Pair plasma relaxation time scales.
Aksenov, A G; Ruffini, R; Vereshchagin, G V
2010-04-01
By numerically solving the relativistic Boltzmann equations, we compute the time scale for relaxation to thermal equilibrium for an optically thick electron-positron plasma with baryon loading. We focus on the time scales of electromagnetic interactions. The collisional integrals are obtained directly from the corresponding QED matrix elements. Thermalization time scales are computed for a wide range of values of both the total-energy density (over 10 orders of magnitude) and of the baryonic loading parameter (over 6 orders of magnitude). This also allows us to study such interesting limiting cases as the almost purely electron-positron plasma or electron-proton plasma as well as intermediate cases. These results appear to be important both for laboratory experiments aimed at generating optically thick pair plasmas as well as for astrophysical models in which electron-positron pair plasmas play a relevant role. PMID:20481841
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; Sorée, Bart; Magnus, Wim; Tőkei, Zsolt
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.
Role of Relaxation Time Scale in Noisy Signal Transduction
Maity, Alok Kumar; Chaudhury, Pinaki; Banik, Suman K
2015-01-01
Intra-cellular fluctuations, mainly triggered by gene expression, are an inevitable phenomenon observed in living cells. It influences generation of phenotypic diversity in genetically identical cells. Such variation of cellular components is beneficial in some contexts but detrimental in others. To quantify the fluctuations in a gene product, we undertake an analytical scheme for studying few naturally abundant linear as well as branched chain network motifs. We solve the Langevin equations associated with each motif under the purview of linear noise approximation and derive the expressions for Fano factor and mutual information in close analytical form. Both quantifiable expressions exclusively depend on the relaxation time (decay rate constant) and steady state population of the network components. We investigate the effect of relaxation time constraints on Fano factor and mutual information to indentify a time scale domain where a network can recognize the fluctuations associated with the input signal more reliably. We also show how input population affects both quantities. We extend our calculation to long chain linear motif and show that with increasing chain length, the Fano factor value increases but the mutual information processing capability decreases. In this type of motif, the intermediate components act as a noise filter that tune up input fluctuations and maintain optimum fluctuations in the output. For branched chain motifs, both quantities vary within a large scale due to their network architecture and facilitate survival of living system in diverse environmental conditions. PMID:25955500
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.
Huge (but Finite) Time Scales in Slow Relaxations: Beyond Simple Aging
NASA Astrophysics Data System (ADS)
Amir, Ariel; Borini, Stefano; Oreg, Yuval; Imry, Yoseph
2011-10-01
Experiments performed in the last years demonstrated slow relaxations and aging in the conductance of a large variety of materials. Here, we present experimental and theoretical results for conductance relaxation and aging for the case-study example of porous silicon. The relaxations are experimentally observed even at room temperature over time scales of hours, and when a strong electric field is applied for a time tw, the ensuing relaxation depends on tw. We derive a theoretical curve and show that all experimental data collapse onto it with a single time scale as a fitting parameter. This time scale is found to be of the order of thousands of seconds at room temperature. The generic theory suggested is not fine-tuned to porous silicon, and thus we believe the results should be universal, and the presented method should be applicable for many other systems manifesting memory and other glassy effects.
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-Wahnstrm 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
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-Wahnstrm 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.
A theoretical study of the stress relaxation in HMX on the picosecond time scale
NASA Astrophysics Data System (ADS)
Long, Yao; Chen, Jun
2015-12-01
The stress relaxation model of ?-HMX on the picosecond time scale is studied by a theoretical approach. The relaxation of normal stress is contributed by lattice vibration, and the relaxation of shear stress is contributed by molecular rotation. Based on this model, the energy dissipation rule of the elastic wave and the profile of the shock wave are investigated. We find at low frequency the dissipation rate of the elastic wave is proportional to the power function of frequency, and under high speed shock loading the width of the stress relaxation zone is less than 0.3 ?m there is a pressure peak with a height of 14 GPa near the wave front.
NASA Astrophysics Data System (ADS)
Kushima, A.; Eapen, J.; Li, Ju; Yip, S.; Zhu, T.
2011-08-01
Atomistic simulation methods are known for timescale limitations in resolving slow dynamical processes. Two well-known scenarios of slow dynamics are viscous relaxation in supercooled liquids and creep deformation in stressed solids. In both phenomena the challenge to theory and simulation is to sample the transition state pathways efficiently and follow the dynamical processes on long timescales. We present a perspective based on the biased molecular simulation methods such as metadynamics, autonomous basin climbing (ABC), strain-boost and adaptive boost simulations. Such algorithms can enable an atomic-level explanation of the temperature variation of the shear viscosity of glassy liquids, and the relaxation behavior in solids undergoing creep deformation. By discussing the dynamics of slow relaxation in two quite different areas of condensed matter science, we hope to draw attention to other complex problems where anthropological or geological-scale time behavior can be simulated at atomic resolution and understood in terms of micro-scale processes of molecular rearrangements and collective interactions. As examples of a class of phenomena that can be broadly classified as materials ageing, we point to stress corrosion cracking and cement setting as opportunities for atomistic modeling and simulations.
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.
Davis, M. J.; Skodje, R. T.; Chemistry; Univ. of Colorado
2001-01-01
A geometric approach to the study of multiple-time-scale kinetics is taken here. The approach to equilibrium for kinetic systems is studied via low-dimensional manifolds, with an application to a nonlinear master equation for vibrational relaxation. One of our main concerns is the asymptotic (in time) behavior of the system and whether there is a well-defined rate of approach to equilibrium. One-dimensional slow manifolds provide a good means for studying such behavior in nonlinear systems, because they are the analogue of the eigenvector with least negative eigenvalue for linear kinetics.
Messina, Fabrizio; Pomarico, Enrico; Silatani, Mahsa; Baranoff, Etienne; Chergui, Majed
2015-11-19
Using femtosecond-resolved photoluminescence up-conversion, we report the observation of the fluorescence of the high-lying ligand-centered (LC) electronic state upon 266 nm excitation of an iridium complex, Ir(ppy)3, with a lifetime of 70 10 fs. It is accompanied by a simultaneous emission of all lower-lying electronic states, except the lowest triplet metal-to-ligand charge-transfer ((3)MLCT) state that shows a rise on the same time scale. Thus, we observe the departure, the intermediate steps, and the arrival of the relaxation cascade spanning ?1.6 eV from the (1)LC state to the lowest (3)MLCT state, which then yields the long-lived luminescence of the molecule. This represents the first measurement of the total relaxation time over an entire cascade of electronic states in a polyatomic molecule. We find that the relaxation cascade proceeds in ?10 fs, which is faster than some of the highest-frequency modes of the system. We invoke the participation of the latter modes in conical intersections and their overdamping to low-frequency intramolecular modes. On the basis of literature, we also conclude that this behavior is not specific to transition-metal complexes but also applies to organic molecules. PMID:26509329
NASA Astrophysics Data System (ADS)
Colmenero, Juan; Alvarez, Fernando; Khairy, Yasmin; Arbe, Arantxa
2013-07-01
In a recent paper [V. N. Novikov, K. S. Schweizer, and A. P. Sokolov, J. Chem. Phys. 138, 164508 (2013)], 10.1063/1.4802771 a simple analytical ansatz has been proposed to describe the momentum transfer (Q) dependence of the collective relaxation time of glass-forming systems in a wide Q-range covering the region of the first maximum of the static structure factor S(Q) and the so-called intermediate length scale regime. In this work we have generalized this model in order to deal with glass-forming systems where the atomic diffusive processes are sub-linear in nature. This is for instance the case of glass-forming polymers. The generalized expression considers a sub-linear jump-diffusion model and reduces to the expression previously proposed for normal diffusion. The generalized ansatz has been applied to the experimental results of the Q- and temperature-dependence of polyisobutylene (PIB), which were previously published. To reduce the number of free parameters of the model to only one, we have taken advantage of atomistic molecular dynamics simulations of PIB properly validated by neutron scattering results. The model perfectly describes the experimental results capturing both, Q- and temperature-dependences. Moreover, the model also reproduces the experimental Q-dependence of the effective activation energy of the collective relaxation time in the temperature range of observation. This non-trivial result gives additional support to the way the crossover between two different relaxation mechanisms of density fluctuations is formulated in the model.
Orientational relaxation of aligned rod-like micelles on a time scale of 300 ms
NASA Astrophysics Data System (ADS)
Herbst, L.; Hoffmann, H.; Kalus, J.; Thurn, H.; Ibel, K.; May, R. P.
1986-04-01
Data on the time dependence of small-angle diffraction patterns of aligned rod-like micelles are presented. The system is a 20 mM solution of cetylpyridinium salicylate in D 2O in the presence of 20 mM NaCl. Under these conditions rod-like micelles are present which are more than 500 long. These micelles can be aligned by a shear gradient ?. The time dependence of the anisotropic neutron small-angle diffraction pattern is followed in time steps of 250 ms after a sudden reduction of ? to zero. The scattering curves can be fitted with a single fit parameter, the rotational diffusion coefficient D. The rotational diffusion coefficient turns out to be time dependent. This probably indicates an interaction between the charged micelles.
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.
Morón, María Carmen; Prada-Gracia, Diego; Falo, Fernando
2016-04-14
The decay dynamics of ambient and low temperature liquid water has been investigated through all-atom molecular dynamics simulations, residence times calculations and time correlation functions from 300 K down to 243 K. Those simulations replicate the experimental value of the self-diffusion constant as a function of temperature by tuning the damping factor of the Langevin equation of motion. A stretched exponential function exp[-(t/τ)(β)] has been found to properly describe the relaxation of residence times calculated at different temperatures for solvent molecules in a nanodrop of free water modelled as a sphere of nanometric dimensions. As the temperature goes down the decay time τ increases showing a divergence at Ts = 227 ± 3 K. The temperature independence of the dimensionless stretched exponent β = 0.59 ± 0.01 suggests the presence of, not a characteristic relaxation time (since β≠ 1), but a distribution of decay times that also holds at low temperature. An explanation for such heterogeneity can be found at the nanoscopic level. Moreover it can be concluded that the distribution of times already reported for the dynamics of water surrounding proteins (β≤ 0.5) can not be exclusively due to the presence of the biomolecule itself since isolated water also exhibits such behaviour. The above reported Ts and β values quantitatively reproduce experimental data. PMID:26782269
Time of relaxation in dusty plasma model
NASA Astrophysics Data System (ADS)
Timofeev, A. V.
2015-11-01
Dust particles in plasma may have different values of average kinetic energy for vertical and horizontal motion. The partial equilibrium of the subsystems and the relaxation processes leading to this asymmetry are under consideration. A method for the relaxation time estimation in nonideal dusty plasma is suggested. The characteristic relaxation times of vertical and horizontal motion of dust particles in gas discharge are estimated by analytical approach and by analysis of simulation results. These relaxation times for vertical and horizontal subsystems appear to be different. A single hierarchy of relaxation times is proposed.
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.
Relaxation time in disordered molecular systems
NASA Astrophysics Data System (ADS)
Rocha, Rodrigo P.; Freire, Jos 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.
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.
Relaxation time approximation for relativistic dense matter
Hakim, R.; Mornas, L.; Peter, P.; Sivak, H.D. )
1992-11-15
In this article the relaxation time approximation for a system of spin-1/2 fermions is studied with a view to calculating those transport properties obeyed by relativistic dense matter such as viscosity coefficients, thermal conductivities, spin diffusion, etc. This is achieved {ital via} the use of covariant Wigner functions. The collision term is, of course, linear in the deviation of the Wigner function from equilibrium, and {ital a} priori involves arbitrary functions of the four-momentum. These functions are restricted from physical arguments and from the requirement of Lorentz invariance. The kinetic equation obeyed by the Wigner function is then split into a mass-shell constraint and true'' kinetic equations, whose solution is sought within the Chapman-Enskog approximation. It is also realized that, in a relativistic quantum framework, there exist {ital two} expansion parameters: the new parameter occurs because of the existence of a new length scale defined by the Compton wavelength; in some cases (e.g., when the effective mass of the fermions goes to zero), this last quantity can be of the order of the mean free path. From the first-order solutions and from the Landau-Lifshitz matching conditions, the main transport properties of the system are obtained as functions of the macroscopic quantities (temperature, density, polarization) {ital and} of various relaxation times to be determined elsewhere by a specific physical model. Finally, all the results obtained are discussed and suggestions for some extensions are given.
A quantum relaxation-time approximation for finite fermion systems
Reinhard, P.-G.; Suraud, E.
2015-03-15
We propose a relaxation time approximation for the description of the dynamics of strongly excited fermion systems. Our approach is based on time-dependent density functional theory at the level of the local density approximation. This mean-field picture is augmented by collisional correlations handled in relaxation time approximation which is inspired from the corresponding semi-classical picture. The method involves the estimate of microscopic relaxation rates/times which is presently taken from the well established semi-classical experience. The relaxation time approximation implies evaluation of the instantaneous equilibrium state towards which the dynamical state is progressively driven at the pace of the microscopic relaxation time. As test case, we consider Na clusters of various sizes excited either by a swift ion projectile or by a short and intense laser pulse, driven in various dynamical regimes ranging from linear to strongly non-linear reactions. We observe a strong effect of dissipation on sensitive observables such as net ionization and angular distributions of emitted electrons. The effect is especially large for moderate excitations where typical relaxation/dissipation time scales efficiently compete with ionization for dissipating the available excitation energy. Technical details on the actual procedure to implement a working recipe of such a quantum relaxation approximation are given in appendices for completeness.
A quantum relaxation-time approximation for finite fermion systems
NASA Astrophysics Data System (ADS)
Reinhard, P.-G.; Suraud, E.
2015-03-01
We propose a relaxation time approximation for the description of the dynamics of strongly excited fermion systems. Our approach is based on time-dependent density functional theory at the level of the local density approximation. This mean-field picture is augmented by collisional correlations handled in relaxation time approximation which is inspired from the corresponding semi-classical picture. The method involves the estimate of microscopic relaxation rates/times which is presently taken from the well established semi-classical experience. The relaxation time approximation implies evaluation of the instantaneous equilibrium state towards which the dynamical state is progressively driven at the pace of the microscopic relaxation time. As test case, we consider Na clusters of various sizes excited either by a swift ion projectile or by a short and intense laser pulse, driven in various dynamical regimes ranging from linear to strongly non-linear reactions. We observe a strong effect of dissipation on sensitive observables such as net ionization and angular distributions of emitted electrons. The effect is especially large for moderate excitations where typical relaxation/dissipation time scales efficiently compete with ionization for dissipating the available excitation energy. Technical details on the actual procedure to implement a working recipe of such a quantum relaxation approximation are given in appendices for completeness.
Probing relaxation times in graphene quantum dots
Volk, Christian; Neumann, Christoph; Kazarski, Sebastian; Fringes, Stefan; Engels, Stephan; Haupt, Federica; Mller, Andr; 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 60100?ns. PMID:23612294
Mirror cosmological relaxation of the electroweak scale
NASA Astrophysics Data System (ADS)
Matsedonskyi, Oleksii
2016-01-01
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 109 GeV.
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.
Relaxation time measurements by an electronic method.
NASA Technical Reports Server (NTRS)
Brousseau, R.; Vanier, J.
1973-01-01
Description of a simple electronic system that permits the direct measurement of time constants of decaying signals. The system was used in connection with relaxation experiments on hydrogen and rubidium masers and was found to operate well. The use of a computing counter in the systems gives the possibility of making averages on several experiments and obtaining the standard deviation of the results from the mean. The program for the computing counter is given.
Scaling behaviour of relaxation dependencies in metaloxide superconductors
NASA Technical Reports Server (NTRS)
Sidorenko, A. S.; Panaitov, G. I.; Gabovich, A. M.; Moiseev, D. P.; Postnikov, V. M.
1990-01-01
Superconducting glass state has been investigated in different types of metaloxide ceramics, Y-Ba-Cu-O, Bi-Sr-Ca-Cu-O, Ba-Pb-Bi-O, using the highly sensitive SQUID magnetometer. The analysis of long-time relaxation processes of thermoremanent magnetization m(sup trm) (+) = M(sub o) - Slnt displayed scaling dependence of the decay rate S = -dM/dlnt on quantity of trapped magnetic flux M(sub o): 1gs = 31g M(sub o) - observed universal dependence S is approximately M(sup 3) (sub o) seems to one of the features of superconducting glass state in metaloxide ceramics.
Are vibrational relaxation times really constant? I. The vibrational relaxation of N 2O
NASA Astrophysics Data System (ADS)
Baalbaki, Z.; Teitelbaum, H.
1986-04-01
The vibrational relaxation of pure N 2O was studied behind shock waves in the temperature range 450-1750 K using a laser beam deflection technique. It is shown that the phenomenological relaxation time,?', is not a time-independent constant. Below 1200 K it increases with time; above 1200 K it decreases with time. The many disparate results in the literature are reconciled in terms of a mechanism whereby the step N 2O(0, 0, 0) ? N 2O(0, 1, 0) is rate determining at low temperatures when the ? 3 mode is not involved, and the parallel step N 2O(1, 0, 0) + N 2O(0, 0, 0) ? N 2O(0, 2, 0) + N 2O(0, 1, 0) takes over at high temperatures close to equilibrium. Rate constants for these processes are extracted from the limiting far-from equilibrium relaxation time, i.e. from ?'(0), where log p?'(0) = 11.0 T-1/3-1.67 (in atm ?s), and from the limiting near-equilibrium relaxation time, i.e. from ?'(?), where log p?'(?) = 19.4 T-1/3-2.46 (in atm ?s). The relaxation process was simulated by solving the master equation numerically. All energy levels up to 5930 cm -1 connected by all possible V?T and inter- and intra-molecular V?V processes were included, subject to the restriction that the energy gap ?? 700 cm -1. Microscopic rate coefficients, scaled according to ? exp(- C ??), were assigned, reducing the problem to one of three parameters: C (for V?T processes), CVV (for V?V processes) and k0110/ k10, where k10 is the rate constant for N 2O(0, 1, 0) ? N 2O(0, 0, 0) and k0110 that for N 2O(0, 0, 0) + N 2O(0, 1, 0) ? N 2O(0, 0, 0)+N 2O(0,1,0). Computer simulations of shock-induced and laser-induced relaxation are made. They are interpreted in terms of the three parameters. There was semi-quantitative agreement with our experimental results, which are consistent with values for C = 0.0038 cm at room temperature; CVV = 0.021 ? 0.0065 cm, and k0110/ k10 ? 5000 ? 12.7 in the range 300 ? 1800 K. It was further found that intermolecular V?V processes are responsible for the time dependence of ?', and that the increasing density of states accessible at longer times and at higher temperatures is responsible for the change in mechanism.
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 Stckelberg 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.
Charge relaxation resistance at atomic scale: An ab initio calculation
NASA Astrophysics Data System (ADS)
Wang, Bin; Wang, Jian
2008-06-01
We report an investigation of ac quantum transport properties of a nanocapacitor from first principles. At low frequencies, the nanocapacitor is characterized by a static electrochemical capacitance C? and the charge relaxation resistance Rq . We carry out a first principle calculation within the nonequilibrium Greens function formalism. In particular, we investigate charge relaxation resistance of a single carbon atom as well as two carbon atoms in a nanocapacitor made of a capped carbon nanotube (CNT) and an alkane chain connected to a bulk Si. The nature of charge relaxation resistance is predicted for this nanocapacitor. Specifically, we find that the charge relaxation resistance shows resonant behavior and it becomes sharper as the distance between plates of nanocapacitor increases. If there is only one transmission channel dominating the charge transport through the nanocapacitor, the charge relaxation resistance Rq is half of resistance quantum h/2e2 . This result shows that the theory of charge relaxation resistance applies at atomic scale.
Short-Time Beta Relaxation in Glass-Forming Liquids Is Cooperative in Nature
NASA Astrophysics Data System (ADS)
Karmakar, Smarajit; Dasgupta, Chandan; Sastry, Srikanth
2016-02-01
Temporal relaxation of density fluctuations in supercooled liquids near the glass transition occurs in multiple steps. Using molecular dynamics simulations for three model glass-forming liquids, we show that the short-time β relaxation is cooperative in nature. Using finite-size scaling analysis, we extract a growing length scale associated with beta relaxation from the observed dependence of the beta relaxation time on the system size. We find, in qualitative agreement with the prediction of the inhomogeneous mode coupling theory, that the temperature dependence of this length scale is the same as that of the length scale that describes the spatial heterogeneity of local dynamics in the long-time α -relaxation regime.
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.
Occupational Cohort Time Scales
Roth, H. Daniel
2015-01-01
Purpose: This study explores how highly correlated time variables (occupational cohort time scales) contribute to confounding and ambiguity of interpretation. Methods: Occupational cohort time scales were identified and organized through simple equations of three time scales (relational triads) and the connections between these triads (time scale web). The behavior of the time scales was examined when constraints were imposed on variable ranges and interrelationships. Results: Constraints on a time scale in a triad create high correlations between the other two time scales. These correlations combine with the connections between relational triads to produce association paths. High correlation between time scales leads to ambiguity of interpretation. Conclusions: Understanding the properties of occupational cohort time scales, their relational triads, and the time scale web is helpful in understanding the origins of otherwise obscure confounding bias and ambiguity of interpretation. PMID:25647318
2010-01-01
To study microsecond processes by relaxation dispersion NMR spectroscopy, low power deposition and short pulses are crucial and encourage the development of experiments that employ 1H Carr?Purcell?Meiboom?Gill (CPMG) pulse trains. Herein, a method is described for the comprehensive study of microsecond to millisecond time scale dynamics of methyl groups in proteins, exploiting their high abundance and favorable relaxation properties. In our approach, protein samples are produced using [1H, 13C]-d-glucose in ?100% D2O, which yields CHD2 methyl groups for alanine, valine, threonine, isoleucine, leucine, and methionine residues with high abundance, in an otherwise largely deuterated background. Methyl groups in such samples can be sequence-specifically assigned to near completion, using 13C TOCSY NMR spectroscopy, as was recently demonstrated (Otten, R.; et al. J. Am. Chem. Soc.2010, 132, 2952?2960). In this Article, NMR pulse schemes are presented to measure 1H CPMG relaxation dispersion profiles for CHD2 methyl groups, in a vein similar to that of backbone relaxation experiments. Because of the high deuteration level of methyl-bearing side chains, artifacts arising from proton scalar coupling during the CPMG pulse train are negligible, with the exception of Ile-?1 and Thr-?2 methyl groups, and a pulse scheme is described to remove the artifacts for those residues. Strong 13C scalar coupling effects, observed for several leucine residues, are removed by alternative biochemical and NMR approaches. The methodology is applied to the transcriptional activator NtrCr, for which an inactive/active state transition was previously measured and the motions in the microsecond time range were estimated through a combination of backbone 15N CPMG dispersion NMR spectroscopy and a collection of experiments to determine the exchange-free component to the transverse relaxation rate. Exchange contributions to the 1H line width were detected for 21 methyl groups, and these probes were found to collectively report on a local structural rearrangement around the phosphorylation site, with a rate constant of (15.5 0.5) 103 per second (i.e., ?ex = 64.7 1.9 ?s). The affected methyl groups indicate that, already before phosphorylation, a substantial, transient rearrangement takes place between helices 3 and 4 and strands 4 and 5. This conformational equilibrium allows the protein to gain access to the active, signaling state in the absence of covalent modification through a shift in a pre-existing dynamic equilibrium. Moreover, the conformational switching maps exactly to the regions that differ between the solution NMR structures of the fully inactive and active states. These results demonstrate that a cost-effective and quantitative study of protein methyl group dynamics by 1H CPMG relaxation dispersion NMR spectroscopy is possible and can be applied to study functional motions on the microsecond time scale that cannot be accessed by backbone 15N relaxation dispersion NMR. The use of methyl groups as dynamics probes extends such applications also to larger proteins. PMID:21058670
Cosmological Relaxation of the Electroweak Scale
NASA Astrophysics Data System (ADS)
Graham, Peter W.; Kaplan, David E.; Rajendran, Surjeet
2015-11-01
A new class of solutions to the electroweak hierarchy problem is presented that does not require either weak-scale dynamics or anthropics. Dynamical evolution during the early Universe drives the Higgs boson mass to a value much smaller than the cutoff. The simplest model has the particle content of the standard model plus a QCD axion and an inflation sector. The highest cutoff achieved in any technically natural model is 108 GeV .
Ultrafast relaxation rates and reversal time in disordered ferrimagnets
NASA Astrophysics Data System (ADS)
Suarez, O. J.; Nieves, P.; Laroze, D.; Altbir, D.; Chubykalo-Fesenko, O.
2015-10-01
In response to ultrafast laser pulses, single-phase metals have been classified as "fast" (with magnetization quenching on the time scale of the order of 100 fs and recovery in the time scale of several picoseconds and below) and "slow" (with longer characteristic time scales). Disordered ferrimagnetic alloys consisting of a combination of "fast" transition (TM) and "slow" rare-earth (RE) metals have been shown to exhibit an ultrafast all-optical switching mediated by the heat mechanism. The behavior of the characteristic time scales of coupled alloys is more complicated and is influenced by many parameters such as the intersublattice exchange, doping (RE) concentration, and the temperature. Here, the longitudinal relaxation times of each sublattice are analyzed within the Landau-Lifshitz-Bloch framework. We show that for moderate intersublattice coupling strength both materials slow down as a function of slow (RE) material concentration. For larger coupling, the fast (TM) material may become faster, while the slow (RE) one is still slower. These conclusions may have important implications in the switching time of disordered ferrimagnets such as GdFeCo with partial clustering. Using atomistic modeling, we show that in the moderately coupled case, the reversal would start in the Gd-rich region, while the situation may be reversed if the coupling strength is larger.
Origin of the relaxation time in dissipative fluid dynamics
Denicol, Gabriel S.; Noronha, Jorge; Niemi, Harri; Rischke, Dirk H.
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.
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.
Magnetic-field dependence of Brownian and Nel relaxation times
NASA Astrophysics Data System (ADS)
Dieckhoff, Jan; Eberbeck, Dietmar; Schilling, Meinhard; Ludwig, Frank
2016-01-01
The investigation of the rotational dynamics of magnetic nanoparticles in magnetic fields is of academic interest but also important for applications such as magnetic particle imaging where the particles are exposed to magnetic fields with amplitudes of up to 25 mT. We have experimentally studied the dependence of Brownian and Nel relaxation times on ac and dc magnetic field amplitude using ac susceptibility measurements in the frequency range between 2 Hz and 9 kHz for field amplitudes up to 9 mT. As samples, single-core iron oxide nanoparticles with core diameters between 20 nm and 30 nm were used either suspended in water-glycerol mixtures or immobilized by freeze-drying. The experimentally determined relaxation times are compared with theoretical models. It was found that the Nel relaxation time decays much faster with increasing field amplitude than the Brownian one. Whereas the dependence of the Brownian relaxation time on the ac and dc field amplitude can be well explained with existing theoretical models, a proper model for the dependence of the Nel relaxation time on ac field amplitude for particles with random distribution of easy axes is still lacking. The extrapolation of the measured relaxation times of the 25 nm core diameter particles to a 25 mT ac field with an empirical model predicts that the Brownian mechanism clearly co-determines the dynamics of magnetic nanoparticles in magnetic particle imaging applications, in agreement with magnetic particle spectroscopy data.
Femtosecond time-resolved electronic relaxation dynamics in tetrathiafulvalene
Staedter, D.; Polizzi, L.; Thiré, N.; 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.
Analysis of the Palierne model by relaxation time spectrum
NASA Astrophysics Data System (ADS)
Kwon, Mi Kyung; Cho, Kwang Soo
2016-02-01
Viscoelasticity of immiscible polymer blends is affected by relaxation of the interface. Several attempts have been made for linear viscoelasticity of immiscible polymer blends. The Palierne model (1990) and the Gramespacher-Meissner model (1992) are representative. The Gramespacher-Meissner model consists of two parts: ingredients and interface. Moreover, it provides us the formula of the peak of interface in weighted relaxation time spectrum, which enables us to analyze the characteristics relating to interface more obviously. However, the Gramespacher-Meissner model is a kind of empirical model. Contrary to the Gramespacher-Meissner model, the Palierne model was derived in a rigorous manner. In this study, we investigated the Palierne model through the picture of the Gramespacher-Meissner model. We calculated moduli of immiscible blend using two models and obtained the weighted relaxation time spectra of them. The fixed-point iteration of Cho and Park (2013) was used in order to determine the weighted relaxation spectra.
Measurement of longitudinal relaxation times for spin-decoupled protons.
NASA Technical Reports Server (NTRS)
Gerace, M. J.; Kuhlmann, K. F.
1972-01-01
Description of an experimental method for the determination of the longitudinal relaxation time for spin-decoupled protons by a modified version of the saturation recovery technique reported by Van Geet and Hume (1965). The described method should facilitate relaxation studies of chemically shifted protons (or fluorines) and can be applied to more complicated spin systems with the aid of triple resonance and noise-decoupling techniques.
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.
Multi-Relaxation Time Lattice Boltzmann Model for Multiphase Flows
NASA Astrophysics Data System (ADS)
Kuzmin, A.; Mohamad, A. A.; Succi, S.
Multi-relaxation time (MRT) for Lattice Boltzmann method is gaining renewed attention among researchers in the field. The advantage of such formulation over the widely popular single-time relaxation version, is twofold: better numerical stability and wider span of physical applications, extending to non-isotropic flows. In this work, the numerical advantages of the MRT model versus single-relaxation time (BGK) operator are quantitatively assessed through direct numerical simulations of droplet formation and capillary wave propagation on interphase boundaries. The results show that by proper tuning of the collision operator, and particularly of the higher-order kinetic modes (ghosts), appreciable improvements in stability limits, of the order of 20%, and viscosity limits, of the order of 80%, can be achieved. Moreover, a theoretical analysis accounting for the reasons behind such stability improvement, is also presented.
Time-dependent corona models - Scaling laws
NASA Technical Reports Server (NTRS)
Korevaar, P.; Martens, P. C. H.
1989-01-01
Scaling laws are derived for the one-dimensional time-dependent Euler equations that describe the evolution of a spherically symmetric stellar atmosphere. With these scaling laws the results of the time-dependent calculations by Korevaar (1989) obtained for one star are applicable over the whole Hertzsprung-Russell diagram and even to elliptic galaxies. The scaling is exact for stars with the same M/R-ratio and a good approximation for stars with a different M/R-ratio. The global relaxation oscillation found by Korevaar (1989) is scaled to main sequence stars, a solar coronal hole, cool giants and elliptic galaxies.
Nernst effect beyond the relaxation-time approximation
NASA Astrophysics Data System (ADS)
Pikulin, D. I.; Hou, Chang-Yu; Beenakker, C. W. J.
2011-07-01
Motivated by recent interest in the Nernst effect in cuprate superconductors, we calculate this magnetothermoelectric effect for an arbitrary (anisotropic) quasiparticle dispersion relation and elastic-scattering rate. The exact solution of the linearized Boltzmann equation is compared with the commonly used relaxation-time approximation. We find qualitative deficiencies in this approximation to the extent that it can get the sign wrong of the Nernst coefficient. Zimans improvement of the relaxation-time approximation, which becomes exact when the Fermi surface is isotropic, also cannot capture the combined effects of anisotropy in dispersion and scattering.
Subsecond pore-scale displacement processes and relaxation dynamics in multiphase flow
Armstrong, Ryan T; Ott, Holger; Georgiadis, Apostolos; Rcker, Maja; Schwing, Alex; Berg, Steffen
2014-01-01
With recent advances at X-ray microcomputed tomography (?CT) synchrotron beam lines, it is now possible to study pore-scale flow in porous rock under dynamic flow conditions. The collection of four-dimensional data allows for the direct 3-D visualization of fluid-fluid displacement in porous rock as a function of time. However, even state-of-the-art fast-?CT scans require between one and a few seconds to complete and the much faster fluid movement occurring during that time interval is manifested as imaging artifacts in the reconstructed 3-D volume. We present an approach to analyze the 2-D radiograph data collected during fast-?CT to study the pore-scale displacement dynamics on the time scale of 40 ms which is near the intrinsic time scale of individual Haines jumps. We present a methodology to identify the time intervals at which pore-scale displacement events in the observed field of view occur and hence, how reconstruction intervals can be chosen to avoid fluid-movement-induced reconstruction artifacts. We further quantify the size, order, frequency, and location of fluid-fluid displacement at the millisecond time scale. We observe that after a displacement event, the pore-scale fluid distribution relaxes to (quasi-) equilibrium in cascades of pore-scale fluid rearrangements with an average relaxation time for the whole cascade between 0.5 and 2.0 s. These findings help to identify the flow regimes and intrinsic time and length scales relevant to fractional flow. While the focus of the work is in the context of multiphase flow, the approach could be applied to many different ?CT applications where morphological changes occur at a time scale less than that required for collecting a ?CT scan. PMID:25745271
Phenomenological Theory of the Translational Relaxation Times in Gases
NASA Technical Reports Server (NTRS)
Zuckerwar, Allan J.
1999-01-01
The exact solution to the classical equations governing the translational dispersion and absorption of sound in a gas obscures its relaxational character because of its mathematical complexity. The approach taken here is to solve the secular equation by the method of Pade approximants, which even to the relatively low order R(sub 11) yields a remarkably close approximation to the exact solution over a wide range of frequency/pressure (f/P) ratios. As a result, translational relaxation can be formulated in terms of a conventional relaxation process with well-defined relaxation times, relaxation strength, collision numbers, additivity relations, etc. To extend the theory to high values of f/P ratio, a model is proposed to account for the noncontinuum behavior of the transport coefficients (viscosity and thermal conductivity) as the molecular mean free path approaches the acoustical enclosure dimensions. The theoretical dispersion and absorption show good agreement with measurements in argon over the classical and transition regions of f/P, but a discrepancy appears at higher values of f/P, where collective propagating modes, assumed in the theory, give way to single-particle modes, prevailing in the experiments.
Electron-ion relaxation time in moderately degenerate plasma
NASA Astrophysics Data System (ADS)
Vronskii, M. A.; Koryakina, Yu. V.
2015-09-01
A formula is derived for the electron-ion relaxation time in a partially degenerate plasma with electron-ion interaction via a central field. The resulting expression in the form of an integral of the transport cross section generalizes the well-known Landau and Brysk approximations.
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.
Wettability and T1 proton relaxation times of sandstone rocks.
Gogolashvili, E
1996-01-01
The spin-lattice relaxation times of water and hydrocarbon (hexane, benzene) protons in saturated model and natural core plug samples have been measured before and after their hydrophobization. The results do not show large differences between water-wet and oil-wet samples. PMID:8970135
Measurement of cyclotron resonance relaxation time in the two-dimensional electron system
Andreev, I. V. Muravev, V. M.; Kukushkin, I. V.; Belyanin, V. N.
2014-11-17
Dependence of cyclotron magneto-plasma mode relaxation time on electron concentration and temperature in the two-dimensional electron system in GaAs/AlGaAs quantum wells has been studied. Comparative analysis of cyclotron and transport relaxation time has been carried out. It was demonstrated that with the temperature increase transport relaxation time tends to cyclotron relaxation time. It was also shown that cyclotron relaxation time, as opposed to transport relaxation time, has a weak electron density dependence. The cyclotron time can exceed transport relaxation time by an order of magnitude in a low-density range.
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.
Relaxation-time limit of the multidimensional bipolar hydrodynamic model in Besov space
NASA Astrophysics Data System (ADS)
Li, Yeping; Zhang, Ting
In this paper, we study a multidimensional bipolar hydrodynamic model for semiconductors or plasmas. This system takes the form of the bipolar Euler-Poisson model with electric field and frictional damping added to the momentum equations. In the framework of the Besov space theory, we establish the global existence of smooth solutions for Cauchy problems when the initial data are sufficiently close to the constant equilibrium. Next, based on the special structure of the nonlinear system, we also show the uniform estimate of solutions with respect to the relaxation time by the high- and low-frequency decomposition methods. Finally we discuss the relaxation-time limit by compact arguments. That is, it is shown that the scaled classical solution strongly converges towards that of the corresponding bipolar drift-diffusion model, as the relaxation time tends to zero.
Hyperpolarized nanodiamond with long spin-relaxation times
NASA Astrophysics Data System (ADS)
Rej, Ewa; Gaebel, Torsten; Boele, Thomas; Waddington, David E. J.; Reilly, David J.
2015-10-01
The use of hyperpolarized agents in magnetic resonance, such as 13C-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 13C liquid-state compounds, which limit the time that the signal remains boosted. Here we demonstrate that 1.1% natural abundance 13C 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.
