Pair plasma relaxation time scales.
Aksenov, A G; Ruffini, R; Vereshchagin, G V
2010-04-01
By numerically solving the relativistic Boltzmann equations, we compute the time scale for relaxation to thermal equilibrium for an optically thick electron-positron plasma with baryon loading. We focus on the time scales of electromagnetic interactions. The collisional integrals are obtained directly from the corresponding QED matrix elements. Thermalization time scales are computed for a wide range of values of both the total-energy density (over 10 orders of magnitude) and of the baryonic loading parameter (over 6 orders of magnitude). This also allows us to study such interesting limiting cases as the almost purely electron-positron plasma or electron-proton plasma as well as intermediate cases. These results appear to be important both for laboratory experiments aimed at generating optically thick pair plasmas as well as for astrophysical models in which electron-positron pair plasmas play a relevant role. PMID:20481841
Resistivity scaling and electron relaxation times in metallic nanowires
Moors, Kristof, E-mail: kristof@itf.fys.kuleuven.be [Instituut voor Theoretische Fysica, KU Leuven, Celestijnenlaan 200D, B-3001 Leuven (Belgium); Imec, Kapeldreef 75, B-3001 Leuven (Belgium); Sorée, Bart; Magnus, Wim [Imec, Kapeldreef 75, B-3001 Leuven (Belgium); Physics Department, Universiteit Antwerpen, Groenenborgerlaan 171, B-2020 Antwerpen (Belgium); T?kei, Zsolt [Imec, Kapeldreef 75, B-3001 Leuven (Belgium)
2014-08-14
We study the resistivity scaling in nanometer-sized metallic wires due to surface roughness and grain-boundaries, currently the main cause of electron scattering in nanoscaled interconnects. The resistivity has been obtained with the Boltzmann transport equation, adopting the relaxation time approximation of the distribution function and the effective mass approximation for the conducting electrons. The relaxation times are calculated exactly, using Fermi's golden rule, resulting in a correct relaxation time for every sub-band state contributing to the transport. In general, the relaxation time strongly depends on the sub-band state, something that remained unclear with the methods of previous work. The resistivity scaling is obtained for different roughness and grain-boundary properties, showing large differences in scaling behavior and relaxation times. Our model clearly indicates that the resistivity is dominated by grain-boundary scattering, easily surpassing the surface roughness contribution by a factor of 10.
Transport relaxation time and length scales in turbulent suspensions
P. Claudin; F. Charru; B. Andreotti
2010-11-03
We show that in a turbulent flow transporting suspended sediment, the unsaturated sediment flux $q(x,t)$ can be described by a first-order relaxation equation. From a mode analysis of the advection-diffusion equation for the particle concentration, the relaxation length and time scales of the dominant mode are shown to be the deposition length $H U/V_{\\rm fall}$ and deposition time $H/V_{\\rm fall}$, where $H$ is the flow depth, $U$ the mean flow velocity and $V_{\\rm fall}$ the sediment settling velocity. This result is expected to be particularly relevant for the case of sediment transport in slowly varying flows, where the flux is never far from saturation. Predictions are shown to be in quantitative agreement with flume experiments, for both net erosion and net deposition situations.
Coupled relaxations at the protein–water interface in the picosecond time scale
Paciaroni, A.; Cornicchi, E.; Marconi, M.; Orecchini, A.; Petrillo, C.; Haertlein, M.; Moulin, M.; Sacchetti, F.
2009-01-01
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. PMID:19640876
NASA Astrophysics Data System (ADS)
Umanodan, Tsugumi; Tanaka, Sei'ichi; Naruse, Suguru; Ishikawa, Tadahiko; Onda, Ken; Koshihara, Shin-ya; Horiuchi, Sachio; Okimoto, Yoichi
2015-07-01
Time-resolved linear and nonlinear optical responses were investigated in an organic supramolecular ferroelectric material composed of protonated 2,3-di(2-pyridinyl)pyrazine (H-dppz) and deprotonated chloranilic acid (Hca). We irradiated nanosecond laser pulses (? = 532 nm) on the crystal, pumped the intramolecular excitation of the Hca molecule, and observed a clear redshift of the molecular vibrational modes of C=O and C-O- just after the photoexcitation. Each softened mode gradually relaxed on different time scales, indicating that the electrons of the Hca molecules were redistributed after the photoexcitation. By the same excitation, a large suppression of the second-harmonic (SH) intensity was observed, driven by the macroscopic disordering of the transferred protons. The decay time of the SH intensity was longer than those of the vibrational modes, suggesting that the microscopic vibrations and macroscopic ferroelectricity have dynamics on different time scales.
NASA Astrophysics Data System (ADS)
Kushima, A.; Eapen, J.; Li, Ju; Yip, S.; Zhu, T.
2011-08-01
Atomistic simulation methods are known for timescale limitations in resolving slow dynamical processes. Two well-known scenarios of slow dynamics are viscous relaxation in supercooled liquids and creep deformation in stressed solids. In both phenomena the challenge to theory and simulation is to sample the transition state pathways efficiently and follow the dynamical processes on long timescales. We present a perspective based on the biased molecular simulation methods such as metadynamics, autonomous basin climbing (ABC), strain-boost and adaptive boost simulations. Such algorithms can enable an atomic-level explanation of the temperature variation of the shear viscosity of glassy liquids, and the relaxation behavior in solids undergoing creep deformation. By discussing the dynamics of slow relaxation in two quite different areas of condensed matter science, we hope to draw attention to other complex problems where anthropological or geological-scale time behavior can be simulated at atomic resolution and understood in terms of micro-scale processes of molecular rearrangements and collective interactions. As examples of a class of phenomena that can be broadly classified as materials ageing, we point to stress corrosion cracking and cement setting as opportunities for atomistic modeling and simulations.
Measurement of magnetic nanoparticle relaxation time
Weaver, John B.; Kuehlert, Esra
2012-01-01
Purpose: Nanoparticle relaxation time measurements have many applications including characterizing molecular binding, viscosity, heating, and local matrix stiffness. The methods capable of in vivo application are extremely limited. The hypothesis investigated by the authors was that the relaxation time could be measured quantitatively using magnetic spectroscopy of nanoparticle Brownian motion (MSB). Methods: The MSB signal (1) reflects the nanoparticle rotational Brownian motion, (2) can be measured from very low nanoparticle concentrations, and (3) is a function of the product of the drive frequency and the relaxation time characterizing Brownian motion. To estimate the relaxation time, the MSB signal was measured at several frequencies. The MSB signal for nanoparticles with altered relaxation time is a scaled version of that for reference nanoparticles with a known relaxation time. The scaling factor linking the altered and reference MSB measurements is the same factor linking the altered and reference relaxation times. The method was tested using glycerol solutions of varying viscosities to obtain continuously variable relaxation times. Results: The measured relaxation time increased with increasing viscosity of the solution in which the nanoparticles resided. The MSB estimated relaxation time matched the calculated relaxation times based on viscosity with 2% average error. Conclusions: MSB can be used to monitor the nanoparticle relaxation time quantitatively through a scale space correlation of the MSB signal as a function of frequency. PMID:22559648
Long spin relaxation times in wafer scale epitaxial graphene on SiC(0001).
Maassen, Thomas; van den Berg, J Jasper; Ijbema, Natasja; Fromm, Felix; Seyller, Thomas; Yakimova, Rositza; van Wees, Bart J
2012-03-14
We developed an easy, upscalable process to prepare lateral spin-valve devices on epitaxially grown monolayer graphene on SiC(0001) and perform nonlocal spin transport measurements. We observe the longest spin relaxation times ?(S) in monolayer graphene, while the spin diffusion coefficient D(S) is strongly reduced compared to typical results on exfoliated graphene. The increase of ?(S) is probably related to the changed substrate, while the cause for the small value of D(S) remains an open question. PMID:22324998
Relaxation time in disk galaxy simulations.
NASA Technical Reports Server (NTRS)
Hohl, F.
1973-01-01
An initially stationary and stable axisymmetric disk of stars with a mass spectrum of stars is used to determine the collisional relaxation time. The relaxation time as determined from the rate of energy equipartition was found to be 560 rotation periods for stars with 10 times the mean star mass and was 1700 rotation periods for stars with 0.55 times the mean star mass. These times are in general agreement with theoretical predictions for the relaxation time of the two mass groups. The results show that the model used for the large-scale gravitational N-body calculations is indeed 'collisionless.'
Xue, Yi; Ward, Joshua M; Yuwen, Tairan; Podkorytov, Ivan S; Skrynnikov, Nikolai R
2012-02-01
With the advent of ultra-long MD simulations it becomes possible to model microsecond time-scale protein dynamics and, in particular, the exchange broadening effects (R(ex)) as probed by NMR relaxation dispersion measurements. This new approach allows one to identify the exchanging species, including the elusive "excited states". It further helps to map out the exchange network, which is potentially far more complex than the commonly assumed 2- or 3-site schemes. Under fast exchange conditions, this method can be useful for separating the populations of exchanging species from their respective chemical shift differences, thus paving the way for structural analyses. In this study, recent millisecond-long MD trajectory of protein BPTI (Shaw et al. Science 2010, 330, 341) is employed to simulate the time variation of amide (15)N chemical shifts. The results are used to predict the exchange broadening of (15)N lines and, more generally, the outcome of the relaxation dispersion measurements using Carr-Purcell-Meiboom-Gill sequence. The simulated R(ex) effect stems from the fast (~10-100 ?s) isomerization of the C14-C38 disulfide bond, in agreement with the prior experimental findings (Grey et al. J. Am. Chem. Soc. 2003, 125, 14324). PMID:22206299
Liang, Binyong; Arora, Ashish; Tamm, Lukas K.
2009-01-01
In order to better understand the dynamics of an integral membrane protein, backbone amide 15N NMR dynamics measurements of the ?-barrel membrane protein OmpA have been performed at three magnetic fields. A total of nine relaxation data sets were globally analyzed using an extended model-free formalism. The diffusion tensor was found to be prolate axially symmetric with an axial ratio of 5.75, indicating a possible rotation of the protein within the micelle. The generalized order parameters gradually decreased from the mid-plane towards the two ends of the barrel, counteracting the dynamic gradient of the lipids in a matching bilayer, and were dramatically reduced in the extracellular loops. Large-scale internal motions on the ns time scale indicate that entire loops most likely undergo concerted (“sea anemone”-like) motions emanating from their anchoring points on the barrel. The case of OmpA in DPC micelles also illustrates inherent limitations of analyzing the data with even the most sophisticated current models of the model-free formalism. It is likely that conformational exchange processes on the ms-µs also play a role in describing the motions of some residues, but their analysis did not produce unique results that could be independently verified. PMID:19665446
NASA Astrophysics Data System (ADS)
Pasko, V. P.
2009-12-01
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].
Alistar Ottochian; Dino Leporini
2011-01-14
The scaling of the slow structural relaxation with the fast caged dynamics is evidenced in the molten salt Ca_{0.4}K_{0.6}(NO_{3}$)_{1.4} (CKN) over about thirteen decades of the structural relaxation time. Glycerol caling was analyzed in detail. In glycerol, the short-time mean-square displacement , a measure of the caged dynamics, is contributed by free-volume. It is seen that, in order to evidence the scaling, the observation time of the fast dynamics must be shorter than the time scales of the relaxation processes. Systems with both negligible (like CKN, glycerol and network glassformers) and high (like van der Waals liquids and polymers) pressure-energy correlations exhibit the scaling between the slow relaxation and the fast caged dynamics. According to the available experiments, an isomorph-invariant expression of the master curve of the scaled data is not distinguishable from a simpler not-invariant expression. Instead, the latter grees better with the simulations on a wide class of model polymers.
Nitrogen rotation relaxation time measured in freejets
A. E. Belikov; G. I. Sukhinin; R. G. Sharafutdinov
1989-01-01
Rotational relaxation times for N2 molecules in free jets of nitrogen over the temperature range of 6-360 K have been measured by the electron beam diagnostics method. This is the first time these relaxation times have been obtained for T = 6-80 K. Numerous comparisons are given between the results on relaxation times obtained in shock waves, ultrasonic measurements, transport
Myomectomy reduces endometrial T2 relaxation times.
Yoshino, Osamu; Hori, Masaaki; Osuga, Yutaka; Hayashi, Toshihiko; Sadoshima, Yoko; Tsuchiya, Hiroko; Nishii, Osamu; Taketani, Yuji
2011-06-30
Magnetic resonance imaging was used to measure the endometrial T2 relaxation times of patients with infertility with fibroma. Although the location of fibromas did not influence the T2 relaxation times, we did observe a significant decrease in endometrial T2 relaxation times after myomectomy. PMID:21315332
NASA Astrophysics Data System (ADS)
Gao, Hayian
2004-10-01
The next generation of searches for the neutron electric dipole moment using ultra cold neutrons will use polarized ^3He as a co-magnetometer. The first such experiment has been proposed, with a goal of improving the current limit on the neutron EDM by two orders of magnitude. This experiment requires a systematic study of the properties of polarized ^3He at cryogenic temperatures under actual experimental conditions. These experimental conditions include polarized ^3He mixed in a bath of superfluid ^4He in low magnetic field and held in an acrylic cell which is coated with deuterated TetraphenylButadiene . Parts of these systematic studies will be done at Duke University using a newly built, novel refillable double cell ^3 He polarizer based on spin exchange optical pumping with Rubidium vapor. The polarimetry for this apparatus is done with a NMR polarimeter using the adiabatic fast passage method. An alternate polarimeter using free induction decay method is also being built. This apparatus is being used to study the relaxation time and other critical properties of polarized ^3He at temperatures ranging from 2.3 - 4.2 K, under simulated experimental conditions. We will present details about this novel polarizer and show preliminary results of our measurements.
A quantum relaxation-time approximation for finite fermion systems
NASA Astrophysics Data System (ADS)
Reinhard, P.-G.; Suraud, E.
2015-03-01
We propose a relaxation time approximation for the description of the dynamics of strongly excited fermion systems. Our approach is based on time-dependent density functional theory at the level of the local density approximation. This mean-field picture is augmented by collisional correlations handled in relaxation time approximation which is inspired from the corresponding semi-classical picture. The method involves the estimate of microscopic relaxation rates/times which is presently taken from the well established semi-classical experience. The relaxation time approximation implies evaluation of the instantaneous equilibrium state towards which the dynamical state is progressively driven at the pace of the microscopic relaxation time. As test case, we consider Na clusters of various sizes excited either by a swift ion projectile or by a short and intense laser pulse, driven in various dynamical regimes ranging from linear to strongly non-linear reactions. We observe a strong effect of dissipation on sensitive observables such as net ionization and angular distributions of emitted electrons. The effect is especially large for moderate excitations where typical relaxation/dissipation time scales efficiently compete with ionization for dissipating the available excitation energy. Technical details on the actual procedure to implement a working recipe of such a quantum relaxation approximation are given in appendices for completeness.
Probing relaxation times in graphene quantum dots
Volk, Christian; Neumann, Christoph; Kazarski, Sebastian; Fringes, Stefan; Engels, Stephan; Haupt, Federica; Müller, André; Stampfer, Christoph
2013-01-01
Graphene quantum dots are attractive candidates for solid-state quantum bits. In fact, the predicted weak spin-orbit and hyperfine interaction promise spin qubits with long coherence times. Graphene quantum dots have been extensively investigated with respect to their excitation spectrum, spin-filling sequence and electron-hole crossover. However, their relaxation dynamics remain largely unexplored. This is mainly due to challenges in device fabrication, in particular concerning the control of carrier confinement and the tunability of the tunnelling barriers, both crucial to experimentally investigate decoherence times. Here we report pulsed-gate transient current spectroscopy and relaxation time measurements of excited states in graphene quantum dots. This is achieved by an advanced device design that allows to individually tune the tunnelling barriers down to the low megahertz regime, while monitoring their asymmetry. Measuring transient currents through electronic excited states, we estimate a lower bound for charge relaxation times on the order of 60–100?ns. PMID:23612294
Alternate Forms Reliability of the Behavioral Relaxation Scale: Preliminary Results
ERIC Educational Resources Information Center
Lundervold, Duane A.; Dunlap, Angel L.
2006-01-01
Alternate forms reliability of the Behavioral Relaxation Scale (BRS; Poppen,1998), a direct observation measure of relaxed behavior, was examined. A single BRS score, based on long duration observation (5-minute), has been found to be a valid measure of relaxation and is correlated with self-report and some physiological measures. Recently,…
Relaxation time of non-conformal plasma
Alex Buchel
2009-11-27
We study effective relaxation time of viscous hydrodynamics of strongly coupled non-conformal gauge theory plasma using gauge theory/string theory correspondence. We compute leading corrections to the conformal plasma relaxation time from the relevant deformations due to dim-2 and dim-3 operators. We discuss in details the relaxation time tau_eff of N=2^* plasma. For a certain choice of masses this theory undergoes a phase transition with divergent specific heat c_V ~ |1-T_c/T|^(-1/2). Although the bulk viscosity remains finite all the way to the critical temperature, we find that tau_eff diverges near the critical point as tau_eff ~ |1-T_c/T|^(-1/2).
Spin-Lattice Relaxation Times in 1H NMR Spectroscopy.
ERIC Educational Resources Information Center
Wink, Donald J.
1989-01-01
Discussed are the mechanisms of nuclear magnetic relaxation, and applications of relaxation times. The measurement of spin-lattice relaxations is reviewed. It is stressed that sophisticated techniques such as these are becoming more important to the working chemist. (CW)
NASA Astrophysics Data System (ADS)
Uneyama, Takashi; Akimoto, Takuma; Miyaguchi, Tomoshige
2012-09-01
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.
Ageing and relaxation times in disordered insulators
NASA Astrophysics Data System (ADS)
Grenet, T.; Delahaye, J.; Cheynet, M. C.
2012-07-01
We focus on the slow relaxations observed in the conductance of disordered insulators at low temperature (especially granular aluminum films). They manifest themselves as a temporal logarithmic decrease of the conductance after a quench from high temperatures and the concomitant appearance of a field effect anomaly centered on the gate voltage maintained. We are first interested in ageing effects, i.e. the age dependence of the dynamical properties of the system. We stress that the formation of a second field effect anomaly at a different gate voltage is not a "history free" logarithmic (lnt) process, but departs from lnt in a way which encodes the system's age. The apparent relaxation time distribution extracted from the observed relaxations is thus not "constant" but evolves with time. We discuss what defines the age of the system and what external perturbation out of equilibrium does or does not rejuvenate it. We further discuss the problem of relaxation times and comment on the commonly used "two dip" experimental protocol aimed at extracting "characteristic times" for the glassy systems (granular aluminum, doped indium oxide...). We show that it is inoperable for systems like granular Al and probably highly doped InOx where it provides a trivial value only determined by the experimental protocol. But in cases where different values are obtained like in lightly doped InOx or some ultra thin metal films, potentially interesting information can be obtained, possibly about the "short time" dynamics of the different systems. Present ideas about the effect of doping on the glassiness of disordered insulators may also have to be reconsidered.
Scaling behaviour of relaxation dependencies in metaloxide superconductors
NASA Technical Reports Server (NTRS)
Sidorenko, A. S.; Panaitov, G. I.; Gabovich, A. M.; Moiseev, D. P.; Postnikov, V. M.
1990-01-01
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.
Relaxation time measurements by an electronic method.
NASA Technical Reports Server (NTRS)
Brousseau, R.; Vanier, J.
1973-01-01
Description of a simple electronic system that permits the direct measurement of time constants of decaying signals. The system was used in connection with relaxation experiments on hydrogen and rubidium masers and was found to operate well. The use of a computing counter in the systems gives the possibility of making averages on several experiments and obtaining the standard deviation of the results from the mean. The program for the computing counter is given.
Are vibrational relaxation times really constant? I. The vibrational relaxation of N 2O
NASA Astrophysics Data System (ADS)
Baalbaki, Z.; Teitelbaum, H.
1986-04-01
The vibrational relaxation of pure N 2O was studied behind shock waves in the temperature range 450-1750 K using a laser beam deflection technique. It is shown that the phenomenological relaxation time,?', is not a time-independent constant. Below 1200 K it increases with time; above 1200 K it decreases with time. The many disparate results in the literature are reconciled in terms of a mechanism whereby the step N 2O(0, 0, 0) ? N 2O(0, 1, 0) is rate determining at low temperatures when the ? 3 mode is not involved, and the parallel step N 2O(1, 0, 0) + N 2O(0, 0, 0) ? N 2O(0, 2, 0) + N 2O(0, 1, 0) takes over at high temperatures close to equilibrium. Rate constants for these processes are extracted from the limiting far-from equilibrium relaxation time, i.e. from ?'(0), where log p?'(0) = 11.0 T-1/3-1.67 (in atm ?s), and from the limiting near-equilibrium relaxation time, i.e. from ?'(?), where log p?'(?) = 19.4 T-1/3-2.46 (in atm ?s). The relaxation process was simulated by solving the master equation numerically. All energy levels up to 5930 cm -1 connected by all possible V?T and inter- and intra-molecular V?V processes were included, subject to the restriction that the energy gap ¦??¦ 700 cm -1. Microscopic rate coefficients, scaled according to ? exp(- C ¦??¦), were assigned, reducing the problem to one of three parameters: C (for V?T processes), CVV (for V?V processes) and k0110/ k10, where k10 is the rate constant for N 2O(0, 1, 0) ? N 2O(0, 0, 0) and k0110 that for N 2O(0, 0, 0) + N 2O(0, 1, 0) ? N 2O(0, 0, 0)+N 2O(0,1,0). Computer simulations of shock-induced and laser-induced relaxation are made. They are interpreted in terms of the three parameters. There was semi-quantitative agreement with our experimental results, which are consistent with values for C = 0.0038 cm at room temperature; CVV = 0.021 ? 0.0065 cm, and k0110/ k10 ? 5000 ? 12.7 in the range 300 ? 1800 K. It was further found that intermolecular V?V processes are responsible for the time dependence of ?', and that the increasing density of states accessible at longer times and at higher temperatures is responsible for the change in mechanism.
Relaxation Mode Analysis and Scale-Dependent Energy Landscape Statistics in Liquids
NASA Astrophysics Data System (ADS)
Cai, Zhikun; Zhang, Yang
2015-03-01
In contrast to the prevailing focus on short-lived classical phonon modes in liquids, we propose a classical treatment of the relaxation modes in liquids under a framework analogous to the normal mode analysis in solids. Our relaxation mode analysis is built upon the experimentally measurable two-point density-density correlation function (e.g. using quasi-elastic and inelastic scattering experiments). We show in the Laplace-inverted relaxation frequency z-domain, the eigen relaxation modes are readily decoupled. From here, important statistics of the scale-dependent activation energy in the energy landscape as well as the scale-dependent relaxation time distribution function can be obtained. We first demonstrate this approach in the case of supercooled liquids when dynamic heterogeneity emerges in the landscape-influenced regime. And then we show, using this framework, we are able to extract the scale-dependent energy landscape statistics from neutron scattering measurements.
G. C Borgia; V Bortolotti; R. J. S Brown; P Fantazzini
1998-01-01
A method is presented for approximating fractional power averages of relaxation times for data equispaced in log time, without the need to invert multiexponential relaxation data. This form of average permits giving emphasis to short or long times depending on the choice of the p value, thus giving the possibility of representing different specific properties of porous media. This method
Occupational Cohort Time Scales
Roth, H. Daniel
2015-01-01
Purpose: This study explores how highly correlated time variables (occupational cohort time scales) contribute to confounding and ambiguity of interpretation. Methods: Occupational cohort time scales were identified and organized through simple equations of three time scales (relational triads) and the connections between these triads (time scale web). The behavior of the time scales was examined when constraints were imposed on variable ranges and interrelationships. Results: Constraints on a time scale in a triad create high correlations between the other two time scales. These correlations combine with the connections between relational triads to produce association paths. High correlation between time scales leads to ambiguity of interpretation. Conclusions: Understanding the properties of occupational cohort time scales, their relational triads, and the time scale web is helpful in understanding the origins of otherwise obscure confounding bias and ambiguity of interpretation. PMID:25647318
2010-01-01
To study microsecond processes by relaxation dispersion NMR spectroscopy, low power deposition and short pulses are crucial and encourage the development of experiments that employ 1H Carr?Purcell?Meiboom?Gill (CPMG) pulse trains. Herein, a method is described for the comprehensive study of microsecond to millisecond time scale dynamics of methyl groups in proteins, exploiting their high abundance and favorable relaxation properties. In our approach, protein samples are produced using [1H, 13C]-d-glucose in ?100% D2O, which yields CHD2 methyl groups for alanine, valine, threonine, isoleucine, leucine, and methionine residues with high abundance, in an otherwise largely deuterated background. Methyl groups in such samples can be sequence-specifically assigned to near completion, using 13C TOCSY NMR spectroscopy, as was recently demonstrated (Otten, R.; et al. J. Am. Chem. Soc.2010, 132, 2952?2960). In this Article, NMR pulse schemes are presented to measure 1H CPMG relaxation dispersion profiles for CHD2 methyl groups, in a vein similar to that of backbone relaxation experiments. Because of the high deuteration level of methyl-bearing side chains, artifacts arising from proton scalar coupling during the CPMG pulse train are negligible, with the exception of Ile-?1 and Thr-?2 methyl groups, and a pulse scheme is described to remove the artifacts for those residues. Strong 13C scalar coupling effects, observed for several leucine residues, are removed by alternative biochemical and NMR approaches. The methodology is applied to the transcriptional activator NtrCr, for which an inactive/active state transition was previously measured and the motions in the microsecond time range were estimated through a combination of backbone 15N CPMG dispersion NMR spectroscopy and a collection of experiments to determine the exchange-free component to the transverse relaxation rate. Exchange contributions to the 1H line width were detected for 21 methyl groups, and these probes were found to collectively report on a local structural rearrangement around the phosphorylation site, with a rate constant of (15.5 ± 0.5) × 103 per second (i.e., ?ex = 64.7 ± 1.9 ?s). The affected methyl groups indicate that, already before phosphorylation, a substantial, transient rearrangement takes place between helices 3 and 4 and strands 4 and 5. This conformational equilibrium allows the protein to gain access to the active, signaling state in the absence of covalent modification through a shift in a pre-existing dynamic equilibrium. Moreover, the conformational switching maps exactly to the regions that differ between the solution NMR structures of the fully inactive and active states. These results demonstrate that a cost-effective and quantitative study of protein methyl group dynamics by 1H CPMG relaxation dispersion NMR spectroscopy is possible and can be applied to study functional motions on the microsecond time scale that cannot be accessed by backbone 15N relaxation dispersion NMR. The use of methyl groups as dynamics probes extends such applications also to larger proteins. PMID:21058670
Immersed boundary lattice Boltzmann model based on multiple relaxation times.
Lu, Jianhua; Han, Haifeng; Shi, Baochang; Guo, Zhaoli
2012-01-01
As an alterative version of the lattice Boltzmann models, the multiple relaxation time (MRT) lattice Boltzmann model introduces much less numerical boundary slip than the single relaxation time (SRT) lattice Boltzmann model if some special relationship between the relaxation time parameters is chosen. On the other hand, most current versions of the immersed boundary lattice Boltzmann method, which was first introduced by Feng and improved by many other authors, suffer from numerical boundary slip as has been investigated by Le and Zhang. To reduce such a numerical boundary slip, an immerse boundary lattice Boltzmann model based on multiple relaxation times is proposed in this paper. A special formula is given between two relaxation time parameters in the model. A rigorous analysis and the numerical experiments carried out show that the numerical boundary slip reduces dramatically by using the present model compared to the single-relaxation-time-based model. PMID:22400705
NASA Astrophysics Data System (ADS)
Stickel, F.; Kremer, F.; Fischer, E. W.
1993-12-01
The scaling of the dielectric and electric relaxation in two low molecular weight glass forming systems (PDE=Phenolphtalein-dimethylether and KDE=Kresolphtalein-di-methylether) is studied in the frequency regime from 10 -3 Hz to 10 9 Hz by use of broadband dielectric spectroscopy. For both the dielectric ?-relaxation and the dc-conductivity the temperature dependence is characterised by a crossover (at a temperature TA) from an Arrhenius to a Vogel-Fulcher-Tammann law. Above TA the dc-conductivity (reflecting translational diffusion of mobile charge carriers) and the ?-relaxation have the same temperature dependence. Below TA a decoupling is found in agreement with recent tracer diffusion experiments (M. Lohfink and H. Sillescu, in: Proc. of the 1st Tohwa University Int. Symp., Fukuoka, Japan, 4-8.11.1991, Am. Inst. Phys. Conf. Series). For the ?-relaxation, the relaxation time distribution shows a pronounced temperature dependence below TA, while it is only weakly varying with temperature above TA.
History-dependent relaxation and the energy scale of correlation in the electron glass
NASA Astrophysics Data System (ADS)
Ovadyahu, Z.; Pollak, M.
2003-11-01
We present an experimental study of the energy relaxation in Anderson-insulating indium-oxide films excited far from equilibrium. In particular, we focus on the effects of history on the relaxation of the excess conductance ?G. The natural relaxation law of ?G is logarithmic: namely, ?G?ln(t). This may be observed over more than five decades following, for example, cool quenching the sample from high temperatures. On the other hand, when the system is excited from a state So in which it has not fully reached equilibrium to a state Sn, the ensuing relaxation law is logarithmic only over time t shorter than the time tw it spent in So. For times t?tw, ?G(t) shows a systematic deviation from the logarithmic dependence. It was previously shown that when the energy imparted to the system in the excitation process is small, this leads to ?G?P(t/tw) (simple aging). Here we test the conjecture that “simple aging” is related to a symmetry in the relaxation dynamics in So and Sn. This is done by using an experimental procedure that is more sensitive to deviations in the relaxation dynamics. It is shown that simple aging may still be obeyed [albeit with a modified P(t/tw)] even when the symmetry of relaxation in So and Sn is perturbed by a certain degree. The implications of these findings to the question of aging and the energy scale associated with correlations are discussed.
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.
Nuclear magnetic spin-rotational relaxation times for linear molecules
James McConnell
1982-01-01
The stochastic differential equation study of nuclear magnetic relaxation by spin-rotational interactions is applied to the linear rotator model of the molecule. Inertial effects are included in the calculations, which are performed analytically. Expressions are derived for the spin-rotational contributions to the longitudinal and transverse relaxation times, and for the spin-rotational correlation time.
NASA Astrophysics Data System (ADS)
Torquato, S.; Avellaneda, M.
1991-11-01
Diffusion and reaction in heterogeneous media plays an important role in a variety of processes arising in the physical and biological sciences. The determination of the relaxation times Tn (n=1,2,...) and the mean survival time ? is considered for diffusion and reaction among partially absorbing traps with dimensionless surface rate constant ?¯. The limits ?¯=? and ?¯=0 correspond to the diffusion-controlled case (i.e., perfect absorbers) and reaction-controlled case (i.e., perfect reflectors), respectively. Rigorous lower bounds on the principal (or largest) relaxation time T1 and mean survival time ? for arbitrary ?¯ are derived in terms of the pore size distribution P(?). Here P(?)d? is the probability that a randomly chosen point in the pore region lies at a distance ? and ?+d? from the nearest point on the pore-trap interface. The aforementioned moments and hence the bounds on T1 and ? are evaluated for distributions of interpenetrable spherical traps. The length scales and 1/2, under certain conditions, can yield useful information about the times T1 and ?, underscoring the importance of experimentally measuring or theoretically determining the pore size distribution P(?). Moreover, rigorous relations between the relaxation times Tn and the mean survival time are proved. One states that ? is a certain weighted sum over the Tn, while another bounds ? from above and below in terms of the principal relaxation time T1. Consequences of these relationships are examined for diffusion interior and exterior to distributions of spheres. Finally, we note the connection between the times T1 and ? and the fluid permeability for flow through porous media, in light of a previously proved theorem, and nuclear magnetic resonance (NMR) relaxation in fluid-saturated porous media.
Rotational relaxation time in CO free jets
A. E. Belikov
2000-01-01
The electron beam fluorescence technique was applied to measure the rotational energy relaxation cross-sections in carbon monoxide free jets. The data were obtained in the low temperature region from 20 to 200 K and compared with the results of ultrasound, thermal conductivity, free jet and line broadening experiments. The overall scatter of the experimental data runs to one order of
Rodriguez, Brian [University College, Dublin] [University College, Dublin; Jesse, Stephen [ORNL] [ORNL; Kim, J. [University of Nebraska, Lincoln] [University of Nebraska, Lincoln; Ducharme, S. [University of Nebraska, Lincoln] [University of Nebraska, Lincoln; Kalinin, Sergei [Oak Ridge National Laboratory (ORNL)] [Oak Ridge National Laboratory (ORNL)
2008-01-01
Time-resolved piezoresponse force spectroscopy (TR-PFS) and spectroscopic imaging are developed to probe the spatial variability of relaxation behavior in nanoscale ferroelectric materials and structures. TR-PFS was applied to study polarization dynamics in polyvinylidine fluoride and trifluoroethylene nanomesas. We demonstrate that polarization relaxation in ferroelectric polymers is slow even on the 10 nm length scale of piezoresponse force microscopy (PFM) signal generation. Furthermore, the relaxation times are found to be nonuniform within the nanomesa, indicative of a complex internal structure. The applicability of TR-PFM for studies of polarization dynamics in ferroelectric polymers and relaxors is discussed.
NASA Astrophysics Data System (ADS)
Gevorkyan, A. S.; Abajyan, H. G.
2012-11-01
We have investigated the statistical properties of an ensemble of disordered 1D spatial spin chains (SSCs) of finite length, placed in an external field, with consideration of relaxation effects. The short-range interaction complex-classical Hamiltonian was first used for solving this problem. A system of recurrent equations is obtained on the nodes of the spin-chain lattice. An efficient mathematical algorithm is developed on the basis of these equations with consideration of advanced Sylvester conditions which allows one to step by step construct a huge number of stable spin chains in parallel. The distribution functions of different parameters of spin glass system are constructed from first principles by analyzing the calculation results of the 1D SSCs ensemble. It is shown that the behaviors of different distributions parameters are quite different even at weak external fields. The ensemble energy and constants of spin-spin interactions are being changed smoothly depending on the external field in the limit of statistical equilibrium, while some of them such as the mean value of polarizations of the ensemble and parameters of its orderings are frustrated. We have also studied some critical properties of the ensemble such as catastrophes in the Clausius-Mossotti equation depending on the value of the external field. We have shown that the generalized complex-classical approach excludes these catastrophes, which allows one to organize continuous parallel computing on the whole region of values of the external field including critical points. A new representation of the partition function is suggested based on these investigations. Being opposite to the usual definition, it is a complex function and its derivatives are everywhere defined, including at critical points.
Dipole moment and relaxation time of ribonuclease
S E Keefe; E H Grant
1974-01-01
Dielectric measurements carried out on aqueous solutions of ribonuclease A show the existence of a dispersion region centred around a relaxation frequency of a few MHz. The dipole moment at pH 8.4 calculated from the static permittivity is about 350D which is higher than that occurring in other comparable globular proteins and indicates a greater charge asymmetry. The activation enthalphy
Origin of the relaxation time in dissipative fluid dynamics
Denicol, Gabriel S.; Noronha, Jorge; Niemi, Harri; Rischke, Dirk H. [Institut fuer Theoretische Physik, Goethe University, 60438 Frankfurt am Main (Germany); Department of Physics, Columbia University, New York, New York 10027 (United States) and Instituto de Fisica, Universidade Federal do Rio de Janeiro, C. P. 68528, 21945-970, Rio de Janeiro (Brazil); Frankfurt Institute for Advanced Studies (FIAS), 60438 Frankfurt am Main (Germany); Institut fuer Theoretische Physik, Goethe University, and Frankfurt Institute for Advanced Studies (FIAS), 60438 Frankfurt am Main (Germany)
2011-04-01
We show how the linearized equations of motion of any dissipative current are determined by the analytical structure of the associated retarded Green's function. If the singularity of Green's function, which is nearest to the origin in the complex-frequency plane, is a simple pole on the imaginary frequency axis, the linearized equations of motion can be reduced to relaxation type equations for the dissipative currents. The value of the relaxation time is given by the inverse of this pole. We prove that, if the relaxation time is sent to zero, or equivalently, the pole to infinity, the dissipative currents approach the values given by the standard gradient expansion.
Relaxation time dispersions in glass forming metallic liquids and glasses
NASA Astrophysics Data System (ADS)
Wang, Li-Min; Liu, Riping; Wang, Wei Hua
2008-04-01
Relaxation time dispersions in glass forming metallic liquids of diverse fragility characters were reviewed mainly based on mechanical relaxations. The compilation of the stretching exponents revealed the common nonexponential dynamic features among the metallic liquids. The time-temperature-superposition law of the relaxation profiles was identified with an average stretching exponent around 0.5 at low frequency regions near the glass transitions. No notable correlation of the stretching parameter with alloy composition was discerned. The construction of the frequency dependence of the stretching exponent across the whole range of liquid dynamics revealed a striking similarity of the nonexponential dynamics between metallic and fragile molecular liquids.
Proton-nuclear magnetic resonance relaxation times in brain edema
Kamman, R.L.; Go, K.G.; Berendsen, H.J. (Univ. of Groningen (Netherland))
1990-01-01
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.
Femtosecond time-resolved electronic relaxation dynamics in tetrathiafulvalene
NASA Astrophysics Data System (ADS)
Staedter, D.; Thiré, N.; Polizzi, L.; Mairesse, Y.; Mayer, P.; Blanchet, V.
2015-05-01
In the present paper, the ultrafast electronic relaxation of tetrathiafulvalene (TTF) initiated around 4 eV is studied by femtosecond time-resolved velocity-map imaging. The goal is to investigate the broad double structure observed in the absorption spectrum at this energy. By monitoring the transients of the parent cation and its fragments and by varying the pump and the probe wavelengths, two internal conversions and intramolecular vibrational relaxation are detected both on the order of a few hundred of femtoseconds. Photoelectron images permit the assignment of a dark electronic state involved in the relaxation. In addition, the formation of the dimer of TTF has been observed.
Femtosecond time-resolved electronic relaxation dynamics in tetrathiafulvalene.
Staedter, D; Thiré, N; Polizzi, L; Mairesse, Y; Mayer, P; Blanchet, V
2015-05-21
In the present paper, the ultrafast electronic relaxation of tetrathiafulvalene (TTF) initiated around 4 eV is studied by femtosecond time-resolved velocity-map imaging. The goal is to investigate the broad double structure observed in the absorption spectrum at this energy. By monitoring the transients of the parent cation and its fragments and by varying the pump and the probe wavelengths, two internal conversions and intramolecular vibrational relaxation are detected both on the order of a few hundred of femtoseconds. Photoelectron images permit the assignment of a dark electronic state involved in the relaxation. In addition, the formation of the dimer of TTF has been observed. PMID:26001460
NSDL National Science Digital Library
1999-01-01
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.
Chuang, Chi-Hung; Lu, Ying-Gang; Lee, Kyureon; Ciston, Jim; Dukovic, Gordana
2015-05-27
(Ga1-xZnx)(N1-xOx) is a visible absorber of interest for solar fuel generation. We present a first report of soluble (Ga1-xZnx)(N1-xOx) nanocrystals (NCs) and their excited-state dynamics over the time window of 10(-13)-10(-4) s. Using transient absorption spectroscopy, we find that excited-state decay in (Ga0.27Zn0.73)(N0.27O0.73) NCs has both a short (<100 ps) and a long-lived component, with a long overall average lifetime of ?30 ?s. We also find that the strength of the visible absorption is comparable to that of direct band gap semiconductors such as GaAs. We discuss how these results may relate to the origin of visible absorption in (Ga1-xZnx)(N1-xOx) and its use in solar fuel generation. PMID:25936370
Felix M. Gradstein; Frits P. Agterberg; James G. Ogg; Jan Hardenbol; Paul van Veen; Jacques Thierry; Zehui Huang
1994-01-01
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
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.
Subsecond pore-scale displacement processes and relaxation dynamics in multiphase flow
NASA Astrophysics Data System (ADS)
Armstrong, Ryan T.; Ott, Holger; Georgiadis, Apostolos; Rücker, Maja; Schwing, Alex; Berg, Steffen
2014-12-01
With recent advances at X-ray microcomputed tomography (?CT) synchrotron beam lines, it is now possible to study pore-scale flow in porous rock under dynamic flow conditions. The collection of four-dimensional data allows for the direct 3-D visualization of fluid-fluid displacement in porous rock as a function of time. However, even state-of-the-art fast-?CT scans require between one and a few seconds to complete and the much faster fluid movement occurring during that time interval is manifested as imaging artifacts in the reconstructed 3-D volume. We present an approach to analyze the 2-D radiograph data collected during fast-?CT to study the pore-scale displacement dynamics on the time scale of 40 ms which is near the intrinsic time scale of individual Haines jumps. We present a methodology to identify the time intervals at which pore-scale displacement events in the observed field of view occur and hence, how reconstruction intervals can be chosen to avoid fluid-movement-induced reconstruction artifacts. We further quantify the size, order, frequency, and location of fluid-fluid displacement at the millisecond time scale. We observe that after a displacement event, the pore-scale fluid distribution relaxes to (quasi-) equilibrium in cascades of pore-scale fluid rearrangements with an average relaxation time for the whole cascade between 0.5 and 2.0 s. These findings help to identify the flow regimes and intrinsic time and length scales relevant to fractional flow. While the focus of the work is in the context of multiphase flow, the approach could be applied to many different ?CT applications where morphological changes occur at a time scale less than that required for collecting a ?CT scan.
NASA Astrophysics Data System (ADS)
Krasnov, Igor; Seydel, Tilo; Müller, Martin
2015-04-01
Structural relaxations in humid silk fibers exposed to tensile stress have been reported to take place on a very wide range of time scales from a few milliseconds to several hours. The time-dependence of the measured tensile force following a quasi-instantaneously applied external strain on the fibers can be understood in terms of a fractional viscoelastic relaxation function introducing memory effects by which the mechanical state of a fiber depends on its tensile history. An analog fractional relaxation also gives rise to the subdiffusion observed on picosecond time scales, which governs the mobility of the amorphous polymer chains and adsorbed water on the molecular level. The reduction of the subdiffusive memory effect in stretched fibers compared to native fibers is consistent with the higher order of the polymers in the stretched state.
Evaluation of brain edema using magnetic resonance proton relaxation times
Fu, Y.; Tanaka, K.; Nishimura, S. (Baba Memorial Hospital, Osaka (Japan))
1990-01-01
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.
Determining protein loop conformation using scaling-relaxation techniques.
Zheng, Q.; Rosenfeld, R.; Vajda, S.; DeLisi, C.
1993-01-01
We recently developed a rapid loop closure algorithm in which bond lengths are scaled to constrain the ends of a segment to match a known distance and then gradually relaxed to their standard values, with boundary constraints maintained. Although the algorithm predicted the Zif286 zinc-finger loop to within approximately 2 A, it had a serious limitation that made its more general use tentative: it omitted the atomic environment of the loop. Here we report an extension of the algorithm to take into account the protein environment surrounding a given loop from the outset of the conformational search and show that it predicts structure with an efficiency and accuracy that could not be achieved without continuous environmental inclusion. The algorithm should be widely applicable to structure determination when complete experimental information is unavailable. PMID:8401209
Improved Upper Bound on -Time-Relaxed -Broadcasting Communication Networks
Averbuch, Amir
1 Improved Upper Bound on -Time-Relaxed -Broadcasting Communication Networks A. Averbuch I. Peeri Y communication link between these vertices. Then, we de£ne broadcasting from a vertex ¨ (the originator@post.tau.ac.il Abstract Broadcasting is a process in which an individual has an item of information which needs
Modeling the Relaxation Time of DNA Confined in a Nanochannel
NASA Astrophysics Data System (ADS)
Wang, Yanwei; Tree, Douglas R.; Dorfman, Kevin D.
2014-03-01
Using a mapping between a dumbbell model and fine-grained Monte Carlo simulations, we have computed the relaxation time of ?-DNA in a high ionic strength buffer confined in a nanochannel (Tree et al., Biomicrofluidics 2013, 7, 054118). The relaxation time thus obtained agrees quantitatively with experimental data (Reisner et al., PRL 2005, 94, 196101) using only a single O(1) fitting parameter to account for the uncertainty in model parameters. In addition to validating our mapping, this agreement supports our previous estimates of the friction coefficient of DNA confined in a nanochannel (Tree et al., PRL 2012, 108, 228105), which have been difficult to validate due to the lack of direct experimental data. Furthermore, our calculation shows that as the channel size passes below ~100 nm (or roughly the Kuhn length of DNA) there is a dramatic drop in the relaxation time. Inasmuch as the chain friction rises with decreasing channel size, the reduction in the relaxation time can be solely attributed to the sharp decline in the fluctuations of the chain extension. Practically, the low variance in the observed DNA extension in such small channels has important implications for genome mapping. This work was supported by the NIH (R01-HG005216 and R01-HG006851) and the NSFC (21204061) and was carried out in part using computing resources at the University of Minnesota Supercomputing Institute.
Phenomenological Theory of the Translational Relaxation Times in Gases
NASA Technical Reports Server (NTRS)
Zuckerwar, Allan J.
1999-01-01
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.
Time distribution and loss of scaling in granular flow
B. Tadic
1999-01-01
: Two cellular automata models with directed mass flow and internal time scales are studied by numerical simulations. Relaxation\\u000a rules are a combination of probabilistic critical height (probability of toppling p) and deterministic critical slope processes with internal correlation time tc equal to the avalanche lifetime, in model A, and ,in model B. In both cases nonuniversal scaling properties of
Scaling vs. Vogel-Fulcher-type structural relaxation in deeply supercooled materials
NASA Astrophysics Data System (ADS)
Richert, Ranko
2000-11-01
A recent scaling-law analysis using ??( T- Tc) - ? with Tc< Tg has concluded that the resulting fits are superior over the Vogel-Fulcher-Tammann temperature dependence as regards the structural relaxation time of supercooled liquids (Colby, Phys. Rev. E 61 (2000) 1783). This issue is investigated based on the dielectric retardation data of poly(vinylacetate) which cover 16 decades in time, from 3 ns to over 1 year. In contrast to Colby's conclusions, the observed temperature dependence rules out a temperature-invariant exponent ? as well as a clear cut critical temperature Tc.
On the derivation of equilibrium relaxation times from aging experiments.
Richert, Ranko; Lunkenheimer, Peter; Kastner, Stefan; Loidl, Alois
2013-10-24
Physical aging below the glass transition temperature, Tg, is generally understood to be governed by the same slow degrees of freedom that are responsible for structural relaxation in the equilibrium state above Tg. Provided a reliable model of aging is at hand, it should thus be possible to extract very long relaxation time constants from experimental data on physical aging. Two very different models of aging are investigated in this respect using data for various molecular glass-forming liquids extending out to aging times of 3 × 10(6) s. It turns out that application of the well-known KAHR or TNM model does not provide a significant advantage over a recently proposed phenomenological approach that is much simpler. PMID:23311902
Temperature of the Magnetic Nanoparticle Microenvironment: Estimation from Relaxation Times
Perreard, IM; Reeves, DB; Zhang, X; Kuehlert, E; Forauer, ER; Weaver, JB
2014-01-01
Accurate temperature measurements are essential to safe and effective thermal therapies for cancer and other diseases. However, conventional thermometry is challenging so using the heating agents themselves as probes allows for ideal local measurements. Here, we present a new noninvasive method for measuring the temperature of the microenvironment surrounding magnetic nanoparticles from the Brownian relaxation time of nanoparticles. Experimentally, the relaxation time can be determined from the nanoparticle magnetization induced by an alternating magnetic field at various applied frequencies. A previously described method for nanoparticle temperature estimation used a low frequency Langevin function description of magnetic dipoles and varied the excitation field amplitude to estimate the energy state distribution and the corresponding temperature. We show that the new method is more accurate than the previous method at higher applied field frequencies that push the system farther from equilibrium. PMID:24556943
Fast Time-Relaxation Algorithm to Solve Plasma Fluid Equations
José Gregorio; Caroline Boisse-Laporte; Luís L. Alves
2010-01-01
This paper presents a fast time-relaxation quasi-implicit algorithm to solve plasma fluid-type equations for the transport of electron particles and mean energy, the transport of heavy species (ions and neutrals), the balance of the gas thermal energy, and the description of the fields (space-charge electrostatic and electromagnetic) affecting the plasma. The algorithm separately solves and converges the different model equations,
Relaxation Times and Rheology in Dense Athermal Suspensions
Peter Olsson
2015-03-29
We study the jamming transition in a model of elastic particles under shear at zero temperature. The key quantity is the relaxation time $\\tau$ which is obtained by stopping the shearing and letting energy and pressure decay to zero. At many different densities and initial shear rates we do several such relaxations to determine the average $\\tau$. We establish that $\\tau$ diverges with the same exponent as the viscosity and determine another exponent from the relation between $\\tau$ and the coordination number. Though most of the simulations are done for the model with dissipation due to the motion of particles relative to an affinely shearing substrate (the RD$_0$ model), we also examine the CD$_0$ model, where the dissipation is instead due to velocity differences of disks in contact, and confirm that the above-mentioned exponent is the same for these two models. We also consider finite size effects on both $\\tau$ and the coordination number.
Relaxation times and rheology in dense athermal suspensions
NASA Astrophysics Data System (ADS)
Olsson, Peter
2015-06-01
We study the jamming transition in a model of elastic particles under shear at zero temperature. The key quantity is the relaxation time ? which is obtained by stopping the shearing and letting energy and pressure decay to zero. At many different densities and initial shear rates we do several such relaxations to determine the average ? . We establish that ? diverges with the same exponent as the viscosity and determine another exponent from the relation between ? and the coordination number. Though most of the simulations are done for the model with dissipation due to the motion of particles relative to an affinely shearing substrate, we also examine a model, where the dissipation is instead due to velocity differences of disks in contact, and confirm that the above-mentioned exponent is the same for these two models. We also consider finite size effects on both ? and the coordination number.
Hanakata, Paul Z; Douglas, Jack F; Starr, Francis W
2014-01-01
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
Comparison of methods for the calculation of superparamagnetic relaxation times
NASA Astrophysics Data System (ADS)
Coffey, W. T.; Crothers, D. S. F.
1996-11-01
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.
NASA Astrophysics Data System (ADS)
Mei, Renwei; Yu, Dazhi; Shyy, Wei; Luo, Li-Shi
2002-11-01
In solving flows with geometrical discontinuities using the method of lattice Boltzmann equation for high Reynolds number incompressible flows, the following paradox exits. On one hand, the density field is required to be nearly constant for the nearly incompressibility condition to be satisfied and the pressure near the geometric discontinuity is linearly proportional to the local density field. On the other hand, the shear stress and the pressure are singular near the geometry singularity, such as sharp corners. This often results in undesirable, strong local spatial oscillations which contaminate the solution for the flow field away from the singular points. The recent work by Lallemand & Luo suggests that the use of a multi-relaxation-time model can improve the computational stability in general and reduce the dispersion. However the difference is often in the higher order. In this paper we report detailed comparison and assessment of the performance of these two LBE models: single-relaxation-time (SRT) and multi-relaxation-time (MRT) for various flows with geometric and flow singularities. Computational results for the pressure, viscous stresses, vorticity, and flow velocity in regions of large gradient show that MRT model significantly reduced the extent of the spatial oscillation near the geometric singular points and improved the quality of the flow field at high Reynolds number. The difference between the solutions of the two models are on the leading order in such cases.
