Truncation of scales by time relaxation
NASA Astrophysics Data System (ADS)
Layton, William; Neda, Monika
2007-01-01
We study a time relaxation regularization of flow problems proposed and tested extensively by Stolz and Adams. The aim of the relaxation term is to drive the unresolved fluctuations in a computational simulation to zero exponentially fast by an appropriate and often problem dependent choice of its coefficient; this relaxation term is thus intermediate between a tunable numerical stabilization and a continuum modeling term. Our aim herein is to understand how this term, by itself, acts to truncate solution scales and to use this understanding to give insight into parameter selection.
Current relaxation time scales in toroidal plasmas
Mikkelsen, D.R.
1987-02-01
An approximate normal mode analysis of plasma current diffusion in tokamaks is presented. The work is based on numerical solutions of the current diffusion equation in cylindrical geometry. Eigenvalues and eigenfunctions are shown for a broad range of plasma conductivity profile shapes. Three classes of solutions are considered which correspond to three types of tokamak operation. Convenient approximations to the three lowest eigenvalues in each class are presented and simple formulae for the current relaxation time scales are given.
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.
Effects of bulk charge and momentum relaxation time scales on ac electrospraying
Chang, Hsueh-Chia
to the interfacial charge, the liquid meniscus sta- bilizes into a conical shape.3 A thin, steady charged jet conEffects of bulk charge and momentum relaxation time scales on ac electrospraying Siddharth that the critical period is approximately 20 times the bulk charge relaxation time scale; the mode transition takes
Active open boundary forcing using dual relaxation time-scales in downscaled ocean models
NASA Astrophysics Data System (ADS)
Herzfeld, M.; Gillibrand, P. A.
2015-05-01
Regional models actively forced with data from larger scale models at their open boundaries often contain motion at different time-scales (e.g. tidal and low frequency). These motions are not always individually well specified in the forcing data, and one may require a more active boundary forcing while the other exert less influence on the model interior. If a single relaxation time-scale is used to relax toward these data in the boundary equation, then this may be difficult. The method of fractional steps is used to introduce dual relaxation time-scales in an open boundary local flux adjustment scheme. This allows tidal and low frequency oscillations to be relaxed independently, resulting in a better overall solution than if a single relaxation parameter is optimized for tidal (short relaxation) or low frequency (long relaxation) boundary forcing. The dual method is compared to the single relaxation method for an idealized test case where a tidal signal is superimposed on a steady state low frequency solution, and a real application where the low frequency boundary forcing component is derived from a global circulation model for a region extending over the whole Great Barrier Reef, and a tidal signal subsequently superimposed.
NASA Astrophysics Data System (ADS)
Ngai, K. L.; Habasaki, J.; Prevosto, D.; Capaccioli, S.; Paluch, Marian
2012-07-01
By now it is well established that the structural ?-relaxation time, ??, of non-associated small molecular and polymeric glass-formers obey thermodynamic scaling. In other words, ?? is a function ? of the product variable, ??/T, where ? is the density and T the temperature. The constant ? as well as the function, ?? = ?(??/T), is material dependent. Actually this dependence of ?? on ??/T originates from the dependence on the same product variable of the Johari-Goldstein ?-relaxation time, ??, or the primitive relaxation time, ?0, of the coupling model. To support this assertion, we give evidences from various sources itemized as follows. (1) The invariance of the relation between ?? and ?? or ?0 to widely different combinations of pressure and temperature. (2) Experimental dielectric and viscosity data of glass-forming van der Waals liquids and polymer. (3) Molecular dynamics simulations of binary Lennard-Jones (LJ) models, the Lewis-Wahnström model of ortho-terphenyl, 1,4 polybutadiene, a room temperature ionic liquid, 1-ethyl-3-methylimidazolium nitrate, and a molten salt 2Ca(NO3)2.3KNO3 (CKN). (4) Both diffusivity and structural relaxation time, as well as the breakdown of Stokes-Einstein relation in CKN obey thermodynamic scaling by ??/T with the same ?. (5) In polymers, the chain normal mode relaxation time, ?N, is another function of ??/T with the same ? as segmental relaxation time ??. (6) While the data of ?? from simulations for the full LJ binary mixture obey very well the thermodynamic scaling, it is strongly violated when the LJ interaction potential is truncated beyond typical inter-particle distance, although in both cases the repulsive pair potentials coincide for some distances.
Ngai, K L; Habasaki, J; Prevosto, D; Capaccioli, S; Paluch, Marian
2012-07-21
By now it is well established that the structural ?-relaxation time, ?(?), of non-associated small molecular and polymeric glass-formers obey thermodynamic scaling. In other words, ?(?) is a function ? of the product variable, ?(?)/T, where ? is the density and T the temperature. The constant ? as well as the function, ?(?) = ?(?(?)/T), is material dependent. Actually this dependence of ?(?) on ?(?)/T originates from the dependence on the same product variable of the Johari-Goldstein ?-relaxation time, ?(?), or the primitive relaxation time, ?(0), of the coupling model. To support this assertion, we give evidences from various sources itemized as follows. (1) The invariance of the relation between ?(?) and ?(?) or ?(0) to widely different combinations of pressure and temperature. (2) Experimental dielectric and viscosity data of glass-forming van der Waals liquids and polymer. (3) Molecular dynamics simulations of binary Lennard-Jones (LJ) models, the Lewis-Wahnström model of ortho-terphenyl, 1,4 polybutadiene, a room temperature ionic liquid, 1-ethyl-3-methylimidazolium nitrate, and a molten salt 2Ca(NO(3))(2)·3KNO(3) (CKN). (4) Both diffusivity and structural relaxation time, as well as the breakdown of Stokes-Einstein relation in CKN obey thermodynamic scaling by ?(?)/T with the same ?. (5) In polymers, the chain normal mode relaxation time, ?(N), is another function of ?(?)/T with the same ? as segmental relaxation time ?(?). (6) While the data of ?(?) from simulations for the full LJ binary mixture obey very well the thermodynamic scaling, it is strongly violated when the LJ interaction potential is truncated beyond typical inter-particle distance, although in both cases the repulsive pair potentials coincide for some distances. PMID:22830715
Schwerdtfeger, Christine A.; Soudackov, Alexander V.; Hammes-Schiffer, Sharon
2014-01-21
The development of efficient theoretical methods for describing electron transfer (ET) reactions in condensed phases is important for a variety of chemical and biological applications. Previously, dynamical dielectric continuum theory was used to derive Langevin equations for a single collective solvent coordinate describing ET in a polar solvent. In this theory, the parameters are directly related to the physical properties of the system and can be determined from experimental data or explicit molecular dynamics simulations. Herein, we combine these Langevin equations with surface hopping nonadiabatic dynamics methods to calculate the rate constants for thermal ET reactions in polar solvents for a wide range of electronic couplings and reaction free energies. Comparison of explicit and implicit solvent calculations illustrates that the mapping from explicit to implicit solvent models is valid even for solvents exhibiting complex relaxation behavior with multiple relaxation time scales and a short-time inertial response. The rate constants calculated for implicit solvent models with a single solvent relaxation time scale corresponding to water, acetonitrile, and methanol agree well with analytical theories in the Golden rule and solvent-controlled regimes, as well as in the intermediate regime. The implicit solvent models with two relaxation time scales are in qualitative agreement with the analytical theories but quantitatively overestimate the rate constants compared to these theories. Analysis of these simulations elucidates the importance of multiple relaxation time scales and the inertial component of the solvent response, as well as potential shortcomings of the analytical theories based on single time scale solvent relaxation models. This implicit solvent approach will enable the simulation of a wide range of ET reactions via the stochastic dynamics of a single collective solvent coordinate with parameters that are relevant to experimentally accessible systems.
Roland, C M; Bogoslovov, R B; Casalini, R; Ellis, A R; Bair, S; Rzoska, S J; Czuprynski, K; Urban, S
2008-06-14
The longitudinal relaxation time tau of a series of alkyl-isothiocyanato-biphenyls (nBT) liquid crystals in the smectic E phase was measured as a function of temperature T and pressure P using dielectric spectroscopy. This relaxation time was found to become essentially constant, independent of T and P, at both the clearing point and the lower temperature crystalline transition. tau(T,P) could also be superposed as a function of the product TV(gamma), where V is the specific volume and gamma is a material constant. It then follows from the invariance of the relaxation time at the transition that the exponent gamma superposing tau(T,V) can be identified with the thermodynamic ratio Gamma=- partial differential log(T(c)) partial differential log(V(c)), where the subscript c denotes the value at the phase transition. Analysis of literature data on other liquid crystals shows that they likewise exhibit a constant tau at their phase transitions. Thus, there is a surprising relationship between the thermodynamic conditions defining the stability limits of a liquid crystalline phase and the dynamic properties reflected in the magnitude of the longitudinal relaxation time. PMID:18554028
Thermodynamical scaling of the low frequency relaxation time in liquid crystalline phases
NASA Astrophysics Data System (ADS)
Urban, Stanis?aw; Würflinger, Albert
2005-08-01
The low frequency relaxation times ?? , which characterize the flip-flop molecular motions in liquid crystalline phases, recently determined in high-pressure experiments for eight liquid crystalline substances, were reanalyzed considering a relation proposed for the glass-forming liquids [C. Dreyfus , Phys. Rev. E 68, 011204 (2003); R. Casalini and C. M. Roland, Phys. Rev. E 69, 062501 (2004)]. The data, measured at constant pressure, constant temperature, and constant molar volume, could be rescaled onto a master line in the ln?? vs 1/(TVm?) plot, with ? as an adjustable parameter ( Vm=1/? is the specific volume). The obtained ? values are in good agreement with other estimations; here, the value of ? parameter was determined for the crystal-like smectic- E phase.
Relaxation times estimation in MRI
NASA Astrophysics Data System (ADS)
Baselice, Fabio; Caivano, Rocchina; Cammarota, Aldo; Ferraioli, Giampaolo; Pascazio, Vito
2014-03-01
Magnetic Resonance Imaging is a very powerful techniques for soft tissue diagnosis. At the present, the clinical evaluation is mainly conducted exploiting the amplitude of the recorded MR image which, in some specific cases, is modified by using contrast enhancements. Nevertheless, spin-lattice (T1) and spin-spin (T2) relaxation times can play an important role in many pathology diagnosis, such as cancer, Alzheimer or Parkinson diseases. Different algorithms for relaxation time estimation have been proposed in literature. In particular, the two most adopted approaches are based on Least Squares (LS) and on Maximum Likelihood (ML) techniques. As the amplitude noise is not zero mean, the first one produces a biased estimator, while the ML is unbiased but at the cost of high computational effort. Recently the attention has been focused on the estimation in the complex, instead of the amplitude, domain. The advantage of working with real and imaginary decomposition of the available data is mainly the possibility of achieving higher quality estimations. Moreover, the zero mean complex noise makes the Least Square estimation unbiased, achieving low computational times. First results of complex domain relaxation times estimation on real datasets are presented. In particular, a patient with an occipital lesion has been imaged on a 3.0T scanner. Globally, the evaluation of relaxation times allow us to establish a more precise topography of biologically active foci, also with respect to contrast enhanced images.
Commonality of Elastic Relaxation Times in Biofilms
NASA Astrophysics Data System (ADS)
Shaw, T.; Winston, M.; Rupp, C. J.; Klapper, I.; Stoodley, P.
2004-08-01
Biofilms, sticky conglomerations of microorganisms and extracellular polymers, are among the Earth's most common life forms. One component for their survival is an ability to withstand external mechanical stress. Measurements indicate that biofilm elastic relaxation times are approximately the same (about 18min) over a wide sample of biofilms though other material properties vary significantly. A possible survival significance of this time scale is that it is the shortest period over which a biofilm can mount a phenotypic response to transient mechanical stress.
Wang, Shuo; Cao, Yang
2015-01-01
Random effect in cellular systems is an important topic in systems biology and often simulated with Gillespie’s stochastic simulation algorithm (SSA). Abridgment refers to model reduction that approximates a group of reactions by a smaller group with fewer species and reactions. This paper presents a theoretical analysis, based on comparison of the first exit time, for the abridgment on a linear chain reaction model motivated by systems with multiple phosphorylation sites. The analysis shows that if the relaxation time of the fast subsystem is much smaller than the mean firing time of the slow reactions, the abridgment can be applied with little error. This analysis is further verified with numerical experiments for models of bistable switch and oscillations in which linear chain system plays a critical role. PMID:26263559
First Passage Times, Lifetimes, and Relaxation Times of Unfolded Proteins
NASA Astrophysics Data System (ADS)
Dai, Wei; Sengupta, Anirvan M.; Levy, Ronald M.
2015-07-01
The dynamics of proteins in the unfolded state can be quantified in computer simulations by calculating a spectrum of relaxation times which describes the time scales over which the population fluctuations decay to equilibrium. If the unfolded state space is discretized, we can evaluate the relaxation time of each state. We derive a simple relation that shows the mean first passage time to any state is equal to the relaxation time of that state divided by the equilibrium population. This explains why mean first passage times from state to state within the unfolded ensemble can be very long but the energy landscape can still be smooth (minimally frustrated). In fact, when the folding kinetics is two-state, all of the unfolded state relaxation times within the unfolded free energy basin are faster than the folding time. This result supports the well-established funnel energy landscape picture and resolves an apparent contradiction between this model and the recently proposed kinetic hub model of protein folding. We validate these concepts by analyzing a Markov state model of the kinetics in the unfolded state and folding of the miniprotein NTL9 (where NTL9 is the N -terminal domain of the ribosomal protein L9), constructed from a 2.9 ms simulation provided by D. E. Shaw Research.
First Passage Times, Lifetimes, and Relaxation Times of Unfolded Proteins.
Dai, Wei; Sengupta, Anirvan M; Levy, Ronald M
2015-07-24
The dynamics of proteins in the unfolded state can be quantified in computer simulations by calculating a spectrum of relaxation times which describes the time scales over which the population fluctuations decay to equilibrium. If the unfolded state space is discretized, we can evaluate the relaxation time of each state. We derive a simple relation that shows the mean first passage time to any state is equal to the relaxation time of that state divided by the equilibrium population. This explains why mean first passage times from state to state within the unfolded ensemble can be very long but the energy landscape can still be smooth (minimally frustrated). In fact, when the folding kinetics is two-state, all of the unfolded state relaxation times within the unfolded free energy basin are faster than the folding time. This result supports the well-established funnel energy landscape picture and resolves an apparent contradiction between this model and the recently proposed kinetic hub model of protein folding. We validate these concepts by analyzing a Markov state model of the kinetics in the unfolded state and folding of the miniprotein NTL9 (where NTL9 is the N-terminal domain of the ribosomal protein L9), constructed from a 2.9 ms simulation provided by D. E. Shaw Research. PMID:26252709
Relaxation time in disordered molecular systems.
Rocha, Rodrigo P; Freire, José A
2015-05-28
Relaxation time is the typical time it takes for a closed physical system to attain thermal equilibrium. The equilibrium is brought about by the action of a thermal reservoir inducing changes in the system micro-states. The relaxation time is intuitively expected to increase with system disorder. We derive a simple analytical expression for this dependence in the context of electronic equilibration in an amorphous molecular system model. We find that the disorder dramatically enhances the relaxation time but does not affect its independence of the nature of the initial state. PMID:26026436
Relaxation time in disordered molecular systems
NASA Astrophysics Data System (ADS)
Rocha, Rodrigo P.; Freire, José A.
2015-05-01
Relaxation time is the typical time it takes for a closed physical system to attain thermal equilibrium. The equilibrium is brought about by the action of a thermal reservoir inducing changes in the system micro-states. The relaxation time is intuitively expected to increase with system disorder. We derive a simple analytical expression for this dependence in the context of electronic equilibration in an amorphous molecular system model. We find that the disorder dramatically enhances the relaxation time but does not affect its independence of the nature of the initial state.
Mirror Cosmological Relaxation of the Electroweak Scale
Matsedonskyi, Oleksii
2015-01-01
The cosmological relaxation mechanism proposed in [1] allows for a dynamically generated large separation between the weak scale and a theory cutoff, using a sharp change of theory behaviour upon crossing the limit between unbroken and broken symmetry phases. In this note we present a variation of this scenario, in which stabilization of the electroweak scale in the right place is ensured by the $Z_2$ symmetry exchanging the Standard Model (SM) with its mirror copy. We sketch the possible ways to produce viable thermal evolution of the Universe and discuss experimental accessibility of the new physics effects. We show that in this scenario the mirror SM can either have sizeable couplings with the ordinary one, or, conversely, can interact with it with a negligible strength. The overall cutoff allowed by such a construction can reach $10^9$ GeV.
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,…
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.
Conformational relaxation of ?-conjugated polymer radical anion on picosecond scale
NASA Astrophysics Data System (ADS)
Ohnishi, Yuko; Saeki, Akinori; Seki, Shu; Tagawa, Seiichi
2009-05-01
We report the conformational relaxation of poly[bis(p-n-butylphenyl)silane] (PBPS) radical anion measured by near-ultraviolet-enhanced picosecond pulse radiolysis in tetrahydrofuran solutions. The peak shift and increase in optical density of the transient photoabsorption spectra were investigated by kinetic analysis including reactions of PBPS with solvated/presolvated electrons, peak extraction protocol, and diffusion theory, demonstrating the correspondence in the rate constant (5±1×102 ps) between the peak shift and increase in oscillator strength. The results were examined by density functional theory and molecular dynamics simulations, where the modeled oligosilane radical anion shows more planner conformation relative to its neutral state and a relaxation time of 8 ps. The difference of the time scale is discussed from the viewpoints of actual experimental factors. To the best of our knowledge, this is the first report on the direct observation of the conformational dynamics of rodlike ?-conjugated polymer: PBPS radical anion.
A Scale Measuring the Ability To Relax Others.
ERIC Educational Resources Information Center
Oliver, Peter V.; Boudreau, Louis A.
The present research developed and validated a self-reported instrument called the "Relaxing Others Scale" (ROS), which is designed to identify individuals who possess the ability to relax others. A second part of the study involved assessing the construct validity of the ROS. Participants in the study were male and female dormitory residents,…
Hyperpolarized Nanodiamond with Long Spin Relaxation Times
Ewa Rej; Torsten Gaebel; Thomas Boele; David E. J. Waddington; David J. Reilly
2015-02-22
The use of hyperpolarized agents in magnetic resonance (MR), such as 13C-labeled compounds, enables powerful new imaging and detection modalities that stem from a 10,000-fold boost in signal. A major challenge for the future of the hyperpolarizaton technique is the inherently short spin relaxation times, typically life-sciences as inexpensive fluorescent markers and non-cytotoxic substrates for gene and drug delivery, these results extend the theranostic capabilities of nanoscale diamonds into the domain of hyperpolarized MR.
Communication: Tracking molecular structure deformation and relaxation in real time.
Wang, Y; Liu, W L; Song, Y F; Liu, Y Q; Duo, L P; Jiang, L L; Yu, G Y; Yang, Y Q
2015-08-01
The CH3I structural deformation induced by strong laser fields is revealed by time- and frequency-resolved ro-vibrational spectra. The experimental results show that the CH3I molecule undergoes ultrafast structural deformation of CH3 "umbrella-closing" induced by the strong fs laser field (more than 10(11) W/cm(2)) and followed by a structural relaxation of "umbrella-opening" within an exponential decay time scale of ?620 fs. This study provides a first glimpse of the immense potential of the time- and frequency-resolved vibrational spectra in studying molecular deformation dynamics. PMID:26254632
Anomalous magnetoconductivity and relaxation times in holography
NASA Astrophysics Data System (ADS)
Jimenez-Alba, Amadeo; Landsteiner, Karl; Liu, Yan; Sun, Ya-Wen
2015-07-01
We study the magnetoconductivity induced by the axial anomaly via the chiral magnetic effect in strongly coupled holographic models. An important ingredient in our models is that the axial charge is non-conserved beyond the axial anomaly. We achieve this either by explicit symmetry breaking via a non-vanishing non-normalisable mode of an axially charged scalar or using a Stückelberg field to make the AdS-bulk gauge field massive. The DC magnetoconductivites can be calculated analytically. They take a universal form in terms of gauge field mass at the horizon and quadratic dependence on the magnetic field. The axial charge relaxation time grows linearly with magnetic field in the large B regime. Most strikingly positive magnetoconductivity is still present even when the relaxation times are short ? 5 ? 1/( ?T) and the axial charge can not be thought of as an approximate symmetry. In the U(1) A explicit breaking model, we also observe that the chiral separation conductivity and the axial magnetic conductivity for the consistent axial current vanish in the limit of strong symmetry breaking.
Anomalous magnetoconductivity and relaxation times in holography
Amadeo Jimenez-Alba; Karl Landsteiner; Yan Liu; Ya-Wen Sun
2015-05-04
We study the magnetoconductivity induced by the axial anomaly via the chiral magnetic effect in strongly coupled holographic models. An important ingredient in our models is that the axial charge is non-conserved beyond the axial anomaly. We achieve this either by explicit symmetry breaking via a non-vanishing non-normalisable mode of an axially charged scalar or using a Stuckelberg field to make the AdS-bulk gauge field massive. The DC magnetoconductivites can be calculated analytically. They take a universal form in terms of gauge field mass at the horizon and quadratic dependence on the magnetic field. The axial charge relaxation time grows linearly with magnetic field in the large $B$ regime. Most strikingly positive magnetoconductivity is still present even when the relaxation times are short $\\tau_5 \\approx 1/(\\pi T)$ and the axial charge can not be thought of as an approximate symmetry. In the $U(1)_A$ explicit breaking model, we also observe that the axial magnetic conductivity in the limit of strong symmetry breaking approaches the same universal value as for anomalous holographic superconductors in the zero temperature limit.
Anomalous magnetoconductivity and relaxation times in holography
Jimenez-Alba, Amadeo; Liu, Yan; Sun, Ya-Wen
2015-01-01
We study the magnetoconductivity induced by the axial anomaly via the chiral magnetic effect in strongly coupled holographic models. An important ingredient in our models is that the axial charge is non-conserved beyond the axial anomaly. We achieve this either by explicit symmetry breaking via a non-vanishing non-normalisable mode of an axially charged scalar or using a Stuckelberg field to make the AdS-bulk gauge field massive. The DC magnetoconductivites can be calculated analytically. They take a universal form in terms of gauge field mass at the horizon and quadratic dependence on the magnetic field. The axial charge relaxation time grows linearly with magnetic field in the large $B$ regime. Most strikingly positive magnetoconductivity is still present even when the relaxation times are short $\\tau_5 \\approx 1/(\\pi T)$ and the axial charge can not be thought of as an approximate symmetry. In the $U(1)_A$ explicit breaking model, we also observe that the axial magnetic conductivity in the limit of strong ...
Estimation of spin-echo relaxation time
NASA Astrophysics Data System (ADS)
Golub, F.; Potter, L. C.; Ash, J. N.; Blank, A.; Ahmad, R.
2013-12-01
In spin-echo-based EPR oximetry, traditional methods to estimate the T2 relaxation time, which encodes the oxygen concentration of the sample, include fitting an exponential to the peaks or the integrated areas of multiple noisy echoes. These methods are suboptimal and result in a loss of estimation precision for a given acquisition time. Here, we present the maximum likelihood estimate (MLE) of T2 from spin-echo data. The MLE provides, for the data considered, approximately 3-fold time savings over echo-integration and more than 40-fold time savings over peak-picking. A one-dimensional line search results in simple computation of the MLE. It is observed that, perhaps counter-intuitively, prior knowledge of the lineshape does not yield additional reduction of estimation error variance at practical noise levels. The result also illuminates the near optimal performance of T2 estimation via principal components calculated by a singular value decomposition. The proposed method is illustrated by application to simulated and experimental EPR data.
Relaxation dynamics of scale-free polymer networks
NASA Astrophysics Data System (ADS)
Galiceanu, M.
2012-10-01
We focus on polymer networks with a scale-free topology. In the framework of generalized Gaussian structures, by making use of the eigenvalue spectrum of the connectivity matrix, we determined numerically the averaged monomer displacement under external forces and the mechanical relaxation moduli (storage and loss modulus). First, we monitor these physical quantities and additionally the eigenvalue spectrum for structures of different sizes, but with the same ?, which is a parameter that measures the connectivity of the structure. Second, we vary the parameter ?, and we keep constant the size of the structures. This allows us to study in detail the crossover behavior from a simple linear chain to a starlike structure. As expected we encounter a more chainlike behavior for high values of ?, while for small values of ? a more starlike behavior is observed. In the intermediate time (frequency) domain, we encounter regions of constant slope for some intermediate values of ?.
Universal relaxation times for electron and nucleon gases
M. Pelc; J. Marciak-Kozlowska; M. Kozlowski
2007-11-11
In this paper we calculate the universal relaxation times for electron and nucleon fermionic gases. We argue that the universal relaxation time tau(i) is equal tau(i)=h/m square v(i) where v(i)=alpha(i)c and alpha(1)=0.15 for nucleon gas and alpha(2)=1/137 for electron gas, c=light velocity. With the universal relaxation time we formulate the thermal Proca equation for fermionic gases. Key words: universal relaxation time, thermal universal Proca equation.
Improvement in the Measurement of Spin-Lattice Relaxation Time in Electron Paramagnetic Resonance
NASA Astrophysics Data System (ADS)
Lopez, Robert
The spin-lattice, or longitudinal, relaxation time T 1 plays an important role in magnetic resonance because it provides significant information about the coupling of a paramagnetic ion with its environment via its dependence on such factors as temperature, frequency (Scott & Jefferies, 1962; Kurtz & Stapleton, 1980), spin concentration (Gill, 1962), and magnetic field (Albart & Pescia, 1980; Nogatchewsky et al., 1977). But the measurement of electronic spin-lattice relaxation times is problematic because the times span the range from the very short (10-15 s) to the very long (1 s; cf. Pescia, 1966). The one microsecond spin-lattice relaxation time demarcates "short" from "long" relaxation times, which traditionally have each required their own methods of measurement. For example, long relaxation times are measured by using cw-EPR spectrometers to record spectra at multiple power levels near and under the condition of saturation; the spin-spin and spin-lattice relaxation times are then calculated from lineshape parameters. But the so-called short relaxation times are not measurable on the time scale of common cw-EPR instrumental detection methods. Short spin-lattice relaxation times are therefore measured by resorting to different (i.e., transient) magnetic resonance techniques such as pulsed saturation, spin echo (cf. Poole & Farach, 1971), and amplitude modulation (Hervé & Pescia, 1960a,b).
A moving mesh method with variable mesh relaxation time
Stockie, John
A moving mesh method with variable mesh relaxation time Ali Reza Soheili a and John M. Stockie b,1Department of Mathematics, Simon Fraser University, Burnaby, BC, Canada Abstract We propose a moving mesh adaptive approach by a moving mesh PDE (MMPDE) in which a mesh relaxation time is employed as a regulariza- tion parameter
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.
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.
Two relaxation time lattice Boltzmann model for rarefied gas flows
NASA Astrophysics Data System (ADS)
Esfahani, Javad Abolfazli; Norouzi, Ali
2014-01-01
In this paper, the lattice Boltzmann equation (LBE) with two relaxation times (TRT) is implemented in order to study gaseous flow through a long micro/nano-channel. A new relation is introduced for the reflection factor in the bounce-back/specular reflection (BSR) boundary condition based on the analytical solution of the Navier-Stokes equations. The focus of the present study is on comparing TRT with the other LBE models called multiple relaxation times (MRT) and single relaxation time (SRT) in simulation of rarefied gas flows. After a stability analysis for the TRT and SRT models, the numerical results are presented and validated by the analytical solution of the Navier-Stokes equations with slip boundary condition, direct simulation of Monte Carlo (DSMC) and information preservation (IP) method. The effect of various gases on flow behavior is also investigated by using the variable hard sphere (VHS) model through the symmetrical relaxation time.
Energy Conversion of Fully Random Thermal Relaxation Times
François Barriquand
2005-07-26
Thermodynamic random processes in thermal systems are generally associated with one or several relaxation times, the inverse of which are formally homogeneous with energy. Here, we show in a precise way that the periodic modification of relaxation times during temperature-constant thermodynamic cycles can be thermodynamically beneficiary to the operator. This result holds as long as the operator who adjusts relaxation times does not attempt to control the randomness associated with relaxation times itself as a Maxwell 'demon' would do. Indirectly, our result also shows that thermal randomness appears satisfactorily described within a conventional quantum-statistical framework, and that the attempts advocated notably by Ilya Prigogine to go beyond a Hilbert space description of quantum statistics do not seem justified - at least according to the present state of our knowledge. Fundamental interpretation of randomness, either thermal or quantum mechanical, is briefly discussed.
S 1-S 0 relaxation time of saturable absorber DDI
NASA Astrophysics Data System (ADS)
Blau, W.; Reber, R.; Penzkofer, A.
1982-10-01
The saturable dye DDI is excited with picosecond ruby laser pulses to the S 1 singlet state and the relaxation to the ground state S 0 is determined by measuring the transmission of the exciting pulses through the sample. The relaxation time is found to be ? = 17 ± 3 ps for DDI dissolved in methanol. Admictures of rhodamine 6G, potassium iodide, or tetrabutylammonium iodide do not change the decay time.
Multiple-Relaxation-Time Lattice Boltzmann Models in 3D
NASA Technical Reports Server (NTRS)
dHumieres, Dominique; Ginzburg, Irina; Krafczyk, Manfred; Lallemand, Pierre; Luo, Li-Shi; Bushnell, Dennis M. (Technical Monitor)
2002-01-01
This article provides a concise exposition of the multiple-relaxation-time lattice Boltzmann equation, with examples of fifteen-velocity and nineteen-velocity models in three dimensions. Simulation of a diagonally lid-driven cavity flow in three dimensions at Re=500 and 2000 is performed. The results clearly demonstrate the superior numerical stability of the multiple-relaxation-time lattice Boltzmann equation over the popular lattice Bhatnagar-Gross-Krook equation.
NASA Astrophysics Data System (ADS)
Qi, Guanrong
1998-06-01
The IAU 21st General Assembly held in 1991 resolved that the Terrestrial Time (TT) replaces the Terrestrial Dynamical Time (TDT) and the new terminologies of Geocentric Coordinate Time (TCG) and Barycentric Coordinate Time (TCB) were introduced. The reasons for introducing these time-like arguments, the relationships between these different time scales and the questions appearing in practical applications are described.
T2 relaxation time abnormalities in bipolar disorder and schizophrenia.
Ongür, Dost; Prescot, Andrew P; Jensen, J Eric; Rouse, Elizabeth D; Cohen, Bruce M; Renshaw, Perry F; Olson, David P
2010-01-01
There are substantial abnormalities in the number, density, and size of cortical neurons and glial cells in bipolar disorder and schizophrenia. Because molecule-microenvironment interactions modulate metabolite signals characteristics, these cellular abnormalities may impact transverse (T2) relaxation times. We measured T2 relaxation times for three intracellular metabolites (N-acetylaspartate+N-acetylaspartylglutamate, creatine+phosphocreatine, and choline-containing compounds) in the anterior cingulate cortex and parieto-occipital cortex from 20 healthy subjects, 15 patients with bipolar disorder, and 15 patients with schizophrenia at 4 T. Spectra used in T2 quantification were collected from 8-cc voxels with varying echo times (30 to 500 ms, in 10-ms steps). Both bipolar disorder and schizophrenia groups had numerically shorter T2 relaxation times than the healthy subjects group in both regions; these differences reached statistical significance for creatine+phosphocreatine and choline-containing compounds in bipolar disorder and for choline-containing compounds in schizophrenia. Metabolite T2 relaxation time shortening is consistent with reduced cell volumes and altered macromolecule structures, and with prolonged water T2 relaxation times reported in bipolar disorder and schizophrenia. These findings suggest that metabolite concentrations reported in magnetic resonance spectroscopy studies of psychiatric conditions may be confounded by T2 relaxation and highlight the importance of measuring and correcting for this variable. PMID:19918902
Ottochian, A; De Michele, C; Leporini, D
2009-12-14
On approaching the glass transition, the microscopic kinetic unit spends increasing time rattling in the cage of the first neighbors, whereas its average escape time, the structural relaxation time tau(alpha), increases from a few picoseconds up to thousands of seconds. A thorough study of the correlation between tau(alpha) and the rattling amplitude, expressed by the Debye-Waller factor, was carried out. Molecular-dynamics simulations of both a model polymer system and a binary mixture were performed by varying the temperature, the density rho, the potential and the polymer length to consider the structural relaxation as well as both the rotational and the translation diffusion. The present simulations, together with MD studies on other glassformers, evidence the scaling between the structural relaxation and the caged dynamics. An analytic model of the master curve is developed in terms of two characteristic length scales a(2) (1/2) and sigma(a(2) ) (1/2), pertaining to the distance to be covered by the kinetic unit to reach a transition state. The model does not imply tau(alpha) divergences. The comparison with the experiments supports the numerical evidence over a range of relaxation times as wide as about eighteen orders of magnitude. A comparison with other scaling and correlation procedures is presented. In particular, the density scaling of the length scales a(2) (1/2), sigma(a(2) ) (1/2) proportional to rho(-1/3) is shown to be not supported by the present simulations. The study suggests that the equilibrium and the moderately supercooled states of the glassformers possess key information on the huge slowing-down of their relaxation close to the glass transition. The latter, according to the present simulations, exhibits features consistent with the Lindemann melting criterion and the free-volume model. PMID:20001067
Real-time relaxation and kinetics in hot scalar QED: Landau damping
Boyanovsky, D. [Department of Physics and Astronomy, University of Pittsburgh, Pittsburgh , Pennsylvania 15260 (United States)] [Department of Physics and Astronomy, University of Pittsburgh, Pittsburgh , Pennsylvania 15260 (United States); de Vega, H.J. [LPTHE, Universite Pierre et Marie Curie (Paris VI) et Denis Diderot (Paris VII), Tour 16, 1er. etage, 4, Place Jussieu, 75252 Paris, Cedex 05 (France)] [LPTHE, Universite Pierre et Marie Curie (Paris VI) et Denis Diderot (Paris VII), Tour 16, 1er. etage, 4, Place Jussieu, 75252 Paris, Cedex 05 (France); Holman, R.; Kumar, S.P. [Department of Physics, Carnegie-Mellon University, Pittsburgh, Pennsylvania 15213 (United States)] [Department of Physics, Carnegie-Mellon University, Pittsburgh, Pennsylvania 15213 (United States); Pisarski, R.D. [Department of Physics, Brookhaven National Laboratory, Upton, New York 11973 (United States)] [Department of Physics, Brookhaven National Laboratory, Upton, New York 11973 (United States)
1998-12-01
The real time evolution of non-equilibrium expectation values with soft length scales {approximately}k{sup {minus}1}{gt}(eT){sup {minus}1} is solved in hot scalar electrodynamics, with a view towards understanding relaxational phenomena in the QGP and the electroweak plasma. We find that the gauge invariant non-equilibrium expectation values relax via {ital power laws} to asymptotic amplitudes that are determined by the quasiparticle poles. The long time relaxational dynamics and relevant time scales are determined by the behavior of the retarded self-energy not at the small frequencies, but at the Landau damping thresholds. This explains the presence of power laws and not of exponential decay. In the process we rederive the HTL effective action using {ital non-equilibrium} field theory. Furthermore we obtain the influence functional, the Langevin equation and the fluctuation-dissipation theorem for the soft modes, identifying the correlators that emerge in the classical limit. We show that a Markovian approximation fails to describe the dynamics {ital both} at short and long times. We find that the distribution function for soft quasiparticles relaxes with a power law through Landau damping. We also introduce a novel kinetic approach that goes beyond the standard Boltzmann equation by incorporating off-shell processes and find that the distribution function for soft quasiparticles relaxes with a power law through Landau damping. We find an unusual dressing dynamics of bare particles and anomalous (logarithmic) relaxation of hard quasiparticles. {copyright} {ital 1998} {ital The American Physical Society}
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
Scaling out the density dependence of the $?$ relaxation in glassforming polymers
C. Alba-Simionesco; A. Cailliaux; A. Alegria; G. Tarjus
2004-04-02
We show that the density and temperature dependences of the $\\alpha$-relaxation time of several glassforming polymers can be described through a single scaling variable $X=e(\\rho)/T$, where $e(\\rho)$ is well fitted by a power law $\\rho^x$, $x$ being a species-specific parameter. This implies that ``fragility'' is an intrinsic, density-independent property of a glassformer characterizing its super-Arrhenius slowing down of relaxations, and it leads us to propose a modification of the celebrated Angell plot.
Nonequilibrium relaxation and aging scaling of the Coulomb and Bose glass.
Shimer, Matthew T; Täuber, Uwe C; Pleimling, Michel
2014-09-01
We employ Monte Carlo simulations to investigate the nonequilibrium relaxation properties of the two- and three-dimensional Coulomb glass with different long-range repulsive interactions. Specifically, we explore the aging scaling laws in the two-time density autocorrelation function. We find that, in the time window and parameter range accessible to us, the scaling exponents are not universal, depending on the filling fraction and temperature: As either the temperature decreases or the filling fraction deviates more from half filling, the exponents reflect markedly slower relaxation kinetics. In comparison with a repulsive Coulomb potential, appropriate for impurity states in strongly disordered semiconductors, we observe that, for logarithmic interactions, the soft pseudogap in the density of states is considerably broader, and the dependence of the scaling exponents on external parameters is much weaker. The latter situation is relevant for flux creep in the disorder-dominated Bose glass phase of type-II superconductors subject to columnar pinning centers. PMID:25314399
Nonequilibrium relaxation and aging scaling of the Coulomb and Bose glass
NASA Astrophysics Data System (ADS)
Shimer, Matthew T.; Täuber, Uwe C.; Pleimling, Michel
2014-09-01
We employ Monte Carlo simulations to investigate the nonequilibrium relaxation properties of the two- and three-dimensional Coulomb glass with different long-range repulsive interactions. Specifically, we explore the aging scaling laws in the two-time density autocorrelation function. We find that, in the time window and parameter range accessible to us, the scaling exponents are not universal, depending on the filling fraction and temperature: As either the temperature decreases or the filling fraction deviates more from half filling, the exponents reflect markedly slower relaxation kinetics. In comparison with a repulsive Coulomb potential, appropriate for impurity states in strongly disordered semiconductors, we observe that, for logarithmic interactions, the soft pseudogap in the density of states is considerably broader, and the dependence of the scaling exponents on external parameters is much weaker. The latter situation is relevant for flux creep in the disorder-dominated Bose glass phase of type-II superconductors subject to columnar pinning centers.
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. )
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.
Mindfulness meditation and relaxation training increases time sensitivity.
Droit-Volet, S; Fanget, M; Dambrun, M
2015-01-01
Two experiments examined the effect of mindfulness meditation and relaxation on time perception using a temporal bisection task. In Experiment 1, the participants performed a temporal task before and after exercises of mindfulness meditation or relaxation. In Experiment 2, the procedure was similar than that used in Experiment 1, except that the participants were trained to mediate or relax every day over a period of several weeks. The results showed that mindfulness meditation exercises increased sensitivity to time and lengthened perceived time. However, this temporal improvement with meditation exercises was primarily observed in the experienced meditators. Our results also showed the experienced meditators were less anxious than the novice participants, and that the sensitivity to time increased when the level of anxiety decreased. Our results were explained by the practice of mindfulness technique that had developed individuals' abilities in devoting more attention resources to temporal information processing. PMID:25460243
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.
Quantitative Assessment of Image Segmentation Quality by Random Walk Relaxation Times
Hamprecht, Fred A.
is scale-free and adaptive to the geometry of segments. We motivate this definition using random walkQuantitative Assessment of Image Segmentation Quality by Random Walk Relaxation Times Bjoern Andres of Heidelberg, Germany 2 Weizmann Institute of Science, Israel Abstract. The purpose of image segmentation
Relaxation Times in the ASEP Model Using a DMRG Method
NASA Astrophysics Data System (ADS)
Nagy, Zoltán; Appert, Cécile; Santen, Ludger
2002-11-01
We compute the largest relaxation times for the totally asymmetric exclusion process (TASEP) with open boundary conditions with a DMRG method. This allows us to reach much larger system sizes than in previous numerical studies. We are then able to show that the phenomenological theory of the domain wall indeed predicts correctly the largest relaxation time for large systems. Besides, we can obtain results even when the domain wall approach breaks down, and show that the KPZ dynamical exponent z=3/2 is recovered in the whole maximal current phase.
Use of relaxation time as a marker for arterial distensibility.
Winchester, C C; Chou, N Y; Winchester, L W
2008-01-01
Arterial stiffening is associated with a number of known cardiovascular risk factors, including advancing age, increased systolic blood pressure (SBP), diabetes, hypertension, heart failure, myocardial infarction, and obesity. Many methodologies, both invasive and noninvasive, have been applied to the assessment of the stiffening of large elastic arteries in vivo, but there is no economically and/or universally accepted means of screening patients for atherosclerosis. From preliminary studies, a novel parameter, arterial relaxation time, has been identified as a potential indicator for inferring the elasticity of arteries. Preliminary measurements of arterial relaxation time of six normotensive subjects are significantly less than measurements of four hypertensive subjects. PMID:19163440
Vibrational relaxation in jet-cooled alkyl benzenes. III. Nanosecond time evolution
NASA Astrophysics Data System (ADS)
Hopkins, J. B.; Powers, D. E.; Smalley, R. E.
1980-07-01
Spectrally resolved fluorescence time decay measurements have been completed with nanosecond resolution on a series of n-alkylbenzenes laser excited into well-localized ring distortion vibrations in the S1 electronic state. Results indicate that those early members of the series which continue to exhibit some sharp, vibrationally unrelaxed emissions do so because they are intermediate case examples with inadequate density of states to permit dynamical relaxation on a nanosecond time scale. The longer chain, statistical limit molecules show a relaxed fluorescence pattern which displays no residual nanosecond time evolution. Intramolecular vibrational relaxation thus appears to proceed to an essentially complete randomization within a time period shorter than the excitation laser pulse.
TI-relaxation time changes over five years in relapsing-remitting multiple sclerosis.
Papadopoulos, Konstantinos; Tozer, Daniel J; Fisniku, Leonora; Altmann, Daniel R; Davies, Gerard; Rashid, Waqar; Thompson, Alan J; Miller, David H; Chard, Declan T
2010-04-01
The pathological effects of multiple sclerosis are not confined to lesions; tissues that appear normal on conventional magnetic resonance imaging scans are also affected, albeit subtly. One imaging technique that has proven sensitive to such effects is T1-relaxation time measurement, with previous work demonstrating abnormalities in normal-appearing white matter and grey matter. In this work we investigated the evolution of T1-relaxation time changes in normal-appearing white matter and grey matter in relapsing-remitting multiple sclerosis. Three- and five-year follow-up data from 35 people with clinically early (a mean of 1.6 years from first clinical event) relapsing-remitting multiple sclerosis and 15 healthy controls were analysed. T1-relaxation time histograms were extracted from normal-appearing white matter and grey matter, and mean, peak height and peak location values were estimated. T1-relaxation time peak height declined in the multiple sclerosis normal-appearing white matter and grey matter, but not the control group (rate difference p = 0.024 in normal-appearing white matter, in normal-appearing grey matter p = 0.038); other T1-relaxation time changes were not significantly different between groups. Changes in T1-relaxation time measures did not correlate with increases in brain T2-weighted lesion loads or Expanded Disability Status Scale scores. These results suggest that the processes underlying changes in normal-appearing white matter and grey matter T1-relaxation times are not immediately linked to white matter lesion formation, and may represent more diffuse but progressive sub-clinical pathology in relapsing-remitting multiple sclerosis. PMID:20086026
The relaxation time of processes in a FitzHugh-Nagumo neural system with time delay
NASA Astrophysics Data System (ADS)
Gong, Ailing; Wang, Hua; Zeng, Chunhua
2011-08-01
In this paper, we study the relaxation time (RT) of the steady-state correlation function in a FitzHugh-Nagumo neural system under the presence of multiplicative and additive white noises and time delay. The noise correlation parameter ? can produce a critical behavior in the RT as functions of the multiplicative noise intensity D, the additive noise intensity Q and the time delay ?. That is, the RT decreases as the noise intensities D and Q increase, and increases as the time delay ? increases below the critical value of ?. However, above the critical value, the RT first increases, reaches a maximum, and then decreases as D, Q and ? increase, i.e. a noise intensity D or Q and a time delay ? exist, at which the time scales of the relaxation process are at their largest. In addition, the additive noise intensity Q can also produce a critical behavior in the RT as a function of ?. The noise correlation parameter ? first increases the RT of processes, then decreases it below the critical value of Q. Above the critical value, ? increases it.
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.
Relaxed Time Slot Negotiation for Grid Resource Allocation
NASA Astrophysics Data System (ADS)
Son, Seokho; Sim, Kwang Mong
Since participants in a computational grid may be independent bodies, some mechanisms are necessary for resolving the differences in their preferences for price and desirable time slots for utilizing/leasing computing resources. Whereas there are mechanisms for supporting price negotiation for grid resource allocation, there is little or no negotiation support for allocating mutually acceptable time slots for grid participants. The contribution of this work is designing a negotiation mechanism for facilitating time slot negotiations between grid participants. In particular, this work adopts a relaxed time slot negotiation protocol designed to enhance the success rate and resource utilization level by allowing some flexibility for making slight adjustments following a tentative agreement for a mutually acceptable time slot. The ideas of the relaxed time slot negotiation are implemented in an agent-based grid testbed, and empirical results of the relaxed time slot negotiation mechanism carried out, (i) a consumer and a provider agent have a mutually satisfying agreement on time slot and price, (ii) consumer agents achieved higher success rates in negotiation, and (iii) provider agents achieved higher utility and resource utilization of overall grid.
Scaling and relaxational dynamics near Kondo-destroying quantum critical points
NASA Astrophysics Data System (ADS)
Pixley, Jedediah; Glossop, Matthew; Kirchner, Stefan; Si, Qimiao
2010-03-01
We study the finite-temperature dynamical scaling in the vicinity of the Kondo-destroying quantum critical points in two quantum impurity models. For the pseudogap Anderson model, we use a combination of renormalization group, continuous time quantum Monte Carlo and large-N techniques to obtain the complete scaling functions of the local susceptibility and single-electron Green's function both in the coherent ( ?>T) and relaxational ( ?
Inversion of generalized relaxation time distributions with optimized damping parameter
NASA Astrophysics Data System (ADS)
Florsch, Nicolas; Revil, André; Camerlynck, Christian
2014-10-01
Retrieving the Relaxation Time Distribution (RDT), the Grains Size Distribution (GSD) or the Pore Size Distribution (PSD) from low-frequency impedance spectra is a major goal in geophysics. The “Generalized RTD” generalizes parametric models like Cole-Cole and many others, but remains tricky to invert since this inverse problem is ill-posed. We propose to use generalized relaxation basis function (for instance by decomposing the spectra on basis of generalized Cole-Cole relaxation elements instead of the classical Debye basis) and to use the L-curve approach to optimize the damping parameter required to get smooth and realistic inverse solutions. We apply our algorithm to three examples, one synthetic and two real data sets, and the program includes the possibility of converting the RTD into GSD or PSD by choosing the value of the constant connecting the relaxation time to the characteristic polarization size of interest. A high frequencies (typically above 1 kHz), a dielectric term in taken into account in the model. The code is provided as an open Matlab source as a supplementary file associated with this paper.
Hyperpolarized nanodiamond with long spin-relaxation times.