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 13C-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 13C liquid-state compounds, which limit the time that the signal remains boosted. Here we demonstrate that 1.1% natural abundance 13C 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
A Bayesian approach for relaxation times estimation in MRI.
Baselice, Fabio; Ferraioli, Giampaolo; Pascazio, Vito
2016-04-01
Relaxation time estimation in MRI field can be helpful in clinical diagnosis. In particular, T1 and T2 changes can be related to tissues modification, being an effective tool for detecting the presence of several pathologies and measure their development, thus their estimation is a useful research field. Currently, most techniques work pixel-wise, and transfer the noise reduction task to post processing filters. A novel method for estimating spin-spin and spin-lattice relaxation times is proposed. The approach exploits Markov Random Field theory for modeling the unknown data and implements an a posteriori estimator in the Bayesian framework. The effect is the joint parameters estimation and noise reduction. Proposed methodology, with respect to already existing techniques, is able to provide effective results while preserving details also in case of few acquisitions or severe signal to noise ratio. The algorithm has been tested on both simulated and real datasets. PMID:26596555
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
Liu, Huabing; Nogueira d'Eurydice, Marcel; Obruchkov, Sergei; Galvosas, Petrik
2014-09-01
Pore length scales and pore surface relaxivities of rock cores with different lithologies were studied on a 2MHz Rock Core Analyzer. To determine the pore length scales of the rock cores, the high eigenmodes of spin bearing molecules satisfying the diffusion equation were detected with optimized encoding periods in the presence of internal magnetic fields Bin. The results were confirmed using a 64MHz NMR system, which supports the feasibility of high eigenmode detection at fields as low as 2MHz. Furthermore, this methodology was combined with relaxometry measurements to a two-dimensional experiment, which provides correlation between pore length and relaxation time. This techniques also yields information on the surface relaxivity of the rock cores. The estimated surface relaxivities were then compared to the results using an independent NMR method. PMID:25123539
Dielectric relaxation, resonance and scaling behaviors in Sr3Co2Fe24O41 hexaferrite
NASA Astrophysics Data System (ADS)
Tang, Rujun; Jiang, Chen; Qian, Wenhu; Jian, Jie; Zhang, Xin; Wang, Haiyan; Yang, Hao
2015-08-01
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.
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
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
Diffusion MRI/NMR magnetization equations with relaxation times
NASA Astrophysics Data System (ADS)
de, Dilip; Daniel, Simon
2012-10-01
Bloch-Torrey diffusion magnetization equation ignores relaxation effects of magnetization. Relaxation times are important in any diffusion magnetization studies of perfusion in tissues(Brain and heart specially). Bloch-Torrey equation cannot therefore describe diffusion magnetization in a real-life situation where relaxation effects play a key role, characteristics of tissues under examination. This paper describes derivations of two equations for each of the y and z component diffusion NMR/MRI magnetization (separately) in a rotating frame of reference, where rf B1 field is applied along x direction and bias magnetic field(Bo) is along z direction. The two equations are expected to further advance the science & technology of Diffusion MRI(DMRI) and diffusion functional MRI(DFMRI). These two techniques are becoming increasingly important in the study and treatment of neurological disorders, especially for the management of patients with acute stroke. It is rapidly becoming a standard for white matter disorders, as diffusion tensor imaging (DTI) can reveal abnormalities in white matter fibre structure and provide models of brain connectivity.
Chiu, Chih-Chung; Hung, Chih-Chang; Chen, Chien-Lin; Cheng, Po-Yuan
2013-08-22
The charge-transfer (CT) state relaxation dynamics of the benzene-tetracyanoethylene (BZ-TCNE) complex was studied with broadband ultrafast time-resolved fluorescence spectroscopy implemented by optical Kerr gating in three solvents of different polarities. The CT state of the BZ-TCNE complex is reached via femtosecond laser excitation, and the subsequent temporal evolutions of the fluorescence spectra were measured. Analyses of various time-dependent spectral properties revealed rapid relaxations along solvent and vibrational coordinates in competition with charge recombination (CR). By comparing the results in solvents of different polarities, we partially separated solvation and vibrational relaxation dynamics and explored the solvent-dependent CR dynamics. Time-dependent dynamic fluorescence Stokes shift (TDFSS) measurements unveiled the solvation and vibrational relaxation contributions to the observed spectral relaxation. The biphasic and slow time scales of the vibrational contributions identified in TDFSS suggested nonstatistical and hindered intramolecular vibrational-energy redistribution that can be attributed to the unique structural properties of EDA complexes. The slowest spectral relaxation of 10-15 ps identified in TDFSS was ascribed to relaxation of the BZ(+)-TCNE(-) intermolecular vibrations, which is equivalent to a structural relaxation from the initial Franck-Condon configuration to the equilibrium CT-state structure. The time scales of vibrational relaxation indicate that a fraction of the CT-state population undergoes CR reactions before complete vibrational/structural equilibrium is achieved. In carbon tetrachloride, a nonexponential temporal profile was observed and attributed to vibrational nonequilibrium CR. In dichloromethane, polar solvation greatly accelerates CR reactions, and a slower reaction-field-induced structural relaxation gives rise to a pronounced biexponential decay. The equilibrium CR time constants of the BZ-TCNE CT state are 29 ps, 150 ps, and 68 ps in dichloromethane, carbon tetrachloride, and cyclohexane, respectively. PMID:23865400
Relaxation time based classification of magnetic resonance brain images
NASA Astrophysics Data System (ADS)
Baselice, Fabio; Ferraioli, Giampaolo; Pascazio, Vito
2015-03-01
Brain tissue classification in Magnetic Resonance Imaging is useful for a wide range of applications. Within this manuscript a novel approach for brain tissue joint segmentation and classification is presented. Starting from the relaxation time estimation, we propose a novel method for identifying the optimal decision regions. The approach exploits the statistical distribution of the involved signals in the complex domain. The technique, compared to classical threshold based ones, is able to improve the correct classification rate. The effectiveness of the approach is evaluated on a simulated case study.
Impact of Internal Magnetic Field Gradients on the NMR Relaxation Time Distribution
NASA Astrophysics Data System (ADS)
Grombacher, D. J.; Fay, E. L.; Knight, R. J.
2014-12-01
We explore the impact of internal magnetic field gradients, which arise due to the presence of a magnetic susceptibility contrast between grains and the pore fluid, on the relaxation time distribution. Relaxation times provide powerful insight into the pore geometry. This link to pore geometry relies on the fast-diffusion assumption, where relaxation is controlled by the pore surface and each pore is treated as isolated and is described by a single relaxation time. This allows the relaxation time distribution to be interpreted as a pore size distribution. However, internal gradients can complicate this interpretation by providing an additional relaxation mechanism impacting the decay. We present both synthetic and laboratory studies investigating the impact of internal gradients on the relaxation time distribution. A COMSOL multiphysics package is employed to determine the magnetic field's spatial distribution across the pore space, and to simulate the pore's NMR relaxation. The NMR simulation accounts for both surface relaxation, and relaxation related to internal gradients. We observe that as the influence of internal gradients increases, through either greater magnetic susceptibility contrasts or the use of longer echo times, the shape of the relaxation time distribution is altered. In these cases, relaxation within a single pore is no longer described by a single characteristic relaxation time, instead requiring multiple relaxation times to capture the time-dependent behavior. As a result, the relaxation time distribution is broadened and shifted to faster relaxation times. Laboratory results, performed for several samples sieved to ensure narrow grain size distributions and with varying magnitudes of magnetic susceptibility contrasts, exhibit similar trends to those observed in the synthetic studies. These results have significant implications for the interpretation of relaxation data to obtain pore size distributions, and the derived estimates of hydraulic conductivity for materials containing magnetic components.
NASA Astrophysics Data System (ADS)
Hanakata, Paul Z.; Douglas, Jack F.; Starr, Francis W.
2014-06-01
Thin polymer films are ubiquitous in manufacturing and medical applications, and there has been intense interest in how film thickness and substrate interactions influence film dynamics. It is appreciated that a polymer-air interfacial layer with enhanced mobility plays an important role in the observed changes and recent studies suggest that the length scale ? of this interfacial layer is related to film relaxation. In the context of the Adam-Gibbs and random first-order transition models of glass formation, these results provide indirect evidence for a relation between ? and the scale of collective molecular motion. Here we report direct evidence for a proportionality between ? and the average length L of string-like particle displacements in simulations of polymer films supported on substrates with variable interaction strength and rigidity. This relation explicitly links ? to the theoretical scale of cooperatively rearranging regions, offering a promising route to experimentally determine this scale of cooperative motion.
A 1-year time course study of the relaxation times and histology for irradiated rat lungs
Shioya, S.; Haida, M.; Fukuzaki, M.; Ono, Y.; Tsuda, M.; Ohta, Y.; Yamabayashi, H. )
1990-05-01
To investigate the NMR relaxation times for irradiated rat lung tissue, we measured T1 and T2 at 11 different times during the injury's 1-year time course. A biexponential analysis of T2 was used to determine T2 fast (T2f) and T2 slow (T2s). In addition, we measured water content and correlated changes in the relaxation times with pathological changes. The correlation indicates the following: (1) Shortly after irradiation, the biexponential T2 decay for 1/3 of the samples became monoexponential and there were no noticeable pathological changes observed using light microscopy. (2) During radiation pneumonitis, T2f and T2s were prolonged. This accompanied acute edematous changes and inflammatory cell infiltration. (3) Finally, during radiation fibrosis T1 shortened and collagen increased. We observed no significant correlation between relaxation time changes and water content changes throughout the 1-year time course.
Tailoring relaxation time spectrum in soft glassy materials.
Kaushal, Manish; Joshi, Yogesh M
2013-07-14
Physical properties of out of equilibrium soft materials depend on time as well as deformation history. In this work we propose to transform this major shortcoming into gain by applying controlled deformation field to tailor the rheological properties. We take advantage of the fact that deformation field of a certain magnitude can prevent particles in an aging soft glassy material from occupying energy wells up to a certain depth, thereby populating only the deeper wells. We employ two soft glassy materials with dissimilar microstructures and demonstrate that increase in strength of deformation field while aging leads to narrowing of spectrum of relaxation times. We believe that, in principle, this philosophy can be universally applied to different kinds of glassy materials by changing nature and strength of impetus. PMID:23862962
Magnetic resonance imaging (MRI) and relaxation time mapping of concrete
NASA Astrophysics Data System (ADS)
Beyea, Steven Donald
2001-07-01
The use of Magnetic Resonance Imaging (MRI) of water in concrete is presented. This thesis will approach the problem of MR imaging of concrete by attempting to design new methods, suited to concrete materials, rather than attempting to force the material to suit the method. A number of techniques were developed, which allow the spatial observation of water in concrete in up to three dimensions, and permits the determination of space resolved moisture content, as well as local NMR relaxation times. These methods are all based on the Single-Point Imaging (SPI) method. The development of these new methods will be described, and the techniques validated using phantom studies. The study of one-dimensional moisture transport in drying concrete was performed using SPI. This work examined the effect of initial mixture proportions and hydration time on the drying behaviour of concrete, over a period of three months. Studies of drying concrete were also performed using spatial mapping of the spin-lattice (T1) and effective spin-spin (T2*) relaxation times, thereby permitting the observation of changes in the water occupied pore surface-to-volume ratio (S/V) as a function of drying. Results of this work demonstrated changes in the S/V due to drying, hydration and drying induced microcracking. Three-dimensional MRI of concrete was performed using SPRITE (Single-Point Ramped Imaging with T1 Enhancement) and turboSPI (turbo Single Point Imaging). While SPRITE allows for weighting of MR images using T 1 and T2*, turboSPI allows T2 weighting of the resulting images. Using relaxation weighting it was shown to be possible to discriminate between water contained within a hydrated cement matrix, and water in highly porous aggregates, used to produce low-density concrete. Three dimensional experiments performed using SPRITE and turboSPI examined the role of self-dessication, drying, initial aggregate saturation and initial mixture conditions on the transport of moisture between porous aggregates and the hydrated matrix. The results demonstrate that water is both added and removed from the aggregates, depending upon the physical conditions. The images also appear to show an influx of cement products into cracks in the solid aggregate. (Abstract shortened by UMI.)
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
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.
An electronic time scale in chemistry
Remacle, F.; Levine, R. D.
2006-01-01
Ultrafast, subfemtosecond charge migration in small peptides is discussed on the basis of computational studies and compared with the selective bond dissociation after ionization as observed by Schlag and Weinkauf. The reported relaxation could be probed in real time if the removal of an electron could be achieved on the attosecond time scale. Then the mean field seen by an electron would be changing rapidly enough to initiate the migration. Tyrosine-terminated tetrapeptides have a particularly fast charge migration where in <1 fs the charge arrives at the other end. A femtosecond pulse can be used to observe the somewhat slower relaxation induced by correlation between electrons of different spins. A slower relaxation also is indicated when removing a deeper-lying valence electron. When a chromophoric amino acid is at one end of the peptide, the charge can migrate all along the peptide backbone up to the N end, but site-selective ionization is probably easier to detect for tryptophan than for tyrosine. PMID:16636279
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
U.S. Geological Survey
2012-01-01
This bookmark, designed for use with U.S. Geological Survey activities at the 2nd USA Science and Engineering Festival (April 2629, 2012), is adapted from the more detailed Fact Sheet 20103059 "Divisions of Geologic Time." The information that it presents is widely sought by educators and students.
NASA Astrophysics Data System (ADS)
Steiner, Emilie; Yemloul, Mehdi; Guendouz, Laous; Leclerc, Sbastien; Robert, Anthony; Canet, Daniel
2010-08-01
Relaxometry dispersion curves display the spin lattice relaxation rate as a function of the measurement frequency. However, as far as proton NMR is considered, dispersion curves usually start around 5 kHz and thus miss the very low frequency region. This gap can be filled by the measurement of the spin-lattice relaxation rate in the rotating frame. The issue of connecting both relaxation rates is considered for two relaxation mechanisms: (i) randomly varying magnetic fields, (ii) dipolar interaction within a system of two equivalent spins. Appropriate data processing is presented and the random field mechanism turns out to be adequate.
Multiple-relaxation-time lattice Boltzmann scheme for homogeneous mixture flows with external force
NASA Astrophysics Data System (ADS)
Asinari, Pietro
2008-05-01
A lattice Boltzmann scheme is developed for homogeneous mixture modeling, based on the multiple-relaxation-time (MRT) formulation, which fully recovers the Maxwell-Stefan diffusion model in the continuum limit with (a) external force and (b) tunable Schmidt number. The theoretical basis of the proposed MRT formulation is a recently proposed Bhatnagar-Gross-Krook-type kinetic model for gas mixtures [Andries , J. Stat. Phys. 106, 993 (2002)] and it substantially extends the applicability of a scheme already proposed by the same author, which used only one relaxation parameter. The recovered equations at the macroscopic level are derived by an innovative expansion technique, based on the Grad moment system. Some numerical simulations are reported for the solvent test case with external force, aiming to find the numerical ranges for the transport coefficients that ensure acceptable accuracies. The numerical results reduce the theoretical expectations, which are based on a strong separation among the characteristic scales.
Kanatharana, J.; Sukpisan, J.; Wang, S.Q.
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.
Unified Theory of Activated Relaxation in Cold Liquids over 14 Decades in Time
NASA Astrophysics Data System (ADS)
Schweizer, Kenneth; Mirigian, Stephen
2014-03-01
We formulate a predictive theory at the level of forces of activated relaxation in thermal liquids that covers in a unified manner the apparent Arrhenius, crossover and deeply supercooled regimes (J.Phys.Chem.Lett.4,3648(2013)). The alpha relaxation event involves coupled cage-scale hopping and a long range cooperative 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. The theory is devoid of fit parameters, has no divergences at finite temperature nor below jamming, and captures the key features of the alpha relaxation time in molecular liquids from picoseconds to hundreds of seconds. The approach is extended to polymer liquids based on the Kuhn length as the key variable. The influence of chain length and backbone stiffness on the glass transition temperature and fragility have been studied where degree of polymerization enters via corrections to asymptotic conformational statistics.
Similarity and scaling in creep and load relaxation of single-crystal halite (NaCl)
NASA Astrophysics Data System (ADS)
Stone, Donald S.; Plookphol, Thawatchai; Cooper, Reid F.
2004-12-01
This work explores the physical basis for Hart's mechanical equation of state in high-temperature plasticity. The experiments seek to identify a possible microstructural basis for the "hardness" parameters associated with load relaxation curves. The experiments also seek to examine the microstructural basis for scaling in load relaxation data and to explore the relationship between creep and load relaxation. Constant stress creep and load relaxation tests were conducted on [100] oriented single crystals of halite at 700C and stresses between 0.6 and 3 MPa. Load relaxation tests were performed at 400C up to a stress level of 13 MPa. After testing, specimens were sectioned, and dislocation densities and subgrain size distributions were measured. Results at 700C reveal that distributions of subgrain size in crystals crept at different stress levels are similar to each other; that is, they have the same shape but different average subgrain sizes depending on stress level. Hardness curves obtained from load relaxation experiments at different levels of work hardening were found to correspond to different average subgrain size. Load relaxation data from 700C and 400C belong to a single-parameter family of curves, with hardness curves translating onto each other with a scaling slope m = 0.33 0.05. Subgrain size distributions generated in creep are statistically identical to those from load relaxation. The hardness parameter, ?*, specified as the (apparent) high-strain rate limit of stress in the load relaxation data, is approximately 50Gb/DI, where G is the shear modulus, b is the Burgers vector, and DI is the mean intercept subgrain diameter. During creep under constant stress the subgrain size evolves until a steady value is approached. The experimental data lend credence to Hart's interpretation that load relaxation data represent (nearly) constant "structure" with subgrain size playing the role of the structural variable.
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.
Measuring Renal Tissue Relaxation Times at 7T
Li, Xiufeng; Bolan, Patrick J.; Ugurbil, Kamil; Metzger, Gregory J.
2014-01-01
As developments in RF coils and RF management strategies make performing ultrahigh field renal imaging feasible, understanding the relaxation times of the tissue becomes increasingly important for tissue characterization and sequence optimization. By using a magnetization prepared single breath-hold fast spin echo imaging method, human renal T1 and T2 imaging studies were successfully performed at 7T while addressing challenges of B1+ inhomogeneity and peak short-term specific absorption rate (SAR). At 7T, measured renal T1 values for the renal cortex and medulla (mean S.D.) were 1661 68 ms and 2094 67 ms, and T2 values were 108 7 ms and 126 6 ms. For comparison, similar measurements were made at 3T where renal cortex and medulla T1 values of 1261 86 ms and 1676 94 ms, and T2 values of 121 5 ms and 138 7 ms were obtained. Measurements at 3T and 7T were significantly different for both T1 and T2 values in both renal tissues. Reproducibility studies at 7T demonstrated that T1 and T2 estimations were robust with group mean percentage differences of less than 4%. PMID:25346367
Reconstruction of relaxation time distribution from linear electrochemical impedance spectroscopy
NASA Astrophysics Data System (ADS)
Zhang, Yanxiang; Chen, Yu; Yan, Mufu; Chen, Fanglin
2015-06-01
Linear electrochemical impedance spectroscopy (EIS), and in particular its representation of distribution of relaxation time (DRT), enables the identification of the number of processes and their nature involved in electrochemical cells. With the advantage of high frequency resolution, DRT has recently drawn increasing attention for applications in solid oxide fuel cells (SOFCs). However, the method of DRT reconstruction is not yet presented clearly in terms of what mathematical treatments and theoretical assumptions have been made. Here we present unambiguously a method to reconstruct DRT function of impedance based on Tikhonov regularization. By using the synthetic impedances and analytic DRT functions of RQ element, generalized finite length Warburg element, and Gerischer element with physical quantities representative to those of SOFC processes, we show that the quality of DRT reconstruction is sensitive to the sampling points per decade (ppd) of frequency from the impedance measurement. The robustness of the DRT reconstruction to resist noise imbedded in impedance data and numerical calculations can be accomplished by optimizing the weighting factor ? according to well defined criterion.
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 AdamGibbs 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 AdamGibbs 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)
Ogawa, M.; Yamamoto, S.; Fujikawa, K.; Hobara, R.; Yukawa, R.; Yamamoto, Sh.; Kitagawa, S.; Pierucci, D.; Silly, M. G.; Lin, C.-H.; Liu, R.-Y.; Daimon, H.; Sirotti, F.; Tang, S.-J.; Matsuda, I.
2013-10-01
We have systematically investigated relaxation of the surface photovoltage effect on the atomically controlled In/Si(111) surfaces with distinctive surface states and different amounts of the surface band bending. The temporal variations were traced in real time by time-resolved photoemission spectroscopy using soft x-ray synchrotron radiation. The relaxation is found to be temporally limited by two steps of the carrier transfer from the bulk to the surface: the tunneling process at a delay time ?100 ns and the thermionic process on the following time scale (?100 ns). Crossover of the two mechanisms can be understood by breakdown of the quantum tunneling regime by the increase in width of the space-charge layer during the relaxation.
Tuning of molecular qubits: very long coherence and spin-lattice relaxation times.
Bader, K; Winkler, M; van Slageren, J
2016-02-23
We report a pulsed EPR study on different transition metal phthalocyanines, elucidating the dependence of spin relaxation on solvent, ligand and metal ion. Coherence times of >40 µs and spin-lattice relaxation times of up to 2 s were found. Minimization of SOMO-environment overlap leads to increased coherence times. PMID:26854001
Time-domain spectrum of dielectric relaxation in relaxor ferroelectrics: Monte Carlo simulation
NASA Astrophysics Data System (ADS)
Liu, J.-M.; Dong, S.; Chan, H. L. W.; Choy, C. L.
2006-10-01
We perform Monte Carlo simulation on the dielectric relaxation behaviour of a model relaxor ferroelectric, based on the Ginzburg-Landau theory of ferroelectrics with dipole-defect induced random field. The coexistence of ferroelectric nanoclusters and paraelectric matrix is demonstrated. It is found that the time-domain spectrum for dielectric relaxation below the ferroelectric transition point exhibits a multi-peaked pattern rather than the diffusive single-peaked pattern, indicating the existence of multi-characteristic times for the dielectric relaxation. The extended multi-peaked time-domain spectrum is responsible for the diffusive ferroelectric transitions and frequency dispersion of the dielectric relaxation, usually observed for relaxor ferroelectrics.
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.
Time Course of Corticospinal Excitability and Intracortical Inhibition Just before Muscle Relaxation
Suzuki, Tomotaka; Sugawara, Kenichi; Ogahara, Kakuya; Higashi, Toshio
2016-01-01
Using transcranial magnetic stimulation (TMS), we investigated how short-interval intracortical inhibition (SICI) was involved with transient motor cortex (M1) excitability changes observed just before the transition from muscle contraction to muscle relaxation. Ten healthy participants performed a simultaneous relaxation task of the ipsilateral finger and foot, relaxing from 10% of their maximal voluntary contraction (MVC) force after the go signal. In the simple reaction time (RT) paradigm, single or paired TMS pulses were randomly delivered after the go signal, and motor evoked potentials (MEPs) were recorded from the right first dorsal interosseous (FDI) muscle. We analyzed the time course prior to the estimated relaxation reaction time (RRT), defined here as the onset of voluntary relaxation. SICI decreased in the 80–100 ms before RRT, and MEPs were significantly greater in amplitude in the 60–80 ms period before RRT than in the other intervals in single-pulse trials. TMS pulses did not effectively increase RRT. These results show that cortical excitability in the early stage, before muscle relaxation, plays an important role in muscle relaxation control. SICI circuits may vary between decreased and increased activation to continuously maintain muscle relaxation during or after a relaxation response. With regard to M1 excitability dynamics, we suggest that SICI also dynamically changes throughout the muscle relaxation process. PMID:26858619
Suzuki, Tomotaka; Sugawara, Kenichi; Ogahara, Kakuya; Higashi, Toshio
2016-01-01
Using transcranial magnetic stimulation (TMS), we investigated how short-interval intracortical inhibition (SICI) was involved with transient motor cortex (M1) excitability changes observed just before the transition from muscle contraction to muscle relaxation. Ten healthy participants performed a simultaneous relaxation task of the ipsilateral finger and foot, relaxing from 10% of their maximal voluntary contraction (MVC) force after the go signal. In the simple reaction time (RT) paradigm, single or paired TMS pulses were randomly delivered after the go signal, and motor evoked potentials (MEPs) were recorded from the right first dorsal interosseous (FDI) muscle. We analyzed the time course prior to the estimated relaxation reaction time (RRT), defined here as the onset of voluntary relaxation. SICI decreased in the 80-100 ms before RRT, and MEPs were significantly greater in amplitude in the 60-80 ms period before RRT than in the other intervals in single-pulse trials. TMS pulses did not effectively increase RRT. These results show that cortical excitability in the early stage, before muscle relaxation, plays an important role in muscle relaxation control. SICI circuits may vary between decreased and increased activation to continuously maintain muscle relaxation during or after a relaxation response. With regard to M1 excitability dynamics, we suggest that SICI also dynamically changes throughout the muscle relaxation process. PMID:26858619
Relaxation-time measurement via a time-dependent helicity balance model
Wrobel, J. S.; Hansen, C. J.; Jarboe, T. R.; Smith, R. J.; Hossack, A. C.; Nelson, B. A.; Marklin, G. J.; Ennis, D. A.; Akcay, C.; Victor, B. S.
2013-01-15
A time-dependent helicity balance model applied to a spheromak helicity-injection experiment enables the measurement of the relaxation time during the sustainment phase of the spheromak. The experiment, the Helicity Injected Torus with Steady Inductive helicity injection (HIT-SI), studies spheromak formation and sustainment through inductive helicity injection. The model captures the dominant plasma behavior seen during helicity injection in HIT-SI by using an empirical helicity-decay rate, a time-dependent helicity-injection rate, and a composite Taylor state to model both the helicity content of the system and to calculate the resulting spheromak current. During single-injector operations, both the amplitude and the phase of the periodic rise and fall of the toroidal current are predicted by this model, with an exchange of helicity between the injector states and the spheromak state proposed as the causal mechanism. This phenomenon allows for the comparison of the delay between the current rises in the experiment and the numerical model, enabling a measurement of the relaxation time. The measured relaxation time of 4.8 {mu}s {+-} 2.8 {mu}s is shorter than the toroidal Alfven timescale. These results validate Hall MHD calculations of the Geospace Environmental Modeling challenge.
Study of relaxation kinetics in argon afterglow by the breakdown time delay measurements
Markovic, V.Lj.; Gocic, S.R.; Stamenkovic, S.N.; Petrovic, Z.Lj.
2005-07-15
In this paper the afterglow kinetics in argon is studied by the breakdown time delay measurements as a function of relaxation time t{sub d}({tau}) ('memory curve'). Measurements were carried out at the pressure of 1.33 mbar in a gas tube with gold-plated copper cathode and approximate and exact numerical models are developed to follow metastable and charged particle decay. It was found that the early afterglow kinetics is governed by the charged particle decay up to hundreds of milliseconds, extending from ambipolar to the free diffusion limit. Quenching processes reduce the effective lifetime of metastable states several orders of magnitude below that relevant for the time scale of the observations if realistic abundances and processes are included in the model. Nitrogen atoms originating from impurities and recombining on the cathode surface can determine the breakdown time delay down to that defined by the level of cosmic rays and natural radioactivity.
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.
NASA Astrophysics Data System (ADS)
Casalini, R.; Roland, C. M.
2014-08-01
An equation is derived that expresses the thermodynamic scaling exponent, ?, which superposes relaxation times ? and other measures of molecular mobility determined over a range of temperatures and densities, in terms of static physical quantities. The latter are available in the literature or can be measured at ambient pressure. We show for 13 materials, both molecular liquids and polymers, that the calculated ? are equivalent to the scaling exponents obtained directly by superpositioning. The assumptions of the analysis are that the glass transition Tg is isochronal (i.e., ?? is constant at Tg, which is true by definition) and that the pressure derivative of the glass temperature is given by the first Ehrenfest relation. The latter, derived assuming continuity of the entropy at the glass transition, has been corroborated for many glass-forming materials at ambient pressure. However, we find that the Ehrenfest relation breaks down at elevated pressure; this limitation is of no consequence herein, since the appeal of the new equation is its applicability to ambient-pressure data. The ability to determine, from ambient-pressure measurements, the scaling exponent describing the high-pressure dynamics extends the applicability of this approach to a broader range of materials. Since ? is linked to the intermolecular potential, the new equation thus provides ready access to information about the forces between molecules.
Shores, D.A.; Stout, J.H.; Gerberich, W.W.
1992-06-01
The high temperature X-ray diffraction system developed for this program is being used to measure the strains which develop during oxidation. This is being applied to Ni/NiO and Cr/Cr[sub 2]O[sub 3]. Our work suggests tat the oxide and metal crystalline texture, anisotropic elastic modulus and anisotropic thermal expansion can have a pronounced effect on strain state of these systems. Acoustic emission is being used to study oxide scale failure (fracture) during oxidation. AE data from 304 stainless steel are being used to develop a statistical model of fracture process. Strength of metal/scale interface is an important property that has been difficult to quantify. Using Nano-indentation and scratch techniques developed for characterizing thin film interfaces, an effort has begun to measure the fracture toughness of the metal/scale interface. Mathematical modelling of origin and time evolution of growth stresses is an extension and improvement of previous models. The current effort employs a more sophisticated stress analysis and expands the scope to include other stress relaxation process. The interaction between the modeling studies and the X-ray diffraction measurements provides a natural credibility check to both efforts.
Flux ropes and 3D dynamics in the relaxation scaling experiment
NASA Astrophysics Data System (ADS)
Intrator, T. P.; Sun, X.; Dorf, L.; Sears, J. A.; Feng, Y.; Weber, T. E.; Swan, H. O.
2013-12-01
Flux ropes form basic building blocks for magnetic dynamics in many plasmas, are macroscopic analogues of magnetic field lines, and are irreducibly three dimensional (3D). We have used the relaxation scaling experiment (RSX) to study flux ropes, and have found many new features involving 3D dynamics, kink instability driven reconnection, nonlinearly stable but kinking flux ropes, and large flows.
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 μm 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.
Length scale of dynamic heterogeneity and its relation to time scales in a glass-forming liquid
NASA Astrophysics Data System (ADS)
Dasgupta, Chandan
2011-03-01
The role of the length scale of dynamic heterogeneity in the enormous increase in the relaxation times of glass-forming liquids upon supercooling has received much attention recently. Using molecular dynamics simulations and finite-size scaling for a realistic glass-forming liquid, we establish that the growth of dynamic heterogeneity with decreasing temperature is governed by a growing dynamic length scale. We also perform a computational study of a four-point structure factor, defined from spatial correlations of mobility, for the same liquid and show that estimates of the dynamic correlation length and susceptibility obtained from this study are consistent with the results of the finite-size scaling analysis. However, the observed dependence of the simultaneously growing time scale of the long-time ? -relaxation on system size does not exhibit the same scaling behavior as the dynamic heterogeneity: this time scale is instead determined, for all studied system sizes and temperatures, by the configurational entropy, in accordance with the Adam-Gibbs relation. We also investigate the dependence of the time scale of the short-time ? -relaxation on temperature and system size. A finite-size scaling analysis of this dependence reveals the existence of a length scale that grows as the temperature is reduced. Surprisingly, the temperature dependence of this length scale is found to be identical to that of the length scale that governs the growth of dynamic heterogeneity at the ? -relaxation time scale. This result suggests a close connection between short-time dynamics and dynamic heterogeneity at time scales of the order of the ? -relaxation time. This talk is based on work done in collaboration with S. Karmakar, S. Sastry and S. Sengupta.
Scaling of spin relaxation and angular momentum dissipation in permalloy nanowires
NASA Astrophysics Data System (ADS)
Moore, T. A.; Klui, M.; Heyne, L.; Mhrke, P.; Backes, D.; Rhensius, J.; Rdiger, U.; Heyderman, L. J.; Thiele, J.-U.; Woltersdorf, G.; Back, C. H.; Fraile Rodrguez, A.; Nolting, F.; Mentes, T. O.; Nio, M. .; Locatelli, A.; Potenza, A.; Marchetto, H.; Cavill, S.; Dhesi, S. S.
2009-10-01
We study the relationship between the damping (?) and the nonadiabaticity of the spin transport (?) in permalloy nanowires. ? is engineered by Ho doping, and from the characteristics of the current-induced domain-wall velocity, determined by high-resolution x-ray magnetic circular-dichroism photoemission electron microscopy, ? due to spin relaxation is measured. We find that ? scales with ? and conclude that the spin relaxation that leads to nonadiabatic spin torque originates from the same underlying mechanism as the angular momentum dissipation that causes viscous damping.
Tuncer, Enis; Bowler, Nicola; Youngs, I. J.; Lymer, K. P.
2006-01-01
The distribution of relaxation times approach, a less frequently employed dielectric data analysis technique, is utilized to better understand the relaxation characteristics of composites consisting of metal-coated, hollow glass spheres dispersed in a paraffin wax matrix. The dielectric properties of the composite samples are measured by means of impedance spectroscopy in the frequency range 0.1 mHz to 10 MHz. The application of a mixture law is not appropriate for the analysis of the frequency-dependent properties of the considered system on this broad frequency range. However, utilization of the distribution of relaxation times procedure to study the dielectric behaviour shows clear trends in the mixtures' relaxation spectra. Relaxation processes of the paraffin wax and those specific to the composites are found from the extracted distribution of relaxation times spectra. The influence of the filler concentration, q, on the dielectric properties is examined; a relaxation with a narrow distribution at intermediate frequencies becomes broad with the addition of the filler. This relaxation, in the form of the low-frequency-dispersions (also known as constant phase angle) phenomenon, dominates the dielectric properties of the composites with high bead concentration, q>0.15. The variation in dielectric properties of individual samples whose bead concentrations q are nominally the same is discussed in terms of possible microstructural variations.
Tuncer, Enis
2006-01-01
The distribution of relaxation times approach, a less frequently employed dielectric data analysis technique, is utilized to better understand the relaxation characteristics of composites consisting of metal-coated, hollow glass spheres dispersed in a paraffin wax matrix. The dielectric properties of the composite samples are measured by means of impedance spectroscopy in the frequency range 0.1mHz to 10 MHz. The application of a mixture law is not appropriate for the analysis of the frequency-dependent properties of the considered system on this broad frequency range. However, utilization of the distribution of relaxation times procedure to study the dielectric behaviour shows clear trends in the mixtures' relaxation spectra. Relaxation processes of the paraffin wax and those specific to the composites are found from the extracted distribution of relaxation times spectra. The influence of the filler concentration, q, on the dielectric properties is examined; a relaxation with a narrow distribution at intermediate frequencies becomes broad with the addition of the filler. This relaxation, in the form of the low-frequency-dispersions (also known as constant phase angle) phenomenon, dominates the dielectric properties of the composites with high bead concentration, q > 0:15. The variation in dielectric properties of individual samples whose bead concentrations q are nominally the same is discussed in terms of possible microstructural variations.
Variable thermal properties and thermal relaxation time in hyperbolic heat conduction
NASA Technical Reports Server (NTRS)
Glass, David E.; Mcrae, D. Scott
1989-01-01
Numerical solutions were obtained for a finite slab with an applied surface heat flux at one boundary using both the hyperbolic (MacCormack's method) and parabolic (Crank-Nicolson method) heat conduction equations. The effects on the temperature distributions of varying density, specific heat, and thermal relaxation time were calculated. Each of these properties had an effect on the thermal front velocity (in the hyperbolic solution) as well as the temperatures in the medium. In the hyperbolic solutions, as the density or specific heat decreased with temperature, both the temperatures within the medium and the thermal front velocity increased. The value taken for the thermal relaxation time was found to determine the 'hyperbolicity' of the heat conduction model. The use of a time dependent relaxation time allowed for solutions where the thermal energy propagated as a high temperature wave initially, but approached a diffusion process more rapidly than was possible with a constant large relaxation time.