Felix M. Gradstein; James G. Ogg; Alan G. Smith
2005-01-01
A successor to A Geologic Time Scale 1989 (Cambridge, 1990), this volume introduces the theory and methodology behind the construction of the new time scale, before presenting the scale itself in extensive detail. An international team of over forty stratigraphic experts develops the most up-to-date international stratigraphic framework for the Precambrian and Phanerozoic eras. A large wallchart summarizing the time
D. A. Vega; M. A. Villar; E. M. Vallés; J. L. Alessandrini
1998-01-01
The present works attempts to explain the viscoelastic behavior of model silicone networks containing well defined amounts of pendant chains of uniform molecular weight. A discrete spectrum of relaxation times is calculated. It is divided in three parts, corresponding to three different mechanisms: a Rouse relaxation type at short times, a modification of the Rouse spectrum for the relaxation of
Time dependent parallel viscosity and relaxation rate of poloidal rotation in the banana regime
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
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
Kanatharana, J.; Sukpisan, J.; Wang, S.Q. [Chulaongkorn Univ., Bangkok (Thailand)] [and others
1995-12-01
The dependences on the polyion concentration through the scaling relations in {eta} {alpha} c{sup {alpha}} and {Tau}{sub q} {alpha} c{sup {beta}}, where {eta} and {Tau}{sub q} are the solution viscosity and the relaxation time obtained from the dynamic light scattering respectively, are investigated for the partially hydrolyzed polyacrylamides at different degrees of hydrolysis. The scaling exponents a and {beta}, as determined in the semidilute regime, depend critically on the amount of salt added or the ionic strength. Both exponents, however, are independent of the amount of glycerol added which suggests that the excluded volume effect is relatively small in comparison with the effect of electrostatic repulsion. The salt-concentration dependence of the solution is also investigated: the corresponding scaling exponents for the 70% HPAM are insensitive to the solvent quality. The present experiment results are compared with recent scaling theories.
Spin-rotation contribution to the relaxation time of the fluorine nuclei in benzotrifluoride
Faulk, Robert Hardy
1965-01-01
SPIN-ROTATION CONTRIBUTION TO THE RELAXATION TIME OF THE FLUORINE NUCLEI IN BENZOTRIFLUORIDE A Thesis By ROBERT HARDY FAULK Submitted to the Graduate College of the Texas ASM University in partial fulfillment of the requirements... Contributions to the Relaxation Time for the Fluorine 6 Hydrogen Relaxation Time and the Correlation Time 33 35 36 I. INTRODUCTION The spin-rotation interaction may be visualized in the following manner. Because of the inhomogeneous distribution of charge...
, holes couple to lower frequency breathing modes and decay over multiple time scales. DOI: 10.1103/Phys of higher energy excitations [10,17]. The participation of both low frequency radial-breathing modes (RBM faster than the holes. The relaxation is primarily mediated by the high-frequency longitudinal optical
U.S. Geological Survey
2012-01-01
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.
NASA Astrophysics Data System (ADS)
Chun, Myung-Suk; Ko, Min Jae
2012-10-01
The Rouse-Zimm model based on the polymer dynamics theory allows us to predict the relaxation time of polyelectrolyte dilute solution as a function of the intrinsic viscosity. In finite concentrated solutions, the empirical analysis adopted in this study is quite useful to examine the relaxation behavior, noting that proper theories are not well-clarified and experimental measurements are rather complicated. For the xanthan biopolymer selected as the polyelectrolyte model of a semiflexible chain, we measured rheological properties of shear viscosity ? and first normal stress difference ? ?1 in dilute and semidilute solutions over a wide range of shear rates dot ?. Power-law scaling relations are commonly observed in the region of dot ? ?slant 1 s-1. Accurate regressions on ? and ? ?1 present empirical plots as functions of the shear rate and the xanthan concentration, from which each of relevant fitting parameters are determined. Empirically determined curves agree well with the experimental data, ensuring that the empirical formula for the characteristic relaxation time ? is applicable at dilute and finite concentrations, which has not been reported in the literature. We further interpreted the non-Newtonian fluid behavior over a full range of shear rates by applying the Carreau A constitutive model.
Relationships between induced polarization relaxation time and hydraulic properties of sandstone
Konstantin Titov; Andrey Tarasov; Yuri Ilyin; Nikita Seleznev; Austin Boyd
2010-01-01
We investigated electrical and physical-chemical properties of six sandstone samples with contrasting mineralogical characteristics and with hydraulic conductivity varying in a wide range. The electrical data were obtained from time domain spectral induced polarization (IP) measurements. We inverted the IP decays to relaxation time distributions, and then compared the modal relaxation times with the dominant pore throat diameters obtained from
Resolving distribution of relaxation times in Poly(propylene glycol) on the crossover region
Enis Tuncer; Marizio Furlani; Bengt-Erik Mellander
2004-03-09
In this paper, a recently developed numerical technique [{\\em Tuncer E and Guba{\\'n}ski S M, IEEE Trans Diel El Insul {\\bf 8}(3)(2001) 310-320}] is applied to poly(propylene glycol) complex dielectric data to extract more information about the molecular relaxation processes. The method is based on a constrained-least-squares (\\clsq) data fitting procedure together with the Monte Carlo (\\mc) method. We preselect the number of relaxation times with no {\\em a-priori} physical assumption, and use the Debye single relaxation as ``kernel'', then the obtained weighting factors at each \\mc step from the \\clsq method builds up a relaxation time spectrum. When the analysis is repeated for data at different temperatures a {\\em relaxation-image} is created. The obtained relaxation are analyzed using the Lorentz (Cauchy) distribution, which is a special form of the L{\\'e}vy statistics. In the present report the $\\beta$ and $\\alpha$ relaxations are resolved for the \\ppg. A comparison of the relaxations to those earlier reported in the literature indicate that the presented method provides additional information compared to methods based on empirical formulas. The distribution of relaxation times analysis is especially useful to probe the crossover region where the $\\alpha$- and $\\beta$- relaxations merge and the results show that the relaxation after the crossover region at higher temperatures is Arrhenius-type as the $\\beta$-relaxation. Moreover, this relaxation is more likely to be the continuation of the $\\beta$-relaxation, but with a different activation energy.
Study of relaxation kinetics in argon afterglow by the breakdown time delay measurements
Markovic, V.Lj.; Gocic, S.R.; Stamenkovic, S.N.; Petrovic, Z.Lj. [Department of Physics, University of Nis, P.O. BOX 224, 18001 Nis (Serbia and Montenegro); Institute of Physics, P.O. BOX 68, Belgrade (Serbia and Montenegro)
2005-07-15
In this paper the afterglow kinetics in argon is studied by the breakdown time delay measurements as a function of relaxation time t{sub d}({tau}) ('memory curve'). Measurements were carried out at the pressure of 1.33 mbar in a gas tube with gold-plated copper cathode and approximate and exact numerical models are developed to follow metastable and charged particle decay. It was found that the early afterglow kinetics is governed by the charged particle decay up to hundreds of milliseconds, extending from ambipolar to the free diffusion limit. Quenching processes reduce the effective lifetime of metastable states several orders of magnitude below that relevant for the time scale of the observations if realistic abundances and processes are included in the model. Nitrogen atoms originating from impurities and recombining on the cathode surface can determine the breakdown time delay down to that defined by the level of cosmic rays and natural radioactivity.
Shores, D.A.; Stout, J.H.; Gerberich, W.W.
1992-06-01
The high temperature X-ray diffraction system developed for this program is being used to measure the strains which develop during oxidation. This is being applied to Ni/NiO and Cr/Cr[sub 2]O[sub 3]. Our work suggests tat the oxide and metal crystalline texture, anisotropic elastic modulus and anisotropic thermal expansion can have a pronounced effect on strain state of these systems. Acoustic emission is being used to study oxide scale failure (fracture) during oxidation. AE data from 304 stainless steel are being used to develop a statistical model of fracture process. Strength of metal/scale interface is an important property that has been difficult to quantify. Using Nano-indentation and scratch techniques developed for characterizing thin film interfaces, an effort has begun to measure the fracture toughness of the metal/scale interface. Mathematical modelling of origin and time evolution of growth stresses is an extension and improvement of previous models. The current effort employs a more sophisticated stress analysis and expands the scope to include other stress relaxation process. The interaction between the modeling studies and the X-ray diffraction measurements provides a natural credibility check to both efforts.
An axisymmetric multiple-relaxation-time lattice Boltzmann scheme
NASA Astrophysics Data System (ADS)
Xie, Wenjun
2015-01-01
A multiple-relaxation-time (MRT) lattice Boltzmann (LB) scheme developed for axisymmetric flows recovers the complete continuity and Navier-Stokes equations. This scheme follows the strategy of the standard D2Q9 model by using a single particle distribution function and a simple "collision-streaming" updating rule. The extra terms related to axisymmetry in the macroscopic equations are recovered by adding source terms into the LB equation, which are simple and involve no gradients. The compressible effect retained in the Navier-Stokes equations is recovered by introducing a term related to the reversed transformation matrix for MRT collision operator, so as to produce a correct bulk viscosity, making it suitable for compressible flows with high frequency and low Mach number. The validity of the scheme is demonstrated by testing the Hagen-Poiseuille flow and 3D Womersley flow, as well as the standing acoustic waves in a closed cylindrical chamber. The numerical experiments show desirable stability at low viscosities, enabling to simulate a standing ultrasound field in centimeters space.
Long-time relaxation in pilot-wave theory
NASA Astrophysics Data System (ADS)
Abraham, Eitan; Colin, Samuel; Valentini, Antony
2014-10-01
We initiate the study of relaxation to quantum equilibrium over long timescales in pilot-wave theory. We simulate the time evolution of the coarse-grained H-function \\bar{H}(t) for a two-dimensional harmonic oscillator. For a (periodic) wave function that is a superposition of the first 25 energy states we confirm an approximately exponential decay of \\bar{H} over five periods. For a superposition of only the first four energy states we are able to calculate \\bar{H}(t) over 50 periods. We find that, depending on the set of phases in the initial wave function, \\bar{H} can decay to a large nonequilibrium residue exceeding 10% of its initial value or it can become indistinguishable from zero (the equilibrium value). We show that a large residue in \\bar{H} is caused by a tendency for the trajectories to be confined to sub-regions of configuration space for some wave functions, and that this is less likely to occur for larger numbers of energy states (if the initial phases are chosen randomly). Possible cosmological implications are briefly discussed.
Reconstruction of relaxation time distribution from linear electrochemical impedance spectroscopy
NASA Astrophysics Data System (ADS)
Zhang, Yanxiang; Chen, Yu; Yan, Mufu; Chen, Fanglin
2015-06-01
Linear electrochemical impedance spectroscopy (EIS), and in particular its representation of distribution of relaxation time (DRT), enables the identification of the number of processes and their nature involved in electrochemical cells. With the advantage of high frequency resolution, DRT has recently drawn increasing attention for applications in solid oxide fuel cells (SOFCs). However, the method of DRT reconstruction is not yet presented clearly in terms of what mathematical treatments and theoretical assumptions have been made. Here we present unambiguously a method to reconstruct DRT function of impedance based on Tikhonov regularization. By using the synthetic impedances and analytic DRT functions of RQ element, generalized finite length Warburg element, and Gerischer element with physical quantities representative to those of SOFC processes, we show that the quality of DRT reconstruction is sensitive to the sampling points per decade (ppd) of frequency from the impedance measurement. The robustness of the DRT reconstruction to resist noise imbedded in impedance data and numerical calculations can be accomplished by optimizing the weighting factor ? according to well defined criterion.
MRI Under Hyperbaric Air and Oxygen: Effects on Local Magnetic Field and Relaxation Times
Duong, Timothy Q.
,2,3,4,6 * Purpose: Hyperbaric oxygen therapy has shown efficacies in the treatment of a number of diseases. The goal; T2*; relaxation time constants INTRODUCTION Hyperbaric oxygen (HBO) therapy has been used to treatMRI Under Hyperbaric Air and Oxygen: Effects on Local Magnetic Field and Relaxation Times Eric R
MRI Under Hyperbaric Air and Oxygen: Effects on Local Magnetic Field and Relaxation Times
Duong, Timothy Q.
,2,3,4,6 * Purpose: Hyperbaric oxygen therapy has shown efficacies in the treatment of a number of diseases. The goal; T2*; relaxation time constants INTRODUCTION Hyperbaric oxygen (HBO) therapy has been used to treatNOTE MRI Under Hyperbaric Air and Oxygen: Effects on Local Magnetic Field and Relaxation Times Eric
Viscosity and longest relaxation time of semi-dilute polymer solutions. I. Good solvent
Paris-Sud XI, Université de
1185 Viscosity and longest relaxation time of semi-dilute polymer solutions. I. Good solvent M expliqués par un modèle de reptation classique. Abstract. 2014 The zero shear viscosity and longest concentration (4 c/c* 70), we find that : 2014 both the relative viscosity ~r and the longest relaxation time TR
ZlatoÂ?, Andrej
RELAXATION ENHANCEMENT BY TIME-PERIODIC FLOWS ALEXANDER KISELEV, ROMAN SHTERENBERG, AND ANDREJ ZLATOS Abstract. We study enhancement of diffusive mixing by fast incompressible time-periodic flows. The class of relaxation-enhancing flows that are especially efficient in speeding up mixing has been
Reduction of spectral phonon relaxation times from suspended to supported Bo Qiu and Xiulin Ruana)
Ruan, Xiulin
Reduction of spectral phonon relaxation times from suspended to supported graphene Bo Qiu 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
Relaxation-time measurement via a time-dependent helicity balance model
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
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.
Relaxation-time approximation and relativistic third-order viscous hydrodynamics from kinetic theory
NASA Astrophysics Data System (ADS)
Jaiswal, Amaresh
2014-11-01
Using the iterative solution of Boltzmann equation in the relaxation-time approximation, the derivation of a third-order evolution equation for shear stress tensor is presented. To this end we first derive the expression for viscous corrections to the phase-space distribution function, f (x , p), up to second-order in derivative expansion. The expression for ?f (x , p) obtained in this method does not lead to violation of the experimentally observed 1 /?{mT} scaling of the femtoscopic radii, as opposed to the widely used Grad's 14-moment approximation. Subsequently, we present the derivation of a third-order viscous evolution equation and demonstrate the significance of this derivation within one-dimensional scaling expansion. We show that results obtained using third-order evolution equations are in excellent accordance with the exact solution of Boltzmann equation as well as with transport results.
Timothy J. Huelsman; Richard C. Nemanick; David C. Munz
1998-01-01
The present study addresses the measurement of trait mood by examining a set of new scales to measure four separate dimensions: positive energy, tiredness, negative arousal, and relaxation. The data were divided into two halves. On the first half of the data, separate exploratory factor analyses were performed for each dimension using 15 items chosen from various sources to represent
Deep Time: The Geologic Time Scale
NSDL National Science Digital Library
2007-01-01
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.
Senior, Ken; Koppang, Paul; Ray, Jim
2003-06-01
Currently, the International GPS Service (IGS) provides a set of clock products for both satellites and tracking receivers, tabulated at 5-min intervals. These products allow users to determine consistent coordinates and clock values for an isolated GPS receiver with an internal accuracy at the few-cm level. However, because the underlying time scale for the IGS combined clocks is based on a linear alignment to broadcast GPS Time for each day separately, the day-to-day stability of this reference is poor. We show the results of a new filter package written to automate the production of an integrated IGS frequency scale based on a dynamically weighted ensemble of the included frequency standards. The new scale is loosely steered to GPS Time. PMID:12839170
Multiple-relaxation-time lattice Boltzmann kinetic model for combustion
Aiguo Xu; Chuandong Lin; Guangcai Zhang; Yingjun Li
2015-03-13
To probe both the Hydrodynamic Non-Equilibrium (HNE) and Thermodynamic Non-Equilibrium (TNE) in the combustion process, a two-dimensional Multiple-Relaxation-Time (MRT) version of Lattice Boltzmann Kinetic Model(LBKM) for combustion phenomena is presented. The chemical energy released in the progress of combustion is dynamically coupled into the system by adding a chemical term to the LB kinetic equation. Beside describing the evolutions of the conserved quantities, the density, momentum and energy, which are what the Navier-Stokes model describes, the MRT-LBKM presents also a coarse-grained description on the evolutions of some non-conserved quantities. The current model works for both subsonic and supersonic flows with or without chemical reaction. In this model both the specific-heat ratio and the Prandtl number are flexible, the TNE effects are naturally presented in each simulation step. The model is verified and validated via well-known benchmark tests. As an initial application, various non-equilibrium behaviours, including the complex interplays between various HNEs, between various TNEs and between the HNE and TNE, around the detonation wave in the unsteady and steady one-dimensional detonation processes are preliminarily probed. It is found that the system viscosity (or heat conductivity) decreases the local TNE, but increase the global TNE around the detonation wave, that even locally, the system viscosity (or heat conductivity) results in two kinds of competing trends, to increase and to decrease the TNE effects. The physical reason is that the viscosity (or heat conductivity) takes part in both the thermodynamic and hydrodynamic responses.
Multiple-relaxation-time lattice Boltzmann kinetic model for combustion.
Xu, Aiguo; Lin, Chuandong; Zhang, Guangcai; Li, Yingjun
2015-04-01
To probe both the hydrodynamic nonequilibrium (HNE) and thermodynamic nonequilibrium (TNE) in the combustion process, a two-dimensional multiple-relaxation-time (MRT) version of lattice Boltzmann kinetic model (LBKM) for combustion phenomena is presented. The chemical energy released in the progress of combustion is dynamically coupled into the system by adding a chemical term to the LB kinetic equation. Aside from describing the evolutions of the conserved quantities, the density, momentum, and energy, which are what the Navier-Stokes model describes, the MRT-LBKM presents also a coarse-grained description on the evolutions of some nonconserved quantities. The current model works for both subsonic and supersonic flows with or without chemical reaction. In this model, both the specific-heat ratio and the Prandtl number are flexible, the TNE effects are naturally presented in each simulation step. The model is verified and validated via well-known benchmark tests. As an initial application, various nonequilibrium behaviors, including the complex interplays between various HNEs, between various TNEs, and between the HNE and TNE, around the detonation wave in the unsteady and steady one-dimensional detonation processes are preliminarily probed. It is found that the system viscosity (or heat conductivity) decreases the local TNE, but increases the global TNE around the detonation wave, that even locally, the system viscosity (or heat conductivity) results in two kinds of competing trends, to increase and to decrease the TNE effects. The physical reason is that the viscosity (or heat conductivity) takes part in both the thermodynamic and hydrodynamic responses. PMID:25974611
Rogers, Harriet J; McGarry, Bryony L; Knight, Michael J; Jokivarsi, Kimmo T; Gröhn, Olli H J; Kauppinen, Risto A
2014-10-22
One in four ischaemic stroke patients are ineligible for thrombolytic treatment due to unknown onset time. Quantification of absolute MR relaxation times and signal intensities are potential methods for estimating stroke duration. We compared the accuracy of these approaches and determined whether changes in relaxation times and signal intensities identify the same ischaemic tissue as diffusion MRI. Seven Wistar rats underwent permanent middle cerebral artery occlusion to induce focal ischaemia and were scanned at six time points. The trace of the diffusion tensor (DAV), T1? and T2 were acquired at 4.7 T. Results show relaxation times, and signal intensities of the MR relaxation parameters increase linearly with ischaemia duration (P<0.001). Using T1? and T2 relaxation times, an estimate of 4.5 h after occlusion has an uncertainty of ± 12 and ± 35 min, respectively, compared with over 50 min for signal intensities. In addition, we present a pixel-by-pixel method that simultaneously estimates stroke onset time and identifies potentially irreversible ischaemic tissue using absolute relaxation times. This method demonstrates signal intensity changes during ischaemia display an ambiguous pattern and highlights the possibility that diffusion MRI overestimates the true extent of irreversible ischaemia. In conclusion, quantification of absolute relaxation times at a single time point enables a more accurate estimation of stroke duration than signal intensities and provides more information about tissue status in ischaemia. PMID:25116145
The Concise Geologic Time Scale
James G. Ogg; Gabi Ogg; Felix M. Gradstein
2008-01-01
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
Analysis of White Noise Limits for Stochastic Systems with Two Fast Relaxation Times
G. A. Pavliotis; A. M. Stuart
2005-01-01
In this paper we present a rigorous asymptotic analysis for stochastic\\u000asystems with two fast relaxation times. The mathematical model analyzed in this\\u000apaper consists of a Langevin equation for the particle motion with\\u000atime-dependent force constructed through an infinite dimensional Gaussian noise\\u000aprocess. We study the limit as the particle relaxation time as well as the\\u000acorrelation time of
A generalized relation between MWD and relaxation time spectrum
Maria Rossella Nobile; Franco Cocchini
2008-01-01
An inversion procedure for converting linear viscoelastic properties of polymer melts into molecular weight distribution (MWD)\\u000a described by the generalized exponential function (GEX) has been implemented and applied in a previous work (Cocchini F, Nobile\\u000a MR. Rheol Acta 42:232–242, 2003). It is based on the elegant relationship between the relaxation spectrum and the MWD function\\u000a proposed by Thimm W, Friedrich
Multiple-relaxation-time lattice Boltzmann modeling of incompressible flows in porous media
NASA Astrophysics Data System (ADS)
Liu, Qing; He, Ya-Ling
2015-07-01
In this paper, a two-dimensional eight-velocity multiple-relaxation-time (MRT) lattice Boltzmann (LB) model is proposed for incompressible porous flows at the representative elementary volume scale based on the Brinkman-Forchheimer-extended Darcy model. In the model, the porosity is included into the pressure-based equilibrium moments, and the linear and nonlinear drag forces of the porous matrix are incorporated into the model by adding a forcing term to the MRT-LB equation in the moment space. Through the Chapman-Enskog analysis, the incompressible generalized Navier-Stokes equations can be recovered. Numerical simulations of several typical porous flows are carried out to validate the present MRT-LB model. It is found that the present numerical results agree well with the analytical solutions and/or other numerical results reported in the literature.
U. Kaatze; K. Giese
1980-01-01
Starting from basic principles of dielectric relaxation measurements, an account is given on the present state of the frequency and time domain methods. The relative merits and limitations of the different techniques of measurement are discussed.
Nonequilibrium electron relaxation in composite thin film containing silver nano-scale particles
J. L. Wu; C. M. Wang
1999-01-01
Under the stimulation of laser pulses with a wavelength of 647 nm and a pulse duration of 150 fs, the optical transient response of Ag–BaO thin film was obtained by the pump-probe method. Optical relaxation is a process in which nonequilibrium electrons, excited by laser pulses and originating from Ag nano-scale particles, return to the equilibrium state. Its optical transient
Time Scales in Particulate Systems
NASA Astrophysics Data System (ADS)
Zhang, Duan
2013-06-01
While there are many interests of studying interactions of individual particles, macroscopic collective behavior of particles are our main interest in many practical applications. In this talk, I will give a brief overview of the multiscale methods connecting the physics at individual particles to macroscopic quantities and averaged equations. The emphasis will be on dense dissipative particulate systems, such as powders. Unlike conservative particle systems, such as molecular systems, in a dissipative particle system the concept of thermodynamic equilibrium is not very useful unless in very special cases, because the only true thermodynamically equilibrium state in these systems is the state in which nothing moves. Other than idealized simple systems, mesoscale structures are common and important in many practical systems, especially in dissipative systems. Spatial correlations of these mesoscale structures, such as force chains in dense granular system, particle clusters and streamers in fluidized beds have received some recent attentions, partly because they can be visualized. This talk will emphasize the effects of time correlations related to the mesoscale structures. To consider time correlations and history information of the system, I will introduce the mathematical foundation of the Liouville equation, its applicability and limitations. I will derive the generalized Liouville equations for particulate systems with and without interstitial fluids, and then use them to study averaged transport equations and related closures. Interactions among the time scale of particle interactions, the time scale of the mesocale structures, and the time scale of the physical problem as represented by strain rate will be discussed. The effect of these interactions on the closure relations will be illustrated. I will also discuss possible numerical methods of solving the averaged equations, and multiscale numerical algorithms bridging the particle level calculations to continuum level calculations. While there are many interests of studying interactions of individual particles, macroscopic collective behavior of particles are our main interest in many practical applications. In this talk, I will give a brief overview of the multiscale methods connecting the physics at individual particles to macroscopic quantities and averaged equations. The emphasis will be on dense dissipative particulate systems, such as powders. Unlike conservative particle systems, such as molecular systems, in a dissipative particle system the concept of thermodynamic equilibrium is not very useful unless in very special cases, because the only true thermodynamically equilibrium state in these systems is the state in which nothing moves. Other than idealized simple systems, mesoscale structures are common and important in many practical systems, especially in dissipative systems. Spatial correlations of these mesoscale structures, such as force chains in dense granular system, particle clusters and streamers in fluidized beds have received some recent attentions, partly because they can be visualized. This talk will emphasize the effects of time correlations related to the mesoscale structures. To consider time correlations and history information of the system, I will introduce the mathematical foundation of the Liouville equation, its applicability and limitations. I will derive the generalized Liouville equations for particulate systems with and without interstitial fluids, and then use them to study averaged transport equations and related closures. Interactions among the time scale of particle interactions, the time scale of the mesocale structures, and the time scale of the physical problem as represented by strain rate will be discussed. The effect of these interactions on the closure relations will be illustrated. I will also discuss possible numerical methods of solving the averaged equations, and multiscale numerical algorithms bridging the particle level calculations to continuum level calculations. This work was sponsored by Stockpile Safety and
Time scales in cognitive neuroscience.
Papo, David
2013-01-01
Cognitive neuroscience boils down to describing the ways in which cognitive function results from brain activity. In turn, brain activity shows complex fluctuations, with structure at many spatio-temporal scales. Exactly how cognitive function inherits the physical dimensions of neural activity, though, is highly non-trivial, and so are generally the corresponding dimensions of cognitive phenomena. As for any physical phenomenon, when studying cognitive function, the first conceptual step should be that of establishing its dimensions. Here, we provide a systematic presentation of the temporal aspects of task-related brain activity, from the smallest scale of the brain imaging technique's resolution, to the observation time of a given experiment, through the characteristic time scales of the process under study. We first review some standard assumptions on the temporal scales of cognitive function. In spite of their general use, these assumptions hold true to a high degree of approximation for many cognitive (viz. fast perceptual) processes, but have their limitations for other ones (e.g., thinking or reasoning). We define in a rigorous way the temporal quantifiers of cognition at all scales, and illustrate how they qualitatively vary as a function of the properties of the cognitive process under study. We propose that each phenomenon should be approached with its own set of theoretical, methodological and analytical tools. In particular, we show that when treating cognitive processes such as thinking or reasoning, complex properties of ongoing brain activity, which can be drastically simplified when considering fast (e.g., perceptual) processes, start playing a major role, and not only characterize the temporal properties of task-related brain activity, but also determine the conditions for proper observation of the phenomena. Finally, some implications on the design of experiments, data analyses, and the choice of recording parameters are discussed. PMID:23626578
Time scales, their users, and leap seconds
P. Kenneth Seidelmann; John H. Seago
2011-01-01
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
Rotational relaxation time of polyelectrolyte xanthan chain via single molecule tracking method
NASA Astrophysics Data System (ADS)
Lee, Jeong Yong; Jung, Hyun Wook; Hyun, Jae Chun
2012-12-01
Effect of solvent viscosity on the longest rotational relaxation time of xanthan molecule has been examined using a single molecule tracking method. Incorporating inverted epi-fluorescence microscope and chargedcoupled device (CCD) camera, various features of xanthan ( i.e., radius of gyration, orientation angle, etc.) were interpreted by image processing algorithm from the captured real xanthan images. From the best-fit of the autocorrelation function on the orientation angle, the longest rotational relaxation time was effectively determined. Rotational relaxation time increases with the medium solvent viscosity due to the slow movement of xanthan molecule. It is confirmed that there is a good agreement between experiments and Brownian dynamics simulations on the relaxation patterns of xanthan chain.
Time scales in spectator fragmentation
NASA Astrophysics Data System (ADS)
Schwarz, C.; Fritz, S.; Bassini, R.; Begemann-Blaich, M.; Gaff-Ejakov, S. J.; Gourio, D.; Groß, C.; Immé, G.; Iori, I.; Kleinevoß, U.; Kunde, G. J.; Kunze, W. D.; Lynen, U.; Maddalena, V.; Mahi, M.; Möhlenkamp, T.; Moroni, A.; Müller, W. F. J.; Nociforo, G.; Ocker, B.; Ohed, T.; Pertruzzelli, F.; Pochodzalla, J.; Raciti, G.; Riccobene, G.; Romano, F. P.; Saija, A.; Schnittker, M.; Schüttauf, A.; Seidel, W.; Serfling, V.; Sfienti, C.; Trautmann, W.; Trzcinski, A.; Verde, G.; Wörner, A.; Xi, Hongfei; Zwieglinski, B.
2001-01-01
Proton-proton correlations and correlations of p-alpha, d-alpha, and t-alpha from spectator decays following Au + Au collisions at 1000 AMeV have been measured with an highly efficient detector hodoscope. The constructed correlation functions indicate a moderate expansion and low breakup densities similar to assumptions made in statistical multifragmentation models. In agreement with a volume breakup rather short time scales were deduced employing directional cuts in proton-proton correlations. PACS numbers: 25.70.Pq, 21.65.+f, 25.70.Mn
Globus, Tatiana; Sizov, Igor; Gelmont, Boris
2014-01-01
Hydrogen bonds (H-bonds) in biological macromolecules are important for the molecular structure and functions. Since interactions via hydrogen bonds are weaker than covalent bonds, it can be expected that atomic movements involving H-bonds have low frequency vibrational modes. Sub-Terahertz (sub-THz) vibrational spectroscopy that combines measurements with molecular dynamics (MD) computational prediction has been demonstrated as a promising approach for biological molecule characterization. Multiple resonance absorption lines have been reported. The knowledge of relaxation times of atomic oscillations is critical for the successful application of THz spectroscopy for hydrogen bond characterization. The purpose of this work is to use atomic oscillations in the 0.35-0.7 THz range, found from molecular dynamic (MD) simulations of E.coli thioredoxin (2TRX), to study relaxation dynamics of two intra-molecular H-bonds, OH-N and OH-C. Two different complimentary techniques are used in this study, one is the analysis of the statistical distribution of relaxation time and dissipation factor values relevant to low frequency oscillations, and the second is the analysis of the autocorrelation function of low frequency quasi-periodic movements. By studying hydrogen bond atomic displacements, it was found that the atoms are involved in a number of collective oscillations, which are characterized by different relaxation time scales ranging from 2-3 ps to more than 150 ps. The existence of long lasting relaxation processes opens the possibility to directly observe and study H-bond vibrational modes in sub-THz absorption spectra of bio-molecules if measured with an appropriate spectral resolution. The results of measurements using a recently developed frequency domain spectroscopic sensor with a spectral resolution of 1 GHz confirm the MD analysis. PMID:25415676
Effective time-reversal symmetry breaking in the spin relaxation in a graphene quantum dot
P. R. Struck; Guido Burkard
2010-01-01
We study the relaxation of a single electron spin in a circular gate-tunable quantum dot in gapped graphene. Direct coupling of the electron spin to out-of-plane phonons via the intrinsic spin-orbit coupling leads to a relaxation time T1 which is independent of the B field at low fields. We also find that Rashba spin-orbit induced admixture of opposite spin states
Effective time-reversal symmetry breaking in the spin relaxation in a graphene quantum dot
Philipp Struck; Guido Burkard
2011-01-01
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
Gate Sizing for Crosstalk Reduction under Timing Constraints by Lagrangian Relaxation
Zhou, Hai
Gate Sizing for Crosstalk Reduction under Timing Constraints by Lagrangian Relaxation Debjit Sinha-- This paper presents a post-route, timing- constrained gate-sizing algorithm for crosstalk reduction. Gate-sizing. It is however critical to ensure that the timing constraints of the circuit are not violated after sizing. We
Papanikolaou, Nickolas; Papadaki, Eufrosini; Karampekios, Spyros; Spilioti, Martha; Maris, Thomas; Prassopoulos, Panos; Gourtsoyiannis, Nicholas
2004-01-01
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
Multiple time scale analysis of runaway phenomena
Lucio Demeio
1998-01-01
The analysis of runaway phenomena with the use of the Boltzmann equation shows that the time evolution of the distribution function and of the other quantities of interest, for example the average velocity, occurs on two time scales: the short time scale of the collisional equilibrium and the long time scale of the runaway flux. Under suitable conditions on the
Ultrafast NMR T1 relaxation measurements: probing molecular properties in real time.
Smith, Pieter E S; Donovan, Kevin J; Szekely, Or; Baias, Maria; Frydman, Lucio
2013-09-16
The longitudinal relaxation properties of NMR active nuclei carry useful information about the site-specific chemical environments and about the mobility of molecular fragments. Molecular mobility is in turn a key parameter reporting both on stable properties, such as size, as well as on dynamic ones, such as transient interactions and irreversible aggregation. In order to fully investigate the latter, a fast sampling of the relaxation parameters of transiently formed molecular species may be needed. Nevertheless, the acquisition of longitudinal relaxation data is typically slow, being limited by the requirement that the time for which the nucleus relaxes be varied incrementally until a complete build-up curve is generated. Recently, a number of single-shot-inversion-recovery methods have been developed capable of alleviating this need; still, these may be challenged by either spectral resolution restrictions or when coping with very fast relaxing nuclei. Here, we present a new experiment to measure the T1s of multiple nuclear spins that experience fast longitudinal relaxation, while retaining full high-resolution chemical shift information. Good agreement is observed between T1s measured with conventional means and T1s measured using the new technique. The method is applied to the real-time investigation of the reaction between D-xylose and sodium borate, which is in turn elucidated with the aid of ancillary ultrafast and conventional 2D TOCSY measurements. PMID:23878001
Zhang, Liqun; Greenfield, Michael L
2007-11-21
Molecular dynamics simulation was used to calculate rotational relaxation time, diffusion coefficient, and zero-shear viscosity for a pure aromatic compound (naphthalene) and for aromatic and aliphatic components in model asphalt systems over a temperature range of 298-443 K. The model asphalt systems were chosen previously to represent real asphalt. Green-Kubo and Einstein methods were used to estimate viscosity at high temperature (443.15 K). Rotational relaxation times were calculated by nonlinear regression of orientation correlation functions to a modified Kohlrausch-Williams-Watts function. The Vogel-Fulcher-Tammann equation was used to analyze the temperature dependences of relaxation time, viscosity, and diffusion coefficient. The temperature dependences of viscosity and relaxation time were related using the Debye-Stokes-Einstein equation, enabling viscosity at low temperatures of two model asphalt systems to be estimated from high temperature (443.15 K) viscosity and temperature-dependent relaxation time results. Semiquantitative accuracy of such an equivalent temperature dependence was found for naphthalene. Diffusion coefficient showed a much smaller temperature dependence for all components in the model asphalt systems. Dimethylnaphthalene diffused the fastest while asphaltene molecules diffused the slowest. Neat naphthalene diffused faster than any component in model asphalts. PMID:18035887
NASA Astrophysics Data System (ADS)
Zhang, Liqun; Greenfield, Michael L.
2007-11-01
Molecular dynamics simulation was used to calculate rotational relaxation time, diffusion coefficient, and zero-shear viscosity for a pure aromatic compound (naphthalene) and for aromatic and aliphatic components in model asphalt systems over a temperature range of 298-443 K. The model asphalt systems were chosen previously to represent real asphalt. Green-Kubo and Einstein methods were used to estimate viscosity at high temperature (443.15 K). Rotational relaxation times were calculated by nonlinear regression of orientation correlation functions to a modified Kohlrausch-Williams-Watts function. The Vogel-Fulcher-Tammann equation was used to analyze the temperature dependences of relaxation time, viscosity, and diffusion coefficient. The temperature dependences of viscosity and relaxation time were related using the Debye-Stokes-Einstein equation, enabling viscosity at low temperatures of two model asphalt systems to be estimated from high temperature (443.15 K) viscosity and temperature-dependent relaxation time results. Semiquantitative accuracy of such an equivalent temperature dependence was found for naphthalene. Diffusion coefficient showed a much smaller temperature dependence for all components in the model asphalt systems. Dimethylnaphthalene diffused the fastest while asphaltene molecules diffused the slowest. Neat naphthalene diffused faster than any component in model asphalts.
Possible sharp quantum relaxation times in "classical" fluids: theory and experiment
Z. Nussinov; F. Nogueira; M. Blodgett; K. F. Kelton
2015-04-02
Quantum effects in material systems are often pronounced at low energies and become insignificant at high temperatures. We find that, perhaps counterintuitively, certain quantum effects may follow the opposite route and become sharp when extrapolated to high temperature within a "classical" liquid phase. In the current work, we suggest basic quantum bounds on relaxation (and thermalization) times, examine kinetic theory by taking into account such possible fundamental quantum time scales, find new general equalities connecting semi-classical dynamics and thermodynamics to Planck's constant, and compute current correlation functions. Our analysis suggests that, on average, the extrapolated high temperature dynamical viscosity of general liquids may tend to a value set by the product of the particle number density ${\\sf n}$ and Planck's constant $h$. We compare this theoretical result with experimental measurements of an ensemble of 23 metallic fluids where this seems to indeed be the case. The extrapolated high temperature viscosity of each of these liquids $\\eta$ divided (for each respective fluid by its value of ${\\sf n} h$) veers towards a Gaussian with an ensemble average value that is close to unity up to an error of size $0.6 \\%$. We invoke similar ideas to discuss other transport properties and demonstrate how simple behaviors including resistivity saturation and linear $T$ resistivity may appear very naturally. Our approach suggests that minimal time lags may be present in fluid dynamics (which in the continuum follow the Navier-Stokes equation).
Relation between the two-body entropy and the relaxation time in supercooled water.
Gallo, P; Rovere, M
2015-01-01
The two-body excess entropy of supercooled water is calculated from the radial distribution functions obtained from computer simulation of the TIP4P model for different densities upon supercooling. This quantity is considered in connection with the relaxation time of the self intermediate scattering function. The relaxation time shows a mode coupling theory (MCT) behavior in the region of mild supercooling and a strong behavior in the deep supercooled region. We find here that the two-body entropy is connected to the relaxation time and shows a logarithmic behavior with an apparent asymptotic divergence at the mode coupling crossover temperature. There is also evidence of a change in behavior of the two-body entropy upon crossing from the fragile (hopping-free) state to the strong (hopping-dominated) state of supercooled water, and the relation that connects the two-body entropy and the relxation time in the MCT region no longer holds. PMID:25679570
NASA Astrophysics Data System (ADS)
Biswas, Swarup; Dutta, Bula; Bhattacharya, Subhratanu
2014-02-01
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.
Kaminski, K.; Adrjanowicz, K.; Paluch, M. [Institute of Physics, Silesian University, Uniwersytecka 4, PL-40-007 Katowice (Poland); Kaminska, E. [Department of Pharmacognosy and Phytochemistry, Medical University of Silesia, Jagiellonska 4, PL-41-200 Sosnowiec (Poland)
2011-06-15
Time-dependent isothermal dielectric measurements were carried out deeply in the glassy state on two very important saccharides: sucrose and trehalose. In both compounds two prominent secondary relaxation processes were identified. The faster one is an inherent feature of the whole family of carbohydrates. The slower one can also be detected in oligo- and polysaccharides. It was shown earlier that the {beta} process is the Johari-Goldstein (JG) relaxation coupled to motions of the glycosidic linkage, while the {gamma} relaxation originates from motions of the exocyclic hydroxymethyl unit. Recently, it was shown that the JG relaxation process can be used to determine structural relaxation times in the glassy state [R. Casalini and C. M. Roland, Phys. Rev. Lett. 102, 035701 (2009)]. In this paper we present the results of an analysis of the data obtained during aging using two independent approaches. The first was proposed by Casalini and Roland, and the second one is based on the variation of the dielectric strength of the secondary relaxation process during aging [J. K. Vij and G. Power, J. Non-Cryst. Solids 357, 783 (2011)]. Surprisingly, we found that the estimated structural relaxation times in the glassy state of both saccharides are almost the same, independent of the type of secondary mode. This finding calls into question the common view that secondary modes of intramolecular origin do not provide information about the dynamics of the glassy state.
A Selectable k-Times Relaxed Anonymous Authentication Scheme
Keita Emura; Atsuko Miyaji; Kazumasa Omote
2009-01-01
In a k-Times Anonymous Authentication (k-TAA) scheme, Application Providers (APs) authenticates each group member in k times. A user can preserve his\\/her own privacy and an AP can restrict the number of used services to just k-times, since users are identified if they access an AP more than k times. In all previous schemes, each AP assumes the same k
Advances in time-scale algorithms
NASA Technical Reports Server (NTRS)
Stein, S. R.
1993-01-01
The term clock is usually used to refer to a device that counts a nearly periodic signal. A group of clocks, called an ensemble, is often used for time keeping in mission critical applications that cannot tolerate loss of time due to the failure of a single clock. The time generated by the ensemble of clocks is called a time scale. The question arises how to combine the times of the individual clocks to form the time scale. One might naively be tempted to suggest the expedient of averaging the times of the individual clocks, but a simple thought experiment demonstrates the inadequacy of this approach. Suppose a time scale is composed of two noiseless clocks having equal and opposite frequencies. The mean time scale has zero frequency. However if either clock fails, the time-scale frequency immediately changes to the frequency of the remaining clock. This performance is generally unacceptable and simple mean time scales are not used. First, previous time-scale developments are reviewed and then some new methods that result in enhanced performance are presented. The historical perspective is based upon several time scales: the AT1 and TA time scales of the National Institute of Standards and Technology (NIST), the A.1(MEAN) time scale of the US Naval observatory (USNO), the TAI time scale of the Bureau International des Poids et Measures (BIPM), and the KAS-1 time scale of the Naval Research laboratory (NRL). The new method was incorporated in the KAS-2 time scale recently developed by Timing Solutions Corporation. The goal is to present time-scale concepts in a nonmathematical form with as few equations as possible. Many other papers and texts discuss the details of the optimal estimation techniques that may be used to implement these concepts.
Can inertial electrostatic confinement work beyond the ion--ion collisional time scale?
Nevins, W.M. [Lawrence Livermore National Laboratory, Livermore, California 94550 (United States)] [Lawrence Livermore National Laboratory, Livermore, California 94550 (United States)
1995-10-01
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}.
Can inertial electrostatic confinement work beyond the ion-ion collisional time scale?
Nevins, W.M.
1995-01-01
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.
Aryl ring rotation in porphyrins. A carbon-13 NMR spin-lattice relaxation time study
Noss, L.; Liddell, P.A.; Moore, A.L.; Moore, T.A.; Gust, D. [Arizona State Univ., Tempe, AZ (United States)] [Arizona State Univ., Tempe, AZ (United States)
1997-01-16
Overall tumbling and internal rotational motions in porphyrins bearing meso aryl substituents and, in some cases, flanking alkyl groups at the {beta}-pyrrolic positions have been determined using {sup 13}C spin-lattice relaxation time measurements. In deuteriochloroform solution at 303 K, the overall reorientation of all three porphyrins investigated occurs with diffusion coefficients of approximately 1x10{sup 9} s{sup -1}. In porphyrins with only hydrogen at the {beta}-pyrrolic positions, the meso phenyl rings undergo rotations about their single bonds to the porphyrin with diffusion coefficients of approximately 4x10{sup 9} s{sup -1}. Introduction of methyl substituents at the {beta}-pyrrolic positions adjacent to the phenyl rings reduces these motions, but only to approximately 1x10{sup 9} s{sup -1}. Thus, significant internal motions are present in both types of molecules. These motions occur on the time scale of many photoinduced electron and energy transfer processes in porphyrins covalently linked to electron or energy donors or acceptors through meso aryl groups. Thus, the internal librational motions may affect rates of photoinduced electron and energy transfer, even in relatively `rigid` molecular constructs. 47 refs., 3 tabs.
NASA Astrophysics Data System (ADS)
Evenson, Z.; Naleway, S. E.; Wei, S.; Gross, O.; Kruzic, J. J.; Gallino, I.; Possart, W.; Stommel, M.; Busch, R.
2014-05-01
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.
Will spin-relaxation times in molecular magnets permit quantum information processing?
Ardavan, Arzhang; Rival, Olivier; Morton, John J L; Blundell, Stephen J; Tyryshkin, Alexei M; Timco, Grigore A; Winpenny, Richard E P
2007-02-01
Using X-band pulsed electron-spin resonance, we report the intrinsic spin-lattice (T1) and phase-coherence (T2) relaxation times in molecular nanomagnets for the first time. In Cr7M heterometallic wheels, with M=Ni and Mn, phase-coherence relaxation is dominated by the coupling of the electron spin to protons within the molecule. In deuterated samples T2 reaches 3 micros at low temperatures, which is several orders of magnitude longer than the duration of spin manipulations, satisfying a prerequisite for the deployment of molecular nanomagnets in quantum information applications. PMID:17358891
Nuclear spin-lattice relaxation times of metallic antimony at low temperatures
NASA Astrophysics Data System (ADS)
Genio, E. B.; Xu, J.; Lang, T.; Ihas, G. G.; Sullivan, N. S.
1995-11-01
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 mixture was immersed in liquid3He to ensure good thermal contact to a sintered silver heat exchanger attached to a copper nuclear demagnetization refrigerator. We report the temperature dependence of the nuclear spin-lattice relaxation times for the multiple level nuclear spin system.
NASA Astrophysics Data System (ADS)
Belmajdoub, A.; Diter, B.; Canet, D.
1986-11-01
This work demonstrates the use of proton longitudinal relaxation to determine correlation times associated with the slow motions affecting a surfactant molecule engaged in a micellar aggregate. The longitudinal relaxation time T1 of the proton signal corresponding to methylenes in the aliphatic chain is monitored as a function of the Larmor frequency ?. T-11 versus ? is interpreted according to the "two-step" model of Halle and Wennerström. The method has been checked on the decylammonium chloride/D 2O system at two different concentrations, corresponding to spherical and elongated micelles respectively. Measurements have been taken from 3.4 to 200 MHz.
Deconvolution analysis to determine relaxation time spectra of internal friction peaks
Cost, J.R.
1985-01-01
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.
Retrieval of transverse relaxation time distribution from spin-echo data by recurrent neural network
NASA Astrophysics Data System (ADS)
Sebastião, R. C. O.; Braga, J. P.
2005-11-01
Inversion of transverse relaxation time decay curve from spin-echo experiments was carried out using Hopfield neural network, to obtain the transverse relaxation time distribution. The performance of this approach was tested against simulated and experimental data. The initial guess, necessary for the integration procedure, was established as the analytical Laplace inversion. Together with errors in the simulated data, inversion was also carried out with errors in this initial guess. The probability density function, calculated by the neural network, is used in multiple sclerosis diagnostics.
Spin-rotation contribution to the relaxation time of the fluorine nuclei in benzotrifluoride
Faulk, Robert Hardy
1965-01-01
to the usual dipole-dipole interaction. The relaxation time of the hydrogen nuclei in C6H5CF3 has been measured as a function of concentration in CS2 at 33 C; however, there o . 1 have been no known investigations of the fluorine relaxation times... the dipoles. 1. J Expanding this expression, transforming to polar coordinates, and then collecting terms, one obtains G = r) Yi (A + B + C + D + E), where (9) I. I + I I . Y i zj j zi] lj 3[ -1 -1 D 3[ +1 +11 * - ? [I. I. j Y2. and E = --[Ii I ]Y2...
Time scales, their users, and leap seconds
NASA Astrophysics Data System (ADS)
Seidelmann, P. Kenneth; Seago, John H.
2011-08-01
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.
Direct Visualization of Short Transverse Relaxation Time Component (ViSTa)
Oh, Se-Hong; Bilello, Michel; Schindler, Matthew; Markowitz, Clyde E.; Detre, John A.; Lee, Jongho
2013-01-01
White matter of the brain has been demonstrated to have multiple relaxation components. Among them, the short transverse relaxation time component (T2 < 40 ms; T2* < 25 ms at 3T) has been suggested to originate from myelin water whereas long transverse relaxation time components have been associated with axonal and/or interstitial water. In myelin water imaging, T2 or T2* signal decay is measured to estimate myelin water fraction based on T2 or T2* differences among the water components. This method has been demonstrated to be sensitive to demyelination in the brain but suffers from low SNR and image artifacts originating from ill-conditioned multi-exponential fitting. In this study, a novel approach that selectively acquires short transverse relaxation time signal is proposed. The method utilizes a double inversion RF pair to suppress a range of long T1 signal. This suppression leaves short T2* signal, which has been suggested to have short T1, as the primary source of the image. The experimental results confirms that after suppression of long T1 signals, the image is dominated by short T2* in the range of myelin water, allowing us to directly visualize the short transverse relaxation time component in the brain. Compared to conventional myelin water imaging, this new method of direct visualization of short relaxation time component (ViSTa) provides high quality images. When applied to multiple sclerosis patients, chronic lesions show significantly reduced signal intensity in ViSTa images suggesting sensitivity to demyelination. PMID:23796545
The effects of bone on proton NMR relaxation times of surrounding liquids
NASA Technical Reports Server (NTRS)
Davis, C. A.; Genant, H. K.; Dunham, J. S.
1986-01-01
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.
Susumu Matsuo; Tsutomu Ishimasa; Hiroshi Nakano
1997-01-01
Time dependence of the magnetic susceptibility of two kinds of Al?Pd?Mn icosahedral quasicrystals was studied to investigate the phason relaxation in the anneal after water quench. Al70Pd21.5Mn8.5 remained in the f-type structure and Al71Pd21Mn8 transformed to p-type. A universal time dependence was found in the initial decrease in the susceptibility characterized by square root of time. The whole time dependence
Nuclear magnetic spin-rotational relaxation times for symmetric molecules
James McConnell
1982-01-01
It is shown that the problem of calculating times related to nuclear magnetic spin-rotational interactions may be solved for the symmetric rotator model of a molecule by employing the method already proposed in a general manner for asymmetric molecules that undergo rotational thermal motion. Expressions are derived for the spin-rotational correlation time and for the contributions arising from spin-rotational interactions
NASA Astrophysics Data System (ADS)
Blair, A.; Daynes, N.; Hamilton, D.; Horne, G.; Heard, P. J.; Hodgson, D. Z. L.; Scott, T. B.; Shterenlikht, A.
2009-08-01
In this paper digital image correlation is used to measure relaxation of residual stresses across an interface. On the macro scale the method is applied to a tri-layer bonded aluminium sample, where the middle layer is in tension and the top and the bottom layers are in compression. High contrast speckle pattern was sprayed onto the surface. The relaxation was done with the slitting saw. Three dimensional image correlation was used. On the micro scale the technique was applied to a heat treated large grain brass loaded in tension. Mechanical and electro polishing was used for surface preparation. A focused ion beam was used for slitting across a grain boundary and for imaging. Grain orientation was measured using electron back-scattering diffraction. Two dimensional image correlation was employed. In all macro- and micro-scale experiments the range of measured relaxation was sub-pixel, almost at the limit of the resolution of the image correlation algorithms. In the macro-scale experiments, the limiting factor was low residual stress, due to low shear strength of the Araldite glue used for bonding. Finite element simulation of the relaxation agreed only qualitatively with the experimental results at both size scales. The methodology is intended for use with inverse methods, i.e. the measured relaxation is applied as the boundary conditions to an appropriate FE model which produces stresses equal to the relaxed residual stresses, but with opposite sign. The main conclusion is that the digital image correlation method could be used to measure relaxation caused by slitting in heterogeneous materials and structures at both macro- and micro-scales. However, the repeatability of the techniques needs to be improved before residual stresses can be determined confidently. Acknowledgments The authors gratefully acknowledge Airbus UK for provision of materials. They thank Dr Richard Burguete, Airbus UK, and Prof Peter Flewitt, Department of Physics, University of Bristol, for advice in all aspects of experimental work.