Rej, Ewa; Gaebel, Torsten; Boele, Thomas; Waddington, David E J; Reilly, David J
2015-01-01
The use of hyperpolarized agents in magnetic resonance, such as (13)C-labelled compounds, enables powerful new imaging and detection modalities that stem from a 10,000-fold boost in signal. A major challenge for the future of the hyperpolarization technique is the inherently short spin-relaxation times, typically <60?s for (13)C liquid-state compounds, which limit the time that the signal remains boosted. Here we demonstrate that 1.1% natural abundance (13)C spins in synthetic nanodiamond can be hyperpolarized at cryogenic and room temperature without the use of free radicals, and, owing to their solid-state environment, exhibit relaxation times exceeding 1?h. Combined with the already established applications of nanodiamonds in the life sciences as inexpensive fluorescent markers and non-cytotoxic substrates for gene and drug delivery, these results extend the theranostic capabilities of nanoscale diamonds into the domain of hyperpolarized magnetic resonance. PMID:26450570
Dielectric relaxation, resonance and scaling behaviors in Sr3Co2Fe24O41 hexaferrite.
Tang, Rujun; Jiang, Chen; Qian, Wenhu; Jian, Jie; Zhang, Xin; Wang, Haiyan; Yang, Hao
2015-01-01
The dielectric properties of Z-type hexaferrite Sr3Co2Fe24O41 (SCFO) have been investigated as a function of temperature from 153 to 503?K between 1 and 2?GHz. The dielectric responses of SCFO are found to be frequency dependent and thermally activated. The relaxation-type dielectric behavior is observed to be dominating in the low frequency region and resonance-type dielectric behavior is found to be dominating above 10(8)?Hz. This frequency dependence of dielectric behavior is explained by the damped harmonic oscillator model with temperature dependent coefficients. The imaginary part of impedance (Z?) and modulus (M?) spectra show that there is a distribution of relaxation times. The scaling behaviors of Z? and M? spectra further suggest that the distribution of relaxation times is temperature independent at low frequencies. The dielectric loss spectra at different temperatures have not shown a scaling behavior above 10(8)?Hz. A comparison between the Z? and the M? spectra indicates that the short-range charges motion dominates at low temperatures and the long-range charges motion dominates at high temperatures. The above results indicate that the dielectric dispersion mechanism in SCFO is temperature independent at low frequencies and temperature dependent at high frequencies due to the domination of resonance behavior. PMID:26314913
Dielectric relaxation, resonance and scaling behaviors in Sr3Co2Fe24O41 hexaferrite
Tang, Rujun; Jiang, Chen; Qian, Wenhu; Jian, Jie; Zhang, Xin; Wang, Haiyan; Yang, Hao
2015-01-01
The dielectric properties of Z-type hexaferrite Sr3Co2Fe24O41 (SCFO) have been investigated as a function of temperature from 153 to 503?K between 1 and 2?GHz. The dielectric responses of SCFO are found to be frequency dependent and thermally activated. The relaxation-type dielectric behavior is observed to be dominating in the low frequency region and resonance-type dielectric behavior is found to be dominating above 108?Hz. This frequency dependence of dielectric behavior is explained by the damped harmonic oscillator model with temperature dependent coefficients. The imaginary part of impedance (Z?) and modulus (M?) spectra show that there is a distribution of relaxation times. The scaling behaviors of Z? and M? spectra further suggest that the distribution of relaxation times is temperature independent at low frequencies. The dielectric loss spectra at different temperatures have not shown a scaling behavior above 108?Hz. A comparison between the Z? and the M? spectra indicates that the short-range charges motion dominates at low temperatures and the long-range charges motion dominates at high temperatures. The above results indicate that the dielectric dispersion mechanism in SCFO is temperature independent at low frequencies and temperature dependent at high frequencies due to the domination of resonance behavior. PMID:26314913
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
NSDL National Science Digital Library
This site contains a large, easy to read, detailed geologic time scale for the Phanerozoic Eon (544 million years ago - Present). This is the period of time, also known as an eon, between the end of the Precambrian and today. The Phanerozoic begins with the start of the Cambrian period, 544 million years ago. It encompasses the period of abundant, complex life on Earth. The chart includes the Era, Period or System, and the Epoch or Series and features a brief description of each.
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.
Strachan, A.; Dorso, C.O. [Departamento de Fisica, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Pabellon I, Ciudad Universitaria, Nunez 1428, Buenos Aires (Argentina)] [Departamento de Fisica, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Pabellon I, Ciudad Universitaria, Nunez 1428, Buenos Aires (Argentina)
1997-02-01
The problem of fragmentation of excited finite systems is explored in the frame of classical molecular dynamics experiments of two-dimensional Lennard-Jones drops. The main objective of this work is to get information about the relative value of the relevant characteristic time scales (CTS) for this kind of process. We investigate the CTS for fragment formation, the stabilization of the radial flux, and the internal {open_quotes}temperature.{close_quotes} It is found that the asymptotic fragments are realized early in phase space, when the system is still dense, by the time the radial flux attains its asymptotic value. It is also shown that the temperature of the system during the breakup is quite homogenous with respect to the expected profile if local thermal equilibration takes place. Special emphasis is put on the investigation of the time scale of stabilization of the statistical properties of the mass spectrum, which is related to the kind of information carried by the asymptotic fragments. {copyright} {ital 1997} {ital The American Physical Society}
Unified Theory of Activated Relaxation in Liquids over 14 Decades in Time
Mirigian, Stephen; Schweizer, Kenneth
2013-01-01
We formulate a predictive theory at the level of forces of activated relaxation in hard-sphere fluids and thermal liquids that covers in a unified manner the apparent Arrhenius, crossover, and deeply supercooled regimes. The alpha relaxation event involves coupled cage-scale hopping and a long-range collective elastic distortion of the surrounding liquid, which results in two inter-related, but distinct, barriers. The strongly temperature and density dependent collective barrier is associated with a growing length scale, the shear modulus, and density fluctuations. Thermal liquids are mapped to an effective hard-sphere fluid based on matching long wavelength density fluctuation amplitudes, resulting in a zeroth-order quasi-universal description. The theory is devoid of fit parameters, has no divergences at finite temperature nor below jamming, and captures the key features of the alpha time of molecular liquids from picoseconds to hundreds of seconds.
Multiple-relaxation-time model for the correct thermohydrodynamic equations.
Zheng, Lin; Shi, Baochang; Guo, Zhaoli
2008-08-01
A coupling lattice Boltzmann equation (LBE) model with multiple relaxation times is proposed for thermal flows with viscous heat dissipation and compression work. In this model the fixed Prandtl number and the viscous dissipation problems in the energy equation, which exist in most of the LBE models, are successfully overcome. The model is validated by simulating the two-dimensional Couette flow, thermal Poiseuille flow, and the natural convection flow in a square cavity. It is found that the numerical results agree well with the analytical solutions and/or other numerical results. PMID:18850971
Effective rotational correlation times of proteins from NMR relaxation interference
NASA Astrophysics Data System (ADS)
Lee, Donghan; Hilty, Christian; Wider, Gerhard; Wüthrich, Kurt
2006-01-01
Knowledge of the effective rotational correlation times, ?c, for the modulation of anisotropic spin-spin interactions in macromolecules subject to Brownian motion in solution is of key interest for the practice of NMR spectroscopy in structural biology. The value of ?c enables an estimate of the NMR spin relaxation rates, and indicates possible aggregation of the macromolecular species. This paper reports a novel NMR pulse scheme, [ 15N, 1H]-TRACT, which is based on transverse relaxation-optimized spectroscopy and permits to determine ?c for 15N- 1H bonds without interference from dipole-dipole coupling of the amide proton with remote protons. [ 15N, 1H]-TRACT is highly efficient since only a series of one-dimensional NMR spectra need to be recorded. Its use is suggested for a quick estimate of the rotational correlation time, to monitor sample quality and to determine optimal parameters for complex multidimensional NMR experiments. Practical applications are illustrated with the 110 kDa 7,8-dihydroneopterin aldolase from Staphylococcus aureus, the uniformly 15N-labeled Escherichia coli outer membrane protein X (OmpX) in 60 kDa mixed OmpX/DHPC micelles with approximately 90 molecules of unlabeled 1,2-dihexanoyl- sn-glycero-3-phosphocholine (DHPC), and the 16 kDa pheromone-binding protein from Bombyx mori, which cover a wide range of correlation times.
Rapid MRI method for mapping the longitudinal relaxation time.
Hsu, Jung-Jiin; Glover, Gary H
2006-07-01
A novel method for mapping the longitudinal relaxation time in a clinically acceptable time is developed based on a recent proposal [J.-J. Hsu, I.J. Lowe, Spin-lattice relaxation and a fast T1-map acquisition method in MRI with transient-state magnetization, J. Magn. Reson. 169 (2004) 270-278] and the speed of the spiral pulse sequence. The method acquires multiple curve-fitting samples with one RF pulse train. It does not require RF pulses of specific flip angles (e.g., 90 degrees or 180 degrees ), nor are the long recovery waiting time and the measurement of the magnetization at thermal equilibrium needed. Given the value of the flip angle, the curve fitting is semi-logarithmic and not computationally intensive. On a heterogeneous phantom, the average percentage difference between measurements of the present method and those of an inversion-recovery method is below 2.7%. In mapping the human brain, the present method, for example, can obtain four curve-fitting samples for five 128 x 128 slices in less than 3.2s and the results are in agreement with other studies in the literature. PMID:16621631
Relaxation time prediction for a light switchable peptide by molecular dynamics.
Denschlag, Robert; Schreier, Wolfgang J; Rieff, Benjamin; Schrader, Tobias E; Koller, Florian O; Moroder, Luis; Zinth, Wolfgang; Tavan, Paul
2010-06-21
We study a monocyclic peptide called cAPB, whose conformations are light switchable due to the covalent integration of an azobenzene dye. Molecular dynamics (MD) simulations using the CHARMM22 force field and its CMAP extension serve us to sample the two distinct conformational ensembles of cAPB, which belong to the cis and trans isomers of the dye, at room temperature. For gaining sufficient statistics we apply a novel replica exchange technique. We find that the well-known NMR distance restraints are much better described by CMAP than by CHARMM22. In cAPB, the ultrafast cis/trans photoisomerization of the dye elicits a relaxation dynamics of the peptide backbone. Experimentally, we probe this relaxation at picosecond time resolution by IR spectroscopy in the amide I range up to 3 ns after the UV/vis pump flash. We interpret the spectroscopically identified decay kinetics using ensembles of non-equilibrium MD simulations, which provide kinetic data on conformational transitions well matching the observed kinetics. Whereas spectroscopy solely indicates that the relaxation toward the equilibrium trans ensemble is by no means complete after 3 ns, the 20 ns MD simulations of the process predict, independently of the applied force field, that the final relaxation into the trans-ensemble proceeds on a time scale of 23 ns. Overall our explicit solvent simulations cover more than 6 micros. PMID:20390205
Bayesian relaxed clock estimation of divergence times in foraminifera.
Groussin, Mathieu; Pawlowski, Jan; Yang, Ziheng
2011-10-01
Accurate and precise estimation of divergence times during the Neo-Proterozoic is necessary to understand the speciation dynamic of early Eukaryotes. However such deep divergences are difficult to date, as the molecular clock is seriously violated. Recent improvements in Bayesian molecular dating techniques allow the relaxation of the molecular clock hypothesis as well as incorporation of multiple and flexible fossil calibrations. Divergence times can then be estimated even when the evolutionary rate varies among lineages and even when the fossil calibrations involve substantial uncertainties. In this paper, we used a Bayesian method to estimate divergence times in Foraminifera, a group of unicellular eukaryotes, known for their excellent fossil record but also for the high evolutionary rates of their genomes. Based on multigene data we reconstructed the phylogeny of Foraminifera and dated their origin and the major radiation events. Our estimates suggest that Foraminifera emerged during the Cryogenian (650-920 Ma, Neo-Proterozoic), with a mean time around 770 Ma, about 220 Myr before the first appearance of reliable foraminiferal fossils in sediments (545 Ma). Most dates are in agreement with the fossil record, but in general our results suggest earlier origins of foraminiferal orders. We found that the posterior time estimates were robust to specifications of the prior. Our results highlight inter-species variations of evolutionary rates in Foraminifera. Their effect was partially overcome by using the partitioned Bayesian analysis to accommodate rate heterogeneity among data partitions and using the relaxed molecular clock to account for changing evolutionary rates. However, more coding genes appear necessary to obtain more precise estimates of divergence times and to resolve the conflicts between fossil and molecular date estimates. PMID:21723398
On the accuracy of the finite element method plus time relaxation
NASA Astrophysics Data System (ADS)
Connors, J.; Layton, W.
2010-04-01
If overline{u} denotes a local, spatial average of u , then u'=u-overline{u} is the associated fluctuation. Consider a time relaxation term added to the usual finite element method. The simplest case for the model advection equation u_{t}+overrightarrow{a}\\cdotnabla u=f(x,t) is (u_{h,t}+overrightarrow{a}\\cdotnabla u_{h},v_{h})+?(u_{h'} ,v_{h'})=(f(x,t),v_{h}). We analyze the error in this and (more importantly) higher order extensions and show that the added time relaxation term not only suppresses excess energy in marginally resolved scales but also increases the accuracy of the resulting finite element approximation.
Fractional relaxation and the time-temperature superposition principle
W. G. Glöckle; T. F. Nonnenmacher
1994-01-01
Relaxation processes in complex systems like polymers or other viscoelastic materials can be described by equations containing fractional differential or integral operators. In order to give a physical motivation for fractional order equations, the fractional relaxation is discussed in the framework of statistical mechanics. We show that fractional relaxation represents a special type of a non-Markovian process. Assuming a separation
The time correlation function perspective of NMR relaxation in proteins
NASA Astrophysics Data System (ADS)
Shapiro, Yury E.; Meirovitch, Eva
2013-08-01
We applied over a decade ago the two-body coupled-rotator slowly relaxing local structure (SRLS) approach to NMR relaxation in proteins. One rotator is the globally moving protein and the other rotator is the locally moving probe (spin-bearing moiety, typically the 15N-1H bond). So far we applied SRLS to 15N-H relaxation from seven different proteins within the scope of the commonly used data-fitting paradigm. Here, we solve the SRLS Smoluchowski equation using typical best-fit parameters as input, to obtain the corresponding generic time correlation functions (TCFs). The following new information is obtained. For actual rhombic local ordering and main ordering axis pointing along C_{i - 1}^? - C_i^?, the measurable TCF is dominated by the (K,K') = (-2,2), (2,2), and (0,2) components (K is the order of the rank 2 local ordering tensor), determined largely by the local motion. Global diffusion axiality affects the analysis significantly when the ratio between the parallel and perpendicular components exceeds approximately 1.5. Local diffusion axiality has a large and intricate effect on the analysis. Mode-coupling becomes important when the ratio between the global and local motional rates falls below 0.01. The traditional method of analysis - model-free (MF) - represents a simple limit of SRLS. The conditions under which the MF and SRLS TCFs are the same are specified. The validity ranges of wobble-in-a-cone and rotation on the surface of a cone as local motions are determined. The evolution of the intricate Smoluchowski operator from the simple diffusion operator for a sphere reorienting in isotropic medium is delineated. This highlights the fact that SRLS is an extension of the established stochastic theories for treating restricted motions. This study lays the groundwork for TCF-based comparison between mesoscopic SRLS and atomistic molecular dynamics.
Dependence of Brownian and Néel relaxation times on magnetic field strength
Deissler, Robert J. Wu, Yong; Martens, Michael A.
2014-01-15
Purpose: In magnetic particle imaging (MPI) and magnetic particle spectroscopy (MPS) the relaxation time of the magnetization in response to externally applied magnetic fields is determined by the Brownian and Néel relaxation mechanisms. Here the authors investigate the dependence of the relaxation times on the magnetic field strength and the implications for MPI and MPS. Methods: The Fokker–Planck equation with Brownian relaxation and the Fokker–Planck equation with Néel relaxation are solved numerically for a time-varying externally applied magnetic field, including a step-function, a sinusoidally varying, and a linearly ramped magnetic field. For magnetic fields that are applied as a step function, an eigenvalue approach is used to directly calculate both the Brownian and Néel relaxation times for a range of magnetic field strengths. For Néel relaxation, the eigenvalue calculations are compared to Brown's high-barrier approximation formula. Results: The relaxation times due to the Brownian or Néel mechanisms depend on the magnitude of the applied magnetic field. In particular, the Néel relaxation time is sensitive to the magnetic field strength, and varies by many orders of magnitude for nanoparticle properties and magnetic field strengths relevant for MPI and MPS. Therefore, the well-known zero-field relaxation times underestimate the actual relaxation times and, in particular, can underestimate the Néel relaxation time by many orders of magnitude. When only Néel relaxation is present—if the particles are embedded in a solid for instance—the authors found that there can be a strong magnetization response to a sinusoidal driving field, even if the period is much less than the zero-field relaxation time. For a ferrofluid in which both Brownian and Néel relaxation are present, only one relaxation mechanism may dominate depending on the magnetic field strength, the driving frequency (or ramp time), and the phase of the magnetization relative to the applied magnetic field. Conclusions: A simple treatment of Néel relaxation using the common zero-field relaxation time overestimates the relaxation time of the magnetization in situations relevant for MPI and MPS. For sinusoidally driven (or ramped) systems, whether or not a particular relaxation mechanism dominates or is even relevant depends on the magnetic field strength, the frequency (or ramp time), and the phase of the magnetization relative to the applied magnetic field.
Time dependent parallel viscosity and relaxation rate of poloidal rotation in the banana regime
Hsu, C.T.; Shaing, K.C.; Gormley, R. )
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
In Vivo T2 Relaxation Time Measurement with Echo-Time Averaging
Prescot, Andrew P.; Shi, Xianfeng; Choi, Changho; Renshaw, Perry. F.
2014-01-01
The accuracy of metabolite concentrations measured using in vivo proton (1H) magnetic resonance spectroscopy (MRS) is enhanced following correction for spin-spin (T2) relaxation effects. In addition, metabolite proton T2 relaxation times provide unique information regarding cellular environment and molecular mobility. Echo-time (TE) averaging 1H MRS involves the collection and averaging of multiple TE steps that greatly simplifies resulting spectra due to the attenuation of spin-coupled and macromolecule resonances. Given the simplified spectral appearance and inherent metabolite T2 relaxation information, the aim of the present proof-of-concept study was to develop a novel data processing scheme to estimate metabolite T2 relaxation times from TE-averaged 1H MRS data. Spectral simulations are used to validate the proposed TE-averaging methods for estimating methyl proton T2 relaxation times for N-acetyl aspartate, total creatine, and choline-containing compounds. The utility of the technique and its reproducibility are demonstrated using data obtained in vivo from the posterior-occipital cortex of ten healthy control subjects. Compared to standard methods, distinct advantages of this approach include built-in macromolecule resonance attenuation, in vivo T2 estimates closer to reported values when maximum TE ? T2, and the potential for T2 calculation of metabolite resonances otherwise inseparable in standard 1H MRS spectra recorded in vivo. PMID:24865447
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.
NASA Astrophysics Data System (ADS)
Seidelmann, P. K.; Fukushima, T.
1992-11-01
At the International Astronomical Union (IAU) General Assembly in Buenos Aires, Argentina in 1991, the name Terrestrial Time (TT) was introduced to replace Terrestrial Dynamical Time (TDT) and the terminologies Geocentric Coordinate Time (TCG) and Barycentric Coordinate Time (TCB) were introduced (IAU 1992). The reasons for these time-like arguments and their applications will be presented. The relationships between the different time-like arguments will be discussed along with their applications and relationships to the astronomical constants.
Growth strains and stress relaxation in alumina scales during high temperature oxidation
Hou, P.Y.; Paulikas, A.P.; Veal, B.W.
2004-03-23
A novel X-ray technique was used, exploiting synchrotron radiation at the Advanced Photon Source at Argonne National Laboratory, to investigate the growth stresses in {alpha}-Al{sub 2}O{sub 3}. In-situ measurements of Debye-Scherrer diffraction patterns from the scale were recorded during oxidation and cooling, and the elliptical distortion of the diffraction rings was analyzed to yield the in-plane strain. Fe-28Al, Fe-40Al, Fe-40Al-0.2Hf, Fe-20Cr-10Al and Ni-50Al (at. %) were studied. Data were acquired in air at temperatures between 950-1100 C and during cool down. In all cases, the steady stage growth strain was relatively low (<0.1%) and was either tensile or compressive depending on the alloy. A higher tensile strain often existed during the initial oxidation period when transition alumina was present. Thermal stresses imposed on NiAl by reducing the sample temperature to 950 C for a period of time showed noticeable stress relaxation by creep. Different degrees of relaxation were also found during cooling depending on alloy composition and scale microstructure. On all Fe-based alloys, the first formed {alpha}-Al{sub 2}O{sub 3} was highly textured with the degree of texture decreasing with further oxidation. The relationships between stress development, scale wrinkling, oxide phase changes, and the effect of reactive element addition on growth stresses are discussed. Results are compared with other reports of growth stresses in Al{sub 2}O{sub 3} scales.
Time dependence of the segmental relaxation time of poly(vinyl acetate)-silica nanocomposites
NASA Astrophysics Data System (ADS)
Boucher, Virginie M.; Cangialosi, Daniele; Alegría, Angel; Colmenero, Juan
2012-10-01
The aging-time dependence of the segmental relaxation time of poly(vinyl acetate) (PVAc) in the glassy state is investigated in the bulk polymer and its nanocomposites with silica (SiO2). These systems present identical segmental dynamics, when this is probed in the equilibrium supercooled liquid by broadband dielectric spectroscopy. An acceleration of the physical aging process of PVAc with SiO2 was detected by monitoring the enthalpy recovery through differential scanning calorimetry. The segmental relaxation time during physical aging, followed by means of BDS, has been shown to increase more rapidly the higher the SiO2 concentration in PVAc is. Thermally stimulated depolarization current experiments show that this is the case over the whole probed glassy state. This means that nanocomposites displaying a relatively slow segmental mobility evolve toward equilibrium more rapidly than the bulk. Furthermore, despite the faster increase in the relaxation time with aging time, so-called self-retardation, the nanocomposites and their bulk counterpart reach the same values of equilibrium relaxation time. These findings not only confirm the assumption of identical equilibrium dynamics even in the aging regime for all nanocomposites and bulk polymers, proposed in previous works, but also highlight the fact that the physical aging rate is not determined solely by the polymer segmental dynamics, the amount of interface being an additional relevant parameter.
Distribution of relaxation times in (KBr)/sub 0. 5/(KCN)/sub 0. 5/
Birge, N.O.; Jeong, Y.H.; Nagel, S.R.; Bhattacharya, S.; Susman, S.
1984-08-15
Measurements of the dielectric response of (KBr)/sub 0.5/(KCN)/sub 0.5/ covering nine decades of frequency are reported. We have shown how the relaxation times proliferate as the temperature is lowered. The anomalously wide distribution of relaxation times can be generated from a Gaussian distribution of energy barriers. As temperature is decreased not only does the spread of relaxation times increase, but more importantly the width of the distribution of activation energies itself increases.
S. Pireaux
2007-03-23
The LISA mission is a space interferometer aiming at the detection of gravitational waves in the [$10^{-4}$,$10^{-1}$] Hz frequency band. In order to reach the gravitational wave detection level, a Time Delay Interferometry (TDI) method must be applied to get rid of (most of) the laser frequency noise and optical bench noise. This TDI analysis is carried out in terms of the coordinate time corresponding to the Barycentric Coordinate Reference System (BCRS), TCB, whereas the data at each of the three LISA stations is recorded in terms of each station proper time. We provide here the required proper time versus BCRS time transformation. We show that the difference in rate of station proper time versus TCB is of the order of $5 10^{-8}$. The difference between station proper times and TCB exhibits an oscillatory trend with a maximum amplitude of about $10^{-3}$ s.
Growing length and time scales in glass-forming liquids
Karmakar, Smarajit; Dasgupta, Chandan; Sastry, Srikanth
2009-01-01
The glass transition, whereby liquids transform into amorphous solids at low temperatures, is a subject of intense research despite decades of investigation. Explaining the enormous increase in relaxation times of a liquid upon supercooling is essential for understanding the glass transition. Although many theories, such as the Adam–Gibbs theory, have sought to relate growing relaxation times to length scales associated with spatial correlations in liquid structure or motion of molecules, the role of length scales in glassy dynamics is not well established. Recent studies of spatially correlated rearrangements of molecules leading to structural relaxation, termed “spatially heterogeneous dynamics,” provide fresh impetus in this direction. A powerful approach to extract length scales in critical phenomena is finite-size scaling, wherein a system is studied for sizes traversing the length scales of interest. We perform finite-size scaling for a realistic glass-former, using computer simulations, to evaluate the length scale associated with spatially heterogeneous dynamics, which grows as temperature decreases. However, relaxation times that also grow with decreasing temperature do not exhibit standard finite-size scaling with this length. We show that relaxation times are instead determined, for all studied system sizes and temperatures, by configurational entropy, in accordance with the Adam–Gibbs relation, but in disagreement with theoretical expectations based on spin-glass models that configurational entropy is not relevant at temperatures substantially above the critical temperature of mode-coupling theory. Our results provide new insights into the dynamics of glass-forming liquids and pose serious challenges to existing theoretical descriptions. PMID:19234111
NASA Astrophysics Data System (ADS)
Armstrong, R. T.; Ott, H.; Georgiadis, A.; Rucker, M.; Berg, S.
2014-12-01
With recent advances at X-ray micro-computed tomography (?CT) synchrotron beam lines, it is now possible to study pore-scale flow in porous rock under dynamic flow conditions. The collection of 4 dimensional (4D) data allows for the direct 3D 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 3D volume. We present an approach to analyze the 2D radiograph data collected during fast-?CT to study the pore-scale displacement dynamics on the time scale of 40 milliseconds 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 re-arrangements with an average relaxation time for the whole cascade between 0.5 and 2.0 seconds. These findings help to identify the flow regimes and intrinsic time and length scales relevant to fractional flow.
Torquato, Salvatore
= 0 correspondto the diffusion-controlled case(i.e., perfect absorbers)and reaction- controlled case of nuclear magnetismin fluid-saturatedporous media. We consider the problem of diffusion and reactionDiffusion and reaction in heterogeneous media: Pore size distribution, relaxation times, and mean
Approximate square-root-time relaxation in glass-forming liquids
Albena I. Nielsen; Tage Christensen; Bo Jakobsen; Kristine Niss; Niels Boye Olsen; Ranko Richert; Jeppe C. Dyre
2007-12-17
We present data for the dielectric relaxation of 43 glass-forming organic liquids, showing that the primary (alpha) relaxation is often close to square-root-time relaxation. The better an inverse power-law description of the high-frequency loss applies, the more accurately is square-root-time relaxation obeyed. These findings suggest that square-root-time relaxation is generic to the alpha process, once a common view, but since long believed to be incorrect. Only liquids with very large dielectric losses deviate from this picture by having consistently narrower loss peaks. As a further challenge to the prevailing opinion, we find that liquids with accurate square-root-time relaxation cover a wide range of fragilities.
NSDL National Science Digital Library
Collins, Allen.
Ride the Web Geological Time Machine at the University of California Museum of Paleontology. Click on an item in the list of 25 geological periods [15 of the 25 periods are available now, the remainder to be completed] and view a page describing each period, its subdivisions, and the life and fossils of that period.
NASA Astrophysics Data System (ADS)
Huang, Tianyi; Xu, Bangxin; Zhang, Hui; Zhu, Jin
This paper reviews the definition and conception of TAI, TDT and TDB, introduces and discusses some problems which are disputed recently among astronomers and physicists. They think, the construction of TAI should depend on the choice of geocentric coordinate system and TDT should be considered as the proper time at geocentre in a fictitious spacetime when the gravitation of the earth were removed.
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.
The derivation of thermal relaxation time between two-phase bubbly flow
NASA Astrophysics Data System (ADS)
Mohammadein, S. A.
2006-03-01
Thermal relaxation time constant is derived analytically for the relaxed model with unequal phase-temperatures of a vapour bubble at saturation temperature and a non-steady temperature field around the growing vapour bubble. The energy and state equation are solved between two finite boundary conditions. Thermal relaxation time perform a good agreement with Mohammadein (in Doctoral thesis, PAN, Gdansk, 1994) and Moby Dick experiment in terms of non-equilibrium homogeneous model (Bilicki et al. in Proc R Soc Lond A428:379-397, 1990) for lower values of initial void fraction. Thermal relaxation is affected by Jacob number, superheating, initial bubble radius and thermal diffusivity.
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
Multiple-relaxation-time lattice Boltzmann kinetic model for combustion
NASA Astrophysics Data System (ADS)
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.
An eigenvalue method for computing the largest relaxation time of disordered systems
NASA Astrophysics Data System (ADS)
Monthus, Cécile; Garel, Thomas
2009-12-01
We consider the dynamics of finite size disordered systems as defined by a master equation satisfying detailed balance. The master equation can be mapped onto a Schrödinger equation in configuration space, where the quantum Hamiltonian H has the generic form of an Anderson localization tight-binding model. The largest relaxation time teq governing the convergence towards Boltzmann equilibrium is determined by the lowest non-vanishing eigenvalue E1 = 1/teq of H (the lowest eigenvalue being E0 = 0). So the relaxation time teq can be computed without simulating the dynamics by any eigenvalue method able to compute the first excited energy E1. Here we use the 'conjugate gradient' method to determine E1 for each disordered sample and present numerical results on the statistics of the relaxation time teq over disordered samples of a given size for two models: (i) for the random walk in a self-affine potential of Hurst exponent H on a two-dimensional square of size L × L, we find the activated scaling lnteq(L)~L? with ? = H as expected; (ii) for the dynamics of the Sherrington-Kirkpatrick spin glass model of N spins, we find the growth lnteq(N)~N? with ? = 1/3 in agreement with most previous Monte Carlo measures. In addition, we find that the rescaled distribution of (lnteq) decays as e-u? for large u with a tail exponent of order \\eta \\simeq 1.36 . We give a rare-event interpretation of this value, that points towards a sample-to-sample fluctuation exponent of order \\psi_{\\mathrm {width}} \\simeq 0.26 for the barrier.
A Domain Decomposition Method for Semilinear Hyperbolic Systems with Two-scale Relaxations
Jin, Shi
of the characteristic speed at the interface is provided to couple the two systems in a domain decomposition settingA Domain Decomposition Method for Semilinear Hyperbolic Systems with Two-scale Relaxations Shi Jin , Jian-guo Liu and Li Wang Abstract We present a domain decomposition method on a semilinear hyperbolic
Origin of the universality of long-time thermal relaxations in hysteretic systems
M. I. Freidlin; I. D. Mayergoyz; M. W. Huang
2000-01-01
It is demonstrated that asymptotic temporal behavior of thermal noise is responsible for the universality of long-time thermal relaxations in hysteretic systems. By using the Preisach hysteresis model and by assuming stationary Gaussian noise, the ln t intermediate asymptotics for the thermal relaxations is derived along with a simple expression for the viscosity coefficient in terms of temperature and differential
Xu, Bin; Li, Haiyue; Zhang, Yanhang
2013-01-01
This study aims to provide understanding of the macroscopic viscoelastic behavior of collagen matrices through studying the relaxation time distribution spectrum obtained from stress relaxation tests. Hydrated collagen gel and dehydrated collagen thin film was exploited as two different hydration levels of collagen matrices. Genipin solution was used to induce crosslinking in collagen matrices. Biaxial stress relaxation tests were performed to characterize the viscoelastic behavior of collagen matrices. The rate of stress relaxation of both hydrated and dehydrated collagen matrices shows a linear initial stress level dependency. Increased crosslinking reduces viscosity in collagen gel, but the effect is negligible for thin film. Relaxation time distribution spectrum was obtained from the stress relaxation data by inverse Laplace transform. For most of the collagen matrices, three peaks at the short (0.3s ~1 s), medium (3s ~90 s), and long relaxation time (> 200 s) were observed in the continuous spectrum, which likely corresponds to relaxation mechanisms involve fiber, inter-fibril, and fibril sliding. Splitting of the middle peak was observed at higher initial stress levels suggesting increased structural heterogeneity at the fibril level with mechanical loading. The intensity of the long-term peaks increases with higher initial stress levels indicating the engagement of collagen fibrils at higher levels of tissue strain. PMID:23628869
Spin-rotation contribution to the relaxation time of the fluorine nuclei in benzotrifluoride
Faulk, Robert Hardy
1965-01-01
to the relaxa- tion time from data on the relaxation time of the hydrogen nuclei in both the pure benzotrifluoride and in a solution of benzotrifluoride and carbon disulfide, since carbon disulfide contains no magnetic dipoles, and since it is assumed... and the viscosities for pure benzotrifluoride and for a solution which is by volume one third benzotrifluoride and two thirds carbon disulfide were measured as a function of temperature. The relaxation time for the fluorine nuclei was measured as a function...
NASA Astrophysics Data System (ADS)
Vandusschoten, D.; Dejager, P. A.; Vanas, H.
Heterogeneous (bio)systems are often characterized by several water-containing compartments that differ in relaxation time values and diffusion constants. Because of the relatively small differences among these diffusion constants, nonoptimal measuring conditions easily lead to the conclusion that a single diffusion constant suffices to describe the water mobility in a heterogeneous (bio)system. This paper demonstrates that the combination of a T2 measurement and diffusion measurements at various echo times (TE), based on the PFG MSE sequence, enables the accurate determination of diffusion constants which are less than a factor of 2 apart. This new method gives errors of the diffusion constant below 10% when two fractions are present, while the standard approach of a biexponential fit to the diffusion data in identical circumstances gives larger (>25%) errors. On application of this approach to water in apple parenchyma tissue, the diffusion constant of water in the vacuole of the cells ( D = 1.7 × 10 -9 m 2/s) can be distinguished from that of the cytoplasm ( D = 1.0 × 10 -9 m 2/s). Also, for mung bean seedlings, the cell size determined by PFG MSE measurements increased from 65 to 100 ?m when the echo time increased from 150 to 900 ms, demonstrating that the interpretation of PFG SE data used to investigate cell sizes is strongly dependent on the T2 values of the fractions within the sample. Because relaxation times are used to discriminate the diffusion constants, we propose to name this approach diffusion analysis by relaxation- time- separated (DARTS) PFG NMR.
Dielectric relaxation time of bulk water at 136-140 K, background loss and crystallization effects
NASA Astrophysics Data System (ADS)
Johari, G. P.
2005-04-01
Dielectric relaxation time, ?, of ultraviscous bulk water has been determined by analyzing its loss tangent, tan?, data, which had been measured on heating the vapor-deposited amorphous solid water and hyperquenched glassy water in our earlier studies. [Johari, Hallbrucker, and Mayer, J. Chem. Phys. 95, 2955 (1991); 97, 5851 (1992)]. As for glasses and liquids generally, the measured tan? of water is the sum of a frequency-independent background loss and a frequency-dependent relaxational loss. A two-frequency method is provided for determining the background loss and used for obtaining the relaxational part of tan?. After considering the structural relaxation and crystal-nuclei growth effects, ? for water has been determined. At 136±1K, it is 2.5±0.6s when a single relaxation time is (untenably) assumed, and 42±14s when a distribution of relaxation times, a characteristic of viscous liquids, is assumed, with Davidson-Cole distribution parameter of 0.75. Structural relaxation time of ˜70s for water at 136K, which was originally estimated from the DSC endotherm [Johari, Hallbrucker, and Mayer, Nature (London) 330, 552 (1987)], has been revised to ˜33s. Temperature dependence of ? could not be determined because ultraviscous water crystallizes too rapidly to cubic ice containing stacking faults and intergranular water. The study demonstrates that water is a liquid over the 136-155K range, thus removing the basis for a recent contention on its state.
NASA Astrophysics Data System (ADS)
Jirsa, M.; Koblischka, M. R.; van Dalen, A. J. J.
1997-07-01
Conventional and dynamic relaxation processes and scaling properties of the magnetic hysteresis loops (MHL) were studied on a Pb-ion irradiated 0953-2048/10/7/004/img7 single crystal by means of the torque magnetometry. The columnar pinning structure produced by irradiation enhanced considerably the induced critical current density and caused the high-field part of the MHL to be field-independent up to 0953-2048/10/7/004/img8. The substantial change of the pinning structure shifted the appearance of the fishtail effect to higher temperatures and fields. The relaxation experiments confirm a correlation between the relaxation rate and the MHL shape and point to quite different relaxation regimes at high and low fields. Correspondingly, the scaling of the MHLs in both field ranges is different. This behaviour is modelled by two separable contributions to the MHL, one being active mainly at high fields and the other at low fields (central peak). Possible origins of these two contributions are discussed.
Multiple-relaxation-time lattice Boltzmann modeling of incompressible flows in porous media
Qing Liu; Ya-Ling He; Chao He
2014-09-20
In this paper, a two-dimensional eight-velocity (D2Q8) multiple-relaxation-time (MRT) lattice Boltzmann (LB) model is proposed for incompressible porous flows at the representative elementary volume scale based on the Brinkman-Forchheimer-extended Darcy formulation. In the model, the porosity is included into the pressure-based equilibrium moments, and the linear and nonlinear drag forces of the porous media are incorporated into the model by adding a forcing term to the MRT-LB equation in the moment space. Through the Chapman-Enskog analysis, the generalized Navier-Stokes equations can be recovered exactly without artificial compressible errors. Numerical simulations of several typical two-dimensional porous flows are carried out to validate the present MRT-LB model. The numerical results of the present MRT-LB model are in good agreement with the analytical solutions and/or other numerical solutions reported in the literature.
Isospin relaxation time in heavy-ion collisions at intermediate energies
Li, Ba; Ko, Che Ming.
1998-01-01
Using an isospin-dependent transport model, we have studied the isospin and momentum relaxation times in the heavy residues formed in heavy-ion collisions at intermediate energies. It is found that only at incident energies ...
Measurements of nuclear thermal relaxation times under conditions of high resolution
Hildebrandt, Alvin Frank
1956-01-01
. Graphical method used to determine the relaxation time T ^ .................... .. . **9 3. Variation of the reciprocal of the thermal relaxation time of the methyl and ring protons of toluene in carbon disulfide. . . . 59 LIST OF TABLES TABLES PAGE 1... for toluene in carbon disulfide at a temperature of 32.5 ? 2.0?C...............................57 1 I. INTRODUCTION Since the first successful experiments on nuclear re? sonance in bulk matter were carried out in 19^6, considerable interest has developed...
Specific viscosity of neutron-rich nuclear matter from a relaxation time approach
Jun Xu
2011-01-01
The specific viscosity of neutron-rich nuclear matter is studied from the relaxation time approach using an isospin- and momentum-dependent interaction and the nucleon-nucleon cross sections taken as those from the experimental data modified by the in-medium effective masses as used in the isospin-dependent Boltzmann-Uehling-Uhlenbeck (IBUU) transport model calculations. The relaxation time of neutrons is larger while that of protons is
Relaxation time ansatz and shear and bulk viscosities of gluon matter
Khvorostukhin, A. S. [Joint Institute for Nuclear Research, 141980 Dubna (Russian Federation); Institute of Applied Physics, Moldova Academy of Science, MD-2028 Kishineu (Moldova, Republic of); Toneev, V. D. [Joint Institute for Nuclear Research, 141980 Dubna (Russian Federation); Voskresensky, D. N. [National Research Nuclear University ''MEPhI,'' Kashirskoe sh. 31, Moscow 115409 (Russian Federation); GSI, Helmholtzzentrum fuer Schwerionenforschung GmbH, Planckstrasse 1, DE-64291 Darmstadt (Germany)
2011-09-15
Shear and bulk viscosity-to-entropy density ratios are calculated for pure gluon matter in a nonequilibrium mean-field quasiparticle approach within the relaxation time approximation. We study how different approximations used in the literature affect the results for the shear and bulk viscosities. Though the results for the shear viscosity turned out to be quite robust, all evaluations of the shear and bulk viscosities obtained in the framework of the relaxation time approximation can be considered only as rough estimations.
Spin-lattice relaxation time in drug discovery and design.
Figueroa-Villar, José Daniel; Tinoco, Luzineide Wanderley
2009-01-01
NMR is one of the most powerful techniques for ligand-biomolecule interaction studies and drug screening and design. There are several methods that are strongly used, including chemical shift perturbation (CSP), saturation transfer difference (STD) and diffusion coefficients. However, one of the most useful and easy to apply NMR parameters in medicinal chemistry studies is the spin-lattice relaxation data, which can be employed to investigate the strength and topology of intermolecular interactions, such as drug-drug, drug-protein, drug-DNA, drug-micelle (or vesicle) and biomolecule-biomolecule interactions. This review deals with the newest applications of T(1) in different studies of interest for drug design and evaluation. PMID:19754396
NASA Astrophysics Data System (ADS)
Ruta, B.; Chushkin, Y.; Monaco, G.; Cipelletti, L.; Pineda, E.; Bruna, P.; Giordano, V. M.; Gonzalez-Silveira, M.
2012-10-01
We use x-ray photon correlation spectroscopy to investigate the structural relaxation process in a metallic glass on the atomic length scale. We report evidence for a dynamical crossover between the supercooled liquid phase and the metastable glassy state, suggesting different origins of the relaxation process across the transition. Furthermore, using different cooling rates, we observe a complex hierarchy of dynamic processes characterized by distinct aging regimes. Strong analogies with the aging dynamics of soft glassy materials, such as gels and concentrated colloidal suspensions, point at stress relaxation as a universal mechanism driving the relaxation dynamics of out-of-equilibrium systems.
Relaxing a constraint on the number of messengers in a low-scale gauge mediation
Sato, Ryosuke; Yonekura, Kazuya [Department of Physics, University of Tokyo, Tokyo 113-0033 (Japan); Institute for the Physics and Mathematics of the Universe (IPMU), University of Tokyo, Chiba 277-8568 (Japan); Yanagida, T. T. [Institute for the Physics and Mathematics of the Universe (IPMU), University of Tokyo, Chiba 277-8568 (Japan); Department of Physics, University of Tokyo, Tokyo 113-0033 (Japan)
2010-02-15
We propose a mechanism for relaxing a constraint on the number of messengers in low-scale gauge mediation models. The Landau pole problem for the standard-model gauge coupling constants in the low-scale gauge mediation can be circumvented by using our mechanism. An essential ingredient is a large positive anomalous dimension of messenger fields given by a large Yukawa coupling in a conformal field theory at high energies. The positive anomalous dimension reduces the contribution of the messengers to the beta function of the standard-model gauge couplings.
NASA Astrophysics Data System (ADS)
Takács, S.
2001-05-01
The basic procedures for determining the time constant of superconductors are the AC losses (low frequency slope of the power loss density per cycle, position of the maximum loss per cycle vs frequency) and relaxation measurements of the induced coupling currents. We show that there are fundamental reasons for some differences between them for flat structures (like Rutherford type cables, filamentary BSCCO tapes, cable-in-conduit conductors). As the main losses in superconducting cables occur by the induced currents between the opposite sides of the cable (transverse losses), there are many cable designs with central insulating layer, mainly for flat cables. Then, the coupling losses between adjacent strands (parallel losses) can prevail. We calculate the time constants for both transverse and parallel components of the coupling currents in flat structures with N strands based on different approaches (AC losses, field shielding, current relaxation). For transverse coupling currents, the time constants from losses differ in the absolute value. The relaxation time is larger than the loss time constant for N<18 and smaller for higher N values. For currents induced between adjacent strands, the ratio of the time constants from the relaxation and AC loss measurements depends on geometrical parameters of the cable. The relaxation time should be generally larger than the time constant from the AC loss measurements.
Liu, Qing
2015-01-01
In this paper, a double multiple-relaxation-time lattice Boltzmann model is developed for simulating transient solid-liquid phase change problems in porous media at the representative elementary volume scale. The model uses two different multiple-relaxation-time lattice Boltzmann equations, one for the flow field and the other for the temperature field with nonlinear latent heat source term. The model is based on the generalized non-Darcy formulation, and the solid-liquid phase change interface is traced through the liquid fraction which is determined by the enthalpy method. The model is validated by numerical simulations of conduction melting in a semi-infinite space, solidification in a semi-infinite corner, and convection melting in a square cavity filled with porous media. The numerical results demonstrate the efficiency and accuracy of the present model for simulating transient solid-liquid phase change problems in porous media.
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
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
A transient solution and scaling laws for vesicle electrodeformation and relaxation
NASA Astrophysics Data System (ADS)
Lin, Hao; Zhang, Jia; Zahn, Jefferey
2012-11-01
A transient analysis for vesicle deformation and relaxation under DC electric fields is presented. The theory extends from a droplet model developed by us, with the additional consideration of a lipid membrane separating two fluids of arbitrary properties. For the latter, both a membrane-charging and a membrane-mechanical model are supplied. The main result is an ODE governing the evolution of the vesicle aspect ratio. The model prediction is extensively compared with experimental data, and is shown to accurately capture the system behavior. More importantly, the comparison reveals that vesicle relaxation obeys a universal behavior regardless of the means of deformation. The process is governed by a single timescale that is a function of the vesicle initial radius, the fluid viscosity, and the initial membrane tension. This universal scaling law can be used to calculate membrane properties from experimental data. NSF award CBET-0747886.
Applications of DNP-NMR for the measurement of heteronuclear T1 relaxation times
NASA Astrophysics Data System (ADS)
Day, Iain J.; Mitchell, John C.; Snowden, Martin J.; Davis, Adrian L.
2007-08-01
Measurement of heteronuclear spin-lattice relaxation times is hampered by both low natural abundance and low detection sensitivity. Combined with typically long relaxation times, this results in extended acquisition times which often renders the experiment impractical. Recently a variant of dynamic nuclear polarisation has been demonstrated in which enhanced nuclear spin polarisation, generated in the cryo-solid state, is transferred to the liquid state for detection. Combining this approach with small flip angle pulse trains, similar to the FLASH- T1 imaging sequence, allows the rapid determination of spin-lattice relaxation times. In this paper we explore this method and its application to the measurement of T1 for both carbon-13 and nitrogen-15 at natural abundance. The effects of RF inhomogeneity and the influence of proton decoupling in the context of this experiment are also investigated.
Kaminski, K.; Adrjanowicz, K.; Paluch, M.; Kaminska, E.
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.
Zujovi?, Zoran D; Bowmaker, Graham A
2006-08-01
A relatively rapid phase alternation of the effective field in the time averaged precession frequency (TAPF) sequence results in averaging of the proton RF spin-lock field. The spin-locking of the proton magnetization becomes less efficient and thus shortens T(1rho)(H), the proton spin-lattice relaxation time in the rotating frame. The relaxation time also depends on the ratio of tau(1) and tau(2) intervals i.e. tau(1)/tau(2) and not only on the number of tau(c)=tau(1)+tau(2) blocks, i.e. the number of the phase transients. Experiments are performed on solid samples of ferrocene and glycine and for some time intervals, T(1rho)(H) is shortened by factors of 9-100 compared to the relaxation times obtained in the standard experiment. PMID:16757196
Mitchell, J; Chandrasekera, T C
2014-12-14
The nuclear magnetic resonance transverse relaxation time T2, measured using the Carr-Purcell-Meiboom-Gill (CPMG) experiment, is a powerful method for obtaining unique information on liquids confined in porous media. Furthermore, T2 provides structural information on the porous material itself and has many applications in petrophysics, biophysics, and chemical engineering. Robust interpretation of T2 distributions demands appropriate processing of the measured data since T2 is influenced by diffusion through magnetic field inhomogeneities occurring at the pore scale, caused by the liquid/solid susceptibility contrast. Previously, we introduced a generic model for the diffusion exponent of the form -ante(k) (where n is the number and te the temporal separation of spin echoes, and a is a composite diffusion parameter) in order to distinguish the influence of relaxation and diffusion in CPMG data. Here, we improve the analysis by introducing an automatic search for the optimum power k that best describes the diffusion behavior. This automated method is more efficient than the manual trial-and-error grid search adopted previously, and avoids variability through subjective judgments of experimentalists. Although our method does not avoid the inherent assumption that the diffusion exponent depends on a single k value, we show through simulation and experiment that it is robust in measurements of heterogeneous systems that violate this assumption. In this way, we obtain quantitative T2 distributions from complicated porous structures and demonstrate the analysis with examples of ceramics used for filtration and catalysis, and limestone of relevance to the construction and petroleum industries. PMID:25494741
NASA Astrophysics Data System (ADS)
Mitchell, J.; Chandrasekera, T. C.