Sykes, B D; Hull, W E; Snyder, G H
1978-01-01
Proton nuclear magnetic resonance (NMR) spin lattice relaxation time (T1) and spin-spin relaxation time (T2) measurements are presented for a number of proteins with molecular weights spanning the range of 6,500-150,000 daltons. These measurements provide experimental evidence for the role of cross-relaxation in 1H NMR T1 measurements in proteins. The relationship between these measurements and the theory recently presented by Kalk and Berendsen is discussed. The results indicate that cross-relaxation dominates the T1 measurements for the larger proteins, even at relatively low resonance frequencies such as 100 MHz. PMID:623862
NASA Astrophysics Data System (ADS)
Li, Jingliang; Zhao, Kongshuang; Liu, Chunyan
2013-04-01
Dielectric properties of poly(acrylic acid)-graft-poly(ethylene oxide) (PAA-g-PEO) aqueous solution were measured as a function of concentration and temperature over a frequency range of 40 Hz to 110 MHz. After subtracting the contribution of electrode polarization, three relaxation processes were observed at about 20 kHz, 220 kHz, and 4 MHz, and they are named low-, mid- and high-frequency relaxation, respectively. The relaxation parameters of these three relaxations (dielectric increment Δɛ and relaxation time τ) showed scaling relations with the polyelectrolyte concentration. The mechanisms of the three relaxations were concluded in light of the scaling theory: The relaxations of low- and mid frequency were attributed to the fluctuation of condensed counterions, while the high-frequency relaxation was ascribed to the fluctuation of free counterions. Based on the dielectric measurements of varying temperatures, the thermodynamic parameters (enthalpy change ΔH and entropy change ΔS) of the three relaxations were calculated and these relaxation processes were also discussed from the microscopic thermodynamical view. In addition, the impacts of PEO side chains on the conformation of PAA-g-PEO chains were discussed. PEO side chains greatly strengthen the hydrogen-bonding interactions between PAA-g-PEO chains, resulting in the chains overlapping at a very low concentration and the formation of a hydrogen-bonding complex. Some physicochemical parameters of PAA-g-PEO molecules were calculated, including the overlap concentration, the effective charge of the chain, the friction coefficient, and the diffusion coefficient of hydrogen counterions.
NASA Astrophysics Data System (ADS)
Garcia-Bernab, Abel; Dominguez-Espinosa, Gustavo; Diaz-Calleja, Ricardo; Riande, Evaristo; Haag, Rainer
2007-09-01
The non-Debye relaxation behavior of hyperbranched polyglycerol was investigated by broadband dielectric spectroscopy. A thorough study of the relaxations was carried out paying special attention to truncation effects on deconvolutions of overlapping processes. Hyperbranched polyglycerol exhibits two relaxations in the glassy state named in increasing order of frequency ? and ? processes. The study of the evolution of these two fast processes with temperature in the time retardation spectra shows that the ? absorption is swallowed by the ? in the glass-liquid transition, the ? absorption being the only relaxation that remains operative in the liquid state. In heating, a temperature is reached at which the ? absorption vanishes appearing the ?? relaxation. Two characteristics of ? absorptions, decrease of the dielectric strength with increasing temperature and rather high activation energy, are displayed by the ?? process. Williams' ansatz seems to hold for these topologically complex macromolecules.
Garcia-Bernab, Abel; Dominguez-Espinosa, Gustavo; Diaz-Calleja, Ricardo; Riande, Evaristo; Haag, Rainer
2007-09-28
The non-Debye relaxation behavior of hyperbranched polyglycerol was investigated by broadband dielectric spectroscopy. A thorough study of the relaxations was carried out paying special attention to truncation effects on deconvolutions of overlapping processes. Hyperbranched polyglycerol exhibits two relaxations in the glassy state named in increasing order of frequency beta and gamma processes. The study of the evolution of these two fast processes with temperature in the time retardation spectra shows that the beta absorption is swallowed by the alpha in the glass-liquid transition, the gamma absorption being the only relaxation that remains operative in the liquid state. In heating, a temperature is reached at which the alpha absorption vanishes appearing the alphagamma relaxation. Two characteristics of alpha absorptions, decrease of the dielectric strength with increasing temperature and rather high activation energy, are displayed by the alphagamma process. Williams' ansatz seems to hold for these topologically complex macromolecules. PMID:17902934
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. This work was sponsored by Stockpile Safety and Surety Program, the Joint DOD/DOE Munitions Technology Development Program, and National Nuclear Security Administrations Science Campaign 2.
Relaxation time ansatz and shear and bulk viscosities of gluon matter
Khvorostukhin, A. S.; Toneev, V. D.; Voskresensky, D. N.
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.
After stress comes relax(ation)
NASA Astrophysics Data System (ADS)
Isa, Lucio
2015-11-01
Viscoelastic materials take a finite time to relax and dissipate stress and this time scale is directly connected to the microstructure of the material itself. In their paper, Gomez-Solano and Bechinger (2015 New J. Phys. 17 103032) perform miniaturized mechanical tests on a range of viscoelastic materials by dragging a micron-sized bead across them using optical tweezers. Upon switching off all the external forces, they watch the bead recoil to its original position and by tracking its motion they pinpoint the relaxation time of the material. These experiments open up a new range of possibilities to characterize stress relaxation at the microscale just by watching it.
NASA Astrophysics Data System (ADS)
Mantz, A. B.; Allen, S. W.; Morris, R. G.; Schmidt, R. W.
2016-03-01
This is the third in a series of papers studying the astrophysics and cosmology of massive, dynamically relaxed galaxy clusters. Our sample comprises 40 clusters identified as being dynamically relaxed and hot (i.e. massive) in Papers I and II of this series. Here we consider the thermodynamics of the intracluster medium, in particular the profiles of density, temperature and related quantities, as well as integrated measurements of gas mass, average temperature, total luminosity and centre-excluded luminosity. We fit power-law scaling relations of each of these quantities as a function of redshift and cluster mass, which can be measured precisely and with minimal bias for these relaxed clusters using hydrostatic arguments. For the thermodynamic profiles, we jointly model the density and temperature and their intrinsic scatter as a function of radius, thus also capturing the behaviour of the gas pressure and entropy. For the integrated quantities, we also jointly fit a multidimensional intrinsic covariance. Our results reinforce the view that simple hydrodynamical models provide a good description of relaxed clusters outside their centres, but that additional heating and cooling processes are important in the inner regions (radii r ≲ 0.5 r2500 ≈ 0.15 r500). The thermodynamic profiles remain regular, with small intrinsic scatter, down to the smallest radii where deprojection is straightforward (˜20 kpc); within this radius, even the most relaxed systems show clear departures from spherical symmetry. Our results suggest that heating and cooling are continuously regulated in a tight feedback loop, allowing the cluster atmosphere to remain stratified on these scales.
Time Scales in Evolutionary Dynamics
NASA Astrophysics Data System (ADS)
Roca, Carlos P.; Cuesta, José A.; Sánchez, Angel
2006-10-01
Evolutionary game theory has traditionally assumed that all individuals in a population interact with each other between reproduction events. We show that eliminating this restriction by explicitly considering the time scales of interaction and selection leads to dramatic changes in the outcome of evolution. Examples include the selection of the inefficient strategy in the Harmony and Stag-Hunt games, and the disappearance of the coexistence state in the Snowdrift game. Our results hold for any population size and in more general situations with additional factors influencing fitness.
Role of potential-energy scaling in the low-temperature relaxation behavior of amorphous materials
NASA Astrophysics Data System (ADS)
Stillinger, Frank H.
1985-09-01
Under the assumption that the Kohlrausch-Williams-Watts (KWW) function describes relaxation near the glass transition for amorphous substances, implications are explored for the character of the many-body potential-energy function. The analysis proceeds in several stages: (1) The configuration space is uniquely divided into minimum-containing cells by a steepest-descent construction on the potential hypersurface. (2) Attention is confined to the amorphous region of configuration space by projecting out all cells containing local crystalline patterns. (3) The potential is separated into a hard-core part ?c and a ``soft'' remainder ?s. (4) ?s is coarse grained (smoothed) over a variable scale of lengths l. (5) A master equation is used to describe the relaxation spectrum subject to the interaction smoothed over any l. The demand that KWW relaxation emerge from the last constrains the statistical topography of ?s. Specifically it requires that on widely separated length scales, multiply branched channels of relatively modest elevation change must exist in ?s. Furthermore, the separating barriers between these channels tend to be largest in those portions of configuration space sampled by the system at the lowest temperatures, and to scale as lnl.
Kinking and merging of flux ropes in the Relaxation Scaling Experiment
NASA Astrophysics Data System (ADS)
Intrator, T.
2006-04-01
In solar, space, laboratory and astrophysics, magnetic fields and currents coexist, and frequently align and twist themselves into current ropes, and form the building blocks of magnetohydrodynamics (MHD). Their relaxation is bound up with the dynamics, which is omitted from the Taylor relaxation picture. For instance, magnetic fields and currents on the Sun are sheared and twisted as they store energy, experience instability, open into interplanetary space, eject the plasma trapped in them, and cause a flare. At LANL, the Relaxation Scaling Experiment (RSX) provides a simple means to systematically characterize the linear and non-linear evolution of driven, dissipative, unstable plasma-current filaments. The topology evolves in three dimensions, supports multiple modes, and can bifurcate to quasi-helical equilibria. We observe saturation to a helical state that is a candidate for a general relaxation process. We characterize experimentally magnetic structure of a kinking, rotating and merging flux ropes. We show that non line tied flux ropes are more unstable than line tied ones, i.e. at half the Kruskal-Shafranov threshold for J/B, and sketch a theoretical model for this. In collaboration with I. Furno, Los Alamos National Laboratory; D. Ryutov, Lawrence Livermore National Laboratory; L. Dorf, T. Nussinov, A. Light, and G. Lapenta, Los Alamos National Laboratory; and S. Abbate, Torino Politecnico.
Relativistic bulk viscosity in the relaxation time approximation: a chaotic velocities approach
NASA Astrophysics Data System (ADS)
Garca-Perciante, A. L.; Mndez, A. R.; Sandoval-Villalbazo, A.
2015-11-01
In this short note, the bulk viscosity for a high temperature dilute gas is calculated by applying the Chapman-Enskog method within Marle's relaxation time approximation. The expression for the stress-tensor established in Ref.[1], using explicitly the concept of chaotic velocity, is used in order to obtain the transport coefficient. The result is compared with previous expressions obtained by other authors using similar methods and emphasis is made on the agreement when a corrected relaxation parameter is considered.
Characteristic time scale of auroral electrojet data
Takalo, J.; Timonen, J.
1994-04-01
The authors study the different time scales which have been observed in the auroral electrojet (AE) data. Structure function data shows the AE time series experiences a scaling change with a time scale of approximately 2 hours. Autocorrelation measurements also reveal a characteristic time of close to two hours. The authors argue here for a relationship between these two times, and for a relationship between these two times and the time scale of breaks in the power spectrum of the AE data.
NASA Astrophysics Data System (ADS)
Liu, Qing; He, Ya-Ling
2015-11-01
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 interface is traced through the liquid fraction which is determined by the enthalpy-based method. The present 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.
Iwanowski, I; Leluk, K; Rudowski, M; Kaatze, U
2006-04-01
Shear viscosity and dynamic light scattering measurements as well as ultrasonic spectrometry studies of the nitroethane/3-methylpentane mixture of critical composition have been performed at various temperatures near the critical temperature, T(c). A combined evaluation of the shear viscosity and mutual diffusion coefficient data yielded the amplitude, xi(0), of the fluctuation correlation length, xi, assumed to follow power law, and the relaxation rate, Gamma, or order parameter fluctuations. The latter was found to follow power law with the theoretical universal exponent. The amplitudes xi(0) = 0.23 +/- 0.02 nm and Gamma(0) = (125 +/- 5) x 10(9) s(-1) nicely agree with literature values. Using the relaxation rates resulting from the viscosity and diffusion coefficient data, the scaling function has been calculated assuming the ultrasonic spectra to be composed of a critical part and a noncritical background contribution. The experimental scaling function fits well to the predictions of the Bhattacharjee-Ferrell dynamic scaling model with scaled half-attenuation frequency, Omega(BF)1/2= 2.1. The amplitude of the sonic spectra yields the amount |g| = 0.26 of the adiabatic coupling constant, g, in fair agreement with -0.29 from another thermodynamic relation. PMID:16571033
T2 Relaxation Time Mapping of the Cartilage Cap of Osteochondromas
Horn, Paul; Dardzinski, Bernard J.; Kim, Dong Hoon; Laor, Tal
2016-01-01
Objective Our aim was to evaluate the cartilage cap of osteochondromas using T2 maps and to compare these values to those of normal patellar cartilage, from age and gender matched controls. Materials and Methods This study was approved by the Institutional Review Board and request for informed consent was waived. Eleven children (ages 5-17 years) with osteochondromas underwent MR imaging, which included T2-weighted fat suppressed and T2 relaxation time mapping (echo time = 9-99/repetition time = 1500 msec) sequences. Lesion origins were femur (n = 5), tibia (n = 3), fibula (n = 2), and scapula (n = 1). Signal intensity of the cartilage cap, thickness, mean T2 relaxation times, and T2 spatial variation (mean T2 relaxation times as a function of distance) were evaluated. Findings were compared to those of patellar cartilage from a group of age and gender matched subjects. Results The cartilage caps showed a fluid-like high T2 signal, with mean thickness of 4.8 mm. The mean value of mean T2 relaxation times of the osteochondromas was 264.0 80.4 msec (range, 151.0-366.0 msec). Mean T2 relaxation times were significantly longer than the values from patellar cartilage (39.0 msec) (p < 0.0001). These findings were observed with T2 spatial variation plots across the entire distance of the cartilage cap, with the most pronounced difference in the middle section of the cartilage. Conclusion Longer T2 relaxation times of the cartilage caps of osteochondromas should be considered as normal, and likely to reflect an increased water content, different microstructure and component. PMID:26798229
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 80C. 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.
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.
Mitchell, J.; Chandrasekera, T. C.
2014-12-14
The nuclear magnetic resonance transverse relaxation time T{sub 2}, measured using the Carr-Purcell-Meiboom-Gill (CPMG) experiment, is a powerful method for obtaining unique information on liquids confined in porous media. Furthermore, T{sub 2} provides structural information on the porous material itself and has many applications in petrophysics, biophysics, and chemical engineering. Robust interpretation of T{sub 2} distributions demands appropriate processing of the measured data since T{sub 2} 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{sub e}{sup k} (where n is the number and t{sub e} 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 T{sub 2} 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.
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.
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.
Lee, Zhuo Qi; Hsu, Wen-Jing; Lin, Miao
2014-01-01
Biased random walk has been studied extensively over the past decade especially in the transport and communication networks communities. The mean first passage time (MFPT) of a biased random walk is an important performance indicator in those domains. While the fundamental matrix approach gives precise solution to MFPT, the computation is expensive and the solution lacks interpretability. Other approaches based on the Mean Field Theory relate MFPT to the node degree alone. However, nodes with the same degree may have very different local weight distribution, which may result in vastly different MFPT. We derive an approximate bound to the MFPT of biased random walk with short relaxation time on complex network where the biases are controlled by arbitrarily assigned node weights. We show that the MFPT of a node in this general case is closely related to not only its node degree, but also its local weight distribution. The MFPTs obtained from computer simulations also agree with the new theoretical analysis. Our result enables fast estimation of MFPT, which is useful especially to differentiate between nodes that have very different local node weight distribution even though they share the same node degrees. PMID:24699325
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.
NASA Astrophysics Data System (ADS)
Zhang, Xiang; Ai, Tinghua; Stoter, Jantien; Zhao, Xi
2014-06-01
The aim of matching spatial data at different map scales is to find corresponding objects at different levels of detail (LODs) that represent the same real-world phenomena. This is a prerequisite for integrating, evaluating and updating spatial data collected and maintained at various scales. However, matching spatial data is not straightforward due to the ambiguities caused by problems like many-to-many correspondence, non-systematic displacement and different LODs between data sets. This paper proposes an approach to matching areal objects (e.g. buildings) based on relaxation labeling techniques widely applied in pattern recognition and computer vision. The underlying idea is to utilize contextual information (quantified by compatibility coefficient) in an iterative process, where the ambiguities are reduced until a consistent matching is achieved. This paper describes (1) a domain-specific extension to previous relaxation schemes and (2) a new compatibility coefficient that exploits relative relationships between areal object pairs in spatial data. Our approach were validated through extensive experiments using building data sets at 1:10k and 1:50k as an example. Our contextual approach showed superior performance against a non-contextual approach in general and especially in ambiguous situations. The proposed approach can also be applied to matching other areal features and/or for a different scale range.
Relaxation-time limit in the multi-dimensional bipolar nonisentropic Euler-Poisson systems
NASA Astrophysics Data System (ADS)
Li, Yeping; Zhou, Zhiming
2015-05-01
In this paper, we consider the multi-dimensional bipolar nonisentropic Euler-Poisson systems, which model various physical phenomena in semiconductor devices, plasmas and channel proteins. We mainly study the relaxation-time limit of the initial value problem for the bipolar full Euler-Poisson equations with well-prepared initial data. Inspired by the Maxwell iteration, we construct the different approximation states for the case ?? = 1 and ? = 1, respectively, and show that periodic initial-value problems of the certain scaled bipolar nonisentropic Euler-Poisson systems in the case ?? = 1 and ? = 1 have unique smooth solutions in the time interval where the classical energy transport equation and the drift-diffusive equation have smooth solution. Moreover, it is also obtained that the smooth solutions converge to those of energy-transport models at the rate of ?2 and those of the drift-diffusive models at the rate of ?, respectively. The proof of these results is based on the continuation principle and the error estimates.
Time scales of magmatic processes
NASA Astrophysics Data System (ADS)
Hawkesworth, Chris; George, Rhiannon; Turner, Simon; Zellmer, Georg
2004-01-01
The development of improved analytical techniques has facilitated the application of short-lived isotopes to the study of magmatic processes, and resulted in a renewed interest in a number of other chronometers. Two approaches have been used to determine the time scales of magmatic processes. Isotopic dating provides absolute ages for the growth of mineral phases. This usually involves analyses of mineral separates such that the textural relations of the individual grains are difficult to establish. An exception is zircon, which can be analysed in situ. The second approach is to use relative chronometry based on major, trace element and isotope profiles in crystals that may have been modified by diffusion. These yield information on how long crystals were at a particular temperature, without indicating when this occurred. The ages are obtained on individual crystals, and so age distributions can be determined on different crystals from the same whole rock. The ages of crystals and the liquid, as represented by the groundmass, in an igneous rock can be different, and in a number of cases it has been shown that even the larger, and therefore typically older crystals formed after the fractional crystallisation responsible for the whole rock composition. One implication is that the processes of magma differentiation responsible for whole rock compositions may not necessarily be inferred from the compositional record of the larger crystals. Different approaches are therefore used to investigate the crystallisation history and the differentiation of magmatic suites. Crystallisation rates are 10 -10-10 -11 cm/s, whereas differentiation to high-silica magmas may take up to 210 5 years. The ages of crystals at the time of eruption can range back to 10 5-10 6 years, the older ages tend to be in the more evolved rock types, and it can take 10 5 years for high-silica magmas to be generated at individual volcanic centres. It appears that the generation of such evolved magmas is thermally controlled, for both fractional crystallisation and the generation of crustal melts, and the rates of fractional crystallisation can, for example, be linked to volcanic power outputs. If crystallisation is in response to magma degassing or decompression, it will be fast and there may be too little time for fractional crystallisation to take place.
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.
A multiple-relaxation-time lattice Boltzmann method for high-speed compressible flows
NASA Astrophysics Data System (ADS)
Li, Kai; Zhong, Cheng-Wen
2015-05-01
This paper presents a coupling compressible model of the lattice Boltzmann method. In this model, the multiple-relaxation-time lattice Boltzmann scheme is used for the evolution of density distribution functions, whereas the modified single-relaxation-time (SRT) lattice Boltzmann scheme is applied for the evolution of potential energy distribution functions. The governing equations are discretized with the third-order Monotone Upwind Schemes for scalar conservation laws finite volume scheme. The choice of relaxation coefficients is discussed simply. Through the numerical simulations, it is found that compressible flows with strong shocks can be well simulated by present model. The numerical results agree well with the reference results and are better than that of the SRT version. Project supported by the Innovation Fund for Aerospace Science and Technology of China (Grant No. 2009200066) and the Aeronautical Science Fund of China (Grant No. 20111453012).
Effective time-reversal symmetry breaking in the spin relaxation in a graphene quantum dot
NASA Astrophysics Data System (ADS)
Struck, Philipp; Burkard, Guido
2011-03-01
We study the relaxation of a single electron spin in a circular gate-tunable quantum dot in gapped graphene. Direct coupling of the spin to out-of-plane phonons via the intrinsic spin-orbit coupling leads to a lowered relaxation time T1 at intermediate B-fields. At low fields, T1 increases as ~B-2 due to the suppression of the phonon density of states at long wavelengths in a finite system. We also find that Rashba spin-orbit induced admixture of opposite spin states in combination with the emission of in-plane phonons provides various further relaxation channels via deformation potential and bond-length change. In the absence of valley mixing, spin relaxation takes place within each valley separately and thus time-reversal symmetry is effectively broken, thus inhibiting the van Vleck cancellation at B = 0 known from GaAs quantum dots. Both the absence of the van Vleck cancellation as well as the out-of-plane phonons lead to a behavior of the spin relaxation rate at low magnetic and intermediate fields which is markedly different from the known results for GaAs. At high fields there is a crossover to T1 ~B-2 or ~B-4 .
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.
Hot-electron energy relaxation time in Ga-doped ZnO films
Šermukšnis, E. Liberis, J.; Ramonas, M.; Matulionis, A.; Toporkov, M.; Liu, H. Y.; Avrutin, V.; Özgür, Ü.; Morkoç, H.
2015-02-14
Hot-electron energy relaxation time is deduced for Ga-doped ZnO epitaxial layers from pulsed hot-electron noise measurements at room temperature. The relaxation time increases from ∼0.17 ps to ∼1.8 ps when the electron density increases from 1.4 × 10{sup 17 }cm{sup −3} to 1.3 × 10{sup 20 }cm{sup −3}. A local minimum is resolved near an electron density of 1.4 × 10{sup 19 }cm{sup −3}. The longest energy relaxation time (1.8 ps), observed at the highest electron density, is in good agreement with the published values obtained by optical time-resolved luminescence and absorption experiments. Monte Carlo simulations provide a qualitative interpretation of our observations if hot-phonon accumulation is taken into account. The local minimum of the electron energy relaxation time is explained by the ultrafast plasmon-assisted decay of hot phonons in the vicinity of the plasmon–LO-phonon resonance.
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)
Bello, A.; Laredo, E.; Grimau, M.
1999-11-01
The existence of a distribution of relaxation times has been widely used to describe the relaxation function versus frequency in glass-forming liquids. Several empirical distributions have been proposed and the usual method is to fit the experimental data to a model that assumes one of these functions. Another alternative is to extract from the experimental data the discrete profile of the distribution function that best fits the experimental curve without any a priori assumption. To test this approach a Monte Carlo algorithm using the simulated annealing is used to best fit simulated dielectric loss data, ?''(?), generated with Cole-Cole, Cole-Davidson, Havriliak-Negami, and Kohlrausch-Williams-Watts (KWW) functions. The relaxation times distribution, G(ln(?)), is obtained as an histogram that follows very closely the analytical expression for the distributions that are known in these cases. Also, the temporal decay functions, ?(t), are evaluated and compared to a stretched exponential. The method is then applied to experimental data for ?-polyvinylidene fluoride over a temperature range 233 K<=T<=278 K and frequencies varying from 3 MHz to 0.001 Hz. These data show the existence of two relaxation processes: the fast segmental ?a process associated with the glass transition and a ?c mode, which is slower and due to changes in conformation that can occur in the crystalline regions. The experimental curves are fitted by the simulated annealing direct signal analysis procedure, and the relaxation times distributions are calculated and found to vary with temperature. The decay function is also evaluated and it shows clearly its bimodal character and a good agreement with a KWW function with a temperature dependent ? for each mode. The relaxation plots are drawn for each mode and the Vogel-Tammann-Fulcher and Arrhenius parameters are found. The fragility parameter for polyvinylidene flouride (PVDF) is found to be 87, which characterizes this polymer as a relatively structurally strong material.
NASA Astrophysics Data System (ADS)
Adrjanowicz, K.; Paluch, M.; Ngai, K. L.
2010-03-01
By using the dielectric relaxation method proposed recently by Casalini and Roland (2009 Phys. Rev. Lett. 102 035701), we were able to determine the structural ?-relaxation times deep in the glassy state of the pharmaceutical, Telmisartan. Normally, deep in the glassy state ?? is so long that it cannot be measured but ??, which is usually much shorter, can be directly determined. The method basically takes advantage of the connection between the ?-relaxation and the secondary ?-relaxation of the Johari-Goldstein kind, including a relation between their relaxation times ?? and ??, respectively. Thus, ?? of Telmisartan were determined by monitoring the change of the dielectric ?-loss, ?'', with physical aging time at temperatures well below the vitrification temperature. The values of ?? were compared with those expected by the coupling model (CM). Unequivocal comparison cannot be made in the case of Telmisartan because its ?-loss peak is extremely broad, and the CM predicts only an order of magnitude agreement between the primitive relaxation frequency and the ?-peak frequency. We also made an attempt to analyze all isothermal and aging susceptibility data after transformation into the electric modulus representation. The ?? found in the glass state by using the method of Casalini and Roland in the modulus representation are similar to those obtained in the susceptibility representation. However, it is remarkable that the stretching parameter ?KWW - M = 0.51 in the electric modulus representation gives more precise fits to the aging data than in the susceptibility representation with ?KWW = 0.61. Our results suggest that the electric modulus representation may be useful as an alternative to analyze aging data, especially in the case of highly polar glassformers having a large ratio of low frequency and high frequency dielectric constants, such as the Telmisartan studied.
Multi-scale freeform surface texture filtering using a mesh relaxation scheme
NASA Astrophysics Data System (ADS)
(Jane Jiang, Xiangqian; Abdul-Rahman, Hussein S.; Scott, Paul J.
2013-11-01
Surface filtering algorithms using Fourier, Gaussian, wavelets, etc, are well-established for simple Euclidean geometries. However, these filtration techniques cannot be applied to today's complex freeform surfaces, which have non-Euclidean geometries, without distortion of the results. This paper proposes a new multi-scale filtering algorithm for freeform surfaces that are represented by triangular meshes based on a mesh relaxation scheme. The proposed algorithm is capable of decomposing a freeform surface into different scales and separating surface roughness, waviness and form from each other, as will be demonstrated throughout the paper. Results of applying the proposed algorithm to computer-generated as well as real surfaces are represented and compared with a lifting wavelet filtering algorithm.
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.
Accelerated Relaxation of Sensitive Nuclei for Enhancement of Signal-to-Noise with Time
NASA Astrophysics Data System (ADS)
Homer, John; Perry, Michael C.; Palfreyman, Stuart A.
1997-03-01
A pulse sequence is proposed that accelerates the relaxation of sensitive nuclei through inverse polarization transfer from insensitive nuclei that have been subject to NOE during their detection: the sequence is designed to replace normal intersequence relaxation delays. Typically, for the observation of {1H}-13C, the13C relaxes during data acquisition and is enhanced by NOE from decoupled1H's. After data acquisition the13C polarization can be transferred to1H in order to step-jump accelerate the relaxation of1H and hence provide1H polarization more rapidly for transfer to13C during the next repetition of polarization-transfer sequences. It is suggested that the sequence (SNARE) can advantageously replace the relaxation delays in many common sequences. The benefits of so doing are illustrated using PENDANT and DEPT for13C investigations. Conditions for the implementation of SNARE are proposed, and it is demonstrated that there is a range of spectral-acquisition parameters of practical interest for which the method can be beneficial. Experimental time savings in achieving a chosenS/Ntypically exceed 30%.
Relaxation-Time Approximation for Analytical Evaluation of Temperature Field in Thermoacoustic Stack
NASA Astrophysics Data System (ADS)
Gusev, V.; Lotton, P.; Bailliet, H.; Job, S.; Bruneau, M.
2000-08-01
The problem of analytical description of temperature fields and heat fluxes in thermoacoustic devices (such as refrigerators and prime-movers) is discussed. It is demonstrated that for the precise analysis of the thermoacoustic process near the edges of the stacks and the heat exchangers, and also for the prediction of the heat fluxes between the stack and the heat exchangers, it is necessary to avoid the traditional 'mean-field' approximation. In other words, on the spatial scale of the order of a particle displacement in the standing acoustic wave, hydrodynamical (advective) transport of heat cannot be described as a diffusional transport with an effective (depending on the acoustic wave power) diffusivity. In order to get insight into the non-linear phenomena, related to axial (along the stack) advective transport of heat, the simplified description of the transverse heat exchange between the gas and the stack (the relaxation-time approximation) has been adopted in the present investigation. The analytical descriptions obtained of the temperature distribution and of the heat flux predict, in particular, that in some cases the thermoacoustic heat flux between two stacks separated by an adiabatic gap can increase with the increasing width of the gap.
NASA Astrophysics Data System (ADS)
Zhang, Yanxiang; Chen, Yu; Li, Mei; Yan, Mufu; Ni, Meng; Xia, Changrong
2016-03-01
A new Tikhonov regularization approach without adjusting parameters is proposed for reconstructing distribution of relaxation time (DRT). It is capable of eliminating the pseudo peaks and capturing discontinuities in the DRT, making it feasible to resolve the number and the nature of electrochemical processes without making assumptions.
Relaxation rate and scaling function of the critical system 3-methylpentane-nitroethane-cyclohexane.
Iwanowski, I; Mirzaev, S Z; Kaatze, U
2008-08-14
The critical system 3-methylpentane-nitroethane-cyclohexane (3-MP-NE-CH) has been investigated and compared to the limiting binary systems 3-MP-NE as well as NE-CH in order to study the degree of renormalization in the critical exponents of the ternary system. The solubility curves of the 3-MP-NE-CH system have been determined at various molar ratios of the nonpolar constituents in order to obtain the plait points as a function of mixture composition. At the col point (the mixture with the lowest transition temperature) and two further plait point compositions shear viscosity, dynamic light scattering, and frequency-dependent ultrasonic attenuation coefficient measurements have been performed as a function of temperature near the critical temperatures. The fluctuation correlation length and the relaxation rate of fluctuations display power law behavior as a function of reduced temperature, with universal critical exponents nu = 0.63 and nuZ(0) = 1.928, respectively, as characteristic for binary critical mixtures. In conformity with the 3-MP-NE and NE-CH critical mixtures the scaling function in the ultrasonic spectra nicely agrees with the empirical scaling function of the Bhattacharjee-Ferrell dynamic scaling theory. Hence with respect to power laws and scaling the 3-MP-NE-CH system behaves like a quasibinary mixture. The individual amplitudes of the relaxation rate show a minimum at the col point composition, corresponding with a maximum in the background viscosity of the liquids. The amount of the adiabatic coupling constant g, derived from the amplitudes in the ultrasonic spectra, increases monotonously when going from NE-CH (/g/ = 0.1) to 3-MP-NE (/g/ = 0.26). PMID:18715094
NASA Astrophysics Data System (ADS)
Vindigni, Alessandro
2008-03-01
The recently discovered Single-Chain Magnets can be considered a novel class of nanomagnets, representing the ultimate miniaturization limit of bistable magnetic nanowires. The name highlights the analogy with Single-Molecule Magnets: Both SMMs and SCMs show remanent magnetization in zero magnetic field due to slow dynamics, in spite of the reduced dimensionality (0D and 1D respectively) which forbids the occurrence of magnetic ordering. Beyond this common feature, the origin of slow dynamics is remarkably different. In particular, for a genuine 1D magnetic system slow dynamics at low temperature comes from the divergence of the relaxation time as the critical point, T=0, is approached. This scenario is actually encountered in SCMs at relatively high T in a regime where each spin chain behaves as if it were infinite. However, for a wide class of molecular chains (i) naturally occurring defects and (ii) non-collinearity between the single-spin anisotropy directions and the crystal axes break the site-by-site translational invariance along the chain. Both these phenomena affect slow relaxation. We will show how this fact can be accounted for through ad hoc extensions of Glauber dynamics. Different relaxation regimes are observed depending on the relationship between the correlation length and the actual distance between two defects, the lattice spacing and the domain-wall size.
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)
Mangeney, A.; Travnicek, P.
2003-12-01
In many situations observed in space plasmas, large MHD scales are believed to act as reservoir for a nonlinear cascade, bringing fluctuation energy to scales where kinetic processes (Landau or cyclotron resonnances) can transform them into thermal energy. These kinetic processes operate at smaller spatial scales and more rapid time scales, so that a numerical simulation describing both the nonlinear cascade and the kinetic processes were, untill recently, out of reach. The rapid increase of computing efficiency allows now to study the competition between these two processes in more realistic simulations. We present here 2D hybrid simulations (the protons are treated as particles and the electrons as a massless fluids) of the relaxation of an initially isotropic spectrum of Alfven waves. The dimensions achieved in these simulations can be as high as 1000x1000 cells in phsysical space ( and 1000 particles per cell), with a resolution of a few tenth of proton inertial lentgh (the electric resistivity being chosen so that the "magnetic Reynolds" number is of the order of 50-100). By changing the plasma beta and the typical wavelength of the initial perturbations, we vary the relative efficiency of the cascade processes and the cyclotron absorption. The results shows a subtle interplay between these two processes, which depend on the initial level of fluctuations (which fixes the nonlinear overturning time). We shall also discuss the relvance of these simulations for the heating of the outer corona and solar wind.
Stability of Rasch Scales over Time
ERIC Educational Resources Information Center
Taylor, Catherine S.; Lee, Yoonsun
2010-01-01
Item response theory (IRT) methods are generally used to create score scales for large-scale tests. Research has shown that IRT scales are stable across groups and over time. Most studies have focused on items that are dichotomously scored. Now Rasch and other IRT models are used to create scales for tests that include polytomously scored items.
NASA Astrophysics Data System (ADS)
Blair, A.; Daynes, N.; Hamilton, D.; Horne, G.; Heard, P. J.; Hodgson, D. Z. L.; Scott, T. B.; Shterenlikht, A.
2009-08-01
In this paper digital image correlation is used to measure relaxation of residual stresses across an interface. On the macro scale the method is applied to a tri-layer bonded aluminium sample, where the middle layer is in tension and the top and the bottom layers are in compression. High contrast speckle pattern was sprayed onto the surface. The relaxation was done with the slitting saw. Three dimensional image correlation was used. On the micro scale the technique was applied to a heat treated large grain brass loaded in tension. Mechanical and electro polishing was used for surface preparation. A focused ion beam was used for slitting across a grain boundary and for imaging. Grain orientation was measured using electron back-scattering diffraction. Two dimensional image correlation was employed. In all macro- and micro-scale experiments the range of measured relaxation was sub-pixel, almost at the limit of the resolution of the image correlation algorithms. In the macro-scale experiments, the limiting factor was low residual stress, due to low shear strength of the Araldite glue used for bonding. Finite element simulation of the relaxation agreed only qualitatively with the experimental results at both size scales. The methodology is intended for use with inverse methods, i.e. the measured relaxation is applied as the boundary conditions to an appropriate FE model which produces stresses equal to the relaxed residual stresses, but with opposite sign. The main conclusion is that the digital image correlation method could be used to measure relaxation caused by slitting in heterogeneous materials and structures at both macro- and micro-scales. However, the repeatability of the techniques needs to be improved before residual stresses can be determined confidently. Acknowledgments The authors gratefully acknowledge Airbus UK for provision of materials. They thank Dr Richard Burguete, Airbus UK, and Prof Peter Flewitt, Department of Physics, University of Bristol, for advice in all aspects of experimental work.
Maier, D; Marth, M; Honerkamp, J; Weese, J
1999-07-20
An important step in analyzing data from dynamic light scattering is estimating the relaxation time spectrum from the correlation time function. This estimation is frequently done by regularization methods. To obtain good results with this step, the statistical errors of the correlation time function must be taken into account [J. Phys. A 6, 1897 (1973)]. So far error models assuming independent statistical errors have been used in the estimation. We show that results for the relaxation time spectrum are better if correlation between statistical errors is taken into account. There are two possible ways to obtain the error sizes and their correlations. On the one hand, they can be calculated from the correlation time function by use of a model derived by Schtzel. On the other hand, they can be computed directly from the time series of the scattered light. Simulations demonstrate that the best results are obtained with the latter method. This method requires, however, storing the time series of the scattered light during the experiment. Therefore a modified experimental setup is needed. Nevertheless the simulations also show improvement in the resulting relaxation time spectra if the error model of Schtzel is used. This improvement is confirmed when a lattice with a bimodal sphere size distribution is applied to experimental data. PMID:18323954
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.
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.
