the geological fits for South America and Africa used by large scale global reconstruction as well as in recent papers. Finally, we will highlight the implications for the choice of the mantle reference frame on African plate velocities.

Clark, S. R.; Smethurst, M. A.; Bianchi, M. C.

2013-12-01

246

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

SciTech Connect

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

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

2008-01-15

247

Temperature dependence of the structural relaxation time in equilibrium below the nominal T(g): results from freestanding polymer films.  

PubMed

When the thickness is reduced to nanometer scale, freestanding high molecular weight polymer thin films undergo large reduction of degree of cooperativity and coupling parameter n in the Coupling Model (CM). The finite-size effect together with the surfaces with high mobility make the ?-relaxation time of the polymer in nanoconfinement, ?(?)(nano)(T), much shorter than ?(?)(bulk)(T) in the bulk. The consequence is avoidance of vitrification at and below the bulk glass transition temperature, T(g)(bulk), on cooling, and the freestanding polymer thin film remains at thermodynamic equilibrium at temperatures below T(g)(bulk). Molecular dynamics simulations have shown that the specific volume of the freestanding film is the same as the bulk glass-former at equilibrium at the same temperatures. Extreme nanoconfinement renders total or almost total removal of cooperativity of the ?-relaxation, and ?(?)(nano)(T) becomes the same or almost the same as the JG ?-relaxation time ?(?)(bulk)(T) of the bulk glass-former at equilibrium and at temperatures below T(g)(bulk). Taking advantage of being able to obtain ?(?)(bulk)(T) at equilibrium density below T(g)(bulk) by extreme nanoconfinement of the freestanding films, and using the CM relation between ?(?)(bulk)(T) and ?(?)(bulk)(T), we conclude that the Vogel-Fulcher-Tammann-Hesse (VFTH) dependence of ?(?)(bulk)(T) cannot hold for glass-formers in equilibrium at temperatures significantly below T(g)(bulk). In addition, ?(?)(bulk)(T) does not diverge at the Vogel temperature, T?, as suggested by the VFTH-dependence and predicted by some theories of glass transition. Instead, ?(?)(bulk)(T) of the glass-former at equilibrium has a much weaker temperature dependence than the VFTH-dependence at temperature below T(g)(bulk) and even below T?. This conclusion from our analysis is consistent with the temperature dependence of ?(?)(bulk)(T) found experimentally in polymers aged long enough time to attain the equilibrium state at various temperatures below T(g)(bulk). PMID:24798795

Ngai, K L; Capaccioli, Simone; Paluch, Marian; Prevosto, Daniele

2014-05-22

248

Time constants in thermal laser medicine: II. Distributions of time constants and thermal relaxation of tissue  

Microsoft Academic Search

The thermal response of a semi-infinite medium in air, irradiated by laser light in a cylindrical geometry, cannot accurately be approximated by single radial and axial time constants for heat conduction. This report presents an analytical analysis of heat conduction where the thermal response is expressed in terms of distributions over radial and axial time constants. The source term for

Martin J. C. van Gemert; Gerald W. Lucassen; A. J. Welch

1996-01-01

249

A perspective on time: Loss frequencies, time scales, and lifetimes  

NASA Astrophysics Data System (ADS)

The need to describe the Earth system and its components with a quantity that has units of time is ubiquitous since the 1970s work of Bolin, Rodhe and Junge. These quantities are often used as metrics of the system to describe the duration or cumulative impact of an action, such as in global-warming and ozone-depletion potentials, as in the SPARC lifetime re-assessment. The quantity designated "lifetime" is often calculated inconsistently and/or misused when applied to the subsequent evaluations of impacts. A careful set of definitions and derivations is needed to ensure that we are reporting, publishing, and comparing the same quantities. There are many different ways to derive metrics of time, and they describe different properties of the system. Here we carefully define several of those metrics - denoted here as loss frequency, time scale, and lifetime - and demonstrate which properties of the system they describe. Three generalizable examples demonstrate (i) how the non-linear chemistry of tropospheric ozone makes simple approaches for tracking pollution in error; (ii) why the lifetime of a gas depends on the history of emissions, and (iii) when multiple reservoirs generate time scales quite separate from the traditionally defined lifetime. Proper use of the many "time" parameters in a system, however, gives a very powerful understanding of the response to anthropogenic perturbations.

Prather, Michael; Holmes, Christopher

2013-04-01

250

Scaling laws from geomagnetic time series  

USGS Publications Warehouse

The notion of extended self-similarity (ESS) is applied here for the X - component time series of geomagnetic field fluctuations. Plotting nth order structure functions against the fourth order structure function we show that low-frequency geomagnetic fluctuations up to the order n = 10 follow the same scaling laws as MHD fluctuations in solar wind, however, for higher frequencies (f > l/5[h]) a clear departure from the expected universality is observed for n > 6. ESS does not allow to make an unambiguous statement about the non triviality of scaling laws in "geomagnetic" turbulence. However, we suggest to use higher order moments as promising diagnostic tools for mapping the contributions of various remote magnetospheric sources to local observatory data. Copyright 1998 by the American Geophysical Union.

Voros, Z.; Kovacs, P.; Juhasz, A.; Kormendi, A.; Green, A. W.

1998-01-01

251

Disruption time scales of star clusters in different galaxies  

NASA Astrophysics Data System (ADS)

The observed average lifetime of the population of star clusters in the Solar Neighbourhood, the Small Magellanic Cloud and in selected regions of M 51 and M 33 is compared with simple theoretical predictions and with the results of N-body simulations. The empirically derived lifetimes (or disruption times) of star clusters depend on their initial mass as tdisemp ? Mcl0.60 in all four galaxies. N-body simulations have shown that the predicted disruption time of clusters in a tidal field scales as tdispred ? trh0.75 tcr0.25, where trh is the initial half-mass relaxation time and tcr is the crossing time for a cluster in equilibrium. We show that this can be approximated accurately by tdispred ? Mcl0.62 for clusters in the mass range of about 103 to 106 M?, in excellent agreement with the observations. Observations of clusters in different extragalactic environments show that tdis also depends on the ambient density in the galaxies where the clusters reside. Linear analysis predicts that the disruption time will depend on the ambient density of the cluster environment as tdis ? rhmo_amb-1/2. This relation is consistent with N-body simulations. The empirically derived disruption times of clusters in the Solar Neighbourhood, in the SMC and in M 33 agree with these predictions. The best fitting expression for the disruption time is tdis=Cenv (Mcl/104 M?)0.62 (rhmoamb / M? pc-3)-0.5 where Mcl is the initial mass of the cluster and Cenv ? 300 - 800 Myr. The disruption times of star clusters in M 51 within 1-5 kpc from the nucleus, is shorter than predicted by about an order of magnitude. This discrepancy might be due to the strong tidal field variations in M 51, caused by the strong density contrast between the spiral arms and interarm regions, or to the disruptive forces from giant molecular clouds.

Lamers, H. J. G. L. M.; Gieles, M.; Portegies Zwart, S. F.

2005-01-01

252

Time correlation function approach to liquid phase vibrational energy relaxation: Dihalogen solutes in rare gas solvents  

NASA Astrophysics Data System (ADS)

A molecular theory of liquid phase vibrational energy relaxation (VER) [S. A. Adelman [et al.], Adv. Chem. Phys. 84, 73 (1993)] is applied to study the temperature T and density rho dependencies of the VER rate constant k(T,rho)=T1-1, where T1 is the energy relaxation time, of model Lennard-Jones systems that roughly simulate solutions of high-mass, low-frequency dihalogen solutes in rare gas solvents; specifically the I2/Xe, I2/Ar, and ICI/Xe solutions. For selected states of these systems, the theory's assumptions are tested against molecular dynamics (MD) results. The theory is based on the expression T1=beta]-1([omegal), where omegal and beta]([omega) are, respectively, the solute's liquid phase vibrational frequency and vibrational coordinate friction kernel. The friction kernel is evaluated as a cosine transform of the fluctuating force autocorrelation function of the solute vibrational coordinate, conditional that this coordinate is fixed at equilibrium. Additionally, the early-time decay of the force autocorrelation function is approximated by a Gaussian function which is exact to order t2. This Gaussian approximation permits evaluation of T1 in terms of integrals over equilibrium solute-solvent pair correlation functions. The pair correlation function formulas yield T1's in semiquantitative agreement with those found by MD evaluations of the Gaussian approximation, but with three orders of magnitude less computational effort. For the isothermal rho dependencies of k(T,rho), the theory predicts for all systems that the Gaussian decay time tau is nearly independent of rho. This in turn implies that k(T,rho) factorizes into a liquid phase structural contribution and a gas phase dynamical contribution, yielding a first-principles form for k(T,rho) similar to that postulated by the isolated binary collision model. Also, the theory predicts both "classical" superlinear rate isotherms, and "nonclassical" sublinear isotherms similar to those recently observed by Troe and co-workers for azulene relaxation in supercritical fluids. The isochoric T dependencies of k(T,rho) are studied in the range 300 to 1000 K. For none of the solutions are the rate isochores found to accurately conform to either Arrhenius or Landau-Teller kinetics.

Miller, David W.; Adelman, Steven A.

2002-08-01

253

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

NASA Astrophysics Data System (ADS)

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

Costabel, Stephan; Yaramanci, Ugur

2013-04-01

254

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

255

The Geologic Time Scale: The Development of Life through time  

NSDL National Science Digital Library

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

256

Time sequence and time scale of intermediate mass fragment emission  

SciTech Connect

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

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

2005-04-01

257

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

NASA Astrophysics Data System (ADS)

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

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

2011-03-01

258

Phase-Field Model of Long-Time Glasslike Relaxation in Binary Fluid Mixtures  

NASA Astrophysics Data System (ADS)

We present a new phase-field model for binary fluids, exhibiting typical signatures of soft-glassy behavior, such as long-time relaxation, aging, and long-term dynamical arrest. The present model allows the cost of building an interface to vanish locally within the interface, while preserving positivity of the overall surface tension. A crucial consequence of this property, which we prove analytically, is the emergence of free-energy minimizing density configurations, hereafter named “compactons,” to denote their property of being localized to a finite-size region of space and strictly zero elsewhere (no tails). Thanks to compactness, any arbitrary superposition of compactons still is a free-energy minimizer, which provides a direct link between the complexity of the free-energy landscape and the morphological complexity of configurational space.

Benzi, R.; Sbragaglia, M.; Bernaschi, M.; Succi, S.

2011-04-01

259

Multi-relaxation time lattice Boltzmann simulation of inertial secondary flow in a curved microchannel  

NASA Astrophysics Data System (ADS)

The inertial secondary flow is particularly important for hydrodynamic focusing and particle manipulation in biomedical research. In this paper, the development of the inertial secondary flow structure in a curved microchannel was investigated by the multi relaxation time lattice Boltzmann equation model with a force term. The numerical results indicate that the viscous and inertial competition dominates the development of secondary flow structure development. The Reynolds number, Dean number, and the cross section aspect ratio influence significantly on the development of the secondary vortexes. Both the intensity of secondary flow and the distance between the normalized vortex centers are functions of Dean numbers but independent of channel curvature radius. In addition, the competition mechanism between the viscous and inertial effects were discussed by performing the particle focusing experiments. The present investigation provides an improved understanding of the development of inertial secondary flows in curved microchannels.

Sun, Dong-Ke; Xiang, Nan; Jiang, Di; Chen, Ke; Yi, Hong; Ni, Zhong-Hua

2013-11-01

260

$\\\\alpha$Scale Decoupling of the Mechanical Relaxation and Diverging Shear Wave Propagation Lengthscale in Triphenylphosphite  

Microsoft Academic Search

We have performed depolarized Impulsive Stimulated Scattering experiments to observe shear acoustic phonons in supercooled triphenylphosphite (TPP) from $\\\\sim$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 (MCT). Our results provide evidence of $\\\\alpha$ coupling between the

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

2011-01-01

261

Parametric instabilities in picosecond time scales  

SciTech Connect

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

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

1993-03-01

262

Multiple time scale analysis of macrotransport processes  

NASA Astrophysics Data System (ADS)

Convective and diffusive transport of a Brownian tracer corpuscle is analyzed within a multidimensional space decomposed into local (internal) and global (external) subspaces. Multiple time scale methods are employed to successively eliminate from the kinetic equation governing the multidimensional microtransport process its dependence upon each of the internal coordinates. The resulting long-time equation describing the residual global-space macrotransport process derived by this systematic perturbation procedure is shown to accord with the well-established results of generalized Taylor dispersion theory, heretofore obtained by ad hoc arguments. By way of example, this macrotransport description is used to analyze the Taylor dispersion of a solute in a Poiseuille-type solvent flow occuring within a rectangular duct of small, but non-zero, aspect ratio. Elementary dispersion results obtained by ignoring the side walls apply only for relatively short times; for longer times the perturbing presence of the side walls acts to substantially increase the axial dispersivity, even in the limit of zero aspect ratio-where intuition would strongly suggest otherwise.