NASA Astrophysics Data System (ADS)
Klimavicius, Vytautas; Gdaniec, Zofia; Balevicius, Vytautas
2014-11-01
NMR relaxation processes of anions were studied in two neat imidazolium-based room temperature ionic liquids (RTILs) 1-decyl-3-methyl-imidazolium bromide- and chloride. The spin-lattice and spin-spin relaxations of 81Br and 35Cl nuclei were found to be extremely fast due to very strong quadrupolar interactions. The determined relaxation rates are comparable with those observed in the solids or in some critical organic solute/water/salt systems. In order to eliminate the acoustic ringing of the probe-head during relaxation times measurements the novel pulse sequence has been devised. It is based on the conventional inversion recovery pulse sequence, however, instead of the last 90° pulse the subsequence of three 90° pulses applied along axes to fulfill the phase cycling condition is used. Using this pulse sequence it was possible to measure T1 for both studied nuclei. The viscosity measurements have been carried out and the rotational correlation times were calculated. The effective 35Cl quadrupolar coupling constant was found to be almost one order lower than that for 81Br, i.e. 1.8 MHz and 16.0 MHz, respectively. Taking into account the facts that the ratio of (Q(35Cl)/Q(81Br))2 ? 0.1 and EFG tensors on the anions are quite similar, analogous structural organizations are expected for both RTILs. The observed T1/T2 (1.27-1.44) ratios were found to be not sufficiently high to confirm the presence of long-living (on the time scale of ?10-8 s) mesoscopic structures or heterogeneities in the studied neat ionic liquids.
Revisiting the measurement of the spin relaxation time in graphene-based spintronic devices
NASA Astrophysics Data System (ADS)
Idzuchi, Hiroshi; Fert, Albert; Otani, Yoshichika
2015-03-01
Spin transport in graphene has strongly drawn attention because of the expected long spin relaxation time ?sf, but, ?sf derived from experiments is rarely above 1 ns, shorter than theoretically expected and also largely dispersed. Here we reanalyze Hanle curves in graphene-based lateral spin valves with various contacts by using the recently established model of Hanle effect taking into account the spin absorption by contacts. We found the reanalysis of Hanle curves of four samples from transparent contacts to tunnel contacts, reported in ref.3, gives longer and much less dispersed ?sf ranging around 500 ps compared to the original values ranging from 84 ps to 495 ps. Extending our analysis to typical recent experiments with long spin diffusion length, ? ~ 10 ?m, we find the spin absorption is even more pronounced because the contact resistance R needed to suppress the spin absorption scales with the spin resistance ~ ? . Thus R in the range of 100 kOhm is generally not large enough to suppress the spin absorption, and taking into account the contacts is more important to characterize the real ?sf in graphene with ? in this range.
Long-time traces of the initial condition in relaxation phenomena near criticality
U. Ritschel; H. W. Diehl
1995-01-01
The time evolution of systems relaxing towards thermal equilibrium is examined near the critical temperature Tc, with special attention paid to the role of the initial value mi of the order parameter phi. To this end, the n-component model A [model A according to P. C. Hohenberg and B. I. Halperin, Rev. Mod. Phys. 49, 435 (1977)] for a cube
E. Birckner; U.-W. Grummt
2004-01-01
The rotational relaxation times of rod like molecules like poly[arylene-ethynylene]s and their low molecular weight model compounds calculated from a simple model agree well with the experimental ones as long as the axial ratio of the corresponding rotational ellipsoid is less than 8. For the polymer (axial ratio >10) the fluorescence depolarization cannot be described by rotational motion perpendicularly to
Relaxation Times of Nano-Colloid Flocculation Induced by Adsorbing and Non-adsorbing Polymers
Ahlers, Guenter
Relaxation Times of Nano-Colloid Flocculation Induced by Adsorbing and Non-adsorbing Polymers nano-colloids mediated by adsorbing and non-adsorbing polymers. By making use of this theory, we have calculated the colloid immersion energy and the potential of the polymer-mediated forces for the above cases
Shear Viscosity Coefficient and Relaxation Time of Causal Dissipative Hydrodynamics in QCD
T. Kodama; E. Nakano; T. Koide
2009-01-01
The shear viscosity coefficient and the corresponding relaxation time for causal dissipative hydrodynamics are calculated based on the microscopic formula proposed in T. Koide and T. Kodama [Phys. Rev. E 78, 051107 (2008)]. Here, the exact formula is transformed into a more compact form and applied to evaluate these transport coefficients in the chiral perturbation theory and perturbative QCD. It
Relaxation Time Constants and Apparent Diffusion Coefficients of Rat Retina at 7 Tesla
Duong, Timothy Q.
Relaxation Time Constants and Apparent Diffusion Coefficients of Rat Retina at 7 Tesla Govind Nair* and ADC of the rat eyes were measured at 50 3 50 3 800 lm at 7 Tesla. Profiles of T1, T2, T2* and ADC
A Short-Time Quantum Mechanical Expansion Approach to Vibrational Relaxation Eran Rabani*,
Rabani, Eran
of the vibrational relaxation of a probe molecule in a condensed phase host has occupied a central place in physical-coupling theories of liquids, the "binary" portion of the memory function for a given time correlation function The "viscoelastic" theory of collective density fluctua- tions in liquids involves a continued fractional
Monitoring of the creep and the relaxation hhh behaviour of concrete since setting time, hh hhhhhhhh
Paris-Sud XI, Université de
by a motor moving the other steel head. The shape of the mould is a dog-bone. The Young's modulus, the creep1 Monitoring of the creep and the relaxation hhh behaviour of concrete since setting time, hh properties change rapidly in function of the advancement of the hydration reaction. Among all the usual
Measurements of nuclear thermal relaxation times under conditions of high resolution
Hildebrandt, Alvin Frank
1956-01-01
dependent perturbations which cause relaxation. This may be seen by transforming to a coordinate system rotating about H0 in which 4 ^ is replaced by 4 ^ + fc>Qt. Now if the inten? sity of the Fourier spectra of the position function 4 ^ in D... move relative to nuclei in neighboring molecules by virtue of diffusion or translation of the molecule. The con? tribution to the relaxation time arising from the rotational motion of the molecule will be denoted by / and that / 1 \\ 1 T...
Determination of (13)C (?) relaxation times in uniformly (13)C/ (15)N-enriched proteins.
Engelke, J; Rüterjans, H
1995-02-01
Relaxation times of (13)C(?) carbons of uniformly (13)C/(15)N-enriched probes have been investigated. The relaxation behaviour was analyzed in terms of a multispin system. Pulse sequences for the determination of T(1), T(2) and the heteronuclear NOE of (13)C(?) in uniformly (13)C/(15)N-enriched ribonuclease T1 are presented. The experiments performed in order to obtain T(1) and the heteronuclear NOE were similar to those of the corresponding (15)N experiments published previously. The determination of T(2) for the C(?)-carbon in a completely labeled protein is more complicated, since the magnetization transfer during the T(2) evolution period owing to the scalar coupling of C(?)-C(?) must be suppressed. Various different pulse sequences for the T(2) evolution period were simulated in order to optimize the bandwidth for which reliable T(2) relaxation times can be obtained. A proof for the quality of these pulse sequences is given by fitting the intensity decay of individual (1)H-(13)C(?) cross peaks, in a series of ((1)H, (13)C)-ct-HSQC spectra with a modified CPMG sequence as well as a T(1p) sequence for the transverse relaxation time, to a single exponential using a simplex algorithm. PMID:22911465
Separation of equilibration time scales in the gradient expansion
NASA Astrophysics Data System (ADS)
Garbrecht, Björn; Konstandin, Thomas
2009-04-01
We study thermalization by applying gradient expansion to the Kadanoff-Baym equations of the two-particle-irreducible effective action to two-loop in a theory with Dirac fermions coupled to scalars. In addition to those chemical potentials that equilibrate in the on-shell limit, we identify modes that are conserved in this approximation, but which relax when off-shell effects are taken into account. This implies that chemical equilibration does not require higher loop contributions to the effective action and is compatible with the gradient expansion. We explicitly calculate the damping time scales of both, on- and off-shell, chemical equilibration rates. It is shown that off-shell equilibration is suppressed by the thermal width of the particles in the plasma, which explains the separation of on- and off-shell chemical equilibration time scales.
`Perfect reconstruction' time-scaling filterbanks
T. F. Quatieri; T. E. Hanna
1999-01-01
A filterbank-based method of time-scale modification is analyzed for elemental signals including clicks, sines, and AM-FM sines. It is shown that with the use of some basic properties of linear systems, as well as FM-to-AM filter transduction, “perfect reconstruction” time-scaling filterbanks can be constructed for these elemental signal classes under certain conditions on the filterbank. Conditions for perfect reconstruction time-scaling
On-chip Brownian relaxation measurements of magnetic nanobeads in the time domain
NASA Astrophysics Data System (ADS)
Østerberg, Frederik Westergaard; Rizzi, Giovanni; Hansen, Mikkel Fougt
2013-06-01
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.
Jürgen E. K. Schawe
2002-01-01
During molecular growth reactions, molecular mobility decreases. Experimentally, an increase in the relaxation time can be detected in the course of isothermal network formation. This process was studied by differential scanning calorimetry (DSC) and temperature modulated DSC using the curing reaction of an epoxy-amine thermosetting system as a classic example. In particular, the conversion dependence of the relaxation time, the
Shores, D.A.; Stout, J.H.; Gerberich, W.W.
1992-06-01
The high temperature X-ray diffraction system developed for this program is being used to measure the strains which develop during oxidation. This is being applied to Ni/NiO and Cr/Cr{sub 2}O{sub 3}. Our work suggests tat the oxide and metal crystalline texture, anisotropic elastic modulus and anisotropic thermal expansion can have a pronounced effect on strain state of these systems. Acoustic emission is being used to study oxide scale failure (fracture) during oxidation. AE data from 304 stainless steel are being used to develop a statistical model of fracture process. Strength of metal/scale interface is an important property that has been difficult to quantify. Using Nano-indentation and scratch techniques developed for characterizing thin film interfaces, an effort has begun to measure the fracture toughness of the metal/scale interface. Mathematical modelling of origin and time evolution of growth stresses is an extension and improvement of previous models. The current effort employs a more sophisticated stress analysis and expands the scope to include other stress relaxation process. The interaction between the modeling studies and the X-ray diffraction measurements provides a natural credibility check to both efforts.
Bradley, T D; McFerran, J J; Jouin, J; Debord, B; Alharbi, M; Thomas, P; Gerome, F; Benabid, F
2015-01-01
We report on the measurement of ground state atomic polarization relaxation tile of Rb vapor confined in five different hypocycloidal core shape Kagome hollow core photonic crystal fibers made with uncoated silica glass. We are able to distinguish between wall-collision and transit-time effects in optical waveguide and deduce the contribution of the atom's dwell time at the core wall surface. In contrast with convetional macroscopic atomic cell configuration, and in agreement with Monte Carlo simulations, the measured relaxation times were found to be at least one order of magnitude longer than the limit set by the atom-wall collisional relaxation from thermal atoms. This extended relaxation time is explained by the combination of a stronger contribution of the slow atoms in the atomic polarization build-up, and of the relatively significant contribution of dwell time to the relaxation process of the ground state polarization.
Driscoll, J.R. (Dept. of Mathematics and Computer Science, Dartmouth College, Hanover, NH (US)); Gabow, H.N.; Shrairman, R. (Dept. of Computer Science, Univ. of Colorado, Boulder, CO (US)); Tarjan, R.E. (Computer Science Dept., Princeton Univ., Princeton, NJ (US))
1988-11-01
The relaxed heap is a priority queue data structure that achieves the same amortized time bounds as the Fibonacci heap - a sequence of m decrease key and n delete min operations takes time O(m + n log n). A variant of relaxed heaps achieves similar bounds in the worst case - O(1) time for decrease key and O(log n) for delete min. Relaxed heaps give a processor-efficient parallel implementation of Dijkstra's shortest path algorithm, and hence other algorithms in network optimization. A relaxed heap is a type of binomial queue that allows heap order to be violated.
Protein dynamics studied by rotating frame 15N spin relaxation times.
Szyperski, T; Luginbühl, P; Otting, G; Güntert, P; Wüthrich, K
1993-03-01
Conformational rate processes in aqueous solutions of uniformly 15N-labeled pancreatic trypsin inhibitor (BPTI) at 36 degrees C were investigated by measuring the rotating frame relaxation times of the backbone 15N spins as a function of the spin-lock power. Two different intramolecular exchange processes were identified. A first local rate process involved the residues Cys38 and Arg39, had a correlation time of about 1.3 ms, and was related to isomerization of the chirality of the disulfide bond Cys14-Cys38. A second, faster motional mode was superimposed on the disulfide bond isomerization and was tentatively attributed to local segmental motions in the polypeptide sequence -Cys14-Ala15-Lys16-. The correlation time for the overall rotational tumbling of the protein was found to be 2 ns, using the assumption that relaxation is dominated by dipolar coupling and chemical shift anisotropy modulated by isotropic molecular reorientation. PMID:7682879
Time domain models for multiple time scale linear systems
R. Silva-Madriz; S. S. Sastry
1984-01-01
We study the multiple time scales structure of linear systems of the form x = A0(¿)x + B0(¿)u y = C0(¿)x with a view to obtaining 'approximate' lower order dynamical models valid at different time scales. Our development includes the classical two time-scale case. We use our results to study the robustness of the positive realness of linear systems systems
Bolinger, Joshua C; Hayes, Sophia C; Reid, Philip J
2004-09-01
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. PMID:15332913
Relationships between induced polarization relaxation time and hydraulic properties of sandstone
NASA Astrophysics Data System (ADS)
Titov, Konstantin; Tarasov, Andrey; Ilyin, Yuri; Seleznev, Nikita; Boyd, Austin
2010-03-01
We investigated electrical and physical-chemical properties of six sandstone samples with contrasting mineralogical characteristics and with hydraulic conductivity varying in a wide range. The electrical data were obtained from time domain spectral induced polarization (IP) measurements. We inverted the IP decays to relaxation time distributions, and then compared the modal relaxation times with the dominant pore throat diameters obtained from the Mercury Injection Capillary Pressure (MICP) data. We found a positive logarithmic relationship between the relaxation time and the pore throat diameter. Also, we found the normalized chargeability (an integral IP parameter) to be positively correlated with the clay content. These two results suggest that the polarization of our sandstones is controlled by the pore throat distribution, and by the clay content. The logarithmic relationship contradicts previous theories, and is not universal. Adopting an approach of Kruschwitz and her co-workers, we calculated the effective diffusivity from IP and MICP data, and we found the effective diffusivity values ranging from 2.9 × 10-13 to 1.6 × 10-10 m2s-1. High diffusivity values, typical of surface diffusion, were obtained for clean sandstones. Low diffusivity values were obtained for clayey sandstones, and they were one to two orders of magnitude lower than those characteristic of the surface diffusion. We proposed two mechanisms to explain the `slow' diffusion: (1) the effect of surface tortuosity of pore throats filled with clay minerals and (2) the effect of pore geometry. These two effects represent an obstacle in assessing the pore throat diameter and hydraulic conductivity of sandstones with large specific surface and clay content on the basis of spectral IP measurements. However, we believe that the sandstones featuring `slow' diffusion can be discriminated based on the integral polarization parameters, and that the relaxation time remains a valuable parameter for assessing hydraulic properties of clean sandstones.
Using Dielectric Relaxation Spectroscopy to Characterize the Glass Transition Time of Polydextrose.
Buehler, Martin G; Kindle, Michael L; Carter, Brady P
2015-06-01
Dielectric relaxation spectroscopy was used to characterize the glass transition time, tg , of polydextrose, where the glass transition temperature, Tg , and water activity, aw (relative humidity), were held constant during polydextrose relaxation. The tg was determined from a shift in the peak frequency of the imaginary capacitance spectrum with time. It was found that when the peak frequency reaches 30 mHz, polydextrose undergoes glass transition. Glass transition time, tg , is the time for polydextrose to undergo glass transition at a specific Tg and aw . Results lead to a modified state diagram, where Tg is depressed with increasing aw . This curve forms a boundary: (a) below the boundary, polydextrose does not undergo glass transition and (b) above the boundary, polydextrose rapidly undergoes glass transition. As the boundary curve is specified by a tg value, it can assist in the selection of storage conditions. An important point on the boundary curve is at aw = 0, where Tg0 = 115 °C. The methodology can also be used to calculate the stress-relaxation viscosity of polydextrose as a function of Tg and aw , which is important when characterizing the flow properties of polydextrose initially in powder form. PMID:25944358
Lattice Boltzmann equation with multiple effective relaxation times for gaseous microscale flow.
Guo, Zhaoli; Zheng, Chuguang; Shi, Baochang
2008-03-01
The standard lattice Boltzmann equation (LBE) is inadequate for simulating gas flows with a large Knudsen number. In this paper we propose a generalized lattice Boltzmann equation with effective relaxation times based on a recently developed generalized Navier-Stokes constitution [Guo, Europhys Lett. 80, 24001 (2007)] for nonequilibrium flows. A kinetic boundary condition corresponding to a generalized second-order slip scheme is also designed for the model. The LBE model and the boundary condition are analyzed for a unidirectional flow, and it is found that in order to obtain the generalized Navier-Stokes equations, the relaxation times must be properly chosen and are related to the boundary condition. Numerical results show that the proposed method is able to capture the Knudsen layer phenomenon and can yield improved predictions in comparison with the standard lattice Boltzmann equation. PMID:18517557
Shear viscosity to relaxation time ratio in SU(3) lattice gauge theory
Yasuhiro Kohno; Masayuki Asakawa; Masakiyo Kitazawa
2013-03-25
We evaluate the ratio of the shear viscosity to the relaxation time of the shear flux above but near the critical temperature $T_c$ in SU(3) gauge theory on the lattice. The ratio is related to Kubo's canonical correlation of the energy-momentum tensor in Euclidean space with the relaxation time approximation and an appropriate regularization. Using this relation, the ratio is evaluated by direct measurements of the Euclidean observables on the lattice. We obtained the ratio with reasonable statistics for the range of temperature $1.3T_c \\lesssim T \\lesssim 4T_c$. We also found that the characteristic speed of the transverse plane wave in gluon media is almost constant, $v \\simeq 0.5$, for $T \\gtrsim 1.5T_c$, which is compatible with the causality in the second order dissipative hydrodynamics.
Shear viscosity coefficient and relaxation time of causal dissipative hydrodynamics in QCD.
Koide, T; Nakano, E; Kodama, T
2009-07-31
The shear viscosity coefficient and the corresponding relaxation time for causal dissipative hydrodynamics are calculated based on the microscopic formula proposed in T. Koide and T. Kodama [Phys. Rev. E 78, 051107 (2008)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 eta reduces to that of the ordinary Green-Kubo-Nakano formula, and the relaxation time tau(pi) is related to eta and pressure P by a simple relationship, tau(pi)=eta/P. PMID:19792491
Shear Viscosity Coefficient and Relaxation Time of Causal Dissipative Hydrodynamics in QCD
Koide, T.; Nakano, E.; Kodama, T. [FIAS, Johann Wolfgang Goethe-Universitaet, Ruth-Moufang Str. 1, 60438, Frankfurt am Main (Germany); Extreme Matter Institute, GSI, Planckstr. 1, D-64291 Darmstadt (Germany); Instituto de Fisica, Universidade Federal do Rio de Janeiro, C. P. 68528, 21945-970, Rio de Janeiro (Brazil)
2009-07-31
The shear viscosity coefficient and the corresponding relaxation time for causal dissipative hydrodynamics are calculated based on the microscopic formula proposed in T. Koide and T. Kodama [Phys. Rev. E 78, 051107 (2008)]. Here, the exact formula is transformed into a more compact form and applied to evaluate these transport coefficients in the chiral perturbation theory and perturbative QCD. It is shown that in the leading order calculation, the causal shear viscosity coefficient eta reduces to that of the ordinary Green-Kubo-Nakano formula, and the relaxation time tau{sub p}i is related to eta and pressure P by a simple relationship, tau{sub p}i=eta/P.
NASA Astrophysics Data System (ADS)
Wilkie, Joshua
2001-12-01
We show that the projection operators P usually employed to derive the Nakajima-Zwanzig master equation are non-Hermitian. As a consequence the operator QLQ which governs the dynamics of subsystem-reservoir interactions (here Q=1-P and L is the Liouville operator) is also non-Hermitian and possesses a complex temperature-dependent spectrum of resonances. We use the self-consistent Born approximation to derive a formula for the spectral density of QLQ. From this spectral density we calculate the memory function and mean relaxation time of subsystem-reservoir correlations. These formulas are compared with numerical results obtained from the spin-spin-bath model to test their accuracy. The memory function and mean relaxation time are essential ingredients for the SRA (statistical resonance approximation) theory of microscopic dissipation and decoherence. We show that the SRA master equation preserves positivity when the memory function derived in this paper is employed.
Metaphor for the geologic time scale
NSDL National Science Digital Library
Cara Thompson
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.
Bulk rotational relaxation time and cross-section in gas mixtures
M. Terzic; D Markushev; J Jovanovi?-Kurepa
2001-01-01
In an earlier paper [M. Terzi?, J. Jovanovi?-Kurepa, D.D. Markušev, J. Phys. B: At. Mol. Opt. Phys. 32 (1999) 1193] we have presented a method for evaluation of the bulk rotational relaxation times and cross-sections in gas mixtures from the measured saturation intensity, IS, vs. buffer gas pressure, pbuff, at constant incident laser energy. According to this method, the bulk
Shear Viscosity Coefficient and Relaxation Time of Causal Dissipative Hydrodynamics in QCD
T. Koide; E. Nakano; T. Kodama
2009-01-01
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
Implicit-correction-based immersed boundary-lattice Boltzmann method with two relaxation times
NASA Astrophysics Data System (ADS)
Seta, Takeshi; Rojas, Roberto; Hayashi, Kosuke; Tomiyama, Akio
2014-02-01
In the present paper, we verify the effectiveness of the two-relaxation-time (TRT) collision operator in reducing boundary slip computed by the immersed boundary-lattice Boltzmann method (IB-LBM). In the linear collision operator of the TRT, we decompose the distribution function into symmetric and antisymmetric components and define the relaxation parameters for each part. The Chapman-Enskog expansion indicates that one relaxation time for the symmetric component is related to the kinematic viscosity. Rigorous analysis of the symmetric shear flows reveals that the relaxation time for the antisymmetric part controls the velocity gradient, the boundary velocity, and the boundary slip velocity computed by the IB-LBM. Simulation of the symmetric shear flows, the symmetric Poiseuille flows, and the cylindrical Couette flows indicates that the profiles of the numerical velocity calculated by the TRT collision operator under the IB-LBM framework exactly agree with those of the multirelaxation time (MRT). The TRT is as effective in removing the boundary slip as the MRT. We demonstrate analytically and numerically that the error of the boundary velocity is caused by the smoothing technique using the ? function used in the interpolation method. In the simulation of the flow past a circular cylinder, the IB-LBM based on the implicit correction method with the TRT succeeds in preventing the flow penetration through the solid surface as well as unphysical velocity distortion. The drag coefficient, the wake length, and the separation points calculated by the present IB-LBM agree well with previous studies at Re = 10, 20, and 40.
Molecular dynamics of diglycine nitrate studied by phase memory relaxation time of glycine radical
S. K. Hoffmann; M. Gramza; W. Hilczer
1995-01-01
The glycine radical NH3 CHCOO was produced by X-ray irradiation and identified by EPR method. Electron spin echo measurements at X-band of the phase memory time TM in temperature range 4.2-300 K show that phase relaxation is different on different hyperfine splitting levels. TM reaches maximal value of 6 ?s at helium temperature and two minima in TM(T) dependence are
M. Alcoutlabi; J. J. Martinez-Vega
1999-01-01
Empirical models corresponding to a constitutive equation with fractional derivatives are proposed for linear viscoelastic polymers. For these models, the relaxation modulus, the dynamic moduli, the relaxation time spectra, and other material functions can be calculated as a function of a few parameters that characterise the behaviour of a viscoelastic polymer. The fractional calculus approach allows us to calculate the
Theory of phonon-modulated electron spin relaxation time based on the projection—reduction method
NASA Astrophysics Data System (ADS)
Nam, Lyong Kang; Sang, Don Choi
2014-08-01
This paper introduces a new method for a formula for electron spin relaxation time of a system of electrons interacting with phonons through phonon-modulated spin—orbit coupling using the projection-reduction method. The phonon absorption and emission processes as well as the photon absorption and emission processes in all electron transition processes can be explained in an organized manner, and the result can be represented in a diagram that can provide intuition for the quantum dynamics of electrons in a solid. The temperature (T) dependence of electron spin relaxation times (T1) in silicon is T1 ? T-1.07 at low temperatures and T1 ? T-3.3 at high temperatures for acoustic deformation constant Pad = 1.4 × 107 eV and optical deformation constant Pod = 4.0 × 1017 eV/m. This means that electrons are scattered by the acoustic deformation phonons at low temperatures and optical deformation phonons at high temperatures, respectively. The magnetic field (B) dependence of the relaxation times is T1 ? B-2.7 at 100 K and T1 ? B-2.3 at 150 K, which nearly agree with the result of Yafet, T1 ? B-3.0 ~ B-2.5.
Viscosity, relaxation time, and dynamics within a model asphalt of larger molecules.
Li, Derek D; Greenfield, Michael L
2014-01-21
The dynamics properties of a new "next generation" model asphalt system that represents SHRP AAA-1 asphalt using larger molecules than past models is studied using molecular simulation. The system contains 72 molecules distributed over 12 molecule types that range from nonpolar branched alkanes to polar resins and asphaltenes. Molecular weights range from 290 to 890 g/mol. All-atom molecular dynamics simulations conducted at six temperatures from 298.15 to 533.15 K provide a wealth of correlation data. The modified Kohlrausch-Williams-Watts equation was regressed to reorientation time correlation functions and extrapolated to calculate average rotational relaxation times for individual molecules. The rotational relaxation rate of molecules decreased significantly with increasing size and decreasing temperature. Translational self-diffusion coefficients followed an Arrhenius dependence. Similar activation energies of ?42 kJ/mol were found for all 12 molecules in the model system, while diffusion prefactors spanned an order of magnitude. Viscosities calculated directly at 533.15 K and estimated at lower temperatures using the Debye-Stokes-Einstein relationship were consistent with experimental data for asphalts. The product of diffusion coefficient and rotational relaxation time showed only small changes with temperature above 358.15 K, indicating rotation and translation that couple self-consistently with viscosity. At lower temperatures, rotation slowed more than diffusion. PMID:25669400
Viscosity, relaxation time, and dynamics within a model asphalt of larger molecules
Li, Derek D.; Greenfield, Michael L., E-mail: greenfield@egr.uri.edu [Department of Chemical Engineering, University of Rhode Island, Kingston, Rhode Island 02881 (United States)
2014-01-21
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.
Orientation relaxation in glassy polymers. II. Dipole-size spectroscopy and short-time kinetics
NASA Astrophysics Data System (ADS)
Patashinski, Alexander Z.; Ratner, Mark A.
1995-12-01
The orientational diffusion of a rodlike particle embedded in a glassy polymeric matrix is considered; the underlying kinetics is that of local rearrangements. A defining parameter of the theory is the length of the particle. The timing of steps of the random walk in orientation space is determined by rearrangements. We discuss the physical properties of the glass state in connection with the rearrangement kinetics. The orientational diffusion is influenced by the local disorder; this influence is different for dipoles of different length. For a short dipole, the resulting diffusion is of generalized Debye type. Nonexponential relaxation of physical quantities may then be caused by the distribution of rearrangement barriers. For longer dipoles and if the orientation is uniquely determined by the configuration of the embedding cluster, the motion is a random walk on a given random map on a sphere. An ensemble of random mappings is considered. For even longer dipoles, hierarchical (multiscale) relaxation is expected. We discuss the relation of the theory to the short time depoling kinetics in a system of dipoles having different length, such as are found in relaxation of electrically poled polymer materials.
Phonon induced spin relaxation times of single donors and donor clusters in silicon
NASA Astrophysics Data System (ADS)
Hsueh, Yuling; Buch, Holger; Hollenberg, Lloyd; Simmons, Michelle; Klimeck, Gerhard; Rahman, Rajib
2014-03-01
The phonon induced relaxation times (T1) of electron spins bound to single phosphorous (P) donors and P donor clusters in silicon is computed using the atomistic tight-binding method. The electron-phonon Hamiltonian is directly computed from the strain dependent tight-binding Hamiltonian, and the relaxation time is computed from Fermi's Golden Rule using the donor states and the electron-phonon Hamiltonian. The self-consistent Hartree method is used to compute the multi-electron wavefunctions in donor clusters. The method takes into account the full band structure of silicon including the spin-orbit interaction, and captures both valley repopulation and single valley g-factor shifts in a unified framework. The single donor relaxation rate varies proportionally to B5, and is of the order of seconds at B =2T, both in good agreement with experimental single donor data (A. Morello et. al., Nature 467, 687 (2010)). T1 calculations in donor clusters show variations for different electron numbers and donor numbers and locations. The computed T1 in a 4P:5e donor cluster match well with a scanning tunneling microscope patterned P donor cluster (H. Buch et. al., Nature Communications 4, 2017 (2013)).
NASA Technical Reports Server (NTRS)
De Mey, S.; Thomas, J. D.; Greenberg, N. L.; Vandervoort, P. M.; Verdonck, P. R.
2001-01-01
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.
NASA Astrophysics Data System (ADS)
Valente, Pedro C.; da Silva, Carlos B.; Pinho, Fernando T.
2013-11-01
We report a numerical study of statistically steady and decaying turbulence of FENE-P fluids for varying polymer relaxation times ranging from the Kolmogorov dissipation time-scale to the eddy turnover time. The total turbulent kinetic energy dissipation is shown to increase with the polymer relaxation time in both steady and decaying turbulence, implying a ``drag increase.'' If the total power input in the statistically steady case is kept equal in the Newtonian and the viscoelastic simulations the increase in the turbulence-polymer energy transfer naturally lead to the previously reported depletion of the Newtonian, but not the overall, kinetic energy dissipation. The modifications to the nonlinear energy cascade with varying Deborah/Weissenberg numbers are quantified and their origins investigated. We report a numerical study of statistically steady and decaying turbulence of FENE-P fluids for varying polymer relaxation times ranging from the Kolmogorov dissipation time-scale to the eddy turnover time. The total turbulent kinetic energy dissipation is shown to increase with the polymer relaxation time in both steady and decaying turbulence, implying a ``drag increase.'' If the total power input in the statistically steady case is kept equal in the Newtonian and the viscoelastic simulations the increase in the turbulence-polymer energy transfer naturally lead to the previously reported depletion of the Newtonian, but not the overall, kinetic energy dissipation. The modifications to the nonlinear energy cascade with varying Deborah/Weissenberg numbers are quantified and their origins investigated. The authors acknowledge the financial support from Fundação para a Ciência e a Tecnologia under grant PTDC/EME-MFE/113589/2009.
Mouse Activity across Time Scales: Fractal Scenarios
Lima, G. Z. dos Santos; Lobão-Soares, B.; do Nascimento, G. C.; França, Arthur S. C.; Muratori, L.; Ribeiro, S.; Corso, G.
2014-01-01
In this work we devise a classification of mouse activity patterns based on accelerometer data using Detrended Fluctuation Analysis. We use two characteristic mouse behavioural states as benchmarks in this study: waking in free activity and slow-wave sleep (SWS). In both situations we find roughly the same pattern: for short time intervals we observe high correlation in activity - a typical 1/f complex pattern - while for large time intervals there is anti-correlation. High correlation of short intervals ( to : waking state and to : SWS) is related to highly coordinated muscle activity. In the waking state we associate high correlation both to muscle activity and to mouse stereotyped movements (grooming, waking, etc.). On the other side, the observed anti-correlation over large time scales ( to : waking state and to : SWS) during SWS appears related to a feedback autonomic response. The transition from correlated regime at short scales to an anti-correlated regime at large scales during SWS is given by the respiratory cycle interval, while during the waking state this transition occurs at the time scale corresponding to the duration of the stereotyped mouse movements. Furthermore, we find that the waking state is characterized by longer time scales than SWS and by a softer transition from correlation to anti-correlation. Moreover, this soft transition in the waking state encompass a behavioural time scale window that gives rise to a multifractal pattern. We believe that the observed multifractality in mouse activity is formed by the integration of several stereotyped movements each one with a characteristic time correlation. Finally, we compare scaling properties of body acceleration fluctuation time series during sleep and wake periods for healthy mice. Interestingly, differences between sleep and wake in the scaling exponents are comparable to previous works regarding human heartbeat. Complementarily, the nature of these sleep-wake dynamics could lead to a better understanding of neuroautonomic regulation mechanisms. PMID:25275515
Electron spin relaxation time in (110) InGaAs/InAlAs quantum wells
Yokota, Nobuhide; Yasuda, Yusuke; Ikeda, Kazuhiro; Kawaguchi, Hitoshi, E-mail: khitoshi@ms.naist.jp [Graduate School of Materials Science, Nara Institute of Science and Technology 8916-5 Takayama, Ikoma, Nara 630-0192 (Japan)
2014-07-14
Electron spin relaxation time ?{sub s} in InGaAs/InAlAs quantum wells (QWs) grown on (110) and (100) InP substrates was investigated by pump-probe transmission measurements. Similar ?{sub s} of 0.83–1.0?ns were measured at room temperature for all the measured (110) and (100) QWs, indicating suppression of the D'yakonov-Perel' spin relaxation mechanism in (110) QWs is not effective in InGaAs/InAlAs QWs as opposed to GaAs/AlGaAs QWs. Contribution of the Bir-Aronov-Pikus mechanism dominant in (110) GaAs/AlGaAs QWs was found to be small in both the (110) and (100) InGaAs/InAlAs QWs from the weak dependences of ?{sub s} on pump intensity at room temperature. These results suggest that the spin relaxation mechanism dominant in InGaAs/InAlAs QWs at a temperature higher than 200?K is the Elliott-Yafet mechanism independent of the crystal orientation among the above three major mechanisms.
Observing Reality on Different Time Scales
NASA Astrophysics Data System (ADS)
Alyushin, Alexey
2005-10-01
In the first part of the paper, I examine cases of acceleration of perception and cognition and provide my explanation of the mechanism of the effect. The explanation rests on the conception of neuronal temporal frames, or windows of simultaneity. Frames have different standard durations and yield to stretching and compressing. I suggest it to be the cause of the effect, as well as the ground for differences in perceptive time scales of living beings. In the second part, I apply the conception of temporal frames to model observation in the extended time scales that reach far beyond the temporal perceptive niche of individual living beings. Duration of a frame is taken as the basic parameter setting a particular time scale. By substituting a different frame duration, we set a hypothetical time scale and emulate observing reality in a wider or a narrower angle of embracing events in time. I discuss the status of observer in its relation to objective reality, and examine how reality does change its appearance when observed in different time scales.
Dynamics of glass-forming liquids. XVIII. Does entropy control structural relaxation times?
Samanta, Subarna; Richert, Ranko
2015-01-28
We study the dielectric dynamics of viscous glycerol in the presence of a large bias field. Apart from dielectric saturation and polarization anisotropy, we observe that the steady state structural relaxation time is longer by 2.7% in the presence of a 225 kV/cm dc-field relative to the linear response counterpart, equivalent to a field induced glass transition (Tg) shift of +84 mK. This result compares favorably with the 3.0% time constant increase predicted on the basis of a recent report [G. P. Johari, J. Chem. Phys. 138, 154503 (2013)], where the field induced reduction of the configurational entropy translates into slower dynamics by virtue of the Adam-Gibbs relation. Other models of field dependent glass transition temperatures are also discussed. Similar to observations related to the electro-optical Kerr effect, the rise time of the field induced effect is much longer than its collapse when the field is removed again. The orientational relaxation time of the plastic crystal cyclo-octanol is more sensitive to a bias field, showing a 13.5% increase at a field of 150 kV/cm, equivalent to an increase of Tg by 0.58 K. PMID:25637992
Time scale synchronization of chaotic oscillators
Alexander Hramov; Alexey Koronovskii
2006-02-25
This paper presents the result of the investigation of chaotic oscillator synchronization. A new approach for detecting of synchronized behaviour of chaotic oscillators has been proposed. This approach is based on the analysis of different time scales in the time series generated by the coupled chaotic oscillators. This approach has been applied for the coupled Rossler and Lorenz systems.
Baum, T.; Joseph, G.B.; Karampinos, D.C.; Jungmann, P.M.; Link, T.M.; Bauer, J.S.
2014-01-01
SUMMARY Objective The purpose of this work was to review the current literature on cartilage and meniscal T2 relaxation time. Methods Electronic searches in PubMed were performed to identify relevant studies about T2 relaxation time measurements as non-invasive biomarker for knee osteoarthritis (OA) and cartilage repair procedures. Results Initial osteoarthritic changes include proteoglycan loss, deterioration of the collagen network, and increased water content within the articular cartilage and menisci. T2 relaxation time measurements are affected by these pathophysiological processes. It was demonstrated that cartilage and meniscal T2 relaxation time values were significantly increased in subjects with compared to those without radiographic OA and focal knee lesions, respectively. Subjects with OA risk factors such as overweight/obesity showed significantly greater cartilage T2 values than normal controls. Elevated cartilage and meniscal T2 relaxation times were found in subjects with vs without knee pain. Increased cartilage T2 at baseline predicted morphologic degeneration in the cartilage, meniscus, and bone marrow over 3 years. Furthermore, cartilage repair tissue could be non-invasively assessed by using T2 mapping. Reproducibility errors for T2 measurements were reported to be smaller than the T2 differences in healthy and diseased cartilage indicating that T2 relaxation time may be a reliable discriminatory biomarker. Conclusions Cartilage and meniscal T2 mapping may be suitable as non-invasive biomarker to diagnose early stages of knee OA and to monitor therapy of OA. PMID:23896316
Enthalpy space analysis of the evolution of the primary relaxation time in ultraslowing systems
NASA Astrophysics Data System (ADS)
Martinez Garcia, J. C.; Tamarit, J. Ll.; Rzoska, S. J.
2011-01-01
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.
The electron-phonon relaxation time in thin superconducting titanium nitride films
Kardakova, A., E-mail: kardakova@rplab.ru [Physics Department, Moscow State Pedagogical University, Moscow 119991 (Russian Federation); Moscow Institute of Physics and Technology (State University), Dolgoprudny 141700 (Russian Federation); Finkel, M.; Kovalyuk, V.; An, P. [Physics Department, Moscow State Pedagogical University, Moscow 119991 (Russian Federation)] [Physics Department, Moscow State Pedagogical University, Moscow 119991 (Russian Federation); Morozov, D.; Dunscombe, C.; Mauskopf, P. [School of Physics and Astronomy, Cardiff University, Cardiff CF24 3AA (United Kingdom)] [School of Physics and Astronomy, Cardiff University, Cardiff CF24 3AA (United Kingdom); Tarkhov, M. [National Research Centre, “Kurchatov Institute,” Moscow 123128 (Russian Federation)] [National Research Centre, “Kurchatov Institute,” Moscow 123128 (Russian Federation); Klapwijk, T. M. [Physics Department, Moscow State Pedagogical University, Moscow 119991 (Russian Federation) [Physics Department, Moscow State Pedagogical University, Moscow 119991 (Russian Federation); Kavli Institute of Nanoscience, Delft University of Technology, 2628 CJ Delft (Netherlands); Goltsman, G. [Physics Department, Moscow State Pedagogical University, Moscow 119991 (Russian Federation) [Physics Department, Moscow State Pedagogical University, Moscow 119991 (Russian Federation); National Research University Higher School of Economics, Moscow 101000 (Russian Federation)
2013-12-16
We report on the direct measurement of the electron-phonon relaxation time, ?{sub eph}, in disordered TiN films. Measured values of ?{sub eph} are from 5.5?ns to 88?ns in the 4.2 to 1.7?K temperature range and consistent with a T{sup ?3} temperature dependence. The electronic density of states at the Fermi level N{sub 0} is estimated from measured material parameters. The presented results confirm that thin TiN films are promising candidate-materials for ultrasensitive superconducting detectors.
NASA Astrophysics Data System (ADS)
Coffey, W. T.
1997-10-01
Exact integral expressions valid for any potential barrier height for mean first passage times (and so the exit time and the reaction rate) for relaxation processes governed by the rotational Fokker-Planck equation with an axially symmetric potential are derived in a manner exactly analogous to that used to derive an integral expression for the correlation time by Coffey and Crothers (W.T. Coffey and D.S.F. Crothers, Phys. Rev. E. 54 (1996) 4768). This is accomplished by constructing the adjoint Fokker-Planck operator (Kolmogorov backward operator) and so forming the partial differential equation for the mean first passage time, which for axial symmetry may be directly integrated by quadratures. The results constitute a generalization of the work of Klein, (G. Klein, Proc. R. Soc. London, Ser. A 211 (1952) 431) originally given for the free rotational Brownian movement, to the rotational Brownian movement in an axially symmetric potential.
Djamel Ayad; Christian Carrot; Jacques Guillet
2001-01-01
The study of the viscoelastic behavior of molten polyvinylidene fluoride (PVDF) was performed in oscillatory shear flow and analyzed in terms of relaxation time distribution. Continuous spectrum having a log normal distribution of relaxation time and discrete spectrum with a limited number of relaxation modes were investigated. Attention was also paid to the correspondence between the two types of spectra.
Time Invariant Scaling in Discrete Fragmentation Models
B. G. Giraud; R. Peschanski
1994-09-13
Linear rate equations are used to describe the cascading decay of an initial heavy cluster into fragments. We consider moments of arbitrary orders of the mass multiplicity spectrum and derive scaling properties pertaining to their time evolution. We suggest that the mass weighted multiplicity is a suitable observable for the discovery of scaling. Numerical tests validate such properties, even for moderate values of the initial mass (nuclei, percolation clusters, jets of particles etc.). Finite size effects can be simply parametrized.
G. C Borgia; R. J. S Brown; P Fantazzini
1998-01-01
In a suite of water-saturated sandstones, we have recently demonstrated that irreducible water saturation can be well estimated using relaxation time only, in the form of any of several “averages” giving more emphasis to short times than does the geometric mean time. The best estimate of permeability came from fits giving more emphasis to slightly longer times. In this paper
RSLAM: A System for Large-Scale Mapping in Constant-Time Using Stereo
Christopher Mei; Gabe Sibley; Mark Cummins; Paul Newman; Ian Reid
2011-01-01
Large scale exploration of the environment requires a constant time estimation engine. Bundle adjustment or pose relaxation\\u000a do not fulfil these requirements as the number of parameters to solve grows with the size of the environment. We describe\\u000a a relative simultaneous localisation and mapping system (RSLAM) for the constant-time estimation of structure and motion using\\u000a a binocular stereo camera system
Structural relaxation by digital-correlation spectroscopy
C. Demoulin; C. J. Montrose; N. Ostrowsky
1974-01-01
The utility of digital-correlation spectroscopy for investigating structural relaxation in liquids on time scales from 1 musec to 1 sec is established. A digital correlator was used to analyze the Rayleigh scattering of light from undercooled glycerol. The correlation function obtained is related to the isothermal structural relaxation dynamics of the liquid. The data were found to join smoothly with
The time scale of evolutionary innovation.
Chatterjee, Krishnendu; Pavlogiannis, Andreas; Adlam, Ben; Nowak, Martin A
2014-09-01
A fundamental question in biology is the following: what is the time scale that is needed for evolutionary innovations? There are many results that characterize single steps in terms of the fixation time of new mutants arising in populations of certain size and structure. But here we ask a different question, which is concerned with the much longer time scale of evolutionary trajectories: how long does it take for a population exploring a fitness landscape to find target sequences that encode new biological functions? Our key variable is the length, L, of the genetic sequence that undergoes adaptation. In computer science there is a crucial distinction between problems that require algorithms which take polynomial or exponential time. The latter are considered to be intractable. Here we develop a theoretical approach that allows us to estimate the time of evolution as function of L. We show that adaptation on many fitness landscapes takes time that is exponential in L, even if there are broad selection gradients and many targets uniformly distributed in sequence space. These negative results lead us to search for specific mechanisms that allow evolution to work on polynomial time scales. We study a regeneration process and show that it enables evolution to work in polynomial time. PMID:25211329
The Time Scale of Evolutionary Innovation
Chatterjee, Krishnendu; Pavlogiannis, Andreas; Adlam, Ben; Nowak, Martin A.
2014-01-01
A fundamental question in biology is the following: what is the time scale that is needed for evolutionary innovations? There are many results that characterize single steps in terms of the fixation time of new mutants arising in populations of certain size and structure. But here we ask a different question, which is concerned with the much longer time scale of evolutionary trajectories: how long does it take for a population exploring a fitness landscape to find target sequences that encode new biological functions? Our key variable is the length, of the genetic sequence that undergoes adaptation. In computer science there is a crucial distinction between problems that require algorithms which take polynomial or exponential time. The latter are considered to be intractable. Here we develop a theoretical approach that allows us to estimate the time of evolution as function of We show that adaptation on many fitness landscapes takes time that is exponential in even if there are broad selection gradients and many targets uniformly distributed in sequence space. These negative results lead us to search for specific mechanisms that allow evolution to work on polynomial time scales. We study a regeneration process and show that it enables evolution to work in polynomial time. PMID:25211329
Pressure jump relaxation setup with IR detection and millisecond time resolution
NASA Astrophysics Data System (ADS)
Schiewek, Martin; Krumova, Marina; Hempel, Günter; Blume, Alfred
2007-04-01
An instrument is described that allows the use of Fourier transform infrared (FTIR) spectroscopy as a detection system for kinetic processes after a pressure jump of up to 100bars. The pressure is generated using a high performance liquid chromatography (HPLC) pump and water as a pressure transducing medium. A flexible membrane separates the liquid sample in the IR cell from the pressure transducing medium. Two electromagnetic switching valves in the setup enable pressure jumps with a decay time of 4ms. The FTIR spectrometer is configured to measure time resolved spectra in the millisecond time regime using the rapid scan mode. All components are computer controlled. For a demonstration of the capability of the method first results on the kinetics of a phase transition between two lamellar phases of an aqueous phospholipid dispersion are presented. This combination of FTIR spectroscopy with the pressure jump relaxation technique can also be used for other systems which display cooperative transitions with concomitant volume changes.
Bulk viscosity and relaxation time of causal dissipative relativistic fluid dynamics
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
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.
Biele, R; Timm, C; D'Agosta, R
2014-10-01
Quantum stochastic methods based on effective wave functions form a framework for investigating the generally non-Markovian dynamics of a quantum-mechanical system coupled to a bath. They promise to be computationally superior to the master-equation approach, which is numerically expensive for large dimensions of the Hilbert space. Here, we numerically investigate the suitability of a known stochastic Schrödinger equation that is local in time to give a description of thermal relaxation and energy transport. This stochastic Schrödinger equation can be solved with a moderate numerical cost, indeed comparable to that of a Markovian system, and reproduces the dynamics of a system evolving according to a general non-Markovian master equation. After verifying that it describes thermal relaxation correctly, we apply it for the first time to the energy transport in a spin chain. We also discuss a portable algorithm for the generation of the coloured noise associated with the numerical solution of the non-Markovian dynamics. PMID:25204376
Ab Initio Electron Relaxation Times and Computational Screening of Thermoelectric Materials
NASA Astrophysics Data System (ADS)
Kozinsky, Boris; Samsonidze, Georgy
2015-03-01
We report recent progress in development of an efficient approximation scheme for computing electron relaxation times in bulk crystalline materials from first principles. This technique takes into account electron-phonon coupling and opens up the possibility for ab initio calculations of electronic transport coefficients: electrical conductivity, the electronic part of thermal conductivity, and Seebeck coefficient. We find that electron relaxation times and transport coefficients are very sensitive to carrier concentration, and their accurate prediction is necessary for computational optimization of thermoelectric material composition. For a given thermoelectric material, we are able to determine the optimal carrier concentration which maximizes ZT at a target temperature. With this methodology at hand, systematic computational screening is performed in the compositional space of half-Heusler materials selected from materials databases and consisting of cheap earth-abundant elements. Good agreement is found with the available experimental data for previously synthesized half-Heusler compounds, and several new promising candidates for thermoelectric applications are identified, which have been synthesized and validated by experimental collaborators. Based on the results of our calculations, we also discuss the validity and applicability limits of the Wiedemann-Franz law for thermoelectric materials.
The hippocampus, time, and memory across scales.
Howard, Marc W; Eichenbaum, Howard
2013-11-01
A wealth of experimental studies with animals have offered insights about how neural networks within the hippocampus support the temporal organization of memories. These studies have revealed the existence of "time cells" that encode moments in time, much as the well-known "place cells" map locations in space. Another line of work inspired by human behavioral studies suggests that episodic memories are mediated by a state of temporal context that changes gradually over long time scales, up to at least a few thousand seconds. In this view, the "mental time travel" hypothesized to support the experience of episodic memory corresponds to a "jump back in time" in which a previous state of temporal context is recovered. We suggest that these 2 sets of findings could be different facets of a representation of temporal history that maintains a record at the last few thousand seconds of experience. The ability to represent long time scales comes at the cost of discarding precise information about when a stimulus was experienced--this uncertainty becomes greater for events further in the past. We review recent computational work that describes a mechanism that could construct such a scale-invariant representation. Taken as a whole, this suggests the hippocampus plays its role in multiple aspects of cognition by representing events embedded in a general spatiotemporal context. The representation of internal time can be useful across nonhippocampal memory systems. PMID:23915126
NASA Astrophysics Data System (ADS)
Prantner, Viktória; Isaksson, Hanna; Närväinen, Johanna; Lammentausta, Eveliina; Nissi, Mikko J.; Avela, Janne; Gröhn, Olli H. J.; Jurvelin, Jukka S.
2010-12-01
Nuclear magnetic resonance (NMR) spectroscopy provides a potential tool for non-invasive evaluation of the trabecular bone structure. The objective of this study was to determine the reproducibility of the NMR relaxation parameters (T2, Carr-Purcel-T2, T1?) for fat and water and relate those to the structural parameters obtained by micro-computed tomography (?CT). Especially, we aimed to evaluate the effect of freezing on the relaxation parameters. For storing bone samples, freezing is the standard procedure during which the biochemical and cellular organization of the bone marrow may be affected. Bovine trabecular bone samples were stored at -20 °C for 7 days and measured by NMR spectroscopy before and after freezing. The reproducibility of NMR relaxation parameters, as expressed by the coefficient of variation, ranged from 3.1% to 27.9%. In fresh samples, some correlations between NMR and structural parameters (Tb.N, Tb.Sp) were significant (e.g. the relaxation rate for T2 of fat versus Tb.Sp: r = -0.716, p < 0.01). Freezing did not significantly change the NMR relaxation times but the correlations between relaxation parameters and the ?CT structural parameters were not statistically significant after freezing, suggesting some nonsystematic alterations of the marrow structure. Therefore, the use of frozen bone samples for NMR relaxation studies may provide inferior information about the trabecular bone structure.
Lifetimes and time scales in atmospheric chemistry
Michael J. Prather
2007-01-01
Atmospheric composition is controlled by the emission, photochemistry, and transport of many trace gases. Understanding the time-scale as well as the chemical and spatial patterns of perturbations to trace gases is needed to evaluate possible environmental damage (e.g., stratospheric ozone depletion or climate change) caused by anthropogenic emissions. This paper reviews lessons learned from treating global atmospheric chemistry as a
Performance of AERMOD at different time scales
Bin Zou; F. Benjamin Zhan; J. Gaines Wilson; Yongnian Zeng
2010-01-01
As high-density monitoring networks observing pollutant concentrations are costly to establish and maintain, researchers often employ various models to estimate concentrations of air pollutants. The AMS\\/EPA Regulatory Model (AERMOD) is a fairly recent and promising model for estimating concentrations of air pollutants, but the effectiveness of this model at different time scales remains to be verified. This paper evaluates the
Dynamical theory of spin noise and relaxation: Prospects for real-time NMR measurements.