Relaxation times of the two-phonon processes with spin-flip and spin-conserving in quantum dots
Wang, Zi-Wu; Liu, Lei; Li, Shu-Shen
2014-04-07
We perform a theoretical investigation on the two-phonon processes of the spin-flip and spin-conserving relaxation in quantum dots in the frame of the Huang-Rhys' lattice relaxation model. We find that the relaxation time of the spin-flip is two orders of magnitude longer than that of the spin-conserving, which is in agreement with previous experimental measurements. Moreover, the opposite variational trends of the relaxation time as a function of the energy separation for two-phonon processes are obtained in different temperature regime. The relaxation times display the oscillatory behaviors at the demarcation point with increasing magnetic field, where the energy separation matches the optical phonon energy and results in the optical phonon resonance. These results are useful in understanding the intraband levels' relaxation in quantum dots and could be helpful in designing photoelectric and spin-memory devices.
NASA Astrophysics Data System (ADS)
Kaminski, K.; Adrjanowicz, K.; Kaminska, E.; Paluch, M.
2011-06-01
Time-dependent isothermal dielectric measurements were carried out deeply in the glassy state on two very important saccharides: sucrose and trehalose. In both compounds two prominent secondary relaxation processes were identified. The faster one is an inherent feature of the whole family of carbohydrates. The slower one can also be detected in oligo- and polysaccharides. It was shown earlier that the ? process is the Johari-Goldstein (JG) relaxation coupled to motions of the glycosidic linkage, while the ? relaxation originates from motions of the exocyclic hydroxymethyl unit. Recently, it was shown that the JG relaxation process can be used to determine structural relaxation times in the glassy state [R. Casalini and C. M. Roland, Phys. Rev. Lett.PRLTAO0031-900710.1103/PhysRevLett.102.035701 102, 035701 (2009)]. In this paper we present the results of an analysis of the data obtained during aging using two independent approaches. The first was proposed by Casalini and Roland, and the second one is based on the variation of the dielectric strength of the secondary relaxation process during aging [J. K. Vij and G. Power, J. Non-Cryst. SolidsJNCSBJ0022-309310.1016/j.jnoncrysol.2010.07.067 357, 783 (2011)]. Surprisingly, we found that the estimated structural relaxation times in the glassy state of both saccharides are almost the same, independent of the type of secondary mode. This finding calls into question the common view that secondary modes of intramolecular origin do not provide information about the dynamics of the glassy state.
Time-resolved photoluminescence study of carrier relaxation dynamics in InAs/GaAs quantum dots
NASA Astrophysics Data System (ADS)
Yang, Weidong; Lee, Hao; Lowe-Webb, Roger R.; Sercel, Peter C.
1997-03-01
We report time-resolved photoluminescence studies of carrier relaxation dynamics in nanometer-scale self-organized InAs/GaAs quantum dots grown by molecular beam epitaxy [1]. While theoretical studies have suggested the possible existence of a phonon-bottleneck in quantum dot samples, we observe nanosecond luminescence decays with sub-nanosecond luminescence rise-times, using the technique of time-correlated single photon counting. These results suggests rapid carrier relaxation from excited states into the ground state recombination channel. Systematic time-resolved photoluminescence measurements of InAs/GaAs quantum dot structures taken at various temperatures and excitation energies are reported. The luminescence rise-times are found to depend on excitation energy, e.g., above-barrier excitation versus excitation into quantum dot excited states. This material is based upon work supported by the National Science Foundation under Grant No. DMR 9304537 and Army Research Office under Grant No. DAAH 04-95-1-0379. [1] G. Wang, S. Fafard, D. Leonard, J. E. Bowers, J. L. Merz and P. M. Petroff. Appl. Phys. Lett., Vol. 64, 2815 (1994).
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
Assink, Roger Alan; Mowery, Daniel Michael; Celina, Mathias Christopher
2004-09-01
Solid-state {sup 1}H NMR relaxometry studies were conducted on a hydroxy-terminated polybutadiene (HTPB) based polyurethane elastomer thermo-oxidatively aged at 80 C. The {sup 1}H T{sub 1}, T{sub 2}, and T{sub 1{rho}} relaxation times of samples thermally aged for various periods of time were determined as a function of NMR measurement temperature. The response of each measurement was calculated from a best-fit linear function of the relaxation time vs. aging time. It was found that the T{sub 2,H} and T{sub 1{rho},H} relaxation times exhibited the largest response to thermal degradation, whereas T{sub 1,H} showed minimal change. All of the NMR relaxation measurements on solid samples showed significantly less sensitivity to thermal aging than the T{sub 2,H} relaxation times of solvent-swollen samples.
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
Relationships between induced polarization relaxation time and hydraulic properties of sandstone
NASA Astrophysics Data System (ADS)
Titov, Konstantin; Tarasov, Andrey; Ilyin, Yuri; Seleznev, Nikita; Boyd, Austin
2010-03-01
We investigated electrical and physical-chemical properties of six sandstone samples with contrasting mineralogical characteristics and with hydraulic conductivity varying in a wide range. The electrical data were obtained from time domain spectral induced polarization (IP) measurements. We inverted the IP decays to relaxation time distributions, and then compared the modal relaxation times with the dominant pore throat diameters obtained from the Mercury Injection Capillary Pressure (MICP) data. We found a positive logarithmic relationship between the relaxation time and the pore throat diameter. Also, we found the normalized chargeability (an integral IP parameter) to be positively correlated with the clay content. These two results suggest that the polarization of our sandstones is controlled by the pore throat distribution, and by the clay content. The logarithmic relationship contradicts previous theories, and is not universal. Adopting an approach of Kruschwitz and her co-workers, we calculated the effective diffusivity from IP and MICP data, and we found the effective diffusivity values ranging from 2.9 10-13 to 1.6 10-10 m2s-1. High diffusivity values, typical of surface diffusion, were obtained for clean sandstones. Low diffusivity values were obtained for clayey sandstones, and they were one to two orders of magnitude lower than those characteristic of the surface diffusion. We proposed two mechanisms to explain the `slow' diffusion: (1) the effect of surface tortuosity of pore throats filled with clay minerals and (2) the effect of pore geometry. These two effects represent an obstacle in assessing the pore throat diameter and hydraulic conductivity of sandstones with large specific surface and clay content on the basis of spectral IP measurements. However, we believe that the sandstones featuring `slow' diffusion can be discriminated based on the integral polarization parameters, and that the relaxation time remains a valuable parameter for assessing hydraulic properties of clean sandstones.
Estimation of stress relaxation time for normal and abnormal breast phantoms using optical technique
NASA Astrophysics Data System (ADS)
Udayakumar, K.; Sujatha, N.
2015-03-01
Many of the early occurring micro-anomalies in breast may transform into a deadliest cancer tumor in future. Probability of curing early occurring abnormalities in breast is more if rightly identified. Even in mammogram, considered as a golden standard technique for breast imaging, it is hard to pick up early occurring changes in the breast tissue due to the difference in mechanical behavior of the normal and abnormal tissue when subjected to compression prior to x-ray or laser exposure. In this paper, an attempt has been made to estimate the stress relaxation time of normal and abnormal breast mimicking phantom using laser speckle image correlation. Phantoms mimicking normal breast is prepared and subjected to precise mechanical compression. The phantom is illuminated by a Helium Neon laser and by using a CCD camera, a sequence of strained phantom speckle images are captured and correlated by the image mean intensity value at specific time intervals. From the relation between mean intensity versus time, tissue stress relaxation time is quantified. Experiments were repeated for phantoms with increased stiffness mimicking abnormal tissue for similar ranges of applied loading. Results shows that phantom with more stiffness representing abnormal tissue shows uniform relaxation for varying load of the selected range, whereas phantom with less stiffness representing normal tissue shows irregular behavior for varying loadings in the given range.
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.
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.
Park, Sang-Won; Kim, Soree; Jung, YounJoon
2015-11-21
We study how dynamic heterogeneity in ionic liquids is affected by the length scale of structural relaxation and the ionic charge distribution by the molecular dynamics simulations performed on two differently charged models of ionic liquid and their uncharged counterpart. In one model of ionic liquid, the charge distribution in the cation is asymmetric, and in the other it is symmetric, while their neutral counterpart has no charge with the ions. It is found that all the models display heterogeneous dynamics, exhibiting subdiffusive dynamics and a nonexponential decay of structural relaxation. We investigate the lifetime of dynamic heterogeneity, ?(dh), in these systems by calculating the three-time correlation functions to find that ?(dh) has in general a power-law behavior with respect to the structural relaxation time, ?(?), i.e., ?(dh) ? ?(?)(?(dh)). Although the dynamics of the asymmetric-charge model is seemingly more heterogeneous than that of the symmetric-charge model, the exponent is found to be similar, ?(dh) ? 1.2, for all the models studied in this work. The same scaling relation is found regardless of interactions, i.e., with or without Coulomb interaction, and it holds even when the length scale of structural relaxation is long enough to become the Fickian diffusion. This fact indicates that ?(dh) is a distinctive time scale from ?(?), and the dynamic heterogeneity is mainly affected by the short-range interaction and the molecular structure. PMID:26467181
Enthalpy Relaxation of a DGEBA Epoxy as a function of Time, Temperature, and Cooling Rate
NASA Astrophysics Data System (ADS)
Clarkson, Caitlyn M.; McCoy, John D.; Kropka, Jamie M.
2015-03-01
Enthalpy relaxation resulting from physical aging of a DGEBA epoxy, Epon 828, cross-linked with an amine curative, Jeffamine T-403, was studied for two isothermal aging temperatures at sequential aging times up to two weeks. Results were analyzed using the peak shift method to obtain the relaxation parameters ?, ? (H*), and ?. The individual effects of cooling rate from the equilibrated state, aging time, and aging temperature were isolated to understand the initial state of the glassy epoxy and its evolution during physical aging. [Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.
In-vivo T2-relaxation times of asymptomatic cervical intervertebral discs.
Driscoll, Sean J; Zhong, Weiye; Torriani, Martin; Mao, Haiqing; Wood, Kirkham B; Cha, Thomas D; Li, Guoan
2016-03-01
Limited research exists on T2-mapping techniques for cervical intervertebral discs and its potential clinical utility. The objective of this research was to investigate the in-vivo T2-relaxation times of cervical discs, including C2-C3 through C7-T1. Ten asymptomatic subjects were imaged using a 3.0T MR scanner and a sagittal multi-slice multi-echo sequence. Using the mid-sagittal image, intervertebral discs were divided into five regions-of-interest (ROIs), centered along the mid-line of the disc. Average T2 relaxation time values were calculated for each ROI using a mono-exponential fit. Differences in T2 values between disc levels and across ROIs of the same disc were examined. For a given ROI, the results showed a trend of increasing relaxation times moving down the spinal column, particularly in the middle regions (ROIs 2, 3 and 4). The C6-C7 and C7-T1 discs had significantly greater T2 values compared to superior discs (discs between C2 and C6). The results also showed spatial homogeneity of T2 values in the C3-C4, C4-C5, and C5-C6 discs, while C2-C3, C6-C7, and C7-T1 showed significant differences between ROIs. The findings indicate there may be inherent differences in T2-relaxation time properties between different cervical discs. Clinical evaluations utilizing T2-mapping techniques in the cervical spine may need to be level-dependent. PMID:26643385
T2 Relaxation Time Quantitation Differs Between Pulse Sequences in Articular Cartilage
Matzat, Stephen J.; McWalter, Emily J.; Kogan, Feliks; Chen, Weitian; Gold, Garry E.
2015-01-01
Background To compare T2 relaxation time measurements between MR pulse sequences at 3 Tesla in agar phantoms and in vivo patellar, femoral, and tibial articular cartilage. Methods T2 relaxation times were quantified in phantoms and knee articular cartilage of eight healthy individuals using a single echo spin echo (SE) as a reference standard and five other pulse sequences: multi-echo SE (MESE), fast SE (2D-FSE), magnetization-prepared spoiled gradient echo (3D-MAPSS), three-dimensional (3D) 3D-FSE with variable refocusing flip angle schedules (3D vfl-FSE), and quantitative double echo steady state (qDESS). Cartilage was manually segmented and average regional T2 relaxation times were obtained for each sequence. A regression analysis was carried out between each sequence and the reference standard, and root-mean-square error (RMSE) was calculated. Results Phantom measurements from all sequences demonstrated strong fits (R2>0.8; P<0.05). For in vivo cartilage measurements, R2 values, slope, and RMSE were: MESE: 0.25/0.42/5.0 ms, 2D-FSE: 0.64/1.31/9.3 ms, 3D-MAPSS: 0.51/0.66/3.8 ms, 3D vfl-FSE: 0.30/ 0.414.2 ms, qDESS: 0.60/0.90/4.6 ms. Conclusion 2D-FSE, qDESS, and 3D-MAPSS demonstrated the best fits with SE measurements as well as the greatest dynamic ranges. The 3D-MAPSS, 3D vfl-FSE, and qDESS demonstrated the closest average measurements to SE. Discrepancies in T2 relaxation time quantitation between sequences suggest that care should be taken when comparing results between studies. PMID:25244647
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)(Tage). The dependence of ??(Tage,tage) on tage is well described by the stretched exponential function, ??(Tage, tage) = Aexp[-((tage)/(?age(Tage)))(?)] + ??(eq)(Tage), 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)(Tage) obtained after 63 days long annealing of CP, deviates from the Vogel-Fulcher-Tammann-Hesse (VFTH?) dependence of ??(T) determined from data taken above Tg and extrapolated down to Tage. Concurrently, ?age(Tage) also deviates from the Vogel-Fulcher-Tammann-Hesse (VFTH?) dependence. The results help to answer the longstanding question of whether the VFTH dependence of ??(T) as well as the structural ?-relaxation time ??(T) holds or not in the equilibrium liquid state far below Tg. PMID:24811641
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.
Time scale evolution of avipoxviruses.
Le Loc'h, Guillaume; Bertagnoli, Stphane; 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 2-810(-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
Driscoll, J.R. ); Gabow, H.N.; Shrairman, R. ); Tarjan, R.E. )
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.
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.
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.
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.
NASA Astrophysics Data System (ADS)
Wilkinson, Iain; Boguslavskiy, Andrey E.; Mikosch, Jochen; Bertrand, Julien B.; Wörner, Hans Jakob; Villeneuve, David M.; Spanner, Michael; Patchkovskii, Serguei; Stolow, Albert
2014-05-01
The excited state dynamics of isolated sulfur dioxide molecules have been investigated using the time-resolved photoelectron spectroscopy and time-resolved photoelectron-photoion coincidence techniques. Excited state wavepackets were prepared in the spectroscopically complex, electronically mixed ({tildeB})1B1/(Ã)1A2, Clements manifold following broadband excitation at a range of photon energies between 4.03 eV and 4.28 eV (308 nm and 290 nm, respectively). The resulting wavepacket dynamics were monitored using a multiphoton ionisation probe. The extensive literature associated with the Clements bands has been summarised and a detailed time domain description of the ultrafast relaxation pathways occurring from the optically bright ({tildeB})1B1 diabatic state is presented. Signatures of the oscillatory motion on the ({tildeB})1B1/(Ã)1A2 lower adiabatic surface responsible for the Clements band structure were observed. The recorded spectra also indicate that a component of the excited state wavepacket undergoes intersystem crossing from the Clements manifold to the underlying triplet states on a sub-picosecond time scale. Photoelectron signal growth time constants have been predominantly associated with intersystem crossing to the ({tildec})3B2 state and were measured to vary between 750 and 150 fs over the implemented pump photon energy range. Additionally, pump beam intensity studies were performed. These experiments highlighted parallel relaxation processes that occurred at the one- and two-pump-photon levels of excitation on similar time scales, obscuring the Clements band dynamics when high pump beam intensities were implemented. Hence, the Clements band dynamics may be difficult to disentangle from higher order processes when ultrashort laser pulses and less-differential probe techniques are implemented.
Shores, D.A.; Stout, J.H.; Gerberich, W.W.
1992-06-01
The high temperature X-ray diffraction system developed for this program is being used to measure the strains which develop during oxidation. This is being applied to Ni/NiO and Cr/Cr{sub 2}O{sub 3}. Our work suggests tat the oxide and metal crystalline texture, anisotropic elastic modulus and anisotropic thermal expansion can have a pronounced effect on strain state of these systems. Acoustic emission is being used to study oxide scale failure (fracture) during oxidation. AE data from 304 stainless steel are being used to develop a statistical model of fracture process. Strength of metal/scale interface is an important property that has been difficult to quantify. Using Nano-indentation and scratch techniques developed for characterizing thin film interfaces, an effort has begun to measure the fracture toughness of the metal/scale interface. Mathematical modelling of origin and time evolution of growth stresses is an extension and improvement of previous models. The current effort employs a more sophisticated stress analysis and expands the scope to include other stress relaxation process. The interaction between the modeling studies and the X-ray diffraction measurements provides a natural credibility check to both efforts.
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.
Long-time stress relaxation of a filled elastomer in vacuum environments
NASA Technical Reports Server (NTRS)
Ward, T. C.
1981-01-01
Samples of a filled elastomeric ablative material were stored at 45 C and 10 to the -6th torr for 7 months. Their tensile stress-relaxation modulus at constant strain was measured throughout the 7 months. Results of the testing are discussed primarily by comparisons of the data to atmospheric-pressure moduli (determined in this work for shorter periods of time) and with moduli predicted from short-time testing. Confirmation of the strengthening effects of vacuum on this composite was obtained. The use of time-temperature superposition techniques as an approximate accelerated testing procedure for this material under these conditions was also verified.
de Julian, C.; Emura, M.; Cebollada, F.; Gonzalez, J.M.
1996-12-01
We present magnetic relaxation data of PrNdFeB magnets. These data were obtained by measuring the time evolution of the magnetization under constant applied demagnetizing fields. The results corresponding to fields far from the range of the coercive force evidenced a nonmonotonic time variation of the magnetization. We propose that the occurrence of magnetic interactions underlies the observed anomalous behavior. This idea is checked through a micromagnetic simulation of the time evolution of the magnetization of a low field reversed nucleus which is exchange and magnetostically coupled to the main hard phase. {copyright} {ital 1996 American Institute of Physics.}
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)
Klein, E.; Fleitout, L.; Vigny, C.; Garaud, J. D.
2016-03-01
Megathrust earthquakes of magnitude close to 9 are followed by large scale (thousands of km) and long-lasting (decades), significant crustal and mantle deformation. This deformation can be observed at the surface and quantified with GPS measurements. Here we report on deformation observed during the 5-years time span after the 2010 Mw8.8 Maule Megathrust Earthquake (February 27, 2010) over the whole South American continent. With the first two years of those data, we use finite element modelling (FEM) to relate this deformation to slip on the plate interface and relaxation in the mantle, using a realistic layered Earth model and Burgers rheologies. Slip alone on the interface, even up to large depths, is unable to provide a satisfactory fit simultaneously to horizontal and vertical displacements. The horizontal deformation pattern requires relaxation both in the asthenosphere and in a Low Viscosity Channel along the deepest part of the plate interface and no additional Low Viscosity Wedge is required by the data. The vertical velocity pattern (intense and quick uplift over the Cordillera) is well fitted only when the channel extends deeper than 100km. Additionally, viscoelastic relaxation alone cannot explain the characteristics and amplitude of displacements over the first 200 km from the trench and aseismic slip on the fault plane is needed. This aseismic slip on the interface generates stresses, which induce additional relaxation in the mantle. In the final model, all three components (relaxation due to the coseismic slip, aseismic slip on the fault plane and relaxation due to aseismic slip) are taken into account. Our best-fit model uses slip at shallow depths on the subduction interface decreasing as function of time and includes (i) an asthenosphere extending down to 200km, with a steady-state Maxwell viscosity of 4.75 × 1018 Pa.s; and (ii) a Low Viscosity Channel along the plate interface extending from depths of 55 to 135 km with viscosities below 1018 Pa.s.
Biogeographic Kinetics: Estimation of Relaxation Times for Avifaunas of Southwest Pacific Islands
Diamond, Jared M.
1972-01-01
When species diversity S on an island is displaced from the equilibrium value by injection or removal of species, S relaxes to equilibrium by an imbalance between immigration and extinction rates. Estimates of exponential relaxation times, tr, for avifaunas of New Guinea satellite islands are calculated from analysis of four “experiments of nature”: recolonization of exploded volcanoes, contraction in island area due to rising sea level, severing of land bridges, and disappearance of landbridge relict species. tr is in the range 3,000-18,000 years for avifaunas of islands of 50-3000 square miles (130-7800 km2), and increases with island area. Immigration coefficients decrease and extinction coefficients increase with increasing S. The results may be relevant to the design of rainforest preserves. PMID:16592024
Zasetsky, A Y; Buchner, R
2011-01-19
We present a new fitting procedure and computer code for numerical evaluation of dielectric relaxation time distribution functions. The technique is based on linear least squares minimization and aims primarily at the analysis of compound experimental spectra of complex dielectric permittivity. It is fast, robust, and easy to use. No prior knowledge about the number of relaxation modes, their characteristic times, relaxation strengths, or the functional form of the underlying relaxation time distribution function is required, the procedure determines these parameters instead. The method is tested by both synthetic spectra with well-defined parameters of dielectric relaxation and experimental wide-band dielectric spectra of different types. We believe that this new fitting instrument, which allows an unbiased approach to the formal description of dielectric spectra, may be of interest in many areas of dielectric spectroscopy. PMID:21406849
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
Long term stability of atomic time scales
NASA Astrophysics Data System (ADS)
Petit, G.; Arias, F.
2015-03-01
We review the stability and accuracy achieved by the reference atomic time scales TAI and TT(BIPM). We show that they presently are in the low 10-16 in relative value, based on the performance of primary standards, of the ensemble time scale and of the time transfer techniques. We consider how the 1 10-16 value could be reached or superseded and which are the present limitations to attain this goal.
Longitudinal rotating frame relaxation time measurements in infarcted mouse myocardium in vivo.
Musthafa, Haja-Sherief N; Dragneva, Galina; Lottonen, Line; Merentie, Mari; Petrov, Lyubomir; Heikura, Tommi; Yl-Herttuala, Elias; Yl-Herttuala, Seppo; Grhn, Olli; Liimatainen, Timo
2013-05-01
Longitudinal relaxation time in the rotating frame (T1?) was measured using continuous wave irradiation in normal and infarcted mouse myocardium in vivo. Significant increase in T1? was found after 7 days of infarction when compared with reference myocardium or in myocardium before infarction. Cine MRI and histology were performed to verify the severity of infarction. The time course of T1? in the infarct fits better with granulation and scar tissue formation than necrosis and edema. The results of the study show that T1? could potentially be a noninvasive quantitative marker for tissue remodeling after ischemic damage. PMID:22736543
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
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.
The timing of eukaryotic evolution: Does a relaxed molecular clock reconcile proteins and fossils?
Douzery, Emmanuel J. P.; Snell, Elizabeth A.; Bapteste, Eric; Delsuc, Frdric; Philippe, Herv
2004-01-01
The use of nucleotide and amino acid sequences allows improved understanding of the timing of evolutionary events of life on earth. Molecular estimates of divergence times are, however, controversial and are generally much more ancient than suggested by the fossil record. The limited number of genes and species explored and pervasive variations in evolutionary rates are the most likely sources of such discrepancies. Here we compared concatenated amino acid sequences of 129 proteins from 36 eukaryotes to determine the divergence times of several major clades, including animals, fungi, plants, and various protists. Due to significant variations in their evolutionary rates, and to handle the uncertainty of the fossil record, we used a Bayesian relaxed molecular clock simultaneously calibrated by six paleontological constraints. We show that, according to 95% credibility intervals, the eukaryotic kingdoms diversified 9501,259 million years ago (Mya), animals diverged from choanoflagellates 761957 Mya, and the debated age of the split between protostomes and deuterostomes occurred 642761 Mya. The divergence times appeared to be robust with respect to prior assumptions and paleontological calibrations. Interestingly, these relaxed clock time estimates are much more recent than those obtained under the assumption of a global molecular clock, yet bilaterian diversification appears to be ?100 million years more ancient than the Cambrian boundary. PMID:15494441
Costabel, Stephan; Yaramanci, Ugur
2013-04-01
[1] For characterizing water flow in the vadose zone, the water retention curve (WRC) of the soil must be known. Because conventional WRC measurements demand much time and effort in the laboratory, alternative methods with shortened measurement duration are desired. The WRC can be estimated, for instance, from the cumulative pore size distribution (PSD) of the investigated material. Geophysical applications of nuclear magnetic resonance (NMR) relaxometry have successfully been applied to recover PSDs of sandstones and limestones. It is therefore expected that the multiexponential analysis of the NMR signal from water-saturated loose sediments leads to a reliable estimation of the WRC. We propose an approach to estimate the WRC using the cumulative NMR relaxation time distribution and approximate it with the well-known van-Genuchten (VG) model. Thereby, the VG parameter n, which controls the curvature of the WRC, is of particular interest, because it is the essential parameter to predict the relative hydraulic conductivity. The NMR curves are calibrated with only two conventional WRC measurements, first, to determine the residual water content and, second, to define a fixed point that relates the relaxation time to a corresponding capillary pressure. We test our approach with natural and artificial soil samples and compare the NMR-based results to WRC measurements using a pressure plate apparatus and to WRC predictions from the software ROSETTA. We found that for sandy soils n can reliably be estimated with NMR, whereas for samples with clay and silt contents higher than 10% the estimation fails. This is the case when the hydraulic properties of the soil are mainly controlled by the pore constrictions. For such samples, the sensitivity of the NMR method for the pore bodies hampers a plausible WRC estimation. Citation: Costabel, S., and U. Yaramanci (2013), Estimation of water retention parameters from nuclear magnetic resonance relaxation time distributions, Water Resour. Res., 49, 2068-2079, doi:10.1002/wrcr.20207. PMID:23935225
Costabel, Stephan; Yaramanci, Ugur
2013-01-01
[1] For characterizing water flow in the vadose zone, the water retention curve (WRC) of the soil must be known. Because conventional WRC measurements demand much time and effort in the laboratory, alternative methods with shortened measurement duration are desired. The WRC can be estimated, for instance, from the cumulative pore size distribution (PSD) of the investigated material. Geophysical applications of nuclear magnetic resonance (NMR) relaxometry have successfully been applied to recover PSDs of sandstones and limestones. It is therefore expected that the multiexponential analysis of the NMR signal from water-saturated loose sediments leads to a reliable estimation of the WRC. We propose an approach to estimate the WRC using the cumulative NMR relaxation time distribution and approximate it with the well-known van-Genuchten (VG) model. Thereby, the VG parameter n, which controls the curvature of the WRC, is of particular interest, because it is the essential parameter to predict the relative hydraulic conductivity. The NMR curves are calibrated with only two conventional WRC measurements, first, to determine the residual water content and, second, to define a fixed point that relates the relaxation time to a corresponding capillary pressure. We test our approach with natural and artificial soil samples and compare the NMR-based results to WRC measurements using a pressure plate apparatus and to WRC predictions from the software ROSETTA. We found that for sandy soils n can reliably be estimated with NMR, whereas for samples with clay and silt contents higher than 10% the estimation fails. This is the case when the hydraulic properties of the soil are mainly controlled by the pore constrictions. For such samples, the sensitivity of the NMR method for the pore bodies hampers a plausible WRC estimation. Citation: Costabel, S., and U. Yaramanci (2013), Estimation of water retention parameters from nuclear magnetic resonance relaxation time distributions, Water Resour. Res., 49, 2068-2079, doi:10.1002/wrcr.20207. PMID:23935225
Relaxation and merging flux ropes and 3D effects in the Reconnection Scaling Experiment at LANL
NASA Astrophysics Data System (ADS)
Intrator, T.; Furno, I.; Light, A.; Madziwa-Nussinov, T.; Lapenta, G.; Ricci, P.; Hemsing, E.
2005-12-01
Magnetic structures are embedded in astrophysical, space, solar and laboratory plasmas. The dynamics and relaxation of these plasmas can involve flows, changes in topology, magnetic reconnection, plasma heating, and dissipation of magnetic energy. This complex behavior is intrinsically three-dimensional (3D). Current-carrying magnetic flux ropes are the fundamental building blocks for many of these cases. At Los Alamos National Laboratory, we have an experimental realization of this model. The Reconnection Scaling Experiment (RSX) is a unique facility that can create multiple current-carrying flux ropes in an MHD experiment. Plasma guns are used to inject magnetic helicity into plasma columns. We show 3D structure with camera views, along with magnetic, electric, and particle probe data. Experiments in the presence of a strong guide magnetic field (Bz/Brcxn>10) show the formation of a current sheet and electron heating during the coalescence of two flux ropes. Computed simulations of the interactions of two current ropes are shown of that predict many of the experimental characteristics. A density wave structure that propagates opposite to the current is measured in the current sheet with wavelength and speed that are consistent with a kinetic Alfven wave. The current channels acquire angular momentum and rotate about each other developing helical structures, both individually and jointly. Parallel pressure gradients (a 3D effect) appear to be an important term in the Ohm's Law.
Relaxation of flux ropes and magnetic reconnection in the Reconnection Scaling Experiment at LANL
NASA Astrophysics Data System (ADS)
Furno, I.; Intrator, T.; Hemsing, E.; Hsu, S.; Lapenta, G.; Abbate, S.
2004-12-01
Magnetic reconnection and plasma relaxation are studied in the Reconnection Scaling Experiment (RSX) with current carrying plasma columns (magnetic flux ropes). Using plasma guns, multiple flux ropes (B? ? 100 Gauss, L=90 cm, r?3 cm) are generated in a three-dimensional (3D) cylindrical geometry and are observed to evolve dynamically during the injection of magnetic helicity. Detailed evolution of electron density, temperature, plasma potential and magnetic field structures is reconstructed experimentally and visible light emission is captured with a fast-gated, intensified CCD camera to provide insight into the global flux rope dynamics. Experiments with two flux ropes in collisional plasmas and in a strong axial guide field (Bz / B? > 10) suggest that magnetic reconnection plays an important role in the initial stages of flux rope evolution. During the early stages of the applied current drive (t? 20 ? Alfv {e}n), the flux ropes are observed to twist, partially coalesce and form a thin current sheet with a scale size comparable to that of the ion sound gyro-radius. Here, non-ideal terms in a generalized Ohm's Law appear to play a significant role in the 3D reconnection process as shown by the presence of a strong axial pressure gradient in the current sheet. In addition, a density perturbation with a structure characteristic of a kinetic Alfvn wave is observed to propagate axially in the current layer, anti-parallel to the induced sheet current. Later in the evolution, when a sufficient amount of helicity is injected into the system, a critical threshold for the kink instability is exceeded and the helical twisting of each individual flux rope can dominate the dynamics of the system. This may prevent the complete coalescence of the flux ropes.
Relaxation of flux ropes and magnetic reconnection in the Reconnection Scaling Experiment at LANL
NASA Astrophysics Data System (ADS)
Furno, Ivo
2004-11-01
Magnetic reconnection and plasma relaxation are studied in the Reconnection Scaling Experiment (RSX) with current carrying plasma columns (magnetic flux ropes). Using plasma guns, multiple flux ropes (B_pol < 100 Gauss, L=90 cm, r < 3 cm) are generated in a three-dimensional (3D) cylindrical geometry and are observed to evolve dynamically during the injection of magnetic helicity. Detailed evolution of electron density, temperature, plasma potential and magnetic field structures is reconstructed experimentally and visible light emission is captured with a fast-gated, intensified CCD camera to provide insight into the global flux rope dynamics. Experiments with two flux ropes in collisional plasmas and in a strong axial guide field (Bz / B_pol > 10) suggest that magnetic reconnection plays an important role in the initial stages of flux rope evolution. During the early stages of the applied current drive (t < 20?_Alfven), the flux ropes are observed to twist, partially coalesce and form a thin current sheet with a scale size comparable to that of the ion sound gyro-radius. Here, non-ideal terms in a generalized Ohm's Law appear to play a significant role in the 3D reconnection process as shown by the presence of a strong axial pressure gradient in the current sheet. In addition, a density perturbation with a structure characteristic of a kinetic Alfvn wave is observed to propagate axially in the current layer, anti-parallel to the induced sheet current. Later in the evolution, when a sufficient amount of helicity is injected into the system, a critical threshold for the kink instability is exceeded and the helical twisting of each individual flux rope can dominate the dynamics of the system. This may prevent the complete coalescence of the flux ropes.
Mouse Activity across Time Scales: Fractal Scenarios
Lima, G. Z. dos Santos; Lobão-Soares, B.; do Nascimento, G. C.; França, Arthur S. C.; Muratori, L.; Ribeiro, S.; Corso, G.
2014-01-01
In this work we devise a classification of mouse activity patterns based on accelerometer data using Detrended Fluctuation Analysis. We use two characteristic mouse behavioural states as benchmarks in this study: waking in free activity and slow-wave sleep (SWS). In both situations we find roughly the same pattern: for short time intervals we observe high correlation in activity - a typical 1/f complex pattern - while for large time intervals there is anti-correlation. High correlation of short intervals ( to : waking state and to : SWS) is related to highly coordinated muscle activity. In the waking state we associate high correlation both to muscle activity and to mouse stereotyped movements (grooming, waking, etc.). On the other side, the observed anti-correlation over large time scales ( to : waking state and to : SWS) during SWS appears related to a feedback autonomic response. The transition from correlated regime at short scales to an anti-correlated regime at large scales during SWS is given by the respiratory cycle interval, while during the waking state this transition occurs at the time scale corresponding to the duration of the stereotyped mouse movements. Furthermore, we find that the waking state is characterized by longer time scales than SWS and by a softer transition from correlation to anti-correlation. Moreover, this soft transition in the waking state encompass a behavioural time scale window that gives rise to a multifractal pattern. We believe that the observed multifractality in mouse activity is formed by the integration of several stereotyped movements each one with a characteristic time correlation. Finally, we compare scaling properties of body acceleration fluctuation time series during sleep and wake periods for healthy mice. Interestingly, differences between sleep and wake in the scaling exponents are comparable to previous works regarding human heartbeat. Complementarily, the nature of these sleep-wake dynamics could lead to a better understanding of neuroautonomic regulation mechanisms. PMID:25275515
Decoherence, time scales and pointer states
NASA Astrophysics Data System (ADS)
Qureshi, Tabish
2012-03-01
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.
Dynamics of glass-forming liquids. XVIII. Does entropy control structural relaxation times?
Samanta, Subarna; Richert, Ranko
2015-01-28
We study the dielectric dynamics of viscous glycerol in the presence of a large bias field. Apart from dielectric saturation and polarization anisotropy, we observe that the steady state structural relaxation time is longer by 2.7% in the presence of a 225 kV/cm dc-field relative to the linear response counterpart, equivalent to a field induced glass transition (Tg) shift of +84 mK. This result compares favorably with the 3.0% time constant increase predicted on the basis of a recent report [G. P. Johari, J. Chem. Phys. 138, 154503 (2013)], where the field induced reduction of the configurational entropy translates into slower dynamics by virtue of the Adam-Gibbs relation. Other models of field dependent glass transition temperatures are also discussed. Similar to observations related to the electro-optical Kerr effect, the rise time of the field induced effect is much longer than its collapse when the field is removed again. The orientational relaxation time of the plastic crystal cyclo-octanol is more sensitive to a bias field, showing a 13.5% increase at a field of 150 kV/cm, equivalent to an increase of Tg by 0.58 K. PMID:25637992
Dynamics of glass-forming liquids. XVIII. Does entropy control structural relaxation times?
NASA Astrophysics Data System (ADS)
Samanta, Subarna; Richert, Ranko
2015-01-01
We study the dielectric dynamics of viscous glycerol in the presence of a large bias field. Apart from dielectric saturation and polarization anisotropy, we observe that the steady state structural relaxation time is longer by 2.7% in the presence of a 225 kV/cm dc-field relative to the linear response counterpart, equivalent to a field induced glass transition (Tg) shift of +84 mK. This result compares favorably with the 3.0% time constant increase predicted on the basis of a recent report [G. P. Johari, J. Chem. Phys. 138, 154503 (2013)], where the field induced reduction of the configurational entropy translates into slower dynamics by virtue of the Adam-Gibbs relation. Other models of field dependent glass transition temperatures are also discussed. Similar to observations related to the electro-optical Kerr effect, the rise time of the field induced effect is much longer than its collapse when the field is removed again. The orientational relaxation time of the plastic crystal cyclo-octanol is more sensitive to a bias field, showing a 13.5% increase at a field of 150 kV/cm, equivalent to an increase of Tg by 0.58 K.