Pagitsas, M.; Nadim, A.; Brenner, H.

1986-04-01

263

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

SciTech Connect

The pulsed nuclear magnetic resonance (NMR) method at a proton frequency of 25 MHz at temperatures of 22-160{sup o}C is used to detect the transverse magnetization decay in polyisoprene rubbers with various molecular masses, to determine the NMR damping time T{sub 2}, and to measure spin-lattice relaxation time T{sub 1} and time T{sub 2eff} of damping of solid-echo signals under the action of a sequence of MW-4 pulses modified by introducing 180{sup o} pulses. The dispersion dependences of T{sub 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{sub 2eff} and the data on T{sub 2} and T{sub 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., E-mail: chernov@csu.ru; Krasnopol'skii, G. S. [Chelyabinsk State University (Russian Federation)

2008-08-15

264

Relaxation times of an electrolytic cell subject to an external electric field: role of ambipolar and free diffusion phenomena.  

PubMed

We evaluate the relaxation times for an electrolytic cell subject to a step-like external voltage, in the case in which the mobility of negative ions is different from that of positive ions. The electrodes of the cell, in the shape of a slab, are supposed to be perfectly blocking. The theoretical analysis is performed by assuming that the applied voltage is so small that the fundamental equations of the problem can be linearized. In this framework, the eigenvalues equations defining all relaxation times of the problem are deduced. In the numerical analysis, we solve the complete set of equations describing the time evolution of the system under the action of the external voltage. Two relaxation processes, connected with the ambipolar and free diffusion phenomena, are sufficient to describe the dynamics of the system, when the diffusion coefficients are of the same order of magnitude. PMID:17973516

Alexe-Ionescu, A L; Barbero, G; Lelidis, I; Scalerandi, M

2007-11-22

265

EDITORIAL: Special issue on time scale algorithms  

NASA Astrophysics Data System (ADS)

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

Matsakis, Demetrios; Tavella, Patrizia

2008-12-01

266

Time scales in nuclear giant resonances  

SciTech Connect

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

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

2010-03-15

267

Gamma-ray burster recurrence time scales  

NASA Technical Reports Server (NTRS)

In the decade since gamma-ray bursters (GRBs) were discovered by Klebesadel et al. (1973), many models have been proposed to explain the GRB phenomenon. A difficulty is related to the small number of predictions which would make it possible to evaluate the models. One verifiable prediction is the recurrence time scale, tau-gamma. One method to measure tau-gamma is to look for possible cases of recurrence as indicated by overlapping error boxes. The analysis considered in the present investigation is composed of three procedures. One of these involves a search through known error regions for cases where the error regions overlap. In addition, the number of overlaps expected by chance coincidence alone has been determined, and a calculation has been performed regarding the number of overlaps which are expected due to recurrence for various assumed tau-gamma and luminosity functions.

Schaefer, B. E.; Cline, T. L.

1985-01-01

268

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

SciTech Connect

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

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

2013-05-23

269

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

270

Strong anisotropy of momentum-relaxation time induced by intermolecular vibrations of single-crystal organic semiconductors  

NASA Astrophysics Data System (ADS)

We present a theoretical study of the relationships between intermolecular vibrations and anisotropic transport properties of pentacene and rubrene single-crystal organic semiconductors. Using our wave-packet approach based on the Kubo formula beyond the effective-mass approximation with the assumption of an isotropic momentum-relaxation time, we find that the intermolecular vibrations induce a strong anisotropic momentum-relaxation time but moderate the anisotropy of carrier mobility much more than that of the effective mass. This clarifies the mechanism behind the deviation of the anisotropic ratio of mobility from that of effective mass observed in angle-resolved photoelectron spectroscopy experiments.

Ishii, Hiroyuki; Kobayashi, Nobuhiko; Hirose, Kenji

2013-11-01

271

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

NASA Astrophysics Data System (ADS)

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

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

2004-07-01

272

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

NASA Astrophysics Data System (ADS)

We have measured the relaxation of Couette shear-induced L ? lamellar states to their isotropic L 3 “sponge” equilibrium phases in the cetylpryridinium-hexanol/dextrose-brine system by (cycled) time-resolved small-angle neutron scattering. Although diffusive motions of adjacent membrane sheets may be estimated to bring them into contact with frequencies ?10 kHz, we observe structural relaxation times on the order of seconds. This indicates a significant activation energy against the re-establishment of the passages characterizing the convoluted sponge structure.

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

273

Characterizing proton relaxation times for metallic and magnetic layer-by-layer-coated, DNA-templated nanoparticle chains.  

PubMed

Metallic and superparamagnetic DNA-templated nanoparticle (NP) chains are examined as potential imaging agents. Proton relaxation times (T(1) and T(2)) are measured for DNA nanostructures using nuclear magnetic resonance (NMR) spectroscopy. The layer-by-layer (LBL) method was used to encapsulate the DNA-templated NP chains and demonstrated a change in proton relaxation times. Results from this study suggest that LBL-coated, DNA-templated nanostructures can serve as effective imaging agents for magnetic resonance imaging (MRI) applications. PMID:20484793

Jaganathan, Hamsa; Gieseck, Richard L; Ivanisevic, Albena

2010-06-18

274

Entropy Maximum Principle and Relaxation Phenomena.  

National Technical Information Service (NTIS)

A Shannon (epoch) entropy is defined in terms of an integral over the full temporal epoch of relaxation. A maximum entropy principle yields a linear exponential as a fundamental form for relaxation to equilibrium. It is observed that the time scale of mea...

A. K. Rajagopal, S. Teitler, K. L. Ngai

1984-01-01

275

Soil and litter phosphorus-31 nuclear magnetic resonance spectroscopy: extractants, metals, and phosphorus relaxation times.  

PubMed

Phosphorus-31 nuclear magnetic resonance (NMR) spectroscopy is an excellent tool with which to study soil organic P, allowing quantitative, comparative analysis of P forms. However, for 31P NMR to be tative, all peaks must be completely visible, and in their correct relative proportions. There must be no line broadening, and adequate delay times must be used to avoid saturation of peaks. The objective of this study was to examine the effects of extractants on delay times and peak saturation. Two samples (a forest litter and a mineral soil sample) and three extractants (0.25 M NaOH, NaOH plus Chelex (Bio-Rad Laboratories, Hercules, CA), and NaOH plus EDTA) were used to determine the differences in the concentration of P and cations solubilized by each extractant, and to measure spin-lattice (T1) relaxation times of P peaks in each extract. For both soil and litter, NaOH-Chelex extracted the lowest concentrations of P. For the litter sample, T1 values were short for all extractants due to the high Fe concentration remaining after extraction. For the soil sample, there were noticeable differences among the extractants. The NaOH-Chelex sample had less Fe and Mn remaining in solution after extraction than the other extractants, and the longest delay times used in the study, 6.4 s, were not long enough for quantitative analysis. Delay times of 1.5 to 2 s for the NaOH and NaOH-EDTA were adequate. Line broadening was highest in the NaOH extracts, which had the highest concentration of Fe. On the basis of these results, recommendations for future analyses of soil and litter samples by solution 31P NMR spectroscopy include: careful selection of an extractant; measurement of paramagnetic ions extracted with P; use of appropriate delay times and the minimum number of scans; and measurement of T1 values whenever possible. PMID:11931434

Cade-Menun, B J; Liu, C W; Nunlist, R; McColl, J G

2002-01-01

276

Accelerated T1rho relaxation quantification in intervertebral disc using limited spin-lock times  

PubMed Central

Objective T1rho relaxation measurement has the potential to identify early biochemical changes in the intervertebral disc. Traditionally, multiple spin-lock times (SLT), often ~5 SLTs, are used to ensure the accuracy and robustness of T1rho mapping. It will be advantageous to use fewer SLT points if comparable accuracy of T1rho mapping can be achieved. In this study, the feasibility of using 3 SLT points to measure intervertebral disc T1rho relaxation time is explored. Materials and methods The lumbar spine of 12 subjects (age range: 30-75 years, disc =60) were studied on 3-T MRI. For T1rho measurement, a rotary echo spin-lock pulse was implemented in a 3D balanced fast field echo (b-FFE) sequence. Spin-lock frequency was set as 500 Hz and the SLTs of 1, 10, 20, 40, and 60 ms were acquired. T1rho maps were generated by fitting each pixel’s intensity as a function of SLT using a non-negative least-square fitting algorithm. Images were analysed in the mid-sagittal section. T1rho maps were re-constructed using all 5 SLT points of 1, 10, 20, 40, and 60 ms, and three SLT points of 1, 20, and 60 ms respectively. ROIs included nucleus pulposus (NP), anterior annulus fibrosus (AF) and posterior annulus fibrosus. Values of anterior AF and posterior AF were averaged as the value for AF. Agreement of T1rho measurements using different SLT points was assessed using intra-class correlation coefficient (ICC) on absolute agreement as well as Bland and Altman plot. Results There was no significant difference for T1rho values by 5-SLT measurement and 3-SLT measurement in both NP (P=0.63) and AF (P=0.31). The ICC for 5-SLT T1rho measurement vs. 3-SLT T1rho measurement was 0.991 and 0.981 respectively for NP and AF T1rho time. The Bland and Altman plots for the comparison showed a mean difference of 3.14 and 1.83 for NP and AF respectively. Polling the T1rho values for NP and AF in 60 discs together, the ICC for 5-SLT T1rho measurement vs. 3-SLT T1rho measurement was 0.993, and the Bland and Altman analysis showed a mean difference of 2.56. Conclusions This study suggests that adopting 3 SLTs of 1, 20, and 60 ms can be an acceptable alternative for the disc T1rho measurement.

Zhao, Feng; Yuan, Jing; Mok, Greta SP; Ahuja, Anil T; Griffith, James F

2013-01-01

277

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

278

Raman spin lattice relaxation time and Debye temperature studies of Cr in ammonium cobalt sulphate hexahydrate single crystal  

NASA Astrophysics Data System (ADS)

Electron paramagnetic resonance (EPR) of Cr doped in (NH4)Co(SO4)·6H2O single crystal has been studied using Q band EPR spectrometer to find spin lattice relaxation time (SLRT) (T1). The observation of resolved chromium spectra at room temperature has been interpreted in terms of random modulation of interaction between trivalent chromium and divalent cobalt ions by SLRT of cobalt ions. The relaxation time of the host is found to be 6.95×10s using Mitsuma theory and 9.85×10s using Misra et al. approach at room temperature (300 K). Debye temperature of the host lattice is evaluated using electron spin lattice relaxation processes. It is found that the Debye temperature of the host is 110 K.

Ravi, S.; Subramanian, P.

2007-08-01

279

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

PubMed Central

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

Walimuni, Indika S.; Hasan, Khader M.

2011-01-01

280

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

PubMed Central

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

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

1998-01-01

281

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

282

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

283

Length, time, and energy scales of photosystems  

Microsoft Academic Search

The design of photosynthetic systems reflects the length scales of the fundamental physical processes. Energy transfer is rapid at the few angstrom scale and continues to be rapid even at the 50-Å scale of the membrane thickness. Electron tunneling is nearly as rapid at the shortest distances, but becomes physiologically too slow well before 20 Å. Diffusion, which starts out

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

2003-01-01

284

Electron Spin Relaxation and Coherence Times in Si/SiGe Quantum Dots  

NASA Astrophysics Data System (ADS)

Single electron spin states in Si/SiGe quantum dots have shown promise as qubits for quantum information processing. Recently, electron spins in gated Si/SiGe quantum dots have displayed relaxation (T1) and coherence (T2) times of 250 ?s at 350mK. The experiments used conventional X-band (10 GHz) pulsed Electron Spin Resonance (pESR) on a large area (3.5 x 20 mm^2), double gated, undoped Si/SiGe heterostructure, which was patterned with 2 x 10^8 quantum dots using e-beam lithography. Dots with 150 nm radii and 700 nm period are induced in a natural Si quantum well by the gates. Smaller dots are expected to reduce the effects of nearly degenerate valley states and spin-orbit coupling on the electron spin coherence. However, the small number of spins makes signal recovery extremely challenging. We have implemented a broadband cryogenic HEMT low-noise-amplifier and a high-speed single-pole double-throw switch operating at liquid helium temperatures. The switch and preamp have improved our signal to noise by an order of magnitude, allowing for smaller samples and shorter measurement times. We will describe these improvements and the data they have enabled.