2014-12-01
The nuclear magnetic resonance transverse relaxation time T2, measured using the Carr-Purcell-Meiboom-Gill (CPMG) experiment, is a powerful method for obtaining unique information on liquids confined in porous media. Furthermore, T2 provides structural information on the porous material itself and has many applications in petrophysics, biophysics, and chemical engineering. Robust interpretation of T2 distributions demands appropriate processing of the measured data since T2 is influenced by diffusion through magnetic field inhomogeneities occurring at the pore scale, caused by the liquid/solid susceptibility contrast. Previously, we introduced a generic model for the diffusion exponent of the form -ant_e^k (where n is the number and te the temporal separation of spin echoes, and a is a composite diffusion parameter) in order to distinguish the influence of relaxation and diffusion in CPMG data. Here, we improve the analysis by introducing an automatic search for the optimum power k that best describes the diffusion behavior. This automated method is more efficient than the manual trial-and-error grid search adopted previously, and avoids variability through subjective judgments of experimentalists. Although our method does not avoid the inherent assumption that the diffusion exponent depends on a single k value, we show through simulation and experiment that it is robust in measurements of heterogeneous systems that violate this assumption. In this way, we obtain quantitative T2 distributions from complicated porous structures and demonstrate the analysis with examples of ceramics used for filtration and catalysis, and limestone of relevance to the construction and petroleum industries.
Time and Temperature Dependence of Viscoelastic Stress Relaxation in Gold and Gold Alloy Thin Films
NASA Astrophysics Data System (ADS)
Mongkolsuttirat, Kittisun
Radio frequency (RF) switches based on capacitive MicroElectroMechanical System (MEMS) devices have been proposed as replacements for traditional solid-state field effect transistor (FET) devices. However, one of the limitations of the existing capacitive switch designs is long-term reliability. Failure is generally attributed to electrical charging in the capacitor's dielectric layer that creates an attractive electrostatic force between a moving upper capacitor plate (a metal membrane) and the dielectric. This acts as an attractive stiction force between them that may cause the switch to stay permanently in the closed state. The force that is responsible for opening the switch is the elastic restoring force due to stress in the film membrane. If the restoring force decreases over time due to stress relaxation, the tendency for stiction failure behavior will increase. Au films have been shown to exhibit stress relaxation even at room temperature. The stress relaxation observed is a type of viscoelastic behavior that is more significant in thin metal films than in bulk materials. Metal films with a high relaxation resistance would have a lower probability of device failure due to stress relaxation. It has been shown that solid solution and oxide dispersion can strengthen a material without unacceptable decreases in electrical conductivity. In this study, the viscoelastic behavior of Au, AuV solid solution and AuV2O5 dispersion created by DC magnetron sputtering are investigated using the gas pressure bulge testing technique in the temperature range from 20 to 80°C. The effectiveness of the two strengthening approaches is compared with the pure Au in terms of relaxation modulus and 3 hour modulus decay. The time dependent relaxation curves can be fitted very well with a four-term Prony series model. From the temperature dependence of the terms of the series, activation energies have been deduced to identify the possible dominant relaxation mechanism. The measured modulus relaxation of Au films also proves that the films exhibit linear viscoelastic behavior. From this, a linear viscoelastic model is shown to fit very well to experimental steady state stress relaxation data and can predict time dependent stress for complex loading histories including the ability to predict stress-time behavior at other strain rates during loading. Two specific factors that are expected to influence the viscoelastic behavior-degree of alloying and grain size are investigated to explore the influence of V concentration in solid solution and grain size of pure Au. It is found that the normalized modulus of Au films is dependent on both concentration (C) and grain size (D) with proportionalities of C1/3 and D 2, respectively. A quantitative model of the rate-equation for dislocation glide plasticity based on Frost and Ashby is proposed and fitted well with steady state anelastic stress relaxation experimental data. The activation volume and the density of mobile dislocations is determined using repeated stress relaxation tests in order to further understand the viscoelastic relaxation mechanism. A rapid decrease of mobile dislocation density is found at the beginning of relaxation, which correlates well with a large reduction of viscoelastic modulus at the early stage of relaxation. The extracted activation volume and dislocation mobility can be ascribed to mobile dislocation loops with double kinks generated at grain boundaries, consistent with the dislocation mechanism proposed for the low activation energy measured in this study.
Vecino, P A; Huang, Z; Mitchell, J; McGregor, J; Daly, H; Hardacre, C; Thomson, J M; Gladden, L F
2015-08-28
Relative strengths of surface interaction for individual carbon atoms in acyclic and cyclic hydrocarbons adsorbed on alumina surfaces are determined using chemically resolved (13)C nuclear magnetic resonance (NMR) T1 relaxation times. The ratio of relaxation times for the adsorbed atoms T1,ads to the bulk liquid relaxation time T1,bulk provides an indication of the mobility of the atom. Hence a low T1,ads/T1,bulk ratio indicates a stronger surface interaction. The carbon atoms associated with unsaturated bonds in the molecules are seen to exhibit a larger reduction in T1 on adsorption relative to the aliphatic carbons, consistent with adsorption occurring through the carbon-carbon multiple bonds. The relaxation data are interpreted in terms of proximity of individual carbon atoms to the alumina surface and adsorption conformations are inferred. Furthermore, variations of interaction strength and molecular configuration have been explored as a function of adsorbate coverage, temperature, surface pre-treatment, and in the presence of co-adsorbates. This relaxation time analysis is appropriate for studying the behaviour of hydrocarbons adsorbed on a wide range of catalyst support and supported-metal catalyst surfaces, and offers the potential to explore such systems under realistic operating conditions when multiple chemical components are present at the surface. PMID:26214614
Conductivity and relaxation time of porous silicon using the Kramers-Kronig relation
NASA Astrophysics Data System (ADS)
Dariani, R. S.; Tavakoli, F.
2015-01-01
To review the dielectric characteristics of porous silicon samples with various porosities, an equivalent circuit including a capacitor and parallel resistance was used. By applying AC voltage with a constant amplitude of 200 mV to the circuit and using impedance measurements of the samples between 10-100 KHz, the variations in the capacitance, dielectric function, refractive index, and resistance for the samples at room temperature and up to 350 °C were studied. The dielectric characteristics of the samples decreased with increasing frequency. In addition, with increasing temperature, the pore diameters increased, and the dielectric characteristics varied. In this paper, we demonstrate that the relaxation time and DC conductivity could be obtained using the Kramers-Kronig function and Hilbert transformation. Our results indicate that the relaxation time and DC conductivity increase with increasing porosity, and with increasing temperature, the relaxation time decreases and the DC conductivity increases.
Kumar, Sudhir
frequently used relaxed-clock methods for estimating these times and their credibility intervals (CrIs the actual model. The 95% CrIs also contain the true time for !95% of the simulated data sets. However are rarely known a priori and are difficult to detect empirically, we suggest building composite CrIs using
NASA Astrophysics Data System (ADS)
Béland, Laurent Karim; Mousseau, Normand
2013-12-01
Diffusion and relaxation of defects in bulk systems is a complex process that can only be accessed directly through simulations. We characterize the mechanisms of low-temperature aging in self-implanted crystalline silicon, a model system used extensively to characterize both amorphization and return to equilibrium processes, over 11 orders of magnitudes in time, from 10 ps to 1 s, using a combination of molecular dynamics and kinetic activation-relaxation technique simulations. These simulations allow us to reassess the atomistic mechanisms responsible for structural relaxations and for the overall logarithmic relaxation, a process observed in a large number of disordered systems and observed here over the whole simulation range. This allows us to identify three microscopic regimes, annihilation, aggregation, and reconstruction, in the evolution of defects and to propose atomistic justification for an analytical model of logarithmic relaxation. Furthermore, we show that growing activation barriers and configurational space exploration are kinetically limiting the system to a logarithmic relaxation. Overall, our long-time simulations do not support the amorphous cluster model but point rather to a relaxation driven by elastic interactions between defect complexes of all sizes.
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.
Relaxation Time of a Chiral Quantum R-L Circuit J. Gabelli,1
Plaçais, Bernard
by the electronic transit time in the circuit. DOI: 10.1103/PhysRevLett.98.166806 PACS numbers: 73.23.Ad, 73.43.Cd-L circuit is not the classical L=R time but the electronic transit time of the circuit. In our workRelaxation Time of a Chiral Quantum R-L Circuit J. Gabelli,1 G. Fe`ve,1 T. Kontos,1 J.-M. Berroir,1
Simple one-dimensional interaction systems with superexponential relaxation times
NASA Astrophysics Data System (ADS)
Toom, Andrei
1995-08-01
Finite one-dimensional random processes with local interaction are presented which keep some information of a topological nature about their initial conditions during time, the logarithm of whose expectation grows asymptotically at least as M 3, where M is the "size" of the set R M of states of one component. Actually R M is a circle of length M. At every moment of the discrete time every component turns into some kind of average of its neighbors, after which it makes a random step along this circle. All these steps are mutually independent and identically distributed. In the present version the absolute values of the steps never exceed a constant. The processes are uniform in space, time, and the set of states. This estimation contributes to our awareness of what kind of stable behavior one can expect from one-dimensional random processes with local interaction.
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.
Time-Dependent Stokes Shift from Solvent Dielectric Relaxation
Jing Xu; Quan-De Wang; Quan Zhu; Ke-Xiang Fu; Fu-Cheng He; Xiang-Yuan Li
2010-01-01
The Stokes shift response function, which is related to the time dependent solvation energy, is calculated with the dielectric response function and a novel expression of nonequilibrium solvation energy. In the derivation, relationship between the polarization and the dielectric response function is used. With the dipole-in-a-sphere model applied to the system coumarin 343 and water as the solvent, encouraging agreement
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.
Klimavicius, Vytautas; Gdaniec, Zofia; Balevicius, Vytautas
2014-11-11
NMR relaxation processes of anions were studied in two neat imidazolium-based room temperature ionic liquids (RTILs) 1-decyl-3-methyl-imidazolium bromide- and chloride. The spin-lattice and spin-spin relaxations of 81Br and 35Cl nuclei were found to be extremely fast due to very strong quadrupolar interactions. The determined relaxation rates are comparable with those observed in the solids or in some critical organic solute/water/salt systems. In order to eliminate the acoustic ringing of the probe-head during relaxation times measurements the novel pulse sequence has been devised. It is based on the conventional inversion recovery pulse sequence, however, instead of the last 90° pulse the subsequence of three 90° pulses applied along axes to fulfill the phase cycling condition is used. Using this pulse sequence it was possible to measure T1 for both studied nuclei. The viscosity measurements have been carried out and the rotational correlation times were calculated. The effective 35Cl quadrupolar coupling constant was found to be almost one order lower than that for 81Br, i.e. 1.8 MHz and 16.0 MHz, respectively. Taking into account the facts that the ratio of (Q(35Cl)/Q(81Br))2?0.1 and EFG tensors on the anions are quite similar, analogous structural organizations are expected for both RTILs. The observed T1/T2 (1.27-1.44) ratios were found to be not sufficiently high to confirm the presence of long-living (on the time scale of ?10(-8) s) mesoscopic structures or heterogeneities in the studied neat ionic liquids. PMID:24938418
NASA Astrophysics Data System (ADS)
Revil, A.; Binley, A.; Mejus, L.; Kessouri, P.
2015-08-01
Low-frequency quadrature conductivity spectra of siliclastic materials exhibit typically a characteristic relaxation time, which either corresponds to the peak frequency of the phase or the quadrature conductivity or a typical corner frequency, at which the quadrature conductivity starts to decrease rapidly toward lower frequencies. This characteristic relaxation time can be combined with the (intrinsic) formation factor and a diffusion coefficient to predict the permeability to flow of porous materials at saturation. The intrinsic formation factor can either be determined at several salinities using an electrical conductivity model or at a single salinity using a relationship between the surface and quadrature conductivities. The diffusion coefficient entering into the relationship between the permeability, the characteristic relaxation time, and the formation factor takes only two distinct values for isothermal conditions. For pure silica, the diffusion coefficient of cations, like sodium or potassium, in the Stern layer is equal to the diffusion coefficient of these ions in the bulk pore water, indicating weak sorption of these couterions. For clayey materials and clean sands and sandstones whose surface have been exposed to alumina (possibly iron), the diffusion coefficient of the cations in the Stern layer appears to be 350 times smaller than the diffusion coefficient of the same cations in the pore water. These values are consistent with the values of the ionic mobilities used to determine the amplitude of the low and high-frequency quadrature conductivities and surface conductivity. The database used to test the model comprises a total of 202 samples. Our analysis reveals that permeability prediction with the proposed model is usually within an order of magnitude from the measured value above 0.1 mD. We also discuss the relationship between the different time constants that have been considered in previous works as characteristic relaxation time, including the mean relaxation time obtained from a Debye decomposition of the spectra and the Cole-Cole time constant.
Scaling and alpha-helix regulation of protein relaxation in a lipid bilayer
NASA Astrophysics Data System (ADS)
Qiu, Liming; Buie, Creighton; Cheng, Kwan Hon; Vaughn, Mark W.
2014-12-01
Protein conformation and orientation in the lipid membrane plays a key role in many cellular processes. Here we use molecular dynamics simulation to investigate the relaxation and C-terminus diffusion of a model helical peptide: beta-amyloid (A?) in a lipid membrane. We observed that after the helical peptide was initially half-embedded in the extracelluar leaflet of phosphatidylcholine (PC) or PC/cholesterol (PC/CHOL) membrane, the C-terminus diffused across the membrane and anchored to PC headgroups of the cytofacial lipid leaflet. In some cases, the membrane insertion domain of the A? was observed to partially unfold. Applying a sigmoidal fit to the process, we found that the characteristic velocity of the C-terminus, as it moved to its anchor site, scaled with ?u-4/3, where ?u is the fraction of the original helix that was lost during a helix to coil transition. Comparing this scaling with that of bead-spring models of polymer relaxation suggests that the C-terminus velocity is highly regulated by the peptide helical content, but that it is independent of the amino acid type. The A? was stabilized by the attachment of the positive Lys28 side chain to the negative phosphate of PC or 3? oxygen of CHOL in the extracellular lipid leaflet and of the C-terminus to its anchor site in the cytofacial lipid leaflet.
NASA Astrophysics Data System (ADS)
Kreemer, C.; Hammond, W. C.; Plag, H.
2007-05-01
We present evidence for the detection of postseismic relaxation from the 1999 M 7.1 Hector Mine earthquake in the non-linearity of time series from the southern BARGEN GPS network. It is important to understand and quantify the transient contributions owing to earthquake cycle effects near the Yucca Mountain nuclear waste repository because these data are used to estimate interseismic secular strain increase that could eventually be released in earthquakes. Most sites from the 35 site continuous GPS network, in operation since 1999, lie over 200 km from the earthquake. However, some of these time series exhibit significant curvature and spatial variation that is similar to the predictions of models of postseismic viscoelastic relaxation following the recent Mojave Desert earthquakes. Central in our analysis is our attempt to distinguish between the expected non-linear signal in the time-series and the network-wide common-mode signals that can occur over similar times-scales as the postseismic signal. We discuss various regional filtering approaches and show their impact on our ability to infer the postseismic relaxation parameters. One such approach investigates time series cross-correlations, which can help distinguish between network-wide common-mode and spatially coherent regional signals predicted by geophysical models. In order to place stronger constraints on the postseismic decay-time, and to better evaluate the significance and correctness of the postseismic displacement field, we estimate a transient component in the time-series of a large number of SCIGN and BARGEN sites. The use of near- and far-field data allows us to infer whether the near- and far-field postseismic deformation signals are significant differently from each other and what that can tell us about the underlying postseismic processes.
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.
A High-Speed Delta-Sigma Modulator with Relaxed DEM Timing Requirement
Moon, Un-Ku
A High-Speed Delta-Sigma Modulator with Relaxed DEM Timing Requirement Sunwoo Kwon and Un-Ku Moon) to around 10 bits [1], [2] depending on the size of the DAC elements. So as to achieve better linearity) techniques [3], [4], component sorting [5], or component sizing method [6]. Both the sorting and sizing
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 Alexander I. Chervanyov and Gert Heinrich Leibniz Institute of Polymer Research Dresden, D-01069 Dresden nano-colloids mediated by adsorbing and non-adsorbing polymers. By making use of this theory, we have
MRI Under Hyperbaric Air and Oxygen: Effects on Local Magnetic Field and Relaxation Times
Duong, Timothy Q.
are saturated with oxygen could provide insight into the role of oxygen on the regulation of cerebral blood flow is known to increase blood T2 and T2* by increasing hemoglobin saturation, i.e., the blood oxygen levelMRI Under Hyperbaric Air and Oxygen: Effects on Local Magnetic Field and Relaxation Times Eric R
RELAXATION TIME OF ANISOTROPIC SIMPLE EXCLUSION PROCESSES AND QUANTUM HEISENBERG MODELS
RELAXATION TIME OF ANISOTROPIC SIMPLE EXCLUSION PROCESSES AND QUANTUM HEISENBERG MODELS PIETRO quantum Heisenberg models and asymmetric di#11;usions on the lattice, we consider an anisotropic simple exclusion process with N particles in a rectangle of Z 2 . Every particle at row h tries to jump
Short-time viscous and density relaxation in glycerol and ortho-terphenyl
NASA Astrophysics Data System (ADS)
Roland, C. M.; Ngai, K. L.
1997-01-01
Coupling model analyses of short-time relaxation data of glycerol from quasielastic neutron scattering and ortho-terphenyl (OTP) by molecular dynamic simulation are shown to account for both the time dependence of the correlation function and its temperature dependence. The latter is expressible over a limited temperature range as an Arrhenius relation with an apparent activation energy for the fast ?-relaxation process, with EA=6.2 and 3.9 kcal/mol for glycerol and OTP, respectively. The viscosities of these glass formers have also been measured up to temperatures sufficiently high that the mean viscosity relaxation time, , becomes short, approaching the crossover time, tc?2 ps, of the coupling model. When this condition is realized, becomes comparable to ?D(T) in both magnitude and temperature dependence. Hence, the asymptotic high temperature activation energy of approximately equals the apparent activation energy of ?D. The experimental data, supporting this connection between macroscopic variables such as viscosity and microscopic dynamics from neutron scattering and molecular dynamics simulation, indicate the significance of the fast ?-relaxation process in both fragile and strong liquids.
NASA Astrophysics Data System (ADS)
Singh, Jaswinder
2013-12-01
The analysis of a three-dimensional (3-D) wavelength/time/space (W-T-S) asynchronous optical CDMA code family is presented considering MAI only under relaxed cross-correlation (?c ? 1). Based on the code performance, it is shown that for code-limited systems (when W and/or T are non-prime), the number of generated codes and hence the supported users can be significantly increased by relaxing the cross-correlation constraint if a slight degradation in code performance can be tolerated.
Only through perturbation can relaxation times be estimated
NASA Astrophysics Data System (ADS)
Ditlevsen, Susanne; Lansky, Petr
2012-11-01
Estimation of model parameters is as important as model building, but is often neglected in model studies. Here we show that despite the existence of well known results on parameter estimation in a simple homogenous Ornstein-Uhlenbeck process, in most practical situations the methods suffer greatly from finite sample sizes and especially the estimator of the time constant of the system is degraded. Therefore an alternative solution is of paramount importance. We present such a solution based on perturbation of the system, observing trajectories far from equilibrium. The results are illustrated on computer experiments based on applications in neuroscience and pharmacokinetics, which show a striking improvement of the quality of estimation. The results are important for judicious designs of experiments to obtain maximal information from each data point, especially when samples are expensive or difficult to obtain.
Option pricing during post-crash relaxation times
NASA Astrophysics Data System (ADS)
Dibeh, Ghassan; Harmanani, Haidar M.
2007-07-01
This paper presents a model for option pricing in markets that experience financial crashes. The stochastic differential equation (SDE) of stock price dynamics is coupled to a post-crash market index. The resultant SDE is shown to have stock price and time dependent volatility. The partial differential equation (PDE) for call prices is derived using risk-neutral pricing. European call prices are then estimated using Monte Carlo and finite difference methods. Results of the model show that call option prices after the crash are systematically less than those predicted by the Black-Scholes model. This is a result of the effect of non-constant volatility of the model that causes a volatility skew.
Thermalization and possible quantum relaxation times in "classical" fluids: theory and experiment
Z. Nussinov; F. Nogueira; M. Blodgett; K. F. Kelton
2015-08-20
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 $0.6 \\%$. Inspired by the Eigenstate Thermalization Hypothesis, we suggest a relation between the lowest equilibration temperature to the melting or liquidus temperature and discuss a possible corollary concerning the absence of finite temperature "ideal glass" transitions. We suggest a general quantum mechanical derivation for the viscosity of glasses at general temperatures. 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.
Thermalization and possible quantum relaxation times in "classical" fluids: theory and experiment
Z. Nussinov; F. Nogueira; M. Blodgett; K. F. Kelton
2015-09-07
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 $0.6 \\%$. Inspired by the Eigenstate Thermalization Hypothesis, we suggest a relation between the lowest equilibration temperature to the melting or liquidus temperature and discuss a possible corollary concerning the absence of finite temperature "ideal glass" transitions. We suggest a general quantum mechanical derivation for the viscosity of glasses at general temperatures. 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.
Temperature dependence of 1H NMR relaxation time, T2, for intact and neoplastic plant tissues
NASA Astrophysics Data System (ADS)
Lewa, Czes?aw J.; Lewa, Maria
Temperature dependences of the spin-spin proton relaxation time, T2, have been shown for normal and tumorous tissues collected from kalus culture Nicotiana tabacum and from the plant Kalanchoe daigremontiana. For neoplastic plant tissues, time T2 was increased compared to that for intact plants, a finding similar to that for animal and human tissues. The temperature dependences obtained were compared to analogous relations observed with animal tissues.
Qing-Xin Chu; Fung-Yuel Chang
1997-01-01
From the finite-difference time-domain (FDTD) simulation of response voltages and currents of a microstrip terminated by a step-pulse excitation voltage source and a resistor load, the time-domain characteristic model (TDCM) of the microstrip is synthesized by use of the waveform relaxation method, which is based on the iteration and deconvolution techniques. As an example, the extracted model is applied to
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.
Surface NMR measurement of proton relaxation times in medium to coarse-grained sand aquifer.
Shushakov, O A
1996-01-01
A surface NMR investigation of groundwater in the geomagnetic field is under study. To detect the surface NMR a wire loop with a diameter of about 100 m, being an antenna for both an exciting field source and the NMR signal receiver, is laid out on the ground. A sinusoidal current pulse with a rectangular envelope is passed through the loop to excite the NMR signal. The carrier frequency of the oscillating current in this pulse is equal to the Larmor frequency of protons in the Earth's magnetic field. The current amplitude is changed up to 200 amps and the pulse duration is fixed and is equal to 40 ms. The exciting pulse is followed by an induction emf signal caused by the Larmor nuclear precession in geomagnetic field. The relaxation times T1, T2, and T2* were measured by the surface NMR for both groundwater in medium to coarse-grained sand at borehole and for bulk water under the ice surface of frozen lake. To determine T1, a longitudinal interference in experiments with repeated pulses was measured. A sequence with equal period between equal excitation pulses was used. The relaxation times T1, T2, measured for bulk water under the ice of the Ob reservoir were 1.0 s and 0.7 s, respectively. To estimate an influence of dissolved oxygen T1 of the same water at the same temperature was measured by lab NMR with and without pumping of oxygen. The relaxation time T1 measured for water in the medium to coarse-grained sand is 0.65 s. The relaxation time T2 estimated by spin echo sequence is found to be equal to 0.15 s. The relaxation time T2* is found to be about 80 ms. This result contradicts published earlier phenomenological correlation between relaxation time T2* and grain size of water-bearing rock. This could be as a result of unsound approach based on grain size or influence of paramagnetic impurities. PMID:8970122
Rate variation and estimation of divergence times using strict and relaxed clocks
2011-01-01
Background Understanding causes of biological diversity may be greatly enhanced by knowledge of divergence times. Strict and relaxed clock models are used in Bayesian estimation of divergence times. We examined whether: i) strict clock models are generally more appropriate in shallow phylogenies where rate variation is expected to be low, ii) the likelihood ratio test of the clock (LRT) reliably informs which model is appropriate for dating divergence times. Strict and relaxed models were used to analyse sequences simulated under different levels of rate variation. Published shallow phylogenies (Black bass, Primate-sucking lice, Podarcis lizards, Gallotiinae lizards, and Caprinae mammals) were also analysed to determine natural levels of rate variation relative to the performance of the different models. Results Strict clock analyses performed well on data simulated under the independent rates model when the standard deviation of log rate on branches, ?, was low (?0.1), but were inappropriate when ?>0.1 (95% of rates fall within 0.0082-0.0121 subs/site/Ma when ? = 0.1, for a mean rate of 0.01). The independent rates relaxed clock model performed well at all levels of rate variation, although posterior intervals on times were significantly wider than for the strict clock. The strict clock is therefore superior when rate variation is low. The performance of a correlated rates relaxed clock model was similar to the strict clock. Increased numbers of independent loci led to slightly narrower posteriors under the relaxed clock while older root ages provided proportionately narrower posteriors. The LRT had low power for ? = 0.01-0.1, but high power for ? = 0.5-2.0. Posterior means of ?2 were useful for assessing rate variation in published datasets. Estimates of natural levels of rate variation ranged from 0.05-3.38 for different partitions. Differences in divergence times between relaxed and strict clock analyses were greater in two datasets with higher ?2 for one or more partitions, supporting the simulation results. Conclusions The strict clock can be superior for trees with shallow roots because of low levels of rate variation between branches. The LRT allows robust assessment of suitability of the clock model as does examination of posteriors on ?2. PMID:21943087
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.
Separation of Equilibration Time-Scales in the Gradient Expansion
Garbrecht, Bjorn
2009-01-01
We study thermalization by applying gradient expansion to the Kadanoff-Baym equations of the 2PI effective action to two-loop in a theory with Dirac fermions coupled to scalars. In addition to those chemical potentials which equilibrate in the on-shell limit, we identify modes which 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.
NASA Technical Reports Server (NTRS)
Spodick, D. H.; Quarry, V. M.; Khan, A. H.
1974-01-01
Systolic and diastolic time intervals in 14 cardiac patients with pulsus alternans revealed significant alternation of preinjection period (PEP), isovolumic contraction time (IVCT), left ventricular ejection time (LVET), ejection time index (ETI), PEP/LVET, and carotid dD/dt with better functional values in the strong beats. Cycle length, duration of electromechanical systole (EMS) and total diastole, i.e., isovolumic relaxation period (IRP) and diastolic filling period (DFP) occurred in 7 out of 8 patients. These diastolic intervals alternated reciprocally such that the IRP of the strong beats encroached upon the DFP of the next (weak) beats.
Time scales - Their history, definition and interpretation
NASA Astrophysics Data System (ADS)
Guinot, B.; Seidelmann, P. K.
1988-04-01
The International Astronomical Union (IAU) adopted in 1976 a recommendation for time scales for dynamical theories and ephemerides. In 1979 the IAU adopted the names Terrestrial Dynamical Time (TDT) and Barycentric Dynamical Time (TDB) for those time scales. In the time period since those adoptions, questions concerning the interpretation, meaning and implications of these time scales have arisen. There have also been discussions at the 1982 IAU General Assembly and at other IAU Colloquia concerning the relativistic implications of the different time scales. In 1985 the IAU appointed a Working Group for Reference Frames with the added requirement that it consider the relationship between TAI and TDT. This paper is meant to clarify the interpretations and meaning concerning these time scales.
Nuclear spin-lattice relaxation-time reduction in small particles
NASA Astrophysics Data System (ADS)
Rabbani, S. R.; Edmonds, D. T.
1994-09-01
A method is described of reducing the nuclear spin-lattice relaxation time in a polycrystalline solid without the introduction of any paramagnetic impurities. It relies on the fact that the relaxation times of nuclei on a surface are usually much shorter than those in the bulk due to greater freedom of movement. Simply reducing the particle size by grinding or other methods is shown to be effective in markedly reducing the spin-lattice relaxation time of all the nuclei in the specimen because of the good thermal contact between like nuclei in the interior and surface of small particles. The nuclear quadrupole resonance (NQR) of 14N, 2D, or 23Na was measured for the same specimens with different particle sizes by nuclear quadrupole double resonance to ensure that the chemical structure of the compound did not alter due to the grinding. In all samples studied, except sodium thiosulphate, the NQR spectrum was unaffected by the grinding except that the time necessary to collect the data was reduced. In the case of sodium thiosulphate a marked change in the NQR spectrum was observed despite the fact that no change in chemical composition could be detected. Data is presented which demonstrates the effectiveness of the technique and a simple model of the underlying mechanism is described.
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
Shores, D.A.; Stout, J.H.; Gerberich, W.W.
1993-06-01
This report summarizes a three-year study of stresses arising in the oxide scale and underlying metal during high temperature oxidation and of scale cracking. In-situ XRD was developed to measure strains during oxidation over 1000{degrees}C on pure metals. Acoustic emission was used to observe scale fracture during isothermal oxidation and cooling, and statistical analysis was used to infer mechanical aspects of cracking. A microscratch technique was used to measure the fracture toughness of scale/metal interface. A theoretical model was evaluated for the development and relaxation of stresses in scale and metal substrate during oxidation.
NASA Astrophysics Data System (ADS)
Wojnarowska, Z.; Ngai, K. L.; Paluch, M.
2014-05-01
Using broadband dielectric spectroscopy we investigate the changes in the conductivity relaxation times ?? observed during the physical aging of the protic ionic conductor carvedilol dihydrogen phosphate (CP). Due to the large decoupling of ion diffusion from host molecule reorientation, the ion conductivity relaxation time ??(Tage,tage) can be directly measured at temperatures Tage below Tg for exceedingly long aging times tage till ??(Tage,tage) has reached the equilibrium value ? _? ^{eq} ( {T_{age} } ). The dependence of ??(Tage,tage) on tage is well described by the stretched exponential function, ? _? ( {T_{age},t_{age} } ) = Aexp[ { - ( {{t_{age} }/{? _{age ( {T_{age} } )}}} )^? } ] + ? _? ^{eq} ( {T_{age} } ), where ? is a constant and ?age(Tage) can be taken as the structural ?-relaxation time of the equilibrium liquid at T = Tage. The value of ? _? ^{eq} ( {T_{age} } ) obtained after 63 days long annealing of CP, deviates from the Vogel-Fulcher-Tammann-Hesse (VFTH?) dependence of ??(T) determined from data taken above Tg and extrapolated down to Tage. Concurrently, ?age(Tage) also deviates from the Vogel-Fulcher-Tammann-Hesse (VFTH?) dependence. The results help to answer the longstanding question of whether the VFTH dependence of ??(T) as well as the structural ?-relaxation time ??(T) holds or not in the equilibrium liquid state far below Tg.
Specific viscosity of neutron-rich nuclear matter from relaxation time approach
Xu, Jun
2011-01-01
The specific viscosity of neutron-rich nuclear matter is studied from the relaxation time approach using an isospin- and momentum-dependent interaction and the nucleon-nucleon cross sections taken as those from the experimental data modified by the in-medium effective masses as used in the IBUU transport model calculations. The relaxation time of neutrons is larger while that of protons is smaller in neutron-rich nuclear matter compared with that in symmetric nuclear matter, and this leads to a larger specific viscosity in neutron-rich nuclear matter. In addition, the specific viscosity decreases with increasing temperature because of more frequent collisions and weaker Pauli blocking effect at higher temperatures. At lower temperatures the specific viscosity increases with increasing density due to the Pauli blocking effect, while at higher temperatures it slightly decreases with increasing density as a result of smaller in-medium effective masses at higher densities.
Specific viscosity of neutron-rich nuclear matter from a relaxation time approach
Jun Xu
2011-12-05
The specific viscosity of neutron-rich nuclear matter is studied from the relaxation time approach using an isospin- and momentum-dependent interaction and the nucleon-nucleon cross sections taken as those from the experimental data modified by the in-medium effective masses as used in the IBUU transport model calculations. The relaxation time of neutrons is larger while that of protons is smaller in neutron-rich nuclear matter compared with that in symmetric nuclear matter, and this leads to a larger specific viscosity in neutron-rich nuclear matter. In addition, the specific viscosity decreases with increasing temperature because of more frequent collisions and weaker Pauli blocking effect at higher temperatures. At lower temperatures the specific viscosity increases with increasing density due to the Pauli blocking effect, while at higher temperatures it slightly decreases with increasing density as a result of smaller in-medium effective masses at higher densities.
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
Spin-Lattice Relaxation Times of Single Donors and Donor Clusters in Silicon
NASA Astrophysics Data System (ADS)
Hsueh, Yu-Ling; Büch, Holger; Tan, Yaohua; Wang, Yu; Hollenberg, Lloyd C. L.; Klimeck, Gerhard; Simmons, Michelle Y.; Rahman, Rajib
2014-12-01
An atomistic method of calculating the spin-lattice relaxation times (T1 ) is presented for donors in silicon nanostructures comprising of millions of atoms. The method takes into account the full band structure of silicon including the spin-orbit interaction. The electron-phonon Hamiltonian, and hence, the deformation potential, is directly evaluated from the strain-dependent tight-binding Hamiltonian. The technique is applied to single donors and donor clusters in silicon, and explains the variation of T1 with the number of donors and electrons, as well as donor locations. Without any adjustable parameters, the relaxation rates in a magnetic field for both systems are found to vary as B5 , in excellent quantitative agreement with experimental measurements. The results also show that by engineering electronic wave functions in nanostructures, T1 times can be varied by orders of magnitude.
Relaxation-time approximation for a Boltzmann gas in Robertson-Walker universe models
NASA Astrophysics Data System (ADS)
Banach, Zbigniew; Makaruk, Hanna
1995-05-01
Given Einstein's theory of gravitation, the relaxation-time approximation for a general-relativistic Boltzmann equation is studied with a view to demonstrating its usefulness in the context of Robertson-Walker universe models. Solutions of the full nonlinear equations for the metric and the distribution function are examined, together with their relation to linearized perturbations. Emphasis is placed on finding analogs of the exact results on strong or weak convergence to equilibrium employed in special-relativistic kinetic theory. At the late stages of cosmic expansion, an explicit choice of the empirical collision frequency is made to fit optimally the relaxation-time model to the “actual” Einstein-Boltzmann system. Finally, perspectives for some future generalizations are outlined.
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.
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.
Spin-Lattice Relaxation-Time Measurements of Trivalent Iron in Single-Crystal Calcite
S. A. Marshall; S. V. Nistor; R. A. Serway
1972-01-01
The spin-lattice relaxation time for the M=-12-->12 transition of trivalent iron in single-crystal calcite has been measured at X band by pulse recovery from 1.4 to 45 K and by spectral line broadening from 40 to 195 K. The resulting transition-probability data are well described by the sum of a direct-process term and a Raman-process term, the latter having a
Long intersubband relaxation times in n-type germanium quantum wells
NASA Astrophysics Data System (ADS)
Ortolani, Michele; Stehr, Dominik; Wagner, Martin; Helm, Manfred; Pizzi, Giovanni; Virgilio, Michele; Grosso, Giuseppe; Capellini, Giovanni; De Seta, Monica
2011-11-01
We measured the non-radiative intersubband relaxation time in n-type modulation-doped Ge/SiGe multi-quantum wells of different thickness by means of degenerate pump-probe experiments. The photon energy was tuned to be resonant with the lowest conduction band intersubband transition energy (14-29 meV), as measured by terahertz absorption spectroscopy and in agreement with band structure calculations. Temperature-independent lifetimes in excess of 30 ps were observed.
Viscosity, relaxation time, and dynamics within a model asphalt of larger molecules
NASA Astrophysics Data System (ADS)
Li, Derek D.; Greenfield, Michael L.
2014-01-01
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.
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.
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.
Natelson, Douglas
spectroscopic method for studying intraband car- rier relaxation in a magnetic field.4 Specifically, this techRelaxation of quasi-two-dimensional electrons in a quantizing magnetic field probed by time-color pump-probe spectroscopy in a magnetic field. The strong conduction-band nonparabolicity of InSb causes
Muscle contraction and relaxation-response time in response to on or off status of visual stimulus
2014-01-01
Background It is unclear whether response time is affected by a stimulus cue, such as a light turned on or off, or if there are differences in response to these cues during a muscle contraction task compared with a muscle relaxation task. The objective of this study was to assess the response time of a relaxation task, including the contraction portion of the task, to a stimulus of a light turned on or off. In addition, we investigated the effect of the pre-contraction level on the relaxation task. Results Contraction response time was significantly shorter during the light-on status than during the light-off status (P <0.01), and relaxation response time in each maximum voluntary contraction was significantly longer during the light-on status than during the light-off status (P <0.01). The relaxation response time became longer in order of 25% to 75% maximum voluntary contraction regardless of light-on or -off status, and was significantly longer than the contraction response time (P <0.05-0.01). Conclusions This study found that as the contraction level increased, the relaxation response time became longer than the contraction response time regardless of light status. However, contraction response time or relaxation response time findings were opposite to this during the light-on status and light-off status: contraction response time became shorter in the light-on status than in the light-off status and relaxation response time became longer in the light-on status than in the light-off status. These results suggest that the length of each response time is affected by motor control in the higher order brain and involves specific processing in the visual system. PMID:25085278
Equilibration time scales of physically relevant observables
Luis Pedro García-Pintos; Noah Linden; Artur S. L. Malabarba; Anthony J. Short; Andreas Winter
2015-09-18
We address the problem of understanding from first principles the conditions under which a closed quantum system equilibrates rapidly with respect to a concrete observable. Previously known general upper bounds on the time scales of equilibration were extremely long, with times scaling linearly with the dimension of the Hilbert space. Moreover, these bounds proved to be tight, since particular constructions of observables scaling in this way were found. In this paper we provide a new upper bound on the equilibration time scales which shows, in fact, equilibration is much faster under some physically reasonable conditions. In particular, we apply this result to give bounds on the time scales of equilibration for a system interacting with a thermal bath which do not scale with the size of the bath.
Review of time scales. [Universal Time-Ephemeris Time-International Atomic Time
NASA Technical Reports Server (NTRS)
Guinot, B.
1974-01-01
The basic time scales are presented: International Atomic Time, Universal Time, and Universal Time (Coordinated). These scales must be maintained in order to satisfy specific requirements. It is shown how they are obtained and made available at a very high level of precision.
Temperature dependence of relaxation times and temperature mapping in ultra-low-field MRI
NASA Astrophysics Data System (ADS)
Vesanen, Panu T.; Zevenhoven, Koos C. J.; Nieminen, Jaakko O.; Dabek, Juhani; Parkkonen, Lauri T.; Ilmoniemi, Risto J.
2013-10-01
Ultra-low-field MRI is an emerging technology that allows MRI and NMR measurements in microtesla-range fields. In this work, the possibilities of relaxation-based temperature measurements with ultra-low-field MRI were investigated by measuring T1 and T2 relaxation times of agarose gel at 50 ?T-52 mT and at temperatures 5-45 °C. Measurements with a 3 T scanner were made for comparison. The Bloembergen-Purcell-Pound relaxation theory was combined with a two-state model to explain the field-strength and temperature dependence of the data. The results show that the temperature dependencies of agarose gel T1 and T2 in the microtesla range differ drastically from those at 3 T; the effect of temperature on T1 is reversed at approximately 5 mT. The obtained results were used to reconstruct temperature maps from ultra-low-field scans. These time-dependent temperature maps measured from an agarose gel phantom at 50 ?T reproduced the temperature gradient with good contrast.
Three-Dimensional Multi-Relaxation Time (MRT) Lattice-Boltzmann Models for Multiphase Flow
Premnath, K N; Abraham, John; Premnath, Kannan N.
2006-01-01
In this paper, three-dimensional (3D) multi-relaxation time (MRT) lattice-Boltzmann (LB) models for multiphase flow are presented. In contrast to the Bhatnagar-Gross-Krook (BGK) model, a widely employed kinetic model, in MRT models the rates of relaxation processes owing to collisions of particle populations may be independently adjusted. As a result, the MRT models offer a significant improvement in numerical stability of the LB method for simulating fluids with lower viscosities. We show through the Chapman-Enskog multiscale analysis that the continuum limit behavior of 3D MRT LB models corresponds to that of the macroscopic dynamical equations for multiphase flow. We extend the 3D MRT LB models developed to represent multiphase flow with reduced compressibility effects. The multiphase models are evaluated by verifying the Laplace-Young relation for static drops and the frequency of oscillations of drops. The results show satisfactory agreement with available data and significant gains in numerical stabilit...
Kalman plus weights: a time scale algorithm
NASA Technical Reports Server (NTRS)
Greenhall, C. A.
2001-01-01
KPW is a time scale algorithm that combines Kalman filtering with the basic time scale equation (BTSE). A single Kalman filter that estimates all clocks simultaneously is used to generate the BTSE frequency estimates, while the BTSE weights are inversely proportional to the white FM variances of the clocks. Results from simulated clock ensembles are compared to previous simulation results from other algorithms.
Relaxation times in single event electrospraying controlled by nozzle front surface modification.
Stachewicz, Urszula; Dijksman, J Frits; Burdinski, Dirk; Yurteri, Caner U; Marijnissen, Jan C M
2009-02-17
Single event electrospraying (SEE) is a method for on-demand deposition of femtoliter to picoliter volumes of fluids. To determine the influence of the size of the meniscus on the characteristics of the single event electrospraying process, glass capillaries were used with and without an antiwetting coating comprising a self-assembled 1H,1H,2H,2H-perfluorodecyltrichlorosilane-based monolayer to control the meniscus size. A large difference was found in driving single event electrospraying from a small meniscus compared to what is needed to generate a single event electrospraying from a large meniscus. Furthermore, after studying the different time constants related to the electrical and the hydrodynamic phenomena, we are able to explain the timing limitations of the deposition process from both a small and a large meniscus. The hydrodynamic relaxation time is significantly reduced in the case of the modified capillary, and the timing of SEE, which determines the deposition time, is limited by the resistor-capacitor RC time of the electrical circuit needed to drive the SEE. We have built a model that describes the almost one-dimensional motion of the liquid in the capillary during pulsing. The model has been used to estimate the hydrodynamic relaxation times related to the meniscus-to-cone and cone-to-meniscus transitions during SEE. By confining the meniscus to the inner diameter of the nozzle, we are able to deposit a volume smaller than 5 pL per SEE. PMID:19159191
Alexandrov, Nikola A; Marinova, Krastanka G; Gurkov, Theodor D; Danov, Krassimir D; Kralchevsky, Peter A; Stoyanov, Simeon D; Blijdenstein, Theodorus B J; Arnaudov, Luben N; Pelan, Eddie G; Lips, Alex
2012-06-15
The pendant-drop method (with drop-shape analysis) and Langmuir trough are applied to investigate the characteristic relaxation times and elasticity of interfacial layers from the protein HFBII hydrophobin. Such layers undergo a transition from fluid to elastic solid films. The transition is detected as an increase in the error of the fit of the pendant-drop profile by means of the Laplace equation of capillarity. The relaxation of surface tension after interfacial expansion follows an exponential-decay law, which indicates adsorption kinetics under barrier control. The experimental data for the relaxation time suggest that the adsorption rate is determined by the balance of two opposing factors: (i) the barrier to detachment of protein molecules from bulk aggregates and (ii) the attraction of the detached molecules by the adsorption layer due to the hydrophobic surface force. The hydrophobic attraction can explain why a greater surface coverage leads to a faster adsorption. The relaxation of surface tension after interfacial compression follows a different, square-root law. Such behavior can be attributed to surface diffusion of adsorbed protein molecules that are condensing at the periphery of interfacial protein aggregates. The surface dilatational elasticity, E, is determined in experiments on quick expansion or compression of the interfacial protein layers. At lower surface pressures (<11 mN/m) the experiments on expansion, compression and oscillations give close values of E that are increasing with the rise of surface pressure. At higher surface pressures, E exhibits the opposite tendency and the data are scattered. The latter behavior can be explained with a two-dimensional condensation of adsorbed protein molecules at the higher surface pressures. The results could be important for the understanding and control of dynamic processes in foams and emulsions stabilized by hydrophobins, as well as for the modification of solid surfaces by adsorption of such proteins. PMID:22480400
Time-resolved torsional relaxation of spider draglines by an optical technique.
Emile, O; Le Floch, A; Vollrath, F
2007-04-20
The sensitivity of the torsional pendulum demonstrates the self-shape-memory effect in different types of spider draglines. Here we report the time-resolved noncovalent bonds recovery in the protein structure. The torsional dynamics of such multilevel structure governed by reversible interactions are described in the frame of a nested model. Measurement of three different relaxation times confirms the existence of three energy storage levels in such two protein spidroin systems. Torsion opens the way to further investigations towards unraveling the tiny torque effects in biological molecules. PMID:17501459
NASA Astrophysics Data System (ADS)
Papadopoulos, P. L.; Zenginoglou, H. M.; Kosmopoulos, J. A.
1999-09-01
The director field of an electrohydrodynamically excited nematic liquid crystal layer exhibits a spatially periodic reorientation, provided the ac voltage applied to the layer is sufficiently close to its threshold value. This fact, combined with the strong optical anisotropy which, as a rule, characterizes any nematic phase, causes the nematic layer to act as a diffraction grating when illuminated by a monochromatic light beam. The time dependence of the intensities of diffraction fringes so formed are a manifestation of the motion of the nematic director. In the present article we propose an experimental method for the determination of the decay time of the nematic director under conditions where the electric field across the nematic layer is temporarily zero. The method is based on a linearized theory of the electrohydrodynamic instability of nematic liquid crystals, as well as, on an optical theory of the diffraction grating action of a periodically reoriented nematic layer. We applied the proposed method in a case where one can compute the respective theoretical value of the relaxation time of the nematic director. The agreement of the experimental result with what one obtains on the grounds of the electrohydrodynamic threshold theory, is found to be fairly satisfactory. Thus, taking advantage of the relatively simple dependence of the measured relaxation time on (a) the experimentally measurable distortion wave number of the electrohydrodynamically excited nematic layer, and (b) the elastic constants and the viscosity coefficients of the nematic material, we get the possibility to obtain further experimental information about the mentioned material parameters, by experimental investigation of the dependence of the director relaxation time on the distortion wave number.
Time-domain ab initio study of charge relaxation and recombination in dye-sensitized TiO2.