The electron-phonon relaxation time in thin superconducting titanium nitride films
Kardakova, A.; Finkel, M.; Kovalyuk, V.; An, P.; Morozov, D.; Dunscombe, C.; Mauskopf, P.; Tarkhov, M.; Klapwijk, T. M.; Kavli Institute of Nanoscience, Delft University of Technology, 2628 CJ Delft ; Goltsman, G.; National Research University Higher School of Economics, Moscow 101000
2013-12-16
We report on the direct measurement of the electron-phonon relaxation time, ?{sub eph}, in disordered TiN films. Measured values of ?{sub eph} are from 5.5?ns to 88?ns in the 4.2 to 1.7?K temperature range and consistent with a T{sup ?3} temperature dependence. The electronic density of states at the Fermi level N{sub 0} is estimated from measured material parameters. The presented results confirm that thin TiN films are promising candidate-materials for ultrasensitive superconducting detectors.
On the relaxation time of Gauss's continued-fraction map I. The Hilbert space approach (Koopmanism)
NASA Astrophysics Data System (ADS)
Mayer, D.; Roepstorff, G.
1987-04-01
It is shown that U *, the adjoint of Koopman's isometric operator Uf(x) = f(Tx) corresponding to the map Tx=x -1 (mod 1) of the unit interval, is isomorphic to a symmetric integral operator when restricted to a Hilbert space of holomorphic functions f This result, also obtained by Babenko in a different setting, allows us to derive new trace formulas. Using generalized Temple's inequalities, we determine the relaxation time of the above system with great accuracy. In contrast to a widespread belief, it appears to be unrelated to the entropy of the map T.
A Novel Statistical Approach for Brain MR Images Segmentation Based on Relaxation Times
Ferraioli, Giampaolo; Pascazio, Vito
2015-01-01
Brain tissue segmentation in Magnetic Resonance Imaging is useful for a wide range of applications. Classical approaches exploit the gray levels image and implement criteria for differentiating regions. Within this paper a novel approach for brain tissue joint segmentation and classification is presented. Starting from the estimation of proton density and relaxation times, we propose a novel method for identifying the optimal decision regions. The approach exploits the statistical distribution of the involved signals in the complex domain. The technique, compared to classical threshold based ones, is able to globally improve the classification rate. The effectiveness of the approach is evaluated on both simulated and real datasets. PMID:26798631
Del Giudice, Francesco; D'Avino, Gaetano; Greco, Francesco; De Santo, Ilaria; Netti, Paolo A; Maffettone, Pier Luca
2016-03-21
Correction for 'Rheometry-on-a-chip: measuring the relaxation time of a viscoelastic liquid through particle migration in microchannel flows' by Francesco Del Giudice et al., Lab Chip, 2015, 15, 783-792. PMID:26926799
NASA Astrophysics Data System (ADS)
Mangeney, J.; Stelmakh, N.; Aniel, F.; Boucaud, P.; Lourtioz, J.-M.
2002-06-01
The absorption saturation relaxation time in light- and heavy-ion-irradiated GaAs saturable absorbers has been measured as a function of the temperature in the range from 7 to 300 K. For both types of samples, the relaxation time is shorter than 4 ps at 7 K. A regular increase of this time with temperature is observed for light-ion-irradiated samples, a value of 9.5 ps being reached at room temperature. In contrast, an almost temperature-independent relaxation time is found for heavy-ion-irradiated samples. The results are interpreted on the basis of a simplified relaxation model accounting for capture and emission from defect levels. We suggest that light-ion irradiation creates shallow centers whereas heavy-ion irradiation creates deep centers.
Relationship between Structural and Stress Relaxation in a Block-Copolymer Melt
Patel, Amish J.; Narayanan, Suresh; Sandy, Alec; Mochrie, Simon G. J.; Garetz, Bruce A.; Watanabe, Hiroshi; Balsara, Nitash P.
2006-06-30
The relationship between structural relaxation on molecular length scales and macroscopic stress relaxation was explored in a disordered block-copolymer melt. Experiments show that the structural relaxation time, measured by x-ray photon correlation spectroscopy is larger than the terminal stress relaxation time, measured by rheology, by factors as large as 100. We demonstrate that the structural relaxation data are dominated by the diffusion of intact micelles while the stress relaxation data are dominated by contributions due to disordered concentration fluctuations.
A method for measuring the Nel 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 Nel 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 Nel relaxation time and estimate a room-temperature magnetocrystalline anisotropy constant of 40 kJ/m3, in agreement with previously published results.
Observing Reality on Different Time Scales
NASA Astrophysics Data System (ADS)
Alyushin, Alexey
2005-10-01
In the first part of the paper, I examine cases of acceleration of perception and cognition and provide my explanation of the mechanism of the effect. The explanation rests on the conception of neuronal temporal frames, or windows of simultaneity. Frames have different standard durations and yield to stretching and compressing. I suggest it to be the cause of the effect, as well as the ground for differences in perceptive time scales of living beings. In the second part, I apply the conception of temporal frames to model observation in the extended time scales that reach far beyond the temporal perceptive niche of individual living beings. Duration of a frame is taken as the basic parameter setting a particular time scale. By substituting a different frame duration, we set a hypothetical time scale and emulate observing reality in a wider or a narrower angle of embracing events in time. I discuss the status of observer in its relation to objective reality, and examine how reality does change its appearance when observed in different time scales.
Baum, T.; Joseph, G.B.; Karampinos, D.C.; Jungmann, P.M.; Link, T.M.; Bauer, J.S.
2014-01-01
SUMMARY Objective The purpose of this work was to review the current literature on cartilage and meniscal T2 relaxation time. Methods Electronic searches in PubMed were performed to identify relevant studies about T2 relaxation time measurements as non-invasive biomarker for knee osteoarthritis (OA) and cartilage repair procedures. Results Initial osteoarthritic changes include proteoglycan loss, deterioration of the collagen network, and increased water content within the articular cartilage and menisci. T2 relaxation time measurements are affected by these pathophysiological processes. It was demonstrated that cartilage and meniscal T2 relaxation time values were significantly increased in subjects with compared to those without radiographic OA and focal knee lesions, respectively. Subjects with OA risk factors such as overweight/obesity showed significantly greater cartilage T2 values than normal controls. Elevated cartilage and meniscal T2 relaxation times were found in subjects with vs without knee pain. Increased cartilage T2 at baseline predicted morphologic degeneration in the cartilage, meniscus, and bone marrow over 3 years. Furthermore, cartilage repair tissue could be non-invasively assessed by using T2 mapping. Reproducibility errors for T2 measurements were reported to be smaller than the T2 differences in healthy and diseased cartilage indicating that T2 relaxation time may be a reliable discriminatory biomarker. Conclusions Cartilage and meniscal T2 mapping may be suitable as non-invasive biomarker to diagnose early stages of knee OA and to monitor therapy of OA. PMID:23896316
Time to Talk: 5 Things to Know about Relaxation Techniques for Stress
... Clinical Research Toolbox Types of Grants and Contracts General Award Mechanisms Small Business Research Grant Program (SBIR) ... oxygen consumption and levels of stress hormones. In theory, voluntarily creating the relaxation response ... Most relaxation techniques can be self-taught and ...
Dimitrov, I E; Charagundla, S R; Rizi, R; Reddy, R; Leigh, J S
1999-02-01
A magnetic resonance imaging method for simultaneous and accurate determination of gaseous diffusion constant and longitudinal relaxation time is presented. The method is based on direct observation of diffusive motion. Initially, a slice-selective saturation of helium-3 (3He) spins was performed on a 3He/O2 phantom (9 atm/2 atm). A time-delay interval was introduced after saturation, allowing spins to diffuse in and out of the labeled slice. Following the delay interval a one-dimensional (1-D) projection image of the phantom was acquired. A series of 21 images was collected, each subsequent image having been acquired with an increased delay interval. Gradual spreading of the slice boundaries due to diffusion was thus observed. The projection profiles were fit to a solution of the Bloch equation corrected for diffusive motion. The fitting procedure yielded a value of D3He = 0.1562+/-0.0013 cm2/s, in good agreement with a measurement obtained with a modified version of the standard pulsed-field gradient technique. The method also enabled us to accurately measure the longitudinal relaxation of 3He spins by fitting the change of the total area under the projection profiles to an exponential. A value of T1 = 1.67 s (2 T field) was recorded, in excellent agreement with an inversion recovery measurement. PMID:10215482
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.
On the nonlinear variation of dc conductivity with dielectric relaxation time
NASA Astrophysics Data System (ADS)
Johari, G. P.; Andersson, Ove
2006-09-01
The long-known observations that dc conductivity ?dc of an ultraviscous liquid varies nonlinearly with the dielectric relaxation time ?, and the slope of the log?dc against log? plot deviates from -1 are currently seen as two of the violations of the Debye-Stokes-Einstein equation. Here we provide a formalism using a zeroth order Bjerrum description for ion association to show that in addition to its variation with temperature T and pressure P, impurity ion population varies with a liquid's equilibrium dielectric permittivity. Inclusion of this electrostatic effect modifies the Debye-Stokes-Einstein equation to log(?dc? )=constant+log?, where ? is the T and P-dependent degree of ionic dissociation of an electrolytic impurity. Variation of a liquid's shear modulus with T and P would add to the nonlinearity of ?dc-? relation, as would a nonequivalence of the shear and dielectric relaxation times, proton transfer along the hydrogen bonds, or occurrence of another chemical process. This is illustrated by using the data for ultraviscous acetaminophen-aspirin liquid.
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.
Bulk viscosity and relaxation time of causal dissipative relativistic fluid dynamics
Huang Xuguang; Rischke, Dirk H.; Kodama, Takeshi; Koide, Tomoi
2011-02-15
The microscopic formulas of the bulk viscosity {zeta} and the corresponding relaxation time {tau}{sub {Pi}} in causal dissipative relativistic fluid dynamics are derived by using the projection operator method. In applying these formulas to the pionic fluid, we find that the renormalizable energy-momentum tensor should be employed to obtain consistent results. In the leading-order approximation in the chiral perturbation theory, the relaxation time is enhanced near the QCD phase transition, and {tau}{sub {Pi}} and {zeta} are related as {tau}{sub {Pi}={zeta}}/[{beta}{l_brace}(1/3-c{sub s}{sup 2})({epsilon}+P)-2({epsilon}-3P)/9{r_brace}], where {epsilon}, P, and c{sub s} are the energy density, pressure, and velocity of sound, respectively. The predicted {zeta} and {tau}{sub {Pi}} should satisfy the so-called causality condition. We compare our result with the results of the kinetic calculation by Israel and Stewart and the string theory, and confirm that all three approaches are consistent with the causality condition.
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
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).
Lsse, S; Claassen, H; Gehrke, T; Hassenpflug, J; Schnke, M; Heller, M; Gler, C C
2000-05-01
Non-invasive assessment of cartilage properties, specifically water content, could prove helpful in the diagnosis of early degenerative joint diseases. Transverse relaxation times T(2) of human articular cartilage (34 cartilage slices of three donors) were measured on a pixel-by-pixel basis in a clinical whole body MR system in vitro. In vivo feasibility to measure quantitative T(2) maps was shown for human patellar cartilage. The relaxation times of cartilage with collagen in the radial zone oriented perpendicular to the magnetic field increased from approximately 10 ms near the bone to approximately 60 ms near the articular surface. Cartilage water content of the tibial plateau and femoral condyles could be determined from the correlation with T(2) (R(2) = 0.71) with an error of approximately 2 wt.%. In vivo, directional variation would need to be considered. If confirmed in vivo, T(2) measurements could potentially serve as a non-invasive tool for the evaluation of the status and distribution of water content in articular cartilage. PMID:10788720
Time scales of turbulent relative dispersion.
Bitane, Rehab; Homann, Holger; Bec, Jrmie
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 of turbulent relative dispersion
NASA Astrophysics Data System (ADS)
Bitane, Rehab; Homann, Holger; Bec, Jrmie
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.
Kloiber, K; Konrat, R
2000-09-01
In this paper it is demonstrated that cross-correlated time modulation of isotropic chemical shifts ('conformational exchange') leads to differential relaxation of double- and zero-quantum coherences, respectively. Quantitative information can be obtained from the time dependence of the interconversion between the two two-spin coherences 2IxSx and 2IySy, induced by the differential relaxation. The effect is illustrated with an application to 13C,15N-labeled quail CRP2(LIM2), by studying 15N-1H(N) multiple-quantum relaxation. Significant cross-correlated fluctuations of isotropic chemical shifts were observed for residues which are part of a disordered loop region connecting two beta-strands in CRP2(LIM2). Differential 1H(N) and 15N exchange contributions to multiple-quantum relaxation observed at these sites illustrate the complex interplay between hydrogen bonding events and conformational reorientations in proteins. PMID:11061226
Method to determine in vivo the relaxation time T1 of hyperpolarized xenon in rat brain.
Choquet, Philippe; Hyacinthe, Jean-Noël; Duhamel, Guillaume; Grillon, Emmanuelle; Leviel, Jean-Louis; Constantinesco, André; Ziegler, Anne
2003-06-01
The magnetic polarization of the stable (129)Xe isotope may be enhanced dramatically by means of optical techniques and, in principle, hyperpolarized (129)Xe MRI should allow quantitative mapping of cerebral blood flow with better spatial resolution than scintigraphic techniques. A parameter necessary for this quantitation, and not previously known, is the longitudinal relaxation time (T(1) (tissue)) of (129)Xe in brain tissue in vivo: a method for determining this is reported. The time course of the MR signal in the brain during arterial injection of hyperpolarized (129)Xe in a lipid emulsion was analyzed using an extended two-compartment model. The model uses experimentally determined values of the RF flip angle and the T(1) of (129)Xe in the lipid emulsion. Measurements on rats, in vivo, at 2.35 T gave T(1) (tissue) = 3.6 +/- 2.1 sec (+/-SD, n = 6). This method enables quantitative mapping of cerebral blood flow. PMID:12768578
Evaluation of time evolution of 3-D Structure in RELAX RFP with SXR Imaging Technique
NASA Astrophysics Data System (ADS)
Sanpei, Akio; Masamune, Sadao; Nishimura, Kanae; Ueba, Ryota; Ishii, Go; Kodera, Ryosuke; Aoki, Yosuke; Himura, Haruhiko; Ohdachi, Satoshi; Mizuguchi, Naoki; Akiyama, Tsuyoshi
2014-10-01
In a low-A RFP machine RELAX (R = 0.51 m/a = 0.25 m (A = 2)), a quasi-periodic transition to quasi-single helicity (QSH) state has been observed. During the QSH state, the fluctuation power concentrates in the dominant m = 1/n = 4 mode, and a (toroidally rotating) 3-D helical structure has been observed with radial array of magnetic probes. We have applied a high-speed (10-microsecond time resolution) dual soft-X ray (SXR) imaging diagnostic system to take SXR images from tangential and vertical directions simultaneously to observe 3-D dynamic structures of the SXR emissivity. The magnetic field topology for the QSH RFP phase in RELAX plasmas are identified with obtained dual SXR images and results of external magnetic measurements. Recently, we have developed a two-dimensional electron temperature diagnostic system for thermal structure studies. The system consists of a SXR camera with two pin-holes for two-kinds of absorber foils, combined with a high-speed camera. We have succeeded in distinguishing Te image in QSH from that in multi-helicity (MH) RFP states. The most recent results using above techniques will be presented, together with discussion on possible reconstruction methods from 3-D imaging.
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.
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.
NASA Astrophysics Data System (ADS)
Bose-Basu, Bidisha; Zajicek, Jaroslav; Bondo, Gail; Zhao, Shikai; Kubsch, Meredith; Carmichael, Ian; Serianni, Anthony S.
2000-06-01
13C and 2H spin-lattice relaxation times have been determined by inversion recovery in a range of site-specific 13C- and 2H-labeled saccharides under identical solution conditions, and the data were used to calculate deuterium nuclear quadrupolar coupling constants (2H NQCC) at specific sites within cyclic and acyclic forms in solution. 13C T1 values ranged from ?0.6 to 8.2 s, and 2H T1 values ranged from ?79 to 450 ms, depending on molecular structure (0.4 M sugar in 5 mM EDTA (disodium salt) in 2H2O-depleted H2O, pH 4.8, 30C). In addition to providing new information on 13C and 2H relaxation behavior of saccharides in solution, the resulting 2H1 NQCC values reveal a dependency on anomeric configuration within aldopyranose rings, whereas 2H NQCC values at other ring sites appear less sensitive to configuration at C1. In contrast, 2H NQCC values at both anomeric and nonanomeric sites within aldofuranose rings appear to be influenced by anomeric configuration. These experimental observations were confirmed by density functional theory (DFT) calculations of 2H NQCC values in model aldopyranosyl and aldofuranosyl rings.
The hippocampus, time, and memory across scales.
Howard, Marc W; Eichenbaum, Howard
2013-11-01
A wealth of experimental studies with animals have offered insights about how neural networks within the hippocampus support the temporal organization of memories. These studies have revealed the existence of "time cells" that encode moments in time, much as the well-known "place cells" map locations in space. Another line of work inspired by human behavioral studies suggests that episodic memories are mediated by a state of temporal context that changes gradually over long time scales, up to at least a few thousand seconds. In this view, the "mental time travel" hypothesized to support the experience of episodic memory corresponds to a "jump back in time" in which a previous state of temporal context is recovered. We suggest that these 2 sets of findings could be different facets of a representation of temporal history that maintains a record at the last few thousand seconds of experience. The ability to represent long time scales comes at the cost of discarding precise information about when a stimulus was experienced--this uncertainty becomes greater for events further in the past. We review recent computational work that describes a mechanism that could construct such a scale-invariant representation. Taken as a whole, this suggests the hippocampus plays its role in multiple aspects of cognition by representing events embedded in a general spatiotemporal context. The representation of internal time can be useful across nonhippocampal memory systems. PMID:23915126
Zhu, Tianqi; Dos Reis, Mario; Yang, Ziheng
2015-03-01
Genetic sequence data provide information about the distances between species or branch lengths in a phylogeny, but not about the absolute divergence times or the evolutionary rates directly. Bayesian methods for dating species divergences estimate times and rates by assigning priors on them. In particular, the prior on times (node ages on the phylogeny) incorporates information in the fossil record to calibrate the molecular tree. Because times and rates are confounded, our posterior time estimates will not approach point values even if an infinite amount of sequence data are used in the analysis. In a previous study we developed a finite-sites theory to characterize the uncertainty in Bayesian divergence time estimation in analysis of large but finite sequence data sets under a strict molecular clock. As most modern clock dating analyses use more than one locus and are conducted under relaxed clock models, here we extend the theory to the case of relaxed clock analysis of data from multiple loci (site partitions). Uncertainty in posterior time estimates is partitioned into three sources: Sampling errors in the estimates of branch lengths in the tree for each locus due to limited sequence length, variation of substitution rates among lineages and among loci, and uncertainty in fossil calibrations. Using a simple but analogous estimation problem involving the multivariate normal distribution, we predict that as the number of loci ([Formula: see text]) goes to infinity, the variance in posterior time estimates decreases and approaches the infinite-data limit at the rate of 1/[Formula: see text], and the limit is independent of the number of sites in the sequence alignment. We then confirmed the predictions by using computer simulation on phylogenies of two or three species, and by analyzing a real genomic data set for six primate species. Our results suggest that with the fossil calibrations fixed, analyzing multiple loci or site partitions is the most effective way for improving the precision of posterior time estimation. However, even if a huge amount of sequence data is analyzed, considerable uncertainty will persist in time estimates. PMID:25503979
Zhu, Tianqi; Dos Reis, Mario; Yang, Ziheng
2015-01-01
Genetic sequence data provide information about the distances between species or branch lengths in a phylogeny, but not about the absolute divergence times or the evolutionary rates directly. Bayesian methods for dating species divergences estimate times and rates by assigning priors on them. In particular, the prior on times (node ages on the phylogeny) incorporates information in the fossil record to calibrate the molecular tree. Because times and rates are confounded, our posterior time estimates will not approach point values even if an infinite amount of sequence data are used in the analysis. In a previous study we developed a finite-sites theory to characterize the uncertainty in Bayesian divergence time estimation in analysis of large but finite sequence data sets under a strict molecular clock. As most modern clock dating analyses use more than one locus and are conducted under relaxed clock models, here we extend the theory to the case of relaxed clock analysis of data from multiple loci (site partitions). Uncertainty in posterior time estimates is partitioned into three sources: Sampling errors in the estimates of branch lengths in the tree for each locus due to limited sequence length, variation of substitution rates among lineages and among loci, and uncertainty in fossil calibrations. Using a simple but analogous estimation problem involving the multivariate normal distribution, we predict that as the number of loci (L) goes to infinity, the variance in posterior time estimates decreases and approaches the infinite-data limit at the rate of 1/L, and the limit is independent of the number of sites in the sequence alignment. We then confirmed the predictions by using computer simulation on phylogenies of two or three species, and by analyzing a real genomic data set for six primate species. Our results suggest that with the fossil calibrations fixed, analyzing multiple loci or site partitions is the most effective way for improving the precision of posterior time estimation. However, even if a huge amount of sequence data is analyzed, considerable uncertainty will persist in time estimates. PMID:25503979
NASA Astrophysics Data System (ADS)
Costabel, Stephan; Yaramanci, Ugur
2013-04-01
For characterizing water flow in the vadose zone, the water retention curve (WRC) of the soil must be known. Because conventional WRC measurements demand much time and effort in the laboratory, alternative methods with shortened measurement duration are desired. The WRC can be estimated, for instance, from the cumulative pore size distribution (PSD) of the investigated material. Geophysical applications of nuclear magnetic resonance (NMR) relaxometry have successfully been applied to recover PSDs of sandstones and limestones. It is therefore expected that the multiexponential analysis of the NMR signal from water-saturated loose sediments leads to a reliable estimation of the WRC. We propose an approach to estimate the WRC using the cumulative NMR relaxation time distribution and approximate it with the well-known van-Genuchten (VG) model. Thereby, the VG parameter n, which controls the curvature of the WRC, is of particular interest, because it is the essential parameter to predict the relative hydraulic conductivity. The NMR curves are calibrated with only two conventional WRC measurements, first, to determine the residual water content and, second, to define a fixed point that relates the relaxation time to a corresponding capillary pressure. We test our approach with natural and artificial soil samples and compare the NMR-based results to WRC measurements using a pressure plate apparatus and to WRC predictions from the software ROSETTA. We found that for sandy soils n can reliably be estimated with NMR, whereas for samples with clay and silt contents higher than 10% the estimation fails. This is the case when the hydraulic properties of the soil are mainly controlled by the pore constrictions. For such samples, the sensitivity of the NMR method for the pore bodies hampers a plausible WRC estimation.
Time-dependent pseudo Jahn-Teller effect: Phonon-mediated long-time nonadiabatic relaxation
Vaikjrv, Taavi Hizhnyakov, Vladimir
2014-02-14
Our system under theoretical consideration is an impurity center in a solid. We are considering the time evolution of the center in a quasi-degenerate electronic state. Strict quantum mechanical treatment of non-adiabadicity of the state is used. The phonon continuum is taken into account in addition to the vibration responsible for the main vibronic interaction. To describe the dynamics of the excited state a master equation has been used. The theoretical considerations are illustrated by the calculations of the long-time evolution of vibrations of the center, influenced by the emission of phonons to the bulk.
Shear viscosities from the Chapman-Enskog and the relaxation time approaches
NASA Astrophysics Data System (ADS)
Wiranata, Anton; Prakash, Madappa
2012-05-01
The interpretation of the measured elliptic and higher order collective flows in heavy-ion collisions in terms of viscous hydrodynamics depends sensitively on the ratio of shear viscosity to entropy density. Here we perform a quantitative comparison between the results of shear viscosities from the Chapman-Enskog and relaxation time methods for selected test cases with specified elastic differential cross sections: (i) the nonrelativistic, relativistic and ultrarelativistic hard sphere gas with angle and energy independent differential cross section, (ii) the Maxwell gas, (iii) chiral pions, and (iv) massive pions for which the differential elastic cross section is taken from experiments. Our quantitative results (i) reveal that the extent of agreement (or disagreement) depends sensitively on the energy dependence of the differential cross sections employed, and (ii) stress the need to perform quantum molecular dynamical (URQMD) simulations that employ Green-Kubo techniques with similar cross sections to validate the codes employed and to test the accuracy of other methods.
Statistically relaxing to generating partitions for observed time-series data
NASA Astrophysics Data System (ADS)
Buhl, Michael; Kennel, Matthew B.
2005-04-01
We introduce a relaxation algorithm to estimate approximations to generating partitions for observed dynamical time series. Generating partitions preserve dynamical information of a deterministic map in the symbolic representation. Our method optimizes an essential property of a generating partition: avoiding topological degeneracies. We construct an energylike functional and use a nonequilibrium stochastic minimization algorithm to search through configuration space for the best assignment of symbols to observed data. As each observed point may be assigned a symbol, the partitions are not constrained to an arbitrary parametrization. We further show how to select particular generating partition solutions which also code low-order unstable periodic orbits in a given way, hence being able to enumerate through a number of potential generating partition solutions.
Modeling of self-diffusion and relaxation time NMR in multi-compartment systems.
Novikov, E G; van Dusschoten, D; Van As, H
1998-12-01
The theory of pulsed field gradient (pfg) NMR applied to molecules in cellular systems which contain different subcellular compartments separated by permeable membranes, acting as diffusion barriers, has been extended. A numerical model of restricted diffusion and magnetization relaxation behavior in pfg-CPMG NMR experiments, based on the Fick's second law of diffusion, is presented. This model is applicable to a wide range of systems and allows the exploration of temporal and spatial behavior of the magnetization with and without the influence of gradient pulses. Results of the numerical experiments show their correspondence to the previously observed ones and demonstrate the importance of the inclusion of the time domain data in analyzing diffusion measurements. PMID:9878479
Time constant of defect relaxation in ion-irradiated 3C-SiC
Wallace, J. B.; Bayu Aji, L. B.; Kucheyev, S. O.; Shao, L.
2015-05-18
Above room temperature, the buildup of radiation damage in SiC is a dynamic process governed by the mobility and interaction of ballistically generated point defects. Here, we study the dynamics of radiation defects in 3C-SiC bombarded at 100?C with 500?keV Ar ions, with the total ion dose split into a train of equal pulses. Damagedepth profiles are measured by ion channeling for a series of samples irradiated under identical conditions except for different durations of the passive part of the beam cycle. Results reveal an effective defect relaxation time constant of ?3 ms (for second order kinetics) and a dynamic annealing efficiency of ?40% for defects in both Si and C sublattices. This demonstrates a crucial role of dynamic annealing at elevated temperatures and provides evidence of the strong coupling of defect accumulation processes in the two sublattices of 3C-SiC.
Time constant of defect relaxation in ion-irradiated 3C-SiC
NASA Astrophysics Data System (ADS)
Wallace, J. B.; Bayu Aji, L. B.; Shao, L.; Kucheyev, S. O.
2015-05-01
Above room temperature, the buildup of radiation damage in SiC is a dynamic process governed by the mobility and interaction of ballistically generated point defects. Here, we study the dynamics of radiation defects in 3C-SiC bombarded at 100 C with 500 keV Ar ions, with the total ion dose split into a train of equal pulses. Damage-depth profiles are measured by ion channeling for a series of samples irradiated under identical conditions except for different durations of the passive part of the beam cycle. Results reveal an effective defect relaxation time constant of 3 ms (for second order kinetics) and a dynamic annealing efficiency of 40 % for defects in both Si and C sublattices. This demonstrates a crucial role of dynamic annealing at elevated temperatures and provides evidence of the strong coupling of defect accumulation processes in the two sublattices of 3C-SiC.
Equilibrium distributions and relaxation times in gaslike economic models: An analytical derivation
NASA Astrophysics Data System (ADS)
Calbet, Xavier; Lpez, Jos-Luis; Lpez-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.
Slutsky, R.A.; Andre, M.P.; Mattrey, R.F.; Brahme, F.J.
1984-01-01
To assess the effects of renal ischemia and reperfusion on in vitro magnetic relaxation times (T/sub 1/ = magnetization recovery, T/sub 2/ = spin echo), we evaluated the spectroscopic characteristics of the renal cortex from 25 rabbits. Eight served as controls (Group 1), nine had one renal pedicle ligated for 1 hr (Group 2), and eight (Group 3) were occluded for 1 hr and reperfused for 30 min. For intraanimal comparison purposes, % H/sub 2/O content, T/sub 1/ (msec), and T/sub 2/ (msec) of the ischemic (reperfused) kidney were normalized to the values from the normal kidney within the same animal. Renal ischemia consistently increased water content, which was exaggerated by reperfusion. In association with ischemia, T/sub 1/ fell, and with reperfusion T/sub 1/ lengthened. T/sub 2/ increased with ischemia and declined from the peak ischemic effects with reperfusion.
Effects of the individual particle relaxation time on superspin glass dynamics
NASA Astrophysics Data System (ADS)
Andersson, Mikael Svante; De Toro, Jose Angel; Lee, Su Seong; Normile, Peter S.; Nordblad, Per; Mathieu, Roland
2016-02-01
The low temperature dynamic magnetic properties of two dense magnetic nanoparticle assemblies with similar superspin glass transition temperatures Tg˜140 K are compared. The two samples are made from batches of 6 and 8 nm monodisperse γ -Fe2O3 nanoparticles, respectively. The properties of the individual particles are extracted from measurements on reference samples where the particles have been covered with a thick silica coating. The blocking temperatures of these dilute assemblies are found at 12.5 K for the 6 nm particles and at 35 K for the 8 nm particles, which implies different anisotropy energy barriers of the individual particles and vastly different temperature evolution of their relaxation times. The results of the measurements on the concentrated particle assemblies suggest a strong influence of the particle energy barrier on the details of the aging dynamics, memory behavior, and apparent superspin dimensionality of the particles.
Stability of graph communities across time scales
Delvenne, J.-C.; Yaliraki, S. N.; Barahona, M.
2010-01-01
The complexity of biological, social, and engineering networks makes it desirable to find natural partitions into clusters (or communities) that can provide insight into the structure of the overall system and even act as simplified functional descriptions. Although methods for community detection abound, there is a lack of consensus on how to quantify and rank the quality of partitions. We introduce here the stability of a partition, a measure of its quality as a community structure based on the clustered autocovariance of a dynamic Markov process taking place on the network. Because the stability has an intrinsic dependence on time scales of the graph, it allows us to compare and rank partitions at each time and also to establish the time spans over which partitions are optimal. Hence the Markov time acts effectively as an intrinsic resolution parameter that establishes a hierarchy of increasingly coarser communities. Our dynamical definition provides a unifying framework for several standard partitioning measures: modularity and normalized cut size can be interpreted as one-step time measures, whereas Fiedler’s spectral clustering emerges at long times. We apply our method to characterize the relevance of partitions over time for constructive and real networks, including hierarchical graphs and social networks, and use it to obtain reduced descriptions for atomic-level protein structures over different time scales. PMID:20615936
Picosecond-Time-Scale Fluctuations of Proteins in Glassy Matrices: The Role of Viscosity
Cornicchi, Elena; Onori, Giuseppe; Paciaroni, Alessandro
2005-10-07
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.
NASA Astrophysics Data System (ADS)
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 π/2 pulses with phases alternated by π enable performing the experiments on-resonance and independently of Tp, when Tp < T2∗. Moreover, a CPMG type sequence with π/2 refocusing pulses shows similar results to CP-CWFP when the pulses are alternated between y and -y axis, CPMG90y-y. In these approaches, the relaxation times are determined using the magnitude of the signals after the first pulse |M0| and in the steady-state |Mss|, as well as the exponential time constant T∗ to reach the steady-state regime, as in conventional CWFP. CP-CWFPx-x shows the highest dynamic range to measure T∗ among CWFP sequences and, therefore, is the best technique to measure T1 and T2 since it is less susceptible to SNR and can be performed for any T1/T2 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
Accuracy metrics for judging time scale algorithms
NASA Technical Reports Server (NTRS)
Douglas, R. J.; Boulanger, J.-S.; Jacques, C.
1994-01-01
Time scales have been constructed in different ways to meet the many demands placed upon them for time accuracy, frequency accuracy, long-term stability, and robustness. Usually, no single time scale is optimum for all purposes. In the context of the impending availability of high-accuracy intermittently-operated cesium fountains, we reconsider the question of evaluating the accuracy of time scales which use an algorithm to span interruptions of the primary standard. We consider a broad class of calibration algorithms that can be evaluated and compared quantitatively for their accuracy in the presence of frequency drift and a full noise model (a mixture of white PM, flicker PM, white FM, flicker FM, and random walk FM noise). We present the analytic techniques for computing the standard uncertainty for the full noise model and this class of calibration algorithms. The simplest algorithm is evaluated to find the average-frequency uncertainty arising from the noise of the cesium fountain's local oscillator and from the noise of a hydrogen maser transfer-standard. This algorithm and known noise sources are shown to permit interlaboratory frequency transfer with a standard uncertainty of less than 10(exp -15) for periods of 30-100 days.
Nuclear magnetic relaxation, correlation time spectrum, and molecular dynamics in a linear polymer
Chernov, V. M. Krasnopol'skii, G. S.
2008-08-15
The pulsed nuclear magnetic resonance (NMR) method at a proton frequency of 25 MHz at temperatures of 22-160{sup o}C is used to detect the transverse magnetization decay in polyisoprene rubbers with various molecular masses, to determine the NMR damping time T{sub 2}, and to measure spin-lattice relaxation time T{sub 1} and time T{sub 2eff} of damping of solid-echo signals under the action of a sequence of MW-4 pulses modified by introducing 180{sup o} pulses. The dispersion dependences of T{sub 2eff} obtained for each temperature are combined into one using the temperature-frequency equivalence principle. On the basis of the combined dispersion dependence of T{sub 2eff} and the data on T{sub 2} and T{sub 1}, the correlation time spectrum of molecular movements is constructed. Analysis of the shape of this spectrum shows that the dynamics of polymer molecules can be described in the first approximation by the Doi-Edwards tube-reptation model.
Soroushian, Behrouz; Yang, Xinmai
2011-01-01
Modulated tone-burst light was employed to measure non-radiative relaxation time of fluorophores with biomedical importance through photoacoustic effect. Non-radiative relaxation time was estimated through the frequency dependence of photoacoustic signal amplitude. Experiments were performed on solutions of new indocyanine green (IR-820), which is a near infrared dye and has biomedical applications, in two different solvents (water and dimethyl sulfoxide (DMSO)). A 1.5 times slower non-radiative relaxation for the solution of dye in DMSO was observed comparing with the aqueous solution. This result agrees well with general finding that non-radiative relaxation of molecules in triplet state depends on viscosity of solvents in which they are dissolved. Measurements of the non-radiative relaxation time can be used as a new source of contrast mechanism in photoacoustic imaging technique. The proposed method has potential applications such as imaging tissue oxygenation and mapping of other chemophysical differences in microenvironment of exogenous biomarkers. PMID:22025981
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.
Hemispheric Asymmetries in Substorm Recovery Time Scales
NASA Technical Reports Server (NTRS)
Fillingim, M. O.; Chua, D H.; Germany, G. A.; Spann, James F.
2009-01-01
Previous statistical observations have shown that the recovery time scales of substorms occurring in the winter and near equinox (when the nighttime auroral zone was in darkness) are roughly twice as long as the recovery time scales for substorms occurring in the summer (when the nighttime auroral region was sunlit). This suggests that auroral substorms in the northern and southern hemispheres develop asymmetrically during solstice conditions with substorms lasting longer in the winter (dark) hemisphere than in the summer (sunlit) hemisphere. Additionally, this implies that more energy is deposited by electron precipitation in the winter hemisphere than in the summer one during substorms. This result, coupled with previous observations that have shown that auroral activity is more common when the ionosphere is in darkness and is suppressed when the ionosphere is in daylight, strongly suggests that the ionospheric conductivity plays an important role governing how magnetospheric energy is transferred to the ionosphere during substorms. Therefore, the ionosphere itself may dictate how much energy it will accept from the magnetosphere during substorms rather than this being an externally imposed quantity. Here, we extend our earlier work by statistically analyzing the recovery time scales for a large number of substorms observed in the conjugate hemispheres simultaneously by two orbiting global auroral imagers: Polar UVI and IMAGE FUV. Our current results are consistent with previous observations. The recovery time scales are observed to be longer in the winter (dark) hemisphere while the auroral activity has a shorter duration in the summer (sunlit) hemisphere. This leads to an asymmetric energy input from the magnetosphere to the ionosphere with more energy being deposited in the winter hemisphere than in the summer hemisphere.