Field, Timothy R
2014-11-01
Recent developments in theoretical aspects of spin noise and relaxation and their interrelationship reveal a modified spin density, distinct from the density matrix, as the necessary object to describe fluctuations in spin systems. These fluctuations are to be viewed as an intrinsic quantum mechanical property of such systems immersed in random magnetic environments and are observed as "spin noise" in the absence of any radio frequency excitation. With the prospect of ultrafast digitization, the role of spin noise in real-time parameter extraction for (NMR) spin systems, and the advantage over standard techniques, is of essential importance, especially for systems containing a small number of spins. In this article we outline prospects for harnessing the recent dynamical theory in terms of spin-noise measurement, with attention to real-time properties. PMID:25493776
Transport coefficients for bulk viscous evolution in the relaxation-time approximation
NASA Astrophysics Data System (ADS)
Jaiswal, Amaresh; Ryblewski, Radoslaw; Strickland, Michael
2014-10-01
We derive the form of the viscous corrections to the phase-space distribution function due to bulk viscous pressure and shear stress tensor using the iterative Chapman-Enskog method. We then calculate the transport coefficients necessary for the second-order hydrodynamic evolution of the bulk viscous pressure and the shear stress tensor. We demonstrate that the transport coefficients obtained using the Chapman-Enskog method are different than those obtained previously using the 14-moment approximation for a finite particle mass. Specializing to the case of boost-invariant and transversally homogeneous longitudinal expansion, we show that the transport coefficients obtained using the Chapman-Enskog method result in better agreement with the exact solution of the Boltzmann equation in the relaxation-time approximation compared to results obtained in the 14-moment approximation. Finally, we explicitly confirm that the time evolution of the bulk viscous pressure is significantly affected by its coupling to the shear stress tensor.
G. C. Borgia; R. J. S. Brown; P. Fantazzini
1997-01-01
Fluid-flow properties of porous media, such as permeability k and irreducible water saturation Swi, can be estimated from water 1H nuclear magnetic resonance (NMR) relaxation data, but there are basic questions regarding data processing and interpretation. We found that Swi and k are better estimated if different forms of “average” relaxation time are used. NMR longitudinal relaxation data for a
NASA Astrophysics Data System (ADS)
Feng, Tianli
The prediction of spectral phonon relaxation time, mean-free-path, and thermal conductivity can provide significant insights into the thermal conductivity of bulk and nanomaterials, which are important for thermal management and thermoelectric applications. We perform frequency-domain normal mode analysis (NMA) on pure bulk argon and pure bulk germanium. Spectral phonon properties, including the phonon dispersion, relaxation time, mean free path, and thermal conductivity of argon and germanium at different temperatures have been calculated. We find the dependence of phonon relaxation time tau on frequency o and temperature T vary from ~o-1.3 to ~o -1.8 and ~T-0.8 to ~T-1.8 for argon, and from ~o-0.6 to ~o-2.8 and ~T -0.4 to ~T-2.5 for germanium. The predicted thermal conductivities are in reasonable agreement with those obtained from the Green-Kubo method. We show, using both analytical derivations and numerical simulations, that the eigenvectors are necessary in time-domain NMA but unnecessary in frequency-domain NMA. The function of eigenvectors in frequency-domain NMA is to distinguish each phonon branch. Furthermore, it is found in solids not only the phonon frequency but also the phonon eigenvector can shift from harmonic lattice profile at finite temperature, due to thermal expansion and anharmonicity of interatomic potential. The anharmonicity of phonon eigenvector, different with that of frequency, only exists in the materials which contain at least two types of atoms and two different interatomic forces. Introducing anharmonic eigenvectors makes it easier to distinguish phonon branches in frequency-domain NMA although does not influence the results. For time-domain NMA, anharmonic eigenvectors make the results more accurate than harmonic eigenvectors. In addition, the phonon spectral relaxation time of defective silicon is calculated from frequency-domain NMA based on molecular dynamics. We show that the thermal conductivity k predicted from this approach is in excellent agreement with the Green-Kubo method. We find that the Matthiessen's rule that combines the intrinsic phonon scattering and defect scattering to yield total phonon scattering rate is not accurate in defective silicon. The defect scattering rate itself is small but causes large increase in the total scattering rate, due to the strong interplay between these phonon-phonon and phonon-impurity scatterings. This finding successfully explains why a small concentration of defects causes large reduction in k. The Mattheissen's rule is found to over-predict k of Ge-doped and mass-doped silicon bulks by a factor of 2~3, and C-doped and vacancy-doped silicon bulks by a factor of 3~8 at 300 K. Furthermore, the phonon scattering caused by the changing the interatomic bonds, often ignored, is found to be not negligible. Our results provide new physical insight into thermal transport in defective materials as well as other perturbed systems, and offer important guidance in nanoscale thermal predictions and applications.
A comment on the use of flushing time, residence time, and age as transport time scales
Monsen, N.E.; Cloern, J.E.; Lucas, L.V.; Monismith, S.G.
2002-01-01
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.
Accuracy metrics for judging time scale algorithms
NASA Technical Reports Server (NTRS)
Douglas, R. J.; Boulanger, J.-S.; Jacques, C.
1994-01-01
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.
NASA Astrophysics Data System (ADS)
Ikeda, Kazuhiro; Kawaguchi, Hitoshi
2015-02-01
We performed measurements at room temperature for a GaAs/AlGaAs multiple quantum well grown on GaAs(110) using a time-resolved microscopic photoluminescence (micro-PL) technique to find what effects spin diffusion had on the measured electron spin relaxation time, ?s, and developed a method of estimating the spin diffusion coefficient, Ds, using the measured data and the coupled drift-diffusion equations for spin polarized electrons. The spatial nonuniformities of ?s and the initial degree of electron spin polarization caused by the pump intensity distribution inside the focal spot were taken into account to explain the dependence of ?s on the measured spot size, i.e., a longer ?s for a smaller spot size. We estimated Ds as ˜100 cm2/s, which is similar to a value reported in the literature. We also provided a qualitative understanding on how spin diffusion lengthens ?s in micro-PL measurements.
Short-time scale behavior modeling within long-time scale fuel cycle evaluations
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
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)
Shear viscosities from the Chapman-Enskog and the relaxation time approaches
NASA Astrophysics Data System (ADS)
Wiranata, Anton; Prakash, Madappa
2012-05-01
The interpretation of the measured elliptic and higher order collective flows in heavy-ion collisions in terms of viscous hydrodynamics depends sensitively on the ratio of shear viscosity to entropy density. Here we perform a quantitative comparison between the results of shear viscosities from the Chapman-Enskog and relaxation time methods for selected test cases with specified elastic differential cross sections: (i) the nonrelativistic, relativistic and ultrarelativistic hard sphere gas with angle and energy independent differential cross section, (ii) the Maxwell gas, (iii) chiral pions, and (iv) massive pions for which the differential elastic cross section is taken from experiments. Our quantitative results (i) reveal that the extent of agreement (or disagreement) depends sensitively on the energy dependence of the differential cross sections employed, and (ii) stress the need to perform quantum molecular dynamical (URQMD) simulations that employ Green-Kubo techniques with similar cross sections to validate the codes employed and to test the accuracy of other methods.
Time constant of defect relaxation in ion-irradiated 3C-SiC
NASA Astrophysics Data System (ADS)
Wallace, J. B.; Bayu Aji, L. B.; Shao, L.; Kucheyev, S. O.
2015-05-01
Above room temperature, the buildup of radiation damage in SiC is a dynamic process governed by the mobility and interaction of ballistically generated point defects. Here, we study the dynamics of radiation defects in 3C-SiC bombarded at 100 °C with 500 keV Ar ions, with the total ion dose split into a train of equal pulses. Damage-depth profiles are measured by ion channeling for a series of samples irradiated under identical conditions except for different durations of the passive part of the beam cycle. Results reveal an effective defect relaxation time constant of ˜ 3 ms (for second order kinetics) and a dynamic annealing efficiency of ˜ 40 % for defects in both Si and C sublattices. This demonstrates a crucial role of dynamic annealing at elevated temperatures and provides evidence of the strong coupling of defect accumulation processes in the two sublattices of 3C-SiC.
T2 Relaxation Time of Cartilage at MR Imaging: Comparison with Severity of Knee Osteoarthritis
Dunn, Timothy C.; Lu, Ying; Jin, Hua; Ries, Michael D.; Majumdar, Sharmila
2015-01-01
PURPOSE To evaluate differences in T2 values in femoral and tibial cartilage at magnetic resonance (MR) imaging in patients with varying degrees of osteoarthritis (OA) compared with healthy subjects and to develop a mapping and display method based on calculation of T2 z scores for visual grading and assessment of cartilage heterogeneity in patients with OA. MATERIALS AND METHODS Knee cartilage was evaluated in 55 subjects who were categorized with radiography as healthy (n=7) or as having mild OA (n=20) or severe OA (n=28). Cartilage regions were determined with manual segmentation of an MR image acquired with spoiled gradients and fat suppression. The segmentation was applied to a map of T2 relaxation time and was analyzed in four knee cartilage compartments (ie, the medial and lateral tibia and femur). Differences between cartilage compartment T2 values and subject groups were analyzed with analysis of covariance. Correlations of cartilage T2 values with clinically reported symptoms and cartilage thickness and volume were examined. Cartilage T2 values were converted to z scores per voxel on the basis of normal population values in the same cartilage compartment to better interpret cartilage heterogeneity and variation from normal. RESULTS Healthy subjects had mean T2 values of 32.1–35.0 msec, while patients with mild and severe OA had mean T2 values of 34.4–41.0 msec. All cartilage compartments except the lateral tibia showed significant (P< .05) increases in T2 relaxation time between healthy and diseased knees; however, no significant difference was found between patients with mild and severe OA. Correlation of T2 values with clinical symptoms and cartilage morphology was found predominantly in medial compartments. CONCLUSION Femoral and medial tibial cartilage T2 values increase with the severity of OA. PMID:15215540
Fletcher, J.W.; Hendershott, L.R.; Fernandez-Pol, J.A.
1984-01-01
The Nuclear Magnetic Resonance (NMR) properties of normal rat kidney (NRK) cells and their cloned transformed derivatives (CTD), Kirsten sarcoma-(K) and Simian virus 40-(SV) NRK cells were studied. Cells were cultured in DME media containing 10% (v/v) calf serum. After washing, cells were harvested, counted, volume determined and viability established. NMR measurements were made on cell pellets with a permanent magnet system operating at 10 MHz and 37/sup 0/C utilizing a Hahn spin-echo sequence. The proton T/sub 1/ for NRK cells was 1332 +- 78msec (+- 1 SD). In contrast, the T/sub 1/ of both CTD was reduced: T/sub 1/ for SV-NRK cells was 1053 +- 108msec and for K-NRK was 912 +- 53msec. Parallel decreases in T/sub 2/ relaxation times were also found in both CTD in comparison with the NRK cells. Shortened T/sub 1/ and T/sub 2/ values were also found when cells were maintained invarious media during NMR measurements. The results indicate that there is a correlation between the malignant phenotype and the shortened T/sub 1/ and T/sub 2/ values of the SV-NRK and K-NRK cell lines in culture. This relationship was strengthened by the finding that similar results were observed when the cells were maintained in a variety of media during the NMR determinations. The shortened NMR proton relaxation times may be due to the position of the SV-NRK and K-NRK cells in the cell cycle as a significant proportion of the CTD are in the S or M phases of the cell cycle in comparison to NRK cells.
Nanosecond Time Scale Motions in Proteins Revealed by High-Resolution NMR Relaxometry
2013-01-01
Understanding the molecular determinants underlying protein function requires the characterization of both structure and dynamics at atomic resolution. Nuclear relaxation rates allow a precise characterization of protein dynamics at the Larmor frequencies of spins. This usually limits the sampling of motions to a narrow range of frequencies corresponding to high magnetic fields. At lower fields one cannot achieve sufficient sensitivity and resolution in NMR. Here, we use a fast shuttle device where the polarization builds up and the signals are detected at high field, while longitudinal relaxation takes place at low fields 0.5 < B0 < 14.1 T. The sample is propelled over a distance up to 50 cm by a blowgun-like system in about 50 ms. The analysis of nitrogen-15 relaxation in the protein ubiquitin over such a wide range of magnetic fields offers unprecedented insights into molecular dynamics. Some key regions of the protein feature structural fluctuations on nanosecond time scales, which have so far been overlooked in high-field relaxation studies. Nanosecond motions in proteins may have been underestimated by traditional high-field approaches, and slower supra-?c motions that have no effect on relaxation may have been overestimated. High-resolution relaxometry thus opens the way to a quantitative characterization of nanosecond motions in proteins. PMID:24228712
Vugmeyster, Liliya; Ostrovsky, Dmitry; Lipton, Andrew S.
2013-05-23
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.
R. I. Chelcea; R. Fechete; E. Culea; D. E. Demco; B. Blümich
2009-01-01
The single-sided NMR-MOUSE sensor that operates in highly inhomogeneous magnetic fields is used to record a CPMG 1H transverse relaxation decay by CPMG echo trains for a series of cross-linked natural rubber samples. Effective transverse relaxation rates 1\\/T2,short and 1\\/T2,long were determined by a bi-exponential fit. A linear dependence of transverse relaxation rates on cross-link density is observed for medium
Nuclear magnetic relaxation, correlation time spectrum, and molecular dynamics in a linear polymer
Chernov, V. M., E-mail: chernov@csu.ru; Krasnopol'skii, G. S. [Chelyabinsk State University (Russian Federation)
2008-08-15
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.
Towards a quaternary time scale*1
NASA Astrophysics Data System (ADS)
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
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.
Time ephemeris and general relativistic scale factor
NASA Astrophysics Data System (ADS)
Fukushima, Toshio
2010-01-01
Time ephemeris is the location-independent part of the transformation formula relating two time coordinates such as TCB and TCG (Fukushima 1995). It is computed from the corresponding (space) ephemerides providing the relative motion of two spatial coordinate origins such as the motion of geocenter relative to the solar system barycenter. The time ephemerides are inevitably needed in conducting precise four dimensional coordinate transformations among various spacetime coordinate systems such as the GCRS and BCRS (Soffel et al. 2003). Also, by means of the time average operation, they are used in determining the information on scale conversion between the pair of coordinate systems, especially the difference of the general relativistic scale factor from unity such as LC. In 1995, we presented the first numerically-integrated time ephemeris, TE245, from JPL's planetary ephemeris DE245 (Fukushima 1995). It gave an estimate of LC as 1.4808268457(10) × 10-8, which was incorrect by around 2 × 10-16. This was caused by taking the wrong sign of the post-Newtonian contribution in the final summation. Four years later, we updated TE245 to TE405 associated with DE405 (Irwin and Fukushima 1999). This time the renewed vale of LC is 1.48082686741(200) × 10-8 Another four years later, by using a precise technique of time average, we improved the estimate of Newtonian part of LC for TE405 as 1.4808268559(6) × 10-8 (Harada and Fukushima 2003). This leads to the value of LC as LC = 1.48082686732(110) × 10-8. If we combine this with the constant defining the mean rate of TCG-TT, LG = 6.969290134 × 10-10 (IAU 2001), we estimate the numerical value of another general relativistic scale factor LB = 1.55051976763(110) × 10-8, which has the meaning of the mean rate of TCB-TT. The main reasons of the uncertainties are the truncation effect in time average and the uncertainty of asteroids' perturbation. The former is a natural limitation caused by the finite length of numerical planetary ephemerides and the latter is due to the uncertainty of masses of some heavy asteroids. As a compact realization of the time ephemeris, we prepared HF2002, a Fortran routine to compute approximate harmonic series of TE405 with the RMS error of 0.446 ns for the period 1600 to 2200 (Harada and Fukushima 2003). It is included in the IERS Convention 2003 (McCarthy and Petit 2003) and available from the IERS web site; http://tai.bipm.org/iers/conv2003/conv2003_c10.html.
Time-dependent pseudo Jahn-Teller effect: Phonon-mediated long-time nonadiabatic relaxation
Vaikjärv, Taavi, E-mail: taavi.vaikjarv@ut.ee; Hizhnyakov, Vladimir [Institute of Physics, University of Tartu, Riia 142, 51014 Tartu (Estonia)] [Institute of Physics, University of Tartu, Riia 142, 51014 Tartu (Estonia)
2014-02-14
Our system under theoretical consideration is an impurity center in a solid. We are considering the time evolution of the center in a quasi-degenerate electronic state. Strict quantum mechanical treatment of non-adiabadicity of the state is used. The phonon continuum is taken into account in addition to the vibration responsible for the main vibronic interaction. To describe the dynamics of the excited state a master equation has been used. The theoretical considerations are illustrated by the calculations of the long-time evolution of vibrations of the center, influenced by the emission of phonons to the bulk.
South Atlantic Spreading Velocities and Time Scales
NASA Astrophysics Data System (ADS)
Clark, S. R.; Smethurst, M. A.; Bianchi, M. C.
2013-12-01
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.
Electron Spin Relaxation and Coherence Times in Si/SiGe Quantum Dots
NASA Astrophysics Data System (ADS)
Jock, R. M.; He, Jianhua; Tyryshkin, A. M.; Lyon, S. A.; Lee, C.-H.; Huang, S.-H.; Liu, C. W.
2013-03-01
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 mm2) , double gated, undoped Si/SiGe heterostructure, which was patterned with 2 x 108 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. 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 mm2) , double gated, undoped Si/SiGe heterostructure, which was patterned with 2 x 108 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. supported by the ARO
Scaling laws from geomagnetic time series
Voros, Z.; Kovacs, P.; Juhasz, A.; Kormendi, A.; Green, A.W.
1998-01-01
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.
G. C. Borgia; V. Bortolotti; R. J. S. Brown; P. Fantazzini
1996-01-01
A method is presented to compute values of geometric mean time Tg that uses only a few data points equispaced in the logarithm of time (or equispaced in time and weighted by 1t) and a few elementary operations for the computation. The method has been tested on a large number of synthetic relaxation data and on actual NMR relaxation measurements
T2 relaxation time post febrile status epilepticus predicts cognitive outcome.
Barry, Jeremy M; Choy, ManKin; Dube, Celine; Robbins, Ashlee; Obenaus, Andre; Lenck-Santini, Pierre Pascal; Scott, Rod C; Baram, Tallie Z; Holmes, Gregory L
2015-07-01
Evidence from animal models and patient data indicates that febrile status epilepticus (FSE) in early development can result in permanently diminished cognitive abilities. To understand the variability in cognitive outcome following FSE, we used MRI to measure dynamic brain metabolic responses to the induction of FSE in juvenile rats. We then compared these measurements to the ability to learn an active avoidance spatial task weeks later. T2 relaxation times were significantly lower in FSE rats that were task learners in comparison to FSE non-learners. While T2 time in whole brain held the greatest predictive power, T2 in hippocampus and basolateral amygdala were also excellent predictors. These signal differences in response to FSE indicate that rats that fail to meet metabolic and oxygen demand are more likely to develop spatial cognition deficits. Place cells from FSE non-learners had significantly larger firing fields and higher in-field firing rate than FSE learners and control animals and imply increased excitability in the pyramidal cells of FSE non-learners. These findings suggest a mechanistic cause for the spatial memory deficits in active avoidance and are relevant to other acute neurological insults in early development where cognitive outcome is a concern. PMID:25939697
NASA Astrophysics Data System (ADS)
Avellaneda, M.; Torquato, S.
1991-11-01
A rigorous expression is derived that relates exactly the static fluid permeability k for flow through porous media to the electrical formation factor F (inverse of the dimensionless effective conductivity) and an effective length parameter L, i.e., k=L2/8F. This length parameter involves a certain average of the eigenvalues of the Stokes operator and reflects information about electrical and momentum transport. From the exact relation for k, a rigorous upper bound follows in terms of the principal viscous relation time ?1 (proportional to the inverse of the smallest eigenvalue): k???1/F, where ? is the kinematic viscosity. It is also demonstrated that ??1?DT1, where T1 is the diffusion relaxation time for the analogous scalar diffusion problem and D is the diffusion coefficient. Therefore, one also has the alternative bound k?DT1/F. The latter expression relates the fluid permeability on the one hand to purely diffusional parameters on the other. Finally, using the exact relation for the permeability, a derivation of the approximate relation k??2/8F postulated by Johnson et al. [Phys. Rev. Lett. 57, 2564 (1986)] is given.
Pulsed-gate measurements of the singlet-triplet relaxation time in a two-electron double quantum dot
Petta, Jason
Pulsed-gate measurements of the singlet-triplet relaxation time in a two-electron double quantum for the manipulation of electron spin because of the relative ease of confining and measuring single electrons.1 A spin for nearly degenerate two-electron spin states. This technique can be used to measure T1 in regimes for which
Pamela M. Barton; Keith C. Hayes
1996-01-01
Objective: To determine the test-retest reliability of a new method for measuring muscular strength, efficiency, and relaxation times of the neck flexor musculature of healthy adults, and to compare these neck flexor muscle properties in subjects who have unilateral neck pain and headache with those in controls.Design: Subjects lay supine and isometrically flexed their necks against a force transducer attached
ERIC Educational Resources Information Center
Gasyna, Zbigniew L.; Jurkiewicz, Antoni
2004-01-01
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.
Paris-Sud XI, Université de
Time-Resolved Torsional Relaxation of Spider Draglines by an Optical Technique O. Emile,1,* A. Le pendulum demonstrates the self-shape-memory effect in different types of spider draglines. Here we report, 78.40.Me, 87.10.+e, 87.15.ÿv Silk fibers and spider draglines have attracted much interest because
Master equation for the Unruh-DeWitt detector and the universal relaxation time in de Sitter space
NASA Astrophysics Data System (ADS)
Fukuma, Masafumi; Sugishita, Sotaro; Sakatani, Yuho
2014-03-01
We derive the master equation that completely determines the time evolution of the density matrix of the Unruh-DeWitt detector in an arbitrary background geometry. We apply the equation to reveal a nonequilibrium thermodynamic character of de Sitter space. This generalizes an earlier study on the thermodynamic property of the Bunch-Davies vacuum that an Unruh-DeWitt detector staying in the Poincaré patch and interacting with a scalar field in the Bunch-Davies vacuum behaves as if it is in a thermal bath of finite temperature. In this paper, instead of the Bunch-Davies vacuum, we consider a class of initial states of scalar field, for which the detector behaves as if it is in a medium that is not in thermodynamic equilibrium and that undergoes a relaxation to the equilibrium corresponding to the Bunch-Davies vacuum. We give a prescription for calculating the relaxation times of the nonequilibrium processes. We particularly show that, when the initial state of the scalar field is the instantaneous ground state at a finite past, the relaxation time is always given by a universal value of half the curvature radius of de Sitter space. We expect that the relaxation time gives a nonequilibrium thermodynamic quantity intrinsic to de Sitter space.
Hyaline articular cartilage: relaxation times, pulse-sequence parameters and MR appearance at 1.5 T
Stylianos M. Chalkias; Roberto S. Pozzi-Mucelli; Massimo Pozzi-Mucelli; Francesca Frezza; Renata Longo
1994-01-01
In order to optimize the parameters for the best visualization of the internal architecture of the hyaline articular cartilage a study both ex vivo and in vivo was performed. Accurate T1 and T2 relaxation times of articular cartilage were obtained with a particular mixed sequence and then used for the creation of isocontrast intensity graphs. These graphs subsequently allowed in
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.
Time scales in nuclear giant resonances
WD Heiss; RG Nazmitdinov; FD Smit
2009-12-18
We propose a general approach to characterise fluctuations of measured cross sections of nuclear giant resonances. Simulated cross sections are obtained from a particular, yet representative self-energy which contains all information about fragmentations. Using a wavelet analysis, we demonstrate the extraction of time scales of cascading decays into configurations of different complexity of the resonance. We argue that the spreading widths of collective excitations in nuclei are determined by the number of fragmentations as seen in the power spectrum. An analytic treatment of the wavelet analysis using a Fourier expansion of the cross section confirms this principle. A simple rule for the relative life times of states associated with hierarchies of different complexity is given.
Time-scale for accretion of matter
F. Combes
1998-11-09
Mass accretion is the key factor for evolution of galaxies. It can occur through secular evolution, when gas in the outer parts is driven inwards by dynamical instabilities, such as spirals or bars. This secular evolution proceeds very slowly when spontaneous, and can be accelerated when triggered by companions. Accretion can also occur directly through merging of small companions, or more violent interaction and coalescence. We discuss the relative importance of both processes, their time-scale and frequency along a Hubble time. Signatures of both processes can be found in the Milky Way. It is however likely that our Galaxy had already gathered the bulk of its mass about 8-10 Gyr ago, as is expected in hierarchical galaxy formation scenarios.
D'Angelo, R; Shah, N; Rubler, S
1975-07-01
Isovolumic relaxation time (IVRT) and rapid filling time (RFT) were used to evaluate elasticity and compliance in 11 control subjects (Group 1), in nine patients with angina (Group 2), in 11 with hypertensive heasrt disease (Group 3), and in ten patients with healed myocardial infarction (Group 4). Pre-ejection period (PEP), pre-ejection period index (PEPI), left ventricular ejection time (LVET), left ventricular ejection time index(LVETI) and PEP/LVET ratio were all derived from simultaneous recordings of phonocardiograms, ECGs, apexcardiograms, and external carotid arterial pulses. No patients were in congestive heart failure and none were receiving medication. LVET and LVETI were the same in control patient groups; PEP was slightly increased in patients with healed myocardial infarctions (p smaller than 0.05); and PEPI was prolonged in the patients with angina (p = 0.001). THE PEP/LVET ratio too was different from the control group in patients with angina and hypertension (Groups 2 and 3-p smaller than 0.02 and smaller than 0.05 respectively). The diastolic time intervals were significantly altered in that the IVRT was prolonged in angina patients (113.4 equals or minus 28.3 msec), compared to control patients (85.7) equal or minus 18.4 msec). It was found that in 6 out of 9 patients with angina, this interval exceeded the highest normal value (108 msec), but that in only one out 11 patients with HCVD and in three out of ten with healed infarctions, was the interval prolonged. RFT was increased in HCVD (113.8 equals or minus 18.8 msec) and in healed myocardial infarction (123.8 equals or minus 30.0 msec) patients, compared to the control group (94.5 equals or minus 12.8 msec). Diastolic time intervals reflecting disorders in elasticity and compliance may occur in conjunction with alterations in systolic time intervals. PMID:1149531
Parametric instabilities in picosecond time scales
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
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.
KUMAR, DEEPAK; SUBBURAJ, KARUPPPASAMY; LIN, WILSON; KARAMPINOS, DIMITRIOS C.; MCCULLOCH, CHARLES E.; LI, XIAOJUAN; LINK, THOMAS M.; SOUZA, RICHARD B.; MAJUMDAR, SHARMILA
2015-01-01
STUDY DESIGN Controlled laboratory study using a cross-sectional design. OBJECTIVES To analyze the relationship of quadriceps-hamstrings and medial-lateral quadriceps anatomical cross-sectional area (ACSA) ratios with knee loads during walking and articular and meniscal cartilage composition in young, healthy subjects. BACKGROUND Muscle forces affect knee loading during walking, but it is not known if muscle morphology is associated with walking mechanics and cartilage composition in young subjects. METHODS Forty-two knees from 27 young, healthy, active volunteers (age, 20-35 years; body mass index, <28 kg/m2) underwent 3-T magnetic resonance imaging (MRI) and 3-D motion capture. Standard MRI sequences were used for articular and meniscal cartilage T1rho and T2 relaxation times and for quadriceps and hamstrings muscle ACSA. Frontal plane kinetics during the stance phase of walking was calculated. Generalized estimating equation models were used to identify muscle variables that predicted MRI and gait parameters. RESULTS Quadriceps-hamstrings and medial-lateral quadriceps ACSA ratios were positively related to frontal plane loading (? = .27-.54, P?.006), global articular cartilage relaxation times (? = .22-.28, P?.041), and the medial-lateral ratio of meniscus T1rho relaxation time (? = .26-.36, P?.049). The medial-lateral quadriceps ACSA ratio was positively related to global meniscus T1rho relaxation times (? = .30, P = .046). CONCLUSION Higher quadriceps-hamstrings and medial-lateral quadriceps ACSA ratios were associated with higher frontal plane loading during walking and with articular and meniscal cartilage T1rho and T2 relaxation times. These findings highlight the relationships between different knee tissues and knee mechanics in young, healthy individuals. PMID:24175607
Radial Transport of Large-scale Magnetic Fields in Accretion Disks. II. Relaxation to Steady States
NASA Astrophysics Data System (ADS)
Takeuchi, Taku; Okuzumi, Satoshi
2014-12-01
We study the time evolution of a large-scale magnetic flux threading an accretion disk. The induction equation of the mean poloidal field is solved under the standard viscous disk model. Magnetic flux evolution is controlled by two timescales: one is the timescale of the inward advection of the magnetic flux, ?adv. This is induced by the dragging of the flux by the accreting gas. The other is the outward diffusion timescale of the magnetic flux ?dif. We consider diffusion due to the Ohmic resistivity. These timescales can be significantly different from the disk viscous timescale ?disk. The behaviors of the magnetic flux evolution are quite different depending on the magnitude relationship of the timescales ?adv, ?dif, and ?disk. The most interesting phenomena occur when ?adv Lt ?dif, ?disk. In such a case, the magnetic flux distribution approaches a quasi-steady profile much faster than the viscous evolution of the gas disk, and the magnetic flux has also been tightly bundled to the inner part of the disk. In the inner part, although the poloidal magnetic field becomes much stronger than the interstellar magnetic field, the field strength is limited to the maximum value that is analytically given by our previous work. We also find a condition for the initial large magnetic flux, which is a fossil of the magnetic field dragging during the early phase of star formation that survives for a duration in which significant gas disk evolution proceeds.
Structural relaxation time and cooling rate of a melt in the glass transition region
NASA Astrophysics Data System (ADS)
Sanditov, D. S.; Sydykov, B. S.
2015-03-01
The nature of the parameter involved in the Bartenev equation q?g = C relating the cooling rate of a glass-forming melt to its structural relaxation time in the glass transition region is discussed on the basis of the Volkenshtein-Ptitsyn theory using a number of known relationships. It is established that parameter C for amorphous substances with the same fragility is linearly temperature dependent. This parameter is shown to equal the narrow temperature range ? T g characterizing the liquid-glass transition region (by Nemilov); i.e., C = ? T g. It is concluded that ? T g for most glassy systems is only ˜0.7% of the glass transition temperature T g. The narrowness of temperature range ? T g is explained by the small fluctuation volume fraction f g "frozen" at the glass transition temperature. The concept of a close relationship between constant C and the structural order at T g (i.e., the characteristic of the inner state of a nonequilibrium "frozen" amorphous system) is developed.
Probe Spin-Velocity Dependent New Interactions by Spin Relaxation Times of Polarized $^{3}He$ Gas
Y. Zhang; G. A. Sun; S. M. Peng; C. B. Fu; Hao Guo; B. Q. Liu; H. Yan
2015-06-18
We have studied how to constrain the $\\alpha\\vec{\\sigma}\\cdot\\vec{v}$ type interactions with the relaxation times ($T_{1}$ and $T_{2}$) of spin polarized noble gases in magnetic fields. Using the best available $T_{2}$ of polarized $^{3}He$ gas and the earth as a source, we obtained constraints on two new interactions. We present a new experimental upper bound to the vector-axial-vector($V_{VA}$) type interaction for ranges between $1\\sim10^{8}$m. In combination with the previous result, we set the most stringent experiment limits on $g_{V}g_{A}$ ranging from $\\sim\\mu m$ to $\\sim10^{8}$m. To our best knowledge, we report the first experimental upper limit on torsion induced by the earth on its surface. The presented method also makes it possible to probe many spin-spin-velocity dependent new interactions which have never been searched before. By dedicated experiments, it is possible to improve sensitivity by a factor of $\\sim100$.
Kendall, William L.; Hines, James E.; Nichols, James D.; Grant, Evan H. Campbell
2013-01-01
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.
Atomic scale strain relaxation in axial semiconductor III-V nanowire heterostructures.
de la Mata, María; Magén, César; Caroff, Philippe; Arbiol, Jordi
2014-11-12
Combination of mismatched materials in semiconductor nanowire heterostructures offers a freedom of bandstructure engineering that is impossible in standard planar epitaxy. Nevertheless, the presence of strain and structural defects directly control the optoelectronic properties of these nanomaterials. Understanding with atomic accuracy how mismatched heterostructures release or accommodate strain, therefore, is highly desirable. By using atomic resolution high angle annular dark field scanning transmission electron microscopy combined with geometrical phase analyses and computer simulations, we are able to establish the relaxation mechanisms (including both elastic and plastic deformations) to release the mismatch strain in axial nanowire heterostructures. Formation of misfit dislocations, diffusion of atomic species, polarity transfer, and induced structural transformations are studied with atomic resolution at the intermediate ternary interfaces. Two nanowire heterostructure systems with promising applications (InAs/InSb and GaAs/GaSb) have been selected as key examples. PMID:25330094
Abdollah Omrani; Ayret Mollova; Carlos Mattea; Siegfried Stapf
2011-01-01
A research work has been conducted to investigate relaxation time changes with curing schedule, time, and concentration of DGEBA cured with Im6NiBr2. Our results demonstrate that low field NMR relaxometry is a facile and easy protocol to evaluate storage stability of one-pot epoxy based compositions. The DGEBA–Im6NiBr2 mixtures consistently display a greater degree of latency and a slower rate of
Thomas Ethofer; Irina Mader; Uwe Seeger; Gunther Helms; Michael Erb; Wolfgang Grodd; Albert Ludolph; Uwe Klose
2003-01-01
In vivo longitudinal relaxation times of N-acetyl compounds (NA), choline-containing substances (Cho), creatine (Cr), myo- inositol (mI), and tissue water were measured at 1.5 and 3 T using a point-resolved spectroscopy (PRESS) sequence with short echo time (TE). T1 values were determined in six different brain regions: the occipital gray matter (GM), occipital white matter (WM), motor cortex, frontoparietal WM,
EDITORIAL: Special issue on time scale algorithms
NASA Astrophysics Data System (ADS)
Matsakis, Demetrios; Tavella, Patrizia
2008-12-01
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
Biller, Joshua R.; Meyer, Virginia; Elajaili, Hanan; Rosen, Gerald M.; Kao, Joseph P.Y.; Eaton, Sandra S.; Eatona, Gareth R.
2011-01-01
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. PMID:21843961
Time scales in nuclear giant resonances
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
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.
MRI of bone marrow in the distal radius: in vivo precision of effective transverse relaxation times
NASA Technical Reports Server (NTRS)
Grampp, S.; Majumdar, S.; Jergas, M.; Lang, P.; Gies, A.; Genant, H. K.
1995-01-01
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.
Fast numerical integration of relaxation oscillator networks based on singular limit solutions
Paul S. Linsay; Deliang L. Wang
1998-01-01
Relaxation oscillations exhibiting more than one time scale arise naturally from many physical systems. When relax- ation oscillators are coupled in a way that resembles chemical synapses, we propose a fast method to numerically integrate such networks. The numerical technique, called the singular limit method, is derived from analysis of relaxation oscillations in the singular limit. In such limit, system
Detection of crossover time scales in multifractal detrended fluctuation analysis
NASA Astrophysics Data System (ADS)
Ge, Erjia; Leung, Yee
2013-04-01
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.
Pollack, L.; Smith, E.N.; Parpia, J.M.; Richardson, R.C. (Cornell Univ., Ithaca, NY (United States))
1992-06-01
Results are presented of measurements on a single crystal sample of scandium metal at temperatures down to 100 {mu}K using nuclear quadrupole resonance (NQR). Two regimes are found in the relaxation curves; an initial fast relaxation, followed by a slower relaxation consistent with the three exponential recovery expected for an I = 7/2 system in zero external magnetic field. The Korringa constant for this longer time relaxation in the sample is 90 {plus minus} 9 msec K{sup {minus}1}. By observing deviations in the ratio of the intensities of adjacent nuclear spin transitions at the lowest attainable temperatures, the authors were able to make a determination of the sign of the total electric field gradient present in the crystal. Results show that the lowest energy state of the nuclear spin system corresponds to m{sub I} = {plus minus} 7/2. A combination of these deviations and pulse NQR allows this system to be used as an absolute thermometer in the {mu}Kelvin regime.
Harsh corporal punishment is associated with increased T2 relaxation time in dopamine-rich regions.
Sheu, Yi-Shin; Polcari, Ann; Anderson, Carl M; Teicher, Martin H
2010-11-01
Harsh corporal punishment (HCP) was defined as frequent parental administration of corporal punishment (CP) for discipline, with occasional use of objects such as straps, or paddles. CP is linked to increased risk for depression and substance abuse. We examine whether long-term exposure to HCP acts as sub-traumatic stressor that contributes to brain alterations, particularly in dopaminergic pathways, which may mediate their increased vulnerability to drug and alcohol abuse. Nineteen young adults who experienced early HCP but no other forms of maltreatment and twenty-three comparable controls were studied. T2 relaxation time (T2-RT) measurements were performed with an echo planar imaging TE stepping technique and T2 maps were calculated and analyzed voxel-by-voxel to locate regional T2-RT differences between groups. Previous studies indicated that T2-RT provides an indirect index of resting cerebral blood volume. Region of interest (ROI) analyses were also conducted in caudate, putamen, nucleus accumbens, anterior cingulate cortex, dorsolateral prefrontal cortex, thalamus, globus pallidus and cerebellar hemispheres. Voxel-based relaxometry showed that HCP was associated with increased T2-RT in right caudate and putamen. ROI analyses also revealed increased T2-RT in dorsolateral prefrontal cortex, substantia nigra, thalamus and accumbens but not globus pallidus or cerebellum. There were significant associations between T2-RT measures in dopamine target regions and use of drugs and alcohol, and memory performance. Alteration in the paramagnetic or hemodynamic properties of dopaminergic cell body and projection regions were observed in subjects with HCP, and these findings may relate to their increased risk for drug and alcohol abuse. PMID:20600981
Kumar, Deepak; Schooler, Joseph; Zuo, Jin; McCulloch, Charles E.; Nardo, Lorenzo; Link, Thomas M.; Li, Xiaojuan; Majumdar, Sharmila
2012-01-01
Objective To analyze knee trabecular bone structure and spatial cartilage T1? and T2 relaxation times using 3-T MRI in subjects with and without tears of posterior horn of medial meniscus (PHMM). Design 3-T MRI from 59 subjects (> 18 years), were used to evaluate PHMM tears based on modified WORMS scoring; and to calculate apparent trabecular bone - volume over total bone volume fraction (app. BV/TV), number (app. Tb.N), separation (app. Tb.Sp) and thickness (app. Tb.Th) for overall femur/tibia and medial/lateral femur/tibia; and relaxation times for deep and superficial layers of articular cartilage. A repeated measures analysis using GEE was performed to compare trabecular bone and cartilage relaxation time parameters between people with (n = 35) and without (n= 24) PHMM tears, while adjusting for age and knee OA presence. Results Subjects with PHMM tears had lower app. BV./TV and app. Tb.N, and greater app. Tb.Th, and app. Tb.Sp. They also had higher T1? times in the deep cartilage layer for lateral tibia and medial femur and higher T2 relaxation times for the deep cartilage layer across all compartments. Conclusions PHMM tears are associated with differences in underlying trabecular bone and deep layer of cartilage. Overload of subchondral bone can lead to its sclerosis and stress shielding of trabecular bone leading to the resorptive changes observed in this study. The results underline the importance of interactions of trabecular bone and cartilage in the pathogenesis of knee OA in people with PHMM tears. PMID:23047010
Relaxation of a 1-D gravitational system
Patrick Valageas
2006-10-03
We study the relaxation towards thermodynamical equilibrium of a 1-D gravitational system. This OSC model shows a series of critical energies $E_{cn}$ where new equilibria appear and we focus on the homogeneous ($n=0$), one-peak ($n=\\pm 1$) and two-peak ($n=2$) states. Using numerical simulations we investigate the relaxation to the stable equilibrium $n=\\pm 1$ of this $N-$body system starting from initial conditions defined by equilibria $n=0$ and $n=2$. We find that in a fashion similar to other long-range systems the relaxation involves a fast violent relaxation phase followed by a slow collisional phase as the system goes through a series of quasi-stationary states. Moreover, in cases where this slow second stage leads to a dynamically unstable configuration (two peaks with a high mass ratio) it is followed by a new sequence ``violent relaxation/slow collisional relaxation''. We obtain an analytical estimate of the relaxation time $t_{2\\to \\pm 1}$ through the mean escape time of a particle from its potential well in a bistable system. We find that the diffusion and dissipation coefficients satisfy Einstein's relation and that the relaxation time scales as $N e^{1/T}$ at low temperature, in agreement with numerical simulations.
NASA Astrophysics Data System (ADS)
Cacciola, M.; Osaci, M.
2015-06-01
This paper presents a series of studies about the modality in which the attempt frequency influences the Neel relaxation time and thus the effective relaxation time, in a spherical-nanoparticle-saturated nanofluid in external magnetic field. The nanoparticles have a random distribution, and their magnetic moments have a magnetic dipole-dipole interaction, along with the distributions of sizes and anisotropy constants. In such a system, the energy of the equilibrium states depends on the total magnetic field experienced by the particle, which includes the magnetic field applied and the dipolar magnetic field produced by the surrounding particles. Because of the high complexity level of the issue, it seems useful to consider the numerical experiments by computational simulation.
Colla, M. -S.; Amin-Ahmadi, B.; Idrissi, H.; Malet, L.; Godet, S.; Raskin, J. -P.; Schryvers, D.; Pardoen, T.
2015-01-01
The high-rate sensitivity of nanostructured metallic materials demonstrated in the recent literature is related to the predominance of thermally activated deformation mechanisms favoured by a large density of internal interfaces. Here we report time-resolved high-resolution electron transmission microscopy creep tests on thin nanograined films using on-chip nanomechanical testing. Tests are performed on palladium, which exhibited unexpectedly large creep rates at room temperature. Despite the small 30-nm grain size, relaxation is found to be mediated by dislocation mechanisms. The dislocations interact with the growth nanotwins present in the grains, leading to a loss of coherency of twin boundaries. The density of stored dislocations first increases with applied deformation, and then decreases with time to drive additional deformation while no grain boundary mechanism is observed. This fast relaxation constitutes a key issue in the development of various micro- and nanotechnologies such as palladium membranes for hydrogen applications. PMID:25557273
Colla, M-S; Amin-Ahmadi, B; Idrissi, H; Malet, L; Godet, S; Raskin, J-P; Schryvers, D; Pardoen, T
2015-01-01
The high-rate sensitivity of nanostructured metallic materials demonstrated in the recent literature is related to the predominance of thermally activated deformation mechanisms favoured by a large density of internal interfaces. Here we report time-resolved high-resolution electron transmission microscopy creep tests on thin nanograined films using on-chip nanomechanical testing. Tests are performed on palladium, which exhibited unexpectedly large creep rates at room temperature. Despite the small 30-nm grain size, relaxation is found to be mediated by dislocation mechanisms. The dislocations interact with the growth nanotwins present in the grains, leading to a loss of coherency of twin boundaries. The density of stored dislocations first increases with applied deformation, and then decreases with time to drive additional deformation while no grain boundary mechanism is observed. This fast relaxation constitutes a key issue in the development of various micro- and nanotechnologies such as palladium membranes for hydrogen applications. PMID:25557273
Chen Mao; Sai Prasanth Chamarthy; Rodolfo Pinal
2006-01-01
Purpose To develop a calorimetry-based model for estimating the time-dependence of molecular mobility during the isothermal relaxation of amorphous organic compounds below their glass transition temperature (T\\u000a g).Methods The time-dependent enthalpy relaxation times of amorphous sorbitol, indomethacin, trehalose and sucrose were estimated based on the nonlinear Adam?Gibbs equation. Fragility was determined from the scanning rate dependence of T\\u000a g. Time evolution of
Age-Related Loss of Brain Volume and T2 Relaxation Time in Youth With Type 1 Diabetes
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
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. PMID:22301124
Masahito Oh-E; Hiroshi Yokoyama; Mattijs Koeberg; Euan Hendry; Mischa Bonn
2006-01-01
Terahertz time-domain spectroscopy has been used to study the dielectric relaxation of pure 4' n-pentyl 4 cyanobiphenyl (5CB) liquid crystal (LC) and its mixtures with 10 mum SiO2 particles in the frequency range 0.2 2 THz. For the pure sample, we find that spatial inhomogeneities consisting of oriented domains, comparable in size to our probe area (~1 mm2), cause a
Jeffrey M. Harbold; Hui Du; Todd D. Krauss; Kyung-Sang Cho; Chris B. Murray; Frank W. Wise
2005-01-01
The relaxation of strongly confined electrons and holes from higher excited states to their lowest excited states in colloidal PbSe nanocrystals has been time resolved using femtosecond transient absorption spectroscopy. In contrast to II-VI and III-V semiconductor nanocrystals, both electrons and holes are strongly confined in PbSe nanocrystals. Despite the large electron and hole energy level spacings (at least 12
An Improved Lagrangian Relaxation Method for VLSI Combinational Circuit Optimization
Huang, Yi-Le
2012-02-14
Gate sizing and threshold voltage (Vt) assignment are very popular and useful techniques in current very large scale integration (VLSI) design flow for timing and power optimization. Lagrangian relaxation (LR) is a common method for handling multi...
SCALING IN SINGULAR PERTURBATION PROBLEMS: BLOWING-UP A RELAXATION OSCILLATOR
ILONA GUCWA; PETER SZMOLYANy
2009-01-01
An introduction to some recently developed methods for the analysis of systems of singularly perturbed ordinary difierential equations is given in the context of a speciflc problem describing glycolytic oscillations. In suitably scaled variables the governing equations are a planar system of ordinary difierential equations depending singularly on two small parameters \\
Singh, Sheela P.; Lu, Chunhua; Han, Lin; Hobbs, Brian P.; Pradeep, Sunila; Choi, Hyun J.; Bankson, James A.
2015-01-01
Purpose To assess whether T1 relaxation time of tumors may be used to assess response to bevacizumab anti-angiogenic therapy. Procedures: 12 female nude mice bearing subcutaneous SKOV3ip1-LC ovarian tumors were administered bevacizumab (6.25ug/g, n=6) or PBS (control, n=6) therapy twice a week for two weeks. T1 maps of tumors were generated before, two days, and 2 weeks after initiating therapy. Tumor weight was assessed by MR and at necropsy. Histology for microvessel density, proliferation, and apoptosis was performed. Results Bevacizumab treatment resulted in tumor growth inhibition (p<0.04, n=6), confirming therapeutic efficacy. Tumor T1 relaxation times increased in bevacizumab treated mice 2 days and 2 weeks after initiating therapy (p<.05, n=6). Microvessel density decreased 59% and cell proliferation (Ki67+) decreased 50% in the bevacizumab treatment group (p<.001, n=6), but not apoptosis. Conclusions Findings suggest that increased tumor T1 relaxation time is associated with response to bevacizumab therapy in ovarian cancer model and might serve as an early indicator of response. PMID:26098849
A multiple time scale solution for the Chapman mechanism
Chang, B.
1994-06-01
The rate equations representing the Chapman mechanism are solved analytically in the Multiple Time Scale Approximation by the exploitation of their stiffness. The widely different time scales of the reactions in the mechanism can be used to disentangle their effects on the solution. The reactions which bring oxygen into equilibrium with ozone are responsible for the overall stiffness, because their time scales are on the extreme ends of time scale spectrum for the reactions comprising the Chapman mechanism. Since catalytic cycles have similar equilibration reactions which may have time scales bordering the time scales of other reactions involving the catalysts, the method of multiple time scales can also be used to cured the stiffness in the rate equations governing these cycles. These analytical solutions may be incorporated into a numerical algorithm to improve its efficiency for the computation of the rate equations governing the chemistry of the atmosphere.
NASA Astrophysics Data System (ADS)
Grzybowska, K.; Grzybowski, A.; Pawlus, S.; Pionteck, J.; Paluch, M.
2015-06-01
In this paper, we investigate how changes in the system entropy influence the characteristic time scale of the system molecular dynamics near the glass transition. Independently of any model of thermodynamic evolution of the time scale, against some previous suppositions, we show that the system entropy S is not sufficient to govern the time scale defined by structural relaxation time ?. In the density scaling regime, we argue that the decoupling between ? and S is a consequence of different values of the scaling exponents ? and ?S in the density scaling laws, ? =f (??/T ) and S =h (??S/T ) , where ? and T denote density and temperature, respectively. It implies that the proper relation between ? and S requires supplementing with a density factor, u (?), i.e., ? =g ( u (? )w (S ) ) . This meaningful finding additionally demonstrates that the density scaling idea can be successfully used to separate physically relevant contributions to the time scale of molecular dynamics near the glass transition. The relation reported by us between ? and S constitutes a general pattern based on nonconfigurational quantities for describing the thermodynamic evolution of the characteristic time scale of molecular dynamics near the glass transition in the density scaling regime, which is a promising alternative to the approaches based as the Adam-Gibbs model on the configurational entropy that is difficult to evaluate in the entire thermodynamic space. As an example, we revise the Avramov entropic model of the dependence ?(T ,?), giving evidence that its entropic basis has to be extended by the density dependence of the maximal energy barrier for structural relaxation. We also discuss the excess entropy Sex, the density scaling of which is found to mimic the density scaling of the total system entropy S .
BeiDou Navigation Satellite System and its time scales
Chunhao Han; Yuanxi Yang; Zhiwu Cai
2011-01-01
The development and current status of BeiDou Navigation Satellite System are briefly introduced. The definition and realization of the system time scales are described in detail. The BeiDou system time (BDT) is an internal and continuous time scale without leap seconds. It is maintained by the time and frequency system of the master station. The frequency accuracy of BDT is
Geologic Time Scale 2004 - why, how, and where next!
Felix Gradstein; James Ogg
2004-01-01
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
Time scaling of trajectories for cooperative multi-robot systems
Seungbin B. Moon; Shaheen Ahmad
1990-01-01
The application of the time scaling method is extended to the multiple redundant robots in cooperative manipulation. The modification of the algorithm previously developed by the authors (Proc. 1990 IEEE Conf., Robotics and Automatio p.506-511, 1990) allows the use of the time scaling method without using the inverse of the Jacobian matrix. The trajectory scaling scheme described requires the use
Optimum signal synthesis for time-scale estimation
Ovarlez Jean
1998-01-01
In signal analysis, the joint estimation of the time-scale parameters which can affect a known signal (Doppler effect or scale effect, delay…) may be a problem of interest. An important result has shown that, even if the quality of the time delay estimation is classically given by the inverse spread of the signal spectral density, the quality of the scale
Linking Response-Time Parameters onto a Common Scale
ERIC Educational Resources Information Center
van der Linden, Wim J.
2010-01-01
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…
Mechanism of Void Nucleation and Growth in bcc Fe: Atomistic Simulations at Experimental Time Scales
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
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.