Duncan, Walter R; Craig, Colleen F; Prezhdo, Oleg V
2007-07-11
In order to investigate the electron dynamics at the alizarin/I2-/TiO2 interface this study uses a novel state-of-the-art quantum-classical approach that combines time-dependent density functional theory with surface hopping in the Kohn-Sham basis. Representing the dye-sensitized semiconductor Grätzel cell with the I-/I3- mediator, the system addresses the problems of an organic/inorganic, molecule/bulk interface that are commonly encountered in molecular electronics, photovoltaics, and photoelectrochemistry. The processes studied include the relaxation of the injected electron inside the TiO2 conduction band (CB), the back electron transfer (ET) from TiO2 to alizarin, the ET from the surface to the electrolyte, and the regeneration of the neutral chromophore by ET from the electrolyte to alizarin. Developing a theoretical understanding of these processes is crucial for improving solar cell design and optimizing photovoltaic current and voltage. The simulations carried out for the entire system that contains many electronic states reproduce the experimental time scales and provide detailed insights into the ET dynamics. In particular, they demonstrate the differences between the optimized geometric and electronic structure of the system at 0 K and the experimentally relevant structure at ambient temperature. The relaxation of the injected electron inside the TiO2 CB, which affects the solar cell voltage, is shown to occur on a 100 fs time scale and occurs simultaneously with the electron delocalization into the semiconductor bulk. The transfer of the electron trapped at the surface to the ground state of alizarin proceeds on a 1 ps time scale and is facilitated by vibrational modes localized on alizarin. If the electrolyte mediator is capable of approaching the semiconductor surface, it can form a stable complex and short-circuit the cell by accepting the photoexcited electron on a subpicosecond time scale. The ET from TiO2 to both alizarin and the electrolyte diminishes the solar cell current. Finally, the simulations show that the electrolyte can efficiently regenerate the neutral chromophore. This is true even though the two species do not form a chemical bond and, therefore, the electronic coupling between them is weaker than in the TiO2-chromophore and TiO2-electrolyte donor-acceptor pairs. The chromophore-electrolyte coupling can occur both directly through space and indirectly through bonding to the semiconductor surface. The ET events involving the electrolyte are promoted primarily by the electrolyte vibrational modes. PMID:17579405
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.
Estimates of expansion time scales
NASA Astrophysics Data System (ADS)
Jones, E. M.
Monte Carlo simulations of the expansion of a spacefaring civilization show that descendants of that civilization should be found near virtually every useful star in the Galaxy in a time much less than the current age of the Galaxy. Only extreme assumptions about local population growth rates, emigration rates, or ship ranges can slow or halt an expansion. The apparent absence of extraterrestrials from the solar system suggests that no such civilization has arisen in the Galaxy.
Electron spin relaxation time in (110) InGaAs/InAlAs quantum wells
NASA Astrophysics Data System (ADS)
Yokota, Nobuhide; Yasuda, Yusuke; Ikeda, Kazuhiro; Kawaguchi, Hitoshi
2014-07-01
Electron spin relaxation time ?s in InGaAs/InAlAs quantum wells (QWs) grown on (110) and (100) InP substrates was investigated by pump-probe transmission measurements. Similar ?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 ?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.
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.
Vold, Robert L; Hoatson, Gina L
2009-05-01
This paper describes EXPRESS (EXchange Program for RElaxing Spin Systems), a computer program that simulates the effects of Markovian jump dynamics for a wide variety of solid state nuclear magnetic resonance experiments. A graphical interface is described that facilitates the definition of rotational jumps around non-commuting axes that may occur at arbitrary, different rates. Solid state deuteron NMR is widely used to investigate such processes, and EXPRESS allows simulations of deuteron quadrupole echo and magic angle spinning line (MAS) shapes, as well as partially relaxed line shapes for measurements of anisotropic relaxation of Zeeman and quadrupolar order. Facilities are included for chemical shift tensors (at user-defined orientations relative to the quadrupole coupling tensors), so that EXPRESS is potentially useful for studies of paramagnetic systems where these interactions are of comparable magnitude. Many of the same techniques used for deuterons can be extended to half-integer quadrupolar nuclei. The same interface that specifies rotational "sites" for deuteron NMR studies is usable in EXPRESS to simulate static line shapes, MAS line shapes, and multiple pulse Carr-Purcell-Meiboom-Gill (CPMG) line shapes for the central transition of high spin quadrupoles with second order quadrupole coupling and chemical shift anisotropy. Representative simulations are displayed that show effects of slow libration on deuteron quadrupole echo line shapes and relaxation time anisotropies. EXPRESS is also used to investigate fundamental differences in the mechanism of echo formation in deuteron MAS and quadrupole CPMG experiments, and to illustrate significant differences between these techniques in the context of high spin quadrupolar nuclei. The program is modular and platform-independent, with facilities for users to add routines for experiments not yet envisioned. PMID:19201232
Relaxation of a dewetting contact line Part 1: A full-scale hydrodynamic calculation
Snoeijer, J H; Delon, G; Fermigier, M
2007-01-01
The relaxation of a dewetting contact line is investigated theoretically in the so-called "Landau-Levich" geometry in which a vertical solid plate is withdrawn from a bath of partially wetting liquid. The study is performed in the framework of lubrication theory, in which the hydrodynamics is resolved at all length scales (from molecular to macroscopic). We investigate the bifurcation diagram for unperturbed contact lines, which turns out to be more complex than expected from simplified 'quasi-static' theories based upon an apparent contact angle. Linear stability analysis reveals that below the critical capillary number of entrainment, Ca_c, the contact line is linearly stable at all wavenumbers. Away from the critical point the dispersion relation has an asymptotic behaviour sigma~|q| and compares well to a quasi-static approach. Approaching Ca_c, however, a different mechanism takes over and the dispersion evolves from |q| to the more common q^2. These findings imply that contact lines can not be treated a...
Determining energy relaxation length scales in two-dimensional electron gases
NASA Astrophysics Data System (ADS)
Billiald, Jordan; Backes, Dirk; König, Jürgen; Farrer, Ian; Ritchie, David; Narayan, Vijay
2015-07-01
We present measurements of the energy relaxation length scale ? in two-dimensional electron gases (2DEGs). A temperature gradient is established in the 2DEG by means of a heating current, and then the elevated electron temperature T e is estimated by measuring the resultant thermovoltage signal across a pair of deferentially biased bar-gates. We adapt a model by Rojek and König [Phys. Rev. B 90, 115403 (2014)] to analyse the thermovoltage signal and as a result extract ? , T e , and the power-law exponent ?i for inelastic scattering events in the 2DEG. We show that in high-mobility 2DEGs, ? can attain macroscopic values of several hundred microns, but decreases rapidly as the carrier density n is decreased. Our work demonstrates a versatile low-temperature thermometry scheme, and the results provide important insights into heat transport mechanisms in low-dimensional systems and nanostructures. These insights will be vital for practical design considerations of future nanoelectronic circuits.
Time scale evolution of avipoxviruses.
Le Loc'h, Guillaume; Bertagnoli, Stéphane; Ducatez, Mariette F
2015-10-01
Avipoxviruses are divided into three clades: canarypox-like viruses, fowlpox-like viruses, and psittacinepox-like viruses. Several molecular clock and demographic models available in the BEAST package were compared on three avipoxvirus genes (P4b, cnpv186 and DNA polymerase genes), which enabled to determine that avipoxviruses evolved at a rate of 2-8×10(-5)substitution/site/year, in the range of poxviruses previously reported evolution rates. In addition, the date of mean time of divergence of avipoxviruses from a common ancestor was extrapolated to be about 10,000-30,000years ago, at the same period as modern poxvirus species. Our findings will facilitate epidemiological investigations on avipoxviruses' spread, origin and circulation. PMID:26231721
Energy and temperature dependence of relaxation time and Wiedemann-Franz law on PbTe
NASA Astrophysics Data System (ADS)
Ahmad, Salameh; Mahanti, S. D.
2010-04-01
Recent revival of interest in high-temperature (T) thermoelectrics has made it necessary to understand in detail the T dependence of different transport coefficients, and different processes contributing to this temperature dependence. Since PbTe is a well-studied prototypical high-temperature thermoelectric, we have carried out theoretical studies to analyze how different physical sources contribute to electronic transport coefficients in this system over a wide T and concentration (n) range; 300K
Comparison of Viscosities from the Chapman-Enskog and Relaxation Time Methods
A. Wiranata; M. Prakash; P. Chakraborty
2012-04-11
A quantitative comparison between the results of shear viscosities from the Chapman-Enskog and relaxation time methods is performed for selected test cases with specified elastic differential cross sections: (i) the non-relativistic, relativistic and ultra-relativistic hard sphere gas with angle and energy independent differential cross section, (ii) the Maxwell gas, (iii) chiral pions and (iv) massive pions. Our quantitative results reveal that the extent of agreement (or disagreement) depends very sensitively on the energy dependence of the differential cross sections employed.
Predicting how nanoconfinement changes the relaxation time of a supercooled liquid
Trond S. Ingebrigtsen; Jeffrey R. Errington; Thomas M. Truskett; Jeppe C. Dyre
2013-11-05
The properties of nanoconfined fluids can be strikingly different from those of bulk liquids. A basic unanswered question is whether the equilibrium and dynamic consequences of confinement are related to each other in a simple way. We study this question by simulation of a liquid comprising asymmetric dumbbell-shaped molecules, which can be deeply supercooled without crystallizing. We find that the dimensionless structural relaxation times - spanning six decades as a function of temperature, density, and degree of confinement - collapse when plotted versus excess entropy. The data also collapse when plotted versus excess isochoric heat capacity, a behaviour that follows from the existence of isomorphs in the bulk and confined states.
An iterative linear method for calculation of spin-lattice relaxation times
NASA Astrophysics Data System (ADS)
Crouch, Ronald; Hurlbert, Stuart; Ragouzeos, Aris
A simple algorithm for the calculation of spin-lattice relaxation times which can be run in a programmable calculator is presented. As was suggested by H. Hanssum et al., an experimentally determined inhomogeneity parameter ( I) can be used with this procedure to compensate for imperfections in the RF field. The effects of variation of pulse width and repetition rate on both I and T1 are investigated with simulated and experimental data sets. The superiority of this approach over three-parameter nonlinear fitting methods is demonstrated by comparisons between data sets generated with different pulse flip angles and sample volumes.
Revisiting the measurement of the spin relaxation time in graphene-based devices
NASA Astrophysics Data System (ADS)
Idzuchi, H.; Fert, A.; Otani, Y.
2015-06-01
A long spin relaxation time (?sf) is the key for the applications of graphene to spintronics but the experimental values of ?sf have been generally much shorter than expected. We show that the usual determination by the Hanle method underestimates ?sf if proper account of the spin absorption by contacts is lacking. By revisiting series of experimental results and taking into account the spin absorption, we find that the corrected ?sf are longer and, for series of graphene samples of the same fabrication, less dispersed, which leads to a more unified picture of the ?sf.
Finite-difference-based multiple-relaxation-times lattice Boltzmann model for binary mixtures.
Zheng, Lin; Guo, Zhaoli; Shi, Baochang; Zheng, Chuguang
2010-01-01
In this paper, we propose a finite-difference-based lattice Boltzmann equation (LBE) model with multiple-relaxation times (MRT), in which the distribution functions of individual species evolve on a same regular lattice without any interpolations. Furthermore, the use of the MRT enables the model more flexible so that it can be applied to mixtures of species with different viscosities and adjustable Schmidt number. Some numerical tests are conducted to validate the model, the numerical results are found to agree well with analytical solutions/or other numerical results, and good numerical stability of the proposed LBE model is also observed. PMID:20365501
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.
NASA Astrophysics Data System (ADS)
Markelov, Denis A.; Matveev, Vladimir V.; Ingman, Petri; Lähderanta, Erkki; Boiko, Natalia I.
2011-09-01
A new theoretical description of the interior mobility of carbosilane dendrimers has been tested. Experiments were conducted using measurements of the 1H NMR spin-lattice relaxation time, T1H, of two-, three- and four-generation carbosilane dendrimers with three different types of terminal groups in dilute chloroform solutions. Temperature dependences of the NMR relaxation rate, 1/T1H, were obtained for the internal CH2 - groups of the dendrimers in the range of 1/T1H maximum, allowing us to directly evaluate the average time of the internal spectrum for each dendrimer. It was found that the temperature of 1/T1H maximum is practically independent of the number of generations, G; therefore, the theoretical prediction was confirmed experimentally. In addition, the average time of the internal spectrum of carbosilane dendrimers was found to be near 0.2 ns at room temperature, and this value correlates well with the values previously obtained for other dendrimer structures using other experimental techniques.
A method for measuring the Néel relaxation time in a frozen ferrofluid
NASA Astrophysics Data System (ADS)
Tackett, Ronald J.; Thakur, Jagdish; Mosher, Nathaniel; Perkins-Harbin, Emily; Kumon, Ronald E.; Wang, Lihua; Rablau, Corneliu; Vaishnava, Prem P.
2015-08-01
We report a novel method of determining the average Néel relaxation time and its temperature dependence by calculating derivatives of the measured time dependence of temperature for a frozen ferrofluid exposed to an alternating magnetic field. The ferrofluid, composed of dextran-coated Fe3O4 nanoparticles (diameter 13.7 nm ± 4.7 nm), was synthesized via wet chemical precipitation and characterized by x-ray diffraction and transmission electron microscopy. An alternating magnetic field of constant amplitude ( H 0 = 20 kA/m) driven at frequencies of 171 kHz, 232 kHz, and 343 kHz was used to determine the temperature dependent magnetic energy absorption rate in the temperature range from 160 K to 210 K. We found that the specific absorption rate of the ferrofluid decreased monotonically with temperature over this range at the given frequencies. From these measured data, we determined the temperature dependence of the Néel relaxation time and estimate a room-temperature magnetocrystalline anisotropy constant of 40 kJ/m3, in agreement with previously published results.
Decoherence, Time Scales and Pointer States
Tabish Qureshi
2011-11-28
Certain issues regarding the time-scales over which environment-induced decoherence occurs, and the nature of emergent pointer states, are discussed. A model system, namely, a Stern-Gerlach setup coupled to a quantum mechanical "heat-bath" is studied. The emergent pointer states for this system are obtained, which are different from those discussed in the literature. It is pointed out that this difference is due to some confusion regarding the decoherence time-scale, which is clarified here.
Trivedi, Dhara J; Wang, Linjun; Prezhdo, Oleg V
2015-03-11
By slowing down electron-phonon relaxation in nanoscale materials, one can increase efficiencies of solar energy conversion via hot electron extraction, multiple exciton generation, and elimination of exciton trapping. The elusive phonon bottleneck is hard to achieve, in particular, due to Auger-type energy exchange between electrons and holes. The Auger channel can be suppressed by hole trapping. Using time-domain ab initio simulation, we show that deep hole traps cannot fully eliminate the Auger channel. The simulations show that the hole-mediated electron relaxation is slowed down only by about 30%, which is in agreement with the recent experiments. The Auger energy exchange and hole relaxation to the trap state occur on similar time scales. Hole trapping is slow, because holes themselves experience a weak bottleneck effect. The study establishes the fundamental mechanisms of the electron and hole relaxation processes with and without hole traps. It shows that more sophisticated hole trapping strategies, for example, involving shell layers, are required in order to achieve the phonon bottleneck and to reduce electronic energy losses. PMID:25639836
Metabolic imaging in multiple time scales.
Ramanujan, V Krishnan
2014-03-15
We report here a novel combination of time-resolved imaging methods for probing mitochondrial metabolism in multiple time scales at the level of single cells. By exploiting a mitochondrial membrane potential reporter fluorescence we demonstrate the single cell metabolic dynamics in time scales ranging from microseconds to seconds to minutes in response to glucose metabolism and mitochondrial perturbations in real time. Our results show that in comparison with normal human mammary epithelial cells, the breast cancer cells display significant alterations in metabolic responses at all measured time scales by single cell kinetics, fluorescence recovery after photobleaching and by scaling analysis of time-series data obtained from mitochondrial fluorescence fluctuations. Furthermore scaling analysis of time-series data in living cells with distinct mitochondrial dysfunction also revealed significant metabolic differences thereby suggesting the broader applicability (e.g. in mitochondrial myopathies and other metabolic disorders) of the proposed strategies beyond the scope of cancer metabolism. We discuss the scope of these findings in the context of developing portable, real-time metabolic measurement systems that can find applications in preclinical and clinical diagnostics. PMID:24013043
NASA Astrophysics Data System (ADS)
Leclaire, S.; Pellerin, N.; Reggio, M.; Trépanier, J.-Y.
2014-03-01
The lattice Boltzmann modeling of immiscible multiphase flows needs to be further validated, especially when density variation occurs between the different flow phases. From this perspective, the goal of this research is to introduce the multiple-relaxation-time operator into a lattice Boltzmann model in order to improve its numerical stability in the presence of large density and viscosity ratios. Essentially, this research shows that the introduction of this operator greatly improves the numerical stability of the approach compared to the original single-relaxation-time collision operator. In many lattice Boltzmann research studies, multiphase lattice Boltzmann methods are validated using a reduced number of test cases, and unsteady flow test cases are frequently omitted before much more complex flow configurations are simulated. In this context, several test cases are proposed to evaluate the behavior of a lattice Boltzmann method for simulating immiscible multiphase flows with high density and viscosity ratios. These are: (1) two-phase Couette flow; (2) three-phase Laplace law; (3) three-phase Zalesak disk; (4) two-phase flow between oscillating plates; (5) two-phase capillary wave; and (6) the two-phase oscillating cylindrical bubble. The first two involve a steady regime, and the remaining four an unsteady regime.
NASA Astrophysics Data System (ADS)
Liang, H.; Shi, B. C.; Guo, Z. L.; Chai, Z. H.
2014-05-01
In this paper, a phase-field-based multiple-relaxation-time lattice Boltzmann (LB) model is proposed for incompressible multiphase flow systems. In this model, one distribution function is used to solve the Chan-Hilliard equation and the other is adopted to solve the Navier-Stokes equations. Unlike previous phase-field-based LB models, a proper source term is incorporated in the interfacial evolution equation such that the Chan-Hilliard equation can be derived exactly and also a pressure distribution is designed to recover the correct hydrodynamic equations. Furthermore, the pressure and velocity fields can be calculated explicitly. A series of numerical tests, including Zalesak's disk rotation, a single vortex, a deformation field, and a static droplet, have been performed to test the accuracy and stability of the present model. The results show that, compared with the previous models, the present model is more stable and achieves an overall improvement in the accuracy of the capturing interface. In addition, compared to the single-relaxation-time LB model, the present model can effectively reduce the spurious velocity and fluctuation of the kinetic energy. Finally, as an application, the Rayleigh-Taylor instability at high Reynolds numbers is investigated.
Mardini, I.A.; McCarter, R.J.; Fullerton, G.D.
1986-03-01
NMR studies of muscle have typically used muscles of mixed fiber composition and have not taken into account the metabolic state of the host. Samples of psoas (type IIB fibers) and soleus (type I fibers) muscles were obtained from 3 groups of rabbits: group C, fed regular chow; group DK fed a potassium deficient diet; and group HC fed a high cholesterol diet. The T/sub 1/ and T/sub 2/ relaxation times of psoas and soleus muscles were not significantly different for group C. Following dietary manipulation, (groups KD and HC), however, the relaxation times of the psoas and soleus muscles were significantly different. There was also a significant difference in water content of psoas muscles in groups KD and HC vs. group C but the observed differences in NMR results could be only partially accounted for by the shift in water content. The authors results suggest that (1) changes in ion or cholesterol concentration are capable of inducing changes in water bonding and structuring in muscle tissues; (2) diet must be added to the growing list of environmental factors that can cause NMR contrast changes; (3) selective use of muscles rich in one fiber type or another for NMR measurements could provide either control or diagnostic information, related to changes in body composition.
Lepage, M; Whittaker, A K; Rintoul, L; Bäck, S A; Baldock, C
2001-04-01
The effects of ionizing radiation in different compositions of polymer gel dosimeters are investigated using FT-Raman spectroscopy and NMR T2 relaxation times. The dosimeters are manufactured from different concentrations of comonomers (acrylamide and N,N'-methylene-bis-acrylamide) dispersed in different concentrations of an aqueous gelatin matrix. Results are analysed using a model of fast exchange of magnetization between three proton pools. The fraction of protons in each pool is determined using the known chemical composition of the dosimeter and FT-Raman spectroscopy. Based on these results, the physical and chemical processes in interplay in the dosimeters are examined in view of their effect on the changes in T2. The precipitation of growing macroradicals and the scavenging of free radicals by gelatin are used to explain the rate of polymerization. The model describes the changes in T2 as a function of the absorbed dose up to 50 Gy for the different compositions. This is expected to aid the theoretical design of new, more efficient dosimeters, since it was demonstrated that the optimum dosimeter (i.e, with the lowest dose resolution) must have a range of relaxation times which match the range of T2 values which can be determined with the lowest uncertainty using an MRI scanner. PMID:11324951
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.
Liang, H; Shi, B C; Guo, Z L; Chai, Z H
2014-05-01
In this paper, a phase-field-based multiple-relaxation-time lattice Boltzmann (LB) model is proposed for incompressible multiphase flow systems. In this model, one distribution function is used to solve the Chan-Hilliard equation and the other is adopted to solve the Navier-Stokes equations. Unlike previous phase-field-based LB models, a proper source term is incorporated in the interfacial evolution equation such that the Chan-Hilliard equation can be derived exactly and also a pressure distribution is designed to recover the correct hydrodynamic equations. Furthermore, the pressure and velocity fields can be calculated explicitly. A series of numerical tests, including Zalesak's disk rotation, a single vortex, a deformation field, and a static droplet, have been performed to test the accuracy and stability of the present model. The results show that, compared with the previous models, the present model is more stable and achieves an overall improvement in the accuracy of the capturing interface. In addition, compared to the single-relaxation-time LB model, the present model can effectively reduce the spurious velocity and fluctuation of the kinetic energy. Finally, as an application, the Rayleigh-Taylor instability at high Reynolds numbers is investigated. PMID:25353927
Du, Fei; Cooper, Alissa; Cohen, Bruce M; Renshaw, Perry F; Öngür, Dost
2012-05-01
Multiple lines of evidence suggest that microstructural abnormalities in the white matter are important in the pathophysiology of schizophrenia. Diffusion MRI approaches which can provide evidence on tissue structure have been widely used to probe these abnormalities in vivo, but transverse relaxation times (T2) may provide additional insights since they are determined by molecule-microenvironment interactions not revealed by diffusion MRI. T2 of water - located both intra and extracellularly - and N-acetylaspartate (NAA - located intracellularly) reflect related but distinct processes due to their differential localization and interactions with other molecules. In this study, we collected water and NAA T2 data from 16 healthy subjects (HC), and 16 patients with schizophrenia (SZ) at 4 T in a 9 cm(3) voxel in the right prefrontal white matter. The SZ group had longer water but shorter NAA T2 relaxation times when compared with the HC group. This pattern resulted in a statistically significant metabolite×group interaction (F(18,1):4.980, p=0.039). Prolongation of water T2 and shortening of NAA T2 is consistent with an impoverishment of white matter macromolecule structures (including myelin) and abnormal intra-axonal milieu and volume in SZ. PMID:22356802
Eugene, M.; Lechat, P.; Hadjiisky, P.; Teillac, A.; Grosgogeat, Y.; Cabrol, C.
1986-01-01
It should be possible to detect heart transplant rejection by nuclear magnetic resonance (NMR) imaging if it induces myocardial T1 and T2 proton relaxation time alterations or both. We studied 20 Lewis rats after a heterotopic heart transplantation. In vitro measurement of T1 and T2 was performed on a Minispec PC20 (Bruker) 3 to 9 days after transplantation. Histologic analysis allowed the quantification of rejection process based on cellular infiltration and myocardiolysis. Water content, a major determinant of relaxation time, was also studied. T1 and T2 were significantly prolonged in heterotopic vs orthotopic hearts (638 +/- 41 msec vs 606 +/- 22 msec for T1, p less than 0.01 and 58.2 +/- 8.4 msec vs 47.4 +/- 1.9 msec for T2, p less than 0.001). Water content was also increased in heterotopic hearts (76.4 +/- 2.3 vs 73.8 +/- 1.0, p less than 0.01). Most importantly, we found close correlations between T1 and especially T2 vs water content, cellular infiltration, and myocardiolysis. We conclude that rejection reaction should be noninvasively detected by NMR imaging, particularly with pulse sequences emphasizing T2.
Theory of the ac spin valve effect: a new method to measure spin relaxation time
NASA Astrophysics Data System (ADS)
Kochan, Denis; Gmitra, Martin; Fabian, Jaroslav
2012-02-01
Parallel (P) and antiparallel (AP) configurations of FNF junctions have, in a dc regime, different resistivities (RAP>RP), giving rise to the giant magnetoresistance (GMR) effect, which can be explained within the spin injection drift-diffusion model. We extend the model to include ac phenomena and predict new spin dynamical phenomenon; the resonant amplification and depletion of spin accumulation in the P and AP configurations, respectively. As the major new effect, the spin valve magnetoimpedance of the FNF junction oscillates with the driving ac frequency, which leads to negative GMR effect (|ZAP|<|ZP|). We show that from the spin-valve oscillation periods, measured all electrically in the GHz regime, the spin relaxation times could be extracted without any magnetic field and sample size changes (contrary to other techniques). For thin tunnel junctions the ac signal becomes pure Lorentzian, also enabling one to obtain the spin relaxation time of the N region from the signal width. This work, was published in Physical Review Letters,10, 176604 (2011).
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.
Picosecond-Time-Scale Fluctuations of Proteins in Glassy Matrices: The Role of Viscosity
NASA Astrophysics Data System (ADS)
Cornicchi, Elena; Onori, Giuseppe; Paciaroni, Alessandro
2005-10-01
Through elastic neutron scattering we investigated the fast dynamics of lysozyme in hydrated powder form or embedded in glycerol-water and glucose-water matrices. We calculated the relaxational contribution to the mean square displacements of protein hydrogen atoms. We found that the inverse of this quantity is linearly proportional to the logarithm of the viscosity of the solvent glassy matrix. This relationship suggests a close connection between the picosecond-time-scale dynamics of protein side chains and the solvent structural relaxation.
Transport coefficients for bulk viscous evolution in the relaxation time approximation
Amaresh Jaiswal; Radoslaw Ryblewski; Michael Strickland
2014-10-31
We derive the form of the viscous corrections to the phase-space distribution function due to the bulk viscous pressure and shear stress tensor using the iterative Chapman-Enskog method. We then calculate the transport coefficients necessary for the second-order hydrodynamic evolution of the bulk viscous pressure and the shear stress tensor. We demonstrate that the transport coefficients obtained using the Chapman-Enskog method are different than those obtained previously using the 14-moment approximation for a finite particle mass. Specializing to the case of boost-invariant and transversally homogeneous longitudinal expansion, we show that the transport coefficients obtained using the Chapman-Enskog method result in better agreement with the exact solution of the Boltzmann equation in the relaxation-time approximation compared to results obtained in the 14-moment approximation. Finally, we explicitly confirm that the time evolution of the bulk viscous pressure is significantly affected by its coupling to the shear stress tensor.
Time scales of turbulent relative dispersion
NASA Astrophysics Data System (ADS)
Bitane, Rehab; Homann, Holger; Bec, Jérémie
2012-10-01
Tracers in a turbulent flow separate according to the celebrated t3/2 Richardson-Obukhov law, which is usually explained by a scale-dependent effective diffusivity. Here, supported by state-of-the-art numerics, we revisit this argument. The Lagrangian correlation time of velocity differences increases too quickly for validating this approach, but acceleration differences decorrelate on dissipative time scales. Phenomenological arguments are used to relate the behavior of separations to that of a “local energy dissipation,” defined as the average ratio between the cube of the longitudinal velocity difference and the distance between the two tracers. This quantity is shown to stabilize on short time scales and this results in an asymptotic diffusion ?t1/2 of velocity differences. The time of convergence to this regime is shown to be that of deviations from Batchelor's initial ballistic regime, given by a scale-dependent energy dissipation time rather than the usual turnover time. It is finally demonstrated that the fluid flow intermittency should not affect this long-time behavior of the relative motion.
Time scales of turbulent relative dispersion.
Bitane, Rehab; Homann, Holger; Bec, Jérémie
2012-10-01
Tracers in a turbulent flow separate according to the celebrated t3/2 Richardson-Obukhov law, which is usually explained by a scale-dependent effective diffusivity. Here, supported by state-of-the-art numerics, we revisit this argument. The Lagrangian correlation time of velocity differences increases too quickly for validating this approach, but acceleration differences decorrelate on dissipative time scales. Phenomenological arguments are used to relate the behavior of separations to that of a "local energy dissipation," defined as the average ratio between the cube of the longitudinal velocity difference and the distance between the two tracers. This quantity is shown to stabilize on short time scales and this results in an asymptotic diffusion ?t1/2 of velocity differences. The time of convergence to this regime is shown to be that of deviations from Batchelor's initial ballistic regime, given by a scale-dependent energy dissipation time rather than the usual turnover time. It is finally demonstrated that the fluid flow intermittency should not affect this long-time behavior of the relative motion. PMID:23214642
Time scales involved in emergent market coherence
NASA Astrophysics Data System (ADS)
Kwapie?, J.; Dro?d?, S.; Speth, J.
2004-06-01
In addressing the question of the time scales characteristic for the market formation, we analyze high-frequency tick-by-tick data from the NYSE and from the German market. By using returns on various time scales ranging from seconds or minutes up to 2 days, we compare magnitude of the largest eigenvalue of the correlation matrix for the same set of securities but for different time scales. For various sets of stocks of different capitalization (and the average trading frequency), we observe a significant elevation of the largest eigenvalue with increasing time scale. Our results from the correlation matrix study can be considered as a manifestation of the so-called Epps effect. There is no unique explanation of this effect and it seems that many different factors play a role here. One of such factors is randomness in transaction moments for different stocks. Another interesting conclusion to be drawn from our results is that in the contemporary markets the emergence of significant correlations occurs on time scales much smaller than in the more distant history.
Calligari, Paolo; Abergel, Daniel
2014-04-10
Fluctuations of NMR resonance frequency shifts and their relation with protein exchanging conformations are usually analyzed in terms of simple two-site jump processes. However, this description is unable to account for the presence of multiple time scale dynamics. In this work, we present an alternative model for the interpretation of the stochastic processes underlying these fluctuations of resonance frequencies. Time correlation functions of (15)N amide chemical shifts computed from molecular dynamics simulations (MD) were analyzed in terms of a transiently fractional diffusion process. The analysis of MD trajectories spanning dramatically different time scales (? 200 ns and 1 ms [ Shaw, D. E.; Science 2010, 330, 341 - 346]) allowed us to show that our model could capture the multiple scale structure of chemical shift fluctuations. Moreover, the predicted exchange contribution Rex to the NMR transverse relaxation rate is in qualitative agreement with experimental results. These observations suggest that the proposed fractional diffusion model may provide significative improvement to the analysis of NMR dispersion experiments. PMID:24628040
7Li relaxation time measurements at very low magnetic field by 1H dynamic nuclear polarization
NASA Astrophysics Data System (ADS)
Zeghib, Nadir; Grucker, Daniel
2001-09-01
Dynamic nuclear polarization (DNP) of water protons was used to measure the relaxation time of lithium at very low magnetic field as a demonstration of the use of DNP for nuclei less abundant than water protons. Lithium (Li+) was chosen because it is an efficient treatment for manic-depressive illness, with an unknown action mechanism. After having recalled the theoretical basis of a three-spin system comprising two nuclei - the water proton of the solvent, the dissolved Li+ ion and the free electron of a free radical - we have developed a transient solution in order to optimize potential biological applications of Li DNP. The three-spin model has allowed computation of all the parameters of the system - the longitudinal relaxation rate per unit of free radical concentration, the dipolar and scalar part of the coupling between the nuclei and the electron, and the maximum signal enhancement achievable for both proton and lithium spins. All these measurements have been obtained solely through the detection of the proton resonance.
Understanding long-time vacancy aggregation in iron: A kinetic activation-relaxation technique study
NASA Astrophysics Data System (ADS)
Brommer, Peter; Béland, Laurent Karim; Joly, Jean-François; Mousseau, Normand
2014-10-01
Vacancy diffusion and clustering processes in body-centered-cubic (bcc) Fe are studied using the kinetic activation-relaxation technique (k-ART), an off-lattice kinetic Monte Carlo method with on-the-fly catalog building capabilities. For monovacancies and divacancies, k-ART recovers previously published results while clustering in a 50-vacancy simulation box agrees with experimental estimates. Applying k-ART to the study of clustering pathways for systems containing from one to six vacancies, we find a rich set of diffusion mechanisms. In particular, we show that the path followed to reach a hexavacancy cluster influences greatly the associated mean-square displacement. Aggregation in a 50-vacancy box also shows a notable dispersion in relaxation time associated with effective barriers varying from 0.84 to 1.1 eV depending on the exact pathway selected. We isolate the effects of long-range elastic interactions between defects by comparing to simulations where those effects are deliberately suppressed. This allows us to demonstrate that in bcc Fe, suppressing long-range interactions mainly influences kinetics in the first 0.3 ms, slowing down quick energy release cascades seen more frequently in full simulations, whereas long-term behavior and final state are not significantly affected.
The Geologic Time Scale in Historical Perspective
NSDL National Science Digital Library
This brief discussion of the development of the Geologic Time Scale begins with Nicolas Steno in 1669 whose ideas have become known as the principles of original horizontal deposition and superposition. Next are James Hutton in 1795 and Charles Lyell in the early 1800s who supported the principle of uniformitarianism. The work of William Smith and the principle of faunal succession is also noted. The site goes on to explain how and why the scale is divided as it is.
Quantum time scales in alpha tunneling
N. G. Kelkar; H. M. Castaneda; M. Nowakowski
2009-02-04
The theoretical treatment of alpha decay by Gamow is revisited by investigating the quantum time scales in tunneling. The time spent by an alpha particle in front of the barrier and traversing it before escape is evaluated using microscopic alpha nucleus potentials. The half-life of a nucleus is shown to correspond to the time spent by the alpha knocking in front of the barrier. Calculations for medium and super heavy nuclei show that from a multitude of available tunneling time definitions, the transmission dwell time gives the bulk of the lifetime of the decaying state, in most cases.
Quantum time scales in alpha tunneling
Kelkar, N G; Nowakowski, M
2008-01-01
The theoretical treatment of alpha decay by Gamow is revisited by investigating the quantum time scales in tunneling. The time spent by an alpha particle in front of the barrier and traversing it before escape is evaluated using microscopic alpha nucleus potentials. The half-life of a nucleus is shown to correspond to the time spent by the alpha knocking in front of the barrier. Calculations for medium and super heavy nuclei show that from a multitude of available tunneling time definitions, the transmission dwell time gives the bulk of the lifetime of the decaying state, in most cases.
The Laplace transform on time scales revisited
NASA Astrophysics Data System (ADS)
Davis, John M.; Gravagne, Ian A.; Jackson, Billy J.; Marks, Robert J., II; Ramos, Alice A.
2007-08-01
In this work, we reexamine the time scale Laplace transform as defined by Bohner and Peterson [M. Bohner, A. Peterson, Dynamic Equations on Time Scales: An Introduction with Applications, Birkhauser, Boston, 2001; M. Bohner, A. Peterson, Laplace transform and Z-transform: Unification and extension, Methods Appl. Anal. 9 (1) (2002) 155-162]. In particular, we give conditions on the class of functions which have a transform, develop an inversion formula for the transform, and further, we provide a convolution for the transform. The notion of convolution leads to considering its algebraic structure--in particular the existence of an identity element--motivating the development of the Dirac delta functional on time scales. Applications and examples of these concepts are given.
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.
NASA Astrophysics Data System (ADS)
Miller, David W.; Adelman, Steven A.
2002-08-01
A molecular theory of liquid phase vibrational energy relaxation (VER) [S. A. Adelman [et al.], Adv. Chem. Phys. 84, 73 (1993)] is applied to study the temperature T and density rho dependencies of the VER rate constant k(T,rho)=T1-1, where T1 is the energy relaxation time, of model Lennard-Jones systems that roughly simulate solutions of high-mass, low-frequency dihalogen solutes in rare gas solvents; specifically the I2/Xe, I2/Ar, and ICI/Xe solutions. For selected states of these systems, the theory's assumptions are tested against molecular dynamics (MD) results. The theory is based on the expression T1=beta]-1([omegal), where omegal and beta]([omega) are, respectively, the solute's liquid phase vibrational frequency and vibrational coordinate friction kernel. The friction kernel is evaluated as a cosine transform of the fluctuating force autocorrelation function of the solute vibrational coordinate, conditional that this coordinate is fixed at equilibrium. Additionally, the early-time decay of the force autocorrelation function is approximated by a Gaussian function which is exact to order t2. This Gaussian approximation permits evaluation of T1 in terms of integrals over equilibrium solute-solvent pair correlation functions. The pair correlation function formulas yield T1's in semiquantitative agreement with those found by MD evaluations of the Gaussian approximation, but with three orders of magnitude less computational effort. For the isothermal rho dependencies of k(T,rho), the theory predicts for all systems that the Gaussian decay time tau is nearly independent of rho. This in turn implies that k(T,rho) factorizes into a liquid phase structural contribution and a gas phase dynamical contribution, yielding a first-principles form for k(T,rho) similar to that postulated by the isolated binary collision model. Also, the theory predicts both "classical" superlinear rate isotherms, and "nonclassical" sublinear isotherms similar to those recently observed by Troe and co-workers for azulene relaxation in supercritical fluids. The isochoric T dependencies of k(T,rho) are studied in the range 300 to 1000 K. For none of the solutions are the rate isochores found to accurately conform to either Arrhenius or Landau-Teller kinetics.
Co-estimation of phylogeny and divergence times of Argonautoidea using relaxed phylogenetics.
Strugnell, Jan; Allcock, A Louise
2010-03-01
This is the first study to investigate molecular phylogenetic relationships among all four genera of the superfamily Argonautoidea, a clade of diverse pelagic cephalopods with extraordinary characters such as ovoviviparity, dwarf males and secondary "shell" development. Phylogenetic relationships and divergence times within the superfamily were co-estimated using relaxed phylogenetic techniques. A sister-taxon relationship was recovered between Argonauta and Ocythoe and between Tremoctopus and Haliphron. The most recent common ancestor of Argonautoidea was estimated to date from the early Tertiary under the scenario that a lack of a "shell" in the ocythoid lineage is a primary characteristic. In contrast, a later Tertiary most recent common ancestor was estimated under the scenario that a "shell" was present in the early ocythoid lineage and was subsequently lost. PMID:19941965
Distillation of HD gas and measurement of spin-lattice relaxation times
NASA Astrophysics Data System (ADS)
Bouchigny, S.; Didelez, J.-P.; Dubois, F.; Rouille, G.
2009-08-01
The polarization (static or dynamic) of HD material requires very pure HD samples, with H2 and D2 impurities concentrations smaller than 0.1%. A new distillation apparatus equipped with a mass spectrometer has been built. It allows reaching such a level of purity and also measurement of the H2 and D2 residual concentrations down to 0.05%. The NMR spin-lattice relaxation times T1H and T1D have also been measured. The apparatus is described as well as the distillation method. T1H and T1D data as a function of [H2] and [D2] concentrations are given, at 0.85 T and 1.8 K.
Multiple-relaxation-time lattice Boltzmann method for immiscible fluids at high Reynolds numbers
NASA Astrophysics Data System (ADS)
Fakhari, Abbas; Lee, Taehun
2013-02-01
The lattice Boltzmann method for immiscible multiphase flows with large density ratio is extended to high Reynolds number flows using a multiple-relaxation-time (MRT) collision operator, and its stability and accuracy are assessed by simulating the Kelvin-Helmholtz instability. The MRT model is successful at damping high-frequency oscillations in the kinetic energy emerging from traveling waves generated by the inclusion of curvature. Numerical results are shown to be in good agreement with prior studies using adaptive mesh refinement techniques applied to the Navier-Stokes equations. Effects of viscosity and surface tension, as well as density ratio, are investigated in terms of the Reynolds and Weber numbers. It is shown that increasing the Reynolds number results in a more chaotic interface evolution and eventually shattering of the interface, while surface tension is shown to have a stabilizing effect.
Equilibrium distributions and relaxation times in gaslike economic models: An analytical derivation
NASA Astrophysics Data System (ADS)
Calbet, Xavier; López, José-Luis; López-Ruiz, Ricardo
2011-03-01
A step-by-step procedure to derive analytically the exact dynamical evolution equations of the probability density functions (PDFs) of well-known kinetic wealth exchange economic models is shown. This technique gives a dynamical insight into the evolution of the PDF, for example, allowing the calculation of its relaxation times. Their equilibrium PDFs can also be calculated by finding its stationary solutions. This gives as a result an integro-differential equation, which can be solved analytically in some cases and numerically in others. This should provide some guidance into the type of PDFs that can be derived from particular economic agent exchange rules or, for that matter, any other kinetic model of gases with particular collision physics.
Multiple-relaxation-time lattice Boltzmann method for immiscible fluids at high Reynolds numbers.
Fakhari, Abbas; Lee, Taehun
2013-02-01
The lattice Boltzmann method for immiscible multiphase flows with large density ratio is extended to high Reynolds number flows using a multiple-relaxation-time (MRT) collision operator, and its stability and accuracy are assessed by simulating the Kelvin-Helmholtz instability. The MRT model is successful at damping high-frequency oscillations in the kinetic energy emerging from traveling waves generated by the inclusion of curvature. Numerical results are shown to be in good agreement with prior studies using adaptive mesh refinement techniques applied to the Navier-Stokes equations. Effects of viscosity and surface tension, as well as density ratio, are investigated in terms of the Reynolds and Weber numbers. It is shown that increasing the Reynolds number results in a more chaotic interface evolution and eventually shattering of the interface, while surface tension is shown to have a stabilizing effect. PMID:23496636
Universal time scaling for Hamiltonian parameter estimation
Haidong Yuan; Chi-Hang Fred Fung
2015-03-24
Time is a valuable resource and it seems intuitive that longer time should lead to better precision in Hamiltonian parameter estimation. However recent studies have put this intuition into question, showing longer time may even lead to worse estimation in certain cases. Here we show that the intuition can be restored if coherent feedback controls are included. By deriving asymptotically optimal feedback controls we present a quantification of the maximal improvement feedback controls can provide in Hamiltonian parameter estimation and show a universal time scaling for the precision limit of Hamiltonian parameter estimation under the optimal feedback scheme.
Analysis of the time scales in time periodic Darcy flows
NASA Astrophysics Data System (ADS)
Zhu, T.; Waluga, C.; Wohlmuth, B.; Manhart, M.
2014-12-01
We investigate unsteady flow in a porous medium under time - periodic (sinusoidal) pressure gradient. DNS were performed to benchmark the analytical solution of the unsteady Darcy equation with two different expressions of the time scale : one given by a consistent volume averaging of the Navier - Stokes equation [1] with a steady state closure for the flow resistance term, another given by volume averaging of the kinetic energy equation [2] with a closure for the dissipation rate . For small and medium frequencies, the analytical solutions with the time scale obtained by the energy approach compare well with the DNS results in terms of amplitude and phase lag. For large frequencies (f > 100 [Hz]) we observe a slightly smaller damping of the amplitude. This study supports the use of the unsteady form of Darcy's equation with constant coefficients to solve time - periodic Darcy flows at low and medium frequencies. Our DNS simulations, however, indicate that the time scale predicted by the VANS approach together with a steady - state closure for the flow resistance term is too small. The one obtained by the energy approach matches the DNS results well. At large frequencies, the amplitudes deviate slightly from the analytical solution of the unsteady Darcy equation. Note that at those high frequencies, the flow amplitudes remain below 1% of those of steady state flow. This result indicates that unsteady porous media flow can approximately be described by the unsteady Darcy equation with constant coefficients for a large range of frequencies, provided, the proper time scale has been found.
A two-time-scale, two-temperature scenario for nonlinear rheology Ludovic Berthier,1,2
Berthier, Ludovic
functions below the glass transition temperature (Tc) display a two-time-scale relaxation pattern, similar on approaching the glass transition. Below the glass transition the same behavior subsists, but now the time or foams 4 . In all these cases, it is known that a driving force has a particularly strong influence
Multiple time scales is well named.
Gibbon, J
1999-01-01
Staddon and Higa's article is a critique of scalar expectancy theory, and a proposed alternative, multiple time scales. The critique is generally flawed, both factually and logically. The alternative is bewildering in its flexibility, opaque in its quantitative description, and never addressed to real data. PMID:10220933
Does the QCD Scale vary in time?
Harald Fritzsch
2004-07-06
Last year I talked at this meeting about a possible time dependence of the QCD coupling constant $\\alpha_s$. This year I shall look into the problem once more, without fully repeating the arguments given last year. Astrophysical indications that the fine structure constant has undergone a small time variation during the cosmological evolution are discussed within the framework of the standard model of the electroweak and strong interactions and of grand unification. A variation of the electromagnetic coupling constant could either be generated by a corresponding time variation of the unified coupling constant or by a time variation of the unification scale, or by both. The various possibilities, differing substantially in their implications for the variation of low energy physics parameters like the nuclear mass scale, are discussed. The case in which the variation is caused by a time variation of the unification scale is of special interest. It is supported in addition by recent hints towards a time change of the proton-electron mass ratio.
Monaretto, Tatiana; Andrade, Fabiana Diuk; Moraes, Tiago Bueno; Souza, Andre Alves; deAzevedo, Eduardo Ribeiro; Colnago, Luiz Alberto
2015-10-01
T1 and T2 relaxation times have been frequently used as probes for physical-chemical properties in several time-domain NMR applications (TD-NMR) such as food, polymers and petroleum industries. T2 measurements are usually achieved using the traditional Carr-Purcell-Meiboom-Gill (CPMG) pulse sequence because it is a fast and robust method. On the other hand, the traditional methods for determining T1, i.e., inversion and saturation recovery, are time-consuming, driving several authors to develop rapid 1D and 2D methods to obtain T1 and T2 or T1/T2 ratio. However, these methods usually require sophisticated processing and/or high signal to noise ratio (SNR). This led us to develop simple methods for rapid and simultaneous determination of T1 and T2 using Continuous Wave Free Precession (CWFP) and Carr-Purcell Continuous Wave Free Precession (CP-CWFP) pulse sequences. Nevertheless, a drawback of these sequences is that they require specific adjustment of the frequency offset or the time interval between pulses (Tp). In this paper we present an alternative form of these sequences, named CWFPx-x, CP-CWFPx-x, where a train of ?/2 pulses with phases alternated by ? enable performing the experiments on-resonance and independently of Tp, when Tp
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.