Liquidity crises on different time scales
NASA Astrophysics Data System (ADS)
Corradi, Francesco; Zaccaria, Andrea; Pietronero, Luciano
2015-12-01
We present an empirical analysis of the microstructure of financial markets and, in particular, of the static and dynamic properties of liquidity. We find that on relatively large time scales (15 min) large price fluctuations are connected to the failure of the subtle mechanism of compensation between the flows of market and limit orders: in other words, the missed revelation of the latent order book breaks the dynamical equilibrium between the flows, triggering the large price jumps. On smaller time scales (30 s), instead, the static depletion of the limit order book is an indicator of an intrinsic fragility of the system, which is related to a strongly nonlinear enhancement of the response. In order to quantify this phenomenon we introduce a measure of the liquidity imbalance present in the book and we show that it is correlated to both the sign and the magnitude of the next price movement. These findings provide a quantitative definition of the effective liquidity, which proves to be strongly dependent on the considered time scales.
NASA Astrophysics Data System (ADS)
Misra, Sushil K.
The measurement of very short spin-lattice, or longitudinal, relaxation (SLR) times (i.e., 10-10 < T 1 < 10-6 s) is of great importance today for the study of relaxation processes. Recent case studies include, for example, glasses doped with paramagnetic ions (Vergnoux et al., 1996; Zinsou et al., 1996), amorphous Si (dangling bonds) and copper-chromium-tin spinel (Cr3+) (Misra, 1998), and polymer resins doped with rare-earth ions (Pescia et al., 1999a; Pescia et al. 1999b). The ability to measure such fast SLR data on amorphous Si and copper-chromium-tin spinel led to an understanding of the role of exchange interaction in affecting spin-lattice relaxation, while the data on polymer resins doped with rare-earth ions provided evidence of spin-fracton relaxation (Pescia et al., 1999a, b). But such fast SLR times are not measurable by the most commonly used techniques of saturation- and inversion-recovery (Poole, 1982; Alger, 1968), which only measure spin-lattice relaxation times longer than 10-6 s. A summary of relevant experimental data is presented in Table 1.
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.
Cade-Menun, B J; Liu, C W; Nunlist, R; McColl, J G
2002-01-01
Phosphorus-31 nuclear magnetic resonance (NMR) spectroscopy is an excellent tool with which to study soil organic P, allowing quantitative, comparative analysis of P forms. However, for 31P NMR to be tative, all peaks must be completely visible, and in their correct relative proportions. There must be no line broadening, and adequate delay times must be used to avoid saturation of peaks. The objective of this study was to examine the effects of extractants on delay times and peak saturation. Two samples (a forest litter and a mineral soil sample) and three extractants (0.25 M NaOH, NaOH plus Chelex (Bio-Rad Laboratories, Hercules, CA), and NaOH plus EDTA) were used to determine the differences in the concentration of P and cations solubilized by each extractant, and to measure spin-lattice (T1) relaxation times of P peaks in each extract. For both soil and litter, NaOH-Chelex extracted the lowest concentrations of P. For the litter sample, T1 values were short for all extractants due to the high Fe concentration remaining after extraction. For the soil sample, there were noticeable differences among the extractants. The NaOH-Chelex sample had less Fe and Mn remaining in solution after extraction than the other extractants, and the longest delay times used in the study, 6.4 s, were not long enough for quantitative analysis. Delay times of 1.5 to 2 s for the NaOH and NaOH-EDTA were adequate. Line broadening was highest in the NaOH extracts, which had the highest concentration of Fe. On the basis of these results, recommendations for future analyses of soil and litter samples by solution 31P NMR spectroscopy include: careful selection of an extractant; measurement of paramagnetic ions extracted with P; use of appropriate delay times and the minimum number of scans; and measurement of T1 values whenever possible. PMID:11931434
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.
Time Ephemeris and General Relativistic Scale Factor
NASA Astrophysics Data System (ADS)
Fukushima, Toshio
2010-11-01
Time ephemeris is the location-independent part of the transformation formula relating two time coordinates such as TCB and TCG (Fukushima 2009). It is computed from the corresponding (space) ephemerides providing the relative motion of two spatial coordinate origins such as the motion of geocenter relative to the solar system barycenter. The time ephemerides are inevitably needed in conducting precise four dimensional coordinate transformations among various spacetime coordinate systems such as the GCRS and BCRS (Soffel et al. 2003). Also, by means of the time average operation, they are used in determining the information on scale conversion between the pair of coordinate systems, especially the difference of the general relativistic scale factor from unity such as LC. In 1995, we presented the first numerically-integrated time ephemeris, TE245, from JPL's planetary ephemeris DE245 (Fukushima 1995). It gave an estimate of LC as 1.4808268457(10) 10-8, which was incorrect by around 2 10-16. This was caused by taking the wrong sign of the post-Newtonian contribution in the final summation. Four years later, we updated TE245 to TE405 associated with DE405 (Irwin and Fukushima 1999). This time the renewed vale of LC is 1.48082686741(200) 10-8 Another four years later, by using a precise technique of time average, we improved the estimate of Newtonian part of LC for TE405 as 1.4808268559(6) 10-8 (Harada and Fukushima 2003). This leads to the value of LC as LC = 1.48082686732(110) 10-8. If we combine this with the constant defining the mean rate of TCG-TT, LG = 6.969290134 10-10 (IAU 2001), we estimate the numerical value of another general relativistic scale factor LB = 1.55051976763(110) 10-8, which has the meaning of the mean rate of TCB-TT. The main reasons of the uncertainties are the truncation effect in time average and the uncertainty of asteroids' perturbation. As a compact realization of the time ephemeris, we prepared HF2002, a Fortran routine to compute approximate harmonic series of TE405 with the RMS error of 0.446 ns for the period 1600 to 2200 (Harada and Fukushima 2003). It is included in the IERS Convention 2003 (McCarthy and Petit 2003) and available from the IERS web site; http://tai.bipm.org/iers/conv2003/conv2003_c10.html.
Electron Spin Relaxation and Coherence Times in Si/SiGe Quantum Dots
NASA Astrophysics Data System (ADS)
Jock, R. M.; He, Jianhua; Tyryshkin, A. M.; Lyon, S. A.; Lee, C.-H.; Huang, S.-H.; Liu, C. W.
2013-03-01
Single electron spin states in Si/SiGe quantum dots have shown promise as qubits for quantum information processing. Recently, electron spins in gated Si/SiGe quantum dots have displayed relaxation (T1) and coherence (T2) times of 250 ?s at 350mK. The experiments used conventional X-band (10 GHz) pulsed Electron Spin Resonance (pESR) on a large area (3.5 x 20 mm2) , double gated, undoped Si/SiGe heterostructure, which was patterned with 2 x 108 quantum dots using e-beam lithography. Dots with 150 nm radii and 700 nm period are induced in a natural Si quantum well by the gates. Smaller dots are expected to reduce the effects of nearly degenerate valley states and spin-orbit coupling on the electron spin coherence. However, the small number of spins makes signal recovery extremely challenging. We have implemented a broadband cryogenic HEMT low-noise-amplifier and a high-speed single-pole double-throw switch operating at liquid helium temperatures. The switch and preamp have improved our signal to noise by an order of magnitude, allowing for smaller samples and shorter measurement times. We will describe these improvements and the data they have enabled. supported by the ARO
Two-relaxation-time lattice Boltzmann method for the anisotropic dispersive Henry problem
NASA Astrophysics Data System (ADS)
Servan-Camas, Borja; Tsai, Frank T.-C.
2010-02-01
This study develops a lattice Boltzmann method (LBM) with a two-relaxation-time collision operator (TRT) to cope with anisotropic heterogeneous hydraulic conductivity and anisotropic velocity-dependent hydrodynamic dispersion in the saltwater intrusion problem. The directional-speed-of-sound technique is further developed to address anisotropic hydraulic conductivity and dispersion tensors. Forcing terms are introduced in the LBM to correct numerical errors that arise during the recovery procedure and to describe the sink/source terms in the flow and transport equations. In order to facilitate the LBM implementation, the forcing terms are combined with the equilibrium distribution functions (EDFs) to create pseudo-EDFs. This study performs linear stability analysis and derives LBM stability domains to solve the anisotropic advection-dispersion equation. The stability domains are used to select the time step at which the lattice Boltzmann method provides stable solutions to the numerical examples. The LBM was implemented for the anisotropic dispersive Henry problem with high ratios of longitudinal to transverse dispersivities, and the results compared well to the solutions in the work of Abarca et al. (2007).
Picosecond-time-resolved studies of nonradiative relaxation in ruby and alexandrite
Gayen, S.K.; Wang, W.B.; Petricevic, V.; Alfano, R.R.
1985-01-01
Dynamics of the nonradiative transitions between the /sup 4/T/sub 2/ pump band and the /sup 2/E storage level of the Cr/sup 3 +/ ion in ruby and alexandrite crystals is studied using the picosecond excite-and-probe absorption technique. A 527-nm picosecond pulse excites the /sup 4/T/sub 2/ state of the Cr/sup 3 +/ ion, and an infrared picosecond probe pulse monitors the subsequent growth and decay of population in the excited states as a function of pump-probe delay. An upper limit of 7 ps is determined for the nonradiative lifetime of the /sup 4/T/sub 2/ state in ruby. A vibrational relaxation time of 25 ps for the /sup 4/T/sub 2/ band in alexandrite is estimated. The time to attain thermal equilibrium population between the /sup 2/E and /sup 4/T/sub 2/ levels of alexandrite following excitation of /sup 4/T/sub 2/ band is estimated to be approx. 100 ps.
Deciphering Time Scale Hierarchy in Reaction Networks.
Nagahata, Yutaka; Maeda, Satoshi; Teramoto, Hiroshi; Horiyama, Takashi; Taketsugu, Tetsuya; Komatsuzaki, Tamiki
2016-03-01
Markovian dynamics on complex reaction networks are one of the most intriguing subjects in a wide range of research fields including chemical reactions, biological physics, and ecology. To represent the global kinetics from one node (corresponding to a basin on an energy landscape) to another requires information on multiple pathways that directly or indirectly connect these two nodes through the entire network. In this paper we present a scheme to extract a hierarchical set of global transition states (TSs) over a discrete-time Markov chain derived from first-order rate equations. The TSs can naturally take into account the multiple pathways connecting any pair of nodes. We also propose a new type of disconnectivity graph (DG) to capture the hierarchical organization of different time scales of reactions that can capture changes in the network due to changes in the time scale of observation. The crux is the introduction of the minimum conductance cut (MCC) in graph clustering, corresponding to the dividing surface across the network having the "smallest" transition probability between two disjoint subnetworks (superbasins on the energy landscape) in the network. We present a new combinatorial search algorithm for finding this MCC. We apply our method to a reaction network of Claisen rearrangement of allyl vinyl ether that consists of 23 nodes and 66 links (saddles on the energy landscape) connecting them. We compare the kinetic properties of our DG to those of the transition matrix of the rate equations and show that our graph can properly reveal the hierarchical organization of time scales in a network. PMID:26641663
Scaling laws from geomagnetic time series
Voros, Z.; Kovacs, P.; Juhasz, A.; Kormendi, A.; Green, A.W.
1998-01-01
The notion of extended self-similarity (ESS) is applied here for the X - component time series of geomagnetic field fluctuations. Plotting nth order structure functions against the fourth order structure function we show that low-frequency geomagnetic fluctuations up to the order n = 10 follow the same scaling laws as MHD fluctuations in solar wind, however, for higher frequencies (f > l/5[h]) a clear departure from the expected universality is observed for n > 6. ESS does not allow to make an unambiguous statement about the non triviality of scaling laws in "geomagnetic" turbulence. However, we suggest to use higher order moments as promising diagnostic tools for mapping the contributions of various remote magnetospheric sources to local observatory data. Copyright 1998 by the American Geophysical Union.
Time sequence and time scale of intermediate mass fragment emission
NASA Astrophysics Data System (ADS)
de Filippo, E.; Pagano, A.; Wilczy?ski, J.; Amorini, F.; Anzalone, A.; Auditore, L.; Baran, V.; Berceanu, I.; Blicharska, J.; Brzychczyk, J.; Bonasera, A.; Borderie, B.; Bougault, R.; Bruno, M.; Cardella, G.; Cavallaro, S.; Chatterjee, M. B.; Chbihi, A.; Cibor, J.; Colonna, M.; D'Agostino, M.; Dayras, R.; di Toro, M.; Frankland, J.; Galichet, E.; Gawlikowicz, W.; Geraci, E.; Giustolisi, F.; Grzeszczuk, A.; Guazzoni, P.; Guinet, D.; Iacono-Manno, M.; Kowalski, S.; La Guidara, E.; Lanzan, G.; Lanzalone, G.; Le Neindre, N.; Li, S.; Maiolino, C.; Majka, Z.; Papa, M.; Petrovici, M.; Piasecki, E.; Pirrone, S.; P?aneta, R.; Politi, G.; Pop, A.; Porto, F.; Rivet, M. F.; Rosato, E.; Rizzo, F.; Russo, S.; Russotto, P.; Sassi, M.; Schmidt, K.; Siwek-Wilczy?ska, K.; Skwira, I.; Sperduto, M. L.; ?widerski, ?.; Trifir, A.; Trimarchi, M.; Vannini, G.; Vigilante, M.; Wieleczko, J. P.; Wu, H.; Xiao, Z.; Zetta, L.; Zipper, W.
2005-04-01
Semiperipheral collisions in the 124Sn+64Ni reaction at 35 MeV/nucleon were studied using the forward part of the Charged Heavy Ion Mass and Energy Resolving Array. Nearly completely determined ternary events involving projectilelike fragments (PLF), targetlike fragments (TLF), and intermediate mass fragments (IMF) were selected. A new method of studying the reaction mechanism, focusing on the analysis of the correlations between relative velocities in the IMF+PLF and IMF+TLF subsystems, is proposed. The relative velocity correlations provide information on the time sequence and time scale of the neck fragmentation processes leading to production of IMFs. It is shown that the majority of light IMFs are produced within 40 80 fm/c after the system starts to reseparate. Heavy IMFs are formed at times of about 120 fm/c or later and can be viewed as resulting from two-step (sequential) neck rupture processes.
Structure-dependent dc conductivity and relaxation time in the Debye-Stokes-Einstein equation.
Power, G; Vij, J K; Johari, G P
2007-09-27
The basis for a modification of the Debye-Stokes-Einstein (DSE) equation between the dc conductivity, sigma(dc), and dielectric relaxation time, tau, has been examined by using broad-band dielectric spectroscopy of LiClO4 solutions in 5-methyl-2-hexanol and 1-propanol and of pure liquids. According to the DSE equation, the log sigma(dc)-log tau plots should have a slope of -1. We find that sigma(dc) begins to depend upon the structure of an electrolytic solution when a variation of solvent's equilibrium dielectric permittivity, epsilon(s), with temperature causes the ion population to vary. As a consequence of this intrinsic dependence, the log sigma(dc)-log tau plots do not obey the DSE equation. Inclusion of the effect of change in epsilon(s) on the DSE equation may be useful in analyzing the measured quantities in terms of Brownian diffusion of both ions and molecules in ultraviscous liquids. Proton translocation along a hydrogen bond contributes little to sigma(dc), which appears to be predominantly determined by the ion population in the two alcohols and the solutions. The effect is briefly discussed in the potential energy landscape paradigm of structure fluctuations, and it is suggested that the high-frequency shear modulus measurements of ionic solutions would help reveal the temperature-dependent deviation from the DSE equation. PMID:17764166
Phylogeography takes a relaxed random walk in continuous space and time.
Lemey, Philippe; Rambaut, Andrew; Welch, John J; Suchard, Marc A
2010-08-01
Research aimed at understanding the geographic context of evolutionary histories is burgeoning across biological disciplines. Recent endeavors attempt to interpret contemporaneous genetic variation in the light of increasingly detailed geographical and environmental observations. Such interest has promoted the development of phylogeographic inference techniques that explicitly aim to integrate such heterogeneous data. One promising development involves reconstructing phylogeographic history on a continuous landscape. Here, we present a Bayesian statistical approach to infer continuous phylogeographic diffusion using random walk models while simultaneously reconstructing the evolutionary history in time from molecular sequence data. Moreover, by accommodating branch-specific variation in dispersal rates, we relax the most restrictive assumption of the standard Brownian diffusion process and demonstrate increased statistical efficiency in spatial reconstructions of overdispersed random walks by analyzing both simulated and real viral genetic data. We further illustrate how drawing inference about summary statistics from a fully specified stochastic process over both sequence evolution and spatial movement reveals important characteristics of a rabies epidemic. Together with recent advances in discrete phylogeographic inference, the continuous model developments furnish a flexible statistical framework for biogeographical reconstructions that is easily expanded upon to accommodate various landscape genetic features. PMID:20203288
Transverse relaxation time reflects brain amyloidosis in young APP/PS1 transgenic mice.
El Tayara, Nadine El Tannir; Volk, Andreas; Dhenain, Marc; Delatour, Benoît
2007-07-01
Amyloid deposits are one of the hallmarks of Alzheimer's disease (AD), one of the most devastating neurodegenerative disorders. In transgenic mice modeling Alzheimer's pathology, the MR transverse relaxation time (T(2)) has been described to be modulated by amyloidosis. This modification has been attributed to the age-related iron deposition that occurs within the amyloid plaques of old animals. In the present study, young APP/PS1 transgenic mice without histochemically detectable iron in the brain were specifically studied. In vivo measurements of T(2) in the hippocampus, at the level of the subiculum, were shown to reflect the density of amyloid plaques. This suggests that T(2) variations can be induced solely by aggregated amyloid deposits in the absence of associated histologically-detectable iron. Thus T(2) from regions with high amyloid load, such as the subiculum, is particularly well suited for following plaque deposition in young animals, i.e., at the earliest stages of the pathological process. PMID:17659609
Phylogeography Takes a Relaxed Random Walk in Continuous Space and Time
Lemey, Philippe; Rambaut, Andrew; Welch, John J.; Suchard, Marc A.
2010-01-01
Research aimed at understanding the geographic context of evolutionary histories is burgeoning across biological disciplines. Recent endeavors attempt to interpret contemporaneous genetic variation in the light of increasingly detailed geographical and environmental observations. Such interest has promoted the development of phylogeographic inference techniques that explicitly aim to integrate such heterogeneous data. One promising development involves reconstructing phylogeographic history on a continuous landscape. Here, we present a Bayesian statistical approach to infer continuous phylogeographic diffusion using random walk models while simultaneously reconstructing the evolutionary history in time from molecular sequence data. Moreover, by accommodating branch-specific variation in dispersal rates, we relax the most restrictive assumption of the standard Brownian diffusion process and demonstrate increased statistical efficiency in spatial reconstructions of overdispersed random walks by analyzing both simulated and real viral genetic data. We further illustrate how drawing inference about summary statistics from a fully specified stochastic process over both sequence evolution and spatial movement reveals important characteristics of a rabies epidemic. Together with recent advances in discrete phylogeographic inference, the continuous model developments furnish a flexible statistical framework for biogeographical reconstructions that is easily expanded upon to accommodate various landscape genetic features. PMID:20203288
Brain T2 relaxation times correlate with regional cerebral blood volume.
Anderson, C M; Kaufman, M J; Lowen, S B; Rohan, M; Renshaw, P F; Teicher, M H
2005-03-01
We previously reported cerebellar and putaminal transverse relaxation time (T2) differences in children with ADHD and in adults with childhood trauma. As brain T2 can be altered by deoxyhemoglobin concentration ([dHb]) and because [dHb] is proportional to regional cerebral blood volume (rCBV), at steady state we attributed those differences to rCBV changes. Studies in other species have established a correlation between T2 and rCBV; however this has yet to be demonstrated in human brain. Echo planar imaging (EPI) T2 relaxometry and dynamic susceptibility-contrast (DSC) MRI were used to measure T2 and rCBV in 11 healthy adults. Significant T2-rCBV correlations were observed in both cerebellar vermis and putamen (r = 0.759,p = 0.007;r = 0.782,p = 0.004, respectively). These correlations predict 9 +/- 3% and 10 +/- 3% rCBV changes, respectively, for each 1-msec change in T2. Consequently, brain T2 measurements may be useful for estimating steady-state rCBV. PMID:15592693
[Time-resolved optical studies of charge relaxation and charge transfer at electrode interfaces
Not Available
1992-01-01
Key components were identified in a quantitative model of carrier relaxation in semiconductor electrodes: nonlinear aspects of nonradiative and radiative recombination, effect of space charge field on carrier dynamics, self-absorption effects in direct gas semiconductors, and influence of surface state population kinetics on charge carrier recombination. For CdSe, the first three are operative (no direct proof of the last one). A realistic kinetic model for carrier recombination in the bulk of CdSe was used which includes important nonlinear effects, both radiative and nonradiative. The change in interfacial recombination velocity with the chemical nature of the sinterface was studied (n-CdSe/silane interfaces). Temperature effect (278 to 328 K) on fluorescence decay of n-CdSe in contact with 0.5 M KOH was found to be weak. An analytical solution was obtained for time-resolved fluoresence from electrodes under potential bias, and is being tested. Fluorescence work on a different material, CdS, indicate different recombination kinetics; this material was used to directly pump an optical transition of a surface state.
[Time-resolved optical studies of charge relaxation and charge transfer at electrode interfaces
Not Available
1992-12-31
Key components were identified in a quantitative model of carrier relaxation in semiconductor electrodes: nonlinear aspects of nonradiative and radiative recombination, effect of space charge field on carrier dynamics, self-absorption effects in direct gas semiconductors, and influence of surface state population kinetics on charge carrier recombination. For CdSe, the first three are operative (no direct proof of the last one). A realistic kinetic model for carrier recombination in the bulk of CdSe was used which includes important nonlinear effects, both radiative and nonradiative. The change in interfacial recombination velocity with the chemical nature of the sinterface was studied (n-CdSe/silane interfaces). Temperature effect (278 to 328 K) on fluorescence decay of n-CdSe in contact with 0.5 M KOH was found to be weak. An analytical solution was obtained for time-resolved fluoresence from electrodes under potential bias, and is being tested. Fluorescence work on a different material, CdS, indicate different recombination kinetics; this material was used to directly pump an optical transition of a surface state.
Ikeda, Kazuhiro Kawaguchi, Hitoshi
2015-02-07
We performed measurements at room temperature for a GaAs/AlGaAs multiple quantum well grown on GaAs(110) using a time-resolved microscopic photoluminescence (micro-PL) technique to find what effects spin diffusion had on the measured electron spin relaxation time, τ{sub s}, and developed a method of estimating the spin diffusion coefficient, D{sub s}, using the measured data and the coupled drift-diffusion equations for spin polarized electrons. The spatial nonuniformities of τ{sub s} and the initial degree of electron spin polarization caused by the pump intensity distribution inside the focal spot were taken into account to explain the dependence of τ{sub s} on the measured spot size, i.e., a longer τ{sub s} for a smaller spot size. We estimated D{sub s} as ∼100 cm{sup 2}/s, which is similar to a value reported in the literature. We also provided a qualitative understanding on how spin diffusion lengthens τ{sub s} in micro-PL measurements.
Calixto, Nathaniel E; Kumar, Deepak; Subburaj, Karupppasamy; Singh, Justin; Schooler, Joseph; Nardo, Lorenzo; Li, Xiaojuan; Souza, Richard B; Link, Thomas M; Majumdar, Sharmila
2016-02-01
This study assessed the effects of static loading on MRI relaxation times of menisci in individuals with and without radiographic knee OA. High-resolution fast spin-echo (FSE) and T1 ? /T2 relaxation time MR sequences were obtained with and without loading at 50% body weight in 124 subjects. T1? /T2 relaxation times were calculated in menisci, and meniscus lesions were assessed through clinical grading. Student's t-test compared OA and control unloaded relaxation times as well as within-group changes with loading, Generalized Linear Models evaluated zonal variation, and ANCOVA compared loading response between groups. Unloaded T1? and T2 in the middle and inner zones of the lateral anterior horn and outer zone of the medial posterior horn were significantly higher in OA and suggest that meniscal OA change occurs unevenly. Zonal T1? and T2 showed differing patterns between anterior and posterior horns, suggesting differences in macromolecular organization. Significant increases with loading were seen largely in the T2 of controls and less frequently in subjects with OA. In the medial posterior horn, T1? and T2 decreased with loading in OA but changed negligibly in controls; these significantly different loading responses between groups may indicate load transmission failure in OA menisci. 2015 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:249-261, 2016. PMID:26223430
ERIC Educational Resources Information Center
Gasyna, Zbigniew L.; Jurkiewicz, Antoni
2004-01-01
An experiment designed for the physical chemistry laboratory where (super 13)C NMR is applied to determine the spin-lattice relaxation time for carbon atoms in n-hexanol is proposed. It is concluded that students learn the principles and concepts of NMR spectroscopy as well as dynamic NMR experiments.
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.
Nanosecond Time Scale Motions in Proteins Revealed by High-Resolution NMR Relaxometry
2013-01-01
Understanding the molecular determinants underlying protein function requires the characterization of both structure and dynamics at atomic resolution. Nuclear relaxation rates allow a precise characterization of protein dynamics at the Larmor frequencies of spins. This usually limits the sampling of motions to a narrow range of frequencies corresponding to high magnetic fields. At lower fields one cannot achieve sufficient sensitivity and resolution in NMR. Here, we use a fast shuttle device where the polarization builds up and the signals are detected at high field, while longitudinal relaxation takes place at low fields 0.5 < B0 < 14.1 T. The sample is propelled over a distance up to 50 cm by a blowgun-like system in about 50 ms. The analysis of nitrogen-15 relaxation in the protein ubiquitin over such a wide range of magnetic fields offers unprecedented insights into molecular dynamics. Some key regions of the protein feature structural fluctuations on nanosecond time scales, which have so far been overlooked in high-field relaxation studies. Nanosecond motions in proteins may have been underestimated by traditional high-field approaches, and slower supra-?c motions that have no effect on relaxation may have been overestimated. High-resolution relaxometry thus opens the way to a quantitative characterization of nanosecond motions in proteins. PMID:24228712
Oscillation Regularity in Noise-Driven Excitable Systems with Multi-Time-Scale Adaptation
NASA Astrophysics Data System (ADS)
Nesse, William H.; Negro, Christopher A. Del; Bressloff, Paul C.
2008-08-01
We investigate oscillation regularity of a noise-driven system modeled with a slow after-hyperpolarizing adaptation current (AHP) composed of multiple-exponential relaxation time scales. Sufficiently separated slow and fast AHP time scales (biphasic decay) cause a peak in oscillation irregularity for intermediate input currents I, with relatively regular oscillations for small and large currents. An analytic formulation of the system as a stochastic escape problem establishes that the phenomena is distinct from standard forms of coherence resonance. Our results explain data on the oscillation regularity of the pre-Btzinger complex, a neural oscillator responsible for inspiratory breathing rhythm generation in mammals.
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.
Radial Transport of Large-scale Magnetic Fields in Accretion Disks. II. Relaxation to Steady States
NASA Astrophysics Data System (ADS)
Takeuchi, Taku; Okuzumi, Satoshi
2014-12-01
We study the time evolution of a large-scale magnetic flux threading an accretion disk. The induction equation of the mean poloidal field is solved under the standard viscous disk model. Magnetic flux evolution is controlled by two timescales: one is the timescale of the inward advection of the magnetic flux, ?adv. This is induced by the dragging of the flux by the accreting gas. The other is the outward diffusion timescale of the magnetic flux ?dif. We consider diffusion due to the Ohmic resistivity. These timescales can be significantly different from the disk viscous timescale ?disk. The behaviors of the magnetic flux evolution are quite different depending on the magnitude relationship of the timescales ?adv, ?dif, and ?disk. The most interesting phenomena occur when ?adv Lt ?dif, ?disk. In such a case, the magnetic flux distribution approaches a quasi-steady profile much faster than the viscous evolution of the gas disk, and the magnetic flux has also been tightly bundled to the inner part of the disk. In the inner part, although the poloidal magnetic field becomes much stronger than the interstellar magnetic field, the field strength is limited to the maximum value that is analytically given by our previous work. We also find a condition for the initial large magnetic flux, which is a fossil of the magnetic field dragging during the early phase of star formation that survives for a duration in which significant gas disk evolution proceeds.
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.
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
NASA Astrophysics Data System (ADS)
Zakharov, Anatoly I.; Adzhemyan, Loran Ts.; Shchekin, Alexander K.
2015-09-01
We have performed direct numerical calculations of the kinetics of relaxation in the system of surfactant spherical micelles under joint action of the molecular mechanism with capture and emission of individual surfactant molecules by molecular aggregates and the mechanism of fusion and fission of the aggregates. As a basis, we have taken the difference equations of aggregation and fragmentation in the form of the generalized kinetic Smoluchowski equations for aggregate concentrations. The calculations have been made with using the droplet model of molecular surfactant aggregates and two modified Smoluchowski models for the coefficients of aggregate-monomer and aggregate-aggregate fusions which take into account the effects of the aggregate size and presence of hydrophobic spots on the aggregate surface. A full set of relaxation times and corresponding relaxation modes for nonequilibrium aggregate distribution in the aggregation number has been found. The dependencies of these relaxation times and modes on the total concentration of surfactant in the solution and the special parameter controlling the probability of fusion in collisions of micelles with other micelles have been studied.
COPD Patients Have Short Lung Magnetic Resonance T1 Relaxation Time.
Alamidi, Daniel F; Morgan, Alexandra R; Hubbard Cristinacce, Penny L; Nordenmark, Lars H; Hockings, Paul D; Lagerstrand, Kerstin M; Young, Simon S; Naish, Josephine H; Waterton, John C; Maguire, Niall C; Olsson, Lars E; Parker, Geoffrey J M
2016-04-01
Magnetic resonance imaging (MRI) may provide attractive biomarkers for assessment of pulmonary disease in clinical trials as it is free from ionizing radiation, minimally invasive and allows regional information. The aim of this study was to characterize lung MRI T1 relaxation time as a biomarker of chronic obstructive pulmonary disease (COPD); and specifically its relationship to smoking history, computed tomography (CT), and pulmonary function test (PFT) measurements in comparison to healthy age-matched controls. Lung T1 and inter-quartile range (IQR) of T1 maps from 24 COPD subjects and 12 healthy age-matched non-smokers were retrospectively analyzed from an institutional review board approved study. The subjects underwent PFTs and two separate MR imaging sessions at 1.5 tesla to test T1 repeatability. CT scans were performed on the COPD subjects. T1 repeatability (intraclass correlation coefficient) was 0.72 for repeated scans acquired on two visits. The lung T1 was significantly shorter (p < 0.0001) and T1 IQR was significantly larger (p = 0.0002) for the COPD subjects compared to healthy controls. Lung T1 significantly (p = 0.001) correlated with lung density assessed with CT. Strong significant correlations (p < 0.0001) between lung T1 and all PFT measurements were observed. Cigarette exposure did not correlate with lung T1 in COPD subjects. In conclusion, lung MRI T1 mapping shows potential as a repeatable, radiation free, non-invasive imaging technique in the evaluation of COPD. PMID:26488310
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.
A numerical study of vector resonant relaxation
NASA Astrophysics Data System (ADS)
Kocsis, Bence; Tremaine, Scott
2015-04-01
Stars bound to a supermassive black hole interact gravitationally. Persistent torques acting between stellar orbits lead to a rapid resonant relaxation of the orbital orientation vectors (`vector' resonant relaxation) and slower relaxation of the eccentricities (`scalar' resonant relaxation), both at rates much faster than two-body or non-resonant relaxation. We describe a new parallel symplectic integrator, N-RING, which follows the dynamical evolution of a cluster of N stars through vector resonant relaxation, by averaging the pairwise interactions over the orbital period and periapsis precession time-scale. We use N-RING to follow the evolution of clusters containing over 104 stars for tens of relaxation times. Among other results, we find that the evolution is dominated by torques among stars with radially overlapping orbits, and that resonant relaxation can be modelled as a random walk of the orbit normals on the sphere, with angular step size ranging from 0.5-1 rad. The relaxation rate in a cluster with a fixed number of stars is proportional to the root mean square (rms) mass of the stars. The rms torque generated by the cluster stars is reduced below the torque between Kepler orbits due to apsidal precession and declines weakly with the eccentricity of the perturbed orbit. However, since the angular momentum of an orbit also decreases with eccentricity, the relaxation rate is approximately eccentricity-independent for e ? 0.7 and grows rapidly with eccentricity for e ? 0.8. We quantify the relaxation using the autocorrelation function of the spherical multipole moments; this decays exponentially and the e-folding time may be identified with the vector resonant relaxation time-scale.
RADIAL TRANSPORT OF LARGE-SCALE MAGNETIC FIELDS IN ACCRETION DISKS. II. RELAXATION TO STEADY STATES
Takeuchi, Taku; Okuzumi, Satoshi
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, τ{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 τ{sub dif}. We consider diffusion due to the Ohmic resistivity. These timescales can be significantly different from the disk viscous timescale τ{sub disk}. The behaviors of the magnetic flux evolution are quite different depending on the magnitude relationship of the timescales τ{sub adv}, τ{sub dif}, and τ{sub disk}. The most interesting phenomena occur when τ{sub adv} << τ{sub dif}, τ{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.
Dynamic Relaxation of Financial Indices
NASA Astrophysics Data System (ADS)
Shen, J.; Zheng, B.; Lin, H.; Qiu, T.
The dynamic relaxation of the German DAX both before and after a large price-change is investigated. The dynamic behavior is characterized by a power law. At the minutely time scale, the exponent p governing the power-law behavior takes a same value before and after the large price change, while at the daily time scale, it is different. Numerical simulations of an interacting EZ herding model are performed for comparison.
Two-exponential analysis of spin-spin proton relaxation times in MR imaging using surface coils
Schad, L.R.; Brix, G.; Semmler, W.; Gueckel, F.L.; Lorenz, W.J. )
1989-07-01
Proton relaxation time measurements were performed on a standard whole body MR imager operating at 1.5 T using a conventional surface coil of the manufacturer. A combined CP/CPMG multiecho, multislice sequence was used for the T1 and T2 relaxation time measurements. Two repetition times of 2000 ms (30 echoes) and 600 ms (2 echoes) with 180 degrees-pulse intervals of 2 tau = 22 ms were interleaved in this sequence. A two-exponential T2 analysis of each pixel of the spin-echo images was computed in a case of an acoustic neurinoma. The two-exponential images show a short component (T2S) due to white and gray matter and a long component (T2S) due to the cerebrospinal fluid. In the fatty tissue two components with T2S = 35 {plus minus} 3 ms and T2L = 164 {plus minus} 7 ms were measured. Comparing with Gd-DTPA imaging the relaxation time images show a clear differentiation of vital tumor tissue and cerebrospinal fluid.
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.
NASA Astrophysics Data System (ADS)
Wojnarowska, Z.; Ngai, K. L.; Paluch, M.
2014-12-01
The article reports the dependence of the conductivity relaxation on temperature T and pressure P in the canonical ionic glass former 0.4 Ca (N O3)2-0.6 KN O3(CKN ) . At constant conductivity relaxation time ??, the entire conductivity relaxation spectra obtained at widely different combinations of T and P superpose almost perfectly, and thus it is the ion-ion interaction but not thermodynamics that determines the frequency dispersion. Moreover, on vitrifying CKN by either elevating P or decreasing T, changes of P or T dependence of ?? at the glass transition pressure Pg and temperature Tg are observed to occur at the same value, i.e., ??(Pg) =??(Tg) , indicating that the relation between ?? and the structural relaxation time ?? is also independent of P and T.
An optimal modification of a Kalman filter for time scales
NASA Technical Reports Server (NTRS)
Greenhall, C. A.
2003-01-01
The Kalman filter in question, which was implemented in the time scale algorithm TA(NIST), produces time scales with poor short-term stability. A simple modification of the error covariance matrix allows the filter to produce time scales with good stability at all averaging times, as verified by simulations of clock ensembles.
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)
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.
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
Kibble-Zurek mechanism beyond adiabaticity: Finite-time scaling with critical initial slip
NASA Astrophysics Data System (ADS)
Huang, Yingyi; Yin, Shuai; Hu, Qijun; Zhong, Fan
2016-01-01
The Kibble-Zurek mechanism demands an initial adiabatic stage before an impulse stage to have a frozen correlation length that generates topological defects in a cooling phase transition. Here we study such a driven critical dynamics but with an initial condition that is near the critical point and that is far away from equilibrium. In this case, there is no initial adiabatic stage at all and thus adiabaticity is broken. However, we show that there again exists a finite length scale arising from the driving that divides the evolution into three stages. A relaxation-finite-time-scaling-adiabatic scenario is then proposed in place of the adiabatic-impulse-adiabatic scenario of the original Kibble-Zurek mechanism. A unified scaling theory, which combines finite-time scaling with critical initial slip, is developed to describe the universal behavior and is confirmed with numerical simulations of a two-dimensional classical Ising model.