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

2013-03-01

285

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

286

Direct spectrum-analysis method for obtaining the relaxation-time spectrum from relaxation-response data: amorphous metals. [Fe/sub 40/Ni/sub 40/P/sub 14/B/sub 6/  

SciTech Connect

A method is described for determining without prior assumptions the distribution of relaxation times from the experimental relaxation response curve for a system approaching equilibrium by a single-step process following first-order kinetics. By analysis of computer-generated data with simulated random experimental error, the method is demonstrated to be capable of reproducing spectra with a single lognormal peak for a broad range of peak widths. This direct spectrum analysis method is applied to previously reported results for a relaxation in the metallic glass Fe/sub 40/Ni/sub 40/P/sub 14/B/sub 6/ and the previous result that the relaxation time spectrum for this relaxation contains four relatively sharp peaks is corroborated.

Cost, J.R.

1982-01-01

287

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

PubMed Central

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

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

2013-01-01

288

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

289

Longer T(2) relaxation time is a marker of hypothalamic gliosis in mice with diet-induced obesity.  

PubMed

A hallmark of brain injury from infection, vascular, neurodegenerative, and other disorders is the development of gliosis, which can be detected by magnetic resonance imaging (MRI). In rodent models of diet-induced obesity (DIO), high-fat diet (HFD) consumption rapidly induces inflammation and gliosis in energy-regulating regions of the mediobasal hypothalamus (MBH), and recently we reported MRI findings suggestive of MBH gliosis in obese humans. Thus, noninvasive imaging may obviate the need to assess MBH gliosis using histopathological end points, an obvious limitation to human studies. To investigate whether quantitative MRI is a valid tool with which to measure MBH gliosis, we performed analyses, including measurement of T(2) relaxation time from high-field MR brain imaging of mice fed HFD and chow-fed controls. Mean bilateral T(2) relaxation time was prolonged significantly in the MBH, but not in the thalamus or cortex, of HFD-fed mice compared with chow-fed controls. Histological analysis confirmed evidence of increased astrocytosis and microglial accumulation in the MBH of HFD-fed mice compared with controls, and T(2) relaxation times in the right MBH correlated positively with mean intensity of glial fibrillary acidic protein staining (a marker of astrocytes) in HFD-fed animals. Our findings indicate that T(2) relaxation time obtained from high-field MRI is a useful noninvasive measurement of HFD-induced gliosis in the mouse hypothalamus with potential for translation to human studies. PMID:23548614

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

2013-06-01

290

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

291

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

292

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, ?SconfE/E2, of 50 dipolar liquids, including those whose static permittivity, ?s, decreases on cooling. The field induced change, ?SconfE, 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 ?SconfE. We conclude that (i) for E in the 105 V/cm range, ?SconfE 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

293

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

294

Experimental study of electric field influence on low temperature long-time relaxation in crystalline ferroelectrics  

NASA Astrophysics Data System (ADS)

Calorimetric measurements with polycrystalline Pb(sub 0.915)La(sub 0.085).(Zr(sub 0.65)Ti(sub 0.35))O3 were performed at helium temperatures in electric field E (0 less than or equal to E less than or equal to 4.3 kV cm). Heat release after cooling from T(sub 1) (1.3 K less than or equal to T(sub 1) less than or equal to 35 K) to T(sub 0) = 1.3 K is very similar to that in amorphous metals and dielectrics. Experimental results disagree with the standard tunneling model. The observed release may be explained assuming the existence of a maximum energy is an element of epsilon sub f in the distribution function. The maximum relaxation time Tau sub max was found as a function of T(sub 1). A similar heat release is observed after switching on or off the electric field. Independent of T for 1.1 K less than or equal to T less than or equal to 3 K, proportional to E sup 2 with Tau sub max approx. E. No heat release was observed in the KH2PO4 single crystal.

Sahling, S.; Kolac, M.; Sahling, A.

295

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.

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

2010-01-01

296

Long-term stress relaxation prediction for elastomers using the time–temperature superposition method  

Microsoft Academic Search

Increasingly, manufacturers need to provide warranties of over 10 years on rubber seals, gaskets and air-springs and warranties of between 20 and 30 years on O-rings for underground applications [Parker Hannifin Corp. Compression set vs. compression stress relaxation. vol. 1, No. 3; 2003.]. In order to expedite the development process, experimental concepts for accelerated forecasts of long-term relaxation are required.

S. Ronan; T. Alshuth; S. Jerrams; N. Murphy

2007-01-01

297

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

298

Current and future realizations of coordinate time scales  

NASA Astrophysics Data System (ADS)

Two atomic time scales maintained at the International Bureau of Weights and Measures (BIPM) are realizations of terrestrial time: International Atomic Time (TAI) and TT(BIPM). They are calculated from atomic clocks realizing proper time in national laboratories. The algorithm for the calculation of TAI has been designed to optimize the frequency stability and accuracy of the time scale. Plans for the future improvement of the reference time scales are presented.

Arias, E. Felicitas

2010-01-01

299

Time domain modeling of plasmas at RF time-scales  

NASA Astrophysics Data System (ADS)

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

Smithe, David N.

2007-07-01

300

Time Scale Separation and Dynamic Heterogeneity in the Low Temperature East Model  

NASA Astrophysics Data System (ADS)

We consider the non-equilibrium dynamics of the East model, a linear chain of 0-1 spins evolving under a simple Glauber dynamics in the presence of a kinetic constraint which forbids flips of those spins whose left neighbor is 1. We focus on the glassy effects caused by the kinetic constraint as {qdownarrow 0} , where q is the equilibrium density of the 0s. In the physical literature this limit is equivalent to the zero temperature limit. We first prove that, for any given L = O(1/q), the divergence as {qdownarrow 0} of three basic characteristic time scales of the East process of length L is the same. Then we examine the problem of dynamic heterogeneity, i.e., non-trivial spatio-temporal fluctuations of the local relaxation to equilibrium, one of the central aspects of glassy dynamics. For any mesoscopic length scale L = O(q -? ), ? < 1, we show that the characteristic time scale of two East processes of length L and ? L respectively are indeed separated by a factor q -? , ? = ?(?) > 0, provided that ? ? 2 is large enough (independent of q, ? = 2 for ? < 1/2). In particular, the evolution of mesoscopic domains, i.e., maximal blocks of the form 111..10, occurs on a time scale which depends sharply on the size of the domain, a clear signature of dynamic heterogeneity. A key result for this part is a very precise computation of the relaxation time of the chain as a function of (q, L), well beyond the current knowledge, which uses induction on length scales on one hand and a novel algorithmic lower bound on the other. Finally we show that no form of time scale separation occurs for ? = 1, i.e., at the equilibrium scale L = 1/q, contrary to what was assumed in the physical literature based on numerical simulations.

Chleboun, P.; Faggionato, A.; Martinelli, F.

2014-03-01

301

Time Scale Separation and Dynamic Heterogeneity in the Low Temperature East Model  

NASA Astrophysics Data System (ADS)

We consider the non-equilibrium dynamics of the East model, a linear chain of 0-1 spins evolving under a simple Glauber dynamics in the presence of a kinetic constraint which forbids flips of those spins whose left neighbor is 1. We focus on the glassy effects caused by the kinetic constraint as , where q is the equilibrium density of the 0s. In the physical literature this limit is equivalent to the zero temperature limit. We first prove that, for any given L = O(1/ q), the divergence as of three basic characteristic time scales of the East process of length L is the same. Then we examine the problem of dynamic heterogeneity, i.e., non-trivial spatio-temporal fluctuations of the local relaxation to equilibrium, one of the central aspects of glassy dynamics. For any mesoscopic length scale L = O( q - ? ), ? < 1, we show that the characteristic time scale of two East processes of length L and ? L respectively are indeed separated by a factor q - ? , ? = ?( ?) > 0, provided that ? ? 2 is large enough (independent of q, ? = 2 for ? < 1/2). In particular, the evolution of mesoscopic domains, i.e., maximal blocks of the form 111..10, occurs on a time scale which depends sharply on the size of the domain, a clear signature of dynamic heterogeneity. A key result for this part is a very precise computation of the relaxation time of the chain as a function of ( q, L), well beyond the current knowledge, which uses induction on length scales on one hand and a novel algorithmic lower bound on the other. Finally we show that no form of time scale separation occurs for ? = 1, i.e., at the equilibrium scale L = 1/ q, contrary to what was assumed in the physical literature based on numerical simulations.

Chleboun, P.; Faggionato, A.; Martinelli, F.

2014-06-01

302

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

303

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

SciTech Connect

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

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

2006-08-22

304

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

305

Potassium-39 nuclear magnetic resonance of potassium-ionophore complexes: Chemical shifts, relaxation times, and quadrupole coupling constants  

NASA Astrophysics Data System (ADS)

The complexation of K + by several ionophores was studied by 39K nuclear magnetic resonance. With the use of a high magnetic field (8.5 tesla) and a probe with sideways solenoid transmitter/receiver coil, very good signal-to-noise ratios could be obtained in a reasonable experiment time for concentrations as low as 20 m M and linewidths of the order of 250 Hz. Chemical shifts and spin-lattice relaxation times for 39K in the ionophore complexes are reported. The 39K chemical shifts show a large variation in different ligand environments. 13C spin-lattice relaxation times were measured for the potassium-ionophore complexes in order to derive correlation times. 39K quadrupole coupling constants in the different complexes could thus also be calculated. Despite the low sensitivity of 39K for the NMR experiment, the results indicate that 39K NMR studies of potassium-ligand interactions are feasible at millimolar concentrations.

Neurohr, Klaus J.; Drakenberg, Torbjorn; Forsén, Sture; Lilja, Hans

306

Dynamic equations on time scales: A survey  

Microsoft Academic Search

Abstract: The studyofdynam9equations ontim scales, which goes back to its founder Stefan Hilger (1988), is an area ofm\\/8#xW#\\/;9that has recently received a lot of attention. It has been created in order to unify the study of di#erential anddi#erence equations. In this paper we give an introduction to the tim scales calculus. We also present various propertiesof the exponential function on

R. Agarwal; M. Bohner; D. O'regan; A. Peterson

2000-01-01

307

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

PubMed Central

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

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

2011-01-01

308

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); and J. Chem. Phys. 133, 044511 (2010)]. We provide comprehensive numerical results obtained from the three-time correlation function for the above models. From these calculations, we examine the time scale of the dynamic heterogeneities and determine the associated lifetime in a consistent and systematic way. Our results indicate that the lifetime of the dynamical heterogeneities becomes much longer than the ?-relaxation time determined from a two-point correlation function in fragile liquids. The decoupling between the two time scales is remarkable, particularly in supercooled states, and the time scales differ by more than an order of magnitude in a more fragile liquid. In contrast, the lifetime is shorter than the ?-relaxation time in tetrahedral network-forming strong liquid, even at lower temperatures.

Kim, Kang; Saito, Shinji

2013-03-01

309

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

NASA Astrophysics Data System (ADS)

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

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

2011-03-01

310

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

311

Time scales in energy balance climate models 2: The intermediate time solutions  

Microsoft Academic Search

We demonstrated in a companion paper (Watts et al., this issue) that the transient response of a globally averaged upwelling diffusion energy balance climate model depends upon three time scales: the mixed-layer thermal-response time scale, the thermocline thermal-response time scale, and the upwelling time scale. These time scales are defined and interpreted physically in that paper. The asymptotic solution for

Michael C. Morantine; Robert G. Watts

1994-01-01

312

BRIEF COMMUNICATIONS: Investigation of the relaxation time of the 0001 level of CO2 in mixtures with O2 and CO  

Microsoft Academic Search

An experimental determination was made of the vibrational relaxation time of the 0001 level of CO2 due to collisions with CO and O2 in the gaseous phase. The relaxation time was determined in the temperature range 300-1000°K with the best currently attainable precision of 10-15%. A comparison was made with the published values.