Liu, Y H; Hawk, R M; Ramaprasad, S
1995-01-01
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
Leyet, Y.; Guerrero, F. [Departamento de Fisica, Facultad de Ciencias Naturales, Universidad de Oriente, CP-90500, Santiago de Cuba (Cuba); Amorin, H. [Instituto de Ciencia de Materiales de Madrid, CSIC, Cantoblanco, 28049 Madrid (Spain); Guerra, J. de Los S. [Instituto de Fisica, Universidade Federal de Uberlandia (UFU), 38400-902 Uberlandia, Minas Gerais Brazil (Brazil); Eiras, J. A. [Departamento de Fisica, Grupo de Ceramicas Ferroeletricas, Universidade Federal de Sao Carlos (UFSCar), CEP 13565-670 Sao Carlos, Sao Paulo (Brazil)
2010-10-18
The influence of the ferroelectric to paraelectric transition on the relaxation parameters of conductive processes in ferroelectric materials is studied in the time domain. Three well-known ferroelectric systems were chosen with transition temperatures in different regions, these are, high-temperature PbNb{sub 2}O{sub 6}-based ceramics; nanostructured Pb(Zr{sub 0.6}Ti{sub 0.4})O{sub 3} ceramics; and submicron BaTiO{sub 3}. The thermal evolution of relaxation parameters shows clear anomalies in their typical behavior when conductivity processes arise in the temperature range where the ferroelectric transition takes place. The method here described allows obtaining information about the correlation between charge transport and the motion of the off-center ions at the phase transition.
Bolinger, Joshua C; Bixby, Teresa J; Reid, Philip J
2005-08-22
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. PMID:16164308
Subburaj, Karupppasamy; Kumar, Deepak; Souza, Richard B.; Alizai, Hamza; Li, Xiaojuan; Link, Thomas M.; Majumdar, Sharmila
2013-01-01
Background Understanding the acute response of healthy knee cartilage to running may provide valuable insight into functional properties. In recent years, quantitative magnetic resonance (MR) imaging techniques (T1? and T2 relaxation measurement) have shown tremendous potential and unique ability to noninvasively and quantitatively determine cartilage response to physiologic levels of loading occurring with physiologic levels of exercise. Purpose To measure the short-term changes in MR T1? and T2 relaxation times of knee articular cartilage and meniscus in healthy individuals immediately after 30 minutes of running. Study Design Descriptive laboratory study. Methods Twenty young healthy volunteers, aged 22 to 35 years, underwent 3T MR imaging of the knee before and immediately after 30 minutes of running. Quantitative assessment of the cartilage and menisci was performed using MR images with a T1? and T2 mapping technique. After adjusting for age, sex, and body mass index, repeated-measures analysis of variance was used to determine the effects of running on MR relaxation times. Results The post-run T1? and T2 measurement showed significant reduction in all regions of cartilage except the lateral tibia when compared with the pre-run condition. The medial tibiofemoral (T1?: 9.4%, P < .0001; T2: 5.4%, P = .0049) and patellofemoral (T1?: 12.5%, P < .0001; T2: 5.7%, P = .0007) compartments experienced the greatest reduction after running. The superficial layer of the articular cartilage showed significantly higher change in relaxation times than the deep layer (?T1?: 9.6% vs 8.2%, P = .050; ?T2: 6.0% vs 3.5%, P = .069). The anterior and posterior horns of the medial meniscus (9.7%, P = .016 and 11.4%, P = .001) were the only meniscal subregions with significant changes in T1? after running. Conclusion Shorter T1? and T2 values after running suggest alteration in the water content and collagen fiber orientation of the articular cartilage. Greater changes in relaxation times of the medial compartment and patellofemoral joint cartilage indicate greater load sharing by these areas during running. PMID:22729505
NASA Astrophysics Data System (ADS)
Kingsley, Peter B.; Monahan, W. Gordon
2000-04-01
In the presence of an off-resonance radiofrequency field, recovery of longitudinal magnetization to a steady state is not purely monoexponential. Under reasonable conditions with zero initial magnetization, recovery is nearly exponential and an effective relaxation rate constant R1eff = 1/ T1eff can be obtained. Exact and approximate formulas for R1eff and steady-state magnetization are derived from the Bloch equations for spins undergoing cross-relaxation and chemical exchange between two sites in the presence of an off-resonance radiofrequency field. The relaxation formulas require that the magnetization of one spin is constant, but not necessarily zero, while the other spin relaxes. Extension to three sites with one radiofrequency field is explained. The special cases of off-resonance effects alone and with cross-relaxation or chemical exchange, cross-relaxation alone, and chemical exchange alone are compared. The inaccuracy in saturation transfer measurements of exchange rate constants by published formulas is discussed for the creatine kinase reaction.
NASA Astrophysics Data System (ADS)
Yulmetyev, R. M.; Hänggi, P.; Yulmetyeva, D. G.; Shimojo, S.; Khusaenova, E. V.; Watanabe, K.; Bhattacharya, J.
2007-09-01
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.
Extended frequency range measurements for determining the Kneser-type acoustic relaxation time.
Linde, B B; Lezhnev, N B
2000-11-01
In the present paper, the authors discuss studies carried out for many years dealing particularly with two compounds: benzene and carbon disulphide and compare them with the results obtained by numerous acoustics researchers. These compounds are typical liquids in which acoustic Kneser-type relaxation occurs, caused by an irreversible vibrational and translational (VT) transition. Since magnitudes describing the relaxation process were diverse in many papers, we have undertaken an attempt to clarify these differences and to indicate how to avoid errors resulting from instrumental imperfections and the disregard of the considerable measurement errors when investigating velocity dispersion in the hypersonic (GHz) range. The results of these researches changed the interpretation of previous papers. PMID:11106005
Long-time relaxation of low energy excitations in Bi 2CaSr 2O 8
NASA Astrophysics Data System (ADS)
Sahling, S.; Sievert, J.
1990-07-01
The long-time power release typical of amorphous solids was observed after rapid cooling of a superconducting polycrystalline ceramic Bi 2CaSr 2Cu 2O 8 from various equilibrium temperatures T1 (2.24 K ? T1 ? 13.68 K) to 1.5 K. The resulting distribution parameter of two-level systems P = 12.5 × 10 44 Jm -3 is close to the values of the other high temperature superconductors and amorphous solids. The upper limit of the relaxation time spectrum was found.
Dufourc, E J; Mayer, C; Stohrer, J; Althoff, G; Kothe, G
1992-01-01
Phospholipid head group dynamics have been studied by pulsed phosphorus-31 nuclear magnetic resonance (31P-NMR) of unoriented and macroscopically aligned dimyristoylphosphatidylcholine model membranes in the temperature range, 203-343 K. Lineshapes and echo intensities have been recorded as a function of interpulse delay times, temperature and macroscopic orientation of the bilayer normal with respect to the magnetic field. The dipolar proton-phosphorus (1H-31P) contribution to the transverse relaxation time, T2E, and to lineshapes was eliminated by means of a proton spin-lock sequence. In case of longitudinal spin relaxation, T1Z, the amount of dipolar coupling was evaluated by measuring the maximum nuclear Overhauser enhancement. Hence, the results could be analyzed by considering chemical shift anisotropy as the only relaxation mechanism. The presence of various minima both in T1Z and T2E temperature plots as well as the angular dependence of these relaxation times allowed description of the dynamics of the phosphate head group in the 31P-NMR time window, by three different motional classes, i.e., intramolecular, intermolecular and collective motions. The intramolecular motions consist of two hindered rotations and one free rotation around the bonds linking the phosphate head group to the glycerol backbone. These motions are the fastest in the hierarchy of time with correlation times varying from less than 10(-12) to 10(-6) s in the temperature range investigated. The intermolecular motions are assigned to phospholipid long axis rotation and fluctuation. They have correlation times ranging from 10(-11) s at high temperatures to 10(-3) s at low temperatures. The slowest motion affecting the 31P-NMR observables is assigned to viscoelastic modes, i.e., so called order director fluctuations and is only detected at high temperatures, above the main transition in pulse frequency dependent T2ECP experiments. Comprehensive analysis of the phosphate head group dynamics is achieved by a dynamic NMR model based on the stochastic Liouville equation. In addition to correlation times, this analysis provides activation energies and order parameters for the various motions, and a value for the bilayer elastic constant. PMID:1540698
Jeffrey M. Harbold; Hui Du; Todd D. Krauss; Kyung-Sang Cho; Chris B. Murray; Frank W. Wise
2005-01-01
The relaxation of strongly-confined electrons and holes between 1P and 1S\\u000alevels in colloidal PbSe nanocrystals has been time-resolved using femtosecond\\u000atransient absorption spectroscopy. In contrast to II-VI and III-V semiconductor\\u000ananocrystals, both electrons and holes are strongly confined in PbSe\\u000ananocrystals. Despite the large electron and hole energy level spacings (at\\u000aleast 12 times the optical phonon energy), we
Polarized Alkali-Metal Vapor with Minute-Long Transverse Spin-Relaxation Time
Balabas, M. V. [S. I. Vavilov State Optical Institute, St. Petersburg, 199034 (Russian Federation); Karaulanov, T.; Ledbetter, M. P. [Department of Physics, University of California at Berkeley, Berkeley, California 94720-7300 (United States); Budker, D. [Department of Physics, University of California at Berkeley, Berkeley, California 94720-7300 (United States); Nuclear Science Division, Lawrence Berkeley National Laboratory, Berkeley California 94720 (United States)
2010-08-13
We demonstrate lifetimes of Zeeman populations and coherences in excess of 60 sec in alkali-metal vapor cells with inner walls coated with an alkene material. This represents 2 orders of magnitude improvement over the best paraffin coatings. We explore the temperature dependence of cells coated with this material and investigate spin-exchange relaxation-free magnetometry in a room-temperature environment, a regime previously inaccessible with conventional coating materials.
Patrick M. Mehl
1996-01-01
The isothermal enthalpy relaxation of glycerol and propylene glycol is studied for different subglass transition annealing temperatures using our usual method. The kinetics of the glass transition is analyzed using the Kohlrausch-Williams-Watts model. The Vogel-Fulcher-Tamman model was previously used for the spectrometric specific heat analysis of glycerol and propylene glycol by Birge and co-workers at temperatures higher than the glass
NASA Astrophysics Data System (ADS)
Saxena, Ram K.; Pagnini, Gianni
2011-02-01
In recent years the interest around the study of anomalous relaxation and diffusion processes is increased due to their importance in several natural phenomena. Moreover, a further generalization has been developed by introducing time-fractional differentiation of distributed order which ranges between 0 and 1. We refer to accelerating processes when the driving power law has a changing-in-time exponent whose modulus tends from less than 1 to 1, and to decelerating processes when such an exponent modulus decreases in time moving away from the linear behaviour. Accelerating processes are modelled by a time-fractional derivative in the Riemann-Liouville sense, while decelerating processes by a time-fractional derivative in the Caputo sense. Here the focus is on the accelerating case while the decelerating one is considered in the companion paper. After a short reminder about the derivation of the fundamental solution for a general distribution of time-derivative orders, we consider in detail the triple-order case for both accelerating relaxation and accelerating diffusion processes and the exact results are derived in terms of an infinite series of H-functions. The method adopted is new and it makes use of certain properties of the generalized Mittag-Leffler function and the H-function, moreover it provides an elegant generalization of the method introduced by Langlands (2006) [T.A.M. Langlands, Physica A 367 (2006) 136] to study the double-order case of accelerating diffusion processes.
Lifshitz quasinormal modes and relaxation from holography
NASA Astrophysics Data System (ADS)
Sybesma, Watse; Vandoren, Stefan
2015-05-01
We obtain relaxation times for field theories with Lifshitz scaling and with holographic duals Einstein-Maxwell-Dilaton gravity theories. This is done by computing quasinormal modes of a bulk scalar field in the presence of Lifshitz black branes. We determine the relation between relaxation time and dynamical exponent z, for various values of boundary dimension d and operator scaling dimension. It is found that for d > z + 1, at zero momenta, the modes are underdamped, where as for d ? z + 1 the system is always overdamped. For d = z + 1 and zero momenta, we present analytical results.
Chelcea, R I; Fechete, R; Culea, E; Demco, D E; Blümich, B
2009-02-01
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
On the Uncertainty of the Annular Mode Time Scale
NASA Astrophysics Data System (ADS)
Kim, Junsu; Reichler, Thomas
2015-04-01
The proper simulation of the annular mode (AM) time scale may be regarded as an important benchmark for climate models. Previous research demonstrated that climate models systematically overestimate this time scale. As suggested by the fluctuation-dissipation theorem, this may imply that models are overly sensitive to external forcings. Previous research also made it clear that calculating the AM time scale is a slowly converging process, necessitating relatively long time series and casting doubts on the usefulness of the historical reanalysis record to constrain climate models in terms of the AM time scale. Here, we use a 4000-year-long control simulation with the GFDL climate model CM2.1 to study the effects of internal atmospheric variability on the stability of the AM time scale. In particular, we ask whether a model's AM time scale and climate sensitivity can be constrained from the 50-year-long reanalysis record. We find that internal variability attaches large uncertainty to the AM time scale when diagnosed from decadal records. Even under fixed forcing conditions, at least 100 years of data are required in order to keep the uncertainty in the AM time scale of the Northern Hemisphere to 10%; over the Southern Hemisphere the required length increases to 200 years. If nature's AM time scale is similarly variable, there is no guarantee that the historical reanalysis record is a fully representative target for model evaluation. We further use the model simulation to investigate the dynamical coupling between the stratosphere and the troposphere from the perspective of the AM time scale. Over the Northern Hemisphere we find only weak indication for influences from stratosphere-troposphere coupling on the AM time scale. The situation is very different over the Southern Hemisphere, where we find robust connections between the AM time scale in the stratosphere and that in the troposphere, confirming and extending earlier results of influences of stratospheric variability on the troposphere.
Controllability and Observability of Linear Time-Varying Impulsive Systems on Time Scales
NASA Astrophysics Data System (ADS)
Zhang, Kexue; Liu, Xinzhi
2011-11-01
This paper studies the problems of controllability and observability of a general linear time-varying impulsive control systems on time scales. By proposing a formula of variation of parameters for this type of systems on time scales, several necessary and sufficient criteria on controllability and observability of the impulsive control system on time scales are established. It is shown that the classical results about controllability and observability of linear continuous impulsive systems can be generalized to the impulsive systems on time scales.
Weiskopf, Nikolaus; Callaghan, Martina F; Josephs, Oliver; Lutti, Antoine; Mohammadi, Siawoosh
2014-01-01
Relaxation rates provide important information about tissue microstructure. Multi-parameter mapping (MPM) estimates multiple relaxation parameters from multi-echo FLASH acquisitions with different basic contrasts, i.e., proton density (PD), T1 or magnetization transfer (MT) weighting. Motion can particularly affect maps of the apparent transverse relaxation rate R2(*), which are derived from the signal of PD-weighted images acquired at different echo times. To address the motion artifacts, we introduce ESTATICS, which robustly estimates R2(*) from images even when acquired with different basic contrasts. ESTATICS extends the fitted signal model to account for inherent contrast differences in the PDw, T1w and MTw images. The fit was implemented as a conventional ordinary least squares optimization and as a robust fit with a small or large confidence interval. These three different implementations of ESTATICS were tested on data affected by severe motion artifacts and data with no prominent motion artifacts as determined by visual assessment or fast optical motion tracking. ESTATICS improved the quality of the R2(*) maps and reduced the coefficient of variation for both types of data-with average reductions of 30% when severe motion artifacts were present. ESTATICS can be applied to any protocol comprised of multiple 2D/3D multi-echo FLASH acquisitions as used in the general research and clinical setting. PMID:25309307
Weiskopf, Nikolaus; Callaghan, Martina F.; Josephs, Oliver; Lutti, Antoine; Mohammadi, Siawoosh
2014-01-01
Relaxation rates provide important information about tissue microstructure. Multi-parameter mapping (MPM) estimates multiple relaxation parameters from multi-echo FLASH acquisitions with different basic contrasts, i.e., proton density (PD), T1 or magnetization transfer (MT) weighting. Motion can particularly affect maps of the apparent transverse relaxation rate R2*, which are derived from the signal of PD-weighted images acquired at different echo times. To address the motion artifacts, we introduce ESTATICS, which robustly estimates R2* from images even when acquired with different basic contrasts. ESTATICS extends the fitted signal model to account for inherent contrast differences in the PDw, T1w and MTw images. The fit was implemented as a conventional ordinary least squares optimization and as a robust fit with a small or large confidence interval. These three different implementations of ESTATICS were tested on data affected by severe motion artifacts and data with no prominent motion artifacts as determined by visual assessment or fast optical motion tracking. ESTATICS improved the quality of the R2* maps and reduced the coefficient of variation for both types of data—with average reductions of 30% when severe motion artifacts were present. ESTATICS can be applied to any protocol comprised of multiple 2D/3D multi-echo FLASH acquisitions as used in the general research and clinical setting. PMID:25309307
Borgia, G.C. [University of Bologna, Dipartimento di Ingegneria Chimica, Mineraria, e Delle Tecnolgie Ambientali, Viale Risorgimento 2, 40136 Bologna (Italy)] [University of Bologna, Dipartimento di Ingegneria Chimica, Mineraria, e Delle Tecnolgie Ambientali, Viale Risorgimento 2, 40136 Bologna (Italy); Brown, R.J. [515 W. 11th Street, Claremont, California 91711-3721 (United States)] [515 W. 11th Street, Claremont, California 91711-3721 (United States); Fantazzini, P. [University of Bologna, Dipartimento of Physics, Via Irnerio 46, 40126 Bologna (Italy)] [University of Bologna, Dipartimento of Physics, Via Irnerio 46, 40126 Bologna (Italy)
1997-11-01
Fluid-flow properties of porous media, such as permeability k and irreducible water saturation S{sub wi}, can be estimated from water {sup 1}H nuclear magnetic resonance (NMR) relaxation data, but there are basic questions regarding data processing and interpretation. We found that S{sub wi} and k are better estimated if different forms of {open_quotes}average{close_quotes} relaxation time are used. NMR longitudinal relaxation data for a suite of 106 water-saturated clean sandstones were used. Sandstones represent a specialized class of porous media, where even for small porosity, substantially all pore space is connected. The sandstones exhibit distributions of relaxation times ranging over factors from at least 10 to more than 10{sup 3}. We tried several forms of {open_quotes}average{close_quotes} relaxation time T. One family of Ts is {l_angle}T{sup p}{r_angle}{sup 1/p}, where limp{r_arrow}0 gives the geometric mean. The best estimator we found for S{sub wi} uses a form of average relaxation time {ital only}, rather than relaxation time cutoff. The time used can be any of several forms of T, giving more emphasis to {ital short times} than the geometric mean does. On the contrary, the best T for estimating permeability without other information is precisely the geometric mean. The best estimates of permeability came from fits of ln(k/{phi}) using Ts with emphasis at {ital slightly longer times}. While S{sub wi} is better estimated by using all the data points (starting from our minimum 0.4 ms), k is better estimated by starting at a few ms, that is by ignoring a {ital non-negligible} fraction of the signal for some samples. These results can be obtained also by using computations that do not need to invert multiexponential relaxation data, and good results are obtained even with only a few data points. (Abstract Truncated)
Resonant relaxation in electroweak baryogenesis
NASA Astrophysics Data System (ADS)
Lee, Christopher; Cirigliano, Vincenzo; Ramsey-Musolf, Michael J.
2005-04-01
We compute the leading, chiral charge-changing relaxation term in the quantum transport equations that govern electroweak baryogenesis using the closed time path formulation of nonequilibrium quantum field theory. We show that the relaxation transport coefficients may be resonantly enhanced under appropriate conditions on electroweak model parameters and that such enhancements can mitigate the impact of similar enhancements in the CP-violating source terms. We also develop a power counting in the time and energy scales entering electroweak baryogenesis and include effects through second order in ratios ? of the small and large scales. We illustrate the implications of the resonantly enhanced O(?2) terms using the Minimal Supersymmetric Standard Model, focusing on the interplay between the requirements of baryogenesis and constraints obtained from collider studies, precision electroweak data, and electric dipole moment searches.
Protein dynamics: from rattling in a cage to structural relaxation.
Khodadadi, S; Sokolov, A P
2015-06-17
We present an overview of protein dynamics based mostly on results of neutron scattering, dielectric relaxation spectroscopy and molecular dynamics simulations. We identify several major classes of protein motions on the time scale from faster than picoseconds to several microseconds, and discuss the coupling of these processes to solvent dynamics. Our analysis suggests that the microsecond backbone relaxation process might be the main structural relaxation of the protein that defines its glass transition temperature, while faster processes present some localized secondary relaxations. Based on the overview, we formulate a general picture of protein dynamics and discuss the challenges in this field. PMID:26027652
NASA Astrophysics Data System (ADS)
Nunes, W. C.; Socolovsky, L. M.; Denardin, J. C.; Cebollada, F.; Brandl, A. L.; Knobel, M.
2005-12-01
Magnetic properties of Co-SiO2 granular films are displayed and explained by means of a phenomenological model that takes into account the effects of magnetic interparticle coupling on the superparamagnetic relaxation behavior. The model is based on the analysis of coupled nanoparticles through a modified random anisotropy model that takes into account the concentration and size of the nanoscopic particles, as well as the field dependence of the correlation length. The proposed model leads to an accurate description of the field dependence of the blocking temperature, substantially better than the power law usually employed to describe noninteracting particles.
Time scale separation in the low temperature East model: Rigorous results
Paul Chleboun; Alessandra Faggionato; Fabio Martinelli
2013-02-07
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 neighbour is 1. We focus on the glassy effects caused by the kinetic constraint as $q\\downarrow 0$, where $q$ is the equilibrium density of the 0's. Specifically we analyse time scale separation and 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 $L=O(q^{-\\gamma})$, $\\gammaseparated by a factor $q^{-a}$, $a=a(\\gamma)>0$, provided that $d'/d$ is large enough independently of $q$. 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. Finally we show that no form of time scale separation can occur for $\\gamma=1$, i.e. at the equilibrium scale $L=1/q$, contrary to what was previously assumed in the physical literature based on numerical simulations.
Slow-time acceleration for modeling multiple-time-scale problems
NASA Astrophysics Data System (ADS)
Haselbacher, A.; Najjar, F. M.; Massa, L.; Moser, R. D.
2010-01-01
The numerical simulation of a system exhibiting a broad range of time scales can be very expensive because the time discretization will in general need to resolve the smallest time scale, and the simulation will have to extend over many times the longest time scale. However, it is common that not all the time scales are of interest for a particular problem. When the long time scales are of primary interest, a number of techniques are available to eliminate the unwanted short time scales from consideration. When the short time scales are of primary interest, a technique for mitigating the consequences of anomalously long time scales is needed. The "slow-time acceleration" technique presented here has been developed to address this problem. In the slow-time acceleration technique, a modified evolution equation is developed in which the longest time scale is much shorter than that of the original system, and which has the same multi-time scale asymptotic structure as the original system. As an example, this approach is applied to the numerical simulation of solid-propellant rockets in which the long time scale is associated with the regression of the burning propellant.
Feng Chen; Aiguo Xu; Guangcai Zhang; Yingjun Li; Sauro Succi
2010-06-01
A new multiple-relaxation-time lattice Boltzmann scheme for compressible flows with arbitrary specific heat ratio and Prandtl number is presented. In the new scheme, which is based on a two-dimensional 16-discrete-velocity model, the moment space and the corresponding transformation matrix are constructed according to the seven-moment relations associated with the local equilibrium distribution function. In the continuum limit, the model recovers the compressible Navier-Stokes equations with flexible specific-heat ratio and Prandtl number. Numerical experiments show that compressible flows with strong shocks can be simulated by the present model up to Mach numbers $Ma \\sim 5$.
NASA Astrophysics Data System (ADS)
Xu, Yuxiao; Shi, Zhiguo; Chi, Hao; Jin, Xiaofeng; Zheng, Shilie; Zhang, Xianmin
2014-11-01
Photonic generation of chirped RF signal based on frequency-to-time mapping (FTM) is investigated in this paper. A new criterion on system parameters (dispersion amounts and pulse duration) for the generation of well-shaped linearly chirped signals is given, which is proved to be less restrictive than the currently known conditions. Therefore, requirement on the dispersion amount can be relaxed, which is highly desired in practical implementation of the FTM-based system. Theoretical results are presented, the correctness of which is verified by numerical and experimental results. The reported theory is a good guidance in designing the photonic system for the generation of chirped signals based on FTM.
NASA Astrophysics Data System (ADS)
Sciolla, Bruno; Poletti, Dario; Kollath, Corinna
2015-05-01
We use two-time correlation functions to study the complex dynamics of dissipative many-body quantum systems. In order to measure, understand, and categorize these correlations we extend the framework of the adiabatic elimination method. We show that, for the same parameters and times, two-time correlations can display two distinct behaviors depending on the observable considered: a fast exponential decay or a much slower dynamics. We exemplify these findings by studying strongly interacting bosons in a double well subjected to phase noise. While the single-particle correlations decay exponentially fast with time, the density-density correlations display slow aging dynamics. We also show that this slow relaxation regime is robust against particle losses. Additionally, we use the developed framework to show that the dynamic properties of dissipatively engineered states can be drastically different from their Hamiltonian counterparts.
SOME MULTIPLE-TIME-SCALE PROBLEMS IN MOLECULAR DYNAMICS
DUS ANKA; JANEZ IC
2002-01-01
Many physical problems, paricularly in chemical and biological systems, involve processes that occur over widely varying time scales. Such problems have motivated the development of new methods for treating multiple- time-scale problems in molecular dynamics (MD). Methods have been developed for determining the vibrational frequencies and normal modes of large systems in full and reduced conformational space. A method is
Singular perturbation and time scale approaches in discrete control systems
NASA Technical Reports Server (NTRS)
Naidu, D. S.; Price, D. B.
1988-01-01
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.
Fragiadakis, D; Roland, C M
2014-05-01
Molecular dynamics simulations were carried out on a series of Lennard-Jones binary mixtures of rigid, asymmetric, dumbbell-shaped molecules. Below an onset temperature, the rotational and translational dynamics split into the slow structural ? relaxation and a higher-frequency Johari-Goldstein ? relaxation. Both processes are dynamically heterogeneous, having broad distributions of relaxation times. However, only the ? relaxation shows strong dynamic correlations; correlations at the ? time scale are weak, in particular for molecules having shorter bonds. Despite the close connection between the two processes, we find no correlation between the ? and ? relaxation times of individual molecules; that is, a molecule exhibiting slow ? motion does not necessarily undergo slow ? dynamics and likewise for fast molecules. However, the single-molecule ? relaxation times do correlate with both the ? and ? relaxation strengths. PMID:25353797
O'Hern, Corey S.
the need to maintain constant chain contour length reduces the characteristic relaxation time by a factor N of the connectivity, uncrossability, and random- walk-like structure of the constituent chains. These alter is ceased. Analysis of these phenomena has focused on stress-assisted thermal ac- tivation of the local
Measurement of the electron spin relaxation time in a silicon quantum dot using single-shot readout
NASA Astrophysics Data System (ADS)
Prance, J. R.; Simmons, C. B.; van Bael, B. J.; Seng Koh, Teck; Shi, Zhan; Savage, D. E.; Lagally, M. G.; Joynt, R.; Friesen, Mark; Coppersmith, S. N.; Eriksson, M. A.
2011-03-01
Electron spins in Si/SiGe quantum dots are promising candidates as qubits for quantum information processing, because spins in silicon couple weakly to the host material. We present a measurement of the spin lifetime for electrons in a silicon quantum dot. The spin state of individual electrons is measured using single-shot charge readout and spin-to-charge conversion: only spin-up electrons will tunnel off the quantum dot. Charge sensing is performed with an integrated quantum point contact that detects single electron tunnel events as steps in current. We determine the relaxation time by measuring the fraction of measurements that contain spin-up tunneling events as a function of the time that the electron spins are held on the quantum dot. We observe a clear decay in this spin-up fraction versus time, and an exponential fit yields T1 ~ 2.8 seconds at a magnetic field of 1.85 T .
Yoshida, Akiko; Itoh, Yosuke; Nagaya, Kei; Takino, Kazuya; Sugawara, Jun-Ichi; Murakami, Takashi; Okamura, Kunihiro; Takahashi, Masahiko
2006-01-01
We present two cases showing significantly prolonged action of vecuronium from magnesium treatment after general anesthesia for urgent cesarean section. The serum magnesium levels were maintained at a therapeutic range for severe eclampsia in one patient (5.6 mg.dl(-1)) and for tocolysis in another with placenta previa totalis (6.9 mg.dl(-1)). The obstetrics-specific emergency in each patient led us to proceed with general anesthesia but using reduced-dose vecuronium, which failed to prevent prolongation of the neuromuscular block. As a result, the patients received prolonged mechanical ventilation. Our cases underscore the need for anesthesiologists as well as obstetricians to be aware of the prolongation of the action of nondepolarizing muscle relaxants as a result of magnesium treatment. PMID:16421674
NASA Astrophysics Data System (ADS)
Hürlimann, M. D.; Venkataramanan, L.; Flaum, C.
2002-12-01
The distribution function between diffusion and spin relaxation time is shown to be a powerful tool to characterize fluid mixtures in porous media. We discuss the nuclear magnetic resonance measurements using diffusion-editing sequences that were developed to measure this quantity. A recently developed two-dimensional inversion routine is used to extract the distribution function from the data. We show both theoretically and experimentally that the technique is suitable for ex situ applications in the presence of grossly inhomogeneous fields. We apply this technique to characterize sedimentary rocks saturated with oil-water mixtures. From the measured diffusion-relaxation time distribution function it is possible to quantify the oil and water saturation, to get a direct indication of the wettability of the porous media, to characterize the bulk properties of the oil and estimate the oil viscosity, and to get information about the geometrical arrangement of the fluid phases in the pore space. We have also identified effects due to susceptibility induced gradients in a sandstone and effects of strongly restricted diffusion in a limestone.
NMR Relaxation and Petrophysical Properties
NASA Astrophysics Data System (ADS)
Fleury, Marc
2011-03-01
NMR relaxation is routinely used in the field of geosciences to give basic petrophysical properties such as porosity, pore size distribution, saturation etc. In this tutorial, we focus on the pore size distribution deduced from NMR. We recall the basic principle used in the interpretation of the NMR signal and compare the results with other standard petrophysical techniques such as mercury pore size distribution, BET specific surface measurements, thin section visualizations. The NMR pore size distribution is a unique information available on water saturated porous media and can give similar results as MICP in certain situations. The scaling of NMR relaxation time distribution (s) into pore sizes (?m) requires the knowledge of the surface relaxivity (?m/s) and we recommend using specific surface measurements as an independent determination of solid surface areas. With usual surface relaxivities, the NMR technique can explore length-scales starting from nano-meters and ending around 100 ?m. Finally, we will introduce briefly recent techniques sensitive to the pore to pore diffusional exchange, providing new information on the connectivity of the pore network, but showing another possibility of discrepancy in the determination of pore size distribution with standard techniques.
Allometric scaling and maximum efficiency in physiological eigen time
Andresen, Bjarne; Shiner, J. S.; Uehlinger, Dominik E.
2002-01-01
General optimization results from physics indicate that maximum efficiency of a process, in the sense of minimum overall entropy production, is achieved when the rate of entropy production is constant over time, however not in ordinary clock time but on an, in general varying, “eigen time” scale, intrinsic to the system. We identify the eigen time of a biological system with “physiological time,” which generally scales with the 1/4 power of body mass, M1/4, over a vast range of species. Since it is equally well established that metabolic rate scales as M3/4, it follows that organisms produce entropy at the same intrinsic rate, fulfilling a necessary condition for maximum efficiency, and are all, furthermore, equally efficient on the physiological eigen time scale. PMID:11959910
Characteristic Variability Time Scales of Long Gamma-Ray Bursts
R. F. Shen; L. M. Song
2003-06-07
We determined the characteristic variability time scales (\\Delta t_p) of 410 bright and long GRBs, by locating the peaks of their Power Density Spectra, defined and calculated in the time domain. We found that the averaged variability time scale decreases with the peak flux. This is consistent with the time-dilation effect expected for the cosmological origin of GRBs. We also found that the occurrence distribution of the characteristic variability time scale shows bimodality, which might be interpreted as that the long GRB sample is composed of two sub-classes with different variability time scales. However, we found no difference for some other characteristics of these two sub-classes.
Domenici, Valentina; Frezzato, Diego; Veracini, Carlo Alberto
2006-12-14
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
Limitations of the Method of Multiple-Time-Scales
Peter B. Kahn; Yair Zarmi
2002-01-01
In the Method of Multiple-Time-Scales (MMTS), the introduction of independent time scales and the elimination of secular terms in the fast time variable, T0 = t, lead to the well-known solvability conditions. Starting from first order, free terms (solutions of the unperturbed equations) emerge in every order in the expansion of the approximate solution. In orders higher than first, the
On the stability of multiple time-scale systems
EYAD H. ABED
1986-01-01
The stability of time-invariant multiparameter singular perturbation problems is considered and the implications of two time-scale stability results for multiple time-scale systems are clarified. An example shows that the asymptotic stability of a multiparameter singular perturbation problem under the ‘bounded mutual ratios’ assumption for arbitrary bounds on the ratios of the small parameters does not imply asymptotic stability under the
Scaling analysis of multi-variate intermittent time series
NASA Astrophysics Data System (ADS)
Kitt, Robert; Kalda, Jaan
2005-08-01
The scaling properties of the time series of asset prices and trading volumes of stock markets are analysed. It is shown that similar to the asset prices, the trading volume data obey multi-scaling length-distribution of low-variability periods. In the case of asset prices, such scaling behaviour can be used for risk forecasts: the probability of observing next day a large price movement is (super-universally) inversely proportional to the length of the ongoing low-variability period. Finally, a method is devised for a multi-factor scaling analysis. We apply the simplest, two-factor model to equity index and trading volume time series.
Modeling orbital changes on tectonic time scales
NASA Technical Reports Server (NTRS)
Crowley, Thomas J.
1992-01-01
Geologic time series indicate significant 100 ka and 400 ka pre-Pleistocene climate fluctuations, prior to the time of such fluctuations in Pleistocene ice sheets. The origin of these fluctuations must therefore depend on phenomena other than the ice sheets. In a previous set of experiments, we tested the sensitivity of an energy balance model to orbital insolation forcing, specifically focusing on the filtering effect of the Earth's geography. We found that in equatorial areas, the twice-yearly passage of the sun across the equator interacts with the precession index to generate 100 ka and 400 ka power in our modeled time series. The effect is proportional to the magnitude of land in equatorial regions. We suggest that such changes may reflect monsoonal variations in the real climate system, and the subsequent wind and weathering changes may transfer some of this signal to the marine record. A comparison with observed fluctuations of Triassic lake levels is quite favorable. A number of problems remain to be studied or clarified: (1) the EBM experiments need to be followed up by a limited number of GCM experiments; (2) the sensitivity to secular changes in orbital forcing needs to be examined; (3) the possible modifying role of sedimentary processes on geologic time series warrants considerably more study; (4) the effect of tectonic changes on Earth's rotation rate needs to be studied; and (5) astronomers need to make explicit which of their predictions are robust and geologists and astronomers have to agree on which of the predictions are most testable in the geologic record.
Liao, Shu-Hsien; Chen, Kuen-Lin; Wang, Chun-Min; Chieh, Jen-Jie; Horng, Herng-Er; Wang, Li-Min; Wu, C. H.; Yang, Hong-Chang
2014-01-01
In this work, we report the use of bio-functionalized magnetic nanoparticles (BMNs) and dynamic magnetic resonance (DMR) to characterize the time-dependent spin-spin relaxation time for sensitive bio-detection. The biomarkers are the human C-reactive protein (CRP) while the BMNs are the anti-CRP bound onto dextran-coated Fe3O4 particles labeled as Fe3O4-antiCRP. It was found the time-dependent spin-spin relaxation time, T2, of protons decreases as time evolves. Additionally, the ?T2 of of protons in BMNs increases as the concentration of CRP increases. We attribute these to the formation of the magnetic clusters that deteriorate the field homogeneity of nearby protons. A sensitivity better than 0.1 ?g/mL for assaying CRP is achieved, which is much higher than that required by the clinical criteria (0.5 mg/dL). The present MR-detection platform shows promise for further use in detecting tumors, viruses, and proteins. PMID:25397920
Subburaj, Karupppasamy; Souza, Richard B.; Wyman, Bradley T.; Le Graverand-Gastineau, Marie-Pierre Hellio; Li, Xiaojuan; Link, Thomas M.; Majumdar, Sharmila
2014-01-01
Purpose To prospectively evaluate changes in T1? and T2 relaxation times in the meniscal body with acute loading using MRI in osteoarthritic knees and to compare these findings with those of age-matched healthy controls. Materials and Methods Female subjects above 40 years of age with (N1 = 20) and without osteoarthritis (OA) (N2 = 10) were imaged on a 3 Tesla MR scanner using a custom made loading device. MR images were acquired, with the knee flexed at 20°, with and without a compressive load of 50% of the subject's bodyweight. The subjects were categorized based on the radiographic evidence of OA. Three different zones (outer, middle, and inner) of meniscus body were defined (each occupying 1/3rd the width). After adjusting for age and body mass index in the general linear regression model, repeated measures analysis of variance was used to detect significant differences in T1? and T2 with and without loading. Results In the unloaded condition, the average T1? and T2 times were elevated in the outer and middle zones of the medial meniscus in OA subjects compared with the controls. In the loaded condition, T1? and T2 times of the outer zone of the medial meniscus was significantly elevated in OA subjects compared with controls. Finally the change (from unloaded to loaded) was significantly higher in controls than OA subjects (15.1% versus 8.3%; P = 0.039 for ?T1?, and 11.5% versus 6.9%, P = 0.049 for ?T2). Conclusion These findings suggest that while the OA process appears to affect the relaxation times of all regions within the meniscus, it may affect some regions sooner or to a greater degree. Furthermore, the differences in the change in relaxation times between unloaded and loaded conditions may reveal evidence about load transmission failure of the outer zone of the medial meniscus in subjects with knee OA. It is possible that these metrics (?T1? and ?T2) may be valuable as an early biomechanical biomarker, which could be used to predict load transmission to the underlying articular cartilage. PMID:24347310
Relaxation of an unstable state in parametrically excited cold atoms.
Moon, Geol; Kim, Yonghee; Heo, Myoung-Sun; Park, Jina; Yum, Dahyun; Lee, Wanhee; Noh, Heung-Ryoul; Jhe, Wonho
2011-09-01
We investigate the scaling behavior of the relaxation process for an unstable state near a subcritical Hopf bifurcation point. When the parametric modulation is applied to a magneto-optical trap, the atomic cloud becomes unstable and decays to the dynamic bistable states. Near the subcritical Hopf bifurcation point, we experimentally show that the relaxation process exhibits the scaling behavior; the relaxation time shows a scaling exponent of -1.002 (±0.024). We also present the passage time distribution for the statistical interpretation of the escape process associated with the relaxation of the unstable state. We compare the experimental results to the numerical and analytic results, demonstrating the good agreement between them. PMID:22060485
Relaxation selective pulses in fast relaxing systems
NASA Astrophysics Data System (ADS)
Lopez, Christopher J.; Lu, Wei; Walls, Jamie D.
2014-05-01
In this work, the selectivity or sharpness of the saturation profiles for relaxation selective pulses (Rs) that suppress magnetization possessing relaxation times of T2 = T2rsp and T1 = ?T2 for ??{1}/{2},? was optimized. Along with sharpening the selectivity of the Rs, the selective saturation of these pulses was also optimized to be robust to both B0 and B1 inhomogeneities. Frequency-swept hyperbolic secant and adiabatic time-optimal saturation pulse inputs were found to work best in the optimizations, and the pulse lengths required to selectivity saturate the magnetization were always found to be less than the inversion recovery delay, T1ln(2). The selectivity of the optimized relaxation selective pulses was experimentally demonstrated in aqueous solutions with varying concentrations of the paramagnetic species, [Mn+2], and for use in solvent suppression. Finally, the “rotational” properties of spin relaxation were explored along with an analytical derivation of adiabatic time-optimal saturation pulses.
NASA Astrophysics Data System (ADS)
Kim, Kang; Saito, Shinji
2013-03-01
We report an extensive and systematic investigation of the multi-point and multi-time correlation functions to reveal the spatio-temporal structures of dynamic heterogeneities in glass-forming liquids. Molecular dynamics simulations are carried out for the supercooled states of various prototype models of glass-forming liquids such as binary Kob-Andersen, Wahnström, soft-sphere, and network-forming liquids. While the first three models act as fragile liquids exhibiting super-Arrhenius temperature dependence in their relaxation times, the last is a strong glass-former exhibiting Arrhenius behavior. First, we quantify the length scale of the dynamic heterogeneities utilizing the four-point correlation function. The growth of the dynamic length scale with decreasing temperature is characterized by various scaling relations that are analogous to the critical phenomena. We also examine how the growth of the length scale depends upon the model employed. Second, the four-point correlation function is extended to a three-time correlation function to characterize the temporal structures of the dynamic heterogeneities based on our previous studies [K. Kim and S. Saito, Phys. Rev. E 79, 060501-R (2009), 10.1103/PhysRevE.79.060501; K. Kim and S. Saito, J. Chem. Phys. 133, 044511 (2010), 10.1063/1.3464331]. We provide comprehensive numerical results obtained from the three-time correlation function for the above models. From these calculations, we examine the time scale of the dynamic heterogeneities and determine the associated lifetime in a consistent and systematic way. Our results indicate that the lifetime of the dynamical heterogeneities becomes much longer than the ?-relaxation time determined from a two-point correlation function in fragile liquids. The decoupling between the two time scales is remarkable, particularly in supercooled states, and the time scales differ by more than an order of magnitude in a more fragile liquid. In contrast, the lifetime is shorter than the ?-relaxation time in tetrahedral network-forming strong liquid, even at lower temperatures.
On time scale invariance of random walks in confined space.
Bearup, Daniel; Petrovskii, Sergei
2015-02-21
Animal movement is often modelled on an individual level using simulated random walks. In such applications it is preferable that the properties of these random walks remain consistent when the choice of time is changed (time scale invariance). While this property is well understood in unbounded space, it has not been studied in detail for random walks in a confined domain. In this work we undertake an investigation of time scale invariance of the drift and diffusion rates of Brownian random walks subject to one of four simple boundary conditions. We find that time scale invariance is lost when the boundary condition is non-conservative, that is when movement (or individuals) is discarded due to boundary encounters. Where possible analytical results are used to describe the limits of the time scaling process, numerical results are then used to characterise the intermediate behaviour. PMID:25481837
Grueneisen relaxation photoacoustic microscopy
Wang, Lidai; Zhang, Chi; Wang, Lihong V.
2014-01-01
The temperature-dependent property of the Grueneisen parameter has been employed in photoacoustic imaging mainly to measure tissue temperature. Here we explore this property using a different approach and develop Grueneisen-relaxation photoacoustic microscopy (GR-PAM), a technique that images non-radiative absorption with confocal optical resolution. GR-PAM sequentially delivers two identical laser pulses with a micro-second-scale time delay. The first laser pulse generates a photoacoustic signal and thermally tags the in-focus absorbers. Owing to the temperature dependence of the Grueneisen parameter, when the second laser pulse excites the tagged absorbers within the thermal relaxation time, a photoacoustic signal stronger than the first one is produced. GR-PAM detects the amplitude difference between the two co-located photoacoustic signals, confocally imaging the non-radiative absorption. We greatly improved axial resolution from 45 µm to 2.3 µm and at the same time slightly improved lateral resolution from 0.63 µm to 0.41 µm. In addition, the optical sectioning capability facilitates the measurement of the absolute absorption coefficient without fluence calibration. PMID:25379919
Time Scaling of Chaotic Systems: Application to Secure Communications
Donatello Materassi; Michele Basso
2007-10-25
The paper deals with time-scaling transformations of dynamical systems. Such scaling functions operate a change of coordinates on the time axis of the system trajectories preserving its phase portrait. Exploiting this property, a chaos encryption technique to transmit a binary signal through an analog channel is proposed. The scheme is based on a suitable time-scaling function which plays the role of a private key. The encoded transmitted signal is proved to resist known decryption attacks offering a secure and reliable communication.
Oliveira, Patrícia D.; Michel, Ricardo C.; McBride, Alan J. A.; Moreira, Angelita S.; Lomba, Rosana F. T.; Vendruscolo, Claire T.
2013-01-01
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
Myosin Dynamics on the Millisecond Time Scale
Burghardt, Thomas P.; Yan Hu, Jimmy; Ajtai, Katalin
2007-01-01
Myosin is a motor protein associating with actin and ATP. It translates along actin filaments against a force by transduction of free energy liberated with ATP hydrolysis. Various myosin crystal structures define time points during ATPase showing the protein undergoes large conformation change during transduction over a cycle with ?10 milliseconds periodicity. The protein conformation trajectory between two intermediates in the cycle is surmised by non-equilibrium Monte Carlo simulation utilizing free energy minimization. The trajectory shows myosin transduction of free energy to mechanical work giving evidence for: (i) a causal relationship between product release and work production in the native isoform that is correctly disrupted in a chemically modified protein, (ii) the molecular basis of ATP sensitive tryptophan fluorescence enhancement and acrylamide quenching, (iii) an actin binding site peptide containing the free energy barrier to ATPase product release defining the rate limiting step and, (iv) a scenario for actin-activation of myosin ATPase. PMID:17913331
Myosin dynamics on the millisecond time scale.
Burghardt, Thomas P; Hu, Jimmy Yan; Ajtai, Katalin
2007-12-01
Myosin is a motor protein associating with actin and ATP. It translates along actin filaments against a force by transduction of free energy liberated with ATP hydrolysis. Various myosin crystal structures define time points during ATPase showing the protein undergoes large conformation change during transduction over a cycle with approximately 10 ms periodicity. The protein conformation trajectory between two intermediates in the cycle is surmised by non-equilibrium Monte Carlo simulation utilizing free-energy minimization. The trajectory shows myosin transduction of free energy to mechanical work giving evidence for: (i) a causal relationship between product release and work production in the native isoform that is correctly disrupted in a chemically modified protein, (ii) the molecular basis of ATP-sensitive tryptophan fluorescence enhancement and acrylamide quenching, (iii) an actin-binding site peptide containing the free-energy barrier to ATPase product release defining the rate limiting step and, (iv) a scenario for actin-activation of myosin ATPase. PMID:17913331
Magnetic relaxation in dipolar magnetic nanoparticle clusters
NASA Astrophysics Data System (ADS)
Hovorka, Ondrej; Barker, Joe; Chantrell, Roy; Friedman, Gary; York-Drexel Collaboration
2013-03-01
Understanding the role of dipolar interactions on thermal relaxation in magnetic nanoparticle (MNP) systems is of fundamental importance in magnetic recording, for optimizing the hysteresis heating contribution in the hyperthermia cancer treatment in biomedicine, or for biological and chemical sensing, for example. In this talk, we discuss our related efforts to quantify the influence of dipolar interactions on thermal relaxation in small clusters of MNPs. Setting up the master equation and solving the associated eigenvalue problem, we identify the observable relaxation time scale spectra for various types of MNP clusters, and demonstrate qualitatively different spectral characteristics depending on the point group of symmetries of the particle arrangement within the cluster - being solely a dipolar interaction effect. Our findings provide insight into open questions related to magnetic relaxation in bulk MNP systems, and may prove to be also of practical relevance, e.g., for improving robustness of methodologies in biological and chemical sensing. Understanding the role of dipolar interactions on thermal relaxation in magnetic nanoparticle (MNP) systems is of fundamental importance in magnetic recording, for optimizing the hysteresis heating contribution in the hyperthermia cancer treatment in biomedicine, or for biological and chemical sensing, for example. In this talk, we discuss our related efforts to quantify the influence of dipolar interactions on thermal relaxation in small clusters of MNPs. Setting up the master equation and solving the associated eigenvalue problem, we identify the observable relaxation time scale spectra for various types of MNP clusters, and demonstrate qualitatively different spectral characteristics depending on the point group of symmetries of the particle arrangement within the cluster - being solely a dipolar interaction effect. Our findings provide insight into open questions related to magnetic relaxation in bulk MNP systems, and may prove to be also of practical relevance, e.g., for improving robustness of methodologies in biological and chemical sensing. OH gratefully acknowledges support from a Marie Curie Intra European Fellowship within the 7th European Community Framework Programme under grant agreement PIEF-GA-2010-273014
Liquidity spillover in international stock markets through distinct time scales.
Righi, Marcelo Brutti; Vieira, Kelmara Mendes
2014-01-01
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
Global Secular Variation from Satellite to Millennia Time Scales
NASA Astrophysics Data System (ADS)
Korte, M.
2003-12-01
Secular variation can be studied on a large range of time scales from direct and indirect measurements of the geomagnetic field. Questions like minimum period and spatial scale of variations originating in the core are investigated with observatory and satellite data. Variations of external origin and mantle filtering are major impediments here. Indirect records of the geomagnetic field from archeo- and paleomagnetic studies provide time series long enough to investigate full periods of secular variation and the underlying core dynamics. While recently first continuous global models on the millennia scale have been developed, dating uncertainties in the individual time series and sparse data coverage challenge their reliability. Here an overview over secular variation features and their implications as determined from global models on decade to millennia time scales is given.
Diffusion Time-Scale of Porous Pressure-Sensitive Paint
NASA Technical Reports Server (NTRS)
Liu, Tianshu; Teduka, Norikazu; Kameda, Masaharu; Asai, Keisuke
2001-01-01
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.
Stability and Stabilization of Two Time Scale Switched Systems in Discrete Time
Ivan Malloci; Jamal Daafouz; Claude Iung
2010-01-01
In this technical note, stability and stabilization of two time scale switched linear systems in the singular perturbation form are addressed in discrete time. We show that, under an arbitrary switching rule, stability of the slow and fast switched subsystems is not sufficient to assess stability of the original two time scale switched system, even if the singular perturbation parameter
Geometric structure of multiple time-scale nonlinear dynamical systems
Sanjay Bharadwaj
1999-01-01
A new methodology to analyze time-scale structure of smooth finite-dimensional nonlinear dynamical systems is developed. This approach does not assume apriori knowledge of slow and fast variables for special coordinates that simplify the form of the nonlinear dynamics. Conventional approaches to analyze time-scale structure of nonlinear dynamics such as singular perturbation theory proceed from such specialized apriori knowledge which is
Time Scales of Observation and Ontological Levels of Reality
Alexey Alyushin
2010-01-01
My goal is to conceive how the reality would look like for hypothetical creatures that supposedly perceive on time scales\\u000a much faster or much slower than that of us humans. To attain the goal, I propose modelling in two steps. At step one, we have\\u000a to single out a unified parameter that sets time scale of perception. Changing substantially the
Scaling approach for the time-dependent Kondo model
Tomaras, C
2010-01-01
We present a new nonperturbative method to deal with the time-dependent quantum many-body problem, which is an extension of Wegner's flow equations to time-dependent Hamiltonians. The formalism provides a scaling procedure for the set of time-dependent interaction constants. We apply these ideas to a Kondo model with a ferromagnetic exchange coupling switched on over a time scale $\\tau$. We show that the asymptotic expectation value of the impurity spin interpolates continuously between its quenched and adiabatic value.
Scaling approach for the time-dependent Kondo model
C. Tomaras; S. Kehrein
2010-11-04
We present a new nonperturbative method to deal with the time-dependent quantum many-body problem, which is an extension of Wegner's flow equations to time-dependent Hamiltonians. The formalism provides a scaling procedure for the set of time-dependent interaction constants. We apply these ideas to a Kondo model with a ferromagnetic exchange coupling switched on over a time scale $\\tau$. We show that the asymptotic expectation value of the impurity spin interpolates continuously between its quenched and adiabatic value.
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
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.