Pawlus, S; Klotz, S; Paluch, M
2013-04-26
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. PMID:23679720
NASA Astrophysics Data System (ADS)
Martinec, Z.; Wolf, D.
2003-04-01
The Fennoscandian relaxation-time spectrum (RTS), based on post-glacial strandlines compiled by Donner (1995) and recently revised by Wieczerkowski et al. (1999), is an observational data set used in studies of glacial-isostatic adjustment (GIA). We invert this data set in terms of a 2D viscosity distribution with a thick cratonic lithosphere below the former Fennoscandian ice sheet and a much thinner lithosphere underlain by an asthenosphere in the peripheral regions. The forward modelling of GIA is implemented in the time domain using the spectral-finite element method developed by Martinec (2000). The computed vertical displacement for individual spherical harmonics is fitted by a single exponential function and the relaxation time is determined. The synthetic RTS for degrees 10 to 40 is then compared with the observational RTS and the acceptability of the underlying earth model is evaluated. The free parameters for the inverse modelling of GIA are either the cratonic-lithosphere thickness and the upper-mantle viscosity or the peripheral-lithosphere thickness and the asthenosphere viscosity. We show that a 2D viscosity distribution with a cratonic lithosphere of 200 km thickness satisfies the observational Fennoscandian RTS as well as a conventional spherically symmetric earth model with a 95 km thick lithosphere. \\vspace{2mm} {References} \\vspace*{-0pt} Donner, J., 1995. The Quaternary History of Scandinavia, Cambridge University Press, Cambridge. \\vspace*{-0pt} Wieczerkowski, K., Mitrovica, J. &Wolf, D., 1999. A revised relaxation-time spectrum for Fennoscandia, Geophys. J. Int., 139, 69-86. \\vspace*{-0pt} Martinec, Z., 2000. Spectral-finite element approach to three-dimensional viscoelastic relaxation in a spherical earth, Geophys. J. Int., 142, 117-141.
Dreher, Wolfgang; Bardenhagen, Ingo; Huang, Li; Bumer, Marcus
2016-04-01
Modern NMR imaging systems used for biomedical research are equipped with B0 gradient systems with strong maximum gradient strength and short switching time enabling (1)H NMR measurements of samples with very short transverse relaxation times. However, background signal originating from non-optimized RF coils may hamper experiments with ultrashort delays between RF excitation and signal reception. We demonstrate that two simple means, outer volume suppression and the use of shaped B0 fields produced by higher-order shim coils, allow a considerable suppression of disturbing background signals. Thus, the quality of NMR images acquired at ultrashort or zero echo time is improved and systematic errors in quantitative data evaluation are avoided. Fields of application comprise MRI with ultrashort echo time or relaxation time analysis, for both biomedical research and characterizing porous media filled with liquids or gases. PMID:26597837
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
Appolonia, L; Borgia, G C; Bortolotti, V; Brown, R J; Fantazzini, P; Rezzaro, G
2001-01-01
The effects of protective hydrophobic products applied to porous media such as stone or mortar vary greatly with the product, the porous medium, and the mode of application. Nuclear Magnetic Resonance (NMR) measurements on fluids in the pore spaces of both treated and untreated samples can give information on the contact of the fluid with the internal surfaces, which is affected by all the above factors. Continuous distributions of relaxation times T(1) and T(2) of water in the pores of both synthetic and natural porous media were obtained before and after hydrophobic treatment. The synthetic porous media are ceramic filter materials characterized by narrow distributions of pore dimensions and show that the treatment does not produce large changes in the relaxation times of the water. For three travertine samples most of a long relaxation time component, presumably from the largest pores, remains after treatment, while the amplitude of an intermediate component is greatly reduced. For three pudding-stone samples, treatment leads to a substantial loss from the long component and an even greater loss from the intermediate component. PMID:11445343
NASA Astrophysics Data System (ADS)
Capaccioli, S.; Kessairi, K.; Prevosto, D.; Thayyil, Md. Shahin; Lucchesi, M.; Rolla, P. A.
The present study demonstrates, by means of broadband dielectric measurements, that the primary ?- and the secondary Johari-Goldstein (JG) ?-processes are strongly correlated, in contrast with the widespread opinion of statistical independence of these processes. This occurs for different glass-forming systems, over a wide temperature and pressure range. In fact, we found that the ratio of the ?- and ?- relaxation times is invariant when calculated at different combinations of P and T that maintain either the primary or the JG relaxation times constant. The ?-? interdependence is quantitatively confirmed by the clear dynamic scenario of two master curves (one for ?-, one for ?-relaxation) obtained when different isothermal and isobaric data are plotted together versus the reduced variable T g (P)/T, where T g is the glass transition temperature. Additionally, the ?-? mutual dependence is confirmed by the overall superposition of spectra measured at different T-P combinations but with an invariant ?-relaxation time.
NASA Astrophysics Data System (ADS)
Chelcea, R. I.; Fechete, R.; Culea, E.; Demco, D. E.; Blmich, B.
2009-02-01
The single-sided NMR-MOUSE sensor that operates in highly inhomogeneous magnetic fields is used to record a CPMG 1H transverse relaxation decay by CPMG echo trains for a series of cross-linked natural rubber samples. Effective transverse relaxation rates 1/ T2,short and 1/ T2,long were determined by a bi-exponential fit. A linear dependence of transverse relaxation rates on cross-link density is observed for medium to large values of cross-link density. As an alternative to multi-exponential fits the possibility to analyze the dynamics of soft polymer network in terms of multi-exponential decays via the inverse Laplace transformation was studied. The transient regime and the effect of the T1/ T2 ratio in inhomogeneous static and radiofrequency magnetic fields on the CPMG decays were studied numerically using a dedicated C++ program to simulate the temporal and spatial dependence of the CPMG response. A correction factor T2/ T2,eff is derived as a function of the T1/ T2 ratio from numerical simulations and compared with earlier results from two different well logging devices. High-resolution T1- T2 correlations maps are obtained by two-dimensional Laplace inversion of CPMG detected saturation recovery curves. The T1- T2 experimental correlations maps were corrected for the T1/ T2 effect using the derived T2/ T2,eff correction factor.
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 (ΔTg). 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 (ΔTg) 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 ΔTg. 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 ΔTg, but the agreement is only qualitative. The comparison plot showed that TAM data is directly proportional to the 1/3 power of ΔTg data, after correcting for an offset. Nevertheless, the correlation between hGH stability and relaxation time remained qualitatively the same as found with using ΔTg derived relaxation data, and it was found that the modest extrapolation of TAM data to higher temperatures using ΔTg 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
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.
NASA Astrophysics Data System (ADS)
Kingsley, Peter B.; Monahan, W. Gordon
2000-04-01
In the presence of an off-resonance radiofrequency field, recovery of longitudinal magnetization to a steady state is not purely monoexponential. Under reasonable conditions with zero initial magnetization, recovery is nearly exponential and an effective relaxation rate constant R1eff = 1/T1eff can be obtained. Exact and approximate formulas for R1eff and steady-state magnetization are derived from the Bloch equations for spins undergoing cross-relaxation and chemical exchange between two sites in the presence of an off-resonance radiofrequency field. The relaxation formulas require that the magnetization of one spin is constant, but not necessarily zero, while the other spin relaxes. Extension to three sites with one radiofrequency field is explained. The special cases of off-resonance effects alone and with cross-relaxation or chemical exchange, cross-relaxation alone, and chemical exchange alone are compared. The inaccuracy in saturation transfer measurements of exchange rate constants by published formulas is discussed for the creatine kinase reaction.
Scaling of Langevin and molecular dynamics persistence times of nonhomogeneous fluids.
Olivares-Rivas, Wilmer; Colmenares, Pedro J
2012-01-01
The existing solution for the Langevin equation of an anisotropic fluid allowed the evaluation of the position-dependent perpendicular and parallel diffusion coefficients, using molecular dynamics data. However, the time scale of the Langevin dynamics and molecular dynamics are different and an ansatz for the persistence probability relaxation time was needed. Here we show how the solution for the average persistence probability obtained from the backward Smoluchowski-Fokker-Planck equation (SE), associated to the Langevin dynamics, scales with the corresponding molecular dynamics quantity. Our SE perpendicular persistence time is evaluated in terms of simple integrals over the equilibrium local density. When properly scaled by the perpendicular diffusion coefficient, it gives a good match with that obtained from molecular dynamics. PMID:22400522
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.
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.
Noether theorem for Birkhoffian systems on time scales
NASA Astrophysics Data System (ADS)
Song, Chuan-Jing; Zhang, Yi
2015-10-01
Birkhoff equations on time scales and Noether theorem for Birkhoffian system on time scales are studied. First, some necessary knowledge of calculus on time scales are reviewed. Second, Birkhoff equations on time scales are obtained. Third, the conditions for invariance of Pfaff action and conserved quantities are presented under the special infinitesimal transformations and general infinitesimal transformations, respectively. Fourth, some special cases are given. And finally, an example is given to illustrate the method and results.
NASA Astrophysics Data System (ADS)
Wang, Can-Jun; Wei, Qun; Mei, Dong-Cheng
2008-03-01
The associated relaxation time T and the normalized correlation function C(s) for a tumor cell growth system subjected to color noises are investigated. Using the Novikov theorem and Fox approach, the steady probability distribution is obtained. Based on them, the expressions of T and C(s) are derived by means of projection operator method, in which the effects of the memory kernels of the correlation function are taken into account. Performing the numerical computations, it is found: (1) With the cross-correlation intensity |?|, the additive noise intensity ? and the multiplicative noise self-correlation time ? increasing, the tumor cell numbers can be restrained; And the cross-correlation time ?, the multiplicative noise intensity D can induce the tumor cell numbers increasing; However, the additive noise self-correlation time ? cannot affect the tumor cell numbers; The relaxation time T is a stochastic resonant phenomenon, and the distribution curves exhibit a single-maximum structure with D increasing. (2) The cross-correlation strength ? weakens the related activity between two states of the tumor cell numbers at different time, and enhances the stability of the tumor cell growth system in the steady state; On the contrast, ? and ? enhance the related activity between two states at different time; However, ? has no effect on the related activity between two states at different time.
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)
Leyet, Y.; Guerrero, F.; Amorn, H.; Guerra, J. de Los S.; Eiras, J. A.
2010-10-01
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 PbNb2O6-based ceramics; nanostructured Pb(Zr0.6Ti0.4)O3 ceramics; and submicron BaTiO3. 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)
Walbrecker, J.; Behroozmand, A.
2011-12-01
Efficient groundwater management requires reliable means of characterizing shallow groundwater aquifers. One key parameter in this respect is hydraulic conductivity. Surface nuclear magnetic resonance (NMR) is a geophysical exploration technique that can potentially provide this type of information in a noninvasive, cost-effective way. The technique is based on measuring the precession of nuclear spins of protons in groundwater molecules. It involves large loop antennas deployed on Earth's surface to generate electromagnetic pulses tuned to specifically excite and detect groundwater proton spins. Naturally, the excited state of spins is transitory - once excited, spins relax back to their equilibrium state. This relaxation process is strongly influenced by the spin environment, which, in the case of groundwater, is defined by the aquifer. By employing empirical relations, changes in relaxation behavior can be used to identify changes in aquifer hydraulic conductivity, making the NMR relaxation signal a very important piece of information. Particularly, efforts are made to record the longitudinal relaxation parameter T1, because it is known from laboratory studies that it often reliably correlates with hydraulic conductivity, even in the presence of magnetic species. In surface NMR, T1 data are collected by recording the NMR signal amplitude following two sequential excitation pulses as a function of the delay time ? between the two pulses. In conventional acquisition, the two pulses have a mutual phase shift of ?. Based on theoretical arguments it was recently shown that T1 times acquired according to this conventional surface-NMR scheme are systematically biased. It was proposed that the bias can be minimized by cycling the phase of the two pulses between ? and zero in subsequent double-pulse experiments, and subtracting the resulting signal amplitudes (phase-cycled pseudosaturation recovery scheme, pcPSR). We present the first surface-NMR T1 data set recorded employing the pcPSR scheme and compare it to conventional T1 data. For our feasibility study we have chosen a site in Skive, Denmark, that features excellent signal/noise conditions, allowing us to collect high quality data in reasonable survey time. In addition, proximate boreholes and TEM measurements suggest a relatively homogeneous aquifer extending from 5 to more than 25m below surface. We may therefore expect roughly constant T1 relaxation times throughout the shallow aquifer, providing us a simple framework for our comparative study. We used a 50x50m surface-NMR loop and employed 16 pulse moments selected to spatially cover the shallow aquifer region. For each pulse moment, we recorded surface-NMR T1 data densely sampled at 14 delay times ? between 250 and 4'000 ms. On this high-quality data set we demonstrate that the pcPSR acquisition approach yields to a good degree homogeneous T1 relaxation times, whereas the conventional approach leads to variations in T1 that could be misinterpreted in terms of changes of aquifer characteristics. Thereby we provide first empirical evidence for the superiority of the pcPSR scheme for surface NMR T1 acquisition.
Schfer-Nolte, Eike; Schlipf, Lukas; Ternes, Markus; Reinhard, Friedemann; Kern, Klaus; Wrachtrup, Jrg
2014-11-21
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. PMID:25479520
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.
Weiskopf, Nikolaus; Callaghan, Martina F; Josephs, Oliver; Lutti, Antoine; Mohammadi, Siawoosh
2014-01-01
Relaxation rates provide important information about tissue microstructure. Multi-parameter mapping (MPM) estimates multiple relaxation parameters from multi-echo FLASH acquisitions with different basic contrasts, i.e., proton density (PD), T1 or magnetization transfer (MT) weighting. Motion can particularly affect maps of the apparent transverse relaxation rate R2(*), which are derived from the signal of PD-weighted images acquired at different echo times. To address the motion artifacts, we introduce ESTATICS, which robustly estimates R2(*) from images even when acquired with different basic contrasts. ESTATICS extends the fitted signal model to account for inherent contrast differences in the PDw, T1w and MTw images. The fit was implemented as a conventional ordinary least squares optimization and as a robust fit with a small or large confidence interval. These three different implementations of ESTATICS were tested on data affected by severe motion artifacts and data with no prominent motion artifacts as determined by visual assessment or fast optical motion tracking. ESTATICS improved the quality of the R2(*) maps and reduced the coefficient of variation for both types of data-with average reductions of 30% when severe motion artifacts were present. ESTATICS can be applied to any protocol comprised of multiple 2D/3D multi-echo FLASH acquisitions as used in the general research and clinical setting. PMID:25309307
NASA Astrophysics Data System (ADS)
Jimnez, No; Camarena, Francisco; Redondo, Javier; Snchez-Morcillo, Vctor; Konofagou, Elisa E.
2015-10-01
We report a numerical method for solving the constitutive relations of nonlinear acoustics, where multiple relaxation processes are included in a generalized formulation that allows the time-domain numerical solution by an explicit finite differences scheme. Thus, the proposed physical model overcomes the limitations of the one-way Khokhlov-Zabolotskaya-Kuznetsov (KZK) type models and, due to the Lagrangian density is implicitly included in the calculation, the proposed method also overcomes the limitations of Westervelt equation in complex configurations for medical ultrasound. In order to model frequency power law attenuation and dispersion, such as observed in biological media, the relaxation parameters are fitted to both exact frequency power law attenuation/dispersion media and also empirically measured attenuation of a variety of tissues that does not fit an exact power law. Finally, a computational technique based on artificial relaxation is included to correct the non-negligible numerical dispersion of the finite difference scheme, and, on the other hand, improve stability trough artificial attenuation when shock waves are present. This technique avoids the use of high-order finite-differences schemes leading to fast calculations. The present algorithm is especially suited for practical configuration where spatial discontinuities are present in the domain (e.g. axisymmetric domains or zero normal velocity boundary conditions in general). The accuracy of the method is discussed by comparing the proposed simulation solutions to one dimensional analytical and k-space numerical solutions.
NASA Astrophysics Data System (ADS)
Pipa, Viktor; Vasko, Fedor; Mitin, Vladimir
1997-03-01
The low temperature energy and momentum relaxation rates of 2D electron gas placed near the free or clamped surface of a semi-infinit sample are calculated. To describe the electron-acoustic phonon interaction with allowance of the surface effect the method of elasticity theory Green functions was used. This method allows to take into account the reflection of acoustic waves from the surface and related mutual conversion of LA and TA waves. It is shown that the strength of the deformation potential scattering at low temperatures substantially depends on the mechanical conditions at the surface: relaxation rates are suppressed for the free surface while for the rigid one the rates are enhanced. The dependence of the conductivity on the distance between the 2D layer and the surface is discussed. The effect is most pronounced in the range of temperatures 2 sl pF < T < (2 hbar s_l)/d, where pF is the Fermi momentum, sl is the velocity of LA waves, d is the width of the quantum well.
Atomic time scales for dynamical astronomy
NASA Astrophysics Data System (ADS)
Guinot, B.
1992-06-01
A series of recommendations on space-time references issued in the framework of the general theory of relativity in 1991 by the International Astronomical Unions (IAU) is presented. The recommendations, their background, the difficulties that were met, and the connection with previous recommendations--with an emphasis on time--are given. For simplicity of theoretical developments in celestial mechanics, several coordinate systems must be defined. The implied definitions of new coordinate times are presented together with their relation between themselves and to other times. International Atomic Time (TAI) is not affected by these recommendations, but appears now as a realization of the ideal terrestrial time having a clear scientific definition.
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.
NASA Astrophysics Data System (ADS)
Talon, L.; Bauer, D.; Gland, N.; Youssef, S.; Auradou, H.; Ginzburg, I.
2012-04-01
The recent advances in 3-D imaging of porous structures have generated a tremendous interest in the simulation of complex single and two-phase flows. Lattice-Boltzmann (LB) schemes present a powerful tool to solve the flow field directly from the binarized 3-D images. However, as viscosity often plays an important role, the LB scheme should correctly treat viscosity effects. This is the case using a LB scheme with two relaxation times (TRT) unlike the broadly used, the single-relaxation rate, BGK, where the velocity of the modeled fluid does not vary as the inverse of the viscosity applying the bounce-back (no-slip) boundary rule. The aim of this work is to apply the LB-TRT approach to different types of porous media (straight channels, 2-D model porous media, sandstone) to solve for the flow field and to evaluate the approach in terms of parameter dependence, error and convergence time on the basis of permeability. We show that the variation of permeability with the free relaxation parameter ? of the TRT scheme depends on the heterogeneity of the sample and on the numerical resolution. The convergence time depends on the applied viscosity and the parameter standing for the speed of sound, thus the computation time can be reduced by choosing appropriate values of those parameters. Two approaches to calculate permeability (Darcy's law and viscous energy dissipation) are proposed and investigated. We recommend to use Darcy's law, as dependence on ? is less important. Periodic (in the presence of a driving body force) and pressure boundary conditions are evaluated in terms of the results.
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.
NASA Astrophysics Data System (ADS)
Yamaguchi, H.; Belk, J. G.; Zhang, X. M.; Sudijono, J. L.; Fahy, M. R.; Jones, T. S.; Pashley, D. W.; Joyce, B. A.
1997-01-01
Strain relaxation in InAs/GaAs(111)A heteroepitaxy has been studied on the atomic scale by scanning tunneling microscopy. The coalescence of small islands and the formation of a dislocation network are identified at the critical layer thickness (CLT), and no three-dimensional growth is observed, even beyond the CLT. The atomic displacement around the threading segments and the strain fields induced by the misfit dislocations are both identified. The measured density of the misfit dislocations indicates that the strain is not fully relaxed at the CLT, but is instead gradually relieved with the additional growth of InAs.
NASA Astrophysics Data System (ADS)
Bertini, Ivano; Luchinat, Claudio; Vasavada, Kashyap V.
Calculated nuclear relaxation rates in paramagnetic systems with S = {1}/{2} are compared for the cases of fast and slow molecular tumbling. It is shown that the two treatments provide the same values before and after the low-field ?S?C = 1 dispersion, but differ in the dispersion region. Then the case of S = {1}/{2} is considered in order to check whether it could be treated with a fictitious S = {1}/{2} spin and large g anisotropy. Comparison is made with the approach which considers zero-field splitting explicitly. It is concluded that the latter approach is the more correct one. The applications are aimed at high-spin cobalt (II) systems. In order to facilitate comparison and future use, the relevant equations given in previous articles are presented in a simplified form and a common notation.
Ellipsoidal Relaxation of Deformed Vesicles
NASA Astrophysics Data System (ADS)
Yu, Miao; Lira, Rafael B.; Riske, Karin A.; Dimova, Rumiana; Lin, Hao
2015-09-01
Theoretical analysis and experimental quantification on the ellipsoidal relaxation of vesicles are presented. The current work reveals the simplicity and universal aspects of this process. The Helfrich formula is shown to apply to the dynamic relaxation of moderate-to-high tension membranes, and a closed-form solution is derived which predicts the vesicle aspect ratio as a function of time. Scattered data are unified by a time scale, which leads to a similarity behavior, governed by a distinctive solution for each vesicle type. Two separate regimes in the relaxation are identified, namely, the "entropic" and the "constant-tension" regimes. The bending rigidity and the initial membrane tension can be simultaneously extracted from the data analysis, posing the current approach as an effective means for the mechanical analysis of biomembranes.
Meng, Xuhui; Guo, Zhaoli
2015-10-01
A lattice Boltzmann model with a multiple-relaxation-time (MRT) collision operator is proposed for incompressible miscible flow with a large viscosity ratio as well as a high Pclet number in this paper. The equilibria in the present model are motivated by the lattice kinetic scheme previously developed by Inamuro etal. [Philos. Trans. R. Soc. London, Ser. A 360, 477 (2002)PTRMAD1364-503X10.1098/rsta.2001.0942]. The fluid viscosity and diffusion coefficient depend on both the corresponding relaxation times and additional adjustable parameters in this model. As a result, the corresponding relaxation times can be adjusted in proper ranges to enhance the performance of the model. Numerical validations of the Poiseuille flow and a diffusion-reaction problem demonstrate that the proposed model has second-order accuracy in space. Thereafter, the model is used to simulate flow through a porous medium, and the results show that the proposed model has the advantage to obtain a viscosity-independent permeability, which makes it a robust method for simulating flow in porous media. Finally, a set of simulations are conducted on the viscous miscible displacement between two parallel plates. The results reveal that the present model can be used to simulate, to a high level of accuracy, flows with large viscosity ratios and/or high Pclet numbers. Moreover, the present model is shown to provide superior stability in the limit of high kinematic viscosity. In summary, the numerical results indicate that the present lattice Boltzmann model is an ideal numerical tool for simulating flow with a large viscosity ratio and/or a high Pclet number. PMID:26565362
NASA Astrophysics Data System (ADS)
Meng, Xuhui; Guo, Zhaoli
2015-10-01
A lattice Boltzmann model with a multiple-relaxation-time (MRT) collision operator is proposed for incompressible miscible flow with a large viscosity ratio as well as a high Pclet number in this paper. The equilibria in the present model are motivated by the lattice kinetic scheme previously developed by Inamuro et al. [Philos. Trans. R. Soc. London, Ser. A 360, 477 (2002), 10.1098/rsta.2001.0942]. The fluid viscosity and diffusion coefficient depend on both the corresponding relaxation times and additional adjustable parameters in this model. As a result, the corresponding relaxation times can be adjusted in proper ranges to enhance the performance of the model. Numerical validations of the Poiseuille flow and a diffusion-reaction problem demonstrate that the proposed model has second-order accuracy in space. Thereafter, the model is used to simulate flow through a porous medium, and the results show that the proposed model has the advantage to obtain a viscosity-independent permeability, which makes it a robust method for simulating flow in porous media. Finally, a set of simulations are conducted on the viscous miscible displacement between two parallel plates. The results reveal that the present model can be used to simulate, to a high level of accuracy, flows with large viscosity ratios and/or high Pclet numbers. Moreover, the present model is shown to provide superior stability in the limit of high kinematic viscosity. In summary, the numerical results indicate that the present lattice Boltzmann model is an ideal numerical tool for simulating flow with a large viscosity ratio and/or a high Pclet number.
Clayton, Steven Michael
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.
NMR spin-lattice relaxation time T(1) of thin films obtained by magnetic resonance force microscopy.
Saun, Seung-Bo; Won, Soonho; Kwon, Sungmin; Lee, Soonchil
2015-05-01
We obtained the NMR spectrum and the spin-lattice relaxation time (T1) for thin film samples by magnetic resonance force microscopy (MRFM). The samples were CaF2 thin films which were 50 nm and 150 nm thick. T1 was measured at 18 K using a cyclic adiabatic inversion method at a fixed frequency. A comparison of the bulk and two thin films showed that T1 becomes shorter as the film thickness decreases. To make the comparison as accurate as possible, all three samples were loaded onto different beams of a multi-cantilever array and measured in the same experimental environment. PMID:25828244
NMR spin-lattice relaxation time T1 of thin films obtained by magnetic resonance force microscopy
NASA Astrophysics Data System (ADS)
Saun, Seung-Bo; Won, Soonho; Kwon, Sungmin; Lee, Soonchil
2015-05-01
We obtained the NMR spectrum and the spin-lattice relaxation time (T1) for thin film samples by magnetic resonance force microscopy (MRFM). The samples were CaF2 thin films which were 50 nm and 150 nm thick. T1 was measured at 18 K using a cyclic adiabatic inversion method at a fixed frequency. A comparison of the bulk and two thin films showed that T1 becomes shorter as the film thickness decreases. To make the comparison as accurate as possible, all three samples were loaded onto different beams of a multi-cantilever array and measured in the same experimental environment.
NASA Astrophysics Data System (ADS)
Wehrenberg, C. E.; Comley, A. J.; Barton, N. R.; Coppari, F.; Fratanduono, D.; Huntington, C. M.; Maddox, B. R.; Park, H.-S.; Plechaty, C.; Prisbrey, S. T.; Remington, B. A.; Rudd, R. E.
2015-09-01
We report direct lattice-level measurements of plastic relaxation kinetics through time-resolved, in situ Laue diffraction of shock-compressed single-crystal [001] Ta at pressures of 27-210 GPa. For a 50-GPa shock, a range of shear strains is observed extending up to the uniaxial limit for early data points (<0.6 ns), and the average shear strain relaxes to a near steady state over 1 ns. For 80- and 125-GPa shocks, the measured shear strains are fully relaxed already at 200 ps, consistent with rapid relaxation associated with the predicted threshold for homogeneous nucleation of dislocations occurring at shock pressure 65 GPa. The relaxation rate and shear stresses are used to estimate the dislocation density, and these quantities are compared to the results of other high-pressure work, flow stress models, and molecular dynamics simulations.
Wehrenberg, C. E.; Comley, A. J.; Barton, N. R.; Coppari, F.; Fratanduono, D.; Huntington, C. M.; Maddox, B. R.; Park, H. -S.; Plechaty, C.; Prisbrey, S. T.; et al
2015-09-29
We report direct lattice level measurements of plastic relaxation kinetics through time-resolved, in-situ Laue diffraction of shock-compressed single-crystal [001] Ta at pressures of 27-210 GPa. For a 50 GPa shock, a range of shear strains is observed extending up to the uniaxial limit for early data points (<0.6 ns) and the average shear strain relaxes to a near steady state over ~1 ns. For 80 and 125 GPa shocks, the measured shear strains are fully relaxed already at 200 ps, consistent with rapid relaxation associated with the predicted threshold for homogeneous nucleation of dislocations occurring at shock pressure ~65 GPa.more » The relaxation rate and shear stresses are used to estimate the dislocation density and these quantities are compared to the Livermore Multiscale Strength model as well as various molecular dynamics simulations.« less
NASA Astrophysics Data System (ADS)
Maciel, Thiago O.; Vianna, Reinaldo O.; Sarthour, Roberto S.; Oliveira, Ivan S.
2015-11-01
We reconstruct the time dependent quantum map corresponding to the relaxation process of a two-spin system in liquid-state NMR at room temperature. By means of quantum tomography techniques that handle informational incomplete data, we show how to properly post-process and normalize the measurements data for the simulation of quantum information processing, overcoming the unknown number of molecules prepared in a non-equilibrium magnetization state (Nj) by an initial sequence of radiofrequency pulses. From the reconstructed quantum map, we infer both longitudinal (T1) and transversal (T2) relaxation times, and introduce the J-coupling relaxation times ({T}1J,{T}2J), which are relevant for quantum information processing simulations. We show that the map associated to the relaxation process cannot be assumed approximated unital and trace-preserving for times greater than {T}2J.
Sciolla, Bruno; Poletti, Dario; Kollath, Corinna
2015-05-01
We use two-time correlation functions to study the complex dynamics of dissipative many-body quantum systems. In order to measure, understand, and categorize these correlations we extend the framework of the adiabatic elimination method. We show that, for the same parameters and times, two-time correlations can display two distinct behaviors depending on the observable considered: a fast exponential decay or a much slower dynamics. We exemplify these findings by studying strongly interacting bosons in a double well subjected to phase noise. While the single-particle correlations decay exponentially fast with time, the density-density correlations display slow aging dynamics. We also show that this slow relaxation regime is robust against particle losses. Additionally, we use the developed framework to show that the dynamic properties of dissipatively engineered states can be drastically different from their Hamiltonian counterparts. PMID:25978211
NASA Astrophysics Data System (ADS)
Sciolla, Bruno; Poletti, Dario; Kollath, Corinna
2015-05-01
We use two-time correlation functions to study the complex dynamics of dissipative many-body quantum systems. In order to measure, understand, and categorize these correlations we extend the framework of the adiabatic elimination method. We show that, for the same parameters and times, two-time correlations can display two distinct behaviors depending on the observable considered: a fast exponential decay or a much slower dynamics. We exemplify these findings by studying strongly interacting bosons in a double well subjected to phase noise. While the single-particle correlations decay exponentially fast with time, the density-density correlations display slow aging dynamics. We also show that this slow relaxation regime is robust against particle losses. Additionally, we use the developed framework to show that the dynamic properties of dissipatively engineered states can be drastically different from their Hamiltonian counterparts.
Mechanism of Void Nucleation and Growth in bcc Fe: Atomistic Simulations at Experimental Time Scales
Fan Yue; Kushima, Akihiro; Yip, Sidney; Yildiz, Bilge
2011-03-25
Evolution of small-vacancy clusters in bcc Fe is simulated using a multiscale approach coupling an atomistic activation-relaxation method for sampling transition-state pathways with environment-dependent reaction coordinate calculations and a kinetic Monte Carlo simulation to reach time scales on the order of {approx}10{sup 4} s. Under vacancy-supersaturated condition, di- and trivacancy clusters form and grow by coalescence (Ostwald ripening). For cluster size greater than four we find a transition temperature of 150 deg. C for accelerated cluster growth, as observed in positron annihilation spectroscopy experiments. Implications for the mechanism of stage-IV radiation-damage-recovery kinetics are discussed.
Souza, Richard B.; Kumar, Deepak; Calixto, Nathan; Singh, Justin; Schooler, Joseph; Subburaj, K.; Li, Xiaojuan; Link, Thomas M.; Majumdar, Sharmila
2014-01-01
Objective The objective of this study was to evaluate the effects of mechanical loading on knee articular cartilage T1? and T2 relaxation times in patients with and without OA. Design MR images were acquired from 137 subjects with and without knee OA under two conditions: unloaded and loaded at 50% body weight. Three sequences were acquired: a high-resolution 3D-CUBE, a T1? relaxation time, and a T2 relaxation time sequences. Cartilage regions of interest included: medial and lateral femur (MF, LF); medial and lateral tibia (MT, LT), laminar analysis (superficial and deep layers), and subcompartments. Changes in relaxation times in response to loading were evaluated using generalized estimating equations adjusting for age, gender, and BMI. Results In response to loading, we observed significant reductions in T1? relaxation times in the MT and LT. In both the MF and LF, loading resulted in significant decreases in the superficial layer and significant increases in the deep layer of the cartilage for T1? and T2. All subcompartment of MT and LT showed significant reduction in T1? relaxation times. Reductions were larger for subjects with OA (range: 1319% change) when compared to healthy controls (range: 313% change). Conclusions Loading of the cartilage resulted in significant changes in relaxation times in the femur and tibia, with novel findings regarding laminar and subcompartmental variations. In general, changes in relaxation times with loading were larger in the OA group suggesting that the collagen-proteoglycan matrix of subjects with OA is less capable of retaining water, and may reflect a reduced ability to dissipate loads. PMID:24792208
[Synergetics of hypnoid relaxation].
Perlitz, Volker; Cotuk, Birol; Schiepek, Gnter; Sen, Akin; Haberstock, Sandra; Schmid-Schnbein, Holger; Petzold, Ernst R; Flatten, Guido
2004-06-01
The Autogenic Training (AT) is a well established relaxation technique and psychotherapy tool. We report the use of nonlinear routines, the Multi-scaled Time-Frequency-Distribution (mTFD) for the graphical display of vegetative rhythms, and Post-Event-Scan (PES) for the direct visual identification of coupling between physiological subsystems. Applying these methods to time series of respiration, arterial blood pressure, and cutaneous forehead blood content fluctuations in controls (n = 11) or AT-experts (ATE, n = 11) induced psychomotor drive reduction during orthostatic stress allowed the instantaneous identification of a 0.15 Hz-rhythm. This rhythm prevailed in ATE significantly longer resulting a significantly robust 1 : 1 coupling between cutaneous blood content fluctuations and respiration. Consequently, we hypothesize that the "0.15 Hz-rhythm" in the cutaneous blood content fluctuations described previously which was associated with the subjective experience of profound psychomotor relaxation reflects an order-order transition in peripheral signals of central nervous origin. Results produced with the aid of these analytic tools support the efficacy of the AT induced, synergetic relaxation response. PMID:15164300
Atmospheric bridge on orbital time scales
NASA Astrophysics Data System (ADS)
Lohmann, Gerrit
2016-01-01
Large-scale atmospheric patterns are examined on orbital timescales using a climate model which explicitly resolves the atmosphere-ocean-sea ice dynamics. It is shown that, in contrast to boreal summer where the climate mainly follows the local radiative forcing, the boreal winter climate is strongly determined by modulation of circulation modes linked to the Arctic Oscillation/North Atlantic Oscillation (AO/NAO) and the Northern/Southern Annular Modes. We find that during a positive phase of the AO/NAO the convection in the tropical Pacific is below normal. The related atmospheric circulation provides an atmospheric bridge for the precessional forcing inducing a non-uniform temperature anomalies with large amplitudes over the continents. We argue that this is important for mechanisms responsible for multi-millennial climate variability and glacial inception.
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)
Tepper, H. L.; Briels, W. J.
2001-11-01
Nonequilibrium molecular dynamics simulations have been carried out on the growth and melting of the Lennard-Jones (100) interface at small undercoolings and superheatings. Two regimes of linear growth rate were discovered: a short-time regime associated with interface relaxation and a long-time regime associated with the macroscopic limit of growth and melting. It was shown that, if system sizes or equilibration times are taken too small, one will find only the initial regime. On the basis of our very accurate results on the macroscopic growth rates close to equilibrium, the possibility of a discontinuity in the temperature dependence of growth and melting rates at the melting point was ruled out.
Grzybowska, K; Grzybowski, A; Pawlus, S; Pionteck, J; Paluch, M
2015-06-01
In this paper, we investigate how changes in the system entropy influence the characteristic time scale of the system molecular dynamics near the glass transition. Independently of any model of thermodynamic evolution of the time scale, against some previous suppositions, we show that the system entropy S is not sufficient to govern the time scale defined by structural relaxation time ?. In the density scaling regime, we argue that the decoupling between ? and S is a consequence of different values of the scaling exponents ? and ?(S) in the density scaling laws, ?=f(?(?)/T) and S=h(?(?(S))/T), where ? and T denote density and temperature, respectively. It implies that the proper relation between ? and S requires supplementing with a density factor, u(?), i.e., ?=g(u(?)w(S)). This meaningful finding additionally demonstrates that the density scaling idea can be successfully used to separate physically relevant contributions to the time scale of molecular dynamics near the glass transition. The relation reported by us between ? and S constitutes a general pattern based on nonconfigurational quantities for describing the thermodynamic evolution of the characteristic time scale of molecular dynamics near the glass transition in the density scaling regime, which is a promising alternative to the approaches based as the Adam-Gibbs model on the configurational entropy that is difficult to evaluate in the entire thermodynamic space. As an example, we revise the Avramov entropic model of the dependence ?(T,?), giving evidence that its entropic basis has to be extended by the density dependence of the maximal energy barrier for structural relaxation. We also discuss the excess entropy S(ex), the density scaling of which is found to mimic the density scaling of the total system entropy S. PMID:26172717
NASA Astrophysics Data System (ADS)
Grzybowska, K.; Grzybowski, A.; Pawlus, S.; Pionteck, J.; Paluch, M.