A. N. Vargin; V. V. Gogokhiya; V. K. Konyukhov; L. M. Pasynkova

1975-01-01

313

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

NASA Astrophysics Data System (ADS)

We present a method for performing parallel temperature-accelerated dynamics (TAD) simulations over extended length scales. In our method, a two-dimensional spatial decomposition is used along with the recently proposed semirigorous synchronous sublattice algorithm of Shim and Amar [Phys. Rev. B 71, 125432 (2005)]. The scaling behavior of the simulation time as a function of system size is studied and compared with serial TAD in simulations of the early stages of Cu/Cu(100) growth as well as for a simple case of surface relaxation. In contrast to the corresponding serial TAD simulations, for which the simulation time tser increases as a power of the system size N (tser˜Nx) with an exponent x that can be as large as three, in our parallel simulations the simulation time increases only logarithmically with system size. As a result, even for relatively small system sizes our parallel TAD simulations are significantly faster than the corresponding serial TAD simulations. The significantly improved scaling behavior of our parallel TAD simulations over the corresponding serial simulations indicates that our parallel TAD method may be useful in performing simulations over significantly larger length scales than serial TAD, while preserving all the atomistic details provided by the TAD method.

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

2007-11-01

314

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

Microsoft Academic Search

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

Felix Gradstein; James Ogg

2004-01-01

315

Linking Response-Time Parameters onto a Common Scale  

ERIC Educational Resources Information Center

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

van der Linden, Wim J.

2010-01-01

316

Why is the internet traffic bursty in short time scales?  

Microsoft Academic Search

Internet traffic exhibits multifaceted burstiness and correlation structure over a wide span of time scales. Previous work analyzed this structure in terms of heavy-tailed session characteristics, as well as TCP timeouts and congestion avoidance, in relatively long time scales. We focus on shorter scales, typically less than 100-1000 milliseconds. Our objective is to identify the actual mechanisms that are responsible

Hao Jiang; Constantinos Dovrolis

2005-01-01

317

The origin of TCP traffic burstiness in short time scales  

Microsoft Academic Search

Internet traffic exhibits multifaceted burstiness and correlation structure over a wide span of time scales. Previous work analyzed this structure in terms of heavy-tailed session characteristics, as well as TCP timeouts and congestion avoid- ance, in relatively long time scales. We focus on shorter scales, typically less than 100-1000 milliseconds. Our objective is to identify the actual mechanisms that are

Hao Jiang; Constantinos Dovrolis

2004-01-01

318

Development of a pulsar-based time-scale  

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

319

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

Microsoft Academic Search

Relaxation rates in NMR are usually measured by intensity modulation as a function of a relaxation delay during which the relaxation mechanism of interest is effective. Other mechanisms are often suppressed during the relaxation delay by pulse sequences which eliminate their effects, or cancel their effects when two data sets with appropriate combinations of relaxation rate effects are added. Cross-correlated

Yizhou Liu; James H. Prestegard

2008-01-01

320

On time scales and time synchronization using LORAN-C as a time reference signal  

NASA Technical Reports Server (NTRS)

The long term performance of the eight LORAN-C chains is presented in terms of the Coordinated Universal Time (UTC) of the U.S. Naval Observatory (USNO); and the use of the LORAN-C navigation system for maintaining the user's clock to a UTC scale is described. The atomic time scale and the UTC of several national laboratories and observatories relative to the international atomic time are reported. Typical performance of several NASA tracking station clocks, relative to the USNO master clock, is also presented.

Chi, A. R.

1974-01-01

321

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.

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

2012-01-01

322

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

SciTech Connect

Proton relaxation time measurements were performed on a standard whole body MR imager operating at 1.5 T using a conventional surface coil of the manufacturer. A combined CP/CPMG multiecho, multislice sequence was used for the T1 and T2 relaxation time measurements. Two repetition times of 2000 ms (30 echoes) and 600 ms (2 echoes) with 180 degrees-pulse intervals of 2 tau = 22 ms were interleaved in this sequence. A two-exponential T2 analysis of each pixel of the spin-echo images was computed in a case of an acoustic neurinoma. The two-exponential images show a short component (T2S) due to white and gray matter and a long component (T2S) due to the cerebrospinal fluid. In the fatty tissue two components with T2S = 35 {plus minus} 3 ms and T2L = 164 {plus minus} 7 ms were measured. Comparing with Gd-DTPA imaging the relaxation time images show a clear differentiation of vital tumor tissue and cerebrospinal fluid.

Schad, L.R.; Brix, G.; Semmler, W.; Gueckel, F.L.; Lorenz, W.J. (Institute of Radiology and Pathophysiology, Heidelberg (Germany, F.R.))

1989-07-01

323

Effect of Sugars on the Molecular Motion of Freeze-Dried Protein Formulations Reflected by NMR Relaxation Times  

Microsoft Academic Search

Purpose  To relate NMR relaxation times to instability-related molecular motions of freeze-dried protein formulations and to examine\\u000a the effect of sugars on these motions.\\u000a \\u000a \\u000a \\u000a \\u000a Methods  Rotating-frame spin-lattice relaxation time (T1?) was determined for both protein and sugar carbons in freeze-dried lysozyme-sugar (trehalose, sucrose and isomaltose) formulations\\u000a using solid-state 13C NMR.\\u000a \\u000a \\u000a \\u000a \\u000a Results  The temperature dependence of T1? for the lysozyme carbonyl carbons in lysozyme

Sumie Yoshioka; Kelly M. Forney; Yukio Aso; Michael J. Pikal

324

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

NASA Astrophysics Data System (ADS)

With the time constants usually considered to be characteristic for polymer dynamics, namely ? (the segment fluctuation time), ? (the entanglement time), and ? (the longest Rouse relaxation time), the time scales of particular interest: (i) tscales: (i) ?relaxation dispersion will be outlined for the scenarios "freely-draining", "entangled", and "confined". In the discussion we will juxtapose "local" versus "global" dynamics on the one hand, and "bulk" versus "confined" systems on the other. The experimental technique of particular interest here is field-cycling NMR relaxometry which predominantly probes conformational fluctuations. A comparison with methods sensitive by contrast to translational fluctuations such as field-gradient NMR diffusometry and neutron scattering will be discussed with respect to sensitivity to confinement phenomena, i.e. the so-called corset effect.

Kimmich, Rainer

2010-03-01

325

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

SciTech Connect

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

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

2002-01-01

326

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

PubMed Central

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

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

2012-01-01

327

Measurement of T1/T2 relaxation times in overlapped regions from homodecoupled 1H singlet signals  

NASA Astrophysics Data System (ADS)

The implementation of the HOmodecoupled Band-Selective (HOBS) technique in the conventional Inversion-Recovery and CPMG-based PROJECT experiments is described. The achievement of fully homodecoupled signals allows the distinction of overlapped 1H resonances with small chemical shift differences. It is shown that the corresponding T1 and T2 relaxation times can be individually measured from the resulting singlet lines using conventional exponential curve-fitting methods.

Castañar, Laura; Nolis, Pau; Virgili, Albert; Parella, Teodor

2014-07-01

328

Vibrational relaxation dynamics in transient grating spectroscopy studied by rate equations based on time-dependent correlation function  

NASA Astrophysics Data System (ADS)

A modified model, a set of rate equations based on time-dependent correlation function, is used to study vibrational relaxation dynamics in transient grating spectroscopy. The dephasing, the population dynamics, and the vibrational coherence concerning two vibrational states are observed respectively in organic dye IR780 perchlorate molecules doped polyvinyl alcohol matrix. The result shows that in addition to the information concerning system-environment interaction and vibrational coherence, the vibrational energy transfer can be described by this modified model.

Yu, Guo-Yang; Song, Yun-Fei; He, Xing; Zheng, Xian-Xu; Tan, Duo-Wang; Chen, Jun; Yang, Yan-Qiang

2012-04-01

329

Deriving time-dependent diffusion and relaxation rate in porous systems using eigenfunctions of the Laplace operator.  

PubMed

Porous systems are investigated using eigendecomposition of the Laplace matrix. Three parameters; tortuosity, surface-to-pore volume ratio and relaxation rate are derived from the eigenvalue spectrum of the Laplace matrix and connected to the parameters in the Padé approximation, an expression often used to describe the time-dependent diffusion coefficient in porous systems. The Padé length is identified for systems with large pore to connector volume ratio. The results are compared with simulations. PMID:19796974

Nordin, Matias; Jacobi, Martin Nilsson; Nydén, Magnus

2009-12-01

330

Direct evidence for mode-specific vibrational energy relaxation from quantum time-dependent perturbation theory. I. Five-coordinate ferrous iron porphyrin model  

NASA Astrophysics Data System (ADS)

The time scales and mechanisms of mode-specific vibrational energy relaxation in imidazole ligated ferrous iron porphine were studied using a non-Markovian time-dependent perturbation theory and density functional theory calculation. Seven normal modes, including ?4, ?7, and five Fe out-of-plane modes (Fe-oop), were treated as the relaxing system mode coupled to all other modes forming the bath. The derived cooling time constants for the ?4 and ?7 modes agree well with the results of previous experimental studies. The pathways for energy transfer from each system mode were identified. The ?7 mode, associated with Fe-oop motion with frequency ~350 cm-1, was observed to couple strongly through its overtone with the ?7 porphine in-plane vibration. This suggests a possible mechanism for the excitation of the ?7 mode, which is distinct from the direct excitation together with Fe-oop motion of the ?4 mode. Four other Fe-oop motions were observed to couple to low frequency modes including those involving significant imidazole ligand motions. Through these couplings, excitation following ligand photodissociation may be efficiently transferred from the heme doming mode to the protein backbone motions essential to conformational changes associated with the protein's function.

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

2009-01-01

331

Detecting time series motifs under uniform scaling  

Microsoft Academic Search

Time series motifs are approximately repeated patterns found within the data. Such motifs have utility for many data min- ing algorithms, including rule-discovery, novelty-detection, summarization and clustering. Since the formalization of the problem and the introduction of ecient linear time al- gorithms, motif discovery has been successfully applied to many domains, including medicine, motion capture, robotics and meteorology. In this

Dragomir Yankov; Eamonn J. Keogh; Jose Medina; Bill Chiu; Victor B. Zordan

2007-01-01

332

Advances in Time-Scale Algorithms.  

National Technical Information Service (NTIS)

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 sing...

S. R. Stein

1992-01-01

333

Scale interactions of turbulence subjected to a straining relaxation destraining cycle  

Microsoft Academic Search

The response of turbulence subjected to planar straining and de-straining is studied experimentally, and the impact of the applied distortions on the energy transfer across different length scales is quantified. The data are obtained using planar particle image velocimetry (PIV) in a water tank, in which high-Reynolds-number turbulence with very low mean velocity is generated by an array of spinning

Jun Chen; Charles Meneveau; Joseph Katz

2006-01-01

334

Characterization of dynamics in complex lyophilized formulations: I. Comparison of relaxation times measured by isothermal calorimetry with data estimated from the width of the glass transition temperature region.  

PubMed

The purposes of this study are to characterize the relaxation dynamics in complex freeze dried formulations and to investigate the quantitative relationship between the structural relaxation time as measured by thermal activity monitor (TAM) and that estimated from the width of the glass transition temperature (?T(g)). The latter method has advantages over TAM because it is simple and quick. As part of this objective, we evaluate the accuracy in estimating relaxation time data at higher temperatures (50 °C and 60 °C) from TAM data at lower temperature (40 °C) and glass transition region width (?T(g)) data obtained by differential scanning calorimetry. Formulations studied here were hydroxyethyl starch (HES)-disaccharide, HES-polyol, and HES-disaccharide-polyol at various ratios. We also re-examine, using TAM derived relaxation times, the correlation between protein stability (human growth hormone, hGH) and relaxation times explored in a previous report, which employed relaxation time data obtained from ?T(g). Results show that most of the freeze dried formulations exist in single amorphous phase, and structural relaxation times were successfully measured for these systems. We find a reasonably good correlation between TAM measured relaxation times and corresponding data obtained from estimates based on ?T(g), but the agreement is only qualitative. The comparison plot showed that TAM data are directly proportional to the 1/3 power of ?T(g) data, after correcting for an offset. Nevertheless, the correlation between hGH stability and relaxation time remained qualitatively the same as found with using ?T(g) derived relaxation data, and it was found that the modest extrapolation of TAM data to higher temperatures using ?T(g) method and TAM data at 40 °C resulted in quantitative agreement with TAM measurements made at 50 °C and 60 °C, provided the TAM experiment temperature, is well below the Tg of the sample. PMID:23608636

Chieng, Norman; Mizuno, Masayasu; Pikal, Michael

2013-10-01

335

Scaling Physiological Pharmacokinetic Models by Physiological Time.  