NASA Astrophysics Data System (ADS)
Tsuji, Yoshiyuki; Sakamoto, Shin-ichi; Ishino, Takahiro; Watanabe, Yoshiaki; Senda, Jiro
2008-05-01
Experimental investigations were carried out to establish a design method for a thermoacoustic cooling system. When a straight acoustic tube is used, the acoustic power is supplied from the tube end. The ceramic stack, which consists of many narrow channels, is inserted into the tube. By changing the insertion position and the stack channel radius, a temperature decrease at the stack end is observed as the energy conversion parameter. A nondimensional parameter, ??, considering the relaxation time ? is determined from resonance frequency and stack channel radius. The temperature decrease is examined using several values of ??. Results show that the insertion position for which the maximum temperature decrease is obtained depends on ??. Therefore, the best stack insertion position can be designed according to the given frequency and stack channel radius. For that reason, ?? is an important index for thermoacoustic cooling systems.
Larionov, A. V., E-mail: larionov@issp.ac.ru [Russian Academy of Sciences, Institute of Solid State Physics (Russian Federation); Il’in, A. I. [Russian Academy of Sciences, Institute of Microelectronics Technology and High-Purity Materials (Russian Federation)
2013-12-15
The coherent spin dynamics of electrons localized in a plane of GaAs quantum wells is studied experimentally by the application of an electrically controlled potential. The localizing potential is produced with the use of a metal gate with submicrometer windows deposited onto the sample surface. The photoinduced spin Kerr effect is used to study the electron spin lifetime as a function of the temperature, applied bias, and magnetic field for gates with different sets of windows. It is shown that, with an electrically controlled laterally localizing potential, it is possible to gradually change the electron spin lifetime from several hundreds of picoseconds to several tens of nanoseconds. The dependence of the electron spin relaxation time on the sizes of the lateral localization region is in good qualitative agreement with theoretical prediction.
Measurement of solute proton spin-lattice relaxation times in water using the 1,3,3,1 sequence
Sankar, S.S.; Mole, P.A.; Coulson, R.L.
1986-12-01
/sup 1/H NMR spin-lattice relaxation times (T1) of the N-CH3 proton resonances of phosphocreatine (PCr) and creatine (Cr) in water solutions were obtained using the 1,3,3,1 pulse sequence. These T1 values were equivalent to those obtained in D/sub 2/O and water using either the conventional inversion-recovery experiment or the 1,3,3,1 pulse sequence. Thus, the 1,3,3,1 sequence of proton NMR can provide an independent means along with phosphorous NMR for assess PCr and for the study of the creatine kinase reaction (PCr + ADP in equilibrium ATP + Cr) in aqueous solutions and perhaps in biological preparations.
Time and scale Hurst exponent analysis for financial markets
NASA Astrophysics Data System (ADS)
Matos, José A. O.; Gama, Sílvio M. A.; Ruskin, Heather J.; Sharkasi, Adel Al; Crane, Martin
2008-06-01
We use a new method of studying the Hurst exponent with time and scale dependency. This new approach allows us to recover the major events affecting worldwide markets (such as the September 11th terrorist attack) and analyze the way those effects propagate through the different scales. The time-scale dependence of the referred measures demonstrates the relevance of entropy measures in distinguishing the several characteristics of market indices: “effects” include early awareness, patterns of evolution as well as comparative behaviour distinctions in emergent/established markets.
Suzuki, Hidetoshi; Sasaki, Takuo; Sai, Akihisa; Ohshita, Yoshio; Kamiya, Itaru; Yamaguchi, Masafumi [Toyota Technological Institute, 2-12-1 Hisakata, Tempaku, Nagoya 468-8511 (Japan); Takahasi, Masamitu; Fujikawa, Seiji [Synchrotron Radiation Research Center, Japan Atomic Energy Agency, Hyogo 679-5148 (Japan)
2010-07-26
Real-time three-dimensional reciprocal space mapping (3D-RSM) measurement during In{sub 0.12}Ga{sub 0.88}As/GaAs(001) molecular beam epitaxial growth has been performed to investigate anisotropy in relaxation processes along [110] and [110] directions caused by alpha and beta misfit dislocations (MDs). Anisotropies, strain relaxation, and crystal quality in both directions were simultaneously evaluated via the position and broadness of 022 diffraction in 3D-RSM. In the small-thickness region, strain relaxation caused by alpha-MDs is higher than that caused by beta-MDs, and therefore crystal quality along [110] is worse than that along [110]. Rapid relaxation along both [110] and [110] directions occurs at almost the same thickness. After rapid relaxation, anisotropy in strain relaxation gradually decreases, whereas crystal quality along [110] direction, presumably due to beta-MDs, becomes better that along [110] direction and the ratio does not decay with thickness.
Wang, Yi-Xiang J; Griffith, James F; Leung, Jason C S; Yuan, Jing
2014-08-01
This report aims to study the age related T1rho and T2 relaxation time changes in lumbar intervertebral disc. Lumbar sagittal magnetic resonance imaging (MRI) was performed with a 3 Tesla scanner in 52 subjects. With a spin-lock frequency of 500 Hz, T1rho was measured using a rotary echo spin-lock pulse embedded in a 3D balanced fast field echo sequence. A multi-echo turbo spin echo sequence was used for T2 mapping. Regions-of-interest were drawn over the T1rho and T2 maps, including nucleus pulposus and annulus fibrosus. For L1/2-L4/5 discs, results showed the age associated reduction of T1rho of nucleus pulposus had a of slope of -1.06, the reduction of T2 of nucleus pulposus had a slope of -1.47, the reduction of T1rho of annulus fibrosus had a slope of -0.25, and the reduction of T2 of annulus fibrosus had a slope of -0.18, with all the slopes significantly non-zero. In nucleus pulposus the slope of T2 was slightly steeper than that of T1rho (P=0.085), while in annulus fibrosus the slope of T1rho was slightly steeper than that of T2 (P=0.31). We conclude that significant age related reduction of T1rho and T2 magnetic resonance relaxation times of lumbar intervertebral disc was observed, however, the relative performances of T1rho vs. T2 were broadly similar. PMID:25202661
Griffith, James F.; Leung, Jason C. S.; Yuan, Jing
2014-01-01
This report aims to study the age related T1rho and T2 relaxation time changes in lumbar intervertebral disc. Lumbar sagittal magnetic resonance imaging (MRI) was performed with a 3 Tesla scanner in 52 subjects. With a spin-lock frequency of 500 Hz, T1rho was measured using a rotary echo spin-lock pulse embedded in a 3D balanced fast field echo sequence. A multi-echo turbo spin echo sequence was used for T2 mapping. Regions-of-interest were drawn over the T1rho and T2 maps, including nucleus pulposus and annulus fibrosus. For L1/2-L4/5 discs, results showed the age associated reduction of T1rho of nucleus pulposus had a of slope of –1.06, the reduction of T2 of nucleus pulposus had a slope of –1.47, the reduction of T1rho of annulus fibrosus had a slope of –0.25, and the reduction of T2 of annulus fibrosus had a slope of –0.18, with all the slopes significantly non-zero. In nucleus pulposus the slope of T2 was slightly steeper than that of T1rho (P=0.085), while in annulus fibrosus the slope of T1rho was slightly steeper than that of T2 (P=0.31). We conclude that significant age related reduction of T1rho and T2 magnetic resonance relaxation times of lumbar intervertebral disc was observed, however, the relative performances of T1rho vs. T2 were broadly similar. PMID:25202661
Multiresolution schemes for time-scaled propagation of wave packets
NASA Astrophysics Data System (ADS)
Frapiccini, Ana Laura; Hamido, Aliou; Mota-Furtado, Francisca; O'Mahony, Patrick F.; Piraux, Bernard
2015-04-01
We present a detailed analysis of the time-scaled coordinate approach and its implementation for solving the time-dependent Schrödinger equation describing the interaction of atoms or molecules with radiation pulses. We investigate and discuss the performance of multiresolution schemes for the treatment of the squeezing around the origin of the bound part of the scaled wave packet. When the wave packet is expressed in terms of B splines, we consider two different types of breakpoint sequences: an exponential sequence with a constant density and an initially uniform sequence with a density of points around the origin that increases with time. These two multiresolution schemes are tested in the case of a one-dimensional Gaussian potential and for atomic hydrogen. In the latter case, we also use Sturmian functions to describe the scaled wave packet and discuss a multiresolution scheme which consists of working in a Sturmian basis characterized by a set of nonlinear parameters. Regarding the continuum part of the scaled wave packet, we show explicitly that, for large times, the group velocity of each ionized wave packet goes to zero while its dispersion is suppressed, thereby explaining why, eventually, the scaled wave packet associated with the ejected electrons becomes stationary. Finally, we show that only the lowest scaled bound states can be removed from the total scaled wave packet once the interaction with the pulse has ceased.
Richardson, P M; Voice, A M; Ward, I M
2013-12-01
Longitudinal relaxation (T1) measurements of (19)F, (7)Li, and (1)H in propylene carbonate/LiBF4 liquid electrolytes are reported. Comparison of T1 values with those for the transverse relaxation time (T2) confirm that the measurements are in the high temperature (low correlation time) limit of the T1 minimum. Using data from pulsed field gradient measurements of self-diffusion coefficients and measurements of solution viscosity measured elsewhere, it is concluded that although in general there are contributions to T1 from both translational and rotational motions. For the lithium ions, this is mainly translational, and for the fluorine ions mainly rotational. PMID:24320385
NASA Astrophysics Data System (ADS)
Richardson, P. M.; Voice, A. M.; Ward, I. M.
2013-12-01
Longitudinal relaxation (T1) measurements of 19F, 7Li, and 1H in propylene carbonate/LiBF4 liquid electrolytes are reported. Comparison of T1 values with those for the transverse relaxation time (T2) confirm that the measurements are in the high temperature (low correlation time) limit of the T1 minimum. Using data from pulsed field gradient measurements of self-diffusion coefficients and measurements of solution viscosity measured elsewhere, it is concluded that although in general there are contributions to T1 from both translational and rotational motions. For the lithium ions, this is mainly translational, and for the fluorine ions mainly rotational.
NASA Astrophysics Data System (ADS)
Harrell, J. W.; Gopalakrishnan, Ramesh
1992-05-01
Proton relaxation time measurements ( T1 and T1?) have been done on 1,6-hexanediol dimethacrylate (HDDMA) as a function of temperature between 77 and 296 K. It has been found that HDDMA can exist in either a glass, crystalline, or mixed glass-crystalline phase, depending on the sample temperature and thermal history. The low-temperature motion in the glass and crystalline phases is characterized by methyl group reorientation. An excellent fit to the low-temperature T1 data can be made using a Cole-Davidson (CD) distribution of cutoff correlation times. A broader distribution is observed in the glass phase than in the crystalline phase. In the melt and in the glass phase at high temperatures, whole-molecule reorientation is observed. The T1 data in this range can be fit using a single Arrhenius correlation time. However, in order to simultaneously fit both the T1 and T1? data, a CD distribution is required with a cutoff correlation time described by a temperature-dependent activation energy. Additional unresolved motions are observed in the crystalline phase at high temperatures.
Multiple-time scales analysis of physiological time series under neural control
NASA Technical Reports Server (NTRS)
Peng, C. K.; Hausdorff, J. M.; Havlin, S.; Mietus, J. E.; Stanley, H. E.; Goldberger, A. L.
1998-01-01
We discuss multiple-time scale properties of neurophysiological control mechanisms, using heart rate and gait regulation as model systems. We find that scaling exponents can be used as prognostic indicators. Furthermore, detection of more subtle degradation of scaling properties may provide a novel early warning system in subjects with a variety of pathologies including those at high risk of sudden death.
Hierarchical structure and multi time-scale in large scale dynamical systems
Koichi Tojo; Koji Tsumura
2008-01-01
In this paper, we deal with approximation methods of large-scale systems which describe the macroscopic behavior of the whole system and simultaneously the partially microscopic one of the objective subsystems. We propose a hierarchical representation of such large-scale systems by employing the connection graph structure of the elements and multiple time-scale dynamics. The approximation accuracy is rigorously induced and numerical
The time-scale associated with flux expulsion
NASA Astrophysics Data System (ADS)
Moffatt, H. K.; Kamkar, H.
A simple model problem is solved in order to show that the time-scale associated with the process of flux expulsion is tfe = Rm1/3t0 where t0 is a time-scale characterising the flow (for example, the eddy turnover time, or inverse shear rate) and Rm is the magnetic Reynolds number. By decomposing the vector potential into a product of a rapidly varying part (in space) and a slowly varying part, it is shown how numerical work can be extended to much higher values of Rm than has been achieved hitherto.
Effects of bulk charge and momentum relaxation time scales on ac electrospraying
Chang, Hsueh-Chia
resonance effects become unimportant, the meniscus oscillates and then changes to a growing conical mode to an oscillating mode and a conical mode is delayed and additional tip-streaming and elongated-fast dripping modes and the ejection frequency of the elongated-fast dripping mode are found to be related to the momentum diffusion
Fast Time-Domain Simulation by Waveform Relaxation Methods J. Sun, H. Grotstollen
Paderborn, Universität
to reduce the simulationtime is presented. Algorithmsfor circuit partitioning, time windowing. The integration of waveform-relation techniques with averaging methodstofurther speed up transientsimulationsis-differential equations consists of numerical so
NASA Astrophysics Data System (ADS)
Yang, J.; Patterson, R.; Feng, Y.; Shrestha, S.; Huang, S.; Conibeer, G.
2015-04-01
Strong optical coupling is a carrier extraction method for hot-carrier solar cells, where carriers are extracted as photons from an absorber material and then reabsorbed by a conventional photovoltaic (PV) cell. The design and working principle of this kind of optically coupled device is investigated using a relaxation-time model with practical operating conditions. This investigation is performed in the so-called "down-conversion" configuration, where the band gap of the absorber material is the same as that in the final photovoltaic cell. In this configuration, carrier impact ionization rates that are faster than thermalization rates by at least 50 times are needed to effectively down-convert the hot carriers' energy to the electronic band edge. Photon emission through radiative recombination must be enhanced by more than 500 times through photonic engineering in order to reduce Auger loss during carrier extraction. The strong luminescence from the PV cell feeding back to the absorber material will further limit the optical extraction in the near-field coupled structure, reducing the overall conversion efficiency to be lower than the ideal expectation reported previously. The strong similarity between the hot-carrier down-conversion and carrier multiplication also suggests the possible application of such optical extraction for multiple-exciton-generation solar cells, making it potentially a general carrier extraction approach for third-generation solar cells.
Zimmerman, Neil M.; Huber, William H. [National Institute of Standards and Technology, Gaithersburg, Maryland 20899 (United States)
2009-11-15
By measuring the long-term charge offset drift in single electron tunneling transistors, we have observed a transient relaxation after fabrication which is correlated with the presence of amorphous insulator. The temperature and time dependence of the transient relaxation are both in agreement with an extension of the standard model for two-level systems in glasses. This technique, which is sensitive to atomic scale motion in femtogram-sized samples, offers the possibility of a technique for investigation of glassy relaxation.
Investigating the Geologic Time Scale: Creating posters to Display Trends in Geologic Time
NSDL National Science Digital Library
kim Atkins
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.
Common scaling patterns in intertrade times of U. S. stocks.
Ivanov, Plamen Ch; Yuen, Ainslie; Podobnik, Boris; Lee, Youngki
2004-05-01
We analyze the sequence of time intervals between consecutive stock trades of thirty companies representing eight sectors of the U.S. economy over a period of 4 yrs. For all companies we find that: (i) the probability density function of intertrade times may be fit by a Weibull distribution, (ii) when appropriately rescaled the probability densities of all companies collapse onto a single curve implying a universal functional form, (iii) the intertrade times exhibit power-law correlated behavior within a trading day and a consistently greater degree of correlation over larger time scales, in agreement with the correlation behavior of the absolute price returns for the corresponding company, and (iv) the magnitude series of intertrade time increments is characterized by long-range power-law correlations suggesting the presence of nonlinear features in the trading dynamics, while the sign series is anticorrelated at small scales. Our results suggest that independent of industry sector, market capitalization and average level of trading activity, the series of intertrade times exhibit possibly universal scaling patterns, which may relate to a common mechanism underlying the trading dynamics of diverse companies. Further, our observation of long-range power-law correlations and a parallel with the crossover in the scaling of absolute price returns for each individual stock, support the hypothesis that the dynamics of transaction times may play a role in the process of price formation. PMID:15244883
Stability of nonlinear systems with three time scales
C. A. Desoer; S. M. Shahruz
1986-01-01
We study the asymptotic stability of a singularly perturbed nonlinear time-invariant systemS?v, which has three vastly different time scales. The systemS?v is approximated by three simpler systems over different time intervals. We give a straightforward proof of the fact that the asymptotic stability ofS?v is guaranteed when the equilibrium points of the three simpler systems are exponentially stable and when
Stelzeneder, David; Kovács, Balázs K.; Goed, Sabine; Welsch, Goetz H.; Hirschfeld, Clemens; Paternostro-Sluga, Tatjana; Friedrich, Klaus M.; Mamisch, Tallal C.; Trattnig, Siegfried
2012-01-01
Background context Diurnal changes in T2 values, indicative for changes in water content, have been reported in the lumbar intervertebral discs. However, data concerning short-term T2 changes are missing. Purpose The purpose of this study was to investigate the short-term effects of unloading on T2 values in lumbar intervertebral discs in vivo. Study design Experimental study with repeated measurements of lumbar discs T2 relaxation time during a period of 38 minutes of supine posture. Patient sample Forty-one patients with acute or chronic low back pain (visual analog scale ?3). Outcome measures T2 relaxation time in the intervertebral disc, lumbar lordosis angle, and intervertebral disc height. Methods Forty-one patients (mean age, 41.6 years) were investigated in the supine position using a 3-tesla magnetic resonance system. Sagittal T2 mapping was performed immediately after unloading and after a mean delay of 38 minutes. No patient movement was allowed between the measurements. One region of interest (ROI) was manually placed in both the anterior and the posterior annulus fibrosus (AF) and three ROIs in the nucleus pulposus (NP). Results There was a statistically significant decrease in the anterior NP (?2.7 ms; p<.05) and an increase in T2 values in the posterior AF (+3.5 ms; p<.001). Discs with initially low T2 values in the NP showed minor increase in the posterior AF (+1.6 ms; p<.05), whereas a major increase in the posterior AF was found in discs with initially high T2 values in the NP (+6.8 ms; p=.001). Patients examined in the morning showed no differences, but those investigated in the afternoon showed a decrease in the anterior NP (?5.3 ms; p<.05) and an increase in the posterior AF (+7.8 ms; p=.002). No significant differences were observed in other regions. Correlation analysis showed moderate correlations between the time of investigation and T2 changes in the posterior AF (r=0.46; p=.002). Conclusions A shift of water from the anterior to the posterior disc regions seems to occur after unloading the lumbar spine in the supine position. The clinical relevance of these changes needs to be investigated. PMID:22469305
Li, S.; Swindle, S.L.; Smith, S.K.; Nieman, R.A.; Moore, A.L.; Moore, T.A.; Gust, D. (Arizona State Univ., Tempe, AZ (United States))
1995-03-09
Analysis of [sup 13]C NMR spin-lattice relaxation times (T[sub 1]) yields information concerning both overall tumbling of molecules in solution and internal rotations about single bonds. Relaxation time and nuclear Overhauser effect data have been obtained for [Beta]-carotene and two related molecules, squalane and squalene, for zinc meso-tetraphenylporphyrin, and for a dyad consisting of a porphyrin covalently linked to a carotenoid polyene through a trimethylene bridge. Squalane and squalene, which lack conjugated double bonds, behave essentially as limp string, with internal rotations at least as rapid as overall isotropic tumbling motions. In contrast, [Beta]-carotene reorients as a rigid rod, with internal motions which are too slow to affect relaxation times. Modeling it as an anisotropic rotor yields a rotational diffusion coefficient for motion about the major axis which is 14 times larger than that for rotation about axes perpendicular to that axis. The porphyrin reorients more nearly isotropically and features internal librational motions about the single bonds to the phenyl groups. The relaxation time data for the carotenoporphyrin are consistent with internal motions similar to those of a medieval military flail. 31 refs., 3 figs., 5 tabs.
On Nonlinear Control Systems with Multiple Time Scales
G. Grammel
2004-01-01
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
Correlated and uncorrelated heart rate fluctuations during relaxing visualization
NASA Astrophysics Data System (ADS)
Papasimakis, N.; Pallikari, F.
2010-05-01
The heart rate variability (HRV) of healthy subjects practicing relaxing visualization is studied by use of three multiscale analysis techniques: the detrended fluctuation analysis (DFA), the entropy in natural time (ENT) and the average wavelet (AWC) coefficient. The scaling exponent of normal interbeat interval increments exhibits characteristics of the presence of long-range correlations. During relaxing visualization the HRV dynamics change in the sense that two new features emerge independent of each other: a respiration-induced periodicity that often dominates the HRV at short scales (<40 interbeat intervals) and the decrease of the scaling exponent at longer scales (40-512 interbeat intervals). In certain cases, the scaling exponent during relaxing visualization indicates the breakdown of long-range correlations. These characteristics have been previously seen in the HRV dynamics during non-REM sleep.
Hemminga, Marcus A.
.1 to 0.5 M Bu4NOH (Emsleytative, comparative analysis of P forms. However, for 31 P NMR to be and Niazi.0 s for orthophosphate and orthophosphateanalyses of soil and litter samples by solution 31 P NMR spectroscopy monoesters, delay times in use for soil ever possible. 31 P NMR spectroscopy include 20 s (Newman and Tate, 1980
Slow relaxation in granular compaction
NASA Astrophysics Data System (ADS)
Ben-Naim, E.; Knight, J. B.; Nowak, E. R.; Jaeger, H. M.; Nagel, S. R.
1998-11-01
Experimental studies show that the density of a vibrated granular material evolves from a low density initial state into a higher density final steady state. The relaxation towards the final density follows an inverse logarithmic law. As the system approaches its final state, a growing number of beads have to be rearranged to enable a local density increase. A free volume argument shows that this number grows as N = {?}/{(1-?)}. The time scale associated with such events increases exponentially ? e N, and as a result a logarithmically slow approach to the final state is found ? ? - ?(t) ? {1}/{lnt }. Furthermore, a one-dimensional toy model that captures this relaxation dynamics as well as the observed density fluctuations is discussed.
Stress Relaxation in Aging Soft Colloidal Glasses
Ranjini Bandyopadhyay; P. Harsha Mohan; Yogesh M. Joshi
2010-03-25
We investigate the stress relaxation behavior on the application of step strains to aging aqueous suspensions of the synthetic clay Laponite. The stress exhibits a two-step decay, from which the slow relaxation modes are extracted as functions of the sample ages and applied step strain deformations. Interestingly, the slow time scales that we estimate show a dramatic enhancement with increasing strain amplitudes. We argue that the system ends up exploring the deeper sections of its energy landscape following the application of the step strain.
Transient relaxation of a charged polymer chain subject to an external field in a random tube
Deutch, John
Transient relaxation of a charged polymer chain subject to an external field in a random tube S. F in a random media is studied theoretically. We consider a chain in a random tube and present scaling results for relaxation times, for displacement of the chain segments inside the tube, and for the dynamics of leaking
Computation of multi-region relaxed magnetohydrodynamic equilibria S. R. Hudson,1,a)
Hudson, Stuart
Computation of multi-region relaxed magnetohydrodynamic equilibria S. R. Hudson,1,a) R. L. Dewar,2 the construction of stepped-pressure equilibria as extrema of a multi-region, relaxed magnetohydrodynamic (MHD-fluid magnetohydrodynam- ics (MHD) is commonly used for modeling the global, long- time-scale state of plasmas
An algorithm for the Italian atomic time scale
NASA Technical Reports Server (NTRS)
Cordara, F.; Vizio, G.; Tavella, P.; Pettiti, V.
1994-01-01
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.
Trends in Surface Radiation Budgets at Climatic Time Scales
NASA Astrophysics Data System (ADS)
Pinker, Rachel T.; Zhang, Banglin; Ma, Yingtao
2015-04-01
For assessment of variability and trends in the Earth Radiation Balance, information is needed at climatic time scales. Satellite observations have been instrumental for advancing the understanding of the radiative balance at global scale, however, due to the frequent changes in the observing systems, the length of available satellite records is limited. In this paper we report on an effort to synthesize satellite observations from independent sources to estimates shortwave, longwave and spectral surface radiative fluxes at climatic time scales and use them to learn about their variability and trends. The radiative fluxes were derived in the framework of the MEaSURES and NEWS programs; they are evaluated against ground observations and compared to independent satellite and model estimates. Attention is given to updates on the radiative balance as compared to what is known from shorter time records and from models.
Time Scales of Conformational Gating in a Lipid-Binding Protein.
Kaieda, Shuji; Halle, Bertil
2015-06-25
Lipid-binding proteins sequester amphiphilic molecules in a large internal cavity occupied by ?30 water molecules, some of which are displaced by the ligand. The role of these internal water molecules in lipid binding and release is not understood. We use magnetic relaxation dispersion (MRD) to directly monitor internal-water dynamics in apo and palmitate-bound rat intestinal fatty acid-binding protein (rIFABP). Specifically, we record the water (2)H and (17)O MRD profiles of the apo and holo forms of rIFABP in solution or immobilized by covalent cross-links. A global analysis of this extensive data set identifies three internal-water classes with mean survival times of ?1 ns, ?100 ns, and ?6 ?s. We associate the two longer time scales with conformational fluctuations of the gap between ?-strands D and E (?6 ?s) and of the portal at the helix-capped end of the ?-barrel (?100 ns). These fluctuations limit the exchange rates of a few highly ordered structural water molecules but not the dissociation rate of the fatty acid. The remaining 90% (apo) or 70% (holo) of cavity waters exchange among internal hydration sites on a time scale of ?1 ns but exhibit substantial orientational order, particularly in the holo form. PMID:26012957
Relaxation time in a non-conserving driven-diffusive system with parallel dynamics
S R Masharian; F H Jafarpour; A Aghamohammadi
2012-01-01
We introduce a two-state non-conserving driven-diffusive system in one dimension under a discrete-time updating scheme. We show that the steady state of the system can be obtained using a matrix product approach. On the other hand, the steady state of the system can be expressed in terms of a linear superposition of Bernoulli shock measures with random walk dynamics. The
Anomalous Temperature Dependence of the Spin-Lattice Relaxation Time in Ferrocene
C. H. Holm; James A. Ibers
1957-01-01
E have observed an unexpected tenfold increase in the signal-to-noise ratio (SjN) of the proton magnetic resonance absorption line of dicyclopenta dienyl iron (II) (ferrocene) as the temperature is de creased from 190° to HOoK. We attribute this increase in SjN to a pronounced reduction in the spin-lattice relaxa tion time (T 1) . The sample of ferrocene used in
Improving the Geologic Time Scale (Jean Baptiste Lamarck Medal Lecture)
NASA Astrophysics Data System (ADS)
Gradstein, Felix M.
2010-05-01
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.
Mixing Time Scales in a Supernova-Driven Interstellar Medium
Miguel A. de Avillez; Mordecai-Mark Mac Low
2002-08-23
We study the mixing of chemical species in the interstellar medium (ISM). Recent observations suggest that the distribution of species such as deuterium in the ISM may be far from homogeneous. This raises the question of how long it takes for inhomogeneities to be erased in the ISM, and how this depends on the length scale of the inhomogeneities. We added a tracer field to the three-dimensional, supernova-driven ISM model of Avillez (2000) to study mixing and dispersal in kiloparsec-scale simulations of the ISM with different supernova (SN) rates and different inhomogeneity length scales. We find several surprising results. Classical mixing length theory fails to predict the very weak dependence of mixing time on length scale that we find on scales of 25--500 pc. Derived diffusion coefficients increase exponentially with time, rather than remaining constant. The variance of composition declines exponentially, with a time constant of tens of Myr, so that large differences fade faster than small ones. The time constant depends on the inverse square root of the supernova rate. One major reason for these results is that even with numerical diffusion exceeding physical values, gas does not mix quickly between hot and cold regions.
Memory on multiple time-scales in an Abelian sandpile
NASA Astrophysics Data System (ADS)
Sokolov, Andrey; Melatos, Andrew; Kieu, Tien; Webster, Rachel
2015-06-01
We report results of a numerical analysis of the memory effects in two-dimensional Abelian sandpiles. It is found that a sandpile forgets its instantaneous configuration in two distinct stages: a fast stage and a slow stage, whose durations roughly scale as N and N2 respectively, where N is the linear size of the sandpile. We confirm the presence of the longer time-scale by an independent diagnostic based on analysing emission probabilities of a hidden Markov model applied to a time-averaged sequence of avalanche sizes. The application of hidden Markov modelling to the output of sandpiles is novel. It discriminates effectively between a sandpile time series and a shuffled control time series with the same time-averaged event statistics and hence deserves further development as a pattern-recognition tool for Abelian sandpiles.
NASA Technical Reports Server (NTRS)
Moshchalcov, V. V.; Zhukov, A. A.; Kuznetzov, V. D.; Metlushko, V. V.; Leonyuk, L. I.
1990-01-01
At the initial time intervals, preceding the thermally activated flux creep regime, fast nonlogarithmic relaxation is found. The fully magnetic moment Pm(t) relaxation curve is shown. The magnetic measurements were made using SQUID-magnetometer. Two different relaxation regimes exist. The nonlogarithmic relaxation for the initial time intervals may be related to the viscous Abrikosov vortices flow with j is greater than j(sub c) for high enough temperature T and magnetic field induction B. This assumption correlates with Pm(t) measurements. The characteristic time t(sub O) separating two different relaxation regimes decreases as temperature and magnetic field are lowered. The logarithmic magnetization relaxation curves Pm(t) for fixed temperature and different external magnetic field inductions B are given. The relaxation rate dependence on magnetic field, R(B) = dPm(B, T sub O)/d(1nt) has a sharp maximum which is similar to that found for R(T) temperature dependences. The maximum shifts to lower fields as temperature goes up. The observed sharp maximum is related to a topological transition in shielding critical current distribution and, consequently, in Abrikosov vortices density. The nonlogarithmic magnetization relaxation for the initial time intervals is found. This fast relaxation has almost an exponentional character. The sharp relaxation rate R(B) maximum is observed. This maximum corresponds to a topological transition in Abrikosov vortices distribution.
J. D. Russell; R. B. Bernstein; C. F. Curtiss
1972-01-01
The rotational relaxation time of nitrogen in an excess of argon was computed by a fully classical, numerically exact procedure, starting from an estimated anisotropic potential for the Ar&sngbnd;N2 system. The method involves integration of the second moment of the rotational inelasticity probability density function P(? Erot) over the impact parameter of the collision and a Boltzmann distribution of translational
NASA Astrophysics Data System (ADS)
Ohnishi, Hiromasa; Tomita, Norikazu; Nasu, Keiichiro
2015-04-01
Concerning with the recent experiment of time-resolved two-photon photo-emission spectral measurements on semiconductors (GaAs, InP), we theoretically study real time relaxation dynamics of macroscopically photo-excited electrons, toward the Fermi degeneracy formation in an originally vacant conduction band of these semiconductors. Very soon after the photo-excitation, the whole electrons are shown to exhibit a quite rapid relaxation, like an avalanching phenomenon, mainly due to successive multi-(optical and acoustic) phonon emission from them. Repeating this multi-phonon process, the whole energy distribution of the electrons is shown to become a multi-peaked structure largely elongated over the lower part of the wide conduction band. However, after around 1 ps from the excitation, this relaxation critically slows down, since the emission of a long-wave acoustic phonon from electrons around the Fermi level becomes prohibitively difficult. By using the electron temperature approximation, we show that this slow relaxation is inversely proportional to time. Thus, the formation of the complete Fermi degeneracy takes an infinite time. These theoretical results are quite consistent to the aforementioned recent experiment.
- ever, cubic anisotropy (which is magnetocrystalline) is weak. In general the anisotropy in a realSuperparamagnetic Relaxation Times for Mixed Cubic and Uniaxial Anisotropy and High Energy Barriers anisotropy. In this article the uniaxial axis is in a 001 crystallographic direction, while in part II
Relativistic fireballs - Energy conversion and time-scales
NASA Technical Reports Server (NTRS)
Rees, M. J.; Meszaros, P.
1992-01-01
The expansion energy of a relativistic fireball can be reconverted into radiation when it interacts with an external medium. For expansion with Lorentz factors greater than or approximately equal to 1000 into a typical galactic environment, the corresponding time-scale in the frame of the observer is of the order of seconds. This mechanism would operate in any cosmological scenario of gamma-ray bursts involving initial energies of order a percent of a stellar rest mass, and implies photon energies and time-scales compatible with those observed in gamma-ray bursts.
Dynamics symmetries of Hamiltonian system on time scales
Peng, Keke, E-mail: pengkeke88@126.com; Luo, Yiping, E-mail: zjstulyp@126.com [Department of Physics, Zhejiang Sci-Tech University, Hangzhou 310018 (China)] [Department of Physics, Zhejiang Sci-Tech University, Hangzhou 310018 (China)
2014-04-15
In this paper, the dynamics symmetries of Hamiltonian system on time scales are studied. We study the symmetries and quantities based on the calculation of variation and Lie transformation group. Particular focus lies in: the Noether symmetry leads to the Noether conserved quantity and the Lie symmetry leads to the Noether conserved quantity if the infinitesimal transformations satisfy the structure equation. As the new application of result, at end of the article, we give a simple example of Noether symmetry and Lie symmetry on time scales.
Time-dependent entropy evolution in microscopic and macroscopic electromagnetic relaxation
Baker-Jarvis, James [National Institute of Standards and Technology, Electromagnetics Division, MS 818.01, Boulder, Colorado 80305 (United States)
2005-12-15
This paper is a study of entropy and its evolution in the time and frequency domains upon application of electromagnetic fields to materials. An understanding of entropy and its evolution in electromagnetic interactions bridges the boundaries between electromagnetism and thermodynamics. The approach used here is a Liouville-based statistical-mechanical theory. I show that the microscopic entropy is reversible and the macroscopic entropy satisfies an H theorem. The spectral entropy development can be very useful for studying the frequency response of materials. Using a projection-operator based nonequilibrium entropy, different equations are derived for the entropy and entropy production and are applied to the polarization, magnetization, and macroscopic fields. I begin by proving an exact H theorem for the entropy, progress to application of time-dependent entropy in electromagnetics, and then apply the theory to relevant applications in electromagnetics. The paper concludes with a discussion of the relationship of the frequency-domain form of the entropy to the permittivity, permeability, and impedance.
Han, Lu; Liang, WanZhen; Zhao, Yi, E-mail: yizhao@xmu.edu.cn [State Key Laboratory of Physical Chemistry of Solid Surfaces, Collaborative Innovation Center of Chemistry for Energy Materials, Fujian Provincial Key Lab of Theoretical and Computational Chemistry, and Department of Chemistry, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005 (China); Zhong, Xinxin [State Key Laboratory of Physical Chemistry of Solid Surfaces, Collaborative Innovation Center of Chemistry for Energy Materials, Fujian Provincial Key Lab of Theoretical and Computational Chemistry, and Department of Chemistry, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005 (China); Institute of Theoretical and Computational Chemistry, College of Chemistry and Molecular Engineering, Beijing National Laboratory for Molecular Sciences, Peking University, Beijing 100871 (China)
2014-06-07
The time-dependent wavepacket diffusive method [X. Zhong and Y. Zhao, J. Chem. Phys. 138, 014111 (2013)] is extended to investigate the energy relaxation and separation of a hot electron-hole pair in organic aggregates with incorporation of Coulomb interaction and electron-phonon coupling. The pair initial condition generated by laser pulse is represented by a Gaussian wavepacket with a central momentum. The results reveal that the hot electron energy relaxation is very well described by two rate processes with the fast rate much larger than the slow one, consistent with experimental observations, and an efficient electron-hole separation is accomplished accompanying the fast energy relaxation. Furthermore, although the extra energy indeed helps the separation by overcoming the Coulomb interaction, the width of initial wavepacket is much sensitive to the separation efficiency and the narrower wavepacket generates the more separated charges. This behavior may be useful to understand the experimental controversy of the hot carrier effect on charge separation.
TIME DELAY AND MOTION ESTIMATORS BASED ON DIGITAL FAST TIME-SCALING OF RANDOM SIGNALS
Gaetano Giunta
The estimation of time-delay and time-scaling is required in many signal processing applications. A parabolic approximation was recently suggested for fine estimation of time delay from sampled signals. The method directly extends to scaling estimation by a parallel multi-rate sampling of the analog received signal. Such rescaling can be implemented by digital techniques and two efficient algorithms are here devised
Time Scale Calculus - a new perspectives for synthetic seismogram calculations
NASA Astrophysics Data System (ADS)
Waskiewicz, Kamil; Debski, Wojciech
2013-04-01
Synthetic, numerically generated seismograms are one of the key factors of any interpretation of recorded seismic data. At the early stage of development, calculation of full seismic waveforms was impossible due to a limited computational resource so we were forced to used only some selected characteristics of seismic waves relatively easy for numerical calculations like first arrival times, maximum amplitude, approximate source spectra, to name a few. Continues development of computational resources as well as progress in numerical techniques has opened possibilities of generation the full, 3-component seismograms incorporating many physically important elements like wave attenuation, anisotropy or randomness of the media. Although achieved results are impressive we still need new numerical methods to tackle existing problems with the synthetic seismogram generation. In this contribution we present a novel approach to discretization of the wave equation which brings together continues and discrete numerical analysis of the seismic waves. The foundations of this new technique, called Time Scale Calculus, have been formulated by Hilger in late eighties and is very dynamically developing. The Time scale calculus, due to its universality seems to have a great potential when practical applications are considered. Thus we have decided to bring the Time Scale calculus concept closer to geophysical, or more precisely to seismological applications. This presentation is intend as a basic introduction to the time scales calculus considered from seismological point of view. We shortly present and discuss the possibility of using the Time Scales (TS) technique for solving the simplest acoustic 2D wave equation keeping in mind its particular applications for mining induced seismicity.
Microscopic relaxation in supercritical and liquid neon
NASA Astrophysics Data System (ADS)
Cunsolo, A.; Pratesi, G.; Verbeni, R.; Colognesi, D.; Masciovecchio, C.; Monaco, G.; Ruocco, G.; Sette, F.
2001-02-01
The high frequency behavior of the dynamic structure factor, S(Q,?), of liquid and supercritical neon is investigated by inelastic x-ray scattering at different temperatures and pressure. The spectral evolution is described in terms of a single-relaxation-time viscoelastic model. The occurrence of a positive dispersion in the sound velocity is clearly visible in both investigated thermodynamic phases. The anomalies in the dispersive behavior deeply reduce at the higher temperatures, probably, as a consequence of important changes in the first shell interactions. More generally, the atomic dynamics is dominated by a relaxation process whose time scale is in the range of fast microscopic degrees of freedom (?10-13 s), and whose strength and typical time scale stay constant over all the explored liquid and supercritical regions.
Satellite attitude prediction by multiple time scales method
NASA Technical Reports Server (NTRS)
Tao, Y. C.; Ramnath, R.
1975-01-01
An investigation is made of the problem of predicting the attitude of satellites under the influence of external disturbing torques. The attitude dynamics are first expressed in a perturbation formulation which is then solved by the multiple scales approach. The independent variable, time, is extended into new scales, fast, slow, etc., and the integration is carried out separately in the new variables. The theory is applied to two different satellite configurations, rigid body and dual spin, each of which may have an asymmetric mass distribution. The disturbing torques considered are gravity gradient and geomagnetic. Finally, as multiple time scales approach separates slow and fast behaviors of satellite attitude motion, this property is used for the design of an attitude control device. A nutation damping control loop, using the geomagnetic torque for an earth pointing dual spin satellite, is designed in terms of the slow equation.
Robust control of multivariable two-time-scale nonlinear systems
Panagiotis D. Christofides; Prodromos Daoutidis
1997-01-01
This paper focuses on the synthesis of well-conditioned multivariable robust controllers for a broad class of multi-input multi-output two-time-scale nonlinear systems with time-varying uncertain variables, modeled within the framework of singular perturbations. The proposed controller stabilizes the fast dynamics, guarantees boundedness of trajectories, and ensures that the ultimate discrepancy between the outputs and the external reference inputs in the closed-loop
Time and frequency scale modification of speech signals
Brett Ninness; Soren John Henriksen
2000-01-01
This paper presents new and improved methods for independently modifying the time and pitch scale of acoustic signals, with an emphasis on speech signals. The algorithms developed here use parametric (sinusoidal) modelling techniques introduced by other authors, but new ideas are presented here that achieve improved output quality with decreased computational load. In particular, speech quality is improved by using
Speech Compensation for Time-Scale-Modified Auditory Feedback
ERIC Educational Resources Information Center
Ogane, Rintaro; Honda, Masaaki
2014-01-01
Purpose: The purpose of this study was to examine speech compensation in response to time-scale-modified auditory feedback during the transition of the semivowel for a target utterance of /ija/. Method: Each utterance session consisted of 10 control trials in the normal feedback condition followed by 20 perturbed trials in the modified auditory…
Gott Time Machines, BTZ Black Hole Formation, and Choptuik Scaling
NASA Astrophysics Data System (ADS)
Birmingham, Danny; Sen, Siddhartha
2000-02-01
We study the formation of Bañados-Teitelboim-Zanelli black holes by the collision of point particles. It is shown that the Gott time machine, originally constructed for the case of vanishing cosmological constant, provides a precise mechanism for black hole formation. As a result, one obtains an exact analytic understanding of the Choptuik scaling.
Improvement of Rate Shift in Average Atomic Time Scale Algorithm
Yuko Hanado; Mizuhiko Hosokawa
2008-01-01
In an average atomic time scale algorithm, we developed a new method of suppressing the influence of a large sudden rate shift in some clocks. The method entails two points. One is to add a clock rate check process. The weight of a bad clock is forced to be zero if its latest rate largely changes from the past rate.
Nonlinear Dynamics in Psychophysiology - Importance of Time Scales
W. Klonowski
2004-08-17
Presented theory of feelings and emotions is based on Nonlinear Dynamics and Theory of Complex Systems. The most important assumption is that the brain may be considered to be composed of subsystems characterized by different characteristic time scales. The theory explains a possible role of feelings and emotions in cognition. We propose to call presented theory Chaosensology.
AGN variability time scales and the discrete-event model
P. Favre; T. J. -L. Courvoisier; S. Paltani
2005-08-29
We analyse the ultraviolet variability time scales in a sample of 15 Type 1 Active Galactic Nuclei (AGN) observed by IUE. Using a structure function analysis, we demonstrate the existence in most objects of a maximum variability time scale of the order of 0.02-1.00 year. We do not find any significant dependence of these maximum variability time scales on the wavelength, but we observe a weak correlation with the average luminosity of the objects. We also observe in several objects the existence of long-term variability, which seems decoupled from the short-term one. We interpret the existence of a maximum variability time scale as a possible evidence that the light curves of Type 1 AGN are the result of the superimposition of independent events. In the framework of the so-called discrete-event model, we study the event energy and event rate as a function of the object properties. We confront our results to predictions from existing models based on discrete events. We show that models based on a fixed event energy, like supernova explosions, can be ruled out. In their present form, models based on magnetic blobs are also unable to account for the observed relations. Stellar collision models, while not completely satisfactory, cannot be excluded.
Multiple-time-scales in singularly perturbed systems
David H. Owens
1985-01-01
Conditions for the existence of well-defined time-scales of a general, autonomous singularly perturbed linear system in Rn are described in terms of asymptotic eigenstructure of the inverse system matrix and related to Wonham's {A,B} - invariant subspace algorithm. One consequence of the results is a strong geometric link between singular perturbation and root-locus theory.
Short Time-Scale Emission Line Variations in Mira B
NASA Astrophysics Data System (ADS)
Chamber, H. L., II; Moffett, T. J.; Barnes, T. G., III
1997-05-01
Spectra of Mira were taken at McDonald Observatory near Mira A minimum in December 1975 using an image tube spectrograph. Series of spectra on a two to three minute time-scale show significant line strength variations in the emission lines associated with Mira B.
Impulsive nonlocal differential equations through differential equations on time scales
Mieczys?aw Cicho?; Bianca Satco; Aneta Sikorska-Nowak
2011-01-01
We propose a non-standard approach to impulsive differential equations in Banach spaces by embedding this type of problems into differential (dynamic) problems on time scales. We give an existence result for dynamic equations and, as a consequence, we obtain an existence result for impulsive differential equations.
Multiple time scale numerical methods for the inverted pendulum problem
Tsai, Yen-Hsi Richard
Multiple time scale numerical methods for the inverted pendulum problem Richard Sharp1, Yen (HMM) [1]. We apply the methods to compute the averaged path of the inverted pendulum under a highly and thus compute the average path of the inverted pendulum. 1 Introduction The focus of this paper
MULTIPLE TIME SCALE NUMERICAL METHODS FOR THE INVERTED PENDULUM PROBLEM
Soatto, Stefano
MULTIPLE TIME SCALE NUMERICAL METHODS FOR THE INVERTED PENDULUM PROBLEM RICHARD SHARP, YEN-HSI TSAI multiscale methods (HMM) [1]. We apply the methods to compute the averaged path of the inverted pendulum approximate the averaged equation and thus compute the average path of the inverted pendulum. 1. INTRODUCTION
1. Forces and thermostats 1 Irreversibility time scale
a system is modeled as an aggregate of molecules interacting via conservative forces. A corresponding1. Forces and thermostats 1 Irreversibility time scale G.Gallavotti I.N.F.N. Roma 1, Fisica Roma1 language, for a system subject to internal conservative forces in teracting with ``external'' thermostats
Gott Time Machines, BTZ Black Hole Formation, and Choptuik Scaling
Danny Birmingham; Siddhartha Sen
1999-08-23
We study the formation of BTZ black holes by the collision of point particles. It is shown that the Gott time machine, originally constructed for the case of vanishing cosmological constant, provides a precise mechanism for black hole formation. As a result, one obtains an exact analytic understanding of the Choptuik scaling.
Causality across rainfall time scales revealed by continuous wavelet transforms
Katul, Gabriel
Click Here for Full Article Causality across rainfall time scales revealed by continuous wavelet; revised 3 December 2009; accepted 27 January 2010; published 31 July 2010. [1] Rainfall variability occurs by atmospheric circulation. A central topic in rainfall research is to determine whether rainfall variability
Simulations of Bingham plastic flows with the multiple-relaxation-time lattice Boltzmann model
NASA Astrophysics Data System (ADS)
Chen, SongGui; Sun, QiCheng; Jin, Feng; Liu, JianGuo
2014-03-01
Fresh cement mortar is a type of workable paste, which can be well approximated as a Bingham plastic and whose flow behavior is of major concern in engineering. In this paper, Papanastasiou's model for Bingham fluids is solved by using the multiplerelaxation-time lattice Boltzmann model (MRT-LB). Analysis of the stress growth exponent m in Bingham fluid flow simulations shows that Papanastasiou's model provides a good approximation of realistic Bingham plastics for values of m > 108. For lower values of m, Papanastasiou's model is valid for fluids between Bingham and Newtonian fluids. The MRT-LB model is validated by two benchmark problems: 2D steady Poiseuille flows and lid-driven cavity flows. Comparing the numerical results of the velocity distributions with corresponding analytical solutions shows that the MRT-LB model is appropriate for studying Bingham fluids while also providing better numerical stability. We further apply the MRT-LB model to simulate flow through a sudden expansion channel and the flow surrounding a round particle. Besides the rich flow structures obtained in this work, the dynamics fluid force on the round particle is calculated. Results show that both the Reynolds number Re and the Bingham number Bn affect the drag coefficients C D , and a drag coefficient with Re and Bn being taken into account is proposed. The relationship of Bn and the ratio of unyielded zone thickness to particle diameter is also analyzed. Finally, the Bingham fluid flowing around a set of randomly dispersed particles is simulated to obtain the apparent viscosity and velocity fields. These results help simulation of fresh concrete flowing in porous media.
Davis, K L; Mehlhorn, U; Schertel, E R; Geissler, H J; Trevas, D; Laine, G A; Allen, S J
1999-02-01
Tau (tau), the time constant for isovolumic relaxation, is often used as a measure of cardiac diastolic function. However, several methods of calculating tau have been published which may produce different results and, thereby, different conclusions. The purpose of this study was to determine if the method of tau calculation effects the results when left ventricular pressure (LVP) is measured at different positions along the base-to-apex axis. In 16 dogs, we measured LVP at 6 positions along the base-to-apex axis. We calculated tau using three different methods: 1) a monoexponential model (P(t) = [P0-Pasym]eAt + Pasym, where t = time, P0 = LVP at t = 0, Pasym is asymptotic pressure as t-->infinity, A is -1/tau) with a zero asymptote 2) a monoexponential model with a variable asymptote in which the monoexponential decay equation is differentiated with respect to time and substituted into the original equation so that dP/dt vs. LVP is A (-1/tau), and 3) a monoexponential decay model with variable asymptote in which Pasym and A are varied until the best fit line is reached by minimizing the residual sum of squares. When tau is calculated using method 1, tau measured at the LV base is 98.01% +/- 8.85% of tau at the apex. If calculated using method 2, tau measured at the LV base was 75.46 +/- 39.4% of tau measured at the apex. When method 3 is used for tau calculations, base tau increases to 117.76 +/- 4.91% of the apical tau. We conclude: 1) the method used to calculate tau will effect the results and, thus, conclusions drawn from tau data. 2) When using Method 3, which appears to be the best method for tau calculation, tau increases at the LV base compared to the apex. PMID:10097829
NASA Astrophysics Data System (ADS)
Plumari, S.; Puglisi, A.; Scardina, F.; Greco, V.
2012-11-01
The shear viscosity ? has been calculated by using the Green-Kubo relation in the framework of a partonic transport approach solved at cascade level. We compare the numerical results for ? obtained from the Green-Kubo correlator with the analytical formulas in both the relaxation time approximation (RTA) and the Chapman-Enskog (CE) approximation. We investigate and emphasize the differences between the isotropic and anisotropic cross sections and between the massless and massive particles. We show that in the range of temperature explored in a heavy ion collision and for perturbative-QCD-like cross section, the RTA significantly underestimates the viscosity by about a factor of 2-3, while a good agreement is found between the CE approximation and Gree-Kubo relation already at first-order of approximation. The agreement with the CE approximation supplies an analytical formula that allows us to develop a kinetic transport theory at fixed shear-viscosity to entropy-density ratio, ?/s. This opens the possibility of exploring dissipative nonequilibrium evolution of the distribution functions versus T-dependent ?/s and particle momenta in the dynamics of the quark-gluon plasma created in ultrarelativistic heavy-ion collisions.
Zhang, Wenhuan; Wang, Yihang
2015-01-01
In this paper, 14-velocity and 18-velocity multiple-relaxation-time (MRT) lattice Boltzmann (LB) models are proposed for three-dimensional incompressible flows. These two models are constructed based on the incompressible LBGK model proposed by He et al. (Chin. Phys., 2004, 13: 40-46) and the MRT LB model proposed by d'Humi\\`{e}res et al. (Philos. Trans. R. Soc., A, 2002, 360: 437-451), which have advantages in the computational efficiency and stability, respectively. Through the Chapman-Enskog analysis, the models can recover to three-dimensional incompressible Navier-Stokes equations in the low Mach number limit. To verify the present models, the steady Poiseuille flow, unsteady pulsatile flow and lid-driven cavity flow in three dimensions are simulated. The simulation results agree well with the analytical solutions or the existing numerical results. Moreover, it is found that the present models show higher accuracy than d'Humi\\`{e}res et al. model and better stability than He et al. model.