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 (2)H NMR longitudinal relaxation times observed previously for methyl groups of L69 in the hydrophobic core of villin headpiece protein at around 90 K (Vugmeyster et al. J. Am. Chem. Soc. 2010, 132, 4038-4039), we extended the measurements to several other methyl groups in the hydrophobic core. We show that, for all methyl groups, relaxation times experience a dramatic jump several orders of magnitude around this temperature. Theoretical modeling supports the conclusion that the origin of the apparent transition in the relaxation times is due to the existence of the distribution of conformers distinguished by their activation energy for methyl three-site hops. It is also crucial to take into account the differential contribution of individual conformers into overall signal intensity. When a particular conformer approaches the regime at which its three-site hop rate constant is on the order of the quadrupolar coupling interaction constant, the intensity of the signal due to this conformer experiences a sharp drop, thus changing the balance of the contributions of different conformers into the overall signal. As a result, the observed apparent transition in the relaxation rates can be explained without the assumption of an underlying transition in the rate constants. This work in combination with earlier results also shows that the model based on the distribution of conformers explains the relaxation behavior in the entire temperature range between 300 and 70 K. PMID:23627365
Adaptive and Recursive Time Relaxed Monte Carlo methods for rarefied gas dynamics
L. Pareschi; S. Trazzi; B. Wennberg
2010-09-14
Recently a new class of Monte Carlo methods, called Time Relaxed Monte Carlo (TRMC), designed for the simulation of the Boltzmann equation close to fluid regimes have been introduced. A generalized Wild sum expansion of the solution is at the basis of the simulation schemes. After a splitting of the equation the time discretization of the collision step is obtained from the Wild sum expansion of the solution by replacing high order terms in the expansion with the equilibrium Maxwellian distribution; in this way speed up of the methods close to fluid regimes is obtained by efficiently thermalizing particles close to the equilibrium state. In this work we present an improvement of such methods which allows to obtain an effective uniform accuracy in time without any restriction on the time step and subsequent increase of the computational cost. The main ingredient of the new algorithms is recursivity. Several techniques can be used to truncate the recursive trees generated by the schemes without deteriorating the accuracy of the numerical solution. Techniques based on adaptive strategies are presented. Numerical results emphasize the gain of efficiency of the present simulation schemes with respect to standard DSMC methods.
Eder, Alexandra; Hansen, Arne; Uebeler, June; Schulze, Thomas; Neuber, Christiane; Schaaf, Sebastian; Yuan, Lei; Christ, Torsten; Vos, Marc A; Eschenhagen, Thomas
2014-01-01
The assessment of proarrhythmic risks of drugs remains challenging. To evaluate the suitability of rat engineered heart tissue (EHT) for detecting proarrhythmic effects. We monitored drug effects on spontaneous contractile activity and, in selected cases, on action potentials (sharp microelectrode) and Ca2+ transients (Fura-2) and contraction under electrical pacing. The Ito-blocker inhibitor 4-aminopyridine increased action potential duration and T2 and caused aftercontractions, which were abolished by inhibitors of ryanodine receptors (RyR2; JTV-519) or sodium calcium exchanger (NCX; SEA0400). 77 Drugs were then tested at 1-10-100× free therapeutic plasma concentrations (FTPC): Inhibitors of IKr, IKs, Ito, antiarrhythmics (8), drugs withdrawn from market for torsades des pointes arrhythmias (TdP, 5), drugs with measurable (7) or isolated TdP incidence (13), drugs considered safe (14), 28 new chemical entities (NCE). Inhibitors of IKr or IKs had no effect alone, but substantially prolonged relaxation time (T2) when combined at high concentration. 15/33 drugs associated with TdP and 6/14 drugs considered non-torsadogenic (cibenzoline, diltiazem, ebastine, ketoconazole, moxifloxacin, and phenytoin) induced concentration-dependent T2 prolongations (10-100× FTPC). Bepridil, desipramine, imipramine, thioridazine, and erythromycin induced irregular beating. Three NCE prolonged T2, one reduced force. Drugs inhibiting repolarization prolong relaxation in rat EHTs and cause aftercontractions involving RyR2 and NCX. Insensitivity to IKr inhibitors makes rat EHTs unsuitable as general proarrhythmia screen, but favors detection of effects on Ito, IKs + Ito or IKs + IKr. Screening a large panel of drugs suggests that effects on these currents, in addition to IKr, are more common than anticipated. PMID:25209140
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, Stephen 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.
Yoshioka, Sumie; Aso, Yukio; Osako, Tsutomu; Kawanishi, Toru
2008-10-01
In order to examine the possibility of determining the molecular mobility of hydration water in active pharmaceutical ingredient (API) hydrates by NMR relaxation measurement, spin-spin relaxation and spin-lattice relaxation were measured for the 11 API hydrates listed in the Japanese Pharmacopeia using pulsed (1)H-NMR. For hydration water that has relatively high mobility and shows Lorentzian decay, molecular mobility as determined by spin-spin relaxation time (T(2)) was correlated with ease of evaporation under both nonisothermal and isothermal conditions, as determined by DSC and water vapor sorption isotherm analysis, respectively. Thus, T(2) may be considered a useful parameter which indicates the molecular mobility of hydration water. In contrast, for hydration water that has low mobility and shows Gaussian decay, T(2) was found not to correlate with ease of evaporation under nonisothermal conditions, which suggests that in this case, the molecular mobility of hydration water was too low to be determined by T(2). A wide range of water mobilities was found among API hydrates, from low mobility that could not be evaluated by NMR relaxation time, such as that of the water molecules in pipemidic acid hydrate, to high mobility that could be evaluated by this method, such as that of the water molecules in ceftazidime hydrate. PMID:18257032
Time Out from Tension: Teaching Young Children How To Relax. Teaching Strategies.
ERIC Educational Resources Information Center
Scully, Patricia
2003-01-01
Discusses how using relaxation and stress reduction activities with individual preschool and elementary school-age children during difficult periods can help them regain control, and how integrating relaxation techniques into everyday activities helps to establish positive behavior patterns to support healthy living. Presents breathing activities…
Separating viscoelasticity and poroelasticity of gels with different length and time scales
NASA Astrophysics Data System (ADS)
Wang, Qi-Ming; Mohan, Anirudh C.; Oyen, Michelle L.; Zhao, Xuan-He
2014-02-01
Viscoelasticity and poroelasticity commonly coexist as time-dependent behaviors in polymer gels. Engineering applications often require knowledge of both behaviors separated; however, few methods exist to decouple viscoelastic and poroelastic properties of gels. We propose a method capable of separating viscoelasticity and poroelasticity of gels in various mechanical tests. The viscoelastic characteristic time and the poroelastic diffusivity of a gel define an intrinsic material length scale of the gel. The experimental setup gives a sample length scale, over which the solvent migrates in the gel. By setting the sample length to be much larger or smaller than the material length, the viscoelasticity and poroelasticity of the gel will dominate at different time scales in a test. Therefore, the viscoelastic and poroelastic properties of the gel can be probed separately at different time scales of the test. We further validate the method by finite-element models and stress-relaxation experiments. [Figure not available: see fulltext.
Nanosecond time scale motions in proteins revealed by high-resolution NMR relaxometry.
Charlier, Cyril; Khan, Shahid Nawaz; Marquardsen, Thorsten; Pelupessy, Philippe; Reiss, Volker; Sakellariou, Dimitris; Bodenhausen, Geoffrey; Engelke, Frank; Ferrage, Fabien
2013-12-11
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
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
Goree, John
2012-01-01
): compressional and transverse. The compressional wave is longitudinal, like a sound wave in air, with a periodicPHYSICAL REVIEW E 85, 066401 (2012) Cutoff wave number for shear waves and Maxwell relaxation time to the atomic spacing, shear sound waves (i.e., transverse phonons) propagate only for very short wavelengths
Harilal, S. S.
technology stimu- lated the development of a new field called ultrafast laser- induced breakdown spectroscopyElectron-ion relaxation time dependent signal enhancement in ultrafast double-pulse laser of collinear double-pulse compared to single-pulse ultrafast laser induced breakdown spectroscopy. Our results
Gusev, Guennady
- ticles composite Fermions at zero-average magnetic field.9 Random electrostatic potential dueSingle-particle relaxation time in a spatially fluctuating magnetic field G. M. Gusev and J. R is spatially modulated, when uniform external magnetic field is applied. We find that the amplitude of the Sd
Relative Geologic Time and the Geologic Time Scale
NSDL National Science Digital Library
Bret Bennington
Students are given a short introduction to fossils, strata, Steno's law of superposition, and the development of the geologic time scale from initial description of systems, through the realization that fossils could be used to correlate between systems, to the assembly of the modern geologic time scale. Then, each student in the course is given a sheet of paper with a simple stratigraphic column and associated fossils representing a geologic system on one side and a short description of the location and history of discovery of the system on the other. On a large wall, students then assemble four geologic columns from their systems representing mainland Europe, Great Britain, the Eastern U.S. and the Western U.S. using the fossils illustrated on their sheets to correlate systems. The instructor guides this process by placing the first system on the wall and by providing some narration as the columns take shape. Europe and Great Britain are assembled first, one sheet at a time, providing when completed the framework of the modern geologic time scale. Once this is up on the wall, the remaining students can assemble the other two columns in minutes using fossils to correlate between American and European systems. A temporal gap in the Grand Canyon sequence provides an opportunity to discuss the incompleteness of the rock record in any one place and a system composed of igneous and metamorphic rocks with no fossils is used to point out the difference between radiometric (absolute) and biostratigraphic (relative) dating.
Marzola, Luca
2015-01-01
Motivated by natural inflation, we propose a relaxation mechanism consistent with inflationary cosmology that explains the hierarchy between the electroweak scale and Planck scale. The scenario predicts the near-criticality and metastability of the standard model vacuum state, explaining the Higgs boson mass observed at the LHC. Once Majorana right-handed neutrinos are introduced to provide a viable reheating channel, our framework yields a corresponding mass scale that allows for the seesaw mechanism as well as for standard thermal leptogenesis. We also argue that considering singlet scalar dark matter extensions of the proposed scenario could solve the vacuum stability problem and discuss how the cosmological constant problem is possibly addressed.
Time Ephemeris and Relativistic Scaling of Ephemerides
NASA Astrophysics Data System (ADS)
Fukushima, Toshio
2009-05-01
Time ephemeris is the location-independent part of the transformation formula relating two time coordinates such as TCB and TCG. It is computed from the corresponding (space) ephemerides providing the relative motion of two spatial coordinate origins associated such as the motion of geocenter relative to the solar system barycenter. The time ephemerides are inevitablly needed in conducting a precise four-dimensional coordinate transformation among various spacetime coodrinate systems such as the GCRS and BCRS. Also, by means of the time average operation, it is useful in determining the information on scale conversion between the pair of coordinate systems, especially scale conversion factors such as LC. In 1995, we presented the first numerically-integrated time ephemeris, TE245, from JPL's planetary ephemeris DE245 (Fukushima 1995, A&Ap, 294, 895-906). Four years later, we updated it to TE405 associated with DE405 (Irwin and Fukushima 1999, A&Ap, 348, 642-652). The former gave an estimate of LC, the scale conversion factor between TCB and TCG, as 1.4808268457(10) x 10-8. Meanwhile the latter renewed it as 1.48082686741(200) x 10-8. Another four years later, by using a precise technique of time avarage, we improved the estimate as 1.4808268559(6) x 10-8 (Harada and Fukushima 2003, AJ, 126, 2557-2561). The main reasons of these 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. In the talk, we review the post-Newtonian formulas to integrate time ephemerides as well as some practical details on their numerical integration. Also, we explain two kinds of techniques of time average. One is a semi-numerical approach as explained in 1991 A&Ap article and the other is purely numerical as given in 2003 AJ paper.
The biology of time across different scales Dean V Buonomano
Buonomano, Dean
The biology of time across different scales Dean V Buonomano Animals time events on scales, biology has developed vastly different mechanisms for timing across these different scales. For both individuals and society as a whole,the ability to precisely track and tell time is critical across scales
Time to Talk: 5 Things to Know about Relaxation Techniques for Stress
5 Things To Know About Relaxation Techniques for Stress When you’re under stress, your body reacts by releasing hormones that produce ... vessels narrow (restricting the flow of blood). Occasional stress is a normal coping mechanism. But over the ...
Sensitivity of muscle proton spin-spin relaxation time as an index of muscle activation.
Yue, G; Alexander, A L; Laidlaw, D H; Gmitro, A F; Unger, E C; Enoka, R M
1994-07-01
The purpose of this study was to determine the minimum number of contractions that are needed to detect an increase in the muscle proton spin-spin relaxation time (T2) at a given exercise intensity. Five healthy human subjects performed five sets of an exercise that included concentric and eccentric contractions of the elbow-flexor muscles with loads that were 25 or 80% of maximum. With the 80% load, the five sets involved 1, 2, 5, 10, or 20 repetitions of the exercise; with the 25% load the five sets were 2, 5, 10, 20, or 40 repetitions. The upper arm of each subject was imaged before and immediately after each set of the exercise. Spin-echo images (repetition time/echo time = 2,000 ms/30, 60, 90, and 120 ms) were collected using an extremity coil, and T2 values were calculated. The signal intensity was measured from the elbow-flexor and -extensor muscles and from the bone marrow of the humerus. With the 80% load, T2 increased in the short head of the biceps brachii after two repetitions of the elbow exercise and after five repetitions in the brachialis and the long head of the biceps brachii. With the 25% load, T2 became longer after five repetitions of the exercise for the short head of the biceps brachii and after 10 repetitions for the brachialis and the long head of the biceps brachii. T2 varied linearly with the number of contraction repetitions for each of the elbow-flexor muscles at either load (r2 > or = 0.97, P < 0.001).(ABSTRACT TRUNCATED AT 250 WORDS) PMID:7961279
Lanier, Hayley C; Olson, Link E
2009-10-01
Although several studies have recently addressed phylogenetic relationships among Asian pikas (Ochotona spp.), the North American species have been relatively neglected and their monophyly generally unquestioned or assumed. Given the high degree of intraspecific diversity in pelage and call structure, the recent identification of previously unrecognized species of pika in Asia, and the increasing evidence for multiple trans-Beringian dispersals in several small mammal lineages, the monophyly of North American pikas warrants reexamination. In addition, previous studies have applied an externally calibrated rate to examine the timing of diversification within the genus. This method has been increasingly shown to return results that, at the very least, are overly narrow in their confidence intervals, and at the worst can be entirely spurious. For this study we combined GenBank sequences from the mitochondrial genes cyt b and ND4 with newly generated sequence data from O. hyperborea and O. collaris to investigate the origin of the North American lineages and the timing of phylogenetic diversification within the genus Ochotona. Specifically, we address three goals (1) summarize and reanalyze the molecular evidence for relationships within the genus using statistically supported models of evolution; (2) add additional sequences from O. collaris and O. hyperborea to rigorously test the monophyly of North American pikas; (3) examine the timing of the diversification within the genus using relaxed molecular clock methods. We found no evidence of multiple trans-Beringian dispersals into North America, thereby supporting the traditional hypothesis of a single invasion of North America. We also provide evidence that the major splits within the genus occurred in the Miocene, and the Nearctic pikas diverged sometime before the Pleistocene. PMID:19501176
Shear Viscosities from the Chapman-Enskog and the Relaxation Time Approaches
Anton Wiranata; Madappa Prakash
2012-03-01
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 non-relativistic, relativistic and ultra-relativistic 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 reveal that (i) 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.
Probe Spin-Velocity Dependent New Interactions by Spin Relaxation Times of Polarized $^{3}He$ Gas
H. Yan; G. A. Sun; S. M. Peng; Y. Zhang; C. B. Fu; Hao Guo; B. Q. Liu
2015-09-18
We have constrained possible new interactions which produce nonrelativistic potentials between polarized neutrons and unpolarized matter proportional to $\\alpha\\vec{\\sigma}\\cdot\\vec{v}$ where $\\vec{\\sigma}$ is the neutron spin and $\\vec{v}$ is the relative velocity. We use existing data from laboratory measurements on the very long $T_{1}$ and $T_{2}$ spin relaxation times of polarized $^{3}$He gas in glass cells.Using the best available measured $T_{2}$ of polarized $^{3}$He gas atoms as the polarized source and the earth as an unpolarized source, we obtain constraints on two new interactions. We present a new experimental upper bound on possible vector-axial-vector($V_{VA}$) type interactions for ranges between $1\\sim10^{8}$m. In combination with previous results, we set the most stringent experiment limits on $g_{V}g_{A}$ ranging from $\\sim\\mu$m to $\\sim10^{8}$m. We also report what is to our knowledge the first experimental upper limit on the possible torsion fields induced by the earth on its surface. Dedicated experiments could further improve these bounds by a factor of $\\sim100$. Our method of analysis also makes it possible to probe many velocity dependent interactions which depend on the spins of both neutrons and other particles which have never been searched for before experimentally.
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
2015-09-09
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 $\\sim100$.
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 $\\sim100$.
The climate time scale in the approach to radiative-convective equilibrium
NASA Astrophysics Data System (ADS)
Cronin, Timothy W.; Emanuel, Kerry A.
2013-12-01
In this paper, we discuss the importance of the surface boundary condition (fixed versus interactive surface temperature) for the long time scale of approach to Radiative-Convective Equilibrium (RCE). Using a simple linearized two-variable model for surface-atmosphere interaction, we derive an analytic expression for ?C, a long climate relaxation time scale that remains well defined and much longer than either mixing time scale of Tompkins and Craig (1998b), even in the limit that the heat capacity of the surface vanishes. We show that the size of ?C is an intrinsic property of the coupling between the atmosphere and surface, and not a result of the thermal inertia of the surface alone. When the surface heat capacity is low, ?C can be several times longer than expected, due to the effects of moisture on the effective heat capacity of the atmosphere. We also show that the theoretical expression for ?C is a good predictor of best fit exponential relaxation time scales in a single-column model with full physics, across a range of surface temperatures and surface heat capacities.
Chen, H; Shepherd, R; Chung, H K; Dyer, G; Faenov, A; Fournier, K B; Hansen, S B; Hunter, J; Kemp, A; Pikuz, T; Ping, Y; Widmann, K; Wilks, S C; Beiersdorfer, P
2006-08-22
The authors have measured the relaxation time of hot electrons in short pulse laser-solid interactions using a picosecond time-resolved x-ray spectrometer and a time-integrated electron spectrometer. Employing laser intensities of 10{sup 17}, 10{sup 18}, and 10{sup 19} W/cm{sup 2}, they find increased laser coupling to hot electrons as the laser intensity becomes relativistic and thermalization of hot electrons at timescales on the order of 10 ps at all laser intensities. They propose a simple model based on collisional coupling and plasma expansion to describe the rapid relaxation of hot electrons. The agreement between the resulting K{sub {alpha}} time-history from this model with the experiments is best at highest laser intensity and less satisfactory at the two lower laser intensities.
RADIAL TRANSPORT OF LARGE-SCALE MAGNETIC FIELDS IN ACCRETION DISKS. II. RELAXATION TO STEADY STATES
Takeuchi, Taku; Okuzumi, Satoshi, E-mail: taku@geo.titech.ac.jp [Department of Earth and Planetary Sciences, Tokyo Institute of Technology, Meguro-ku, Tokyo 152-8551 (Japan)
2014-12-20
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, ?{sub 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 ?{sub dif}. We consider diffusion due to the Ohmic resistivity. These timescales can be significantly different from the disk viscous timescale ?{sub disk}. The behaviors of the magnetic flux evolution are quite different depending on the magnitude relationship of the timescales ?{sub adv}, ?{sub dif}, and ?{sub disk}. The most interesting phenomena occur when ?{sub adv} << ?{sub dif}, ?{sub 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.
Ab Initio Time-Domain Study of Phonon-Assisted Relaxation of Charge Carriers in a PbSe Quantum Dot
Ab Initio Time-Domain Study of Phonon-Assisted Relaxation of Charge Carriers in a PbSe Quantum Dot The phonon-induced relaxation dynamics of charge carriers in a PbSe quantum dot is studied for the first time of inorganic semiconductors, known as artificial atoms or quantum dots (QD), exhibit a variety of unique
Postseismic Relaxation at the Central Nevada Seismic Belt Observed in Vertical GPS Time Series
NASA Astrophysics Data System (ADS)
Hammond, W. C.; Plag, H.; Blewitt, G.; Kreemer, C.
2007-12-01
Between 1872 and 1954 the Basin and Range province of the western United States experienced six major earthquakes that occurred in a quasi-linear belt known as the Central Nevada Seismic Belt (CNSB). These strike-slip to normal events account for most of the seismic moment release that has occurred in the Basin and Range in historic time. Several studies have noted the possible presence of a contemporary geodetic signal owing to postseismic relaxation from these earthquakes, implying that this signal has persisted for decades after the events. Observations that support the existence of this postseismic signal are: 1) GPS-derived horizontal strain rates that are relatively high compared to the surrounding regions, 2) 3-4 mm/yr vertical upward doming observed with Interferometric Synthetic Aperture Radar (InSAR) that is consistent with models of viscoelastic relaxation of the mantle, 3) possible rapid vertical postseismic motion observed using leveling measurements immediately following the 1954 events, 4) disagreement between geodetically and geologically inferred strain rates that is consistent with elevated contemporary transient strain. Since 2004 the University of Nevada, Reno has operated a semi-continuous GPS network with ~20 km spacing (the Mobile Array of GPS for Nevada Transtension: MAGNET) that complements the spatially less dense Basin and Range Geodetic Network (BARGEN) and Plate Boundary Observatory (PBO) continuously recording networks. MAGNET is ideally deployed to observe the ongoing transient deformation associated with the central Nevada earthquake cycle because it spans the CNSB faults where the predicted postseismic signal is greatest. We analyze the GPS data with the GIPSY/OASIS II software package in precise point positioning and apply regional filtering to remove common mode effects (uniform displacements and/or rotations that are present in all the time series). These common mode signals have a much larger impact on the vertical than on horizontal rates, especially for shorter time series, so accounting for them is essential for studying vertical motions with GPS. The filtered time series enhance our resolution of the relative vertical motion between sites. Our preliminary results based on 2.5-3.3 years of GPS data from MAGNET indeed detect a horizontal gradients in the vertical rates of 3 - 4 mm/yr that is consistent with earlier studies based on InSAR and campaign GPS. We find that the MAGNET sites directly east of Dixie Valley (in the Clan Alpine Range) have the greatest vertical uplift rate, suggesting that the 1954 Dixie Valley earthquake makes a larger contribution to the contemporary uplift than the other earthquakes associated with the CNSB. The largest amplitudes in the vertical signal appear to be limited to the MAGNET sites, highlighting the need for arrays denser than provided by the continuous networks (i.e. PBO and BARGEN) in this region.
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
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.
K. Grzybowska; A. Grzybowski; S. Pawlus; J. Pionteck; M. Paluch
2014-10-23
In this Letter, we investigate how changes in the system entropy influence the characteristic time scale of the system molecular dynamics near the glass transition. Independently of any model of thermodynamic evolution of the time scale, against some previous suppositions, we show that the system entropy $S$ is not sufficient to govern the time scale defined by structural relaxation time $\\tau $. In the density scaling regime, we argue that the decoupling between $\\tau $ and $S$ is a consequence of different values of the scaling exponents $\\gamma $ and $\\gamma_S $ in the density scaling laws, $\\tau = f(\\rho ^\\gamma /T)$ and $S = h(\\rho ^{\\gamma_S}/T)$, where $\\rho $ and $T$ denote density and temperature, respectively. It implies that the proper relation between $\\tau $ and $S$ requires supplementing with a density factor, $u(\\rho)$, i.e.,$\\tau = g(u(\\rho)w(S))$. This meaningful finding additionally demonstrates that the density scaling idea can be successfully used to separate physically relevant contributions to the time scale of molecular dynamics near the glass transition. As an example, we revise the Avramov entropic model of the dependence $\\tau (T,\\rho)$, giving evidence that its entropic basis has to be extended by the density dependence of the maximal energy barrier for structural relaxation. We also discuss the excess entropy $S_{ex}$, the density scaling of which is found to mimic the density scaling of the total system entropy $S$.
Long-time structural relaxation in poly(vinyl-chloride) below glass transition
NASA Astrophysics Data System (ADS)
Lebedev, V. T.; Török, Gy; Cser, L.
2000-03-01
We have studied the plasticized poly(vinyl-chloride) in the bulk by polarized neutrons. The long heat treatment (?10 6 s) at T=45°C< TG=60°C below glass transition induces molecular ordering at distances larger than coil size. The annealing at 180°C< TM=230°C below melting temperature of crystallites breaks the structure to segmental scale fluctuation for time ?10 3 s. The reptation mechanism of ordering is discussed.
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.
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.
Parametric instabilities in picosecond time scales
Baldis, H.A.; Rozmus, W.; Labaune, C.; Mounaix, Ph.; Pesme, D.; Baton, S.; Tikhonchuk, V.T.
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.
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
Slip-flow in complex porous media as determined by a multi-relaxation-time lattice Boltzmann model
NASA Astrophysics Data System (ADS)
Landry, C. J.; Prodanovic, M.; Eichhubl, P.
2014-12-01
The pores and throats of shales and mudrocks are predominantly found within a range of 1-100 nm, within this size range the flow of gas at reservoir conditions will fall within the slip-flow and low transition-flow regime (0.001 < Kn < 0.5). Currently, the study of slip-flows is for the most part limited to simple tube and channel geometries, however, the geometry of mudrock pores is often sponge-like (organic matter) and/or platy (clays). Molecular dynamics (MD) simulations can be used to predict slip-flow in complex geometries, but due to prohibitive computational demand are generally limited to small volumes (one to several pores). Here we present a multi-relaxation-time lattice Boltzmann model (LBM) parameterized for slip-flow (Guo et al. 2008) and adapted here to complex geometries. LBMs are inherently parallelizable, such that flow in complex geometries of significant (near REV-scale) volumes can be readily simulated at a fraction of the computational cost of MD simulations. At the macroscopic-scale the LBM is parameterized with local effective viscosities at each node to capture the variance of the mean-free-path of gas molecules in a bounded system. The corrected mean-free-path for each lattice node is determined using the mean distance of the node to the pore-wall and Stop's correction for mean-free-paths in an infinite parallel-plate geometry. At the microscopic-scale, a combined bounce-back specular-reflection boundary condition is applied to the pore-wall nodes to capture Maxwellian-slip. The LBM simulation results are first validated in simple tube and channel geometries, where good agreement is found for Knudsen numbers below 0.1, and fair agreement is found for Knudsen numbers between 0.1 and 0.5. More complex geometries are then examined including triangular-ducts and ellipsoid-ducts, both with constant and tapering/expanding cross-sections, as well as a clay pore-network imaged from a hydrocarbon producing shale by sequential focused ion-beam scanning electron microscopy. These results are analyzed to determine grid-independent resolutions, and used to explore the relationship between effective permeability and Knudsen number in complex geometries.
Chieng, Norman; Mizuno, Masayasu; Pikal, Michael
2013-01-01
The purposes of this study are to characterize the relaxation dynamics in complex freeze dried formulations and to investigate the quantitative relationship between the structural relaxation time as measured by thermal activity monitor (TAM) and that estimated from the width of the glass transition temperature (?Tg). The latter method has advantages over TAM because it is simple and quick. As part of this objective, we evaluate the accuracy in estimating relaxation time data at higher temperatures (50°C and 60°C) from TAM data at lower temperature (40°C) and glass transition region width (?Tg) data obtained by differential scanning calorimetry. Formulations studied here were hydroxyethyl starch (HES)-disaccharide, HES-polyol and HES-disaccharide-polyol at various ratios. We also re-examine, using TAM derived relaxation times, the correlation between protein stability (human growth hormone, hGH) and relaxation times explored in a previous report, which employed relaxation time data obtained from ?Tg. Results show that most of the freeze dried formulations exist in single amorphous phase, and structural relaxation times were successfully measured for these systems. We find a reasonably good correlation between TAM measured relaxation times and corresponding data obtained from estimates based on ?Tg, but the agreement is only qualitative. The comparison plot showed that TAM data is directly proportional to the 1/3 power of ?Tg data, after correcting for an offset. Nevertheless, the correlation between hGH stability and relaxation time remained qualitatively the same as found with using ?Tg derived relaxation data, and it was found that the modest extrapolation of TAM data to higher temperatures using ?Tg method and TAM data at 40°C resulted in quantitative agreement with TAM measurements made at 50 °C and 60 °C, provided the TAM experiment temperature is well below the Tg of the sample. PMID:23608636
Chieng, Norman; Mizuno, Masayasu; Pikal, Michael
2013-10-01
The purposes of this study are to characterize the relaxation dynamics in complex freeze dried formulations and to investigate the quantitative relationship between the structural relaxation time as measured by thermal activity monitor (TAM) and that estimated from the width of the glass transition temperature (?T(g)). The latter method has advantages over TAM because it is simple and quick. As part of this objective, we evaluate the accuracy in estimating relaxation time data at higher temperatures (50 °C and 60 °C) from TAM data at lower temperature (40 °C) and glass transition region width (?T(g)) data obtained by differential scanning calorimetry. Formulations studied here were hydroxyethyl starch (HES)-disaccharide, HES-polyol, and HES-disaccharide-polyol at various ratios. We also re-examine, using TAM derived relaxation times, the correlation between protein stability (human growth hormone, hGH) and relaxation times explored in a previous report, which employed relaxation time data obtained from ?T(g). Results show that most of the freeze dried formulations exist in single amorphous phase, and structural relaxation times were successfully measured for these systems. We find a reasonably good correlation between TAM measured relaxation times and corresponding data obtained from estimates based on ?T(g), but the agreement is only qualitative. The comparison plot showed that TAM data are directly proportional to the 1/3 power of ?T(g) data, after correcting for an offset. Nevertheless, the correlation between hGH stability and relaxation time remained qualitatively the same as found with using ?T(g) derived relaxation data, and it was found that the modest extrapolation of TAM data to higher temperatures using ?T(g) method and TAM data at 40 °C resulted in quantitative agreement with TAM measurements made at 50 °C and 60 °C, provided the TAM experiment temperature, is well below the Tg of the sample. PMID:23608636
Relaxations in gels: Analogies to ? and ? relaxations in glasses
NASA Astrophysics Data System (ADS)
Ren, S. Z.; Sorensen, C. M.
1993-03-01
We present dynamic light scattering data which show that aqueous gelatin gels display a power-law relaxation to a nonergodic background. In the pregel sol this power law is termined by a stretched exponential which restores ergodicity and which has a q dependent characteristic time proportional to the viscosity. The power-law exponent is q dependent and related to a characteristic length in the gel. Except for the q dependences these behaviors are similar to the ? and ? relaxation behavior in glasses. It is proposed that the different q dependences of the gels and glasses is a result of different characteristic length scales.
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
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.
NASA Astrophysics Data System (ADS)
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.
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
Lalitha Vaithianathar; Chris R. Tench; Paul S. Morgan; Martin Wilson; Lance D. Blumhardt
2002-01-01
. T1 relaxation time (T1) is a quantitative magnetic resonance measure that enables a global evaluation of white matter disease in multiple sclerosis\\u000a (MS). We aimed to investigate whether mapping of T1 values in critical white matter tracts, defined by diffusion tensor (DT) imaging, could provide a stronger surrogate marker\\u000a of disability. 25 patients with relapsing-remitting MS and 14 healthy
NASA Astrophysics Data System (ADS)
Pawlus, S.; Klotz, S.; Paluch, M.
2013-04-01
High pressure viscosity and dielectric measurements were carried out on two monohydroxy alcohols, 2-ethyl-1-hexanol and 5-methyl-2-hexanol, at room temperature. Analysis of the dielectric relaxation times versus viscosity revealed the breakdown of the Einstein-Debye relation above some characteristic pressure. The failure of the Einstein-Debye relation is a manifestation of pressure induced changes of supramolecular hydrogen bonded structures which occur in these liquids.
Time Horizon and Social Scale in Communication
NASA Astrophysics Data System (ADS)
Krantz, D. H.
2010-12-01
In 2009 our center (CRED) published a first version of The Psychology of Climate Change Communication. In it, we attempted to summarize facts and concepts from psychological research that could help guide communication. While this work focused on climate change, most of the ideas are at least partly applicable for communication about a variety of natural hazards. Of the many examples in this guide, I mention three. Single-action bias is the human tendency to stop considering further actions that might be needed to deal with a given hazard, once a single action has been taken. Another example is the importance of group affiliation in motivating voluntary contributions to joint action. A third concerns the finding that group participation enhances understanding of probabilistic concepts and promotes action in the face of uncertainty. One current research direction, which goes beyond those included in the above publication, focuses on how time horizons arise in the thinking of individuals and groups, and how these time horizons might influence hazard preparedness. On the one hand, individuals sometimes appear impatient, organizations look for immediate results, and officials fail to look beyond the next election cycle. Yet under some laboratory conditions and in some subcultures, a longer time horizon is adopted. We are interested in how time horizon is influenced by group identity and by the very architecture of planning and decision making. Institutional changes, involving long-term contractual relationships among communities, developers, insurers, and governments, could greatly increase resilience in the face of natural hazards. Communication about hazards, in the context of such long-term contractual relationships might look very different from communication that is first initiated by immediate threat. Another new direction concerns the social scale of institutions and of communication about hazards. Traditionally, insurance contracts share risk among a large number of insurees: each contributes a small premium toward a fund that is adequate to cover the large losses that occasionally occur. Participatory processes are needed that extend risk sharing to larger social scales and that reduce adversarial relationships between insurers, insurees, insurance regulators, and governments that intervene or fail to intervene on an ad hoc rather than a contractual basis.
Quarkonia and heavy-quark relaxation times in the quark-gluon plasma
Riek, F.; Rapp, Ralf.
2010-01-01
in the static reduction scheme of the four-dimensional Bethe-Salpeter equation are elucidated. The quarkonium spectral functions are used to calculate Euclidean correlators which are discussed in light of lattice QCD results, while heavy-quark relaxation rates...
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
Time-resolved intraband electronic relaxation dynamics of Hgn ,,n713,15,18... excited at 1.0eV
Neumark, Daniel M.
January 2005 Time-resolved photoelectron imaging has been used to study the relaxation dynamics of small at earliest temporal delays that are interpreted as early coherent nuclear motion on the excited potential, electronic intraband relaxation dynamics-- produced through clustering of divalent metal atoms. In contrast
Self-Similar Approach to Violent Relaxation
Richard Henriksen; Lawrence M. Widrow
1996-12-02
We consider the evolution of an initially cold, spherically symmetric system of self-gravitating particles. At early times the system undergoes self-similar collapse of the type described by Fillmore & Goldreich and Bertschinger. This stage of phase mixing soon gives way to a period of violent relaxation driven by an instability in the similarity solution. The onset of violent relaxation is illustrated by numerical simulations and supported by non-linear analysis of the ``scaled'' collisionless Boltzmann and Poisson equations.
Simple time-variant filtering by operator scaling
Park, Choon Byong; Black, Ross A.
1995-09-01
A convolutional method of time?variant, band?pass filtering presented shows that a change of filter cutoff frequencies with time is achieved by frequency scaling the amplitude spectrum of a reference operator. According to the scaling property...
NASA Astrophysics Data System (ADS)
Ramirez-Garcia, E.; Michaillat, M.; Aniel, F.; Zerounian, N.; Enciso-Aguilar, M.; Rideau, D.
2011-07-01
We present an original method for the detailed evaluation of different device region contributions to the whole SiGe:C heterojunction bipolar transistor transit time in the frame of modeling studies. This method is based on AC analysis with structures of several base widths. The two-dimensional hydrodynamic solver relies on analytical models of electron and hole mobilities, and of energy relaxation times, calculated from results of the Boltzmann Transport Equation in highly acceptor doped and strained SiGe:C, using a full band Monte Carlo solver. The simulation results are compared to DC and AC measurements and exhibit good agreement. The proposed transit time analysis scheme and the analytical model for mobilities and energy relaxation times may be used for device optimization, toward highest dynamic performances.
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...
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.
Leyet, Y.; Guerrero, F.; Amorin, H.; Guerra, J. de Los S.; Eiras, J. A.
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.
NASA Astrophysics Data System (ADS)
Kay, Lewis E.; Bull, T. E.; Nicholson, L. K.; Griesinger, C.; Schwalbe, H.; Bax, A.; Torchia, D. A.
Pulse schemes for the measurement of 13C transverse relaxation times in AX 33 spin systems are described which make use of the sensitive 1H spin for detection. The experiments are based on reverse-DEPT and reverse-INEPT polarization-transfer sequences. It is shown that relaxation rates obtained from 13C-direct-observe and from polarization-transfer experiments are identical only if magnetization from each of the 13C transitions is transferred equally to the detected 1H spins. This requires judicious choices in pulse angles and delays in reverse-DEPT and reverse-INEPT experiments. For application to macromolecules, experimental and theoretical results suggest that polarization-transfer schemes based on reverse INEPT are superior to reverse-DEPT-based sequences and give results which are in good agreement with values measured via 13C-observe methods.
Bokes, Peter
2009-06-14
Stroboscopic wavepacket basis sets [P. Bokes, F. Corsetti, R. W. Godby, Phys. Rev. Lett., 2008, 101, 046402] are specifically tailored for a description of time-dependent processes in extended systems, such as non-periodic geometries of various contacts consisting of solids and molecules. The explanation of the construction of such a basis for two simple finite systems is followed by a review of the general theory for extended systems with continuous spectrum. The latter is further elaborated with the introduction of the interaction representation which takes full advantage of the time-dynamics built into the basis. The formalism is applied to a semi-analytical example of electronic transport through resonant tunnelling barrier in 1D. Through the time-dependent generalisation of the Landauer formula given in terms of the Fourier expansion of the transmission amplitude we analyze the temporal character of the onset of the steady-state. Various time-scales in this process are shown to be directly related to the energetic structure of the resonant barrier. PMID:19475178
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
NASA Astrophysics Data System (ADS)
Virgilio, Michele; Ortolani, Michele; Teich, Martin; Winnerl, Stephan; Helm, Manfred; Sabbagh, Diego; Capellini, Giovanni; De Seta, Monica
2014-01-01
In this paper, we have experimentally and numerically studied the nonradiative intersubband (ISB) relaxation in n-type Ge/SiGe quantum well (QW) systems. Relaxation times have been probed by means of pump-probe experiments. An energy balance model has been used to interpret the experimental differential transmission spectra and to assess the relevance in the nonradiative relaxation dynamics of both electron and lattice temperature as well as of the carrier density. The comparison between experimental data and theoretical simulation allowed us to calibrate the interaction parameters which describe the electron-optical phonon scattering in two-dimensional (2D) Ge systems. Characteristic relaxation times has been calculated and compared with those of GaAs QWs as a function of the 2D electron density, of the subband energy separation, and of the lattice and electronic temperature. We found that ISB relaxation times for the Ge/SiGe systems are generally shorter than that previously calculated when the electron distribution was neglected. Nonetheless, our main result is that the relaxation time in Ge/SiGe QW systems is longer than 10 ps, also for transition energies above the Ge optical phonon energy, up to 300 K. Furthermore, we obtained that the relaxation times are at least one order of magnitude longer than in GaAs-based systems.
NASA Astrophysics Data System (ADS)
van der Weerd, Louise; Melnikov, Sergey M.; Vergeldt, Frank J.; Novikov, Eugene G.; Van As, Henk
2002-06-01
Multicompartment characteristics of relaxation and diffusion in a model for (plant) cells and tissues have been simulated as a means to test separating the signal into a set of these compartments. A numerical model of restricted diffusion and magnetization relaxation behavior in PFG-CPMG NMR experiments, based on Fick's second law of diffusion, has been extended for two-dimensional diffusion in systems with concentric cylindrical compartments separated by permeable walls. This model is applicable to a wide range of (cellular) systems and allows the exploration of temporal and spatial behavior of the magnetization with and without the influence of gradient pulses. Numerical simulations have been performed to show the correspondence between the obtained results and previously reported studies and to investigate the behavior of the apparent diffusion coefficients for the multicompartment systems with planar and cylindrical geometry. The results clearly demonstrate the importance of modelling two-dimensional diffusion in relation to the effect of restrictions, permeability of the membranes, and the bulk relaxation within the compartments. In addition, the consequences of analysis by multiexponential curve fitting are investigated.
NASA Astrophysics Data System (ADS)
Geissman, J. W.; Walker, J. D.
2012-12-01
Geologic time scales, of one form or another, are used in most undergraduate geosciences courses, even including introductory physical geology or equivalent. However, satisfactory discussions of how geologic time scales originated, and how they have evolved to modern versions, are far too often conveniently or inconveniently left out of classroom discussions. Yet it is these kinds of discussions that have the potential of solidifying student appreciation of deep time and rates of geologic processes. We use the history and development of the Geological Society of America Geologic Time Scale, which reflects major developments in the fields of stratigraphy, geochronology, magnetic polarity stratigraphy, astrochronology, and chemostratigraphy, as a focus of how specific details of time scales can be used to teach about time. Advances in all of these fields have allowed many parts of the time scale to be calibrated to precisions approaching less than 0.05 %. Notable time intervals for which collaborative, multifaceted efforts have led to dramatic improvements in our understanding of the character and temporal resolution of key evolutionary events, in both marine and terrestrial environments, include the Triassic-Jurassic, Permo-Triassic, and Neoproterozoic-Phanerozoic boundaries (or transitions). Many of the details, but certainly not all, can be incorporated in discussions of how we know about geologic time in the classroom. For example, we presently understand that both the end-Permian ecological crisis and the biostratigraphic Permian-Triassic boundary, as calibrated by conodonts, lie within a ca. 700 ka long normal polarity chron. The reverse to normal polarity transition at the beginning of this chron is ca. 100 ka earlier than the ecological crisis and thus slightly older than the current estimate, based on high precision U-Pb zircon age determinations, of ca. 252.4 Ma for the Permian-Triassic boundary. This polarity transition occurred during the early part of the major negative del 13C isotope excursion that is estimated to have lasted ca. 500 ka beginning in the very latest Permian. Current geologic time scales are vastly improved over the first geologic time scale published by Holmes, nearly a hundred years ago in 1913, that used a total of eight numerical ages to establish the Phanerozoic time scale.
Relaxing the Electroweak Scale: the Role of Broken dS Symmetry
Patil, Subodh P
2015-01-01
Recently, a novel mechanism to address the hierarchy problem has been proposed [1], where the hierarchy between weak scale physics and any putative `cutoff' $M$ is translated into a parametrically large field excursion for the so-called relaxion field, driving the Higgs mass to values much less than $M$ through cosmological dynamics. In its simplest incarnation, the relaxion mechanism requires nothing beyond the standard model other than an axion (the relaxion field) and an inflaton. In this note, we critically re-examine the requirements for successfully realizing the relaxion mechanism and point out that parametrically larger field excursions can be obtained for a given number of e-folds by simply requiring that the background break exact de Sitter invariance. We discuss several corollaries of this observation, including the interplay between the upper bound on the scale $M$ and the order parameter $\\epsilon$ associated with the breaking of dS symmetry, and the possibility that the relaxion could play the r...
NASA Astrophysics Data System (ADS)
Zhou, Y.; Yu, T.; Wu, M. W.
2013-06-01
We report an anomalous scaling of the D’yakonov-Perel’ spin relaxation with the momentum relaxation in semiconductor quantum wells under a strong magnetic field in the Voigt configuration. We focus on the case in which the external magnetic field is perpendicular to the spin-orbit-coupling-induced effective magnetic field and its magnitude is much larger than the latter one. It is found that the longitudinal spin relaxation time is proportional to the momentum relaxation time even in the strong-scattering limit, indicating that the D’yakonov-Perel’ spin relaxation demonstrates Elliott-Yafet-like behavior. Moreover, the transverse spin relaxation time is proportional (inversely proportional) to the momentum relaxation time in the strong- (weak-) scattering limit, both in the opposite trends against the well-established conventional D’yakonov-Perel’ spin relaxation behaviors. We further demonstrate that all the above anomalous scaling relations come from the unique form of the effective inhomogeneous broadening.
Butterwick, Joel A; Loria, J Patrick; Astrof, Nathan S; Kroenke, Christopher D; Cole, Roger; Rance, Mark; Palmer, Arthur G
2004-06-11
Backbone conformational fluctuations on multiple time scales in a cysteine-free Thermus thermophilus ribonuclease HI mutant (ttRNH(*)) are quantified using (15)N nuclear magnetic spin relaxation. Laboratory-frame relaxation data acquired at 310 K and at static magnetic field strengths of 11.7, 14.1 and 18.8 T are analysed using reduced spectral density mapping and model-free approaches. Chemical exchange line broadening is characterized using Hahn-echo transverse and multiple quantum relaxation data acquired over a temperature range of 290-320 K and at a static magnetic field strength of 14.1 T. Results for ttRNH(*) are compared to previously published data for a mesophilic homologue, Escherichia coli ribonuclease HI (ecRNH). Intramolecular conformational fluctuations on the picosecond-to-nanosecond time scale generally are similar for ttRNH(*) and ecRNH. beta-Strands 3 and 5 and the glycine-rich region are more rigid while the substrate-binding handle region and C-terminal tail are more flexible in ttRNH(*) than in ecRNH. Rigidity in the two beta-strands and the glycine-rich region, located along the periphery of the central beta-sheet, may be associated with the increased thermodynamic stability of the thermophilic enzyme. Chemical exchange line broadening, reflecting microsecond-to-millisecond time scale conformational changes, is more pronounced in ttRNH(*) than in ecRNH, particularly for residues in the handle and surrounding the catalytic site. The temperature dependence of chemical exchange show an increase of approximately 15 kJ/mol in the apparent activation energies for ttRNH(*) residues in the handle compared to ecRNH. Increased activation barriers, coupled with motion between alpha-helices B and C not present in ecRNH, may be associated with the reduced catalytic activity of the thermophilic enzyme at 310 K. PMID:15165855
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.
Mechanism of Void Nucleation and Growth in bcc Fe: Atomistic Simulations at Experimental Time Scales
NASA Astrophysics Data System (ADS)
Fan, Yue; Kushima, Akihiro; Yip, Sidney; Yildiz, Bilge
2011-03-01
Evolution of small-vacancy clusters in bcc Fe is simulated using a multiscale approach coupling an atomistic activation-relaxation method for sampling transition-state pathways with environment-dependent reaction coordinate calculations and a kinetic Monte Carlo simulation to reach time scales on the order of ˜104s. Under vacancy-supersaturated condition, di- and trivacancy clusters form and grow by coalescence (Ostwald ripening). For cluster size greater than four we find a transition temperature of 150°C for accelerated cluster growth, as observed in positron annihilation spectroscopy experiments. Implications for the mechanism of stage-IV radiation-damage-recovery kinetics are discussed.
Relaxation dynamics of a linear molecule in a random static medium: a scaling analysis.
Moreno, Angel J; Kob, Walter
2004-07-01
We present extensive molecular dynamics simulations of the motion of a single linear rigid molecule in a two-dimensional random array of fixed overlapping disklike obstacles. The diffusion constants for the center of mass translation, D(CM), and for rotation, D(R), are calculated for a wide range of the molecular length, L, and the density of obstacles, rho. The obtained results follow a master curve Drho(micro) approximately (L(2)rho)(-nu) with an exponent micro=-3/4 and 1/4 for D(R) and D(CM), respectively, that can be deduced from simple scaling and kinematic arguments. The nontrivial positive exponent nu shows an abrupt crossover at L(2)rho=zeta(1). For D(CM) we find a second crossover at L(2)rho=zeta(2). The values of zeta(1) and zeta(2) correspond to the average minor and major axis of the elliptic holes that characterize the random configuration of the obstacles. A violation of the Stokes-Einstein-Debye relation is observed for L(2)rho>zeta(1), in analogy with the phenomenon of enhanced translational diffusion observed in supercooled liquids close to the glass transition temperature. PMID:15260557
NASA Astrophysics Data System (ADS)
Liu, Zhirong; Chan, Hue Sun
2015-09-01
How type-2 topoisomerases discern global topology from local properties of DNA is not known precisely but the hypothesis that the enzymes selectively pass double-helix strands at hook-like juxtapositions is promising. Building upon an investigation of unknotting and decatenating using an improved wormlike DNA model, here we focus primarily on the enzymes' action in narrowing the distribution of linking number (Lk) in supercoiled DNA. Consistent with experiments, with selective passage at a hooked juxtaposition, the simulated narrowing factor RLk diminishes with decreasing DNA circle size but approaches an asymptotic RLk ? 1.7–1.8 for circle size ?3.5 kb. For the larger DNA circles, we found that (RLk ? 1) ? 0.42log10RK ? 0.68log10RL and thus RK ? (RL)1.6 holds for the computed RLk and knot and catenane reduction factors RK and RL attained by selective passage at different juxtaposition geometries. Remarkably, this general scaling relation is essentially identical to that observed experimentally for several type-2 topoisomerases from a variety of organisms, indicating that the different disentangling powers of the topoisomerases likely arise from variations in the hooked geometries they select. Taken together, our results suggest strongly that type-2 topoisomerases recognize not only the curvature of the G-segment but also that of the T-segment.