National Technical Information Service (NTIS)

This paper shows that a multicompartment physiological pharmacokinetic model, used to account for inhalation exposure to volatile chlorohydrocarbons in mammalian species, can be made species-independent if chronological time is re-expressed in terms of ph...

R. C. Ward C. C. Travis

1987-01-01

336

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

NASA Astrophysics Data System (ADS)

Surface nuclear magnetic resonance (surface NMR) is a geophysical technique used in the exploration of shallow aquifers. It is based on measuring the NMR response of water molecules to excitation by electromagnetic pulses. By increasing the moment of applied pulses, successively deeper regions of an aquifer can be probed. The longitudinal relaxation time T1, determined from the NMR experiment, depends on pore size and can be potentially used to estimate hydraulic conductivity. A novel scheme was recently proposed that was shown theoretically to be more reliable for acquiring surface-NMR T1 data than traditional acquisition. In this proof-of-concept study we provide the first empirical evidence for the superiority of the novel scheme. We chose a survey site close to Skive, Denmark, where proximate boreholes indicate a homogeneous sandy aquifer in the top 30 m. The homogeneous composition implies that the distribution of pore sizes does not vary significantly across the formation. Because pore size is reflected by the T1 relaxation time, we therefore assume that the homogeneous aquifer can be characterized by a single T1 independent of the applied pulse moment (i.e., sampled depth region)—this is the benchmark condition we tested with our surface-NMR measurements. We collected surface-NMR T1 data employing the traditional as well as the novel acquisition scheme at various pulse moments. For each pulse moment we infer a T1 relaxation time based on extensively sampled data (14 delay-time data points). The T1 relaxation times obtained using the novel scheme show a constant value of about 820 ms (± 38 ms) for all pulse moments. In contrast, the T1 relaxation times determined using the traditional scheme vary significantly between 530 and 750 ms with pulse moment, which in an inversion would result in a spatial variation of T1 across the aquifer. The results based on the novel scheme are consistent with a homogeneous aquifer, which we expect based on the borehole information, whereas the variation of T1 obtained by the traditional scheme could be misinterpreted as a variation of pore size or hydraulic conductivity.

Walbrecker, Jan O.; Behroozmand, Ahmad A.

2012-12-01

337

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

SciTech Connect

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

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

2011-03-25

338

Relaxation and phase space singularities in time series of human magnetoencephalograms as indicator of photosensitive epilepsy  

NASA Astrophysics Data System (ADS)

To analyze the crucial role of fluctuation and relaxation effects for the function of the human brain we studied some statistical quantifiers that support the information characteristics of neuromagnetic brain responses (magnetoencephalogram, MEG). The signals to a flickering stimulus of different color combinations have been obtained from a group of control subjects which is then contrasted with those of a patient suffering photosensitive epilepsy (PSE). We found that the existence of the specific stratification of the phase clouds and the concomitant relaxation singularities of the corresponding nonequilibrium dynamics of the chaotic behavior of the signals in separate areas in a patient provide likely indicators for the zones which are responsible for the appearance of PSE.

Yulmetyev, R. M.; Hänggi, P.; Yulmetyeva, D. G.; Shimojo, S.; Khusaenova, E. V.; Watanabe, K.; Bhattacharya, J.

2007-09-01

339

Electric relaxation studies of synthetic membrane cells: time-dependent rectification  

Microsoft Academic Search

We studied electric relaxation across bi-ionic (asymmetric) cells of the form electrode||solution A||membrane||solution B||electrode. Solutions A and B differ either in concentration or in chemical composition. Response curves were measured at 25 °C as a function of external current and voltage, membrane thickness, and various salts and solution concentration. Cellulose acetate films, between 3×10-4 and 21×10-4 cm thick, were used

J. E. Anderson; W. Pusch

1977-01-01

340

Real-time scale selection in hybrid multi-scale representations  

Microsoft Academic Search

Local scale information extracted from visual data in a bottom- up manner constitutes an important cue for a large number of visual tasks. This article presents a framework for how the computation of such scale descriptors can be performed in real time on a standard computer. The proposed scale selection framework is expressed within a novel type of multi-scale representation,referred

Tony Lindeberg; Lars Bretzner

2003-01-01

341

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

PubMed

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

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

2009-02-01

342

The time-local view of nonequilibrium statistical mechanics. I. Linear theory of transport and relaxation  

NASA Astrophysics Data System (ADS)

The various approaches to nonequilibrium statistical mechanics may be subdivided into convolution and convolutionless (time-local) ones. While the former, put forward by Zwanzig, Mori, and others, are used most commonly, the latter are less well developed, but have proven very useful in recent applications. The aim of the present series of papers is to develop the time-local picture (TLP) of nonequilibrium statistical mechanics on a new footing and to consider its physical implications for topics such as the formulation of irreversible thermodynamics. The most natural approach to TLP is seen to derive from the Fourier-Laplace transformwidetilde{C}(z)) of pertinent time correlation functions, which on the physical sheet typically displays an essential singularity at z=? and a number of macroscopic and microscopic poles in the lower half-plane corresponding to long- and short-lived modes, respectively, the former giving rise to the autonomous macrodynamics, whereas the latter are interpreted as doorway modes mediating the transfer of information from relevant to irrelevant channels. Possible implications of this doorway mode concept for socalled extended irreversible thermodynamics are briefly discussed. The pole structure is used for deriving new kinds of generalized Green-Kubo relations expressing macroscopic quantities, transport coefficients, e.g., by contour integrals over current-current correlation functions obeying Hamiltonian dynamics, the contour integration replacing projection. The conventional Green-Kubo relations valid for conserved quantities only are rederived for illustration. Moreover,widetilde{C}(z) may be expressed by a Laurent series expansion in positive and negative powers of z, from which a rigorous, general, and straightforward method is developed for extracting all macroscopic quantities from so-called secularly divergent expansions ofwidetilde{C}(z) as obtained from the application of conventional many-body techniques to the calculation ofwidetilde{C}(z). The expressions are formulated as time scale expansions, which should rapidly converge if macroscopic and microscopic time scales are sufficiently well separated, i.e., if lifetime ("memory") effects are not too large.

der, R.

1987-01-01

343

In vivo relaxation time measurements on a murine tumor model--prolongation of T1 after photodynamic therapy.  

PubMed

RIF tumors implanted on mice feet were investigated for changes in relaxation times (T1 and T2) after photodynamic therapy (PDT). Photodynamic therapy was performed using Photofrin II as the photosensitizer and laser light at 630 nm. A home-built proton solenoid coil in the balanced configuration was used to accommodate the tumors, and the relaxation times were measured before, immediately after, and up to several hours after therapy. Several control experiments were performed untreated tumors, tumors treated with Photofrin II alone, or tumors treated with laser light alone. Significant increases in T1s of water protons were observed after PDT treatment. In all experiments, 31P spectra were recorded before and after the therapy to study the tumor status and to confirm the onset of PDT. These studies show significant prolongation of T1s after the PDT treatment. The spin-spin relaxation measurements, on the other hand, did not show such prolongation in T2 values after PDT treatment. PMID:7739367

Liu, Y H; Hawk, R M; Ramaprasad, S

1995-01-01

344

Origin of the Correlation Time Dependence of Coherence Transfer Distortions in Rotating Frame Cross-Relaxation Spectra  

NASA Astrophysics Data System (ADS)

HOHAHA distortions in conventional (CW) ROESY experiments are known to be prominent when the frequency of the spin-lock field is near the midpoint between the resonance frequencies of a pair of coupled spins. That the disappearance of these distortions with offset from the midpoint is more rapid for large molecules than smaller ones is less widely known, and less well understood. We provide a quantitative explanation of the latter phenomenon using a combination of theory and numerical simulations. The cause of this effect can be found in the differential relaxation of the various magnetization modes which are involved in HOHAHA transfer. These modes experience enhanced relaxation far from a Hartmann-Hahn match. This enhancement is larger for molecules which have long correlation times.

Ghose, Ranajeet; Evans, C. Anderson; Prestegard, James H.

1997-10-01

345

Time-resolved infrared absorption studies of the solvent-dependent vibrational relaxation dynamics of chlorine dioxide  

NASA Astrophysics Data System (ADS)

We report a series of time-resolved infrared absorption studies on chlorine dioxide (OClO) dissolved in H2O, D2O, and acetonitrile. Following the photoexcitation at 401 nm, the evolution in optical density for frequencies corresponding to asymmetric stretch of OClO is measured with a time resolution of 120+/-50 fs. The experimentally determined optical-density evolution is compared with theoretical models of OClO vibrational relaxation derived from collisional models as well as classical molecular-dynamics (MD) studies. The vibrational relaxation rates in D2O are reduced by a factor of 3 relative to H2O consistent with the predictions of MD. This difference reflects modification of the frequency-dependent solvent-solute coupling accompanying isotopic substitution of the solvent. Also, the geminate-recombination quantum yield for the primary photofragments resulting in the reformation of ground-state OClO is reduced in D2O relative to H2O. It is proposed that this reduction reflects enhancement of the dissociation rate accompanying vibrational excitation along the asymmetric-stretch coordinate. In contrast to H2O and D2O, the vibrational-relaxation dynamics in acetonitrile are not well described by the theoretical models. Reproduction of the optical-density evolution in acetonitrile requires significant modification of the frequency-dependent solvent-solute coupling derived from MD. It is proposed that this modification reflects vibrational-energy transfer from the asymmetric stretch of OClO to the methyl rock of acetonitrile. In total, the results presented here provide a detailed description of the solvent-dependent geminate-recombination and vibrational-relaxation dynamics of OClO in solution.

Bolinger, Joshua C.; Bixby, Teresa J.; Reid, Philip J.

2005-08-01

346

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

NASA Astrophysics Data System (ADS)

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

Walbrecker, J.; Behroozmand, A.

2011-12-01

347

A Relaxation Approach to Dynamic Sensor Selection in Large-Scale Wireless Networks  

Microsoft Academic Search

Abstract Wireless sensor networks (WSNs) require more complex sensor selection strategies than other distributed networks to perform optimal state estimation. In addition to con- straints associated with distributed state estimation, wire- less sensor networks have limitations on bandwidth, energy consumption, and transmission range. This paper intro- duces and empirically evaluates a dynamic,sensor selec- tion strategy. A discrete-time Kalman filter is

James E. Weimer; Bruno Sinopoli; Bruce H. Krogh

2008-01-01

348

Diffusion Time-Scale of Porous Pressure-Sensitive Paint.  

National Technical Information Service (NTIS)

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

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

2001-01-01

349

Relations between the scales of length, time and mass  

Microsoft Academic Search

It is considered the model of the homogeneous and isotropic universe. The scale of length is defined via the laboratory scale of time by the motion of photon. This leads to the appearance of the inertial forces. The properties of the space and time are defined both by these inertial forces and by the matter. Within the framework of classical

D. L. Khokhlov

1999-01-01

350

Singular perturbation and time scale approaches in discrete control systems  

NASA Technical Reports Server (NTRS)

After considering a singularly perturbed discrete control system, a singular perturbation approach is used to obtain outer and correction subsystems. A time scale approach is then applied via block diagonalization transformations to decouple the system into slow and fast subsystems. To a zeroth-order approximation, the singular perturbation and time-scale approaches are found to yield equivalent results.

Naidu, D. S.; Price, D. B.

1988-01-01

351

Scaling the Martian Walls of Time  

NASA Astrophysics Data System (ADS)

On Earth, when scientists want to investigate planetary history they take a core sample, with deeper fragments corresponding to older materials. In essence, descending through sedimentary layers is like going back in time. But creating a robot capable of taking samples more than a few meters below the planetary surface is still beyond the current available technology. The cliffhanger idea takes advantage of the natural surface features of Mars to explore the history of the planet without digging. So interesting and difficult questions can be answered not with the brute force of a drill, but with creative mission design. Penn State University HEDS-UP team has designed a novel Mars mission approach. A main Lander with a Rover and a Cliffhanger will land near cliffs of Valles Mariners. Especially design cannon (gas, guided munitions or rocket) will deploy a long rope into the canyon. The rover will carry the cliffhanger to the edge of Valles Marineris following the rope, attach the cliffhanger to the rope. The Cliffhanger will then climb a 2 km down the rope and will allow the team to study sedimentary layers of rock on the side of the cliff. Samples and high-resolution images will be taken and delivered to the Lander for further investigation (optical multispectral imaging microscope, spectrometry) and sending the results to Earth. The robot has been designed to have the capability for locomotion at any angle (including somewhat uphill slopes) but maximum effective After the mission of rope-climbing is completed, the Rover am Lander will embark on another long-term mission to provide meteorological and geological data over a long period of time (long-term Mars Observatory), and perform acoustic and seismic experiments on the surface of Mars in preparation for human arrival.