NASA Astrophysics Data System (ADS)
Kruk, D.; Korpa?a, A.; Taheri, S. Mehdizadeh; Koz?owski, A.; Förster, S.; Rössler, E. A.
2014-05-01
Magnetic nanoparticles that induce nuclear relaxation are the most promising materials to enhance the sensitivity in Magnetic Resonance Imaging. In order to provide a comprehensive understanding of the magnetic field dependence of the relaxation enhancement in solutions, Nuclear Magnetic Resonance 1H spin-lattice relaxation for decalin and toluene solutions of various Fe2O3 nanoparticles was investigated. The relaxation experiments were performed in a frequency range of 10 kHz-20 MHz by applying Field Cycling method, and in the temperature range of 257-298 K, using nanoparticles differing in size and shape: spherical - 5 nm diameter, cubic - 6.5 nm diameter, and cubic - 9 nm diameter. The relaxation dispersion data were interpreted in terms of a theory of nuclear relaxation induced by magnetic crystals in solution. The approach was tested with respect to its applicability depending on the magnetic characteristics of the nanocrystals and the time-scale of translational diffusion of the solvent. The role of Curie relaxation and the contributions to the overall 1H spin-lattice relaxation associated with the electronic spin-lattice and spin-spin relaxation was thoroughly discussed. It was demonstrated that the approach leads to consistent results providing information on the magnetic (electronic) properties of the nanocrystals, i.e., effective electron spin and relaxation times. In addition, features of the 1H spin-lattice relaxation resulting from the electronic properties of the crystals and the solvent diffusion were explained.
Spectral decomposition of time-scales in hyporheic exchange
NASA Astrophysics Data System (ADS)
Wörman, Anders; Riml, Joakim
2015-04-01
Hyporheic exchange of heat and solute mass in streams is manifested both in form of different exchange mechanisms and their associated distributions of residence times as well as the range of time-scales characterizing the forcing boundary conditions. A recently developed analytical technique separates the spectrum of time-scales and relates the forcing boundary fluctuations of heat and solute mass through a physical model of the hydrological transport to the response of heat and solute mass. This spectral decomposition can be done both for local (point-scale) observations in the hyporhiec zone itself as well as for transport processes on the watershed scale that can be considered 'well-behaved' in terms of knowledge of the forcing (input) quantities. This paper presents closed-form solutions in spectral form for the point-, reach- and watershed-scale and discusses their applicability to selected data of heat and solute concentration. We quantify the reliability and highlight the benefits of the spectral approach to different scenarios and, peculiarly, the importance for linking the periods in the spectral decomposition of the solute response to the distribution of transport times that arise due to the multitude of exchange mechanisms existing in a watershed. In a point-scale example the power spectra of in-stream temperature is related to the power spectrum of the temperature at a specific sediment depth by means of exact solutions of a physically based formulation of the vertical heat transport. It is shown that any frequency (?) of in-stream temperature fluctuation scales with the effective thermal diffusivity (?e) and the vertical separation distance between the pairs of temperature (É?) data as ? ? ?e/(2É?2), which implies a decreasing weight to higher frequencies (shorter periods) with depth. Similarly on the watershed-scale one can link the watershed dispersion to the damping of the concentration fluctuations in selected frequency intervals reflecting various environments responsible for the damping. The frequency-dependent parameters indicate that different environments dominate the response at different temporal scales.
J. Liberis; A. Matulionis
Gated modulation-type radiometric technique for microwave noise measurement is upgraded for convenient investigation of hot-electron energy relaxation and hot-phonon dynamics in a channel with a high-density electron gas. The technique is applied to a GaN-based structure held at 80 and 293 K channel temperature. The results are discussed in terms of hot-phonon effect on hot-electron energy relaxation. The hot-phonon lifetime,
New time scale based k-epsilon model for near-wall turbulence
Z. Yang; T. H. Shih
1993-01-01
A k-epsilon model is proposed for wall bonded turbulent flows. In this model, the eddy viscosity is characterized by a turbulent velocity scale and a turbulent time scale. The time scale is bounded from below by the Kolmogorov time scale. The dissipation equation is reformulated using this time scale and no singularity exists at the wall. The damping function used
BeiDou Navigation Satellite System and its time scales
NASA Astrophysics Data System (ADS)
Han, Chunhao; Yang, Yuanxi; Cai, Zhiwu
2011-08-01
The development and current status of BeiDou Navigation Satellite System are briefly introduced. The definition and realization of the system time scales are described in detail. The BeiDou system time (BDT) is an internal and continuous time scale without leap seconds. It is maintained by the time and frequency system of the master station. The frequency accuracy of BDT is superior to 2 × 10-14 and its stability is better than 6 × 10-15/30 days. The satellite synchronization is realized by a two-way time transfer between the uplink stations and the satellite. The measurement uncertainty of satellite clock offsets is less than 2 ns. The BeiDou System has three modes of time services: radio determination satellite service (RDSS) one-way, RDSS two-way and radio navigation satellite service (RNSS) one-way. The uncertainty of the one-way time service is designed to be less than 50 ns, and that of the two-way time service is less than 10 ns. Finally, some coordinate tactics of UTC from the viewpoint of global navigation satellite systems (GNSS) are discussed. It would be helpful to stop the leap second, from our viewpoint, but to keep the UTC name, the continuity and the coordinate function unchanged.
NASA Astrophysics Data System (ADS)
Mainali, Laxman; Feix, Jimmy B.; Hyde, James S.; Subczynski, Witold K.
2011-10-01
There are no easily obtainable EPR spectral parameters for lipid spin labels that describe profiles of membrane fluidity. The order parameter, which is most often used as a measure of membrane fluidity, describes the amplitude of wobbling motion of alkyl chains relative to the membrane normal and does not contain explicitly time or velocity. Thus, this parameter can be considered as nondynamic. The spin-lattice relaxation rate ( T1-1) obtained from saturation-recovery EPR measurements of lipid spin labels in deoxygenated samples depends primarily on the rotational correlation time of the nitroxide moiety within the lipid bilayer. Thus, T1-1 can be used as a convenient quantitative measure of membrane fluidity that reflects local membrane dynamics. T1-1 profiles obtained for 1-palmitoyl-2-( n-doxylstearoyl)phosphatidylcholine ( n-PC) spin labels in dimyristoylphosphatidylcholine (DMPC) membranes with and without 50 mol% cholesterol are presented in parallel with profiles of the rotational diffusion coefficient, R?, obtained from simulation of EPR spectra using Freed's model. These profiles are compared with profiles of the order parameter obtained directly from EPR spectra and with profiles of the order parameter obtained from simulation of EPR spectra. It is shown that T1-1 and R? profiles reveal changes in membrane fluidity that depend on the motional properties of the lipid alkyl chain. We find that cholesterol has a rigidifying effect only to the depth occupied by the rigid steroid ring structure and a fluidizing effect at deeper locations. These effects cannot be differentiated by profiles of the order parameter. All profiles in this study were obtained at X-band (9.5 GHz).
SOUZA, RICHARD B.; BAUM, THOMAS; WU, SAMUEL; FEELEY, BRIAN T.; KADEL, NANCY; LI, XIAOJUAN; LINK, THOMAS M.; MAJUMDAR, SHARMILA
2013-01-01
STUDY DESIGN Case series. BACKGROUND It has been shown in rodent and canine models that cartilage composition is significantly altered in response to long-term unloading. To date, however, no in vivo human studies have investigated this topic. The objective of this case series was to determine the influence of unloading and reloading on T1rho and T2 relaxation times of articular cartilage in healthy young joints. CASE DESCRIPTION Ten patients who required 6 to 8 weeks of non–weight bearing (NWB) for injuries affecting the distal lower extremity participated in the study. Quantitative T1rho and T2 imaging of the ipsilateral knee joint was performed at 3 time points: (1) prior to surgery (baseline), (2) immediately after a period of NWB (post-NWB), and (3) after 4 weeks of full weight bearing (post-FWB). Cartilage regions of interest were segmented and overlaid on T1rho and T2 relaxation time maps for quantification. Descriptive statistics are provided for all changes. OUTCOMES Increases of 5% to 10% in T1rho times of all femoral and tibial compartments were noted post-NWB. All values returned to near-baseline levels post-FWB. Increases in medial tibia T2 times were noted post-NWB and remained elevated post-FWB. The load-bearing regions showed the most significant changes in response to unloading, with increases of up to 12%. DISCUSSION The observation of a transient shift in relaxation times confirms that cartilage composition is subject to alterations based on loading conditions. These changes appear to be mostly related to proteoglycan content and more localized to the load-bearing regions. However, following 4 weeks of full weight bearing, relaxation times of nearly all regions had returned to baseline levels, demonstrating reversibility in compositional fluctuations. LEVEL OF EVIDENCE Therapy, level 4. PMID:22402583
NASA Astrophysics Data System (ADS)
Hazarika, Neep; Lowe, David
1997-04-01
In this work we describe a method of estimating and characterizing appropriate data and model complexity in the context of long term iterated time series forecasting using embeddings and multiple time-scale decomposition techniques. An embedding of a signal is obtained which decouples multiple time scale effects such as seasonality and trend. The complexity and stability of networks are estimated and the performance of long term iteration is examined. The performance of the technique is tested using the real world time series problems of electricity load forecasting, and financial futures contracts.
Differential force microscope for long time-scale biophysical measurements
Choy, Jason L.; Parekh, Sapun H.; Chaudhuri, Ovijit; Liu, Allen P.; Bustamante, Carlos; Footer, Matthew J.; Theriot, Julie A.; Fletcher, Daniel A.
2011-01-01
Force microscopy techniques including optical trapping, magnetic tweezers, and atomic force microscopy (AFM) have facilitated quantification of forces and distances on the molecular scale. However, sensitivity and stability limitations have prevented the application of these techniques to biophysical systems that generate large forces over long times, such as actin filament networks. Growth of actin networks drives cellular shape change and generates nano-Newtons of force over time scales of minutes to hours, and consequently network growth properties have been difficult to study. Here, we present an AFM-based differential force microscope with integrated epifluorescence imaging in which two adjacent cantilevers on the same rigid support are used to provide increased measurement stability. We demonstrate 14 nm displacement control over measurement times of 3 hours and apply the instrument to quantify actin network growth in vitro under controlled loads. By measuring both network length and total network fluorescence simultaneously, we show that the average cross-sectional density of the growing network remains constant under static loads. The differential force microscope presented here provides a sensitive method for quantifying force and displacement with long time-scale stability that is useful for measurements of slow biophysical processes in whole cells or in reconstituted molecular systems in vitro. PMID:17477674
Space-Time Scaling In The Atmospheric Boundary-Layer
NASA Astrophysics Data System (ADS)
Fitton, George; Tchiguirinskaia, Ioulia; Schertzer, Daniel
2015-04-01
We study the (multi-) scaling properties of the velocity time-increments as function a height (between 50 and 150m) using wind measurements from the well known Growian experiment. The Growian wind turbine experiment was a German Federal Ministry of Research and Technology's project that took place over the years 1983 to 1987. The experiment provides vertical wind profiles of wind speed and direction at 2.5Hz at 50, 75, 100, 125, and 150m. Velocity vectors are computed from the wind speed and direction allowing us to analyse the vertical velocity profiles in the so-called 'mixing-layer'. Plotting the scaling exponents of the structure functions of the time-increments of the velocity as a function of height shows that the space and time scalings of the velocity increments can be easily related to each other through their corresponding space-time fractal and multi-fractal properties. These properties are then confirmed for other datasets. Since the fractal and multi-fractal properties of a field are directly related to the extremes of field we are able to propose a high-order statistical model for wind extremes in the atmospheric boundary-layer (ABL). The same model can be used to generate synthetic ABL wind fields that can be useful for numerical model inflow conditions.
Accuracy Assessment in rainfall upscaling in multiple time scales
NASA Astrophysics Data System (ADS)
Yu, H.; Wang, C.; Lin, Y.
2008-12-01
Long-term hydrologic parameters, e.g. annual precipitations, are usually used to represent the general hydrologic characteristics in a region. Recently, the analysis of the impact of climate change to hydrological patterns primarily relies on the measurement and/or the estimations in long time scales, e.g. year. Under the general condition of the prevalence of short-term measurements, therefore, it is important to understand the accuracy of upscaling for the long-term estimations of hydrologic parameters. This study applies spatiotemporal geostatistical method to analyze and discuss the accuracy of precipitation upscaling in Taiwan under the different time scales, and also quantifies the uncertainty in the upscaled long-term precipitations. In this study, two space-time upscaling approaches developed by Bayesian Maximum Entropy method (BME) are presented 1) UM1: data aggregation followed by BME estimation and 2) UM2: BME estimation followed by aggregation. The investigation and comparison are also implemented to assess the performance of the rainfall estimations in multiple time scales in Taiwan by the two upscaling. Keywords: upscaling, geostatistics, BME, uncertainty analysis
Forecast Solar Irradiance Variability on Multiple Time Scales
NASA Astrophysics Data System (ADS)
Tobiska, W.; Schatten, K.; Pryor, W.; Bouwer, D.; Detman, T.; Woods, T.; Pankratz, C.; Eparvier, F. G.; Viereck, R.; Puga, L.
2001-12-01
We report on research that is improving current solar spectral irradiance forecasting capabilities. In particular, the portion of the solar spectrum chosen is that applicable to operational atmospheric density specifications related to low-Earth orbiting satellites. There are six time scales of solar variability for which we are developing forecast algorithms. These include 1-72 hour time scales associated with large flares, 3-14 day Earth-facing solar disk irradiances, 14-28 day solar far side events, 1-6 month active region evolution, 1/2-11 year solar cycle variability, and 1-5 solar cycle climatological specification. Many current algorithms use the first-order assumption of solar irradiance persistence over specific time scales. The basis for forecasting on each of these time derives from a different source. For example, the nowcast, current 24-hour period uses the method of Viereck et al. (2001) where EUV (proxy) = 0.6 MgII (daily) + 0.4 MgII (29-day avg). The 72-hour forecast is generated with an autoregressive technique to determine the trend of the next 3 days. The 14-day forecast simply uses the previous data from 14-days ago to the present epoch. The 28-day forecast uses the previous 28-days of data convolved with a triangular function to reduce noise. The 6-month forecast uses the previous 6-months of data convolved with a 30-day wide triangular function. The 11-year forecast has used the previous 11-years of data similarly convolved. The 55-year forecast uses the mean value of the previous 5 solar cycles. Improvements to these algorithms are demonstrated that will reduce the uncertainty and quantify the variability in each forecast time scale, as these algorithms are used in forecasting solar irradiances for space system operations. Viereck , R., et al., Geophys. Res. Lett., 28, 1343-1346, 2001.
Thermal lens measurements in liquids on a submicrosecond time scale
Isak, S. J.; Komorowski, S. J.; Merrow, C. N.; Poston, P. E.; Eyring, E. M.
1989-03-01
The use of the thermal lens method is shown to be quite suitable for kinetic studies of quenching on a submicrosecond time scale. The lower limit of time resolution that can be achieved is determined by the acoustic transit time, /tau//sub /ital a//, in the medium. A thermal lens signal with a 100-ns time constant due to the quenched triplet state of benzophenone is readily measured. The thermal lens method is superior to the photoacoustic (PA) method in the breadth of the accessible time range, and in the significantly fewer measurements required to obtain accurate data, including no requirement for a reference sample; it is also less sensitive to geometrical and laser power requirements than is the PA method.
Time-average based on scaling law in anomalous diffusions
NASA Astrophysics Data System (ADS)
Kim, Hyun-Joo
2015-05-01
To solve the obscureness in measurement brought about from the weak ergodicity breaking appeared in anomalous diffusions, we have suggested the time-averaged mean squared displacement (MSD) /line{? 2 (? )}? with an integral interval depending linearly on the lag time ?. For the continuous time random walk describing a subdiffusive behavior, we have found that /line{? 2 (? )}? ˜ ? ? like that of the ensemble-averaged MSD, which makes it be possible to measure the proper exponent values through time-average in experiments like a single molecule tracking. Also, we have found that it has originated from the scaling nature of the MSD at an aging time in anomalous diffusion and confirmed them through numerical results of the other microscopic non-Markovian model showing subdiffusions and superdiffusions with the origin of memory enhancement.
Lo, Y. C. [National Sun Yat-Sen University, Taiwan; Chou, H. S. [National Sun Yat-Sen University, Taiwan; Cheng, Y. T. [National Sun Yat-Sen University, Taiwan; Huang, J. C. [National Sun Yat-Sen University, Taiwan; Morris, James R [ORNL; Liaw, Peter K [University of Tennessee, Knoxville (UTK)
2010-01-01
Bulk metallic glasses are generally regarded as highly brittle materials at room temperature, with deformation localized within a few principal shear bands. In this simulation work, it is demonstrated that when the Zr-Cu metallic glass is in a small size-scale, it can deform under cyclic loading in a semi-homogeneous manner without the occurrence of pronounced mature shear bands. Instead, the plastic deformation in simulated samples proceeds via the network-like shear-transition zones (STZs) by the reversible and irreversible structure-relaxations during cyclic loading. Dynamic recovery and reversible/irreversible structure rearrangements occur in the current model, along with annihilation/creation of excessive free volumes. This behavior would in-turn retard the damage growth of metallic glass. Current studies can help to understand the structural relaxation mechanism in metallic glass under loading. The results also imply that the brittle bulk metallic glasses can become ductile with the sample size being reduced. The application of metallic glasses in the form of thin film or nano pieces in micro-electro-mechanical systems (MEMS) could be promising.
Time scale of diffusion in molecular and cellular biology
NASA Astrophysics Data System (ADS)
Holcman, D.; Schuss, Z.
2014-05-01
Diffusion is the driver of critical biological processes in cellular and molecular biology. The diverse temporal scales of cellular function are determined by vastly diverse spatial scales in most biophysical processes. The latter are due, among others, to small binding sites inside or on the cell membrane or to narrow passages between large cellular compartments. The great disparity in scales is at the root of the difficulty in quantifying cell function from molecular dynamics and from simulations. The coarse-grained time scale of cellular function is determined from molecular diffusion by the mean first passage time of molecular Brownian motion to a small targets or through narrow passages. The narrow escape theory (NET) concerns this issue. The NET is ubiquitous in molecular and cellular biology and is manifested, among others, in chemical reactions, in the calculation of the effective diffusion coefficient of receptors diffusing on a neuronal cell membrane strewn with obstacles, in the quantification of the early steps of viral trafficking, in the regulation of diffusion between the mother and daughter cells during cell division, and many other cases. Brownian trajectories can represent the motion of a molecule, a protein, an ion in solution, a receptor in a cell or on its membrane, and many other biochemical processes. The small target can represent a binding site or an ionic channel, a hidden active site embedded in a complex protein structure, a receptor for a neurotransmitter on the membrane of a neuron, and so on. The mean time to attach to a receptor or activator determines diffusion fluxes that are key regulators of cell function. This review describes physical models of various subcellular microdomains, in which the NET coarse-grains the molecular scale to a higher cellular-level, thus clarifying the role of cell geometry in determining subcellular function.
Extending the astronomical (polarity) time scale into the Miocene
F. J. Hilgen; W. Krijgsman; C. G. Langereis; L. J. Lourens; A. Santarelli; W. J. Zachariasse
1995-01-01
An astronomical time scale is presented for the late Miocene based on the correlation of characteristic sedimentary cycle patterns in marine sections in the Mediterranean to the 65°N summer insolation curve of La90[1,2] with present-day values for the dynamical ellipticity of the Earth and tidal dissipation by the moon. This correlation yields ages for all sedimentary cycles and hence also
Control systems on regular time scales and their differential rings
Zbigniew Bartosiewicz; Ülle Kotta; Ewa Pawluszewicz; Malgorzata Wyrwas
2011-01-01
The paper describes an algebraic construction of the inversive differential ring, associated with a nonlinear control system,\\u000a defined on a nonhomogeneous but regular time scale. The ring of meromorphic functions in system variables is constructed under\\u000a the assumption that the system is submersive, and equipped with three operators (delta- and nabla-derivatives, and the forward\\u000a shift operator) whose properties are studied.
Output feedback control of nonlinear two-time-scale systems
Panagiotis D. Christofides
1997-01-01
This work focuses on dynamic output feedback control of a class of nonlinear singularly perturbed systems. A nonlinear two-time-scale output feedback controller is synthesized which guarantees stability and enforces output tracking in the closed-loop system, provided that the singular perturbation parameter is sufficiently small. The proposed controller is successfully tested on a chemical process modeled by a nonlinear singularly perturbed
Solar Irradiance Variations on Active Region Time Scales
NASA Technical Reports Server (NTRS)
Labonte, B. J. (editor); Chapman, G. A. (editor); Hudson, H. S. (editor); Willson, R. C. (editor)
1984-01-01
The variations of the total solar irradiance is an important tool for studying the Sun, thanks to the development of very precise sensors such as the ACRIM instrument on board the Solar Maximum Mission. The largest variations of the total irradiance occur on time scales of a few days are caused by solar active regions, especially sunspots. Efforts were made to describe the active region effects on total and spectral irradiance.
Biogenic Calcium Phosphate Transformation in Soils over Millennium Time Scales
Sato, S.; Neves, E; Solomon, D; Liang, B; Lehmann, J
2009-01-01
Changes in bioavailability of phosphorus (P) during pedogenesis and ecosystem development have been shown for geogenic calcium phosphate (Ca-P). However, very little is known about long-term changes of biogenic Ca-P in soil. Long-term transformation characteristics of biogenic Ca-P were examined using anthropogenic soils along a chronosequence from centennial to millennial time scales. Phosphorus fractionation of Anthrosols resulted in overall consistency with the Walker and Syers model of geogenic Ca-P transformation during pedogenesis. The biogenic Ca-P (e.g., animal and fish bones) disappeared to 3% of total P within the first ca. 2,000 years of soil development. This change concurred with increases in P adsorbed on metal-oxides surfaces, organic P, and occluded P at different pedogenic time. Phosphorus K-edge X-ray absorption near-edge structure (XANES) spectroscopy revealed that the crystalline and therefore thermodynamically most stable biogenic Ca-P was transformed into more soluble forms of Ca-P over time. While crystalline hydroxyapatite (34% of total P) dominated Ca-P species after about 600-1,000 years, {Beta}-tricalcium phosphate increased to 16% of total P after 900-1,100 years, after which both Ca-P species disappeared. Iron-associated P was observable concurrently with Ca-P disappearance. Soluble P and organic P determined by XANES maintained relatively constant (58-65%) across the time scale studied. Conclusions - Disappearance of crystalline biogenic Ca-P on a time scale of a few thousand years appears to be ten times faster than that of geogenic Ca-P.
Is there a break in scaling on centennial time scale in Holocene temperature records?
NASA Astrophysics Data System (ADS)
Nilsen, Tine; Rypdal, Kristoffer; Fredriksen, Hege-Beate
2015-04-01
A variety of paleoclimatic records have been used to study scaling properties of past climate, including ice core paleotemperature records and multi-proxy reconstructions. Records extending further back in time than the Holocene are divided into glacial/interglacial segments before analysis. The methods used to infer the scaling include the power spectral density (Lomb-Scargle periodogram and standard periodogram), detrended fluctuation analysis, wavelet variance analysis and the Haar fluctuation function. All the methods have individual strengths, weaknesses, uncertainties and biases, and for this reason it is useful to compare results from different methods when possible. Proxy-based reconstructions have limited spatial and temporal coverage, and must be used and interpreted with great care due to uncertainties. By elaborating on physical mechanisms for the actual climate fluctuations seen in the paleoclimatic temperature records as well as uncertainties in both data and methods, we demonstrate the possible pitfalls that may lead to the conclusion that the variability in temperature time series can be separated into different scaling regimes. Categorizing the Earth's surface temperature variability into a «macroweather» and "climate" regime has little or no practical meaning since the different components in the climate system are connected and interact on all time scales. Our most important result is that a break between two different scaling regimes at time scales around one century cannot be identified in Holocene climate. We do, however, observe departures from scaling, which can be attributed to variability such as a single internal quasi-periodic oscillation, an externally forced trend, or a combination of factors. If two scaling regimes are claimed to be present in one single time series, both regimes must be persistent. We show that the limited temporal resolution/length of the records significantly lowers the confidence for such persistence. A total of six Holocene ice core paleotemperature records were studied, (GRIP, GISP2 and NGRIP from Greenland, EPICA, Vostok and Taylor Dome from Antarctica). For all time series the estimated scaling exponent ? is between 0.1 and 0.3 up to millennial time scales, where a deviation is observed and a seemingly higher value of ? is inferred on longer time scales. The Holocene ice core records have by Lovejoy et al. (2012) been claimed to be exceptionally stable, compared to other proxy records such as marine sediment cores. Such a statement should be followed by a discussion about different types of proxy reconstructions and climate conditions. This presentation highlights that care should be taken when comparing the climate of continental land covered by ice, with a marine sediment record representing an oceanographically dynamic area. Different proxies are representative of different environmental variables, and the reconstructions are created to give a general paleoclimatic overview of a certain area, and are in that manner only blurred snapshots of the past climate.
Modeling of streamflow processes at different time scales
NASA Astrophysics Data System (ADS)
Bartolini, Paolo; Salas, Jose D.
1993-08-01
The analysis and modeling of streamflow processes has attracted the attention of water resources specialists for several decades. A number of models have been suggested in the past for representing seasonal and annual streamflow processes. The topic addressed in this paper centers around the compatibility of stochastic models of streamflow at different time scales. More specifically, given a model for monthly flows, the models for the processes obtained by aggregation, i.e., models for bimonthly, quarterly, etc., time scales, are derived. Likewise, parameter space and covariance properties of such derived processes as well as the relationship of such properties of different time scales are given. These concepts are applied to modeling streamflow of the Niger River. The developments are restricted to the family of periodic autoregressive moving average (PARMA) processes. For instance, it was found that monthly flows based on the PARMA(2, 1) process leads to PARMA(2, 2) bimonthly flows and stationary ARMA(2, 2) annual flows. Furthermore, applications to modeling the Niger River flows suggest that one can reproduce the seasonal and annual second-order statistics without using disaggregation if PARMA models are used for modeling the seasonal flows.
Scaling brain size, keeping timing: evolutionary preservation of brain rhythms.
Buzsáki, György; Logothetis, Nikos; Singer, Wolf
2013-10-30
Despite the several-thousand-fold increase of brain volume during the course of mammalian evolution, the hierarchy of brain oscillations remains remarkably preserved, allowing for multiple-time-scale communication within and across neuronal networks at approximately the same speed, irrespective of brain size. Deployment of large-diameter axons of long-range neurons could be a key factor in the preserved time management in growing brains. We discuss the consequences of such preserved network constellation in mental disease, drug discovery, and interventional therapies. PMID:24183025
Relaxation selective pulses in fast relaxing systems.
Lopez, Christopher J; Lu, Wei; Walls, Jamie D
2014-05-01
In this work, the selectivity or sharpness of the saturation profiles for relaxation selective pulses (R^rsps) that suppress magnetization possessing relaxation times of T2=T2(rsp) and T1=?T2 for ??12,? was optimized. Along with sharpening the selectivity of the R^rsps, the selective saturation of these pulses was also optimized to be robust to both B0 and B1 inhomogeneities. Frequency-swept hyperbolic secant and adiabatic time-optimal saturation pulse inputs were found to work best in the optimizations, and the pulse lengths required to selectivity saturate the magnetization were always found to be less than the inversion recovery delay, T1ln(2). The selectivity of the optimized relaxation selective pulses was experimentally demonstrated in aqueous solutions with varying concentrations of the paramagnetic species, [Mn(+2)], and for use in solvent suppression. Finally, the "rotational" properties of spin relaxation were explored along with an analytical derivation of adiabatic time-optimal saturation pulses. PMID:24631803
Anomalous relaxation in fractal structures
Fujiwara, S.; Yonezawa, F. (Department of Physics, Keio University, 3-14-1 Hiyoshi, Kohoku-ku, Yokohama 223 (Japan))
1995-03-01
For the purpose of studying some interesting properties of anomalous relaxation in fractal structures, we carry out Monte Carlo simulations of random walks on two-dimensional fractal structures (Sierpinski carpets with different cutouts and site-percolation clusters in a square lattice at the critical concentration). We find that the relaxation is of the Cole-Cole type [J. Chem. Phys. 9, 341 (1941)], which is one of the empirical laws of anomalous relaxation. Scaling properties are found in the relaxation function as well as in the particle density. We also find that, in strucures with almost the same fractal dimension, relaxation in structures with dead ends is slower than that in structures without them. This paper ascertains that the essential aspects of the anomalous relaxation due to many-body effects can be explained in the framework of the one-body model.
Two-time-scale population evolution on a singular landscape
NASA Astrophysics Data System (ADS)
Xu, Song; Jiao, Shuyun; Jiang, Pengyao; Ao, Ping
2014-01-01
Under the effect of strong genetic drift, it is highly probable to observe gene fixation or gene loss in a population, shown by singular peaks on a potential landscape. The genetic drift-induced noise gives rise to two-time-scale diffusion dynamics on the bipeaked landscape. We find that the logarithmically divergent (singular) peaks do not necessarily imply infinite escape times or biological fixations by iterating the Wright-Fisher model and approximating the average escape time. Our analytical results under weak mutation and weak selection extend Kramers's escape time formula to models with B (Beta) function-like equilibrium distributions and overcome constraints in previous methods. The constructed landscape provides a coherent description for the bistable system, supports the quantitative analysis of bipeaked dynamics, and generates mathematical insights for understanding the boundary behaviors of the diffusion model.
Two-time-scale population evolution on a singular landscape.
Xu, Song; Jiao, Shuyun; Jiang, Pengyao; Ao, Ping
2014-01-01
Under the effect of strong genetic drift, it is highly probable to observe gene fixation or gene loss in a population, shown by singular peaks on a potential landscape. The genetic drift-induced noise gives rise to two-time-scale diffusion dynamics on the bipeaked landscape. We find that the logarithmically divergent (singular) peaks do not necessarily imply infinite escape times or biological fixations by iterating the Wright-Fisher model and approximating the average escape time. Our analytical results under weak mutation and weak selection extend Kramers's escape time formula to models with B (Beta) function-like equilibrium distributions and overcome constraints in previous methods. The constructed landscape provides a coherent description for the bistable system, supports the quantitative analysis of bipeaked dynamics, and generates mathematical insights for understanding the boundary behaviors of the diffusion model. PMID:24580274
NASA Astrophysics Data System (ADS)
Han, S. C.; Sauber, J. M.; Pollitz, F. F.; Riva, R.; Okal, E. A.
2014-12-01
We analyzed spatially- and temporally-continuous GRACE gravity observations by decomposing the gravity field changes into five independent moment tensor elements to understand the regional surface and interior deformation in response to post-earthquake stress/strain redistribution. For the 2011 Tohoku-Oki thrust earthquake, the GRACE data revealed postseismic gravity increase by 6 microGal over a 500-km scale within a couple of years, which is nearly 40-50 % of the coseismic gravity change. It originates mostly from changes in the isotropic component corresponding to the Mrr moment tensor element. For the 2012 Indian Ocean strike-slip earthquakes, the postseismic gravity change was similar to the coseismic change (including the Mw 8.6 and Mw 8.2 ruptures) with the magnitude smaller by ~80 % in two years. The gravity change corresponding to the Mtp moment tensor element is dominant (and also Mtt-Mpp to a lesser extent). In both earthquakes, the exponential decay with rapid change within a year and gradual change afterwards is a characteristic temporal pattern. We also compared the two earthquakes in terms of their respective seafloor vertical and interior deformation (Bouguer gravity). The processes responsible for the coseismic and postseismic gravity changes at a such spatial scale are, respectively, the density change (dilatation) and the viscoelastic deformation without much perturbation in density. The postseismic gravity variation is best modeled by bi-viscous relaxation with a transient and steady-state viscosity of 10^18 and 10^19 Pa s, respectively, for the asthenosphere. Furthermore, we found viscoelastic relaxation triggered by the partially-ruptured elastic lithosphere is a main driver of the local subsidence above the rupture region reported from the GPS-acoustic seafloor surveying after the 2011 Tohoku-Oki earthquake.
Richardson, P. M., E-mail: phy5pmr@leeds.ac.uk; Voice, A. M., E-mail: a.m.voice@leeds.ac.uk; Ward, I. M., E-mail: i.m.ward@leeds.ac.uk [Soft Matter Physics, School of Physics and Astronomy, University of Leeds, Leeds LS2 9JT (United Kingdom)
2013-12-07
Longitudinal relaxation (T{sub 1}) measurements of {sup 19}F, {sup 7}Li, and {sup 1}H in propylene carbonate/LiBF{sub 4} liquid electrolytes are reported. Comparison of T{sub 1} values with those for the transverse relaxation time (T{sub 2}) confirm that the measurements are in the high temperature (low correlation time) limit of the T{sub 1} minimum. Using data from pulsed field gradient measurements of self-diffusion coefficients and measurements of solution viscosity measured elsewhere, it is concluded that although in general there are contributions to T{sub 1} from both translational and rotational motions. For the lithium ions, this is mainly translational, and for the fluorine ions mainly rotational.
NASA Astrophysics Data System (ADS)
Baskar, Geetha; Baran Mandal, Asit
1997-03-01
Molecular dynamics studies performed by 1H NMR spin-lattice relaxation time measurements suggest the occurrence of a mutual interaction between aqueous micelles of a macromonomer (acrylic ester of ?-methoxypolyethyleneglycol, Mol. wt. 460) and sodium dodecylsulfate (SDS). The ?-CH 2 of SDS and ?-OCH 3 of the macromonomer seem to contribute to the maximum electrostatic interaction. The counterion association for SDS micelles is also hindered in the presence of larger macromonomer micelles as observed by conductivity measurements.
Ellingson, Arin M.; Nagel, Tina M.; Polly, David W.; Ellermann, Jutta; Nuckley, David J.
2014-01-01
Degeneration alters the biochemical composition of the disc, affecting the mechanical integrity leading to spinal instability. Quantitative T2* MRI probes water mobility within the macromolecular network, a potentially more sensitive assessment of disc health. We determined the relationship between T2* relaxation time and proteoglycan content, collagen content, and compressive mechanics throughout the degenerative spectrum. Eighteen human cadaveric lumbar (L4–L5) discs were imaged using T2* MRI. The T2* relaxation time at five locations (nucleous pulposus or NP, anterior annulus fibrosis or AF, posterior AF, inner AF, and outer AF) was correlated with sulfated-glycosaminoglycan (s-GAG) content, hydroxyproline content, and residual stress and strain at each location. T2* relaxation times were significantly correlated with s-GAG contents in all test locations and were particularly strong in the NP (r = 0.944; p < 0.001) and inner AF (r = 0.782; p < 0.001). T2* relaxation times were also significantly correlated with both residual stresses and excised strains in the NP (r = 0.857; p < 0.001: r = 0.816; p < 0.001), inner AF (r = 0.535; p = 0.022: r = 0.516; p = 0.028), and outer AF (r = 0.668; p = 0.002: r = 0.458; p = 0.041). These strong correlations highlight T2* MRI’s ability to predict the biochemical and mechanical health of the disc. T2* MRI assessment of disc health is a clinically viable tool showing promise as a biomarker for distinguishing degenerative changes. PMID:24788830
Ethan Jefferson Fairbanks
1994-01-01
Off-resonance spin locking makes use of the novel relaxation time T_{1rho} ^{rm off}, which may be useful in characterizing breast disease. Knowledge of T _{rm 1rho}^{rm off} is essential for optimization of spin -locking imaging methods. The purpose of this work was to develop an optimal imaging technique for in vivo measurement of T_{rm 1rho}^ {rm off}. Measurement of T
Biller, Joshua R.; Meyer, Virginia M.; Elajaili, Hanan; Rosen, Gerald M.; Eaton, Sandra S.; Eaton, Gareth R.
2012-01-01
Electron spin relaxation times of perdeuterated tempone (PDT) 1 and of a nitronyl nitroxide 2-(4-carboxy-phenyl)-4,4,5,5-tetramethylimidazoline-3-oxide-1-oxyl) 2 in aqueous solution at room temperature were measured by 2-pulse electron spin echo (T2) or 3-pulse inversion recovery (T1) in the frequency range of 250 MHz to 34 GHz. At 9 GHz values of T1 measured by long-pulse saturation recovery were in good agreement with values determined by inversion recovery. Below 9 GHz for 1 and below 1.5 GHz for 2, T1~ T2, as expected in the fast tumbling regime. At higher frequencies T2 was shorter than T1 due to incomplete motional averaging of g and A anisotropy. The frequency dependence of 1/T1 is modeled as the sum of spin rotation, modulation of g and A-anisotropy, and a thermally-activated process that has maximum contribution at about 1.5 GHz. The spin lattice relaxation times for the nitronyl nitroxide were longer than for PDT by a factor of about 2 at 34 GHz, decreasing to about a factor of 1.5 at 250 MHz. The rotational correlation times, ?R are calculated to be 9 ps for 1 and about 25 ps for 2. The longer spin lattice relaxation times for 2 than for 1 at 9 and 34 GHz are due predominantly to smaller contributions from spin rotation that arise from slower tumbling. The smaller nitrogen hyperfine couplings for the nitronyl 2 than for 1 decrease the contribution to relaxation due to modulation of A anisotropy. However, at lower frequencies the slower tumbling of 2 results in a larger value of ??R (? is the resonance frequency) and larger values of the spectral density function, which enhances the contribution from modulation of anisotropic interactions for 2 to a greater extent than for 1. PMID:23123770
Sylwester J. Rzoska; Aleksandra Drozd-Rzoska
2010-01-01
This contribution presents the extended, pressure-related Vogel–Fulcher–Tammann equation applied to portray the pressure evolution of viscosity ? (P) and the related dynamic properties, such as the primary relaxation time ? (P), in soft-matter systems as well as the modified Simon–Glatzel-type equation for describing pressure dependences of the glass temperature Tg (P), the melting temperature Tm (P) and the fragile-to-strong dynamical
Thermodynamic Relaxation Drives Expulsion in Giant Unilamellar Vesicles
C. T. Leirer; B. Wunderlich; A. Wixforth; M. F. Schneider
2013-03-26
We investigated the thermodynamic relaxation of giant unilamellar vesicles (GUVs) which contained small vesicles within their interior. Quenching these vesicles from their fluid phase (T>Tm) through the phase transition in the gel state (T
Nanosecond Relaxation Dynamics of Hydrated Proteins: Water versus protein contributions
Khodadadi, S [University of Akron; Curtis, J. E. [National Institute of Standards and Technology (NIST), Gaithersburg, MD; Sokolov, Alexei P [ORNL
2011-01-01
We have studied picosecond to nanosecond dynamics of hydrated protein powders using dielectric spectroscopy and molecular dynamics (MD) simulations. Our analysis of hydrogen-atom single particle dynamics from MD simulations focused on main ( main tens of picoseconds) and slow ( slow nanosecond) relaxation processes that were observed in dielectric spectra of similar hydrated protein samples. Traditionally, the interpretation of these processes observed in dielectric spectra has been ascribed to the relaxation behavior of hydration water tightly bounded to a protein and not to protein atoms. Detailed analysis of the MD simulations and comparison to dielectric data indicate that the observed relaxation process in the nanosecond time range of hydrated protein spectra is mainly due to protein atoms. The relaxation processes involve the entire structure of protein including atoms in the protein backbone, side chains, and turns. Both surface and buried protein atoms contribute to the slow processes; however, surface atoms demonstrate slightly faster relaxation dynamics. Analysis of the water molecule residence and dipolar relaxation correlation behavior indicates that the hydration water relaxes at much shorter time scales.
Multi-scale modeling of time-dependent response of smart sandwich constructions
Jeong Sik Kim; L. Arronche; A. Farrugia; A. Muliana; V. La Saponara
2011-01-01
Polymer and polymer based composite structures exhibit time-dependent response, leading to their being described as viscoelastic bodies. The rate of creep (or stress relaxation) in viscoelastic bodies increases with increasing the temperature of the bodies. In this study, we are interested in analyzing the time-dependent response of smart sandwich composites comprising of glass fiber reinforced polymer (GFRP) skins, polyurethane foam
Optimal detection using bilinear time-frequency and time-scale representations
A. M. Sayeed; D. L. Jones
1995-01-01
Bilinear time-frequency representations (TFRs) and time-scale representations (TSRs) are potentially very useful for detecting a nonstationary signal in the presence of nonstationary noise or interference. As quadratic signal representations, they are promising for situations in which the optimal detector is a quadratic function of the observations. All existing time-frequency formulations of quadratic detection either implement classical optimal detectors equivalently in
Broadband time-domain-reflectometry dielectric spectroscopy using variable-time-scale sampling
N. E. Hager
1994-01-01
Methods for increasing the bandwidth of time-domain-reflectometry (TDR) dielectric spectroscopy using variable-time-scale sampling are presented. Consecutive segments of the TDR transient are sampled with increasing time increments and the entire transient transformed into the frequency domain using a running Laplace transform. Instrumentation artifacts are identified and controlled by examining reflected transients for stray artifacts prior to transformation, either on individual
Picosecond Time-Resolved Strain Rosette at Atomic Length Scale
NASA Astrophysics Data System (ADS)
Campana, Maria I.; Williams, G. Jackson; Heyong Lee, Soo; Walko, Donald; Landahl, Eric
2013-03-01
Ultrafast optical absorption in a crystalline solid generates coherent motions of strain, which propagate through the bulk at the speed of sound. Energy relaxation dynamics of the excited lattice system and the subsequent transport properties of the strains have been actively studied. Recently, these high-speed transient dynamics have been studied using laser based pump-probe techniques and time resolved x-ray diffraction (TRXD). However, the interpretation of these studies always assumes a uniaxial spatial profile for the strain (i.e. strain is exerted only along the direction of surface normal of the sample). This assumption comes from a symmetry argument originally given by Thomsen: if the illuminated area of the pump laser beam on the sample surface is much larger than the optical penetration depth, strain gradient along surface normal is expected to be much steeper than along lateral direction, and therefore, the strain generated is usually assumed to be one dimensional. While this assumption simplifies the analysis of the data, (and makes possible such applications as picosecond ultrasonics for the in-situ measurement of semiconductor heterostructure thickness), it overlooks any physical processes that take place along transverse direction. Here we report the experimental generation and detection of the transverse component of the impulsively generated strain in a single GaAs crystal using TRXD. Our analysis is based on a strain rosette applied to three non-collinear Bragg reflections. Ultrafast optical absorption in a crystalline solid generates coherent motions of strain, which propagate through the bulk at the speed of sound. Energy relaxation dynamics of the excited lattice system and the subsequent transport properties of the strains have been actively studied. Recently, these high-speed transient dynamics have been studied using laser based pump-probe techniques and time resolved x-ray diffraction (TRXD). However, the interpretation of these studies always assumes a uniaxial spatial profile for the strain (i.e. strain is exerted only along the direction of surface normal of the sample). This assumption comes from a symmetry argument originally given by Thomsen: if the illuminated area of the pump laser beam on the sample surface is much larger than the optical penetration depth, strain gradient along surface normal is expected to be much steeper than along lateral direction, and therefore, the strain generated is usually assumed to be one dimensional. While this assumption simplifies the analysis of the data, (and makes possible such applications as picosecond ultrasonics for the in-situ measurement of semiconductor heterostructure thickness), it overlooks any physical processes that take place along transverse direction. Here we report the experimental generation and detection of the transverse component of the impulsively generated strain in a single GaAs crystal using TRXD. Our analysis is based on a strain rosette applied to three non-collinear Bragg reflections. Present affiliation: University of California, Davis
PROTON SPIN-LATTICE RELAXATION TIME IN THE SUPERCONDUCTING INTERCALATION COMPLEX TaS2(PYRIDINE)1/2
Boyer, Edmond
the dominant relaxation mechanism at low temperatures [6]. We prepared two powdered polycrystalline samples of the conduction electrons in the metallic layers. The intercalation modifies the properties of the conduction of the present study concerns the possibility of detecting the effects of superconducting fluctuations near Tc
Terrestrial Waters and Sea Level Variations on Interannual Time Scale
NASA Technical Reports Server (NTRS)
Llovel, W.; Becker, M.; Cazenave, A.; Jevrejeva, S.; Alkama, R.; Decharme, B.; Douville, H.; Ablain, M.; Beckley, B.
2011-01-01
On decadal to multi-decadal time scales, thermal expansion of sea waters and land ice loss are the main contributors to sea level variations. However, modification of the terrestrial water cycle due to climate variability and direct anthropogenic forcing may also affect sea level. For the past decades, variations in land water storage and corresponding effects on sea level cannot be directly estimated from observations because these are almost non-existent at global continental scale. However, global hydrological models developed for atmospheric and climatic studies can be used for estimating total water storage. For the recent years (since mid-2002), terrestrial water storage change can be directly estimated from observations of the GRACE space gravimetry mission. In this study, we analyse the interannual variability of total land water storage, and investigate its contribution to mean sea level variability at interannual time scale. We consider three different periods that, each, depend on data availability: (1) GRACE era (2003-2009), (2) 1993-2003 and (3) 1955-1995. For the GRACE era (period 1), change in land water storage is estimated using different GRACE products over the 33 largest river basins worldwide. For periods 2 and 3, we use outputs from the ISBA-TRIP (Interactions between Soil, Biosphere, and Atmosphere-Total Runoff Integrating Pathways) global hydrological model. For each time span, we compare change in land water storage (expressed in sea level equivalent) to observed mean sea level, either from satellite altimetry (periods 1 and 2) or tide gauge records (period 3). For each data set and each time span, a trend has been removed as we focus on the interannual variability. We show that whatever the period considered, interannual variability of the mean sea level is essentially explained by interannual fluctuations in land water storage, with the largest contributions arising from tropical river basins.
Jeworrek, Christoph; Pühse, Matthias; Winter, Roland
2008-10-21
By using the pressure-jump relaxation technique in combination with time-resolved synchrotron small-angle X-ray diffraction (TRSAXS), the kinetics of lipid phase transformations of ternary lipid mixtures serving as model systems of heterogeneous raftlike membranes were investigated. To this end, we first established the temperature-pressure phase diagram of a model lipid raft mixture, 1,2-dioleoyl- sn-glycero-3-phosphatidylcholine (DOPC)/1,2-dipalmitoyl- sn-glycero-3-phosphatidylcholine (DPPC)/cholesterol (1:2:1), using Fourier transform infrared spectroscopy and SAXS, covering the pressure range from 1 bar to 10 kbar at temperatures in the range from 7 to 80 degrees C. We then studied the kinetics of interlamellar phase transitions of the ternary lipid system involving transitions from the fluidlike (liquid-disordered, l d) phase to the liquid-ordered (l o)/liquid-disordered (l d) two-phase coexistence region as well as between the two- and three-phase coexistence regions of the system, where also solid-ordered phases (s o) are involved. The phase transition from the all-fluid l d phase to the l o+l d two-phase coexistence region turns out to be rather rapid. Phases appear or disappear within the 25 ms time resolution of the technique, followed by a slow lattice relaxation process, which, depending on the pressure-jump amplitude, takes several seconds. Contrary to many one-component phospholipid phase transitions, the kinetics of the l d <--> l o+l d transition follows a similar time scale and mechanism for the pressurization and depressurization direction. A similar behavior is observed for the phase transition kinetics of the s o+l o+l d <--> l o+l d transformation and even for the s o+l o+l d <--> l d transformation, jumping across the l o+l d two-phase region. All transitions are fully reversible, and no intermediate states are populated. As indicated by the complex relaxation profiles observed, the overall rates observed seem to reflect the effect of coupling of various dynamical processes through the transformation, involving fast conformational changes in the sub-millisecond time regime and slow relaxation of the lattices growing, probably being largely controlled by the transport and redistribution of water into and in the new phases of the multilamellar vesicle assemblies. PMID:18767826
Heterogenous scaling in interevent time of on-line bookmarking
Wang, Peng; Yeung, Chi Ho; Wang, Bing-Hong
2010-01-01
In this paper, we study the statistical properties of bookmarking behaviors in Delicious.com. We find that the interevent time distributions of bookmarking decays powerlike as interevent time increases at both individual and population level. Remarkably, we observe a significant change in the exponent when interevent time increases from intra-day to inter-day range. In addition, dependence of exponent on individual Activity is found to be different in the two ranges. These results suggests that mechanisms driving human actions are different in intra- and inter-day range. Instead of monotonically increasing with Activity, we find that inter-day exponent peaks at value around 3. We further show that less active users are more likely to resemble poisson process in bookmarking. Based on the temporal-preference model, preliminary explanations for this dependence have been given . Finally, a universal behavior in inter-day scale is observed by considering the rescaled variable.
Decay of surface nanostructures via long-time-scale dynamics
Voter, A.F.; Stanciu, N.
1998-11-01
This is the final report of a three-year, Laboratory Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). The authors have developed a new approach for extending the time scale of molecular dynamics simulations. For infrequent-event systems, the category that includes most diffusive events in the solid phase, this hyperdynamics method can extend the simulation time by a few orders of magnitude compared to direct molecular dynamics. The trajectory is run on a potential surface that has been biased to raise the energy in the potential basins without affecting the transition state region. The method is described and applied to surface and bulk diffusion processes, achieving microsecond and millisecond simulation times. The authors have also developed a new parallel computing method that is efficient for small system sizes. The combination of the hyperdynamics with this parallel replica dynamics looks promising as a general materials simulation tool.
Multiple-Time Scaling and Universal Behavior of the Earthquake Interevent Time Distribution
Bottiglieri, M.; Godano, C.; Lippiello, E. [Department of Environmental Sciences and CNISM, Second University of Naples, Caserta (Italy); Arcangelis, L. de [IfB, ETH, Schafmattstr. 6, 8093 Zuerich (Switzerland) and Department of Information Engineering and CNISM, Second University of Naples, Aversa (Italy)
2010-04-16
The interevent time distribution characterizes the temporal occurrence in seismic catalogs. Universal scaling properties of this distribution have been evidenced for entire catalogs and seismic sequences. Recently, these universal features have been questioned and some criticisms have been raised. We investigate the existence of universal scaling properties by analyzing a Californian catalog and by means of numerical simulations of an epidemic-type model. We show that the interevent time distribution exhibits a universal behavior over the entire temporal range if four characteristic times are taken into account. The above analysis allows us to identify the scaling form leading to universal behavior and explains the observed deviations. Furthermore, it provides a tool to identify the dependence on the mainshock magnitude of the c parameter that fixes the onset of the power law decay in the Omori law.
Many roads to synchrony: Natural time scales and their algorithms
NASA Astrophysics Data System (ADS)
James, Ryan G.; Mahoney, John R.; Ellison, Christopher J.; Crutchfield, James P.
2014-04-01
We consider two important time scales—the Markov and cryptic orders—that monitor how an observer synchronizes to a finitary stochastic process. We show how to compute these orders exactly and that they are most efficiently calculated from the ?-machine, a process's minimal unifilar model. Surprisingly, though the Markov order is a basic concept from stochastic process theory, it is not a probabilistic property of a process. Rather, it is a topological property and, moreover, it is not computable from any finite-state model other than the ?-machine. Via an exhaustive survey, we close by demonstrating that infinite Markov and infinite cryptic orders are a dominant feature in the space of finite-memory processes. We draw out the roles played in statistical mechanical spin systems by these two complementary length scales.
The surface relaxation of water.
Liu, Maoyuan; Beattie, James K; Gray-Weale, Angus
2012-08-01
We examine three possible explanations for the millisecond relaxation time of the dynamic surface tension of water: the diffusion of surfactant contaminants from the aqueous phase to the surface, the reorientation of surface water molecules' dipole moments, and the buildup of a charged surface layer of hydroxide ions. The relaxation time expected for hydroxide is by far the closest to the measured time. Our model for the surface layer agrees with static equilibrium experiments and, as we show here, predicts the relaxation time. The results strongly imply that the equilibrium surface of water is highly charged by a flow of hydroxide to the surface. The model predicts that neither diffusion nor autolysis dominates and shows that both processes are needed to describe the relaxation of the surface tension. We find a salt and pH dependence of the relaxation time and propose further experiments. PMID:22582761
Time scales in the context of general relativity.