Liu, Zhirong; Chan, Hue Sun
2015-09-01
How type-2 topoisomerases discern global topology from local properties of DNA is not known precisely but the hypothesis that the enzymes selectively pass double-helix strands at hook-like juxtapositions is promising. Building upon an investigation of unknotting and decatenating using an improved wormlike DNA model, here we focus primarily on the enzymes' action in narrowing the distribution of linking number (Lk) in supercoiled DNA. Consistent with experiments, with selective passage at a hooked juxtaposition, the simulated narrowing factor RLk diminishes with decreasing DNA circle size but approaches an asymptotic RLk ? 1.7-1.8 for circle size ?3.5 kb. For the larger DNA circles, we found that (RLk - 1) ? 0.42log10RK ? 0.68log10RL and thus RK ? (RL)(1.6) holds for the computed RLk and knot and catenane reduction factors RK and RL attained by selective passage at different juxtaposition geometries. Remarkably, this general scaling relation is essentially identical to that observed experimentally for several type-2 topoisomerases from a variety of organisms, indicating that the different disentangling powers of the topoisomerases likely arise from variations in the hooked geometries they select. Taken together, our results suggest strongly that type-2 topoisomerases recognize not only the curvature of the G-segment but also that of the T-segment. PMID:26291958
NASA Astrophysics Data System (ADS)
Schäfer-Nolte, Eike; Schlipf, Lukas; Ternes, Markus; Reinhard, Friedemann; Kern, Klaus; Wrachtrup, Jörg
2014-11-01
We demonstrate the tracking of the spin dynamics of ensemble and individual magnetic ferritin proteins from cryogenic up to room temperature using the nitrogen-vacancy color center in diamond as a magnetic sensor. We employ different detection protocols to probe the influence of the ferritin nanomagnets on the longitudinal and transverse relaxation of the nitrogen-vacancy center, which enables magnetic sensing over a wide frequency range from Hz to GHz. The temperature dependence of the observed spectral features can be well understood by the thermally induced magnetization reversals of the ferritin and enables the determination of the anisotropy barrier of single ferritin molecules.
NASA Astrophysics Data System (ADS)
Poole, Gregory B.; Babul, Arif; McCarthy, Ian G.; Fardal, Mark A.; Bildfell, C. J.; Quinn, Thomas; Mahdavi, Andisheh
2007-09-01
We use the suite of simulations presented by Poole et al. to examine global X-ray and Sunyaev-Zel'dovich (SZ) observables for systems of merging relaxed X-ray clusters. The time evolution of our merging systems' X-ray luminosities, temperatures, total mass measures, SZ central Compton parameters and integrated SZ fluxes are presented and the resulting impact on their scaling relations examined. In all cases, and for all parameters, we observe a common time evolution: two rapid transient increases during first and second pericentric passage, with interceding values near or below their initial levels. This is in good qualitative agreement with previous idealized merger simulations, although we find several important differences related to the inclusion of radiative cooling in our simulations. These trends translate into a generic evolution in the scaling-relation planes as well: a rapid transient roughly along the mass scaling relations, a subsequent slow drift across the scatter until virialization, followed by a slow evolution along and up the mass scaling relations as cooling recovers in the cluster cores. However, this drift is not sufficient to account for the observed scatter in the scaling relations. We also study the effects of mergers on several theoretical temperature measures of the intracluster medium: emission-weighted measures (Tew), the spectroscopic-like measure (Tsl) proposed by Mazzotta et al. and plasma model fits to the integrated spectrum of the system (Tspec). We find that Tsl tracks Tspec for the entire duration of our mergers, illustrating that it remains a good tool for observational comparison even for highly disturbed systems. Furthermore, the transient temperature increases produced during first and second pericentric passage are 15-40 per cent larger for Tew than for Tsl or Tspec. This suggests that the effects of transient temperature increases on ?8 and ?M derived by Randall et al. are over estimated. Lastly, we examine the X-ray SZ proxy proposed by Kravtsov, Vikhlinin & Nagai (2006) and find that the tight mass scaling relation they predict remains secure through the entire duration of a merger event, independent of projection effects.
Yoon, S; Sorbaro Sindaci, M; Goltsev, A V; Mendes, J F F
2015-03-01
We study the impact of network heterogeneity on relaxation dynamics of the Kuramoto model on uncorrelated complex networks with scale-free degree distributions. Using the Ott-Antonsen method and the annealed-network approach, we find that the critical behavior of the relaxation rate near the synchronization phase transition does not depend on network heterogeneity and critical slowing down takes place at the critical point when the second moment of the degree distribution is finite. In the case of a complete graph we obtain an explicit result for the relaxation rate when the distribution of natural frequencies is Lorentzian. We also find a response of the Kuramoto model to an external field and show that the susceptibility of the model is inversely proportional to the relaxation rate. We reveal that network heterogeneity strongly impacts a field dependence of the relaxation rate and the susceptibility when the network has a divergent fourth moment of degree distribution. We introduce a pair correlation function of phase oscillators and show that it has a sharp peak at the critical point, signaling emergence of long-range correlations. Our numerical simulations of the Kuramoto model support our analytical results. PMID:25871164
NASA Astrophysics Data System (ADS)
Nüchter, J. A.; Stöckhert, B.
2005-12-01
Metamorphic rocks approaching the crustal scale brittle-ductile transition (BDT) during exhumation are expected to become increasingly affected by short term stress fluctuations related to seismic activity in the overlying seismogenic layer (schizosphere), while still residing in a long-term viscous environment (plastosphere). The structural and microstructural record of quartz veins in low grade - high pressure metamorphic rocks from southern Evia, Greece, yields insight into the processes and conditions just beneath the long-term BDT at temperatures of about 300 to 350°C, which switches between brittle failure and viscous flow as a function of imposed stress or strain rate. The following features are characteristic: (1) The veins have formed from tensile fractures, with a typical length on the order of 10-1 to 101 m; (2) The veins are discordant with respect to foliation and all pre-existing structures, with a uniform orientation over more than 500 km2; (3) The veins show a low aspect ratio of about 10 to 100 and an irregular or characteristic flame shape, which requires distributed ductile deformation of the host rock; (4) Fabrics of the sealing vein quartz indicate that - at a time - the veins were wide open cavities; (5) The sealing quartz crystals reveal a broad spectrum of microstructural features indicative of crystal plastic deformation at high stress and temperatures of about 300 to 350°C. These features indicate that opening and sealing of the fractures commenced immediately after brittle failure, controlled by ductile deformation of the host rock. Vein-parallel shortening was generally less than about 2%. Crystals formed early during sealing were plastically deformed upon progressive deformation and opening of the vein. The structural and microstructural record is interpreted as follows: Brittle failure is proposed to be a consequence of short term co-seismic loading. Subsequent opening of the fracture and sealing to become a vein is interpreted to reflect the slower (but still very short term on geological time scales) deformation during post-seismic stress relaxation, with precipitation of minerals from the pore fluid percolating into the evolving cavity. The record provides insight into earthquake-related damage in the uppermost plastosphere and the transient crustal properties during post-seismic creep and stress relaxation.
Relaxation and flow in linearly sheared two-dimensional foams
NASA Astrophysics Data System (ADS)
Möbius, M. E.; Katgert, G.; van Hecke, M.
2010-05-01
We probe the relation between rheology and shear-induced relaxation in experiments on two-dimensional foams at steady shear. The characteristic relaxation time tr, which we extract from the non-affine part of the bubble displacements, scales non-linearly with the local strain rate \\dot{\\gamma} . In particular, the relative strength of the non-affine part grows when \\dot{\\gamma} \\rightarrow 0 —hence the foam flow is not quasistatic down to the lowest experimentally accessible shear rate. Furthermore, we establish a direct connection between the relaxation time scaling and the macroscopic rheology.
Detecting separate time scales in genetic expression data
2010-01-01
Background Biological processes occur on a vast range of time scales, and many of them occur concurrently. As a result, system-wide measurements of gene expression have the potential to capture many of these processes simultaneously. The challenge however, is to separate these processes and time scales in the data. In many cases the number of processes and their time scales is unknown. This issue is particularly relevant to developmental biologists, who are interested in processes such as growth, segmentation and differentiation, which can all take place simultaneously, but on different time scales. Results We introduce a flexible and statistically rigorous method for detecting different time scales in time-series gene expression data, by identifying expression patterns that are temporally shifted between replicate datasets. We apply our approach to a Saccharomyces cerevisiae cell-cycle dataset and an Arabidopsis thaliana root developmental dataset. In both datasets our method successfully detects processes operating on several different time scales. Furthermore we show that many of these time scales can be associated with particular biological functions. Conclusions The spatiotemporal modules identified by our method suggest the presence of multiple biological processes, acting at distinct time scales in both the Arabidopsis root and yeast. Using similar large-scale expression datasets, the identification of biological processes acting at multiple time scales in many organisms is now possible. PMID:20565716
Clayton, Steven Michael [Los Alamos National Laboratory
2010-12-03
A method is presented to calculate the spin relaxation times T{sub 1}, T{sub 2} due to a nonuniform magnetic field, and the linear-in-electric-field precession frequency shift {delta}{omega}{sub E} when an electric field is present, in the diffusion approximation for spins confined to a rectangular cell. It is found that the rectangular cell geometry admits of a general result for T{sub 1}, T{sub 2}, and {delta}{omega}{sub E} in terms of the spatial cosine-transform components of the magnetic field.
Critical conditions for failure; stress levels, length scales, time scales
NASA Astrophysics Data System (ADS)
Bourne, Neil
2015-06-01
There is a range of thresholds for the response of condensed matter under loading in compression, from the yield point to that at which the bond strength is overcome and warm dense matter is formed. Yield stress shows a correlation between the length scale swept by the rise of the pulse and the defect distribution within the target for a range of materials. Strain rate is also a useful term that reflects the evolution of the stress state within a target but must also be defined for a volume element containing a particular defect distribution to reflect continuum conditions acting within and thus applies to a defined length scale within a target. Examples are shown using shock pulses to spall metal targets. Different stacking shows differing behaviour yet in each case momentum is conserved. This overview of behaviour suggests concepts borrowed from rate-independent plasticity may be viewed in a different manner and accompanying behaviours such as brittle-ductile transition may be reviewed when explaining a range of dynamic failure modes under load for materials and structures.
Optical time-frequency scaling for signal processing applications
NASA Astrophysics Data System (ADS)
Madsen, C. K.; Chintanpalli, A.
2006-05-01
Optical time-frequency processing requires a combination of high-speed, quadratic phase modulators and dispersive delay lines. The latter is typically achieved using optical fibers, but can be compactly implemented and tunable using dispersive filters. Time scaling, either dilation or compression, can be achieved with these building blocks. While basic time scaling followed by direct detection has been demonstrated, we focus on cascading time-scale operations for potential signal processing applications and implementations using integrated-optic platforms. For cascaded operations, both the phase and amplitude of the scaled output must be correct. Time scaling is studied analytically and by simulations. Practical implementation issues are addressed such as the time aperture limits imposed by using sinusoidal phase modulation to approximate the desired quadratic response. The chirp and dispersion relationships are given for "factor of one half" and "factor of two" time scaling. The evolution of the signal's time support at intermediate points in the time-scaling operation is shown to be a critical parameter for practical implementations. Two optical time-scaling architectures are studied, and one is clearly better in this respect. Furthermore, a special case arises for a Gaussian input pulse whereby the number of elements needed to realize the time scaling can reduced by a factor of two. Applications for cascaded time scaling operations are discussed, including optical wavelet processing and photonic-assisted analog-to-digital conversion. By using the time-scale operation in the optical domain to mimic the discrete-time downsampling operation, we show that physical scaling of the optical filters between subsequent decomposition levels is not required.
On time scales and time synchronization using LORAN-C as a time reference signal
NASA Technical Reports Server (NTRS)
Chi, A. R.
1974-01-01
The long term performance of the eight LORAN-C chains is presented in terms of the Coordinated Universal Time (UTC) of the U.S. Naval Observatory (USNO); and the use of the LORAN-C navigation system for maintaining the user's clock to a UTC scale is described. The atomic time scale and the UTC of several national laboratories and observatories relative to the international atomic time are reported. Typical performance of several NASA tracking station clocks, relative to the USNO master clock, is also presented.
A Quaternary Geomagnetic Instability Time Scale
NASA Astrophysics Data System (ADS)
Singer, B. S.
2013-12-01
Reversals and excursions of Earth's geomagnetic field create marker horizons that are readily detected in sedimentary and volcanic rocks worldwide. An accurate and precise chronology of these geomagnetic field instabilities is fundamental to understanding several aspects of Quaternary climate, dynamo processes, and surface processes. For example, stratigraphic correlation between marine sediment and polar ice records of climate change across the cryospheres benefits from a highly resolved record of reversals and excursions. The temporal patterns of dynamo behavior may reflect physical interactions between the molten outer core and the solid inner core or lowermost mantle. These interactions may control reversal frequency and shape the weak magnetic fields that arise during successive dynamo instabilities. Moreover, weakening of the axial dipole during reversals and excursions enhances the production of cosmogenic isotopes that are used in sediment and ice core stratigraphy and surface exposure dating. The Geomagnetic Instability Time Scale (GITS) is based on the direct dating of transitional polarity states recorded by lava flows using the 40Ar/39Ar method, in parallel with astrochronologic age models of marine sediments in which O isotope and magnetic records have been obtained. A review of data from Quaternary lava flows and sediments yields a GITS comprising 10 polarity reversals and 27 excursions during the past 2.6 million years. Nine of the ten reversals bounding chrons and subchrons are associated with 40Ar/39Ar ages of transitionally-magnetized lava flows. The tenth, the Guass-Matuyama chron boundary, is tightly bracketed by 40Ar/39Ar dated ash deposits. Of the 27 well-documented excursions, 14 occurred during the Matuyama chron and 13 during the Brunhes chron; 19 have been dated directly using the 40Ar/39Ar method on transitionally-magnetized volcanic rocks and form the backbone of the GITS. Excursions are clearly not the rare phenomena once thought. Rather, during the Quaternary period, they occur nearly three times as often as full polarity reversals. I will address analytical issues, including the size and consistency of system blanks, that have led to the recognition of minor (1%) discrepencies between the 40Ar/39Ar age for a particular reversal or excursion and the best astrochronologic estimates from ODP sediment cores. For example, re-analysis of lava flows from Haleakala volcano, Maui that record in detail the Matuyama-Brunhes polarity reversal have been undertaken with blanks an order of magntitude smaller and more stable than was common a decade ago. Using the modern astrochronologic calibration of 28.201 Ma for the age of the Fish Canyon sanidine standard, results thus far yield an 40Ar/39Ar age of 772 × 11 ka for the reversal that is identical to the most precise and accurate astrochronologic age of 773 × 2 ka for this reversal from ODP cores. Similarly, new dating of sanidine in the Cerro Santa Rosa I rhyolite dome, New Mexico reveals an age of 932 × 5 ka for the excursion it records, in perfect agreement with astrochronologically dated ODP core records. Work underway aims at refining the 40Ar/39Ar ages that underpin the entire GITS by further eliminating the bias between the radioisotopic and astrochronologically determined ages for several reversals and excursions.
Kojima, Masakazu
â?¢ X # # S 1+n + , â?¢ X = xx T 4 #12; 2. SDP and LiftÂandÂProject LP relaxations of QOPs SDP Relaxation # min. M 0 . X s.t. M i . X # 0 (1 # i # m), X = # 1 x T x â?¢ X # # S 1+n + LiftÂandÂProject LP. SDP and LiftÂandÂProject LP relaxations of QOPs 3. SOCP relaxation --- 1 4. SOCP relaxation --- 2 5
Monte Carlo simulation of catalytic reactions with widely varying time scales
Lutsevich, L.V.; Tkachenko, O.A. (USSR Academy of Sciences, Novosibirsk (Russian Federation))
1992-08-01
An algorithm for Monte Carlo simulation (MC simulation) of catalytic reactions with widely varying time scales is described. The idea of the proposed algorithm is that the system is divided into fast and slow subsystems, which are stimulated separately, each in its own time scale. A MC model of a heterogeneous catalytic reaction, A + 1/2B{sub 2} {yields} AB, which occurs through the Langmuir-Hinshelwood mechanism, supplemented with a slow stage of reversible adsorption of inert particles, is also investigated. It has been shown that, in this model, various relaxation oscillations exist and the rate constant of desorption of particles A is a crucial parameter in the formation of oscillations.
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.
Observation time scale, free-energy landscapes, and molecular symmetry
Salamon, Peter
Observation time scale, free-energy landscapes, and molecular symmetry David J. Walesa,1 and Peter structures that interconvert on a given time scale are lumped together, the corresponding free-energy surface that are connected by free-energy barriers below a certain threshold. We illustrate this time dependence for some
Assessment of Nanosecond Time Scale Motions in Native and Non-Native States of Ubiquitin.
Morozova, Olga B; Yurkovskaya, Alexandra V
2015-10-01
The paramagnetic relaxation times of the aromatic and ? protons of Tyr59 and His68 residues of the native ubiquitin and of Tyr59 residue of the non-native ubiquitin were determined from an analysis of chemically induced dynamic nuclear polarization (CIDNP) kinetics obtained during the photoreaction of the protein and 2,2'-dipyridyl excited in the triplet state. Using the paramagnetic relaxation times determined earlier for the radicals of free amino acids as an internal standard and assuming that the hyperfine interaction (HFI) anisotropy is very similar for the radicals of free amino acids and the corresponding radicals of amino acid residues in the proteins, we determined parameters that characterize the intramolecular mobility of different protons in native and two non-native states of ubiquitin. The latter are denatured at pH 2 and 57 °C, and the A-state at pH 2 in a 60%/40% methanol/water mixture. The determination of the two parameters of intramolecular mobility (i.e., the correlation time of internal motion, ?e, and the order parameter, S(2)) was only possible by analyzing paramagnetic relaxation data obtained at two magnetic fields (4.7 and 9.4 T) using nuclear magnetic resonance (NMR) spectrometry. Intramolecular correlation times fall into the submicrosecond-microsecond time scale. Longer correlation times and higher order parameters were found for the less accessible Tyr59 residue than for the His68 residue, as well as for the more buried ? protons than for the aromatic protons for both of the protein residues in the native state. For Tyr59, intramolecular mobility increases following the loss of the tertiary structure of ubiquitin. These findings strongly support the reliability of the obtained data. PMID:26367543
Scale relativity and fractal space-time: theory and applications
Nottale, Laurent
Scale relativity and fractal space-time: theory and applications Laurent Nottale CNRS, LUTH, Paris In the first part of this contribution, we review the development of the theory of scale relativity and its concern of the theory of scale relativity is about the foundation of quantum mechanics. As it is now well
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
NASA Astrophysics Data System (ADS)
Jeon, Jae-Hyung; Leijnse, Natascha; Oddershede, Lene B.; Metzler, Ralf
2013-04-01
We report the results of single tracer particle tracking by optical tweezers and video microscopy in micellar solutions. From careful analysis in terms of different stochastic models, we show that the polystyrene tracer beads of size 0.52-2.5 ?m after short-time normal diffusion turn over to perform anomalous diffusion of the form
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
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
A new generalization of Ostrowski type inequality on time scales
Wenjun Liu; Quoc Anh Ngo; Wenbin Chen
2008-05-04
In this paper we first extend a generalization of Ostrowski type inequality on time scales for functions whose derivatives are bounded and then unify corresponding continuous and discrete versions. We also point out some particular integral type inequalities on time scales as special cases.
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.
Local-time effect on small space-time scale
V. A. Panchelyuga; V. A. Kolombet; M. S. Panchelyuga; S. E. Shnoll
2006-10-18
The paper presents an investigation of local-time effect - one of the manifestations of macroscopic fluctuations phenomena. Was shown the existence of the named effect for longitudinal distance between locations of measurements up to 500 meters. Also a structure of intervals distribution in neighborhood of local-time peak was studied and splitting of the peak was found out. Obtained results lead to conclusion about sharp anisotropy of space-time.
Relaxation of anharmonic molecules
NASA Astrophysics Data System (ADS)
Dubrovskii, G. V.; Strelchenia, V. M.
1986-06-01
The vibrational relaxation of anharmonic oscillators is investigated analytically. A method proposed in an earlier study (Vasilev et al., 1984) is generalized to the case of equations with time-dependent velocity coefficients and used to describe relaxation processes in a gas flow. The properties of a solution to the problem of the VT-relaxation of anharmonic molecules are analyzed, and the problem of the inclusion of sources of various types is examined. A method is proposed for taking account of multiquantum transitions; the method is generalized to the case of an arbitrary gas mixture. Ways in which the solutions obtained here can be applied to relaxation gas dynamics are discussed.
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 and Rheology in Dense Athermal Suspensions
Peter Olsson
2013-02-26
We study relaxation and rheology of dense athermal suspensions of frictionless particles close below the jamming density. Our key quantity, the relaxation time---determined from the exponential decay of the energy after the shearing has suddenly been switched off---is argued to be a determining factor behind the algebraic divergence of various quantities as the jamming density is approached from below. We also define and measure the ``dissipation time'', which is obtained directly in shearing simulations and find that it behaves similarly to the relaxation time. Comparing shear viscosity with the expression for the dissipation time we identify a non-divergent factor that explains the need for correction terms in the scaling analyses of the shear viscosity.
Optimal dynamic voltage scaling for wireless sensor nodes with real-time constraints
NASA Astrophysics Data System (ADS)
Cassandras, Christos G.; Zhuang, Shixin
2005-11-01
Sensors are increasingly embedded in manufacturing systems and wirelessly networked to monitor and manage operations ranging from process and inventory control to tracking equipment and even post-manufacturing product monitoring. In building such sensor networks, a critical issue is the limited and hard to replenish energy in the devices involved. Dynamic voltage scaling is a technique that controls the operating voltage of a processor to provide desired performance while conserving energy and prolonging the overall network's lifetime. We consider such power-limited devices processing time-critical tasks which are non-preemptive, aperiodic and have uncertain arrival times. We treat voltage scaling as a dynamic optimization problem whose objective is to minimize energy consumption subject to hard or soft real-time execution constraints. In the case of hard constraints, we build on prior work (which engages a voltage scaling controller at task completion times) by developing an intra-task controller that acts at all arrival times of incoming tasks. We show that this optimization problem can be decomposed into two simpler ones whose solution leads to an algorithm that does not actually require solving any nonlinear programming problems. In the case of soft constraints, this decomposition must be partly relaxed, but it still leads to a scalable (linear in the number of tasks) algorithm. Simulation results are provided to illustrate performance improvements in systems with intra-task controllers compared to uncontrolled systems or those using inter-task control.
Scaling the Martian Walls of Time
Nikki Thornton; Joseph Yagloski; Joe Fledderman; Gregg OMarr; Ben Weber; Chris Carlins; Shubh Krishna; Kevin Sloan; Taite Merriman; David Borowski
2000-01-01
On Earth, when scientists want to investigate planetary history they take a core sample, with deeper fragments corresponding to older materials. In essence, descending through sedimentary layers is like going back in time. But creating a robot capable of taking samples more than a few meters below the planetary surface is still beyond the current available technology. The cliffhanger idea
Multiple-time-scale concepts in turbulent transport modelling
NASA Technical Reports Server (NTRS)
Hanjalic, K.; Launder, B. E.; Schiestel, R.
1979-01-01
The paper reports progress in developing a closure employing two or more independently calculated time scales with which to characterize the rates of progress of different turbulent interactions. The approach contrasts with that used by earlier single-point models which adopt just a single time scale, proportional to the turbulence energy turnover time. The present treatment divides the energy containing part of the spectrum into two regions which respond at different rates and in different ways to changes in the environment. Computational results are reported for several thin shear flows which show striking improvement in the level of agreement with experiment over that obtained with models employing only one time scale.
Replenish and Relax: Explaining Logarithmic Annealing in Ion-Implanted c-Si
NASA Astrophysics Data System (ADS)
Béland, Laurent Karim; Anahory, Yonathan; Smeets, Dries; Guihard, Matthieu; Brommer, Peter; Joly, Jean-François; Pothier, Jean-Christophe; Lewis, Laurent J.; Mousseau, Normand; Schiettekatte, François
2013-09-01
We study ion-damaged crystalline silicon by combining nanocalorimetric experiments with an off-lattice kinetic Monte Carlo simulation to identify the atomistic mechanisms responsible for the structural relaxation over long time scales. We relate the logarithmic relaxation, observed in a number of disordered systems, with heat-release measurements. The microscopic mechanism associated with this logarithmic relaxation can be described as a two-step replenish and relax process. As the system relaxes, it reaches deeper energy states with logarithmically growing barriers that need to be unlocked to replenish the heat-releasing events leading to lower-energy configurations.
Biological Scaling and Physiological Time: Biomedical Applications
Van M. Savage; Geoffrey B. West
A framework for the development of quantitative theories that capture the body size and body temperature dependence of many\\u000a cellular and physiological rates and times is presented. These theories rely on basic properties of biological systems, such\\u000a as the invariance of terminal units, and on fundamental constraints taken from physics and chemistry, such as energy minimization\\u000a of flow through resource-distribution
Acceleration time scale in an ultrarelativistic shock
Janusz Bednarz
2000-05-10
The acceleration mechanism at ultrarelativistic shocks is investigated using the Monte Carlo simulations. We apply a method of discrete small amplitude particle momentum scattering to reproduce highly anisotropic conditions at the shock and carefully describe the acceleration mechanism. The obtained acceleration times equal $1.0 r_{g}/c$ if the spectral index reach the value of 2.2, independent of physical conditions in the shock. Some other parameters of the acceleration process are also provided.
Larionov, A. V.; Il’in, A. I.
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.
Besson, J A; Craig, E; Ebmeier, K P; Foster, M A; Wheatley, D N
1991-03-01
Red blood cell proton relaxation times T1 and T2 were measured in samples from chronic alcoholic patients abstinent for varying periods from 1 week to over 6 months. T1 and T2 were elevated in the early stages of abstinence and declined to the values of controls after 8 weeks. Changes in the water content of the red blood cells and the mean corpuscular volume paralleled these changes but were more closely associated with T2. It is suggested that T1 and T2 may reflect different aspects in water content and free-to-bound ratio of water. The significance of these findings is discussed in the context of changes previously observed in the brains of alcoholic patients, and in rats fed a diet supplemented with alcohol for 6 months. PMID:2058792
NASA Astrophysics Data System (ADS)
Hammou, H.; Ginzburg, I.; Boulerhcha, M.
2011-06-01
We develop two-relaxation-times Lattice Boltzmann schemes (TRT) with two relaxation functions ?±(r?,t) for solving highly non-linear equations for groundwater modeling in d-dimensions, namely, the Richards equation for water content distribution ?(r?,t) in unsaturated flow and the associated transport equation for solute concentration C(r?,t), advected by the local Darcian water flux. The method is verified against the analytical solutions and the HYDRUS code where the TRT schemes behave more robustly for small diffusion coefficients and sharp infiltration profiles. The focus is on the stability and efficiency of two transport schemes. The first scheme conventionally prescribes C for diffusive flux equilibrium variable while conserving ?C. The second scheme prescribes ?C for both variables, expecting to retain the stable parameter areas and velocity amplitudes recently predicted by linear von Neumann stability analysis. We show that the first scheme reduces the stable diffusion range, e.g. from ?-/ d to ??-/ d for simplest velocity sets, but it also modifies the linearized numerical diffusion, from - ?-U?U? to - ??-U?U?, giving rise to possible enhancement of stable velocity U2, max by a factor 1/ ?. This analysis indicates that the first scheme is most efficient for infiltration into dry soil. When the product ?+?- is kept constant, we find a good agreement between the attainable velocity and our predictions providing that ?- does not exceed ?5. Otherwise, approaching two opposite stability limits, ?+ ? 0 when ?- ? ? , the stable velocity amplitude drastically falls for the two transport TRT schemes. At the same time, their BGK submodels ?+ = ?- may keep the optimal stability for diffusion-dominant problems but their boundary and bulk approximations are completely destroyed. The analysis presented here may serve as a starting point for construction of the suitable equilibrium transformations, based on the analytical stability argument and a proper parameter choice.
Bridging the Time and Length Scales
NASA Astrophysics Data System (ADS)
Ortiz, Michael
1997-08-01
The field of nanomechanics clearly exemplifies many of the challenges commonly encountered in micromechanics. For instance, one of the main difficulties inherent to nanomechanics is the need to consider multiple length and temporal scales straddling the grey zone between atomistics and continuum behavior. A case in point is nanoindentation. While much of the material under the indentor can be idealized as a continuum to a good approximation---making it grossly inefficient to carry out direct atomistic simulations in such regions---the plasticity which ensues during the early stages of indentation is carried by a small number of discrete dislocations. Recent experimental observations of nanoindentation in Fe-3wt%Si single crystals by Gerberich et al. (1985) reveal that, when an indentor with a tip radius of 66 nm is driven to depths of 6 to 26 nm, roughly 15-70 dislocations can be impugned as the primary carriers of irreversible deformation. Evidently, such low dislocation numbers defy effective treatment by continuum theories, and demand an explicit consideration of the individual dislocations. From the standpoint of modeling, these issues pose competing resolution demands---and point to the need for---models that can effect a seamless transition from regions that are well described as continua to those requiring an explicit treatment of the lattice degrees of freedom. A second point as concerns the development of models is the desirability of ensuring that the constitutive description of the material is faithful to the underlying atomistics. Direct atomistic simulation, e. g., by molecular dynamics, trivially satisfies this requirement. There, each and every lattice degree of freedom is explicitly accounted for, and the deformation of the crystal follows directly from the atomic interactions. However, the trend toward simulating ever larger systems (with the present record somewhere in the neighborhood of 10^9 atoms) leaves us faced with a daunting bookkeeping task. Continuum models, by way of contrast, are often amenable to analytical treatment, at least for simple geometries. The analytical solutions are often instructive and effective at guiding physical intuition. Complex continuum models are routinely solved numerically with the aid of such powerful and versatile computational tools as the finite element method. Yet the Achilles heel of continuum theories resides in the constitutive description of the material, which is often mired in coarse phenomenology. Tadmor, Ortiz and Phillips (1996), and Shenoy, Ortiz and Phillips (1997), have recently advanced a quasicontinuum theory which seizes upon the strengths of both atomistic and continuum theories and allows for the simultaneous consideration of multiple length and temporal scales. The theory starts from an underlying conventional molecular dynamics model and strives to systematically elimate unnecessary degrees of freedom. This is accomplished by constraining large numbers of atoms to move in concert with a piecewise linear displacement field in regions where the fields vary slowly. This operation may be regarded as an orthogonal projection acting on the full atomistic phase space. The energy associated with the complementary projection, which defines the fluctuation fields, is regarded as heat. In this manner, molecular dynamics and continuum thermodynamics arise as particular limits of---and are seamlessly bridged by---the theory. It bears emphasis, however, that all mechanical and thermal properties of the system emanate directly from atomistics. It should also be emphasized that, by stressing heat over temperature and entropy, the theory does not make any a priori assumptions regarding the thermal equilibrium of the system. In particular, heat conduction is accounted for. We have demonstrated the soundness and versatility of the theory by way of selected applications including dynamic nanoindentation and dislocation emission from crack tips.
Marc Bienert; Jorge Flores; Sergey Yu. Kun
2006-06-07
We estimate how accurate the phase relaxation time of quantum many-body systems can be determined from data on forward peaking of evaporating protons from a compound nucleus. The angular range and accuracy of the data needed for a reliable determination of the phase relaxation time are evaluated. The general method is applied to analyze the inelastic scattering of 18 MeV protons from Pt for which previously measured double differential cross sections for two angles in the evaporating domain of the spectra show a strong forward peaking. A new experiment for an improved determination of the phase relaxation time is proposed. The experiment is also highly desirable for an accurate test of a formation of thermalized non-equilibrated matter in quantum many-body systems.
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.
Scaling the Martian Walls of Time
NASA Astrophysics Data System (ADS)
Thornton, Nikki; Yagloski, Joseph; Fledderman, Joe; OMarr, Gregg; Weber, Ben; Carlins, Chris; Krishna, Shubh; Sloan, Kevin; Merriman, Taite; Borowski, David
2000-01-01
On Earth, when scientists want to investigate planetary history they take a core sample, with deeper fragments corresponding to older materials. In essence, descending through sedimentary layers is like going back in time. But creating a robot capable of taking samples more than a few meters below the planetary surface is still beyond the current available technology. The cliffhanger idea takes advantage of the natural surface features of Mars to explore the history of the planet without digging. So interesting and difficult questions can be answered not with the brute force of a drill, but with creative mission design. Penn State University HEDS-UP team has designed a novel Mars mission approach. A main Lander with a Rover and a Cliffhanger will land near cliffs of Valles Mariners. Especially design cannon (gas, guided munitions or rocket) will deploy a long rope into the canyon. The rover will carry the cliffhanger to the edge of Valles Marineris following the rope, attach the cliffhanger to the rope. The Cliffhanger will then climb a 2 km down the rope and will allow the team to study sedimentary layers of rock on the side of the cliff. Samples and high-resolution images will be taken and delivered to the Lander for further investigation (optical multispectral imaging microscope, spectrometry) and sending the results to Earth. The robot has been designed to have the capability for locomotion at any angle (including somewhat uphill slopes) but maximum effective After the mission of rope-climbing is completed, the Rover am Lander will embark on another long-term mission to provide meteorological and geological data over a long period of time (long-term Mars Observatory), and perform acoustic and seismic experiments on the surface of Mars in preparation for human arrival.
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.
Yesinowski, James P
2015-03-01
Measuring true spin-lattice relaxation times T(1) of half-integral quadrupolar nuclei having non-zero nuclear quadrupole coupling constants (NQCCs) presents challenges due to the presence of satellite-transitions (STs) that may lie outside the excitation bandwidth of the central transition (CT). This leads to complications in establishing well-defined initial conditions for the population differences in these multi-level systems. In addition, experiments involving magic-angle spinning (MAS) can introduce spin exchange due to zero-crossings of the ST and CT (or possibly rotational resonance recoupling in the case of multiple sites) and greatly altered initial conditions as well. An extensive comparison of pulse sequences that have been previously used to measure T(1) in such systems is reported, using the (71)Ga (I=3/2) NMR of a Ge-doped h-GaN n-type semiconductor sample as the test case. The T(1) values were measured at the peak maximum of the Knight shift distribution. Analytical expressions for magnetization-recovery of the CT appropriate to the pulse sequences tested were used, involving contributions from both a magnetic relaxation mechanism (rate constant W) and a quadrupolar one (rate constants W(1) and W(2), approximately equal in this case). An asynchronous train of high-power saturating pulses under MAS that is able to completely saturate both CT and STs is found to be the most reliable and accurate method for obtaining the "true T(1)", defined here as (2W+2W1,2)(-)(1). All other methods studied yielded poor agreement with this "true T(1)" value or even resulted in gross errors, for reasons that are analyzed in detail. These methods involved a synchronous train of saturating pulses under MAS, an inversion-recovery sequence under MAS or static conditions, and a saturating comb of pulses on a static sample. Although the present results were obtained on a sample where the magnetic relaxation mechanism dominated the quadrupolar one, the asynchronous saturating pulse train approach is not limited to this situation. The extent to which W(1) and W(2) are unequal does affect the interpretability of the experiment however, particularly when the quadrupolar mechanism dominates. A numerically approximate solution for the I=3/2 recovery case reveals the quantitative effects of any such inequality. PMID:25700115
NASA Astrophysics Data System (ADS)
Yesinowski, James P.
2015-03-01
Measuring true spin-lattice relaxation times T1 of half-integral quadrupolar nuclei having non-zero nuclear quadrupole coupling constants (NQCCs) presents challenges due to the presence of satellite-transitions (STs) that may lie outside the excitation bandwidth of the central transition (CT). This leads to complications in establishing well-defined initial conditions for the population differences in these multi-level systems. In addition, experiments involving magic-angle spinning (MAS) can introduce spin exchange due to zero-crossings of the ST and CT (or possibly rotational resonance recoupling in the case of multiple sites) and greatly altered initial conditions as well. An extensive comparison of pulse sequences that have been previously used to measure T1 in such systems is reported, using the 71Ga (I = 3/2) NMR of a Ge-doped h-GaN n-type semiconductor sample as the test case. The T1 values were measured at the peak maximum of the Knight shift distribution. Analytical expressions for magnetization-recovery of the CT appropriate to the pulse sequences tested were used, involving contributions from both a magnetic relaxation mechanism (rate constant W) and a quadrupolar one (rate constants W1 and W2, approximately equal in this case). An asynchronous train of high-power saturating pulses under MAS that is able to completely saturate both CT and STs is found to be the most reliable and accurate method for obtaining the "true T1", defined here as (2W + 2W1,2)-1. All other methods studied yielded poor agreement with this "true T1" value or even resulted in gross errors, for reasons that are analyzed in detail. These methods involved a synchronous train of saturating pulses under MAS, an inversion-recovery sequence under MAS or static conditions, and a saturating comb of pulses on a static sample. Although the present results were obtained on a sample where the magnetic relaxation mechanism dominated the quadrupolar one, the asynchronous saturating pulse train approach is not limited to this situation. The extent to which W1 and W2 are unequal does affect the interpretability of the experiment however, particularly when the quadrupolar mechanism dominates. A numerically approximate solution for the I = 3/2 recovery case reveals the quantitative effects of any such inequality.
NASA Astrophysics Data System (ADS)
Morsali, A.; Goharshadi, E. K.; Shahtahmasbi, N.
2006-03-01
High-frequency elastic moduli ( G? and K?) for a Lennard-Jones (LJ) fluid have been calculated using three known analytical expressions for radial distribution function (RDF) at different temperatures and densities and compared with the corresponding values of these properties obtained from molecular dynamics (MD). The shear relaxation time of a LJ fluid at different temperatures and densities has been calculated for three expressions for RDF and using an analytical expression for viscosity and compared with those of obtained MD. The values of reduced shear relaxation time at different reduced temperatures and densities have been fitted to obtain an analytical equation.
Multiple Time Scale Complexity Analysis of Resting State FMRI
Smith, Robert X.; Yan, Lirong; Wang, Danny J.J.
2014-01-01
The present study explored multi-scale entropy (MSE) analysis to investigate the entropy of resting state fMRI signals across multiple time scales. MSE analysis was developed to distinguish random noise from complex signals since the entropy of the former decreases with longer time scales while the latter signal maintains its entropy due to a self-resemblance” across time scales. A long resting state BOLD fMRI (rs-fMRI) scan with 1000 data points was performed on five healthy young volunteers to investigate the spatial and temporal characteristics of entropy across multiple time scales. A shorter rs-fMRI scan with 240 data points was performed on a cohort of subjects consisting of healthy young (age 23±2 years, n=8) and aged volunteers (age 66±3 years, n=8) to investigate the effect of healthy aging on the entropy of rs-fMRI. The results showed that MSE of gray matter, rather than white matter, resembles closely that of f?1 noise over multiple time scales. By filtering out high frequency random fluctuations, MSE analysis is able to reveal enhanced contrast in entropy between gray and white matter, as well as between age groups at longer time scales. Our data support the use of MSE analysis as a validation metric for quantifying the complexity of rs-fMRI signals. PMID:24242271
Time Scales for Achieving Astronomical Consensus
NASA Astrophysics Data System (ADS)
Trimble, Virginia
The history of science can be recounted in many ways: by addressing the work of one person or school; by starting with the ancients and working chronologically up to the present; by focusing on a particular century; or by tracing a particular important idea as far back and forward as it can be found. The present discussion does none of these. Rather, it adopts the ordering of a standard introductory astronomy textbook, from the solar system via stars and galaxies, to the universe as a whole, and in each regime picks out a few issues that were controversial or wrongly decided for a long time. For each, I attempt to identify a duration of the period of uncertainty or error and some of the causes of the confusion. This is surely not an original idea, though I am not aware of having encountered it elsewhere, and it is not one that is likely to appeal to most 21st century historians of science, for whom the question "Who first got it right?" is not necessarily an important, or even appropriate, one. Some of the stories have been told as historical introductions to conferences and are here summarized and brought up to date. Others I had not previously addressed.
Effective masses, relaxation times, and carrier mobilities in some chloride intercalants of graphite
NASA Technical Reports Server (NTRS)
Woollam, J. A.; Haugland, E.; Dowell, M. B.; Underhill, C.
1981-01-01
The effective masses, carrier scattering times and carrier mobilities have been measured in selected graphite intercalation compounds using the Shubnikov-de Haas effect at a series of temperatures between 4 and 50 K. Effective masses are less than or equal to 0.1 of the free-electron mass, scattering times are about 10 to the -13th/s and carrier mobilities are on the order of 10,000 sq cm/V s.
Relaxation properties in classical diamagnetism
NASA Astrophysics Data System (ADS)
Carati, A.; Benfenati, F.; Galgani, L.
2011-06-01
It is an old result of Bohr that, according to classical statistical mechanics, at equilibrium a system of electrons in a static magnetic field presents no magnetization. Thus a magnetization can occur only in an out of equilibrium state, such as that produced through the Foucault currents when a magnetic field is switched on. It was suggested by Bohr that, after the establishment of such a nonequilibrium state, the system of electrons would quickly relax back to equilibrium. In the present paper, we study numerically the relaxation to equilibrium in a modified Bohr model, which is mathematically equivalent to a billiard with obstacles, immersed in a magnetic field that is adiabatically switched on. We show that it is not guaranteed that equilibrium is attained within the typical time scales of microscopic dynamics. Depending on the values of the parameters, one has a relaxation either to equilibrium or to a diamagnetic (presumably metastable) state. The analogy with the relaxation properties in the Fermi Pasta Ulam problem is also pointed out.
Relaxation properties in classical diamagnetism.
Carati, A; Benfenati, F; Galgani, L
2011-06-01
It is an old result of Bohr that, according to classical statistical mechanics, at equilibrium a system of electrons in a static magnetic field presents no magnetization. Thus a magnetization can occur only in an out of equilibrium state, such as that produced through the Foucault currents when a magnetic field is switched on. It was suggested by Bohr that, after the establishment of such a nonequilibrium state, the system of electrons would quickly relax back to equilibrium. In the present paper, we study numerically the relaxation to equilibrium in a modified Bohr model, which is mathematically equivalent to a billiard with obstacles, immersed in a magnetic field that is adiabatically switched on. We show that it is not guaranteed that equilibrium is attained within the typical time scales of microscopic dynamics. Depending on the values of the parameters, one has a relaxation either to equilibrium or to a diamagnetic (presumably metastable) state. The analogy with the relaxation properties in the Fermi Pasta Ulam problem is also pointed out. PMID:21721776
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
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
Short-Time Existence for Scale-Invariant Hamiltonian Waves
Hunter, John K.
Short-Time Existence for Scale-Invariant Hamiltonian Waves John K. Hunter Department of Mathematics- tions that describe the self-interaction of weakly nonlinear scale-invariant waves. These equations include ones that describe weakly nonlinear hy- perbolic surface waves, such as nonlinear Rayleigh waves
NASA Astrophysics Data System (ADS)
Kang, Nam Lyong
2014-12-01
The electron spin relaxation times in a system of electrons interacting with piezoelectric phonons mediated through spin-orbit interactions were calculated using the formula derived from the projection-reduction method. The results showed that the temperature and magnetic field dependence of the relaxation times in InSb and InAs were similar. The piezoelectric material constants obtained by a comparison with the reported experimental result were Ppe=4.0 ×1022 eV/m for InSb and Ppe=1.2 ×1023 eV/m for InAs. The result also showed that the relaxation of the electron spin by the Elliot-Yafet process is more relevant for InSb than InAs at a low density.
Modes and emergent time scales of embayed beach dynamics
NASA Astrophysics Data System (ADS)
Ratliff, Katherine M.; Murray, A. Brad
2014-10-01
In this study, we use a simple numerical model (the Coastline Evolution Model) to explore alongshore transport-driven shoreline dynamics within generalized embayed beaches (neglecting cross-shore effects). Using principal component analysis (PCA), we identify two primary orthogonal modes of shoreline behavior that describe shoreline variation about its unchanging mean position: the rotation mode, which has been previously identified and describes changes in the mean shoreline orientation, and a newly identified breathing mode, which represents changes in shoreline curvature. Wavelet analysis of the PCA mode time series reveals characteristic time scales of these modes (typically years to decades) that emerge within even a statistically constant white-noise wave climate (without changes in external forcing), suggesting that these time scales can arise from internal system dynamics. The time scales of both modes increase linearly with shoreface depth, suggesting that the embayed beach sediment transport dynamics exhibit a diffusive scaling.
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.
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.
Proton T1 relaxation times of metabolites in human occipital white and gray matter at 7 T.
Xin, Lijing; Schaller, Benoît; Mlynarik, Vladimir; Lu, Huanxiang; Gruetter, Rolf
2013-04-01
Proton T1 relaxation times of metabolites in the human brain have not previously been published at 7 T. In this study, T1 values of CH3 and CH2 group of N-acetylaspartate and total creatine as well as nine other brain metabolites were measured in occipital white matter and gray matter at 7 T using an inversion-recovery technique combined with a newly implemented semi-adiabatic spin-echo full-intensity acquired localized spectroscopy sequence (echo time = 12 ms). The mean T1 values of metabolites in occipital white matter and gray matter ranged from 0.9 to 2.2 s. Among them, the T1 of glutathione, scyllo-inositol, taurine, phosphorylethanolamine, and N-acetylaspartylglutamate were determined for the first time in the human brain. Significant differences in T1 between white matter and gray matter were found for water (-28%), total choline (-14%), N-acetylaspartylglutamate (-29%), N-acetylaspartate (+4%), and glutamate (+8%). An increasing trend in T1 was observed when compared with previously reported values of N-acetylaspartate (CH3 ), total creatine (CH3 ), and total choline at 3 T. However, for N-acetylaspartate (CH3 ), total creatine, and total choline, no substantial differences compared to previously reported values at 9.4 T were discernible. The T1 values reported here will be useful for the quantification of metabolites and signal-to-noise optimization in human brain at 7 T. PMID:22648904
NASA Astrophysics Data System (ADS)
Washburn, K. E.; Eccles, C. D.; Callaghan, P. T.