Thornton, Nikki; Yagloski, Joseph; Fledderman, Joe; OMarr, Gregg; Weber, Ben; Carlins, Chris; Krishna, Shubh; Sloan, Kevin; Merriman, Taite; Borowski, David

2000-01-01

352

Time scales of tunneling decay of a localized state  

SciTech Connect

Motivated by recent time-domain experiments on ultrafast atom ionization, we analyze the transients and time scales that characterize, aside from the relatively long lifetime, the decay of a localized state by tunneling. While the tunneling starts immediately, some time is required for the outgoing flux to develop. This short-term behavior depends strongly on the initial state. For the initial state, tightly localized so that the initial transients are dominated by over-the-barrier motion, the time scale for flux propagation through the barrier is close to the Buettiker-Landauer traversal time. Then a quasistationary, slow-decay process follows, which sets ideal conditions for observing diffraction in time at longer times and distances. To define operationally a tunneling time at the barrier edge, we extrapolate backward the propagation of the wave packet that escaped from the potential. This extrapolated time is considerably longer than the time scale of the flux and density buildup at the barrier edge.

Ban, Yue; Muga, J. G. [Department of Physical Chemistry, Universidad del Pais Vasco UPV-EHU, E-48080 Bilbao (Spain); Sherman, E. Ya. [Department of Physical Chemistry, Universidad del Pais Vasco UPV-EHU, E-48080 Bilbao (Spain); IKERBASQUE, Basque Foundation for Science, E-48011 Bilbao (Spain); Buettiker, M. [Departement de Physique Theorique, Universite de Geneve, CH-1211 Geneve 4 (Switzerland)

2010-12-15

353

Relaxations in gels: Analogies to ? and ? relaxations in glasses  

NASA Astrophysics Data System (ADS)

We present dynamic light scattering data which show that aqueous gelatin gels display a power-law relaxation to a nonergodic background. In the pregel sol this power law is termined by a stretched exponential which restores ergodicity and which has a q dependent characteristic time proportional to the viscosity. The power-law exponent is q dependent and related to a characteristic length in the gel. Except for the q dependences these behaviors are similar to the ? and ? relaxation behavior in glasses. It is proposed that the different q dependences of the gels and glasses is a result of different characteristic length scales.

Ren, S. Z.; Sorensen, C. M.

1993-03-01

354

Thermal Time Scales in a Color Glass Condensate  

NASA Astrophysics Data System (ADS)

In a model of relativistic heavy ion collisions wherein the unconfined quark-gluon plasma is condensed into glass, we derive the Vogel-Fulcher-Tammann cooling law. This law is well known to hold true in condensed matter glasses. The high energy plasma is initially created in a very hot negative temperature state and cools down to the Hagedorn glass temperature at an ever decreasing rate. The cooling rate is largely determined by the QCD string tension derived from hadronic Regge trajectories. The ultimately slow relaxation time is characteristic of a color glass condensate.

Parihar, Vivek; Widom, Allan; Srivastava, Yogi

2006-04-01

355

Thermal time scales in a color glass condensate  

NASA Astrophysics Data System (ADS)

In a model of relativistic heavy-ion collisions wherein the unconfined quark-gluon plasma is condensed into glass, we derive the Vogel-Fulcher-Tammann cooling law. This law is well known to hold true in condensed matter glasses. The high-energy plasma is initially created in a very hot negative temperature state and cools down to the Hagedorn glass temperature at an ever decreasing rate. The cooling rate is largely determined by the QCD string tension derived from hadronic Regge trajectories. The ultimately slow relaxation time is a defining characteristic of a color glass condensate.

Parihar, V.; Widom, A.; Srivastava, Y. N.

2006-01-01

356

Time Scales for Achieving Astronomical Consensus  

NASA Astrophysics Data System (ADS)

The history of science can be recounted in many ways: by addressing the work of one person or school; by starting with the ancients and working chronologically up to the present; by focusing on a particular century; or by tracing a particular important idea as far back and forward as it can be found. The present discussion does none of these. Rather, it adopts the ordering of a standard introductory astronomy textbook, from the solar system via stars and galaxies, to the universe as a whole, and in each regime picks out a few issues that were controversial or wrongly decided for a long time. For each, I attempt to identify a duration of the period of uncertainty or error and some of the causes of the confusion. This is surely not an original idea, though I am not aware of having encountered it elsewhere, and it is not one that is likely to appeal to most 21st century historians of science, for whom the question "Who first got it right?" is not necessarily an important, or even appropriate, one. Some of the stories have been told as historical introductions to conferences and are here summarized and brought up to date. Others I had not previously addressed.

Trimble, Virginia

357

A relaxation of tilt angle in a ferroelectric liquid crystal studied by time-resolved FT-IR  

NASA Astrophysics Data System (ADS)

Polarization angle dependences of infrared (IR) and time-resolved IR have been measured for a FLC mixture containing 20% cis-(2R,4R)-?-butyrolactone 1 (YK230C) as a chiral dopant and 80% 5-octyl-2-(4-nonyloxyphenyl) pyrimidine (ONPP) as a nonchiral smectic base LC. These measurements and the measurements of the dichroic ratios of IR bands show that the apparent tilt angle and dichroic ratio in the dynamic state are larger than those in the static state. It seemed therefore that the order of the orientation is higher in the dynamic state than in the static state. In order to confirm the higher orientation order in the dynamic state, we performed time-resolved IR measurements of the FLC mixture for the delay time ranging from 0 to 500?s, which is much longer than the response time. The relaxation process was clearly observed after the response time.

Matsumoto, T.; Sakaguchi, K.; Yasuda, A.; Ozaki, Y.

1998-06-01

358

Time-resolved photoelectron imaging of the chloranil radical anion: ultrafast relaxation of electronically excited electron acceptor states.  

PubMed

The spectroscopy and dynamics of near-threshold excited states of the isolated chloranil radical anion are investigated using photoelectron imaging. The photoelectron images taken at 480 nm clearly indicate resonance-enhanced photodetachment via a bound electronic excited state. Time-resolved photoelectron imaging reveals that the excited state rapidly decays on a timescale of 130 fs via internal conversion. The ultrafast relaxation dynamics of excited states near threshold are pertinent to common electron acceptor molecules based on the quinone moiety and may serve as doorway states that enable efficient electron transfer in the highly exergonic inverted regime, despite the presence of large free energy barriers. PMID:21971531

Horke, Daniel A; Verlet, Jan R R

2011-11-21

359

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

360

Energy level structure and electron relaxation times in InAs\\/InxGa1-xAs quantum dot-in-a-well structures  

Microsoft Academic Search

Complementary interband and intraband optical spectroscopic techniques are used to investigate the band structure and carrier relaxation times in technologically important InAs\\/InGaAs\\/GaAs quantum dot-in-a-well (DWELL) structures. We determine the dot ground to first excited state energies to be 42 meV in the conduction band and 18 meV in the valence band. Using intraband pump-probe experiments, electron relaxation times from the

P. Aivaliotis; S. Menzel; E. A. Zibik; J. W. Cockburn; L. R. Wilson; M. Hopkinson

2007-01-01

361

Separation of time scales in aircraft trajectory optimization  

NASA Technical Reports Server (NTRS)

Two methods for analyzing the time-scale properties of aircraft trajectory optimization problems are presented. Time-scale properties must be identified before solutions can be obtained by using singular perturbation methods. Both methods only require a knowledge of the state equations, the aircraft characteristics, and the bounds on the state and control variables. Although these methods give only rough estimates of time-scale separation, they do not require that an 'exact' optimal trajectory be known, as do the more rigorous methods, and they are an improvement on the ad hoc methods currently in use. The two methods are applied to an example problem for a high performance aircraft.

Ardema, M. D.; Rajan, N.

1983-01-01

362

Dominant time scale for brittle fragmentation of vesicular magma by decompression  

NASA Astrophysics Data System (ADS)

Brittle fragmentation was examined in a vesicular material analogous to magma, in this case, maltose syrup with bubbles. All the key time scales for magma fragmentation are controlled in the experiment using a rapid decompression facility. It was found that the onset of fragmentation can be well characterized using the Maxwell relaxation time ? r and the decompression time ?t dec, in the case where sufficiently large stress is generated in the material. As the ratio ?t dec/? r increases from less than unity to over fifty, the response of the specimen changes from brittle fragmentation to ductile expansion without fragmentation. During the transition, the specimen exhibits small ductile deformation before the onset of fragmentation. The transition occurs even though the stress at the bubble wall is the same. The results suggest that ?t dec/? r is the controlling parameter not only for the onset of, but also for the variation of magma fragmentation by decompression.

Kameda, Masaharu; Kuribara, Hideaki; Ichihara, Mie

2008-07-01

363

Multiple time scale complexity analysis of resting state FMRI.  

PubMed

The present study explored multi-scale entropy (MSE) analysis to investigate the entropy of resting state fMRI signals across multiple time scales. MSE analysis was developed to distinguish random noise from complex signals since the entropy of the former decreases with longer time scales while the latter signal maintains its entropy due to a "self-resemblance" across time scales. A long resting state BOLD fMRI (rs-fMRI) scan with 1000 data points was performed on five healthy young volunteers to investigate the spatial and temporal characteristics of entropy across multiple time scales. A shorter rs-fMRI scan with 240 data points was performed on a cohort of subjects consisting of healthy young (age 23 ± 2 years, n = 8) and aged volunteers (age 66 ± 3 years, n = 8) to investigate the effect of healthy aging on the entropy of rs-fMRI. The results showed that MSE of gray matter, rather than white matter, resembles closely that of f (-1) noise over multiple time scales. By filtering out high frequency random fluctuations, MSE analysis is able to reveal enhanced contrast in entropy between gray and white matter, as well as between age groups at longer time scales. Our data support the use of MSE analysis as a validation metric for quantifying the complexity of rs-fMRI signals. PMID:24242271

Smith, Robert X; Yan, Lirong; Wang, Danny J J

2014-06-01

364

Liquidity spillover in international stock markets through distinct time scales.  

PubMed

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

Righi, Marcelo Brutti; Vieira, Kelmara Mendes

2014-01-01

365

Hydromagnetic interpretation of short time scale structures in solar flares  

Microsoft Academic Search

Hydromagnetic interpretation of the solar flare short time scale structure indicated in microwave and hard X-ray emission during the impulsive phase is presented. The main assumption is that the plasma ejection from the current sheet may be considered as a forced convection by an isolated source. From this point of view some analogies with small scale short lasting hydrodynamic and

V. M. Dermendjiev

1986-01-01

366

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

367

Structural Decomposition of Multiple Time Scale Markov Processes,  

National Technical Information Service (NTIS)

A straightforward algorithm for the multiple time scale decomposition of singularly perturbed Markov processes has been presented. That algorithm provides a uniform approximation of the probability transition function over the interval t > or = 0 through ...

J. R. Rohlicek A. S. Willsky

1987-01-01

368

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

369

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

370

Interest point detection and scale selection in space-time  

Microsoft Academic Search

Several types of interest point detectors have been proposed for spatial images. This paper investigates how this notion can be gener- alised to the detection of interesting events in space-time data. Moreover, we develop a mechanism for spatio-temporal scale selection and detect events at scales corresponding to their extent in both space and time. To detect spatio-temporal events, we build

Ivan Laptev; Tony Lindeberg

2003-01-01

371

Shape invariant time-scale and pitch modification of speech  

Microsoft Academic Search

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

Thomas F. Quatieri; Robert J. McAulay

1992-01-01

372

Short time scale monitoring of SiO sources  

Microsoft Academic Search

We present the results of a short time scale monitoring of SiO maser emission (v=1 J=1-0 transition) in four known strong sources. These sources were monitored nightly for a period of about a month. The aim of these observations is to investigate the possible presence of variations in the maser lines on time scales of a few days to weeks,

F. P. Pijpers; J. R. Pardo; V. Bujarrabal

1994-01-01

373

Short-time scaling of variable ordering of OBDDs  

Microsoft Academic Search

A short-time scaling criterion of variable ordering of OBDDs is proposed. By this criterion it is easy and fast to determine\\u000a which one is better when several variable orders are given, especially when they differ 10% or more in resulted BDD size from\\u000a each other. An adaptive variable order selection method, based on the short-time scaling criterion, is also presented.