Guinot, Bernard
2011-10-28
Towards 1967, the accuracy of caesium frequency standards reached such a level that the relativistic effect could not be ignored anymore. Corrections began to be applied for the gravitational frequency shift and for distant time comparisons. However, these corrections were not applied to an explicit theoretical framework. Only in 1991 did the International Astronomical Union provide metrics (then improved in 2000) for a definition of space-time coordinates in reference systems centred at the barycentre of the Solar System and at the centre of mass of the Earth. In these systems, the temporal coordinates (coordinate times) can be realized on the basis of one of them, the International Atomic Time (TAI), which is itself a realized time scale. The definition and the role of TAI in this context will be recalled. There remain controversies regarding the name to be given to the unit of coordinate times and to other quantities appearing in the theory. However, the idea that astrometry and celestial mechanics should adopt the usual metrological rules is progressing, together with the use of the International System of Units, among astronomers. PMID:21930569
Vibrational Relaxation and Dynamical Transitions in Atactic Polystyrene
NASA Astrophysics Data System (ADS)
Zhao, Hanqing; Park, Yung; Painter, Paul
2009-03-01
Infrared bands and Raman lines recorded in the frequency domain have a counterpart in the time domain in the form of time-correlation functions, which are sensitive to molecular dynamics on the picosecond time scale. This is explored by calculating time correlation functions and their variation with temperature for the conformationally insensitive modes observed near 1601 cm-1 and 1583 cm-1 in the infrared spectrum of atactic polystyrene. The correlation functions were modeled by assuming that there is a fast relaxation process characterized by a single relaxation time that is inhomogeneously broadened by a slower process, also characterized by a single relaxation time. The fundamental mode, near 1583 cm-1, is inhomogeneously broadened, but the relaxation time calculated for this mode is sensitive to temperature as a result of anharmonic coupling to a combination mode. A change in the modulation of the 1583 cm-1 band becomes apparent about 10--20 degrees below the thermally measured Tg. Relaxation times at first increase then decrease and becomes negligible at temperatures near 180 degrees. These results are consistent with theories of the glass transition.
Time scale algorithms for an inhomogeneous group of atomic clocks
NASA Technical Reports Server (NTRS)
Jacques, C.; Boulanger, J.-S.; Douglas, R. J.; Morris, D.; Cundy, S.; Lam, H. F.
1993-01-01
Through the past 17 years, the time scale requirements at the National Research Council (NRC) have been met by the unsteered output of its primary laboratory cesium clocks, supplemented by hydrogen masers when short-term stability better than 2 x 10(exp -12)tau(sup -1/2) has been required. NRC now operates three primary laboratory cesium clocks, three hydrogen masers, and two commercial cesium clocks. NRC has been using ensemble averages for internal purposes for the past several years, and has a realtime algorithm operating on the outputs of its high-resolution (2 x 10(exp -13) s at 1 s) phase comparators. The slow frequency drift of the hydrogen masers has presented difficulties in incorporating their short-term stability into the ensemble average, while retaining the long-term stability of the laboratory cesium frequency standards. We report on this work on algorithms for an inhomogeneous ensemble of atomic clocks, and on our initial work on time scale algorithms that could incorporate frequency calibrations at NRC from the next generation of Zacharias fountain cesium frequency standards having frequency accuracies that might surpass 10(exp -15), or from single-trapped-ion frequency standards (Ba+, Sr+,...) with even higher potential accuracies. The requirements for redundancy in all the elements (including the algorithms) of an inhomogeneous ensemble that would give a robust real-time output of the algorithms are presented and discussed.
Stress Relaxation on Geometrically Complex Faults
NASA Astrophysics Data System (ADS)
Dieterich, J.; Smith, D. E.
2006-12-01
Slip of geometrically complex faults involves interactions and processes that do not occur in standard planar fault models. These include off-fault yielding and stress relaxation, which are required to prevent the development of pathological stress conditions on the fault (or in extreme cases fault lock-up). The necessity of incorporating yielding to allow slip past geometric complexities was recognized by Nielsen and Knopoff [1998] who employed a simplified form of viscoelastic stress relaxation consisting of a monotonic time-dependent exponential decay of fault stresses. However, the characteristics of stress relaxation in the brittle seismogenic crust, which are dominated by faulting processes, may be quite different from that predicted by viscoelastic models. For example, slip over a slight fault irregularity with a slope change of only one part in 100 will give rise to shear strains adjacent to the irregularity on the order of 0.01. This greatly exceeds the strain needed to fracture rock under conditions in crust. The fractal-like character of fault systems and fault roughness insures that slight movements of secondary faults, at all scales, will be necessary to accommodate slip of major through-going faults. We surmise that these adjustments occur as co-seismic slip on secondary faults during large earthquakes, as delayed stress relaxation in the form of aftershocks, and as spatially distributed background seismicity. To model the integrated effect of these processes on the stress conditions on major faults, we employ an earthquake rate formulation [Dieterich, 1994], which incorporates laboratory-derived rate- and state-dependent frictional properties. Models of the earthquake cycle with uniform inter-event times using faults with simple bends, and random fractal geometries have the following characteristics. Slip produces spatially heterogeneous stress, where in the absence of relaxation processes, continues to grow without limit. When relaxation processes are included, using the earthquake rate formulation from rate- and state- dependent friction, deviations from the spatial mean stress decay at a rate proportional to 1/t. The 1/t decay is consistent with our assumption that stress relaxation occurs largely by aftershock processes. Where slip is inhibited by geometric irregularities, the relaxation processes reload the fault to favor additional slip, thus preventing pathological stress conditions such as fault lock-up. We can also calculate stress rotations during the relaxation process, where the amplitude of the rotations depends on the constitutive properties, the amplitude of the fault trace heterogeneity, and the initial background stress.
Zarzycki, Piotr P.; Rosso, Kevin M.
2009-06-16
Replica Kinetic Monte Carlo simulations were used to study the characteristic time scales of potentiometric titration of the metal oxides and (oxy)hydroxides. The effect of surface heterogeneity and surface transformation on the titration kinetics were also examined. Two characteristic relaxation times are often observed experimentally, with the trailing slower part attributed to surface non-uniformity, porosity, polymerization, amorphization, and other dynamic surface processes induced by unbalanced surface charge. However, our simulations show that these two characteristic relaxation times are intrinsic to the proton binding reaction for energetically homogeneous surfaces, and therefore surface heterogeneity or transformation do not necessarily need to be invoked. However, all such second-order surface processes are found to intensify the separation and distinction of the two kinetic regimes. The effect of surface energetic-topographic non-uniformity, as well dynamic surface transformation, interface roughening/smoothing were described in a statistical fashion. Furthermore, our simulations show that a shift in the point-of-zero charge is expected from increased titration speed and the pH-dependence of the titration measurement error is in excellent agreement with experimental studies.
Formation processes and time scales for meteorite parent bodies
NASA Technical Reports Server (NTRS)
Weidenschilling, S. J.
1988-01-01
The transition from small particles suspended in the solar nebula to the planetesimals (asteroids) that became the parent bodies of meteorites is examined. Planetesimals probably grew by coagulation of grain aggregates that collided due to different rates of settling and drag-induced orbital decay. Their growth was accompanied by radial transport of solids, possibly sufficient to deplete the primordial mass in the asteroid zone, but with relatively little mixing. The formation of asteroid-sized planetesimals was probably rapid, on a time scale less than 1 Myr.
Dynamics of Sulfonated Polystyrene Ionomers by Dielectric Relaxation Spectroscopy
NASA Astrophysics Data System (ADS)
Castagna, Alicia; Wang, Wenqin; Winey, Karen; Runt, James
2010-03-01
Broadband dielectric spectroscopy was used to investigate the dynamics of sulfonated polystyrene (SPS) ionomers, in both the acid and neutralized form. This study seeks to elucidate the role of counter ion type (Zn, Na, and Cs), degree of sulfonation (9 and 6%), and ion cluster morphology on the relaxation phenomena of SPS. Degree of neutralization and ion type have been found to significantly impact the breadth and time scale of the segmental relaxation process. High temperature relaxation processes, tentatively proposed to arise from Maxwell-Wagner-Sillars interfacial polarization and a hydrogen bonding relaxation, have also been identified. Bands in the sulfonate stretching region of FTIR spectra reveal information about ion coordination in the local aggregate environment. A combination of scanning transmission electron microscopy imaging and X-ray scattering confirmed the presence of homogeneously distributed, nearly monodisperse spherical ionic aggregates in the polymer matrix.
Time scales for charge equilibration in heavy ion collisions
K. E. Rehm; H. Essel; K. Hartel; P. Kienle; H. J. Körner; R. E. Segel; P. Sperr; W. Wagner
1979-01-01
Charge equilibration was investigated in the reaction208Pb+110Pd at 1,180 and 1,280 MeV incident energy. It is found that the relaxation timet' connected with this degree of freedom shows an increase with increasing bombarding energy. This behaviour can be explained within Langevin's classical theory of Brownian motion.
Polly, David
for each period of geologic time (e.g. Cambrian west to east transgression; Late Jurassic widespread that you know the geologic time scale, at least to the period level. Knowing the time scale is essential
NASA Technical Reports Server (NTRS)
1987-01-01
Environ Corporation's relaxation system is built around a body lounge, a kind of super easy chair that incorporates sensory devices. Computer controlled enclosure provides filtered ionized air to create a feeling of invigoration, enhanced by mood changing aromas. Occupant is also surrounded by multidimensional audio and the lighting is programmed to change colors, patterns, and intensity periodically. These and other sensory stimulators are designed to provide an environment in which the learning process is stimulated, because research has proven that while an individual is in a deep state of relaxation, the mind is more receptive to new information.
Yulmetyev, R M; Hänggi, P; Khusaenova, E V; Shimojo, S; Yulmetyeva, D G
2006-01-01
To analyze the crucial role of the fluctuation and relaxational effects in the human brain functioning we have studied a some statistical quantifiers that support the informational characteristics of neuromagnetic responses of magnetoencephalographic (MEG) signals. The signals to a flickering stimulus of different color combinations has been obtained from a group of control subjects which is contrasted with those for a patient with photosensitive epilepsy (PSE). We have revealed that the existence of the specific stratification of the phase clouds and the concomitant relaxation singularities of the corresponding nonequilibrium processes of chaotic behavior of the signals in the separate areas for a patient most likely shows the pronounced zones responsible the appearance of PSE.
Mid-infrared diffuse reflection on ultrafast time scales.
Brauns, Eric B
2014-01-01
This paper describes an instrument capable of studying diffuse reflection of mid-infrared (mid-IR) photons on ultrafast time scales. Femtosecond mid-IR pulses are generated by difference frequency mixing the output of an optical parametric amplifier that is pumped using a regeneratively amplified Ti:Sapphire laser. Time resolution is achieved by up-converting the diffusely reflected photons with pulses from the Ti:Sapphire oscillator. Experiments were performed on a series of powdered KBr samples containing varying amounts of carbon black. The results suggest that diffusely reflected mid-IR photons fall into two distinct categories. A small fraction of the photons travel relatively long effective path lengths (1.3-2.3 mm), while the majority traverse a much shorter distance (0.2-0.05 mm). PMID:24405947
Speed of Markovian relaxation toward the ground state
Vogl, Malte; Schaller, Gernot; Brandes, Tobias [Institut fuer Theoretische Physik, Technische Universitaet Berlin, Hardenbergstr. 36, D-10623 Berlin (Germany)
2010-01-15
For sufficiently low reservoir temperatures, it is known that open quantum systems subject to decoherent interactions with the reservoir relax toward their ground state in the weak coupling limit. Within the framework of quantum master equations, this is formalized by the Born-Markov-secular (BMS) approximation, where one obtains the system Gibbs state with the reservoir temperature as a stationary state. When the solution to some problem is encoded in the (isolated) ground state of a system Hamiltonian, decoherence can therefore be exploited for computation. The computational complexity is then given by the scaling of the relaxation time with the system size n. We study the relaxation behavior for local and nonlocal Hamiltonians that are coupled dissipatively with local and nonlocal operators to a bosonic bath in thermal equilibrium. We find that relaxation is generally more efficient when coherences of the density matrix in the system energy eigenbasis are taken into account. In addition, the relaxation speed strongly depends on the matrix elements of the coupling operators between initial state and ground state. We show that Dicke superradiance is a special case of our relaxation models and can thus be understood as a coherence-assisted relaxation speedup.
Source of Relaxation in the One Dimensional Gravitating System
NASA Astrophysics Data System (ADS)
Miller, Bruce
1996-05-01
Recent numerical experiments suggest that the one dimensional system consisting of N parallel mass sheets relaxes on two time scales: a rapid violent phase with duration of order T (a typical system crossing time) resulting in a quasi-equilibrium (QE) state followed by (2) a succession of QE states leading finally to thermal equilibrium. Within each QE state fluctuations relax on a time scale of order NT while complete thermalization occurs in about 10^4NT. Here I show that both time scales can be explained within the context of a diffusion model developed by the author and K. Yawn* (K. R. Yawn and B. N. Miller, Phys. Rev. E v.52, p. 3390 (1995).) specifically for this system.
NASA Astrophysics Data System (ADS)
Wang, Nian; Xia, Yang
2013-10-01
A number of experimental issues in the measurement of multi-component T2 and T1? relaxations in native and enzymatically digested articular cartilage were investigated by microscopic MRI (?MRI). The issues included the bath solutions (physiological saline and phosphate buffered saline (PBS)), the imaging resolution (35-140 ?m), the specimen orientations (0° and 55°), and the strength of spin-lock frequencies (0.5-2 kHz) in the T1? experiments. In addition to cartilage, the samples of agar gel and doped water solution were also used in the investigation. Two imaging sequences were used: CPMG-SE and MSME. All raw data were analyzed by the non-negative least square (NNLS) method. The MSME sequence was shown to result in the observation of multi-component T2, even in the gel and liquid samples, demonstrating the artificial uncleanness of this sequence in the multi-component measurements. The soaking of cartilage in PBS reduced the observable T2 components to one at both 0° and 55°, suggesting the effect of phosphate ions on proton exchange between different pools of water molecules. The cartilage orientation with respect to the external magnetic field and the spin-lock strengths in the T1? experiment both affected the quantification of the multi-component relaxation. The transitions between a mono-component and multi-components in cartilage under various experimental conditions call for the extra caution in interpreting the relaxation results.
Reusable Launch Vehicle Control in Multiple Time Scale Sliding Modes
NASA Technical Reports Server (NTRS)
Shtessel, Yuri
1999-01-01
A reusable launch vehicle control problem during ascent is addressed via multiple-time scaled continuous sliding mode control. The proposed sliding mode controller utilizes a two-loop structure and provides robust, de-coupled tracking of both orientation angle command profiles and angular rate command profiles in the presence of bounded external disturbances and plant uncertainties. Sliding mode control causes the angular rate and orientation angle tracking error dynamics to be constrained to linear, de-coupled, homogeneous, and vector valued differential equations with desired eigenvalues placement. The dual-time scale sliding mode controller was designed for the X-33 technology demonstration sub-orbital launch vehicle in the launch mode. 6DOF simulation results show that the designed controller provides robust, accurate, de-coupled tracking of the orientation angle command profiles in presence of external disturbances and vehicle inertia uncertainties. It creates possibility to operate the X-33 vehicle in an aircraft-like mode with reduced pre-launch adjustment of the control system.
Reusable Launch Vehicle Control In Multiple Time Scale Sliding Modes
NASA Technical Reports Server (NTRS)
Shtessel, Yuri; Hall, Charles; Jackson, Mark
2000-01-01
A reusable launch vehicle control problem during ascent is addressed via multiple-time scaled continuous sliding mode control. The proposed sliding mode controller utilizes a two-loop structure and provides robust, de-coupled tracking of both orientation angle command profiles and angular rate command profiles in the presence of bounded external disturbances and plant uncertainties. Sliding mode control causes the angular rate and orientation angle tracking error dynamics to be constrained to linear, de-coupled, homogeneous, and vector valued differential equations with desired eigenvalues placement. Overall stability of a two-loop control system is addressed. An optimal control allocation algorithm is designed that allocates torque commands into end-effector deflection commands, which are executed by the actuators. The dual-time scale sliding mode controller was designed for the X-33 technology demonstration sub-orbital launch vehicle in the launch mode. Simulation results show that the designed controller provides robust, accurate, de-coupled tracking of the orientation angle command profiles in presence of external disturbances and vehicle inertia uncertainties. This is a significant advancement in performance over that achieved with linear, gain scheduled control systems currently being used for launch vehicles.
Dynamic response of materials on sub-nanosecond time scales
NASA Astrophysics Data System (ADS)
Swift, Damian
2004-11-01
During the past few years, substantial progress has been made in developing experimental techniques capable of investigating the response of materials to dynamic loading on nanosecond time scales and shorter, with multiple diagnostics probing different aspects of the behavior. These relatively short time scales are scientifically interesting because plastic flow and phase changes in common materials with simple crystal structures - such as iron - may be suppressed, allowing unusual states to be induced and the dynamics of plasticity and polymorphism to be explored. Loading by laser ablation can be particularly convenient. The TRIDENT laser has been used to impart shocks and isentropic compression waves from ˜1 to 200 GPa in a range of elements and alloys, with diagnostics including surface velocimetry (line-imaging VISAR), surface displacement (framed area imaging), x-ray diffraction (single crystal and polycrystal), ellipsometry, and Raman spectroscopy. A major motivation has been the study of the properties of beryllium under conditions relevant to the ICF fuel capsule: magnetically-driven shock and isentropic compression shots at Z were used to investigate the equation of state and shock melting characteristics, complemented by laser ablation experiments to investigate plasticity and heterogeneous response. These results will help to constrain acceptable tolerances on manufacturing, and possible loading paths, for ICF ignition experiments at the National Ignition Facility. Laser-based techniques are being developed further for future material dynamics experiments at NIF, where it should be possible to obtain high quality data on strength and phase changes up to at least 1 TPa.
Nonlinear Dynamics of Extended Hydrologic Systems over long time scales
NASA Astrophysics Data System (ADS)
Lall, Upmanu
2014-05-01
We often view our knowledge of hydrology and hence of nature as intransient, at least over the time scales over which we study processes we wish to predict and understand. Over the last few decades, this assumption has come under question, largely because of the vocal expression of a changing climate, but also the recurrent demonstration of significant land use change, both of which significantly affect the boundary conditions for terrestrial hydrology that is our forte. Most recently, the concepts of hydromorphology and social hydrology have entered the discussion, and the notion that climate and hydrology influence human action, which in turn shapes hydrology, is being recognized. Finally, as a field, we seem to be coming to the conclusion that the hydrologic system is an open system, whose boundaries evolve in time, and that the hydrologic system, at many scales, has a profound effect on the systems that drive it -- whether they be the ecological and climatic systems, or the social system. What a mess! Complexity! Unpredictability! At a certain level of abstraction, one can consider the evolution of these coupled systems with nonlinear feedbacks and ask what types of questions are relevant in terms of such a coupled evolution? What are their implications at the planetary scale? What are their implications for a subsistence farmer in an arid landscape who may under external influence achieve a new transient hydro-ecological equilibrium? What are the implications for the economy and power of nations? In this talk, I will try to raise some of these questions and also provide some examples with very simple dynamical systems that suggest ways of thinking about some practical issues of feedback across climate, hydrology and human behavior.
NASA Astrophysics Data System (ADS)
Watanabe, Hiroshi
2006-05-01
The current tube models for the entanglement dynamics of flexible polymers are mostly based on the molecular picture of dynamic tube dilation (DTD). The full-DTD picture, assuming the equivalence of the relaxed portions of the chains and a simple solvent at any time t, fails for binary blends of long and short linear polyisoprene (PI) chains at intermediate t, as revealed from comparison of viscoelastic and dielectric data. In contrast, the data are well described with the partial-DTD picture that considers the extent of DTD determined by the constraint release (CR) process and achieves consistent coarse-graining of the length and time scales. The failure of the full-DTD picture and success of partial-DTD picture are noted also for star-branched PI chains. The partial-DTD picture would serve as a good starting point for constructing refined molecular models for entangled polymers.
NASA Astrophysics Data System (ADS)
Montero, R.; Conde, A. Peralta; Castano, F.; Longarte, A.
2010-06-01
The ultrafast dynamics of the non-adiabatic coupling between the L_a(S_2)/L_b(S_1) electronic excited states of naphthalene has been investigated, regarding the coherent aspects of the preparation and subsequent relaxation of the system. This electronic coupling represents a well known case of non-adiabatic behavior that has been used for years as a benchmark to test theoretical models. The jet cooled naphthalene molecule was prepared in the L_a and L_b states by femtosecond pump pulses in the UV region (318-268 nm), while the temporal evolution of the system was tracked by multiphoton ionization of the molecule with probe pulses centered at 800 nm. The time dependent signals collected at excitation wavelengths corresponding to the weak S_0-L_b transition are dominated by the CPR (Coherent Population Transfer) effect induced by the blue-shifted stronger S_0-L_a absorption. The CPR effect results in the transient population of the L_a state during the interaction of the pump pulse with the system, revealing the coherent nature of the excitation process. The transients collected after excitation to the L_a state reveal the ultrafast relaxation to the strongly coupled L_b state. The electronic and/or vibrational nature of the periodic recurrences observed along the relaxation of the electronic population will be discussed.
NASA Astrophysics Data System (ADS)
Grigonis, R.; Derevyanko, Nadezhda A.; Ishchenko, Aleksandr A.; Sirutkaitis, V. A.
2001-11-01
The relaxation times ? of the bleached states of polymethine dyes absorbing light in the 750 — 850-nm are determined by the direct pump — probe method. The effect of the dye structure and the solvent type on the relaxation time is discussed. The role of different intra- and intermolecular interactions in the relaxation of excited electronic states of the dyes is analysed. Polymethine dyes are found (with ?=11 — 75 ps) that are promising for passive mode locking in Cr3+:LiCaAlF6, Cr3+:KZnF3, and Cr3+:LiSrAlF6 crystal lasers.
Critical time scales for advection-diffusion-reaction processes
NASA Astrophysics Data System (ADS)
Ellery, Adam J.; Simpson, Matthew J.; McCue, Scott W.; Baker, Ruth E.
2012-04-01
The concept of local accumulation time (LAT) was introduced by Berezhkovskii and co-workers to give a finite measure of the time required for the transient solution of a reaction-diffusion equation to approach the steady-state solution [A. M. Berezhkovskii, C. Sample, and S. Y. Shvartsman, Biophys. J.BIOJAU0006-349510.1016/j.bpj.2010.07.045 99, L59 (2010); A. M. Berezhkovskii, C. Sample, and S. Y. Shvartsman, Phys. Rev. EPLEEE81539-375510.1103/PhysRevE.83.051906 83, 051906 (2011)]. Such a measure is referred to as a critical time. Here, we show that LAT is, in fact, identical to the concept of mean action time (MAT) that was first introduced by McNabb [A. McNabb and G. C. Wake, IMA J. Appl. Math.IJAMDM0272-496010.1093/imamat/47.2.193 47, 193 (1991)]. Although McNabb's initial argument was motivated by considering the mean particle lifetime (MPLT) for a linear death process, he applied the ideas to study diffusion. We extend the work of these authors by deriving expressions for the MAT for a general one-dimensional linear advection-diffusion-reaction problem. Using a combination of continuum and discrete approaches, we show that MAT and MPLT are equivalent for certain uniform-to-uniform transitions; these results provide a practical interpretation for MAT by directly linking the stochastic microscopic processes to a meaningful macroscopic time scale. We find that for more general transitions, the equivalence between MAT and MPLT does not hold. Unlike other critical time definitions, we show that it is possible to evaluate the MAT without solving the underlying partial differential equation (pde). This makes MAT a simple and attractive quantity for practical situations. Finally, our work explores the accuracy of certain approximations derived using MAT, showing that useful approximations for nonlinear kinetic processes can be obtained, again without treating the governing pde directly.
Modelling Time and Length Scales of Scour Around a Pipeline
NASA Astrophysics Data System (ADS)
Smith, H. D.; Foster, D. L.
2002-12-01
The scour and burial of submarine objects is an area of interest for engineers, oceanographers and military personnel. Given the limited availability of field observations, there exists a need to accurately describe the hydrodynamics and sediment response around an obstacle using numerical models. In this presentation, we will compare observations of submarine pipeline scour with model predictions. The research presented here uses the computational fluid dynamics (CFD) model FLOW-3D. FLOW-3D, developed by Flow Science in Santa Fe, NM, is a 3-dimensional finite-difference model that solves the Navier-Stokes and continuity equations. Using the Volume of Fluid (VOF) technique, FLOW-3D is able to resolve fluid-fluid and fluid-air interfaces. The FAVOR technique allows for complex geometry to be resolved with rectangular grids. FLOW-3D uses a bulk transport method to describe sediment transport and feedback to the hydrodynamic solver is accomplished by morphology evolution and fluid viscosity due to sediment suspension. Previous investigations by the authors have shown FLOW-3D to well-predict the hydrodynamics around five static scoured bed profiles and a stationary pipeline (``Modelling of Flow Around a Cylinder Over a Scoured Bed,'' submit to Journal of Waterway, Port, Coastal, and Ocean Engineering). Following experiments performed by Mao (1986, Dissertation, Technical University of Denmark), we will be performing model-data comparisons of length and time scales for scour around a pipeline. Preliminary investigations with LES and k-? closure schemes have shown that the model predicts shorter time scales in scour hole development than that observed by Mao. Predicted time and length scales of scour hole development are shown to be a function of turbulence closure scheme, grain size, and hydrodynamic forcing. Subsequent investigations consider variable wave-current flow regimes and object burial. This investigation will allow us to identify different regimes for the scour process based on dimensionless parameters such as the Reynolds number, the Keulegan-Carpenter number, and the sediment mobility number. This research is sponsored by the Office of Naval Research - Mine Burial Program.
Scale Analysis of Convective Activity on Titan: Is the Surface Setting the Time Scale?
NASA Astrophysics Data System (ADS)
Ingersoll, A. P.; Roe, H. G.; Schaller, E. L.; Brown, M. E.
2005-08-01
A fundamental number for convective activity is the time tau needed to re-humidify the atmosphere. This is M/E, where M is the mass of condensate per unit area (50 kg/m2 for Earth) and E is the evaporation rate (1.5 m of liquid water/yr). Alternately, tau is ML/F, where L is the latent heat of vaporization and F is the surface heat flux (125 W/m2 for Earth). With these numbers, tau = 12 days for Earth. This number also controls the time that a parcel spends in the descending branch of the Hadley cell, since the parcel must radiate away the heat of vaporization that it gained in the ascending branch. Tropical convective activity fluctuates on comparable time scales. Equatorial wave disturbances propagate to the west with a period of 4-5 days (Holton, 2004, p. 375). The equatorial intraseasonal oscillation, also known as the Madden-Julian oscillation (MJO), propagates to the east on a timescale of 30-60 days (Holton, 2004, p. 385). These bracket the time scale tau. Other oscillations like El Nino Southern Oscillation (ENSO) and the quasi-biennial oscillation (QBO) involve the oceans and the stratosphere, and are less relevant to the timescales of tropical convection. The value of tau for Titan is hundreds of times greater than for Earth, because the surface heat flux is much less and the latent heat content is about the same as on Earth. The polar cloud outbreaks at intervals of months around Titan's southern summer solstice are then a puzzle, as are the short-term variations of mid-latitude clouds observed after the solstice. One possibility (Roe et al., 2005, submitted; Schaller et al., 2005, submitted) is that the clouds originate from eruptions at the surface, which is controlling the variability of the atmosphere.
Response time of large-scale electrochromic devices
Randin, J.P. [ASULAB S.A., Neuchatel (Switzerland)
1990-12-31
The studies related to electrochromic phenomena performed in the seventies were mainly aimed at the development of information displays. Such applications require small electrode sizes, i.e. with active surface areas of between about 0.01 to 10 cm{sup 2}. The development of large information devices and chiefly smart windows require much larger switching areas. This paper deals with the influence of increasing the active surface area on the response time. The latter depends on both properties of the cell components (transparent conducting layer, electrochromic film, electrolyte and counter electrode) and structure of the cell (size, shape, gap, resistivity of the busbar). Experimental devices were constructed with given components and cell geometry. The effect of a series resistance arisen mainly from the cell size was investigated and explained by the effect of the additional series resistance on the response time of a diffusion-controlled process. The study indicates that the scaling-up of WO{sub 3} devices will be limited by an increase of the response time with increasing active area.
Variations in solar Lyman alpha irradiance on short time scales
NASA Technical Reports Server (NTRS)
Pap, J. M.
1992-01-01
Variations in solar UV irradiance at Lyman alpha are studied on short time scales (from days to months) after removing the long-term changes over the solar cycle. The SME/Lyman alpha irradiance is estimated from various solar indices using linear regression analysis. In order to study the nonlinear effects, Lyman alpha irradiance is modeled with a 5th-degree polynomial as well. It is shown that the full-disk equivalent width of the He line at 1083 nm, which is used as a proxy for the plages and active network, can best reproduce the changes observed in Lyman alpha. Approximately 72 percent of the solar-activity-related changes in Lyman alpha irradiance arise from plages and the network. The network contribution is estimated by the correlation analysis to be about 19 percent. It is shown that significant variability remains in Lyman alpha irradiance, with periods around 300, 27, and 13.5d, which is not explained by the solar activity indices. It is shown that the nonlinear effects cannot account for a significant part of the unexplained variation in Lyman alpha irradiance. Therefore, additional events (e.g., large-scale motions and/or a systematic difference in the area and intensity of the plages and network observed in the lines of Ca-K, He 1083, and Lyman alpha) may explain the discrepancies found between the observed and estimated irradiance values.
Scale relativity and fractal space-time: theory and applications
Laurent Nottale
2008-12-19
In the first part of this contribution, we review the development of the theory of scale relativity and its geometric framework constructed in terms of a fractal and nondifferentiable continuous space-time. This theory leads (i) to a generalization of possible physically relevant fractal laws, written as partial differential equation acting in the space of scales, and (ii) to a new geometric foundation of quantum mechanics and gauge field theories and their possible generalisations. In the second part, we discuss some examples of application of the theory to various sciences, in particular in cases when the theoretical predictions have been validated by new or updated observational and experimental data. This includes predictions in physics and cosmology (value of the QCD coupling and of the cosmological constant), to astrophysics and gravitational structure formation (distances of extrasolar planets to their stars, of Kuiper belt objects, value of solar and solar-like star cycles), to sciences of life (log-periodic law for species punctuated evolution, human development and society evolution), to Earth sciences (log-periodic deceleration of the rate of California earthquakes and of Sichuan earthquake replicas, critical law for the arctic sea ice extent) and tentative applications to system biology.
Polaronic relaxation in perovskites
O. Bidault; M. Maglione; M. Actis; M. Kchikech; B. Salce
1995-01-01
We report a low-temperature loss anomaly in several oxidic perovskites such as KTaO3, KTaO3:Nb, SrTiO3, SrTiO3:Ca, PbTiO3:La, Cu, and BaTiO3:La. We show that this anomaly arises from a low-frequency dielectric relaxation. The activation energy and the relaxation time of this process are nearly the same for all the investigated perovskites disregarding their composition, texture, and ferroelectric properties. We thus ascribe
Ion time scale dispersion relations and fluctuations at comets
NASA Astrophysics Data System (ADS)
Gunell, Herbert; Nilsson, Hans; Eriksson, Anders; Wedlund, Cyril Simon; Stenberg Wieser, Gabriella; Kallio, Esa; Yamauchi, Masatoshi; Behar, Etienne; Maggiolo, Romain; Dhooghe, Frederik; De Keyser, Johan
2015-04-01
The Rosetta spacecraft has been accompanying comet 67P/Churyumov-Gerasimenko since 2014. As the comet approached the sun, the outgassing rate increased, and the thus created neutral atmosphere started to interact with the solar wind. The Rosetta Plasma Consortium (RPC) ion instruments have observed these interaction processes at this low activity comet. These observations include deflection of solar wind protons and alpha particles; singly charged helium ions being produced in charge exchange collisions between solar wind alpha particles and cometary neutrals; and water ions of cometary origin that have been accelerated by the solar wind electric field. These populations combine to form an ion distribution function. We use the RPC Ion Composition Analyser (RPC-ICA) to measure that distribution function, which we then analyse for fluctuations and dispersion relations on the ion time scale.
Time-scale modelling of the invasive species Robinia pseudoacacia
NASA Astrophysics Data System (ADS)
Tomaž, Podobnikar; Andraž, Ä.?Arni; Imelda, Somodi
2010-05-01
Our contribution is part of the TransEcoNet project (Transnational Ecological Networks in Central Europe) that aims to investigate transboundary ecological networks across Central Europe. An objective of this project is to contribute towards awareness rising on the value and role of ecological networks. This poster presents the activities that are carried out in Pomurje region, Slovenia as our case study area. Pomurje region borders with Austria in the north, to Hungary in the east, and to Croatia in the south. We are investigating the spread of the invasive species Robinia pseudacacia and the underlying causes, and assess landscape scale ecological dynamics (e.g. Mura River floodplains) in ecological networks. The study comprises investigation and mapping of the R. pseudacacia spread with time-series analysis to understand its spatial dynamics. The preliminary studies show that the R. pseudacacia had the most expanded in the region since 1980s. Some of the surfaces were cut and converted back to fields. This reflects the socioeconomic situation in the region. The further study will include statistic, GIS (geographical information systems) and remote sensing techniques. We will apply various character data: satellite imagery, IR-orthophotos, digital elevation models, including LIDAR, contemporary and historical maps, and other spatial/non-spatial data sources. The outputs will include reconstruction of R. pseudacacia-dynamics in the recent decade, modelling the distribution of R. pseudacacia in relation to abiotic environmental factors and land use, and modelling (prediction) the expected distribution of R. pseudacacia in case of climate and land use change. Keywords: invasive species, Robinia pseudacacia, spatial analysis, time-scale analysis, remote sensing, land use change, climate change
Water relations and leaf expansion: importance of time scale.
Munns, R; Passioura, J B; Guo, J; Chazen, O; Cramer, G R
2000-09-01
The role of leaf water relations in controlling cell expansion in leaves of water-stressed maize and barley depends on time scale. Sudden changes in leaf water status, induced by sudden changes in humidity, light and soil salinity, greatly affect leaf elongation rate, but often only transiently. With sufficiently large changes in salinity, leaf elongation rates are persistently reduced. When plants are kept fully turgid throughout such sudden environmental changes, by placing their roots in a pressure chamber and raising the pressure so that the leaf xylem sap is maintained at atmospheric pressure, both the transient and persistent changes in leaf elongation rate disappear. All these responses show that water relations are responsible for the sudden changes in leaf elongation rate resulting from sudden changes in water stress and putative root signals play no part. However, at a time scale of days, pressurization fails to maintain high rates of leaf elongation of plants in either saline or drying soil, indicating that root signals are overriding water relations effects. In both saline and drying soil, pressurization does raise the growth rate during the light period, but a subsequent decrease during the dark results in no net effect on leaf growth over a 24 h period. When transpirational demand is very high, however, growth-promoting effects of pressurization during the light period outweigh any reductions in the dark, resulting in a net increase in growth of pressurized plants over 24 h. Thus leaf water status can limit leaf expansion rates during periods of high transpiration despite the control exercised by hormonal effects on a 24 h basis. PMID:11006301
Das, Anuradha; Das, Suman; Biswas, Ranjit
2015-01-21
Temperature dependent relaxation dynamics, particle motion characteristics, and heterogeneity aspects of deep eutectic solvents (DESs) made of acetamide (CH3CONH2) and urea (NH2CONH2) have been investigated by employing time-resolved fluorescence measurements and all-atom molecular dynamics simulations. Three different compositions (f) for the mixture [fCH3CONH2 + (1 - f)NH2CONH2] have been studied in a temperature range of 328-353 K which is ?120-145 K above the measured glass transition temperatures (?207 K) of these DESs but much lower than the individual melting temperature of either of the constituents. Steady state fluorescence emission measurements using probe solutes with sharply different lifetimes do not indicate any dependence on excitation wavelength in these metastable molten systems. Time-resolved fluorescence anisotropy measurements reveal near-hydrodynamic coupling between medium viscosity and rotation of a dissolved dipolar solute. Stokes shift dynamics have been found to be too fast to be detected by the time-resolution (?70 ps) employed, suggesting extremely rapid medium polarization relaxation. All-atom simulations reveal Gaussian distribution for particle displacements and van Hove correlations, and significant overlap between non-Gaussian (?2) and new non-Gaussian (?) heterogeneity parameters. In addition, no stretched exponential relaxations have been detected in the simulated wavenumber dependent acetamide dynamic structure factors. All these results are in sharp contrast to earlier observations for ionic deep eutectics with acetamide [Guchhait et al., J. Chem. Phys. 140, 104514 (2014)] and suggest a fundamental difference in interaction and dynamics between ionic and non-ionic deep eutectic solvent systems. PMID:25612718
NASA Astrophysics Data System (ADS)
Das, Anuradha; Das, Suman; Biswas, Ranjit
2015-01-01
Temperature dependent relaxation dynamics, particle motion characteristics, and heterogeneity aspects of deep eutectic solvents (DESs) made of acetamide (CH3CONH2) and urea (NH2CONH2) have been investigated by employing time-resolved fluorescence measurements and all-atom molecular dynamics simulations. Three different compositions (f) for the mixture [fCH3CONH2 + (1 - f)NH2CONH2] have been studied in a temperature range of 328-353 K which is ˜120-145 K above the measured glass transition temperatures (˜207 K) of these DESs but much lower than the individual melting temperature of either of the constituents. Steady state fluorescence emission measurements using probe solutes with sharply different lifetimes do not indicate any dependence on excitation wavelength in these metastable molten systems. Time-resolved fluorescence anisotropy measurements reveal near-hydrodynamic coupling between medium viscosity and rotation of a dissolved dipolar solute. Stokes shift dynamics have been found to be too fast to be detected by the time-resolution (˜70 ps) employed, suggesting extremely rapid medium polarization relaxation. All-atom simulations reveal Gaussian distribution for particle displacements and van Hove correlations, and significant overlap between non-Gaussian (?2) and new non-Gaussian (?) heterogeneity parameters. In addition, no stretched exponential relaxations have been detected in the simulated wavenumber dependent acetamide dynamic structure factors. All these results are in sharp contrast to earlier observations for ionic deep eutectics with acetamide [Guchhait et al., J. Chem. Phys. 140, 104514 (2014)] and suggest a fundamental difference in interaction and dynamics between ionic and non-ionic deep eutectic solvent systems.
NASA Astrophysics Data System (ADS)
Dimitrakopoulos, Panagiotis; Dissanayake, Inuka D.
2003-11-01
This talk considers the relaxation of a single stiff polymer chain from an initial straight configuration in a viscous solvent. Examples of stiff polymers include biopolymers such as actin filaments and microtubules, as well as a host of stiff synthetic polymers such as Kevlar and polyesters. To study this problem, Brownian Dynamics simulations based on a discretized version of the wormlike model are employed. The relaxation of the full stress tensor is presented over a broad range of time scales, polymer lengths and chain stiffness. The configuration relaxation is presented over the same extended time periods as the stress relaxation; this is achieved by employing proper conformational functions and applying the scaling law methodology. Based on this coupling, the polymer relaxation is shown to have two intermediate-time behaviors; an explanation for this finding is provided. The anisotropy of the stress relaxation at both early and late intermediate times is shown to result from the corresponding anisotropy in the configuration relaxation. This work is partially supported by the Minta Martin Research Fund at the University of Maryland, the National Center for Supercomputing Applications in Illinois and an Academic Equipment Grant from Sun Microsystems Inc.
Use of a Walk Through Time to Facilitate Student Understandings of the Geological Time Scale
NASA Astrophysics Data System (ADS)
Shipman, H. L.
2004-12-01
Students often have difficulties in appreciating just how old the earth and the universe are. While they can simply memorize a number, they really do not understand just how big that number really is, in comparison with other, more familiar student referents like the length of a human lifetime or how long it takes to eat a pizza. (See, e.g., R.D. Trend 2001, J. Research in Science Teaching 38(2): 191-221) Students, and members of the general public, also display such well-known misconceptions as the "Flintstone chronology" of believing that human beings and dinosaurs walked the earth at the same time. (In the classic American cartoon "The Flintstones," human beings used dinosaurs as draft animals. As scientists we know this is fiction, but not all members of the public understand that.) In an interdisciplinary undergraduate college class that dealt with astronomy, cosmology, and biological evolution, I used a familiar activity to try to improve student understanding of the concept of time's vastness. Students walked through a pre-determined 600-step path which provided a spatial analogy to the geological time scale. They stopped at various points and engaged in some pre-determined discussions and debates. This activity is as old as the hills, but reports of its effectiveness or lack thereof are quite scarce. This paper demonstrates that this activity was effective for a general-audience, college student population in the U.S. The growth of student understandings of the geological time scale was significant as a result of this activity. Students did develop an understanding of time's vastness and were able to articulate this understanding in various ways. This growth was monitored through keeping track of several exam questions and through pre- and post- analysis of student writings. In the pre-writings, students often stated that they had "no idea" about how to illustrate the size of the geological time scale to someone else. While some post-time walk responses simply restated what was done in the walk through time, some students were able to develop their own ways of conceptualizing the vastness of the geological time scale. A variety of findings from student understandings will be presented. This work has been supported in part by the Distinguished Scholars Program of the National Science Foundation (DUE-0308557).
Observing real time motion of nano-scale objects
NASA Astrophysics Data System (ADS)
van de Vondel, Joris; Timmermans, Matias; Samuely, Tomás; Raes, Bart; Serrier-Garcia, Lise; Moshchalkov, Victor
2015-03-01
The dynamics of nanoscale objects is a very interesting field of research with a strong technological impact. Still, the combination of a technique resolving (sub)nanometer particles within a time frame relevant to observe dynamics is a very challenging task. Due to the inherent atomic-scale resolution, scanning tunneling microscopy (STM) is an ideal candidate to achieve this goal. Nevertheless, in most physical systems the dynamic events of the objects under investigation cannot be resolved by conventional STM image acquisition and will only reveal an average trace of the moving object. This is why a strong drive exists to develop new functionalities of STM, which allow studying dynamic events at the nanoscale. We address this issue, for vortex matter in NbSe2, by driving the vortices using an ac magnetic field and probing the induced periodic tunnel current modulations. Our results reveal different dynamical modes of the driven vortex lattice. In addition, by extending a known functionality of STM, (i.e. the `Lazy Fisherman' technique) we can use single pixel information to obtain the overall dynamics of the vortex lattice with submillisecond time resolution and subnanometer spatial resolution. This work is supported by the FWO and the Methusalem funding of the Flemish government.
Effects of relaxation on psychobiological wellbeing during pregnancy: a randomized controlled trial.
Urech, Corinne; Fink, Nadine S; Hoesli, Irène; Wilhelm, Frank H; Bitzer, Johannes; Alder, Judith
2010-10-01
Prenatal maternal stress is associated with adverse birth outcomes and may be reduced by relaxation exercises. The aim of the present study was to compare the immediate effects of two active and one passive 10-min relaxation technique on perceived and physiological indicators of relaxation. 39 healthy pregnant women recruited at the outpatient department of the University Women's Hospital Basel participated in a randomized controlled trial with an experimental repeated measure design. Participants were assigned to one of two active relaxation techniques, progressive muscle relaxation (PMR) or guided imagery (GI), or a passive relaxation control condition. Self-reported relaxation on a visual analogue scale (VAS) and state anxiety (STAI-S), endocrine parameters indicating hypothalamic-pituitary-adrenal (HPA) axis (cortisol and ACTH) and sympathetic-adrenal-medullary (SAM) system activity (norepinephrine and epinephrine), as well as cardiovascular responses (heart rate, systolic and diastolic blood pressure) were measured at four time points before and after the relaxation exercise. Between group differences showed, that compared to the PMR and control conditions, GI was significantly more effective in enhancing levels of relaxation and together with PMR, GI was associated with a significant decrease in heart rate. Within the groups, passive as well as active relaxation procedures were associated with a decline in endocrine measures except epinephrine. Taken together, these data indicate that different types of relaxation had differential effects on various psychological and biological stress systems. GI was especially effective in inducing self-reported relaxation in pregnant women while at the same time reducing cardiovascular activity. PMID:20417038
Geometric integrators for multiple time-scale simulation
NASA Astrophysics Data System (ADS)
Jia, Zhidong; Leimkuhler, Ben
2006-05-01
In this paper, we review and extend recent research on averaging integrators for multiple time-scale simulation such as are needed for physical N-body problems including molecular dynamics, materials modelling and celestial mechanics. A number of methods have been proposed for direct numerical integration of multiscale problems with special structure, such as the mollified impulse method (Garcia-Archilla, Sanz-Serna and Skeel 1999 SIAM J. Sci. Comput. 20 930-63) and the reversible averaging method (Leimkuhler and Reich 2001 J. Comput. Phys. 171 95-114). Features of problems of interest, such as thermostatted coarse-grained molecular dynamics, require extension of the standard framework. At the same time, in some applications the computation of averages plays a crucial role, but the available methods have deficiencies in this regard. We demonstrate that a new approach based on the introduction of shadow variables, which mirror physical variables, has promised for broadening the usefulness of multiscale methods and enhancing accuracy of or simplifying computation of averages. The shadow variables must be computed from an auxiliary equation. While a geometric integrator in the extended space is possible, in practice we observe enhanced long-term energy behaviour only through use of a variant of the method which controls drift of the shadow variables using dissipation and sacrifices the formal geometric properties such as time-reversibility and volume preservation in the enlarged phase space, stabilizing the corresponding properties in the physical variables. The method is applied to a gravitational three-body problem as well as a partially thermostatted model problem for a dilute gas of diatomic molecules.
Studying the Dynamics of Problem Behavior Across Multiple Time Scales: Prospects and Challenges
George W. Howe
2004-01-01
As a commentary on the Special Issue, this paper discusses recent advances in the study of change across several time scales. It points out the importance of specifying time scales and putative patterns of change when characterizing problem behavior over developmental time scales. Methods for studying risk and protective mechanisms through observation of social interaction are also discussed as a
Dielectric Relaxation of Aqueous Trimethylamineoxide Solutions
Toshiyuki Shikata; Shyuji Itatani
2002-01-01
Dielectric relaxation was examined for aqueous trimethylamineoxide (TMAO) solutions over a wide concentration (c) range. The dielectric relaxation of TMAO was described by a Debye-type function with a relaxation time of about 3 × 10-11 s, with the strength proportional to c. The number of water molecules tightly hydrated to unprotonated TMAO was estimated to be two. Ab initio calculations
NASA Astrophysics Data System (ADS)
Okamoto, Hiromi; Hayashi, Hidenori; Yoshihara, Keitaro; Tasumi, Mitsuo
1991-07-01
Femtosecond time-resolved coherent anti-Stokes Raman scattering has been observed from two carotenoids, rhodopin and spirilloxanthin, in vivo and in vitro. Intracytoplasmic membranes of a species of photosynthetic bacteria have been used as the in vivo sample where the carotenoids exist in the pigment—protein complexes. The vibrational phase relaxation rate in vitro is almost the same as that of ?-carotene previously reported, but that in vivo is definitely faster.
NASA Astrophysics Data System (ADS)
Fitz, Benjamin David
Segmental dynamics are investigated in model compounds, polymers, and network-forming polymers. Two aspects of these materials are investigated: (1) the role of molecular structure and connectivity on determining the characteristics of the segmental relaxation, and (2) monitoring the variations in the segmental dynamics during network-forming chemical reactions. We quantify the most important aspects of the dynamics: the relaxation shape, the relaxation strength, the relaxation time, and the temperature dependencies of these properties. Additionally, two general segmental dynamics issues of interest are the length-scale and the homogeneous/heterogeneous aspects. A judicious choice of network-forming polymer provides for the determination of an upper bound on the length-scale. A comparison of relaxation characteristics between dynamic light scattering (measuring density fluctuations) and dielectric relaxation spectroscopy (measuring segmental dipolar reorientation) provides one evaluation of the heterogeneity issue. Dipole dynamics in small molecule model compounds show the influence of molecular connectivity on the cooperative molecular response associated with the glass transition. A rigid, nonpolar, cyanate ester network is shown to develop an anomalous relaxation process during crosslinking. A specific local mode of motion is assigned. Additionally, the main relaxation becomes extraordinarily broad during the course of the network formation, due to markedly increased segmental rigidity and loss of configurational entropy.
Leone, Nancy; Villari, Valentina; Micali, Norberto [CNR-Istituto per i Processi Chimico-Fisici, V.le F. Stagno D'Alcontres 37, 98158 Messina (Italy)
2012-08-15
We present a simple, compact, and versatile experimental setup working in the heterodyne detection mode with modulation of the reference beam. The system is implemented with a collection optics based on a unimodal optical fiber coupler. This choice allows the heterodyne to be used in a wide range of scattering angles, even for very small ones, without losing the optical beating. The apparatus can be successfully used to study translational diffusive dynamics of dispersed particles at scattering angles smaller than 5 Degree-Sign and it is suitable for exploring slow relaxation processes in sub-Hertz frequency domain, for example, in glass-forming systems. It is also possible to measure the electrophoretic mobility by applying an electric field into a charged particles solution.
NASA Astrophysics Data System (ADS)
Wilson, Gregory J.
Nuclear magnetic resonance relaxation measurements of 129Xe in tissue homogenates and blood were performed to explore the feasibility of magnetic resonance (MR) imaging of laser-polarized (LP) 129Xe in tissues. Laser polarization of 129Xe by optical pumping and spin exchange increases the signal obtained from 129Xe to a sufficient level that, after inhalation of LP 129Xe, it may be detected by MR throughout the body. Image signal-to-noise ratio (SNR) will depend on longitudinal (T1) and transverse (T2) relaxation times of 129Xe in tissues and blood. 129Xe T1 and T2 were measured at 9.4 T and 10°C in rat whole blood and homogenates of rat liver, brain, kidney, and lung at varying oxygenation levels. T1 values ranged from 4.4 +/- 0.4 to 22 +/- 2 s. T2 values ranged from 1.4 +/- 1.0 to 7.00 +/- 0.09 ms. Oxygenation dependence of the relaxation times varied between tissues. The observed oxygen dependence suggests relaxation due to paramagnetic deoxyhemoglobin dominates that due to free oxygen in tissues with sufficiently high fractions of blood. In addition, T1 and T2 of 129Xe in separated blood plasma were measured at both 9.4 and 1.89 T to explore the dependence on field strength. T1 of 129Xe in plasma decreased from 46 +/- 8 to 20 +/- 3 s and T2 increased from 11 +/- 2 to 127 +/- 8 ms when the field strength decreased from 9.4 to 1.89 T. When an inhalation model of gas delivery to tissue is used, the expected intrinsic SNR for LP 129Xe in gray matter at 9.4 T is approximately 3% of the conventional proton intrinsic SNR at 1.5 T. Short 129Xe T2 values (at 9.4 T) and the finite amount of magnetization available for imaging LP 129Xe further reduce the expected image SNR compared to conventional proton imaging. Several common pulse sequences were modeled to predict their relative effectiveness for imaging LP 129Xe at both 9.4 and 1.89 T. Each modeled sequence predicted higher SNR at 1.89 that at 9.4 T.