2008-09-01
Magnetic susceptibility differences in porous media produce local gradients within the pore space. At high magnetic fields, these inhomogeneities have the potential to greatly affect nuclear magnetic resonance measurements. We undertake a study using a new NMR technique to measure the internal gradients present in highly heterogeneous samples over a wide range of magnetic field strengths. Our results show that even at ultra-high fields there can exist signal at internal gradient strengths sufficiently small that techniques for suppressing unwanted side effects have the possibility to be used. Our findings encourage the use of these high and ultra-high field strengths for a broader range of samples. Our results also give experimental evidence to support the theory of internal gradient scaling as a function of field strength within pores.
NASA Astrophysics Data System (ADS)
Serrai, Hacene; Senhadji, Lotfi; de Certaines, Jacques D.; Coatrieux, Jean Louis
1997-01-01
The wavelet-transform method is used to quantify the magnetic resonance spectroscopy (MRS) parameters: chemical shift, apparent relaxation timeT*2, resonance amplitude, and phase. Wavelet transformation is a time-frequency representation which separates each component from the FID, then successively quantifies it and subtracts it from the raw signal. Two iterative procedures have been developed. They have been combined with a nonlinear regression analysis method and tested on both simulated and real sets of biomedical MRS data selected with respect to the main problems usually encountered in quantifying biomedical MRS, specifically "chemical noise," resulting from overlapping resonances, and baseline distortion. The results indicate that the wavelet-transform method can provide efficient and accurate quantification of MRS data.
Kibble-Zurek mechanism and finite-time scaling
NASA Astrophysics Data System (ADS)
Huang, Yingyi; Yin, Shuai; Feng, Baoquan; Zhong, Fan
2014-10-01
The Kibble-Zurek (KZ) mechanism has been applied to a variety of systems ranging from low-temperature Bose-Einstein condensations to grand unification scales in particle physics and cosmology and from classical phase transitions to quantum phase transitions. Here, we show that finite-time scaling (FTS) provides a detailed improved understanding of the mechanism. In particular, the finite time scale, which is introduced by the external driving (or quenching) and results in FTS, is the origin of the division of the adiabatic regimes from the impulse regime in the KZ mechanism. The origin of the KZ scaling for the defect density, generated during the driving through a critical point, is not that the correlation length ceases growing in the nonadiabatic impulse regime, but rather, is that it is taken over by the effective finite length scale corresponding to the finite time scale. We also show that FTS accounts well for and improves the scaling ansatz proposed recently by Liu, Polkovnikov, and Sandvik, [Phys. Rev. B 89, 054307 (2014), 10.1103/PhysRevB.89.054307]. Further, we show that their universal power-law scaling form applies only to some observables in cooling but not to heating. Even in cooling, it is invalid either when an appropriate external field is present. However, this finite-time-finite-size scaling calls for caution in application of FTS. Detailed scaling behaviors of the FTS and finite-size scaling, along with their crossover, are explicitly demonstrated, with the dynamic critical exponent z being estimated for two- and three-dimensional Ising models under the usual Metropolis dynamics. These values of z are found to give rise to better data collapses than the extant values do in most cases but take on different values in heating and cooling in both two- and three-dimensional spaces.
Loose Synchrony in Relaxation Oscillator Networks with Time Delays Shannon Campbell
Indiana University
[7]. Findings of synchronous oscillations in the brain have motivated much research (see [9/s in unmyelinated axons of the brain [3]. Since some fibers are known to extend over several millimeters [1], time in biological systems, and are inevitable in physical implementations (e.g. VLSI chips), it is nec essary
RELAXATION TIMES FOR ATOM DISLOCATIONS IN CRYSTALS STEFANIA PATRIZI AND ENRICO VALDINOCI
, but its jump points evolve in time, according to the external stress and a singular potential. Roughly differential equations which describe the position of the jump points x1(t), . . . , xN (t). We refer the evolution of the dislocation function v and the system of ODE's which drives the particles x1, . . . , x
Characteristic Time Scales of Characteristic Magmatic Processes and Systems
NASA Astrophysics Data System (ADS)
Marsh, B. D.
2004-05-01
Every specific magmatic process, regardless of spatial scale, has an associated characteristic time scale. Time scales associated with crystals alone are rates of growth, dissolution, settling, aggregation, annealing, and nucleation, among others. At the other extreme are the time scales associated with the dynamics of the entire magmatic system. These can be separated into two groups: those associated with system genetics (e.g., the production and transport of magma, establishment of the magmatic system) and those due to physical characteristics of the established system (e.g., wall rock failure, solidification front propagation and instability, porous flow). The detailed geometry of a specific magmatic system is particularly important to appreciate; although generic systems are useful, care must be taken to make model systems as absolutely realistic as possible. Fuzzy models produce fuzzy science. Knowledge of specific time scales is not necessarily useful or meaningful unless the hierarchical context of the time scales for a realistic magmatic system is appreciated. The age of a specific phenocryst or ensemble of phenocrysts, as determined from isotopic or CSD studies, is not meaningful unless something can be ascertained of the provenance of the crystals. For example, crystal size multiplied by growth rate gives a meaningful crystal age only if it is from a part of the system that has experienced semi-monotonic cooling prior to chilling; crystals entrained from a long-standing cumulate bed that were mechanically sorted in ascending magma may not reveal this history. Ragged old crystals rolling about in the system for untold numbers of flushing times record specious process times, telling more about the noise in the system than the life of typical, first generation crystallization processes. The most helpful process-related time scales are those that are known well and that bound or define the temporal style of the system. Perhaps the most valuable of these times comes from the observed durations and rates of volcanism. There can be little doubt that the temporal styles of volcanism are the same as those of magmatism in general. Volcano repose times, periodicity, eruptive fluxes, acoustic emission structures, lava volumes, longevity, etc. must also be characteristic of pluton-dominated systems. We must therefore give up some classical concepts (e.g., instantaneous injection of crystal-free magma as an initial condition) for any plutonic/chambered system and move towards an integrated concept of magmatism. Among the host of process-related time scales, probably the three most fundamental of any magmatic system are (1) the time scale associated with crystal nucleation (J) and growth (G) (tx}=C{1(G3 J)-{1}/4; Zieg & Marsh, J. Pet. 02') along with the associated scales for mean crystal size (L) and population (N), (2) the time scale associated with conductive cooling controlled by a local length scale (d) (tc}=C{2 d2/K; K is thermal diffusivity), and (3) the time scale associated with intra-crystal diffusion (td}=C{3 L2/D; D is chemical diffusivity). It is the subtle, clever, and insightful application of time scales, dovetailed with realistic system geometry and attention paid to the analogous time scales of volcanism, that promises to reveal the true dynamic integration of magmatic systems.
Signatures of discrete scale invariance in Dst time series
NASA Astrophysics Data System (ADS)
Balasis, Georgios; Papadimitriou, Constantinos; Daglis, Ioannis A.; Anastasiadis, Anastasios; Athanasopoulou, Labrini; Eftaxias, Konstantinos
2011-07-01
Self-similar systems are characterized by continuous scale invariance and, in response, the existence of power laws. However, a significant number of systems exhibits discrete scale invariance (DSI) which in turn leads to log-periodic corrections to scaling that decorate the pure power law. Here, we present the results of a search of log-periodic corrections to scaling in the squares of Dst index increments which are taken as proxies of the energy dissipation rate in the magnetosphere. We show that Dst time series exhibit DSI and discuss the consequence of this feature, as well as the possible implications of Dst DSI on space weather forecasting efforts.
Time Scales in Probabilistic Models of Wireless Sensor Networks
Anatoly Manita
2013-02-28
We consider a stochastic model of clock synchronization in a wireless network consisting of N sensors interacting with one dedicated accurate time server. For large N we find an estimate of the final time sychronization error for global and relative synchronization. Main results concern a behavior of the network on different time scales $t=t_N \\to \\infty$, $N \\to \\infty$. We discuss existence of phase transitions and find exact time scales on which an effective clock synchronization of the system takes place.
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.
Russian national time scale long-term stability
NASA Technical Reports Server (NTRS)
Alshina, A. P.; Gaigerov, B. A.; Koshelyaevsky, N. B.; Pushkin, S. B.
1994-01-01
The Institute of Metrology for Time and Space NPO 'VNIIFTRI' generates the National Time Scale (NTS) of Russia -- one of the most stable time scales in the world. Its striking feature is that it is based on a free ensemble of H-masers only. During last two years the estimations of NTS longterm stability based only on H-maser intercomparison data gives a flicker floor of about (2 to 3) x 10(exp -15) for averaging times from 1 day to 1 month. Perhaps the most significant feature for a time laboratory is an extremely low possible frequency drift -- it is too difficult to estimate it reliably. The other estimations, free from possible inside the ensemble correlation phenomena, are available based on the time comparison of NTS relative to the stable enough time scale of outer laboratories. The data on NTS comparison relative to the time scale of secondary time and frequency standards at Golitzino and Irkutsk in Russia and relative to NIST, PTB and USNO using GLONASS and GPS time transfer links gives stability estimations which are close to that based on H-maser intercomparisons.
Russian national time scale long-term stability
NASA Astrophysics Data System (ADS)
Alshina, A. P.; Gaigerov, B. A.; Koshelyaevsky, N. B.; Pushkin, S. B.
1994-05-01
The Institute of Metrology for Time and Space NPO 'VNIIFTRI' generates the National Time Scale (NTS) of Russia -- one of the most stable time scales in the world. Its striking feature is that it is based on a free ensemble of H-masers only. During last two years the estimations of NTS longterm stability based only on H-maser intercomparison data gives a flicker floor of about (2 to 3) x 10(exp -15) for averaging times from 1 day to 1 month. Perhaps the most significant feature for a time laboratory is an extremely low possible frequency drift -- it is too difficult to estimate it reliably. The other estimations, free from possible inside the ensemble correlation phenomena, are available based on the time comparison of NTS relative to the stable enough time scale of outer laboratories. The data on NTS comparison relative to the time scale of secondary time and frequency standards at Golitzino and Irkutsk in Russia and relative to NIST, PTB and USNO using GLONASS and GPS time transfer links gives stability estimations which are close to that based on H-maser intercomparisons.
Fast Structural Relaxations In Hemoglobin And Myoglobin: An Analysis Of Time Resolved Raman Studies
NASA Astrophysics Data System (ADS)
Friedman, Joel M.; Ondrias, Mark R.
1989-07-01
There was a time not too long ago when proteins were viewed as static structures. It is now apparent that proteins exhibit a wide variety of local and global dynamics; nevertheless, an understanding of both how proteins move and how these motions influence protein reactivity remains a fundamental, unanswered and illusive problem within biophysics. Most of the recent detailed studies to date have been theoretical endeavors utilizing molecular dynamics simulations. Unfortunately comparable experiments that are structurally specific or detailed are lacking. In this manuscript, several picosecond time resolved resonance Raman studies of hemoglobin and myoglobin are reviewed, explored and compared with the purpose of extracting dynamical information on these well characterized "model" protein systems.
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.
RELAXATION PROCESSES IN SOLAR WIND TURBULENCE
Servidio, S.; Carbone, V. [Dipartimento di Fisica, Università della Calabria, I-87030 Rende (CS) (Italy); Gurgiolo, C. [Bitterroot Basic Research, Hamilton, MT 59840 (United States); Goldstein, M. L., E-mail: sergio.servidio@fis.unical.it [Heliospheric Physics Laboratory, Code 672, NASA Goddard Space Flight Center, Greenbelt, MD 20771 (United States)
2014-07-10
Based on global conservation principles, magnetohydrodynamic (MHD) relaxation theory predicts the existence of several equilibria, such as the Taylor state or global dynamic alignment. These states are generally viewed as very long-time and large-scale equilibria, which emerge only after the termination of the turbulent cascade. As suggested by hydrodynamics and by recent MHD numerical simulations, relaxation processes can occur during the turbulent cascade that will manifest themselves as local patches of equilibrium-like configurations. Using multi-spacecraft analysis techniques in conjunction with Cluster data, we compute the current density and flow vorticity and for the first time demonstrate that these localized relaxation events are observed in the solar wind. Such events have important consequences for the statistics of plasma turbulence.
Time scale construction from multiple sources of information (Invited)
NASA Astrophysics Data System (ADS)
Malinverno, A.
2013-12-01
Geological age estimates are provided by diverse chronometers, such as radiometric measurements, astrochronology, and the spacing of magnetic anomalies recorded on mid-ocean ridges by seafloor spreading. These age estimates are affected by errors that can be systematic (e.g., biased radiometric dates due to imperfect assumptions) or random (e.g., imprecise recording of astronomical cycles in sedimentary records). Whereas systematic errors can be reduced by improvements in technique and calibration, uncertainties due to random errors will always be present and need to be dealt with. A Bayesian framework can be used to construct an integrated time scale that is based on several uncertain sources of information. In this framework, each piece of data and the final time scale have an associated probability distribution that describes their uncertainty. The key calculation is to determine the uncertainty in the time scale from the uncertain data that constrain it. In practice, this calculation can be performed by Monte Carlo sampling. In Markov chain Monte Carlo algorithms, the time scale is iteratively perturbed and the perturbed time scale is accepted or rejected depending on how closely it fits the data. The final result is a large ensemble of possible time scales that are consistent with all the uncertain data; while the average of this ensemble defines a 'best' time scale, the ensemble variability quantifies the time scale uncertainty. An example of this approach is the M-sequence (Late Jurassic-Early Cretaceous, ~160-120 Ma) MHTC12 geomagnetic polarity time scale (GPTS) of Malinverno et al. (2012, J. Geophys. Res., B06104, doi:10.1029/2012JB009260). Previous GPTSs were constructed by interpolating between dated marine magnetic anomalies while assuming constant or smoothly varying spreading rates. These GPTSs were typically based on magnetic lineations from one or a few selected spreading centers, and an undesirable result is that they imply larger spreading rate fluctuations on other ridges. On the other hand, the Monte Carlo algorithm used in MHTC12 makes it easy to sample GPTSs that result in small spreading rate variations over multiple spreading centers (in the Western Pacific, North Atlantic, and Indian Ocean NW of Australia). MHTC12 also accounts for the duration of five polarity chrons estimated from floating astrochronologies (CM0r through CM3r). A Bayesian framework and Monte Carlo sampling offer a useful strategy to construct time scales that incorporate different types of chronological information, have a quantified uncertainty, and can be easily updated with additional data that may become available in the future.
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.
NASA Astrophysics Data System (ADS)
Livingstone, Ruth A.; Thompson, James O. F.; Iljina, Marija; Donaldson, Ross J.; Sussman, Benjamin J.; Paterson, Martin J.; Townsend, Dave
2012-11-01
Time-resolved photoelectron imaging was used to investigate the dynamical evolution of the initially prepared S1 (??*) excited state of phenol (hydroxybenzene), catechol (1,2-dihydroxybenzene), resorcinol (1,3-dihydroxybenzene), and hydroquinone (1,4-dihydroxybenzene) following excitation at 267 nm. Our analysis was supported by ab initio calculations at the coupled-cluster and CASSCF levels of theory. In all cases, we observe rapid (<1 ps) intramolecular vibrational redistribution on the S1 potential surface. In catechol, the overall S1 state lifetime was observed to be 12.1 ps, which is 1-2 orders of magnitude shorter than in the other three molecules studied. This may be attributed to differences in the H atom tunnelling rate under the barrier formed by a conical intersection between the S1 state and the close lying S2 (??*) state, which is dissociative along the O-H stretching coordinate. Further evidence of this S1/S2 interaction is also seen in the time-dependent anisotropy of the photoelectron angular distributions we have observed. Our data analysis was assisted by a matrix inversion method for processing photoelectron images that is significantly faster than most other previously reported approaches and is extremely quick and easy to implement.
Moffat, Keith
Molecular Movie from Time-Resolved Laue X-ray Diffraction Vukica Srajer,*,,§ Zhong Ren,,§,4 Tsu-Yi Teng://pubs.acs.org/biochemistry. ABSTRACT: A time-resolved Laue X-ray diffraction technique has been used to explore protein relaxation are probed by 150 ps or 1 µs X-ray pulses at 14 laser/X-ray delay times, ranging from 1 ns to 1.9 ms. Very
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.
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.
Han, Lu; Liang, WanZhen; Zhao, Yi; Zhong, Xinxin
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.
Fayer, Michael D.
effect experiments, which measures the time derivative of the polarizability polarizability experimental and theoretical studies be- cause of the intrinsic interest in molecular systems that self, the macroscopic director.1 This molecular ordering strongly affects the orientational relax- ation behavior
Multiple time scales in the microwave ionization of Rydberg atoms
Buchleitner, A.; Delande, D.; Zakrzewski, J.; Mantegna, R.N.; Arndt, M.; Walther, H.
1995-11-20
We investigate the time dependence of the ionization probability of Rydberg atoms driven by microwave fields, both numerically and experimentally. Our exact quantum results provide evidence for an algebraic decay law on suitably chosen time scales, a phenomenon that is considered to be the signature of nonhyperbolic scattering in unbounded classically chaotic motion. {copyright} {ital 1995} {ital The} {ital American} {ital Physical} {ital Society}.
Anomalous Multiphoton Photoelectric Effect in Ultrashort Time Scales
J. Kupersztych; M. Raynaud
2005-01-01
In a multiphoton photoelectric process, an electron needs to absorb a given number of photons to escape the surface of a metal. It is shown for the first time that this number is not a constant depending only on the characteristics of the metal and light, but varies with the interaction duration in ultrashort time scales. The phenomenon occurs when
Return times for stochastic processes with power-law scaling.
Olla, Piero
2007-07-01
An analytical study of the return time distribution of extreme events for stochastic processes with power-law correlation has been carried out. The calculation is based on an epsilon expansion in the correlation exponent: C(t)=/t/-1+epsilon. The fixed point of the theory is associated with stretched exponential scaling of the distribution; analytical expressions have been provided in the preasymptotic regime. Also, the permanence time distribution appears to be characterized by stretched exponential scaling. The conditions for application of the theory to non-Gaussian processes have been analyzed and the relations with the issue of return times in the case of multifractal measures have been discussed. PMID:17677425
ERIC Educational Resources Information Center
Ramey, Kyle
2004-01-01
Relaxed intensity refers to a professional philosophy, demeanor, and way of life. It is the key to being an effective educational leader. To be successful one must be relaxed, which means managing stress efficiently, having fun, and enjoying work. Intensity allows one to get the job done and accomplish certain tasks or goals. Educational leaders…
Thermodynamics constrains allometric scaling of optimal development time in insects.
Dillon, Michael E; Frazier, Melanie R
2013-01-01
Development time is a critical life-history trait that has profound effects on organism fitness and on population growth rates. For ectotherms, development time is strongly influenced by temperature and is predicted to scale with body mass to the quarter power based on 1) the ontogenetic growth model of the metabolic theory of ecology which describes a bioenergetic balance between tissue maintenance and growth given the scaling relationship between metabolism and body size, and 2) numerous studies, primarily of vertebrate endotherms, that largely support this prediction. However, few studies have investigated the allometry of development time among invertebrates, including insects. Abundant data on development of diverse insects provides an ideal opportunity to better understand the scaling of development time in this ecologically and economically important group. Insects develop more quickly at warmer temperatures until reaching a minimum development time at some optimal temperature, after which development slows. We evaluated the allometry of insect development time by compiling estimates of minimum development time and optimal developmental temperature for 361 insect species from 16 orders with body mass varying over nearly 6 orders of magnitude. Allometric scaling exponents varied with the statistical approach: standardized major axis regression supported the predicted quarter-power scaling relationship, but ordinary and phylogenetic generalized least squares did not. Regardless of the statistical approach, body size alone explained less than 28% of the variation in development time. Models that also included optimal temperature explained over 50% of the variation in development time. Warm-adapted insects developed more quickly, regardless of body size, supporting the "hotter is better" hypothesis that posits that ectotherms have a limited ability to evolutionarily compensate for the depressing effects of low temperatures on rates of biological processes. The remaining unexplained variation in development time likely reflects additional ecological and evolutionary differences among insect species. PMID:24391935
Thermodynamics Constrains Allometric Scaling of Optimal Development Time in Insects
Dillon, Michael E.; Frazier, Melanie R.
2013-01-01
Development time is a critical life-history trait that has profound effects on organism fitness and on population growth rates. For ectotherms, development time is strongly influenced by temperature and is predicted to scale with body mass to the quarter power based on 1) the ontogenetic growth model of the metabolic theory of ecology which describes a bioenergetic balance between tissue maintenance and growth given the scaling relationship between metabolism and body size, and 2) numerous studies, primarily of vertebrate endotherms, that largely support this prediction. However, few studies have investigated the allometry of development time among invertebrates, including insects. Abundant data on development of diverse insects provides an ideal opportunity to better understand the scaling of development time in this ecologically and economically important group. Insects develop more quickly at warmer temperatures until reaching a minimum development time at some optimal temperature, after which development slows. We evaluated the allometry of insect development time by compiling estimates of minimum development time and optimal developmental temperature for 361 insect species from 16 orders with body mass varying over nearly 6 orders of magnitude. Allometric scaling exponents varied with the statistical approach: standardized major axis regression supported the predicted quarter-power scaling relationship, but ordinary and phylogenetic generalized least squares did not. Regardless of the statistical approach, body size alone explained less than 28% of the variation in development time. Models that also included optimal temperature explained over 50% of the variation in development time. Warm-adapted insects developed more quickly, regardless of body size, supporting the “hotter is better” hypothesis that posits that ectotherms have a limited ability to evolutionarily compensate for the depressing effects of low temperatures on rates of biological processes. The remaining unexplained variation in development time likely reflects additional ecological and evolutionary differences among insect species. PMID:24391935
Common scaling patterns in intertrade times of U. S. stocks
NASA Astrophysics Data System (ADS)
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.
Deviations from uniform power law scaling in nonstationary time series
NASA Technical Reports Server (NTRS)
Viswanathan, G. M.; Peng, C. K.; Stanley, H. E.; Goldberger, A. L.
1997-01-01
A classic problem in physics is the analysis of highly nonstationary time series that typically exhibit long-range correlations. Here we test the hypothesis that the scaling properties of the dynamics of healthy physiological systems are more stable than those of pathological systems by studying beat-to-beat fluctuations in the human heart rate. We develop techniques based on the Fano factor and Allan factor functions, as well as on detrended fluctuation analysis, for quantifying deviations from uniform power-law scaling in nonstationary time series. By analyzing extremely long data sets of up to N = 10(5) beats for 11 healthy subjects, we find that the fluctuations in the heart rate scale approximately uniformly over several temporal orders of magnitude. By contrast, we find that in data sets of comparable length for 14 subjects with heart disease, the fluctuations grow erratically, indicating a loss of scaling stability.
Straub, John E.
-specific vibrational energy relaxation in imidazole ligated ferrous iron porphine were studied using a non strongly through its overtone with the 7 porphine in-plane vibration. This suggests a possible mechanism
S. Plumari; A. Puglisi; F. Scardina; V. Greco
2012-08-02
The shear viscosity $\\eta$ has been calculated by using the Green-Kubo relation in the framework of a partonic transport approach solved at cascade level. We compare the numerical results for $\\eta$ obtained from the Green-Kubo correlator with the analytical formulas in both the Relaxation Time Approximation (RTA) and the Chapman-Enskog approximation (CE). We investigate and emphasize the differences between the isotropic and anisotropic cross sections and between the massless and massive particles. We show that in the range of temperature explored in a Heavy Ion collision and for pQCD-like cross section the RTA significantly underestimates the viscosity by about a factor of 2-3, while a good agreement is found between the CE approximation and Gree-Kubo relation already at first order of approximation. The agreement with the CE approximation supplies an analytical formula that allows to develop kinetic transport theory at fixed shear viscosity to entropy density ratio, $\\eta/s$. This open the possibility to explore dissipative non-equilibrium evolution of the distribution functions vs T-dependent $\\eta/s$ and particle momenta in the dynamics of the Quark-Gluon Plasma created in ultra-relativistic heavy-ion collisions.
Inferring synaptic structure in presence of neural interaction time scales.
Capone, Cristiano; Filosa, Carla; Gigante, Guido; Ricci-Tersenghi, Federico; Del Giudice, Paolo
2015-01-01
Biological networks display a variety of activity patterns reflecting a web of interactions that is complex both in space and time. Yet inference methods have mainly focused on reconstructing, from the network's activity, the spatial structure, by assuming equilibrium conditions or, more recently, a probabilistic dynamics with a single arbitrary time-step. Here we show that, under this latter assumption, the inference procedure fails to reconstruct the synaptic matrix of a network of integrate-and-fire neurons when the chosen time scale of interaction does not closely match the synaptic delay or when no single time scale for the interaction can be identified; such failure, moreover, exposes a distinctive bias of the inference method that can lead to infer as inhibitory the excitatory synapses with interaction time scales longer than the model's time-step. We therefore introduce a new two-step method, that first infers through cross-correlation profiles the delay-structure of the network and then reconstructs the synaptic matrix, and successfully test it on networks with different topologies and in different activity regimes. Although step one is able to accurately recover the delay-structure of the network, thus getting rid of any a priori guess about the time scales of the interaction, the inference method introduces nonetheless an arbitrary time scale, the time-bin dt used to binarize the spike trains. We therefore analytically and numerically study how the choice of dt affects the inference in our network model, finding that the relationship between the inferred couplings and the real synaptic efficacies, albeit being quadratic in both cases, depends critically on dt for the excitatory synapses only, whilst being basically independent of it for the inhibitory ones. PMID:25807389
Inferring Synaptic Structure in Presence of Neural Interaction Time Scales
Capone, Cristiano; Filosa, Carla; Gigante, Guido; Ricci-Tersenghi, Federico; Del Giudice, Paolo
2015-01-01
Biological networks display a variety of activity patterns reflecting a web of interactions that is complex both in space and time. Yet inference methods have mainly focused on reconstructing, from the network’s activity, the spatial structure, by assuming equilibrium conditions or, more recently, a probabilistic dynamics with a single arbitrary time-step. Here we show that, under this latter assumption, the inference procedure fails to reconstruct the synaptic matrix of a network of integrate-and-fire neurons when the chosen time scale of interaction does not closely match the synaptic delay or when no single time scale for the interaction can be identified; such failure, moreover, exposes a distinctive bias of the inference method that can lead to infer as inhibitory the excitatory synapses with interaction time scales longer than the model’s time-step. We therefore introduce a new two-step method, that first infers through cross-correlation profiles the delay-structure of the network and then reconstructs the synaptic matrix, and successfully test it on networks with different topologies and in different activity regimes. Although step one is able to accurately recover the delay-structure of the network, thus getting rid of any a priori guess about the time scales of the interaction, the inference method introduces nonetheless an arbitrary time scale, the time-bin dt used to binarize the spike trains. We therefore analytically and numerically study how the choice of dt affects the inference in our network model, finding that the relationship between the inferred couplings and the real synaptic efficacies, albeit being quadratic in both cases, depends critically on dt for the excitatory synapses only, whilst being basically independent of it for the inhibitory ones. PMID:25807389
ERIC Educational Resources Information Center
Hites, Lacey S.; Lundervold, Duane A.
2013-01-01
Forty-four individuals, 18-47 (MN 21.8, SD 5.63) years of age, took part in a study examining the magnitude and direction of the relationship between self-report and direct observation measures of relaxation and mindfulness. The Behavioral Relaxation Scale (BRS), a valid direct observation measure of relaxation, was used to assess relaxed behavior…
Physics in space-time with scale-dependent metrics
NASA Astrophysics Data System (ADS)
Balankin, Alexander S.
2013-10-01
We construct three-dimensional space R?3 with the scale-dependent metric and the corresponding Minkowski space-time M?,?4 with the scale-dependent fractal (DH) and spectral (DS) dimensions. The local derivatives based on scale-dependent metrics are defined and differential vector calculus in R?3 is developed. We state that M?,?4 provides a unified phenomenological framework for dimensional flow observed in quite different models of quantum gravity. Nevertheless, the main attention is focused on the special case of flat space-time M1/3,14 with the scale-dependent Cantor-dust-like distribution of admissible states, such that DH increases from DH=2 on the scale ??0 to DH=4 in the infrared limit ??0, where ?0 is the characteristic length (e.g. the Planck length, or characteristic size of multi-fractal features in heterogeneous medium), whereas DS?4 in all scales. Possible applications of approach based on the scale-dependent metric to systems of different nature are briefly discussed.
A scale-invariant internal representation of time.
Shankar, Karthik H; Howard, Marc W
2012-01-01
We propose a principled way to construct an internal representation of the temporal stimulus history leading up to the present moment. A set of leaky integrators performs a Laplace transform on the stimulus function, and a linear operator approximates the inversion of the Laplace transform. The result is a representation of stimulus history that retains information about the temporal sequence of stimuli. This procedure naturally represents more recent stimuli more accurately than less recent stimuli; the decrement in accuracy is precisely scale invariant. This procedure also yields time cells that fire at specific latencies following the stimulus with a scale-invariant temporal spread. Combined with a simple associative memory, this representation gives rise to a moment-to-moment prediction that is also scale invariant in time. We propose that this scale-invariant representation of temporal stimulus history could serve as an underlying representation accessible to higher-level behavioral and cognitive mechanisms. In order to illustrate the potential utility of this scale-invariant representation in a variety of fields, we sketch applications using minimal performance functions to problems in classical conditioning, interval timing, scale-invariant learning in autoshaping, and the persistence of the recency effect in episodic memory across timescales. PMID:21919782
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.
Scaling Properties in Time-Varying Networks with Memory
Kim, Hyewon; Jeong, Hawoong
2015-01-01
The formation of network structure is influenced by individual node's activity and its memory. Usually activity can be interpreted as the inherent property of node and memory can be represented by the interaction strength among nodes. In our study, we define the activity through the appearance pattern in the time-aggregated network representation, and quantify the memory through the contact pattern of empirical temporal networks. To address the role of activity and memory in epidemics on temporal networks, we propose temporal-pattern coarsening of activity-driven growing networks with memory. In particular, we focus on the relation between coarsening time scale and spreading dynamics in the context of dynamic scaling and finite-size scaling. Finally, we discuss the universality issue of spreading dynamics on time-varying networks for various memory causality aspects.
Scaling law for crystal nucleation time in glasses
Mokshin, Anatolii V
2015-01-01
Due to high viscosity, glassy systems evolve slowly to the ordered state. Results of molecular dynamics simulation reveal that the structural ordering in glasses becomes observable over "experimental" (finite) time-scale for the range of phase diagram with high values of pressure. We show that the structural ordering in glasses at such conditions is initiated through the nucleation mechanism, and the mechanism spreads to the states at extremely deep levels of supercooling. We find that the scaled values of the nucleation time, $\\tau_1$ (average waiting time of the first nucleus with the critical size), in glassy systems as a function of the reduced temperature, $\\widetilde{T}$, are collapsed onto a single line reproducible by the power-law dependence. This scaling is supported by the simulation results for the model glassy systems for a wide range of temperatures as well as by the experimental data for the stoichiometric glasses at the temperatures near the glass transition.
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.
Evaluation of Scaling Invariance Embedded in Short Time Series
Pan, Xue; Hou, Lei; Stephen, Mutua; Yang, Huijie; Zhu, Chenping
2014-01-01
Scaling invariance of time series has been making great contributions in diverse research fields. But how to evaluate scaling exponent from a real-world series is still an open problem. Finite length of time series may induce unacceptable fluctuation and bias to statistical quantities and consequent invalidation of currently used standard methods. In this paper a new concept called correlation-dependent balanced estimation of diffusion entropy is developed to evaluate scale-invariance in very short time series with length . Calculations with specified Hurst exponent values of show that by using the standard central moving average de-trending procedure this method can evaluate the scaling exponents for short time series with ignorable bias () and sharp confidential interval (standard deviation ). Considering the stride series from ten volunteers along an approximate oval path of a specified length, we observe that though the averages and deviations of scaling exponents are close, their evolutionary behaviors display rich patterns. It has potential use in analyzing physiological signals, detecting early warning signals, and so on. As an emphasis, the our core contribution is that by means of the proposed method one can estimate precisely shannon entropy from limited records. PMID:25549356
NASA Astrophysics Data System (ADS)
Yoder, Jacob
The Neutron Electric Dipole Moment (nEDM) experiment that will take place at the Spallation Neutron Source (SNS) in Oak Ridge, Tennessee will measure the electric dipole moment (EDM) of the neutron with a precision of order 10-28 e-cm, utilizing spin-polarized 3He in bulk liquid 4He to detect neutron precession in a 10 mG magnetic field and 50 kV/cm electric field. Since depolarized 3He will produce a background, relaxation of the polarized 3He, characterized by the probability of depolarization per bounce, Pd, was measured for materials that will be in contact with polarized 3He. Depolarization probabilities were determined from measurements of the longitudinal relaxation time of polarized 3He in bulk liquid 4He inside an acrylic cell coated with the wavelength shifter deuterated tetraphenyl butadiene (d-TPB), which will be used to coat the nEDM measurement cell. Relaxation measurements were also performed while rods, made from plumbing material Torlon and valve bellows material BeCu, were present in the cell. The BeCu was coated with Pyralin resin prior to relaxation measurements, while relaxation measurements were performed both before and after the Torlon rod was coated with Pyralin resin. The depolarization probabilities were found to be Pd-TPBd <1.32x10-7 PBareTorlon d=1.01+/-0.08 x10-6 PCoatedTorlon d=2.5+/-0.1 x10-7 PCoatedBeCu d=7.9+/-0.3 x10-7 The relaxation rates extrapolated from the observed values of Pd for d-TPB, coated Torlon, and coated BeCu in the nEDM apparatus were found to be consistent with design goals.
Hyeon-Deuk, Kim; Madrid, Angeline B; Prezhdo, Oleg V
2009-12-01
State-of-the-art time domain density functional theory and non-adiabatic (NA) molecular dynamic simulations are used to study phonon-induced relaxation of photoexcited electrons and holes in Ge and Si quantum dots (QDs). The relaxation competes with productive processes and causes energy and voltage losses in QD solar cells. The ab initio calculations show that quantum confinement makes the electron and hole density of states (DOS) more symmetric in Si and Ge QDs compared to bulk. Surprisingly, in spite of the symmetric DOS, the electron and hole relaxations are quite asymmetric: the electrons decay faster than the holes. The asymmetry arises due to stronger NA coupling in the conduction band (CB) than in the valence band (VB). The stronger NA coupling of the electrons compared to the holes is rationalized by the larger contribution of the high-frequency Ge-H and Si-H surface passivating bonds to the CB relative to the VB. Linear relationships between the electron and hole relaxation rates and the CB and VB DOS are found in agreement with Fermi's golden rule. The faster relaxation of the electrons compared to the holes in the Ge and Si QDs is unexpected and is in contrast with the corresponding dynamics in the majority of binary QDs, such as CdSe. It suggests that Auger processes will transfer energy from holes to electrons rather than in the opposite direction as in CdSe, and that a larger fraction of the photoexcitation energy will be transferred to phonons coupled with electrons rather than holes. The difference in the phonon-induced electron and hole decay rates is larger in Ge than Si, indicating that the Auger processes should be particularly important in Ge QDs. The simulations provide direct evidence that the high-frequency ligand modes on the QD surface play a pivotal role in the electron-phonon relaxation dynamics of semiconductor QDs. PMID:19904435
Time scales for molecule formation by ion-molecule reactions
NASA Technical Reports Server (NTRS)
Langer, W. D.; Glassgold, A. E.
1976-01-01
Analytical solutions are obtained for nonlinear differential equations governing the time-dependence of molecular abundances in interstellar clouds. Three gas-phase reaction schemes are considered separately for the regions where each dominates. The particular case of CO, and closely related members of the Oh and CH families of molecules, is studied for given values of temperature, density, and the radiation field. Nonlinear effects and couplings with particular ions are found to be important. The time scales for CO formation range from 100,000 to a few million years, depending on the chemistry and regime. The time required for essentially complete conversion of C(+) to CO in the region where the H3(+) chemistry dominates is several million years. Because this time is longer than or comparable to dynamical time scales for dense interstellar clouds, steady-state abundances may not be observed in such clouds.
Kruk, D.; Korpa?a, A.; Institute of Physics, Jagiellonian University, Reymonta 4, 30-059 Kraków ; Taheri, S. Mehdizadeh; Förster, S.; Koz?owski, A.; Rössler, E. A.
2014-05-07
Magnetic nanoparticles that induce nuclear relaxation are the most promising materials to enhance the sensitivity in Magnetic Resonance Imaging. In order to provide a comprehensive understanding of the magnetic field dependence of the relaxation enhancement in solutions, Nuclear Magnetic Resonance {sup 1}H spin-lattice relaxation for decalin and toluene solutions of various Fe{sub 2}O{sub 3} nanoparticles was investigated. The relaxation experiments were performed in a frequency range of 10 kHz–20 MHz by applying Field Cycling method, and in the temperature range of 257–298 K, using nanoparticles differing in size and shape: spherical – 5 nm diameter, cubic – 6.5 nm diameter, and cubic – 9 nm diameter. The relaxation dispersion data were interpreted in terms of a theory of nuclear relaxation induced by magnetic crystals in solution. The approach was tested with respect to its applicability depending on the magnetic characteristics of the nanocrystals and the time-scale of translational diffusion of the solvent. The role of Curie relaxation and the contributions to the overall {sup 1}H spin-lattice relaxation associated with the electronic spin-lattice and spin-spin relaxation was thoroughly discussed. It was demonstrated that the approach leads to consistent results providing information on the magnetic (electronic) properties of the nanocrystals, i.e., effective electron spin and relaxation times. In addition, features of the {sup 1}H spin-lattice relaxation resulting from the electronic properties of the crystals and the solvent diffusion were explained.
Detecting separate time scales in genetic expression data
Orlando, David A.; Brady, Siobhan M.; Fink, Thomas M. A.; Benfey, Philip N.; Ahnert, Sebastian E.
2010-06-16
processes acting at multiple time scales in many organisms is now possible. Background Biological processes in living organisms occur on a vast range of time scales, from 10-9s (nanoseconds) to 109s (decades), many of them taking place simultaneously... of the Vascular Bundle in Arabidopsis Root Encompasses the Pericycle and Is Reflected in Distich Lateral Root Initiation. Plant Physiology 2008, 146:140-148. 15. Qian J, Dolled-Filhart M, Lin J, Yu H, Gerstein M: Beyond synexpression relationships: Local...
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.
Time scale analysis of a digital flight control system
NASA Technical Reports Server (NTRS)
Naidu, D. S.; Price, D. B.
1986-01-01
In this paper, consideration is given to the fifth order discrete model of an aircraft (longitudinal) control system which possesses three slow (velocity, pitch angle and altitude) and two fast (angle of attack and pitch angular velocity) modes and exhibits a two-time scale property. Using the recent results of the time scale analysis of discrete control systems, the high-order discrete model is decoupled into low-order slow and fast subsystems. The results of the decoupled system are found to be in excellent agreement with those of the original system.
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).
Discrete scale vectors and decomposition of time-frequency kernels
NASA Astrophysics Data System (ADS)
Aviyente, Selin; Williams, William J.
2000-11-01
Previous work has shown that time-frequency distributions (TFDs) belonging to Cohen's class can be represented as a sum of weighted spectrograms. This representation offers the means of reducing the computational complexity of TFDs. The windows in the spectrogram representation may either be the eigenfunctions obtained from an eigen decomposition of the kernel or any complete set of orthonormal basis functions. The efficiency of the computation can further be increased by using a set of scaled and shifted functions like wavelets. In this paper, the concept of scaling is considered in discrete-time domain. The scale operator in the frequency domain is formulated and the vectors which correspond to the solutions of this eigenvalue problem in discrete-time are derived. These new eigenvectors are very similar in structure to the eigenvectors obtained from eigensystem decomposition of reduced interference distribution (RID) kernels. The relationship between these two sets of window functions is illustrated and a new efficient way of decomposing time-frequency kernels is introduced. The results are compared to the previous decomposition methods. Finally, some possible applications of these discrete scale functions in obtaining new time-frequency distributions are discussed.
NASA Technical Reports Server (NTRS)
Stephenson, Jack D.
1960-01-01
This report describes a technique which combines theory and experiments for determining relaxation times in gases. The technique is based on the measurement of shapes of the bow shock waves of low-fineness-ratio cones fired from high-velocity guns. The theory presented in the report provides a means by which shadowgraph data showing the bow waves can be analyzed so as to furnish effective relaxation times. Relaxation times in air were obtained by this technique and the results have been compared with values estimated from shock tube measurements in pure oxygen and nitrogen. The tests were made at velocities ranging from 4600 to 12,000 feet per second corresponding to equilibrium temperatures from 35900 R (19900 K) to 6200 R (34400 K), under which conditions, at all but the highest temperatures, the effective relaxation times were determined primarily by the relaxation time for oxygen and nitrogen vibrations.
Appropriate time scales for nonlinear analyses of deterministic jump systems
NASA Astrophysics Data System (ADS)
Suzuki, Tomoya
2011-06-01
In the real world, there are many phenomena that are derived from deterministic systems but which fluctuate with nonuniform time intervals. This paper discusses the appropriate time scales that can be applied to such systems to analyze their properties. The financial markets are an example of such systems wherein price movements fluctuate with nonuniform time intervals. However, it is common to apply uniform time scales such as 1-min data and 1-h data to study price movements. This paper examines the validity of such time scales by using surrogate data tests to ascertain whether the deterministic properties of the original system can be identified from uniform sampled data. The results show that uniform time samplings are often inappropriate for nonlinear analyses. However, for other systems such as neural spikes and Internet traffic packets, which produce similar outputs, uniform time samplings are quite effective in extracting the system properties. Nevertheless, uniform samplings often generate overlapping data, which can cause false rejections of surrogate data tests.
Time scale algorithm: Definition of ensemble time and possible uses of the Kalman filter
NASA Technical Reports Server (NTRS)
Tavella, Patrizia; Thomas, Claudine
1990-01-01
The comparative study of two time scale algorithms, devised to satisfy different but related requirements, is presented. They are ALGOS(BIPM), producing the international reference TAI at the Bureau International des Poids et Mesures, and AT1(NIST), generating the real-time time scale AT1 at the National Institute of Standards and Technology. In each case, the time scale is a weighted average of clock readings, but the weight determination and the frequency prediction are different because they are adapted to different purposes. The possibility of using a mathematical tool, such as the Kalman filter, together with the definition of the time scale as a weighted average, is also analyzed. Results obtained by simulation are presented.
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.
Scaling Invariance in a Time-Dependent Elliptical Billiard
Diego F. M. Oliveira; Marko Robnik
2011-03-31
We study some dynamical properties of a classical time-dependent elliptical billiard. We consider periodically moving boundary and collisions between the particle and the boundary are assumed to be elastic. Our results confirm that although the static elliptical billiard is an integrable system, after to introduce time-dependent perturbation on the boundary the unlimited energy growth is observed. The behaviour of the average velocity is described using scaling arguments.
NASA Astrophysics Data System (ADS)
Miller, David W.; Adelman, Steven A.
2002-08-01
The theoretical treatment in Paper I [D. W. Miller and S. A. Adelman, J. Chem. Phys. 117, 2672, (2002), preceding paper] of the vibrational energy relaxation (VER) of low-frequency, large mass dihalogen solutes is extended to the VER of the high-frequency, small mass molecular hydrogen solutes H2 and D2 in a Lennard-Jones argon-like solvent. As in Paper I, values of the relaxation times T1 predicted by the theory are tested against molecular dynamics (MD) results and are found to be of semiquantitative accuracy. To start, it is noted that standard Lennard-Jones site-site potentials derived from macroscopic data can be very inaccurate in the steep repulsive slope region crucial for T1. Thus, the H-Ar Lennard-Jones diameter sigmaUV is not taken from literature values but rather is chosen as sigmaUV=1.39 A, the value needed to make the theory reproduce the experimental H2/Ar gas phase VER rate constant. Next, by MD simulation it is shown that the vibrational coordinate fluctuating force autocorrelation function
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.
BGP Routing: A study at Large Time Scale Georgos Siganos
Faloutsos, Michalis
BGP Routing: A study at Large Time Scale Georgos Siganos U.C. Riverside Dept. of Comp. Science siganos@cs.ucr.edu Michalis Faloutsos U.C. Riverside Dept. of Comp. Science michalis@cs.ucr.edu Abstract-prefix). In a high level, we observe that BGP routing is characterized by a) fairly robust routing with usually few
Cognitive Components of Speech at Different Time Scales
component analysis (COCA) in [7]: the process of unsupervised grouping of data such that the resulting group structure is well-aligned with that resulting from human cog- nitive activity. The basic scheme of COCA (COCA) of speech. MFCCs are extracted at a basic time scale (20ms). Features are integrated in windows
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.
Food Expenditure, Food Preparation Time and Household Economies of Scale
Victoria Vernon
2004-01-01
This paper is concerned with the effect of household size on the allocation of household money and time to food consumption. A broad literature has examined household economies of scale. Since food is a private good, it might be expected that larger households, which could economize on shared goods such as housing, would spend more per equivalent household member on
LINK BETWEEN COSMIC RAYS AND CLOUDS ON DIFFERENT TIME SCALES
Usoskin, Ilya G.
LINK BETWEEN COSMIC RAYS AND CLOUDS ON DIFFERENT TIME SCALES ILYA G. USOSKIN and GENNADY A is related to a link between the cosmic ray flux and cloudiness. Here we review evidences relating of these facts alone is conclusive, in the aggregate they strongly support the link between cos- mic rays
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…
Research paper Refining the Quaternary Geomagnetic Instability Time Scale (GITS)
Demouchy, Sylvie
Research paper Refining the Quaternary Geomagnetic Instability Time Scale (GITS): Lava flow Available online 11 January 2013 Keywords: Geomagnetic field lava excursion geochronology a b s t r a c Geomagnetic excursions, during which the intensity of Earth's magnetic field wanes as its direction shifts
STURMLIOUVILLE OPERATORS ON TIME SCALES JONATHAN ECKHARDT AND GERALD TESCHL
Teschl, Gerald
[12] that the Hilger derivative, the natural derivative on a time scale, can in fact be viewed then this approach has had an enormous impact and developed into a new field of mathematics (see e.g. [5], [6 Equ. Appl. 18, 1875Â1887 (2012). Research supported by the Austrian Science Fund (FWF) under Grant No
Behavioral Programming, Decentralized Control, and Multiple Time Scales
Weiss, Gera
Behavioral Programming, Decentralized Control, and Multiple Time Scales David Harel, Assaf Marron University of the Negev geraw@cs.bgu.ac.il Abstract Behavioral programming is a recently proposed approach, such as behavioral decomposition, synchronized execution of independent behaviors, and event block- ing, can help
Multiple time scale numerical methods for the inverted pendulum problem
Tsai, Yen-Hsi Richard
(t/)f(x). Figure 1. The inverted pendulum. A mass is connected to an arm of length l which makes an angleMultiple 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
MULTIPLE TIME SCALE NUMERICAL METHODS FOR THE INVERTED PENDULUM PROBLEM
Ferguson, Thomas S.
.1. The inverted pendulum. A mass is connected to an arm of length l which makes an angle with the vertical axesMULTIPLE 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
Kinetic equations for hopping transport and spin relaxation in a random magnetic field
NASA Astrophysics Data System (ADS)
Shumilin, A. V.; Kabanov, V. V.
2015-07-01
We derive the kinetic equations for a hopping transport that take into account an electron spin and the possibility of double occupation. In the Ohmic regime, the equations are reduced to the generalized Miller-Abrahams resistor network. We apply these equations to the problem of the magnetic moment relaxation due to the interaction with the random hyperfine fields. It is shown that in a wide range of parameters the relaxation rate is governed by the hops with the similar rates as spin precession frequency. It is demonstrated that at the large time scale spin relaxation is nonexponential. We argue that the nonexponential relaxation of the magnetic moment is related to the spin of electrons in the slow-relaxing traps. Interestingly, the traps can significantly influence the spin relaxation in the infinite conducting cluster at large times.