Wangning Long; Yinghua Min; Shiyuan Yang; Shibai Tong

1997-01-01

374

Short-time scale variability in some Be stars  

Microsoft Academic Search

The short-time scale spectroscopic variability of some Be stars has been investigated with an optical fiber spectrograph and a CCD camera. Findings on a time-scale of hours and days include: (1) weak changes in the H-alpha emission line profile of gamma Cas; (2) changes in the structure and the intensity of the H-alpha emission line core and sometimes in the

H. Hubert; B. Dagostinoz; A. M. Hubert; M. Floquet

1987-01-01

375

Signatures of discrete scale invariance in Dst time series  

NASA Astrophysics Data System (ADS)

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

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

2011-07-01

376

Slow dynamics of banana-shaped molecules: a theoretical approach to analyze 2H-NMR T2 relaxation times.  

PubMed

In the present work, we analyze pulsed deuterium NMR experiments performed on the isotropic and nematic phases of the banana-shaped liquid-crystalline mesogen 4-chloro-1,3-phenylene bis{4-4'-(11-undecenyloxy) benzoyloxy} benzoate (ClPbis11BB) selectively deuterated on the central ring. Starting from a previous evidence of unusual slow dynamics in the isotropic phase (Domenici V. et al., J. Phys. Chem. B 2005, 109, 769), a quantitative and model-supported analysis of the deuterium NMR data is performed here by accounting for slow-motional modulation of the magnetic anisotropies through the full solution of the stochastic Liouville equation. Focusing on the quadrupolar echo experiments performed in the nematic phase, the analysis of the transverse relaxation rate has been carried out by considering single-molecule motions and fluctuations of the local director. The main conclusions are: (a) director fluctuations are not relevant on driving the signal relaxation; (b) molecular reorientations about transverse axes control the dynamic regime of the signal relaxation and impose a full slow-motional treatment; (c) the small amplitude tumbling of the molecule within the wells of orientational potential occurs with characteristic times up to the microsecond. The outcome of our analysis has to be taken as indicative of very slow dynamics concerning out-of-plane motions of the molecules. Besides the specific application, this paper also offers the methodological tools to treat the pulsed deuterium NMR experiment in the slow-motional regime of reorientational motions and provides a detailed comparison with the usually employed fast-motional approximation. PMID:17149909

Domenici, Valentina; Frezzato, Diego; Veracini, Carlo Alberto

2006-12-14

377

Russian national time scale long-term stability  

NASA Technical Reports Server (NTRS)

The Institute of Metrology for Time and Space NPO 'VNIIFTRI' generates the National Time Scale (NTS) of Russia -- one of the most stable time scales in the world. Its striking feature is that it is based on a free ensemble of H-masers only. During last two years the estimations of NTS longterm stability based only on H-maser intercomparison data gives a flicker floor of about (2 to 3) x 10(exp -15) for averaging times from 1 day to 1 month. Perhaps the most significant feature for a time laboratory is an extremely low possible frequency drift -- it is too difficult to estimate it reliably. The other estimations, free from possible inside the ensemble correlation phenomena, are available based on the time comparison of NTS relative to the stable enough time scale of outer laboratories. The data on NTS comparison relative to the time scale of secondary time and frequency standards at Golitzino and Irkutsk in Russia and relative to NIST, PTB and USNO using GLONASS and GPS time transfer links gives stability estimations which are close to that based on H-maser intercomparisons.

Alshina, A. P.; Gaigerov, B. A.; Koshelyaevsky, N. B.; Pushkin, S. B.

1994-01-01

378

Time/scale-adjusted dyadic wavelet packet bases  

NASA Astrophysics Data System (ADS)

This paper generalizes the dyadic wavelet packet bases (DWP), developed by Coifman and Wickerhauser, to time/scale-adjusted DWP bases. These generalized DWP bases provide more flexibility in matching the time-scale characteristics of the input signal. Development of these generalized bases is achieved by combining the previously defined time-invariant DWP bases of Pesquet, Krim, Carfantan, and Proakis with a generalized scale sampling. The generalized scale sampling extends the usual dyadic sampling by adding a real-valued offset parameter to the integer power of two in the scale parameter. This offset parameter value is taken between zero and one. By combining both scale and translation generalizations, signal components existing between consecutive dyadic scales, or consecutive time translations, may be captured. It is shown how these DWP coefficients may be generated from a two step process; first projecting the input signal onto an appropriate space. Then, performing the usual wavelet low and highpass filtering operations, followed by downsampling. The projection operation is shown to be equivalent to a filtering operation. An expression for the filter taps is derived, and basic properties are proven. A translation-invariant transform defined on these scale-adjusted wavelet packets, is developed. An application to transient detection is presented, by developing a transient detector based on this transform. ROC curves, generated by Monte- Carlo simulation, are presented demonstrating detector performance. Detector performance is shown to be independent of the signal translation. It is further shown how matching the basis functions to the time-scale-frequency characteristics of the transient can provide improved detection performance.

del Marco, Stephen P.

1996-03-01

379

Vibrational Energy Relaxation of Benzene Dimer Studied by Picosecond Time-Resolved Infrared-Ultraviolet Pump-Probe Spectroscopy  

NASA Astrophysics Data System (ADS)

The benzene dimer is excited to the CH stretching vibrational levels by a picosecond IR pulse, and the time evolution of the population of the pumped and redistributed levels are probed by (1+1)REMPI with a picosecond UV pulse. In order to accomplish IR excitation localized in the site of the T-shaped dimer, two dimer isotopomers [(1) Top=C_6H_6, Stem=C_6D_6, (2) Top=C_6D_6, Stem=C_6H_6] are used. From the time profiles of the pumped and the relaxed levels, the rate constants of intracluster vibrational redistribution (ICVR) at each site and subsequent vibrational predissociation (VP) are discussed.

Kusaka, R.; Ebata, T.

2010-06-01

380

Anomalous D'yakonov-Perel' spin relaxation in semiconductor quantum wells under a strong magnetic field in the Voigt configuration  

NASA Astrophysics Data System (ADS)

We report an anomalous scaling of the D’yakonov-Perel’ spin relaxation with the momentum relaxation in semiconductor quantum wells under a strong magnetic field in the Voigt configuration. We focus on the case in which the external magnetic field is perpendicular to the spin-orbit-coupling-induced effective magnetic field and its magnitude is much larger than the latter one. It is found that the longitudinal spin relaxation time is proportional to the momentum relaxation time even in the strong-scattering limit, indicating that the D’yakonov-Perel’ spin relaxation demonstrates Elliott-Yafet-like behavior. Moreover, the transverse spin relaxation time is proportional (inversely proportional) to the momentum relaxation time in the strong- (weak-) scattering limit, both in the opposite trends against the well-established conventional D’yakonov-Perel’ spin relaxation behaviors. We further demonstrate that all the above anomalous scaling relations come from the unique form of the effective inhomogeneous broadening.

Zhou, Y.; Yu, T.; Wu, M. W.

2013-06-01

381

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.

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

2013-01-01

382

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

383

Spin-lattice relaxation times for 13C in isotope-enriched glycine accumulated in frog muscle.  

PubMed Central

Spin-lattice relaxation times (T1's) of 13C-enriched glycine accumulated in frog muscles were determined at 1 degrees C by the inversion-recovery (180 degrees -tau-90 degree pulse sequence) method and compared with the values obtained in free solution. The value of T1 for the alpha-13C nucleus of glycine in the tissue was 50% of that obtained in free solution. The observed value for T1 in the tissue was not concentration-dependent, and no difference in chemical shift was observed between tissue and free solution. Quantification of the area under the glycine peak suggested that the observed signal represents at least 80% of the intracellular glycine. An average nuclear Overhauser enhancement of 2.83 for intracellular glycine indicates that the relaxation mechanism within the cell is predominantly dipolar, as in free solution. The value of T1 for the 13C' nucleus of glycine in the tissue was 67% of that in a solution of similar concentration. A quantitative analysis of the findings suggests that the observed difference in the value of T1 between tissue and free solution results from a difference in viscosity. The data provide no evidence either for special organization of intracellular water or for glycine binding. It is proposed that intracellular diffusion coefficients may be determined from measurements of 13C T1's of 13C-enriched intracellular solutes.

Neville, M C; Wyssbrod, H R

1977-01-01

384

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

NASA Astrophysics Data System (ADS)

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

McKenna, Gregory

2013-03-01

385

Scaling Behavior of the Time-Dependent SGEMP Boundary Layer  

Microsoft Academic Search

The analysis and results given here show that boundary layer dynamics obeys very useful scaling laws which permit one solution of the basic equations to hold for many cases. In particular, during the time that the X-ray pulse is linearly rising, or when the pulse time history changes slowly after a rapid rise, (or when the pulse behaves as any

N. J. CarronandC; C. L. Longmire

1978-01-01

386

High quality time-scale modification for speech  

Microsoft Academic Search

We present a new and simple method for speech rate modification that yields high quality rate-modified speech. Earlier algorithms either required a significant amount of computation for good quality output speech or resulted in poor quality rate-modified speech. The algorithm we describe allows arbitrary linear or nonlinear scaling of the time axis. The algorithm operates in the time domain using

Salim Roucos

1985-01-01

387

Short time-scale structural variation in 3C 273  

Microsoft Academic Search

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

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

1999-01-01

388

Current and Future Realizations of Coordinate Time Scales  

NASA Astrophysics Data System (ADS)

Time metrology provides references for experiments in the vicinity of a clock and also for applications in astro-geodetic sciences on extended environments, where time constitutes a coordinate in a space-time coordinate system. Only a coordinate time scale can be the basis of a world-time reference. We adopt a rotating geocentric reference system where the time-coordinate is the geocentric coordinate time. Such a time scale is constructed from a clock ensemble with an appropriate algorithm. The choice of the algorithm will depend on the interval over which the frequency stability is to be assured, on the compromise between frequency stability and accuracy, and should be adapted to the type of standards and the techniques used for their comparison. This algorithm should produce a time scale more stable and accurate than any of the individual participating clocks. To profit at best the quality of the time and frequency standards, algorithms should be in the framework of general relativity. International atomic time (TAI) is a realization of terrestrial time maintained at the Bureau International des Poids et Mesures from data of industrial atomic clocks and primary frequency standards in time metrology laboratories. TAI is calculated from thirty-day data sets and is published monthly with adelay of about 15 days after the last date of data. The frequency stability of TAI at one month is better than 0.4 ×10-15, and its frequency accuracy is of order 10-15. However, long term drifts limit the stability of TAI making it inadequate for some applications. Another atomic time scale is calculated under the acronym TT(BIPMYY) using an algorithm that eliminates the instabilities of TAI. This presentation describes TAI and TT(BIPMYY) and tries to predict their features in view of the progress in atomic physics and technology.

Felicitas Arias, Elisa

2009-05-01

389

Auroral Substorm Time Scales: Seasonal and IMF Variations  

NASA Technical Reports Server (NTRS)

The time scales and phases of auroral substorm, activity are quantied in this study using the hemispheric power computed from Polar Ultraviolet Imager (UVI) images. We have applied this technique to several hundred substorm events and we are able to quantify how the characterist act, of substorms vary with season and IMF Bz orientation. We show that substorm time scales vary more strongly with season than with IMF Bz orientation. The recovery time for substorm. activity is well ordered by whether or not the nightside oral zone is sunlit. The recovery time scales for substorms occurring in the winter and equinox periods are similar and are both roughly a factor of two longer than in summer when the auroral oval is sunlit. Our results support the hypothesis that the ionosphere plays an active role in governing the dynamics of the aurora.

Chua, D.; Parks, G. K.; Brittnacher, M.; Germany, G. A.; Spann, J. F.; Six, N. Frank (Technical Monitor)

2002-01-01

390

On Nonlinear Control Systems with Multiple Time Scales  

Microsoft Academic Search

An order reduction procedure for nonlinear control systems with multiple time scales is introduced. A limit system for the slowest motion describing the situation that all singular perturbation parameters vanish is constructed. For this purpose a refined two-scale averaging method is used in a way that allows a re-iteration. For vanishing control range the results reduce to the well-known Tychonoff

G. Grammel

2004-01-01

391

Short time scale monitoring of SiO sources  

Microsoft Academic Search

We present the results of a short time scale monitoring of SiO maser emission\\u000a(v=1 J=1-0 transition) in four known strong sources. These sources were\\u000amonitored nightly for a period of about a month. The aim of these observations\\u000ais to investigate the possible presence of variations in the maser lines on\\u000atime scales of a few days to weeks,

F. P. Pijpers; J. R. Pardo; V. Bujarrabal

1994-01-01

392

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

393

On the nature of slow ?-relaxation in supercooled liquids  

NASA Astrophysics Data System (ADS)

We propose a model for reorientational motions of molecules associated with secondary beta-relaxation in supercooled liquids. The secondary relaxation is attributed to relaxation within a given local minimum, while the primary relaxation is attributed to transitions between distinct free-energy minima. We find that (i) at the temperature where the peak frequency of the extrapolated beta-relaxation intersects the alpha-relaxation, the actual and the extrapolated spectra differ in their time constants by approximately one decade; (ii) there is no clear division between the imaginary part of the dielectric susceptibility for the alpha- and the beta-relaxation for temperatures larger than 1.1 Tg. Thus, one must proceed with caution to extrapolate low temperature data of beta-relaxation to higher temperatures in order to estimate the temperature at which the time scales for the two processes cross. The relaxation times for the alpha- and the beta-processes cannot cross except at high temperature, where only the primary relaxation remains.

Mohanty, Udayan; Diezemann, Gregor; Oppenheim, Irwin

2000-07-01

394

The timing of eukaryotic evolution: Does a relaxed molecular clock reconcile proteins and fossils?  

Microsoft Academic Search

The use of nucleotide and amino acid sequences allows improved understanding of the timing of evolutionary events of life on earth. Molecular estimates of divergence times are, however, controversial and are generally much more ancient than suggested by the fossil record. The limited number of genes and species explored and pervasive variations in evolutionary rates are the most likely sources

Emmanuel J. P. Douzery; Elizabeth A. Snell; Eric Bapteste; Frédéric Delsuc; Hervé Philippe

2004-01-01

395

Tensile Plasticity in Metallic Glasses with Pronounced ? Relaxations  

NASA Astrophysics Data System (ADS)

Metallic glasses are commonly brittle, as they generally fail catastrophically under uniaxial tension. Here we show pronounced macroscopic tensile plasticity achieved in a La-based metallic glass which possesses strong ? relaxations and nanoscale heterogeneous structures. We demonstrate that the ? relaxation is closely correlated with the activation of the structural units of plastic deformations and global plasticity, and the transition from brittle to ductile in tension and the activation of the ? relaxations follow a similar time-temperature scaling relationship. The results have implications for understanding the mechanisms of plastic deformation and structural origin of ? relaxations as well as for solving the brittleness in metallic glasses.

Yu, H. B.; Shen, X.; Wang, Z.; Gu, L.; Wang, W. H.; Bai, H. Y.

2012-01-01

396

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

Microsoft Academic Search

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

Eric Moulines; Jean Laroche

1995-01-01

397

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

PubMed

Time-resolved photoelectron imaging was used to investigate the relaxation dynamics of electronically excited aniline in the gas-phase following ultraviolet irradiation in the 273-266 nm region. We find that at all wavelengths studied, excitation is predominantly to the long-lived (>1 ns) S1(??(*)) state, which exhibits ultrafast intramolecular vibrational redistribution on a <1 ps timescale. At excitation wavelengths centred on resonant transitions in the aniline absorption spectrum that have previously been assigned to the higher lying S2(3s???(*)) state, we also see clear evidence of this state playing a role in the dynamics. However, we see no indication of any non-adiabatic coupling between the S1(??(*)) and S2(3s???(*)) states over the range of excitation wavelengths studied. PMID:23883036

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

2013-07-21

398

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

NASA Astrophysics Data System (ADS)

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

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

2013-07-01

399

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

SciTech Connect

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

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

2013-07-22

400

A longitudinally detected high-field ESR spectrometer for the measurement of spin-lattice relaxation times.  

PubMed

We describe a high-field longitudinally detected electron spin resonance (LOD-ESR) spectrometer operating at 35 and 75 GHz. The lack of resonant microwave circuits facilitates operation at different microwave frequencies without changing the probehead. A very low noise radio frequency detection compensates partially the resulting low sensitivity. The major elements of the LOD-ESR spectrometer are commercially available and may be adapted to usual high frequency spectrometers. The instrument allows field and frequency dependent spin lattice relaxation time (T1) studies. T1 in the range of 2-80 ns can be determined from the phase sensitively detected LOD-ESR spectra. We demonstrate the performance of the apparatus by the measurement of T1 in the normal state of RbC60, an electrically conducting alkaline fulleride polymer. PMID:15040977

Murányi, Ferenc; Simon, Ferenc; Fülöp, Ferenc; Jánossy, András

2004-04-01

401

Experimental study of electric field influence on low-temperature, long-time relaxation in crystalline ferroelectrics  

NASA Astrophysics Data System (ADS)

Calorimetric measurements with polycrystalline Pb0.915La0.085. (Zr0.65Ti0.35)O3 were performed at liquid helium temperatures in an electric field E (0? E?4.3 kV/cm). Heat released after cooling from T 1 (1.3 K< T 1?35 K) to T 0=1.3 K is very similar to that in amorphous metals and dielectrics. Experimental results disagree with the standard tunneling model. The observed heat release may be explained assuming the existence of a maximum energy ? f in the distribution function. The maximum relaxation time ?max was found as a function of T 1. A similar heat release is observed after switching on or off the electric field, independent of T for 1.1 K? T?3 K, proportional to E 2 with ?max˜ E. No heat release was observed in the KH2PO4 single crystal.

Sahling, S.; Kolá?, M.; Sahling, A.

1988-12-01

402

Slow secondary relaxation in a free-energy landscape model for relaxation in glass-forming liquids  

NASA Astrophysics Data System (ADS)

Within the framework of a free-energy landscape model for the relaxation in supercooled liquids the primary (?) relaxation is modeled by transitions among different free-energy minima. The secondary (?) relaxation then corresponds to intraminima relaxation. We consider a simple model for the reorientational motions of the molecules associated with both processes and calculate the dielectric susceptibility as well as the spin-lattice relaxation times. The parameters of the model can be chosen in a way that both quantities show a behavior similar to that observed in experimental studies on supercooled liquids. In particular we find that it is not possible to obtain a crossing of the time scales associated with ? and ? relaxation. In our model these processes always merge at high temperatures and the ? process remains above the merging temperature. The relation to other models is discussed.

Diezemann, Gregor; Mohanty, Udayan; Oppenheim, Irwin

1999-02-01

403

Vibrational energy relaxation of benzene dimer and trimer in the CH stretching region studied by picosecond time-resolved IR-UV pump-probe spectroscopy  

NASA Astrophysics Data System (ADS)

Vibrational energy relaxation (VER) of the Fermi polyads in the CH stretching vibration of the benzene dimer (Bz2) and trimer (Bz3) has been investigated by picosecond (ps) time-resolved IR-UV pump-probe spectroscopy in a supersonic beam. The vibrational bands in the 3000-3100 cm-1 region were excited by a ps IR pulse and the time evolutions at the pumped and redistributed (bath) levels were probed by resonance enhanced multiphoton ionization with a ps UV pulse. For Bz2, a site-selective excitation in the T-shaped structure was achieved by using the isotope-substituted heterodimer hd, where h = C6H6 and d = C6D6, and its result was compared with that of hh homodimer. In the hd heterodimer, the two isomers, h(stem)d(top) and h(top)d(stem), show remarkable site-dependence of the lifetime of intracluster vibrational energy redistribution (IVR); the lifetime of the Stem site [h(stem)d(top), 140-170 ps] is ~2.5 times shorter than that of the Top site [h(top)d(stem), 370-400 ps]. In the transient UV spectra, a broad electronic transition due to the bath modes emerges and gradually decays with a nanosecond time scale. The broad transition shows different time profile depending on UV frequency monitored. These time profiles are described by a three-step VER model involving IVR and vibrational predissociation: initial --> bath1(intramolecular) --> bath2(intermolecular) --> fragments. This model also describes well the observed time profile of the Bz fragment. The hh homodimer shows the stepwise VER process with time constants similar to those of the hd dimer, suggesting that the excitation-exchange coupling of the vibrations between the two sites is very weak. Bz3 also exhibited the stepwise VER process, though each step is faster than Bz2.

Kusaka, Ryoji; Inokuchi, Yoshiya; Ebata, Takayuki

2012-01-01

404

An algorithm for the Italian atomic time scale  

NASA Technical Reports Server (NTRS)

During the past twenty years, the time scale at the IEN has been realized by a commercial cesium clock, selected from an ensemble of five, whose rate has been continuously steered towards UTC to maintain a long term agreement within 3 x 10(exp -13). A time scale algorithm, suitable for a small clock ensemble and capable of improving the medium and long term stability of the IEN time scale, has been recently designed taking care of reducing the effects of the seasonal variations and the sudden frequency anomalies of the single cesium clocks. The new time scale, TA(IEN), is obtained as a weighted average of the clock ensemble computed once a day from the time comparisons between the local reference UTC(IEN) and the single clocks. It is foreseen to include in the computation also ten cesium clocks maintained in other Italian laboratories to further improve its reliability and its long term stability. To implement this algorithm, a personal computer program in Quick Basic has been prepared and it has been tested at the IEN time and frequency laboratory. Results obtained using this algorithm on the real clocks data relative to a period of about two years are presented.

Cordara, F.; Vizio, G.; Tavella, P.; Pettiti, V.

1994-01-01

405

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

406

Large-scale fluctuations in underground muon time series  

SciTech Connect

We study the self-affine properties of intensity fluctuations of underground muons generated by primary cosmic rays of rigiditygreater than or equal to1600 GV. The muon time series were recorded at a vertical depth of 570 Hg/cm/sup 2/ during the years 1981--1983. This time interval includes a period of intense solar activity in the summer of 1982 which was characterized by the creation of large solar wind shocks and associated production of major interplanetary disturbances. The purpose of our analysis is to obtain from the behavior of the muon intensity some insight into the large-scale behavior of interplanetary magnetic field fluctuations and their effects on the propagation of high-rigidity galactic cosmic rays. The results give good evidence for fractal behavior of large-scale muon fluctuations in the range from a few hours to more than 10 days, with scaling exponent H varying according to the time interval analyzed. We find that the large time scale muon fluctuations evolve from a preshock condition in late 1981 to early 1982 characterized by a scaling exponent H = 0.28 and power spectrum f/sup -1.6/ to a condition with H = 0.07 and an f/sup 1.1/ power spectrum during the most intense solar activity in 1982, followed by a slow return in 1983 to the original preshock conditions (H = 0.14, f/sup -1.3/).

Bergamasco, L.; Provenzale, A.; Osborne, A.R.; Castagnoli, G.C.; Kudryavtsev, V.A.; Kuznetsov, V.A.; Ryazhkaya, O.G.

1989-03-01

407

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

408

Crystallization time scales for polydisperse hard-sphere fluids  

NASA Astrophysics Data System (ADS)

We study the evolution of crystallization in dense mono- and polydisperse hard sphere fluids, initially quenched to an amorphous configuration. We use as signatures of crystallization both the decay of the reduced pressure Z and the increase in the local and global orientational order parameters Q¯6. For a given realization of the crystallization process these parameters show sudden changes, both large and small, separated by long periods of quiescence. However, averaging over a large number of realizations, a well-defined scenario for their evolution appears. We find an initial fast relaxation to a disordered state, followed by a period of slow variation, associated to the presence of nucleation events, followed by a fast change, composed of the growth of a few crystals with different orientations, and a final and slow coarsening in a domain-growth process. No clear scaling for this whole process was found. We also find that the transition to an stable glassy fluid is quite sharp as the polydispersity is increased, showing a probable first-order phase transition behavior. A well-defined boundary between crystallizing and permanently amorphous fluids should exist, at least for a region in packing fractions. We looked for segregation at large values of polydispersity, but no effects of this type were found.

Vargas, M. Cristina; Pérez-Ángel, Gabriel

2013-04-01

409

The Galaxy Viewed at Very Short Time-Scales  

NASA Astrophysics Data System (ADS)

We present high time-resolution astronomical observations recorded with the Berkeley Visible Image Tube (BVIT) photon counting detector mounted on the 10m South African Large Telescope (SALT). Relative B and V-band photometric fluxes were obtained as a function of time for targets that included Polar-type cataclysmic variables (UZ For, OY Car, V1033Cen), low-mass X-ray bin