Kawamura, Izuru; Ohmine, Masato; Tanabe, Junko; Tuzi, Satoru; Saitô, Hazime; Naito, Akira
2007-12-01
Local dynamics of interhelical loops in bacteriorhodopsin (bR), the extracellular BC, DE and FG, and cytoplasmic AB and CD loops, and helix B were determined on the basis of a variety of relaxation parameters for the resolved 13C and 15N signals of [1-13C]Tyr-, [15N]Pro- and [1-13C]Val-, [15N]Pro-labeled bR. Rotational echo double resonance (REDOR) filter experiments were used to assign [1-13C]Val-, [15N]Pro signals to the specific residues in bR. The previous assignments of [1-13C]Val-labeled peaks, 172.9 or 171.1 ppm, to Val69 were revised: the assignment of peak, 172.1 ppm, to Val69 was made in view of the additional information of conformation-dependent 15N chemical shifts of Pro bonded to Val in the presence of 13C-15N correlation, although no assignment of peak is feasible for 13C nuclei not bonded to Pro. 13C or 15N spin-lattice relaxation times (T1), spin-spin relaxation times under the condition of CP-MAS (T2), and cross relaxation times (TCH and TNH) for 13C and 15N nuclei and carbon or nitrogen-resolved, 1H spin-lattice relaxation times in the rotating flame (1H T1 rho) for the assigned signals were measured in [1-13C]Val-, [15N]Pro-bR. It turned out that V69-P70 in the BC loop in the extracellular side has a rigid beta-sheet in spite of longer loop and possesses large amplitude motions as revealed from 13C and 15N conformation-dependent chemical shifts and T1, T2, 1H T1 rho and cross relaxation times. In addition, breakage of the beta-sheet structure in the BC loop was seen in bacterio-opsin (bO) in the absence of retinal. PMID:18036552
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.
Evidence for non-diverging time-scales in glass-forming liquids
NASA Astrophysics Data System (ADS)
McKenna, Gregory
2013-03-01
One perceived important signature of the ``ideal'' glass transition and of the complex fluid nature of glass-forming liquids remains the apparent divergence of the dynamics at temperatures above zero Kelvin. Recently, however, this perception has been increasingly challenged both through experiments and in new theories of the dynamics of glass forming systems. In this presentation we summarize some of the prior evidence suggesting that time scales actually do not diverge in glasses that are aged into equilibrium, perhaps 15 K below the conventional glass transition temperature Tg. We then show new results from an extremely densified glass, 20 Ma old Jamaican amber, in which we were able to obtain the upper bound to the relaxation times through a step-wise temperature scan in which the stress relaxation response of the amber was measured both below and above the fictive temperature TF . We find that in the case of the upper bound responses at T>TF , there is a strong deviation of the response from the Super-Arrhenius Vogel-Fulcher behavior and this persists to the fictive temperature which is some 33.8 K below Tg. The results are compared to the parabolic model of Chandler and co-workers and we find the model to be consistent with our results if the value of Tx in the model is taken to be the calorimetric glass transition temperature. The significance of the results will be discussed. One perceived important signature of the ``ideal'' glass transition and of the complex fluid nature of glass-forming liquids remains the apparent divergence of the dynamics at temperatures above zero Kelvin. Recently, however, this perception has been increasingly challenged both through experiments and in new theories of the dynamics of glass forming systems. In this presentation we summarize some of the prior evidence suggesting that time scales actually do not diverge in glasses that are aged into equilibrium, perhaps 15 K below the conventional glass transition temperature Tg. We then show new results from an extremely densified glass, 20 Ma old Jamaican amber, in which we were able to obtain the upper bound to the relaxation times through a step-wise temperature scan in which the stress relaxation response of the amber was measured both below and above the fictive temperature TF . We find that in the case of the upper bound responses at T>TF , there is a strong deviation of the response from the Super-Arrhenius Vogel-Fulcher behavior and this persists to the fictive temperature which is some 33.8 K below Tg. The results are compared to the parabolic model of Chandler and co-workers and we find the model to be consistent with our results if the value of Tx in the model is taken to be the calorimetric glass transition temperature. The significance of the results will be discussed. We acknowledge NSF grants DMR-0804438 and DMR-1207070 for support of this work
NASA Astrophysics Data System (ADS)
Marzegalli, Anna; Brunetto, Matteo; Salvalaglio, Marco; Montalenti, Francesco; Nicotra, Giuseppe; Scuderi, Mario; Spinella, Corrado; De Seta, Monica; Capellini, Giovanni
2013-10-01
We present a synergic experimental and theoretical investigation of the plastic relaxation onset in low-temperature Ge growth on Si(001). High-resolution transmission electron microscopy reveals that misfit is released by pairs of coupled 60° dislocations. Atomic resolution proved to be key in distinguishing pairs from single 90° dislocations because of the revealed small intrapair dislocation distance (even less than 1 nm). By exploiting dislocation theory and molecular dynamics simulations, we demonstrate that the observed pairing naturally occurs as a result of the mutual interactions between the two dislocations. In particular, analytical models show that the stress field arising in a thin film when a dislocation segment lies at the interface with the substrate determines the most favored nucleation site for a new (complementary) dislocation that leads, after migration, to the coupling with the first in a stable position. At the growth temperature, further motion or recombination due to atomic scale effects is excluded by classical molecular dynamics simulations. A clear picture of the early stages in the strain relaxation emerges, gliding out of the interface and/or short-range climbing (as typically produced by annealing or higher temperature steps but not taking place under the present growth conditions) being required to transform pairs into edge dislocations. The present results also offer answers to the long-asked puzzling question about the mechanism originating 90° dislocation in high-mismatch Ge/Si systems.
In situ determination of surface relaxivities for unconsolidated sediments
NASA Astrophysics Data System (ADS)
Duschl, Markus; Galvosas, Petrik; Brox, Timothy I.; Pohlmeier, Andreas; Vereecken, Harry
2015-08-01
NMR relaxometry has developed into a method for rapid pore-size determination of natural porous media. Nevertheless, it is prone to uncertainties because of unknown surface relaxivities which depend mainly on the chemical composition of the pore walls as well as on the interfacial dynamics of the pore fluid. The classical approach for the determination of surface relaxivities is the scaling of NMR relaxation times by surface to volume ratios measured by gas adsorption or mercury intrusion. However, it is preferable that a method for the determination of average pore sizes uses the same substance, water, as probe molecule for both relaxometry and surface to volume measurements. One should also ensure that in both experiments the dynamics of the probe molecule takes place on similar length scales, which are in the order of some microns. Therefore, we employed NMR diffusion measurements with different observation times using bipolar pulsed field gradients and applied them to unconsolidated sediments (two purified sands, two natural sands, and one soil). The evaluation by Mitra's short-time model for diffusion in restricted environments yielded information about the surface to volume ratios which is independent of relaxation mechanisms. We point out that methods based on NMR diffusometry yield pore dimensions and surface relaxivities consistent with a pore space as sampled by native pore fluids via the diffusion process. This opens a way to calibrate NMR relaxation measurements with other NMR techniques, providing information about the pore-size distribution of natural porous media directly from relaxometry.
ERIC Educational Resources Information Center
Trueman, Mark; Hartley, James
This paper reports to attempt to replicate in Britain Britton and Tesser's (1991) study of the relationship between scores on a time management scale and college grades using a larger sample size and a British (rather than American) student population. Subjects were 302 psychology students who completed the 18-item scale after their first term of…
Structural Relaxation and Mode Coupling in a Simple Liquid: Depolarized Light Scattering in Benzene
Sabine Wiebel; Joachim Wuttke
2002-04-18
We have measured depolarized light scattering in liquid benzene over the whole accessible temperature range and over four decades in frequency. Between 40 and 180 GHz we find a susceptibility peak due to structural relaxation. This peak shows stretching and time-temperature scaling as known from $\\alpha$ relaxation in glass-forming materials. A simple mode-coupling model provides consistent fits of the entire data set. We conclude that structural relaxation in simple liquids and $\\alpha$ relaxation in glass-forming materials are physically the same. A deeper understanding of simple liquids is reached by applying concepts that were originally developed in the context of glass-transition research.
Relaxations in the metastable rotator phase of n-eicosane
NASA Astrophysics Data System (ADS)
Di Giambattista, C.; Sanctuary, R.; Perigo, E.; Baller, J.
2015-08-01
We present relaxations in the metastable rotator phase of the n-alkane eicosane (C20H42). The relaxation times found by calorimetry increase with increasing temperature on approaching the melting temperature of the rotator phase. This is the opposite behavior than the one found for classical activated processes. The relaxation behavior found by calorimetry is confirmed by investigations of the lattice structure with X-ray diffraction. It is shown that one lattice parameter of the orthorhombic phase relaxes on the same time scales found in calorimetry, whereas another lattice parameter reacts almost instantly on temperature perturbations. Increasing cooperativity for the creation of conformational defects in the alkane chains is proposed to be responsible for the observed behaviour.
Relaxations in the metastable rotator phase of n-eicosane.
Di Giambattista, C; Sanctuary, R; Perigo, E; Baller, J
2015-08-01
We present relaxations in the metastable rotator phase of the n-alkane eicosane (C20H42). The relaxation times found by calorimetry increase with increasing temperature on approaching the melting temperature of the rotator phase. This is the opposite behavior than the one found for classical activated processes. The relaxation behavior found by calorimetry is confirmed by investigations of the lattice structure with X-ray diffraction. It is shown that one lattice parameter of the orthorhombic phase relaxes on the same time scales found in calorimetry, whereas another lattice parameter reacts almost instantly on temperature perturbations. Increasing cooperativity for the creation of conformational defects in the alkane chains is proposed to be responsible for the observed behaviour. PMID:26254661
Tracking Primary Thermalization Events in Graphene with Photoemission at Extreme Time Scales.
Gierz, I; Calegari, F; Aeschlimann, S; Chávez Cervantes, M; Cacho, C; Chapman, R T; Springate, E; Link, S; Starke, U; Ast, C R; Cavalleri, A
2015-08-21
Direct and inverse Auger scattering are amongst the primary processes that mediate the thermalization of hot carriers in semiconductors. These two processes involve the annihilation or generation of an electron-hole pair by exchanging energy with a third carrier, which is either accelerated or decelerated. Inverse Auger scattering is generally suppressed, as the decelerated carriers must have excess energies higher than the band gap itself. In graphene, which is gapless, inverse Auger scattering is, instead, predicted to be dominant at the earliest time delays. Here, <8??fs extreme-ultraviolet pulses are used to detect this imbalance, tracking both the number of excited electrons and their kinetic energy with time-and angle-resolved photoemission spectroscopy. Over a time window of approximately 25 fs after absorption of the pump pulse, we observe an increase in conduction band carrier density and a simultaneous decrease of the average carrier kinetic energy, revealing that relaxation is in fact dominated by inverse Auger scattering. Measurements of carrier scattering at extreme time scales by photoemission will serve as a guide to ultrafast control of electronic properties in solids for petahertz electronics. PMID:26340199
Tracking Primary Thermalization Events in Graphene with Photoemission at Extreme Time Scales
NASA Astrophysics Data System (ADS)
Gierz, I.; Calegari, F.; Aeschlimann, S.; Chávez Cervantes, M.; Cacho, C.; Chapman, R. T.; Springate, E.; Link, S.; Starke, U.; Ast, C. R.; Cavalleri, A.
2015-08-01
Direct and inverse Auger scattering are amongst the primary processes that mediate the thermalization of hot carriers in semiconductors. These two processes involve the annihilation or generation of an electron-hole pair by exchanging energy with a third carrier, which is either accelerated or decelerated. Inverse Auger scattering is generally suppressed, as the decelerated carriers must have excess energies higher than the band gap itself. In graphene, which is gapless, inverse Auger scattering is, instead, predicted to be dominant at the earliest time delays. Here, <8 fs extreme-ultraviolet pulses are used to detect this imbalance, tracking both the number of excited electrons and their kinetic energy with time-and angle-resolved photoemission spectroscopy. Over a time window of approximately 25 fs after absorption of the pump pulse, we observe an increase in conduction band carrier density and a simultaneous decrease of the average carrier kinetic energy, revealing that relaxation is in fact dominated by inverse Auger scattering. Measurements of carrier scattering at extreme time scales by photoemission will serve as a guide to ultrafast control of electronic properties in solids for petahertz electronics.
Richardson, P. M. Voice, A. M. Ward, I. M.
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.
Scaling of average sending time on weighted Koch networks
NASA Astrophysics Data System (ADS)
Dai, Meifeng; Liu, Jie
2012-10-01
Random walks on weighted complex networks, especially scale-free networks, have attracted considerable interest in the past. But the efficiency of a hub sending information on scale-free small-world networks has been addressed less. In this paper, we study random walks on a class of weighted Koch networks with scaling factor 0 < r ? 1. We derive some basic properties for random walks on the weighted Koch networks, based on which we calculate analytically the average sending time (AST) defined as the average of mean first-passage times (MFPTs) from a hub node to all other nodes, excluding the hub itself. The obtained result displays that for 0 < r < 1 in large networks the AST grows as a power-law function of the network order with the exponent, represented by log 43r+1/r, and for r = 1 in large networks the AST grows with network order as N ln N, which is larger than the linear scaling of the average receiving time defined as the average of MFPTs for random walks to a given hub node averaged over all starting points.
Towards an orbital time scale for chinese loess deposits
NASA Astrophysics Data System (ADS)
Ding, Z.; Yu, Z.; Rutter, N. W.; Liu, T.
In this study, we analyzed the grain size of the Baoji loess-soil sequence at 10 cm intervals. Results show that grain size variations are very sensitive to loess-soil alternations, with loess units being much coarser than soils. Such a change in loess-soil grains is interpreted as the result of the glacial-interglacial cyclic variations in the intensity of the winter monsoon winds out of Siberia. The grain size record is thus employed as a proxy indicator of the winter monsoon circulation and tuned to the orbital records calculated recently by Berger and Loutre (1991) under the control of major magnetic reversals. The tuning is independent of any correlation with ?18O signals in the deep-sea sediments. The resulting grain size time scale is tightly constrained, as suggested by the following facts: (1) the filtered obliquity and precession components from the grain size data on the orbital time scale closely match the theoretical orbital records; (2) ages of the major magnetic reversals estimated from the grain size time scale are in good agreement with the {K}/{Ar}-dated ages; (3) there is close coherence between the Baoji grain size time series and the orbital variations at the orbital frequency bands over the entire 0-2.5 Ma period; and (4) the grain size record on the orbital time scale shows a close similarity to the orbitally-tuned DSDP Site 607 and ODP Site 677 ?18O records. Examination of time-dependent characteristics of the grain size record suggests that there are two major shifts of dominant periodicities in the long-term monsoonal cycles, one occurring at about 0.8 Ma BP and the other around 1.7 Ma BP.
Time scales and heterogeneous structure in geodynamic earth models
Bunge; Richards; Lithgow-Bertelloni; Baumgardner; Grand; Romanowicz
1998-04-01
Computer models of mantle convection constrained by the history of Cenozoic and Mesozoic plate motions explain some deep-mantle structural heterogeneity imaged by seismic tomography, especially those related to subduction. They also reveal a 150-million-year time scale for generating thermal heterogeneity in the mantle, comparable to the record of plate motion reconstructions, so that the problem of unknown initial conditions can be overcome. The pattern of lowermost mantle structure at the core-mantle boundary is controlled by subduction history, although seismic tomography reveals intense large-scale hot (low-velocity) upwelling features not explicitly predicted by the models. PMID:9525864
Brownian motion at fast time scales and thermal noise imaging
NASA Astrophysics Data System (ADS)
Huang, Rongxin
This dissertation presents experimental studies on Brownian motion at fast time scales, as well as our recent developments in Thermal Noise Imaging which uses thermal motions of microscopic particles for spatial imaging. As thermal motions become increasingly important in the studies of soft condensed matters, the study of Brownian motion is not only of fundamental scientific interest but also has practical applications. Optical tweezers with a fast position-sensitive detector provide high spatial and temporal resolution to study Brownian motion at fast time scales. A novel high bandwidth detector was developed with a temporal resolution of 30 ns and a spatial resolution of 1 A. With this high bandwidth detector, Brownian motion of a single particle confined in an optical trap was observed at the time scale of the ballistic regime. The hydrodynamic memory effect was fully studied with polystyrene particles of different sizes. We found that the mean square displacements of different sized polystyrene particles collapse into one master curve which is determined by the characteristic time scale of the fluid inertia effect. The particle's inertia effect was shown for particles of the same size but different densities. For the first time the velocity autocorrelation function for a single particle was shown. We found excellent agreement between our experiments and the hydrodynamic theories that take into account the fluid inertia effect. Brownian motion of a colloidal particle can be used to probe three-dimensional nano structures. This so-called thermal noise imaging (TNI) has been very successful in imaging polymer networks with a resolution of 10 nm. However, TNI is not efficient at micrometer scale scanning since a great portion of image acquisition time is wasted on large vacant volume within polymer networks. Therefore, we invented a method to improve the efficiency of large scale scanning by combining traditional point-to-point scanning to explore large vacant space with thermal noise imaging at the proximity of the object. This method increased the efficiency of thermal noise imaging by more than 40 times. This development should promote wider applications of thermal noise imaging in the studies of soft materials and biological systems.
Laura Calderan; Paolo F Fabene; Elena Nicolato; Pasquina Marzola; Francesco Osculati; Andrea Sbarbati
2004-01-01
We analyzed modifications in transversal relaxation time (T2) and regional cerebral blood volume (rCBV) in two areas of the limbic system, i.e., olfactory bulb (OB) and amygdala (AMY), in pre-puberty and post-puberty female rats. The aim of this work was to extend the knowledge about physiological modifications of these MRI parameters at different developmental phases. No significant difference was observed
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
-Wall Semiconducting Carbon Nanotube Bradley F. Habenicht, Colleen F. Craig, and Oleg V. Prezhdo* Department; published 11 May 2006) The electron and hole relaxation in the 7; 0 zigzag carbon nanotube is simulated, and electronic prop- erties of carbon nanotubes (CNT) [1] have suggested a variety of applications including
Probing Fission Time Scales with Neutrons and GDR Gamma Rays
Schmitt, R. P.; Botting, Tye; Chubarian, G G; Wolf, K; Hurst, B J; Jabs, H; Hamelin, M; Bacak, A; Oganessian, Yuri Ts.; Itkis, M. G.; Kozulin, E M; Kondratiev, N. A.; Salamatin, V S; Pokrovsky, I V; Hanappe, F; de Goes Brennand, E.; Huck, A; Stuttge, L; Liatard, E; Beene, James R; Varner Jr, Robert L; Halbert, Melvyn L; Gan, Ning
2003-06-01
The time scales for nuclear fission have been explored using both pre-and postfission neutrons and GDR gamma rays. Four systems were investigated: 133-MeV 16O + 176Yb and 208Pb and 104-MeV 4He + 188Os and 209Bi. Fission fragments were measured in coincidence with PPACs. The neutrons were detected using eight detectors from the DEMON array, while gamma rays were measured using the US BaF2 array. The pre-and postfission gamma rays were determined using moving source fits parallel and perpendicular to the fission fragment emission directions. The time scales for fission for the neutrons were determined using the neutron clock technique. The gamma-ray data were fitted using a statistical model calculation based on the code CASCADE. The results of the fits from both data types were used to extract nuclear friction coefficients, ?, and fission time scales. The ? values ranged from 7 to 20, while the fission times were (31-105) 10?21 s. From Yadernaya Fizika, Vol. 66, No. 6, 2003, pp. 1199-1203.
NASA Astrophysics Data System (ADS)
Chu, Hao; Torchinsky, Darius; Zhao, Liuyan; Rall, Patrick; Terrace, Jasminka; Cao, Gang; Hsieh, David; Institute for Quantum Information; Matter, California Institute of Technology Collaboration; Department of Physics; Astronomy, University of Kentucky Collaboration
2015-03-01
Ca2RuO4 is a multiband strongly correlated electron system that undergoes a structural phase transition at Ts 360K that is concomitant with an insulator-to-metal transition and a rearrangement of orbital occupancy. Understanding its structural and electronic response to ultrafast optical excitation can provide insight about the microscopic mechanism of this phase transition.We report temperature and fluence dependent time resolved optical reflectivity measurements from lightly doped Ca2RuO4 single crystals. Abrupt changes in both the electronic relaxation dynamics and multiple lattice vibrational modes are observed, including the softening of two optical phonon modes as Ts is approached. We will discuss the relevance of our results to existing theories of the mechanism underlying the structural phase transition in Ca2RuO4 as well as the possibility of photo-inducing this phase transition on ultrafast time scales.
Sublinear scaling for time-dependent stochastic density functional theory
NASA Astrophysics Data System (ADS)
Gao, Yi; Neuhauser, Daniel; Baer, Roi; Rabani, Eran
2015-01-01
A stochastic approach to time-dependent density functional theory is developed for computing the absorption cross section and the random phase approximation (RPA) correlation energy. The core idea of the approach involves time-propagation of a small set of stochastic orbitals which are first projected on the occupied space and then propagated in time according to the time-dependent Kohn-Sham equations. The evolving electron density is exactly represented when the number of random orbitals is infinite, but even a small number (?16) of such orbitals is enough to obtain meaningful results for absorption spectrum and the RPA correlation energy per electron. We implement the approach for silicon nanocrystals using real-space grids and find that the overall scaling of the algorithm is sublinear with computational time and memory.
The Effects of Suggestibility on Relaxation.
ERIC Educational Resources Information Center
Rickard, Henry C.; And Others
1985-01-01
Selected undergraduates (N=32) on the basis of Creative Imagination Scale scores and randomly assigned high and low suggestibility subjects to progressive relaxation (PR) and suggestions of relaxation (SR) training modes. Results revealed a significant pre-post relaxation effect, and main efffects for both suggestibility and training mode. (NRB)
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.
Space and time scales in human-landscape systems.
Kondolf, G Mathias; Podolak, Kristen
2014-01-01
Exploring spatial and temporal scales provides a way to understand human alteration of landscape processes and human responses to these processes. We address three topics relevant to human-landscape systems: (1) scales of human impacts on geomorphic processes, (2) spatial and temporal scales in river restoration, and (3) time scales of natural disasters and behavioral and institutional responses. Studies showing dramatic recent change in sediment yields from uplands to the ocean via rivers illustrate the increasingly vast spatial extent and quick rate of human landscape change in the last two millennia, but especially in the second half of the twentieth century. Recent river restoration efforts are typically small in spatial and temporal scale compared to the historical human changes to ecosystem processes, but the cumulative effectiveness of multiple small restoration projects in achieving large ecosystem goals has yet to be demonstrated. The mismatch between infrequent natural disasters and individual risk perception, media coverage, and institutional response to natural disasters results in un-preparedness and unsustainable land use and building practices. PMID:23716006
Space and Time Scales in Human-Landscape Systems
NASA Astrophysics Data System (ADS)
Kondolf, G. Mathias; Podolak, Kristen
2014-01-01
Exploring spatial and temporal scales provides a way to understand human alteration of landscape processes and human responses to these processes. We address three topics relevant to human-landscape systems: (1) scales of human impacts on geomorphic processes, (2) spatial and temporal scales in river restoration, and (3) time scales of natural disasters and behavioral and institutional responses. Studies showing dramatic recent change in sediment yields from uplands to the ocean via rivers illustrate the increasingly vast spatial extent and quick rate of human landscape change in the last two millennia, but especially in the second half of the twentieth century. Recent river restoration efforts are typically small in spatial and temporal scale compared to the historical human changes to ecosystem processes, but the cumulative effectiveness of multiple small restoration projects in achieving large ecosystem goals has yet to be demonstrated. The mismatch between infrequent natural disasters and individual risk perception, media coverage, and institutional response to natural disasters results in un-preparedness and unsustainable land use and building practices.
Sub-diffusive scaling with power-law trapping times
NASA Astrophysics Data System (ADS)
Luo, Liang; Tang, Lei-Han
2014-07-01
Thermally driven diffusive motion of a particle underlies many physical and biological processes. In the presence of traps and obstacles, the spread of the particle is substantially impeded, leading to subdiffusive scaling at long times. The statistical mechanical treatment of diffusion in a disordered environment is often quite involved. In this short review, we present a simple and unified view of the many quantitative results on anomalous diffusion in the literature, including the scaling of the diffusion front and the mean first-passage time. Various analytic calculations and physical arguments are examined to highlight the role of dimensionality, energy landscape, and rare events in affecting the particle trajectory statistics. The general understanding that emerges will aid the interpretation of relevant experimental and simulation results.
HMC algorithm with multiple time scale integration and mass preconditioning
C. Urbach; K. Jansen; A. Shindler; U. Wenger
2005-09-02
We present a variant of the HMC algorithm with mass preconditioning (Hasenbusch acceleration) and multiple time scale integration. We have tested this variant for standard Wilson fermions at beta=5.6 and at pion masses ranging from 380 MeV to 680 MeV. We show that in this situation its performance is comparable to the recently proposed HMC variant with domain decomposition as preconditioner. We give an update of the ``Berlin Wall'' figure, comparing the performance of our variant of the HMC algorithm to other published performance data. Advantages of the HMC algorithm with mass preconditioning and multiple time scale integration are that it is straightforward to implement and can be used in combination with a wide variety of lattice Dirac operators.
De Vis, J.B.; Hendrikse, J.; Groenendaal, F.; de Vries, L.S.; Kersbergen, K.J.; Benders, M.J.N.L.; Petersen, E.T.
2014-01-01
Background and purpose The longitudinal relaxation time of blood (T1b) is influenced by haematocrit (Hct) which is known to vary in neonates. The purpose of this study was threefold: to obtain T1b values in neonates, to investigate how the T1b influences quantitative arterial spin labelling (ASL), and to evaluate if known relationships between T1b and haematocrit (Hct) hold true when Hct is measured by means of a point-of-care device. Materials and methods One hundred and four neonates with 120 MR scan sessions (3 T) were included. The T1b was obtained from a T1 inversion recovery sequence. T1b-induced changes in ASL cerebral blood flow estimates were evaluated. The Hct was obtained by means of a point-of-care device. Linear regression analysis was used to investigate the relation between Hct and MRI-derived R1 of blood (the inverse of the T1b). Results Mean T1b was 1.85 s (sd 0.2 s). The mean T1b in preterm neonates was 1.77 s, 1.89 s in preterm neonates scanned at term-equivalent age (TEA) and 1.81 s in diseased neonates. The T1b in the TEA was significantly different from the T1b in the preterm (p < 0.05). The change in perfusion induced by the T1b was ?11% (sd 9.1%, p < 0.001). The relation between arterial-drawn Hct and R1b was R1b = 0.80 × Hct + 0.22, which falls within the confidence interval of the previously established relationships, whereas capillary-drawn Hct did not correlate with R1b. Conclusion We demonstrated a wide variability of the T1b in neonates and the implications it could have in methods relying on the actual T1b as for instance ASL. It was concluded that arterial-drawn Hct values obtained from a point-of-care device can be used to infer the T1b whereas our data did not support the use of capillary-drawn Hct for T1b correction. PMID:24818078
Adaptive Haar transforms with arbitrary time and scale splitting
NASA Astrophysics Data System (ADS)
Egiazarian, Karen O.; Astola, Jaakko T.
2001-05-01
The Haar transform is generalized to the case of an arbitrary time and scale splitting. To any binary tree we associate an orthogonal system of Haar-type functions - tree-structured Haar (TSH) functions. Unified fast algorithm for computation of the introduced tree-structured Haar transforms is presented. It requires 2(N - 1) additions and 3N - 2 multiplications, where N is transform order or, equivalently, the number of leaves of the binary tree.
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.
On transport phenomena and equilibration time scales in thermodenuders
NASA Astrophysics Data System (ADS)
Saleh, R.; Shihadeh, A.; Khlystov, A.
2010-07-01
This paper presents a theoretical and experimental investigation of thermodenuders that addresses two controversial issues: 1) equilibration time scales and 2) the need for an activated carbon (AC) denuder in the cooling section. We describe a plug flow model for transport phenomena in a TD, which can be used to simulate the rate of vapor build-up in the gas phase and the corresponding change in particle size distribution. Model simulations were found to have excellent agreement with experiments performed with pure and mixed dicarboxylic acid aerosols. Both simulations and experiments showed that the aerosols approached equilibrium within reasonable residence times (15 s-30 s) for aerosol concentrations and size distributions typical for laboratory measurements. However, for size distributions relevant for ambient aerosols, equilibration time scales were much larger than residence times available with current TD designs. We have also performed dimensional analysis on the problem of equilibration in TDs, and derived a dimensionless equilibration parameter which can be used to determine the residence time needed for an aerosol of given size distribution and kinetic properties to approach equilibrium. It is also shown theoretically and empirically that aerosol volatility has no effect on the equilibration time scales. Model simulations and experiments showed that with aerosol size distributions relevant to both ambient and laboratory measurements re-condensation in the cooling section, with and without an AC denuder, was negligible. Thus, there is no significant benefit in using an AC denuder in the cooling section. Due to the risk of stripping volatile material from the aerosol, the use of AC denuders in the cooling section should be avoided. Finally, we present a rationale for why ? C is the proper measure of volatility, while using mass fraction remaining (MFR) can be misleading.
On transport phenomena and equilibration time scales in thermodenuders
NASA Astrophysics Data System (ADS)
Saleh, R.; Shihadeh, A.; Khlystov, A.
2011-03-01
This paper presents a theoretical and experimental investigation of thermodenuders that addresses two controversial issues: (1) equilibration time scales and (2) the need for an activated carbon (AC) denuder in the cooling section. We describe a plug flow model for transport phenomena in a TD, which can be used to simulate the rate of vapor build-up in the gas phase and the corresponding change in particle size distribution. Model simulations were found to have excellent agreement with experiments performed with pure and mixed dicarboxylic acid aerosols. Both simulations and experiments showed that the aerosols approached equilibrium within reasonable residence times (15 s-30 s) for aerosol concentrations and size distributions typical for laboratory measurements, and that volatility studies at sufficiently high aerosol loadings, therefore, need not resort to kinetic models for inference of thermodynamic properties. However, for size distributions relevant for ambient aerosols, equilibration time scales were much larger than residence times available with current TD designs. We have also performed dimensional analysis on the problem of equilibration in TDs, and derived a dimensionless equilibration parameter which can be used to determine the residence time needed for an aerosol of given size distribution and kinetic properties to approach equilibrium. It is also shown theoretically and empirically that aerosol volatility has no effect on the equilibration time scales. Model simulations and experiments showed that with aerosol size distributions relevant to both ambient and laboratory measurements re-condensation in the cooling section, with and without an AC denuder, was negligible. Thus, there is no significant benefit in using an AC denuder in the cooling section. Due to the risk of stripping volatile material from the aerosol, the use of AC denuders in the cooling section should be avoided. Finally, we present a rationale for why ?C is the proper measure of volatility, while using mass fraction remaining (MFR) can be misleading.
Scaling Brain Size, Keeping Timing: Evolutionary Preservation of Brain Rhythms
Buzsáki, György; Logothetis, Nikos; Singer, Wolf
2014-01-01
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
Scale and time dependence of serial correlations in word-length time series of written texts
NASA Astrophysics Data System (ADS)
Rodriguez, E.; Aguilar-Cornejo, M.; Femat, R.; Alvarez-Ramirez, J.
2014-11-01
This work considered the quantitative analysis of large written texts. To this end, the text was converted into a time series by taking the sequence of word lengths. The detrended fluctuation analysis (DFA) was used for characterizing long-range serial correlations of the time series. To this end, the DFA was implemented within a rolling window framework for estimating the variations of correlations, quantified in terms of the scaling exponent, strength along the text. Also, a filtering derivative was used to compute the dependence of the scaling exponent relative to the scale. The analysis was applied to three famous English-written literary narrations; namely, Alice in Wonderland (by Lewis Carrol), Dracula (by Bram Stoker) and Sense and Sensibility (by Jane Austen). The results showed that high correlations appear for scales of about 50-200 words, suggesting that at these scales the text contains the stronger coherence. The scaling exponent was not constant along the text, showing important variations with apparent cyclical behavior. An interesting coincidence between the scaling exponent variations and changes in narrative units (e.g., chapters) was found. This suggests that the scaling exponent obtained from the DFA is able to detect changes in narration structure as expressed by the usage of words of different lengths.
Horizontal structure of winter time 250 mb jet stream variations on the fifteen day time scale
Park, Sangwook
1993-01-01
The horizontal structure of the 250 mb jet stream on the fifteen-day time scale during Northern Hemisphere winter is presented. The winter season is divided into six fifteen-day periods for the 24-year NMC data set. The fifteen-day time...
Scaling and Time Warping in Time Series Querying Ada Wai-chee Fu1
Zordan, Victor
Scaling and Time Warping in Time Series Querying Ada Wai-chee Fu1 Eamonn Keogh2 Leo Yung Hang Lau1 Chotirat Ann Ratanamahatana2 Department of Computer Science and Engineering1 Department of Computer Science and Engineering2 The Chinese University of Hong Kong University of California Shatin, Hong Kong Riverside, USA
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.
Lee, Hyojin; Yang, Seungbin; Lee, Ji-Hoon; Soo Park, Young
2014-05-12
We examined the electrooptical properties of a nematic liquid crystal (LC) sample whose substrates were coated with a mixture of carbon nanotube (CNT) and polyimide (PI). The relaxation time of the sample coated with 1.5?wt.?% CNT mixture was about 35% reduced compared to the pure polyimide sample. The elastic constant and the order parameter of the CNT-mixture sample were increased and the fast relaxation of LC could be approximated to the mean-field theory. We found the CNT-mixed polyimide formed more smooth surface than the pure PI from atomic force microscopy images, indicating the increased order parameter is related to the smooth surface topology of the CNT-polyimide mixture.
Collisionless relaxation in gravitational systems: from violent relaxation to gravothermal collapse.
Levin, Yan; Pakter, Renato; Rizzato, Felipe B
2008-08-01
Theory and simulations are used to study collisionless relaxation of a gravitational N -body system. It is shown that when the initial one-particle distribution function satisfies the virial condition--potential energy is minus twice the kinetic energy--the system quickly relaxes to a metastable state described quantitatively by the Lynden-Bell distribution with a cutoff. If the initial distribution function does not meet the virial requirement, the system undergoes violent oscillations, resulting in a partial evaporation of mass. The leftover particles phase-separate into a core-halo structure. The theory presented allows us to quantitatively predict the amount and the distribution of mass left in the central core, without any adjustable parameters. On a longer time scale tauG-N , collisionless relaxation leads to a gravothermal collapse. PMID:18850809
Intrinsic short time scale variability of W3(OH) maser
R. Ramachandran; A. A. Deshpande; W. M. Goss
2006-08-04
We have studied the OH masers in the star forming region, W3(OH), with data obtained from the Very Long Baseline Array (VLBA). The data provide an angular resolution of $\\sim$5 mas, and a velocity resolution of 106 m s$^{-1}$. A novel analysis procedure allows us to differentiate between broadband temporal intensity fluctuations introduced by instrumental gain variations plus interstellar diffractive scintillation, and intrinsic narrowband variations. Based on this 12.5 hours observation, we are sensitive to variations with time scales of minutes to hours. We find statistically significant intrinsic variations with time scales of $\\sim$15--20 minutes or slower, based on the {\\it velocity-resolved fluctuation spectra}. These variations are seen predominantly towards the line shoulders. The peak of the line profile shows little variation, suggesting that they perhaps exhibit saturated emission. The associated modulation index of the observed fluctuation varies from statistically insignificant values at the line center to about unity away from the line center. Based on light-travel-time considerations, the 20-minute time scale of intrinsic fluctuations translates to a spatial dimension of $\\sim$2--3 AU along the sight-lines. On the other hand, the transverse dimension of the sources, estimated from their observed angular sizes of about $\\sim$3 mas, is about 6 AU. We argue that these source sizes are intrinsic, and are not affected by interstellar scatter broadening. The implied peak brightness temperature of the 1612/1720 maser sources is about $\\sim2\\times 10^{13}$ K, and a factor of about five higher for the 1665 line.
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.
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.
Diller, Anna; Prakash, Shipra; Alia, A; Gast, Peter; Matysik, Jörg; Jeschke, Gunnar
2007-09-01
During the photocycle of quinone-blocked photosynthetic reaction centers (RCs), photochemically induced dynamic nuclear polarization (photo-CIDNP) is produced by polarization transfer from the initially totally electron polarized electron pair and can be observed by 13C magic-angle spinning (MAS) NMR as a strong modification of signal intensities. The same processes creating net nuclear polarization open up light-dependent channels for polarization loss. This leads to coherent and incoherent enhanced signal recovery, in addition to the recovery due to light-independent longitudinal relaxation. Coherent mixing between electron and nuclear spin states due to pseudosecular hyperfine coupling within the radical pair state provides such a coherent loss channel for nuclear polarization. Another polarization transfer mechanism called differential relaxation, which is based on the long lifetime of the triplet state of the donor, provides an efficient incoherent relaxation path. In RCs of the purple bacterium Rhodobacter sphaeroides R26, the photochemical active channels allow for accelerated signal scanning by a factor of 5. Hence, photo-CIDNP MAS NMR provides the possibility to drive the NMR technique beyond the T1 limit. PMID:17696523
Computational Modeling of Semiconductor Dynamics at Femtosecond Time Scales
NASA Technical Reports Server (NTRS)
Agrawal, Govind P.; Goorjian, Peter M.
1998-01-01
The main objective of the Joint-Research Interchange NCC2-5149 was to develop computer codes for accurate simulation of femtosecond pulse propagation in semiconductor lasers and semiconductor amplifiers [I]. The code should take into account all relevant processes such as the interband and intraband carrier relaxation mechanisms and the many-body effects arising from the Coulomb interaction among charge carriers [2]. This objective was fully accomplished. We made use of a previously developed algorithm developed at NASA Ames [3]-[5]. The new algorithm was tested on several problems of practical importance. One such problem was related to the amplification of femtosecond optical pulses in semiconductors. These results were presented in several international conferences over a period of three years. With the help of a postdoctoral fellow, we also investigated the origin of instabilities that can lead to the formation of femtosecond pulses in different kinds of lasers. We analyzed the occurrence of absolute instabilities in lasers that contain a dispersive host material with third-order nonlinearities. Starting from the Maxwell-Bloch equations, we derived general multimode equations to distinguish between convective and absolute instabilities. We find that both self-phase modulation and intensity-dependent absorption can dramatically affect the absolute stability of such lasers. In particular, the self-pulsing threshold (the so-called second laser threshold) can occur at few times the first laser threshold even in good-cavity lasers for which no self-pulsing occurs in the absence of intensity-dependent absorption. These results were presented in an international conference and published in the form of two papers.
Thermopeaking in alpine streams: event characterization and time scales
NASA Astrophysics Data System (ADS)
Zolezzi, Guido; Siviglia, Annunziato; Toffolon, Marco; Maiolini, Bruno
2010-05-01
The present study provides a detailed quantification of the "thermopeaking" phenomenon, which consists of sharp intermittent alterations of stream thermal regime associated with hydropeaking releases from hydroelectricity plants. The study refers to the Noce River (Northern Italy), a typical hydropower-regulated Alpine stream, where water stored in highaltitude reservoirs often has a different temperature compared to the receiving bodies. The analysis is based on a river water temperature dataset that has been continuously collected for one year at 30' intervals in four different sections along the Noce River. A suitable threshold-based procedure is developed to quantify the main characteristics of thermopeaking, which is responsible for thermal alterations at different scales. The application of Wavelet Transform allows to separately investigate thermal regime alterations at sub-daily, daily and weekly scales. Moreover, at a seasonal scale, patterns of "warm" and "cold" thermopeaking can be clearly detected and quantified. The study highlights the relevance of investigating a variety of short-term alterations at multiple time scales for a better quantitative understanding of the complexity that characterises the river thermal regime. The outcomes of the analysis raise important interdisciplinary research questions concerning the effects of thermopeaking and of the related short- and medium-term effects on biological communities, which have been rather poorly investigated in ecological studies.
Time Scale Hierarchies in the Functional Organization of Complex Behaviors
Perdikis, Dionysios; Huys, Raoul; Jirsa, Viktor K.
2011-01-01
Traditional approaches to cognitive modelling generally portray cognitive events in terms of ‘discrete’ states (point attractor dynamics) rather than in terms of processes, thereby neglecting the time structure of cognition. In contrast, more recent approaches explicitly address this temporal dimension, but typically provide no entry points into cognitive categorization of events and experiences. With the aim to incorporate both these aspects, we propose a framework for functional architectures. Our approach is grounded in the notion that arbitrary complex (human) behaviour is decomposable into functional modes (elementary units), which we conceptualize as low-dimensional dynamical objects (structured flows on manifolds). The ensemble of modes at an agent’s disposal constitutes his/her functional repertoire. The modes may be subjected to additional dynamics (termed operational signals), in particular, instantaneous inputs, and a mechanism that sequentially selects a mode so that it temporarily dominates the functional dynamics. The inputs and selection mechanisms act on faster and slower time scales then that inherent to the modes, respectively. The dynamics across the three time scales are coupled via feedback, rendering the entire architecture autonomous. We illustrate the functional architecture in the context of serial behaviour, namely cursive handwriting. Subsequently, we investigate the possibility of recovering the contributions of functional modes and operational signals from the output, which appears to be possible only when examining the output phase flow (i.e., not from trajectories in phase space or time). PMID:21980278
Time dependence of coupling in frequency-scaled bimanual coordination.
James, Eric G; Molenaar, Peter C M; Newell, Karl M
2011-02-25
Prior research has shown that fluctuations in the relative phase of bimanual coordination do not reflect a white Gaussian noise process. The present study furthered the examination of time-dependent properties in bimanual coordination by comparing the magnitude of relative phase variability and the degree of effector independence within the time domain. The original Kelso (1984) [10] bimanual frequency-scaling protocol was reproduced in which phase transitions from antiphase to in-phase were induced with increasing movement frequency. The results showed that as movement frequency was scaled-up the amount of relative phase variability increased and the effector movements became more dependent prior to the transition. This is consistent with previous modeling showing that stronger effector coupling can prevent the occurrence of phase transitions when long range correlations in relative phase are present. It appears that, as movement frequency is scaled up, increases in effector coupling strength minimize loss of pattern stability and delay the onset of phase transitions. PMID:21194554
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.
Speed of Markovian relaxation toward the ground state
Vogl, Malte; Schaller, Gernot; Brandes, Tobias
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.
Thin film magnetism in the picosecond time scale
NASA Astrophysics Data System (ADS)
Pescia, Danilo
2002-03-01
The precessional motion of the spin is a very fast process and magnetic recording devices based on precessional switching might project recording speed into the picosecond time scale. There are several open questions, which will be addressed in this talk. i) We show that precessional switching is a bifurcation process: this means that strategies must be found for it to become technologically relevant. ii) The dynamics of the magnetization vector, even in simple magnetic elements, develops complex patterns in time and space, which we have measured by means of magnetic imaging with picosecond time resolution. We present an analytical solution of the local Landau-Lifshitz equation which essentially explains this complexity and show that the way toward "practical" precessional switching is a difficult one. iii) We have developed a new scheme for producing ultrafast local magnetic fields, based on optically pumping a Schottky barrier. Our attempt to generate, with the same scheme, stronger fields by spin injection has not been successful yet.
Many Roads to Synchrony: Natural Time Scales and Their Algorithms
Ryan G. James; John R. Mahoney; Christopher J. Ellison; James P. Crutchfield
2013-12-20
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 epsilon-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 epsilon-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.
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
Ti diffusion in quartz inclusions: implications for metamorphic time scales
NASA Astrophysics Data System (ADS)
Spear, Frank S.; Ashley, Kyle T.; Webb, Laura E.; Thomas, Jay B.
2012-12-01
Quartz inclusions in garnet from samples collected from the staurolite zone in central New England are zoned in cathodoluminescence (CL). The CL intensity is interpreted to be a proxy for Ti concentration and the zoning attributed to Ti diffusion into the quartz grains driven by Ti exchange between quartz and enclosing garnet as a function of changing temperature. The CL zoning has been interpreted using a numerical diffusion model to constrain the time scales over which the diffusion has occurred. Temperature-time histories are sensitive to the presumed peak temperature but not to other model parameters. The total time of the metamorphic heating and cooling cycle from around 450 °C to the peak temperature (550-600 °C) back to 450 °C is surprisingly short and encompasses only 0.2-2 million years for peak temperatures of 600-550 °C. The metamorphism was accompanied by large-scale nappe and dome formation, and it is suggested that this occurred as a consequence of in-sequence thrusting resulting in a mid-crustal ductile duplex structure.
River channel lateral mobility: metrics, time scales, and controls
NASA Astrophysics Data System (ADS)
Wickert, Andrew D.; Martin, John M.; Tal, Michal; Kim, Wonsuck; Sheets, Ben; Paola, Chris
2013-06-01
Alluvial river channels are intrinsically mobile. We mapped channel planform extent in a series of experiments to measure instantaneous rates of channel motion, loss of planform overlap with the original positions of the channels, and reworking of the fluvial surface over which the channels moved. These experiments comprise two aggrading deltas, one subsiding delta that underwent cyclical base level changes, and one braided channel system that was seeded with vegetation. We find that the amounts of channel planform overlap and remaining unreworked fluvial surface area both decay exponentially with time, and that these metrics and the instantaneously-measured rates of channel motion scale predictably with one another in spite of the different time scales of the processes they record. Rates of channel planform change increase with increasing sediment flux and bed and planform irregularity, and decrease with the establishment of riparian vegetation. Aggradation does not noticeably affect channel mobility, but induces avulsions that allow the channels to more rapidly rework the fluvial surface. Additional findings include that: (1) sediment flux in the braided experiment equals its rate of bar migration, (2) channel widths are normally distributed with time, and (3) we can use our channel mobility metrics to connect surface processes with the resultant fluvial stratigraphy.
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.
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.
NASA Astrophysics Data System (ADS)
de Jong, Saskia; van Vliet, Ton; de Jongh, Harmen H. J.
2015-08-01
The recoverable energy (RE), defined as the ratio of the work exerted on a test specimen during compression and recovered upon subsequent decompression, has been shown to correlate to sensory profiling of protein-based food products. Understanding the mechanism determining the time-dependency of RE is primordial. This work aims to identify the protein-specific impact on the recoverable energy by stress dissipation via relaxation of (micro)structural rearrangements within protein gels. To this end, caseinate and gelatin gels are studied for their response to time-dependent mechanical deformation as they are known to develop structurally distinct network morphologies. This work shows that in gelatin gels no significant stress relaxation occurs on the seconds timescale, and consequently no time-dependency of the amount of energy stored in this material is observed. In caseinate gels, however, the energy dissipation via relaxation processes does contribute significantly to the time-dependency of reversible stored energy in the network. This can explain the obtained RE as a function of applied deformation at slow deformation rates. At faster deformation, an additional contribution to the dissipated energy is apparent, that increases with the deformation rate, which might point to the role of energy dissipation related to friction of the serum entrapped by the protein-network. This work shows that engineering strategies focused on controlling viscous flow in protein gels could be more effective to dictate the ability to elastically store energy in protein gels than routes that direct protein-specific aggregation and/or network-assembly.