2015-06-01
In this paper, we investigate how changes in the system entropy influence the characteristic time scale of the system molecular dynamics near the glass transition. Independently of any model of thermodynamic evolution of the time scale, against some previous suppositions, we show that the system entropy S is not sufficient to govern the time scale defined by structural relaxation time ?. In the density scaling regime, we argue that the decoupling between ? and S is a consequence of different values of the scaling exponents ? and ?S in the density scaling laws, ? =f (??/T ) and S =h (??S/T ) , where ? and T denote density and temperature, respectively. It implies that the proper relation between ? and S requires supplementing with a density factor, u (?), i.e., ? =g ( u (? )w (S ) ) . This meaningful finding additionally demonstrates that the density scaling idea can be successfully used to separate physically relevant contributions to the time scale of molecular dynamics near the glass transition. The relation reported by us between ? and S constitutes a general pattern based on nonconfigurational quantities for describing the thermodynamic evolution of the characteristic time scale of molecular dynamics near the glass transition in the density scaling regime, which is a promising alternative to the approaches based as the Adam-Gibbs model on the configurational entropy that is difficult to evaluate in the entire thermodynamic space. As an example, we revise the Avramov entropic model of the dependence ?(T ,?), giving evidence that its entropic basis has to be extended by the density dependence of the maximal energy barrier for structural relaxation. We also discuss the excess entropy Sex, the density scaling of which is found to mimic the density scaling of the total system entropy S .
On the depletion and accretion time-scales of cold gas in local early-type galaxies
NASA Astrophysics Data System (ADS)
Davis, Timothy A.; Bureau, Martin
2016-03-01
We consider what can be learnt about the processes of gas accretion and depletion from the kinematic misalignment between the cold/warm gas and stars in local early-type galaxies. Using simple analytic arguments and a toy model of the processes involved, we show that the lack of objects with counter-rotating gas reservoirs strongly constrains the relaxation, depletion and accretion time-scales of gas in early-type galaxies. Standard values of the accretion rate, star-formation efficiency and relaxation rate are not simultaneously consistent with the observed distribution of kinematic misalignments. To reproduce that distribution, both fast gas depletion (tdep ≲ 108 yr; e.g. more efficient star formation) and fast gas destruction (e.g. by active galactic nucleus feedback) can be invoked, but both also require a high rate of gas-rich mergers (>1 Gyr-1). Alternatively, the relaxation of misaligned material could happen over very long time-scales (≃100 dynamical times or ≈1-5 Gyr). We explore the various physical processes that could lead to fast gas depletion and/or slow gas relaxation, and discuss the prospects of using kinematic misalignments to probe gas-rich accretion processes in the era of large integral-field spectroscopic surveys.
NASA Astrophysics Data System (ADS)
Biele, R.; Timm, C.; D'Agosta, R.
2014-10-01
Quantum stochastic methods based on effective wave functions form a framework for investigating the generally non-Markovian dynamics of a quantum-mechanical system coupled to a bath. They promise to be computationally superior to the master-equation approach, which is numerically expensive for large dimensions of the Hilbert space. Here, we numerically investigate the suitability of a known stochastic Schrödinger equation that is local in time to give a description of thermal relaxation and energy transport. This stochastic Schrödinger equation can be solved with a moderate numerical cost, indeed comparable to that of a Markovian system, and reproduces the dynamics of a system evolving according to a general non-Markovian master equation. After verifying that it describes thermal relaxation correctly, we apply it for the first time to the energy transport in a spin chain. We also discuss a portable algorithm for the generation of the coloured noise associated with the numerical solution of the non-Markovian dynamics.
Le Chatelier's principle with multiple relaxation channels
NASA Astrophysics Data System (ADS)
Gilmore, R.; Levine, R. D.
1986-05-01
Le Chatelier's principle is discussed within the constrained variational approach to thermodynamics. The formulation is general enough to encompass systems not in thermal (or chemical) equilibrium. Particular attention is given to systems with multiple constraints which can be relaxed. The moderation of the initial perturbation increases as additional constraints are removed. This result is studied in particular when the (coupled) relaxation channels have widely different time scales. A series of inequalities is derived which describes the successive moderation as each successive relaxation channel opens up. These inequalities are interpreted within the metric-geometry representation of thermodynamics.
NASA Astrophysics Data System (ADS)
Gonzlez, R. L.; Leyet, Y.; Guerrero, F.; Guerra, J. de Los S.; Venet, M.; Eiras, J. A.
2007-04-01
The relaxation dynamics of the conductive process present in PbNb2O6 piezoelectric ceramics was investigated. A relaxation function in the time domain, ?(t), was found from the frequency dependence of the dielectric modulus (imaginary component, M'') by using a relaxation function in the frequency domain, F*(?). The best relaxation function, F*(?), was found to be a Cole-Cole distribution function, in which relaxation characteristic parameters, such as ? and ?CC, are involved. On the other hand, the relaxation function, ?(t), obtained by the time domain method, was found to be a Kohlrausch-Williams-Watts (KWW) function type. The thermal evolution of the characteristics parameters of the KWW function (? and ?*) was analysed. The values of the activation energy (Ea), obtained in the whole investigated temperature interval, suggest the existence of a relaxation mechanism (a conductive process), which may be interpreted by an ion hopping between neighbouring sites within the crystalline lattice. The results are corroborated with the formalism of the AC conductivity.
Modeling orbital changes on tectonic time scales
NASA Technical Reports Server (NTRS)
Crowley, Thomas J.
1992-01-01
Geologic time series indicate significant 100 ka and 400 ka pre-Pleistocene climate fluctuations, prior to the time of such fluctuations in Pleistocene ice sheets. The origin of these fluctuations must therefore depend on phenomena other than the ice sheets. In a previous set of experiments, we tested the sensitivity of an energy balance model to orbital insolation forcing, specifically focusing on the filtering effect of the Earth's geography. We found that in equatorial areas, the twice-yearly passage of the sun across the equator interacts with the precession index to generate 100 ka and 400 ka power in our modeled time series. The effect is proportional to the magnitude of land in equatorial regions. We suggest that such changes may reflect monsoonal variations in the real climate system, and the subsequent wind and weathering changes may transfer some of this signal to the marine record. A comparison with observed fluctuations of Triassic lake levels is quite favorable. A number of problems remain to be studied or clarified: (1) the EBM experiments need to be followed up by a limited number of GCM experiments; (2) the sensitivity to secular changes in orbital forcing needs to be examined; (3) the possible modifying role of sedimentary processes on geologic time series warrants considerably more study; (4) the effect of tectonic changes on Earth's rotation rate needs to be studied; and (5) astronomers need to make explicit which of their predictions are robust and geologists and astronomers have to agree on which of the predictions are most testable in the geologic record.
Scaling of events spaced in time.
Fetterman, J G; Stubbs, D A; Dreyfus, L R
1986-06-01
Pigeons were trained to peck on a key, which could be lit by red or green light, and produce feeder-light stimuli intermittently. On some trials, food followed the fourth feeder flash providing the key color was red, while on other trials food followed the sixteenth flash providing the color was green. The change in color from red to green was produced by a peck to a second, changeover key. Pigeons typically responded in the presence of red until four or more flashes occured and then, if food had not been delivered, changed the main-key color and responded on the green key. Following training, the variable-interval schedule arranging-feeder light events was changed to longer and shorter values to alter the amount of time (and number of responses) between events. Data from these test days indicate that the change from red to green was influenced by the number of events, but also by the time elapsed and/or responses emitted since the onset of a trial. The results suggest multiple sources of related information and stimulus control when events and behavior occur over time. PMID:24924863
Probing Photosynthesis on a Picosecond Time Scale
Seibert, Michael; Alfano, Robert R.
1974-01-01
Fluorescent emission kinetics of isolated spinach chloroplasts have been observed at room temperature with an instrument resolution time of 10 ps using a frequency doubled, mode-locked Nd:glass laser and an optical Kerr gate. At 685 nm two maxima are apparent in the time dependency of the fluorescence; the first occurs at 15 ps and the second at 90 ps after the flash. The intervening minimum occurs at about 50 ps. On the basis of theoretical models, lifetimes of the components associated with the two peaks and spectra (in escarole chloroplasts), the fluorescence associated with the first peak is interpreted as originating from Photosystem I (PSI) (risetime ?10 ps, lifetime ?10 ps) and the second peak from Photosystem II (PSII) (lifetime, 210 ps in spinach chloroplasts and 320 ps in escarole chloroplasts). The fact that there are two fluorescing components with a quantum yield ratio ?0.048 explains the previous discrepancy between the quantum yield of fluorescence measured in chloroplasts directly and that calculated from the lifetime of PSII. The 90 ps delay in the peak of PSII fluorescence is probably explained by energy transfer between accessory pigments such as carotenoids and Chl a. Energy spillover between PSI and PSII is not apparent during the time of observation. The results of this work support the view that the transfer of excitation energy to the trap complex in both photosystems occurs by means of a molecular excitation mechanism of intermediate coupling strength. Although triplet states are not of major importance in energy transfer to PSII traps, the possibility that they are involved in PSI photochemistry has not been eliminated. PMID:4830466
Slow-time acceleration for modeling multiple-time-scale problems
NASA Astrophysics Data System (ADS)
Haselbacher, A.; Najjar, F. M.; Massa, L.; Moser, R. D.
2010-01-01
The numerical simulation of a system exhibiting a broad range of time scales can be very expensive because the time discretization will in general need to resolve the smallest time scale, and the simulation will have to extend over many times the longest time scale. However, it is common that not all the time scales are of interest for a particular problem. When the long time scales are of primary interest, a number of techniques are available to eliminate the unwanted short time scales from consideration. When the short time scales are of primary interest, a technique for mitigating the consequences of anomalously long time scales is needed. The "slow-time acceleration" technique presented here has been developed to address this problem. In the slow-time acceleration technique, a modified evolution equation is developed in which the longest time scale is much shorter than that of the original system, and which has the same multi-time scale asymptotic structure as the original system. As an example, this approach is applied to the numerical simulation of solid-propellant rockets in which the long time scale is associated with the regression of the burning propellant.
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
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 ΔT2 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 μg/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)
Scully, C. N.; Cregg, P. J.; Crothers, D. S. F.
1992-01-01
It is known that the direction of the magnetization vector of very fine single-domain ferromagnetic particles fluctuates under the influence of thermal agitation. Perturbation theory is applied rigorously to a singular integral equation to derive an asymptotic formula for the relaxation time of the magnetization, for the case of uniaxial anisotropy and an applied magnetic field. The result agrees with that of Brown [Phys. Rev. 130, 1677 (1963)] as described succinctly by Aharoni [Phys. Rev. 177, 793 (1969)]. It should be emphasized that both Gilbert's equation and the earlier Landau-Lifshitz equation are merely phenomenological equations, which are used to explain the time decay of the average magnetization. Brown suggested that the Gilbert equation should be augmented by a white-noise driving term in order to explain the effect of thermal fluctuations of the surroundings on the magnetization.
Ovejas, Virginia; Montero, Ral; Fernndez-Fernndez, Marta; Longarte, Asier
2015-04-01
The relaxation of 2,5-dimethylpyrrole after excitation in the 290-239 nm range, which covers the weak absorption of the S1 (1)A2 ??* state, dissociative along the N-H bond, and the stronger band mostly attributed to the (1)B2 ??* state, has been investigated by time-resolved ion and photoelectron techniques. The measurements yield an invariant lifetime of ?55 fs for the (1)??* state, after preparation in its Franck-Condon region with increasing vibrational content. This ultrafast rate indicates that, contrary to the observations made in pyrrole (Roberts et al. Faraday Discuss. 2013, 163, 95-116), the molecule reaches the dissociative part of the potential without any barrier effect, although calculations predict the latter to be higher than in the pyrrole case. The results are rationalized in terms of a barrier free multidimensional pathway that very likely involves out-of-plane vibrations. Additionally, a lifetime of ?100 fs is found after excitation along the higher (1)B2 ??* ? S0 transition. The relaxation of this state by coupling to a very short living S1 (1)??* state, or by alternative routes, is discussed in the light of the collected photoelectron measurements. PMID:25781497
Oliveira, Patrcia 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
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.
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.
Dehghani, Mehdi; Sadeghipour, Hamed; Shafaroodi, Hamed; Honar, Hooman; Riazi, Kiarash; Ebrahimkhani, Mohammad Reza; Hajrasouliha, Amir Reza; Tavakoli, Sina; Dehpour, Ahmad Reza
2004-08-01
The endothelium-dependent relaxation of corpus cavernosum smooth muscle and the roles of nitric oxide (NO) and arachidonic acid products of cyclooxygenase were investigated in non-operated, SHAM-operated, and bile duct-ligated rats. We further investigated the time-dependent alterations of corpus cavernosum relaxation in 2-, 7-, and 14-day bile duct-ligated animals. Acetylcholine produced concentration-dependent relaxation in phenylephrine-precontracted strips of corpus cavernosum. A significant reduction in the acetylcholine-induced relaxation was observed 2 days after bile duct ligation, and a greater reduction was observed on subsequent days. Incubation with 20 microM indomethacin reduced the acetylcholine-induced relaxation of the corpus cavernosum of unoperated rats while it had no effect in the corpus cavernosum of bile duct-ligated rats. Chronic treatment with Nomega-Nitro-L-Arginine Methyl Ester (L-NAME, 3 mg/kg/day, intraperitoneally) reduced the relaxation responses in the unoperated group while it had no effect in the bile duct-ligated group. These results show that acetylcholine-induced corporal relaxation is impaired in cholestatic rats, and this may be related to deficient nitric oxide production by the endothelium. The involvement of prostaglandins in this impairment seems unlikely. PMID:15288589
A molecular time-scale for eukaryote evolution recalibrated with the continuous microfossil record
Berney, Cdric; Pawlowski, Jan
2006-01-01
Recent attempts to establish a molecular time-scale of eukaryote evolution failed to provide a congruent view on the timing of the origin and early diversification of eukaryotes. The major discrepancies in molecular time estimates are related to questions concerning the calibration of the tree. To limit these uncertainties, we used here as a source of calibration points the rich and continuous microfossil record of dinoflagellates, diatoms and coccolithophorids. We calibrated a small-subunit ribosomal RNA tree of eukaryotes with four maximum and 22 minimum time constraints. Using these multiple calibration points in a Bayesian relaxed molecular clock framework, we inferred that the early radiation of eukaryotes occurred near the MesoproterozoicNeoproterozoic boundary, about 1100 million years ago. Our results indicate that most Proterozoic fossils of possible eukaryotic origin cannot be confidently assigned to extant lineages and should therefore not be used as calibration points in molecular dating. PMID:16822745
Nanosecond relaxation in polymer electrolyte nanocomposites
NASA Astrophysics Data System (ADS)
Marie-Louise, Saboungi; Price, David L.; Smith, Luis J.; Zanotti, Jean-Marc; Armand, Michel
2004-03-01
We present recent results on the dynamics and relaxation of nanocomposite polymer electrolytes. We have measured the relaxation on the 10-100 nsec time scale in PEO-LiClO_4-based nanocomposites using quasielastic neutron scattering (QENS). Complementary information on the conductivity have been derived on the same samples. Our results show that, on the time scale of the QENS measurements -- 0.01 to 0.1 ns --- the addition of ceramic nanoparticles has no significant effect on the dynamics of the polymer electrolyte while the confinement in porous materials such as Vycor and synthetic hectorite clays induces a spectacular slowing down of the dynamics.
Resonant relaxation in electroweak baryogenesis
NASA Astrophysics Data System (ADS)
Lee, Christopher; Cirigliano, Vincenzo; Ramsey-Musolf, Michael J.
2005-04-01
We compute the leading, chiral charge-changing relaxation term in the quantum transport equations that govern electroweak baryogenesis using the closed time path formulation of nonequilibrium quantum field theory. We show that the relaxation transport coefficients may be resonantly enhanced under appropriate conditions on electroweak model parameters and that such enhancements can mitigate the impact of similar enhancements in the CP-violating source terms. We also develop a power counting in the time and energy scales entering electroweak baryogenesis and include effects through second order in ratios ? of the small and large scales. We illustrate the implications of the resonantly enhanced O(?2) terms using the Minimal Supersymmetric Standard Model, focusing on the interplay between the requirements of baryogenesis and constraints obtained from collider studies, precision electroweak data, and electric dipole moment searches.
KUMAR, DEEPAK; SOUZA, RICHARD B.; SINGH, JUSTIN; CALIXTO, NATHANIEL E.; NARDO, LORENZO; LINK, THOMAS M.; LI, XIAOJUAN; MAJUMDAR, SHARMILA
2015-01-01
STUDY DESIGN Cross-sectional. OBJECTIVES To investigate the association between knee loadingrelated osteoarthritis (OA) risk factors (obesity, malalignment, and physical activity) and medial knee laminar (superficial and deep) T1rho and T2 relaxation times. BACKGROUND The interaction of various modifiable loading-related knee risk factors and cartilage health in knee OA is currently not well known. METHODS Participants with and without knee OA (n = 151) underwent magnetic resonance imaging at 3 T for superficial and deep cartilage T1rho and T2 magnetic resonance relaxation times in the medial femur (MF) and medial tibia (MT). Other variables included radiographic Kellgren-Lawrence (KL) grade, alignment, pain and symptoms using the Knee injury and Osteoarthritis Outcome Score, and physical activity using the International Physical Activity Questionnaire (IPAQ). Individuals with a KL grade of 4 were excluded. Group differences were calculated using 1-way analysis of variance, adjusting for age and body mass index. Linear regression models were created with age, sex, body mass index, alignment, KL grade, and the IPAQ scores to predict the laminar T1rho and T2 times. RESULTS Total IPAQ scores were the only significant predictors among the loading-related variables for superficial MF T1rho (P = .005), deep MT T1rho (P = .026), and superficial MF T2 (P = .049). Additionally, the KL grade predicted the superficial MF T1rho (P = .023) and deep MT T1rho (P = .022). CONCLUSION Higher physical activity levels and worse radiographic severity of knee OA, but not obesity or alignment, were associated with worse cartilage composition. PMID:25353261
Kumar, Deepak; Kothari, Abbas; Souza, Richard B.; Wu, Samuel; Ma, C. Benjamin; Li, Xiaojuan
2014-01-01
Background The objective of this pilot study was to evaluate cartilage T1? and T2 relaxation times and knee mechanics during walking and drop-landing for individuals with anterior cruciate ligament reconstruction (ACL-R). Methods Nine patients (6 men and 3 women, Age 35.85.4 years, BMI 23.52.5 kg/m2) participated 1.50.8 years after single-bundle two-tunnel ACL reconstruction. Peak knee adduction moment (KAM), flexion moment (KFM), extension moment (KEM), and peak varus were calculated from kinematic and kinetic data obtained during walking and drop-landing tasks. T1? and T2 times were calculated for medial femur (MF), and medial tibia (MT) cartilage and compared between subjects with low KAM and high KAM. Biomechanical variables were compared between limbs. Results The high KAM group had higher T1? for MT (p = 0.01), central MT (p = 0.05), posterior MF (p = 0.04), posterior MT (p = 0.01); and higher T2 for MT (p = 0.02), MF (p = 0.05) posterior MF (p = 0.002) and posterior MT (p = 0.01). During walking, ACL-R knees had greater flexion at initial contact (p =0.04), and lower KEM (p = 0.02). During drop-landing, the ACL-R knees had lower KAM (p = 0.03) and KFM (p = 0.002). Conclusion Patients with ACL-R who have higher KAM during walking had elevated MR relaxation times in the medial knee compartments. These data suggest that those individuals who have undergone ACL-R and have higher frontal plane loading, may be at a greater risk of knee osteoarthritis. PMID:24993277
Allometric scaling and maximum efficiency in physiological eigen time
Andresen, Bjarne; Shiner, J. S.; Uehlinger, Dominik E.
2002-01-01
General optimization results from physics indicate that maximum efficiency of a process, in the sense of minimum overall entropy production, is achieved when the rate of entropy production is constant over time, however not in ordinary clock time but on an, in general varying, eigen time scale, intrinsic to the system. We identify the eigen time of a biological system with physiological time, which generally scales with the 1/4 power of body mass, M1/4, over a vast range of species. Since it is equally well established that metabolic rate scales as M3/4, it follows that organisms produce entropy at the same intrinsic rate, fulfilling a necessary condition for maximum efficiency, and are all, furthermore, equally efficient on the physiological eigen time scale. PMID:11959910
NASA Astrophysics Data System (ADS)
Mayer, D.; Roepstorff, G.
1988-01-01
The spectrum of the transfer operator ? for the map Tx=1/ x-[1/ x] when restricted to a certain Banach space of holomorphic functions is shown to coincide with the spectrum of the adjoint U* of Koopman's isometric operator Uf( x)= f T( x) when the former is restricted to the Hilbert space ?(?) introduced in part I of this work. If N denotes the operator ?- P 1 with P 1 the projector onto the eigenfunction to the dominant eigenvalue ? 1 =1 of ?, then - N is a u 0-positive operator with respect to some cone and therefore has a dominant positive, simple eigenvalue - ? 2. A minimax principle holds giving rigorous upper and lower bounds both for ? 2 and the relaxation time of the map T.
Measurement of solute proton spin-lattice relaxation times in water using the 1,3,3,1 sequence
Sankar, S.S.; Mole, P.A.; Coulson, R.L.
1986-12-01
/sup 1/H NMR spin-lattice relaxation times (T1) of the N-CH3 proton resonances of phosphocreatine (PCr) and creatine (Cr) in water solutions were obtained using the 1,3,3,1 pulse sequence. These T1 values were equivalent to those obtained in D/sub 2/O and water using either the conventional inversion-recovery experiment or the 1,3,3,1 pulse sequence. Thus, the 1,3,3,1 sequence of proton NMR can provide an independent means along with phosphorous NMR for assess PCr and for the study of the creatine kinase reaction (PCr + ADP in equilibrium ATP + Cr) in aqueous solutions and perhaps in biological preparations.
Larionov, A. V.; Ilin, 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.
NASA Astrophysics Data System (ADS)
Xie, Hai-Qiong; Zeng, Zhong; Zhang, Liang-Qi; Liang, Gong-You; Hiroshi, Mizuseki; Yoshiyuki, Kawazoe
2012-12-01
In this paper, an improved incompressible multi-relaxation-time lattice Boltzmann-front tracking approach is proposed to simulate two-phase flow with a sharp interface, where the surface tension is implemented. The lattice Boltzmann method is used to simulate the incompressible flow with a stationary Eulerian grid, an additional moving Lagrangian grid is adopted to track explicitly the motion of the interface, and an indicator function is introduced to update the fluid properties accurately. The interface is represented by using a four-order Lagrange polynomial through fitting a set of discrete marker points, and then the surface tension is directly computed by using the normal vector and curvature of the interface. Two benchmark problems, including Laplace's law for a stationary bubble and the dispersion relation of the capillary wave between two fluids are conducted for validation. Excellent agreement is obtained between the numerical simulations and the theoretical results in the two cases.
Single-particle and transport relaxation times in back-gated undoped AlGaAs/GaAs
NASA Astrophysics Data System (ADS)
Pettersen, E. K.; Williams, D. A.; Ahmed, H.
1996-08-01
The magnetotransport properties of a two-dimensional electron gas were studied at low temperatures in an inverted GaAs - AlGaAs heterostructure whose electron density could be changed between 0268-1242/11/8/005/img1 and 0268-1242/11/8/005/img2 by the application of a substrate bias. The epitaxial layers were grown undoped to reduce the influence of remote ionized impurity scattering and so a biased back-gate was needed to create the two-dimensional electron gas. The conductive back-gate required the use of a shallow Pd/AuGe/Ag/Au contact recipe. We present the magnetoresistance response for a range of back-gate biases (electron densities) and compare the mobilities, the transport scattering and the single-particle relaxation times with theory.
Effective masses, relaxation times, and carrier mobilities in some chloride intercalants of graphite
NASA Astrophysics Data System (ADS)
Woollam, J. A.; Haugland, E.; Dowell, M. B.; Underhill, C.
1981-04-01
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.
Imaging of relaxation times and microwave field strength in a microfabricated vapor cell
NASA Astrophysics Data System (ADS)
Horsley, Andrew; Du, Guan-Xiang; Pellaton, Matthieu; Affolderbach, Christoph; Mileti, Gaetano; Treutlein, Philipp
2013-12-01
We present a characterization technique for atomic vapor cells, combining time-domain measurements with absorption imaging to obtain spatially resolved information on decay times, atomic diffusion, and coherent dynamics. The technique is used to characterize a 5-mm-diameter, 2-mm-thick microfabricated Rb vapor cell, with N2 buffer gas, placed inside a microwave cavity. Time-domain Franzen and Ramsey measurements are used to produce high-resolution images of the population (T1) and coherence (T2) lifetimes in the cell, while Rabi measurements yield images of the ?-, ?, and ?+ components of the applied microwave magnetic field. For a cell temperature of 90?C, the T1 times across the cell center are found to be a roughly uniform 265?s, while the T2 times peak at around 350?s. We observe a skin of reduced T1 and T2 times around the edge of the cell due to the depolarization of Rb after collisions with the silicon cell walls. Our observations suggest that these collisions are far from being 100% depolarizing, consistent with earlier observations made with Na and glass walls. Images of the microwave magnetic field reveal regions of optimal field homogeneity, and thus coherence. Our technique is useful for vapor cell characterization in atomic clocks, atomic sensors, and quantum information experiments.
Interface roughness mediated phonon relaxation rates in Si quantum dots.
NASA Astrophysics Data System (ADS)
Ferdous, Rifat; Hsueh, Yuling; Klimeck, Gerhard; Rahman, Rajib
2015-03-01
Si QDs are promising candidates for solid-state quantum computing due to long spin coherence times. However, the valley degeneracy in Si adds an additional degree of freedom to the electronic structure. Although the valley and orbital indices can be uniquely identified in an ideal Si QD, interface roughness mixes valley and orbital states in realistic dots. Such valley-orbit coupling can strongly influence T1 times in Si QDs. Recent experimental measurements of various relaxation rates differ from previous predictions of phonon relaxation in ideal Si QDs. To understand how roughness affects different relaxation rates, for example spin relaxation due to spin-valley coupling, which is a byproduct of spin-orbit and valley-orbit coupling, we need to understand the effect of valley-orbit coupling on valley relaxation first. Using a full-band atomistic tight-binding description for both the system's electron and electron-phonon hamiltonian, we analyze the effect of atomic-scale interface disorder on phonon induced valley relaxation and spin relaxation in a Si QD. We find that, the valley splitting dependence of valley relaxation rate governs the magnetic field dependence of spin relaxation rate. Our results help understand experimentally measured relaxation times.
NASA Astrophysics Data System (ADS)
Mastikhin, Igor V.
2005-02-01
For samples with T1s longer than 10 s, calibration of the RF probe and a measurement of T1 can be very time-consuming. A technique is proposed for use in imaging applications where one wishes to rapidly obtain information about the RF flip angle and sample T1 prior to imaging. The flip angle measurement time is less than 1 s for a single scan. Prior knowledge of the RF flip angle is not required for the measurement of T1. The resulting time savings in measuring the values of flip angle and T1 are particularly significant in the case of samples with very long T1 and short T2?. An imaging extension of the technique provides RF flip angle mapping without the need for incrementing the pulse duration, i.e., RF mapping can be performed at fixed RF amplifier output.
Protein dynamics: from rattling in a cage to structural relaxation.
Khodadadi, S; Sokolov, A P
2015-07-01
We present an overview of protein dynamics based mostly on results of neutron scattering, dielectric relaxation spectroscopy and molecular dynamics simulations. We identify several major classes of protein motions on the time scale from faster than picoseconds to several microseconds, and discuss the coupling of these processes to solvent dynamics. Our analysis suggests that the microsecond backbone relaxation process might be the main structural relaxation of the protein that defines its glass transition temperature, while faster processes present some localized secondary relaxations. Based on the overview, we formulate a general picture of protein dynamics and discuss the challenges in this field. PMID:26027652
Strong relaxation limit of multi-dimensional isentropic Euler equations
NASA Astrophysics Data System (ADS)
Xu, Jiang
2010-06-01
This paper is devoted to study the strong relaxation limit of multi-dimensional isentropic Euler equations with relaxation. Motivated by the Maxwell iteration, we generalize the analysis of Yong (SIAM J Appl Math 64:1737-1748, 2004) and show that, as the relaxation time tends to zero, the density of a certain scaled isentropic Euler equations with relaxation strongly converges towards the smooth solution to the porous medium equation in the framework of Besov spaces with relatively lower regularity. The main analysis tool used is the Littlewood-Paley decomposition.
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
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
NASA Astrophysics Data System (ADS)
Sauvage, S.; Boucaud, P.; Glotin, F.; Prazeres, R.; Ortega, J.-M.; Lematre, A.; Grard, J.-M.; Thierry-Flieg, V.
1998-12-01
We have observed the saturation of intraband absorption in InAs/GaAs self-assembled quantum dots. The investigated n-doped self-assembled quantum dots exhibit an intraband absorption within the conduction band, which is peaked at an 8 ?m wavelength. The saturation of the intraband absorption is achieved with an infrared pump delivered by a pulsed free-electron laser. The saturation of the transition is observed for an intensity around ?0.6 MW cm-2. The electron relaxation time under intraband excitation is measured by time-resolved pump-probe experiments. An electron relaxation time T1?3 ps is reported.
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)
Kusaka, Ryoji; Inokuchi, Yoshiya; Ebata, Takayuki
2012-01-01
Vibrational energy relaxation (VER) of the Fermi polyads in the CH stretching vibration of the benzene dimer (Bz2) and trimer (Bz3) has been investigated by picosecond (ps) time-resolved IR-UV pump-probe spectroscopy in a supersonic beam. The vibrational bands in the 3000-3100 cm-1 region were excited by a ps IR pulse and the time evolutions at the pumped and redistributed (bath) levels were probed by resonance enhanced multiphoton ionization with a ps UV pulse. For Bz2, a site-selective excitation in the T-shaped structure was achieved by using the isotope-substituted heterodimer hd, where h = C6H6 and d = C6D6, and its result was compared with that of hh homodimer. In the hd heterodimer, the two isomers, h(stem)d(top) and h(top)d(stem), show remarkable site-dependence of the lifetime of intracluster vibrational energy redistribution (IVR); the lifetime of the Stem site [h(stem)d(top), 140-170 ps] is ˜2.5 times shorter than that of the Top site [h(top)d(stem), 370-400 ps]. In the transient UV spectra, a broad electronic transition due to the bath modes emerges and gradually decays with a nanosecond time scale. The broad transition shows different time profile depending on UV frequency monitored. These time profiles are described by a three-step VER model involving IVR and vibrational predissociation: initial → bath1(intramolecular) → bath2(intermolecular) → fragments. This model also describes well the observed time profile of the Bz fragment. The hh homodimer shows the stepwise VER process with time constants similar to those of the hd dimer, suggesting that the excitation-exchange coupling of the vibrations between the two sites is very weak. Bz3 also exhibited the stepwise VER process, though each step is faster than Bz2.
V?a?n, Peter
2015-08-01
The class Litostomatea comprises a diverse assemblage of free-living and endosymbiotic ciliates. To understand diversification dynamic of litostomateans, divergence times of their main groups were estimated with the Bayesian molecular dating, a technique allowing relaxation of molecular clock and incorporation of flexible calibration points. The class Litostomatea very likely emerged during the Cryogenian around 680 Mya. The origin of the subclass Rhynchostomatia is dated to about 415 Mya, while that of the subclass Haptoria to about 654 Mya. The order Pleurostomatida, emerging about 556 Mya, was recognized as the oldest group within the subclass Haptoria. The order Spathidiida appeared in the Paleozoic about 442 Mya. The three remaining haptorian orders evolved in the Paleozoic/Mesozoic periods: Didiniida about 419 Mya, Lacrymariida about 269 Mya, and Haptorida about 194 Mya. The subclass Trichostomatia originated from a spathidiid ancestor in the Mesozoic about 260 Mya. A further goal of this study was to investigate the impact of various settings on posterior divergence time estimates. The root placement and tree topology as well as the priors of the rate-drift model, birth-death process and nucleotide substitution rate, had no significant effect on calculation of posterior divergence time estimates. However, removal of calibration points could significantly change time estimates at some nodes. PMID:26204556
Ultrafast relaxation dynamics observed through time-resolved photoelectron angular distributions.
Lecointre, Julien; Roberts, Gareth M; Horke, Daniel A; Verlet, Jan R R
2010-10-28
Time-resolved photoelectron imaging of the 7,7,8,8-tetracyanoquinodimethane (TCNQ) radical anion is presented. Photoelectron angular distributions (PADs) are qualitatively analyzed in terms of the simple s-p model that is based on symmetry arguments. The internal conversion dynamics from the first excited state (1(2)B(3u)) to the ground state ((2)B(2g)) may be observed through temporal changes in the PADs of the spectrally overlapping photoelectron features arising from photodetachment of the ground state and the excited state. A formulism for extracting the population dynamics from the ?(2) anisotropy parameter of overlapping spectroscopic features is presented. This is used to extract the lifetime of the first excited state, which is in good agreement with that observed in the time-resolved photoelectron spectra. PMID:20961158
Asymmetry of charge relaxation times in quantum dots: The influence of degeneracy
NASA Astrophysics Data System (ADS)
Beckel, A.; Kurzmann, A.; Geller, M.; Ludwig, A.; Wieck, A. D.; Knig, J.; Lorke, A.
2014-05-01
Using time-resolved transconductance spectroscopy, we study the tunneling dynamics between a two-dimensional electron gas (2DEG) and self-assembled quantum dots (QDs), embedded in a field-effect transistor structure. We find that the tunneling of electrons from the 2DEG into the QDs is governed by a different time constant than the reverse process, i.e., tunneling from the QDs to the 2DEG. This asymmetry is a clear signature of Coulomb interaction and makes it possible to determine the degeneracy of the quantum-dot orbitals even when the individual states cannot be resolved energetically because of inhomogeneous broadening. Our experimental data can be qualitatively explained within a master-equation approach.
NASA Astrophysics Data System (ADS)
Polson, James M.; Fyfe, J. D. Dean; Jeffrey, Kenneth R.
1991-03-01
Deuterium nuclear magnetic resonance (NMR) spectra and spin-lattice relaxation times were determined in order to study the dynamics of t-butyl groups in butylated hydroxytoluene. The results are consistent with a model first proposed by Beckmann et al. [J. Magn. Reson. 36, 199 (1979)], where there is an inequivalence between the methyl groups within each t-butyl group. While two methyl groups reorient rapidly relative to the whole t-butyl rotation, the remaining methyl group is more restricted in its motion, reorienting at a rate comparable to that of the t-butyl group itself. The spin-lattice relaxation data show two T1 minima, the high temperature minimum (40 C) corresponding to the combined t-butyl and ``slow'' methyl rotations, and the low temperature minimum corresponding to ``fast'' methyl group rotation. Using an explicitly defined T1 fitting function, the T1 data yield activation energies of 2.2 and 6.0 kcal/mol for the fast methyl and t-butyl rotations, respectively, both in agreement with Beckmann's values obtained from proton T1 experiments. It was also possible to simulate the low temperature deuterium NMR spectra from T=-160 C to T=-80 C using the aforementioned dynamical inequivalence between the t-butyl methyl groups. While the fast methyl group rotation was in the motional narrowing region for T>-160 C, it was possible, from the simulations, to determine the t-butyl exchange rates to within 10%. The jump rates are remarkably close to the values predicted from the T1 results. Above -80 C, the spectra could not be simulated, implying that a third motion must be present to further alter the high temperature line shapes. The effective axial asymmetry of the T>-20 spectra indicates that the additional motion involves a two site exchange.
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.
The limit order book on different time scales
NASA Astrophysics Data System (ADS)
Eisler, Zoltán; Kertész, János; Lillo, Fabrizio
2007-06-01
Financial markets can be described on several time scales. We use data from the limit order book of the London Stock Exchange (LSE) to compare how the fluctuation dominated microstructure crosses over to a more systematic global behavior.
NASA Astrophysics Data System (ADS)
Plookphol, Thawatchai
This work explores the physical basis for Hart's [1970] mechanical equation of state behavior in rock salt and olivine. Specifically, the experiments were designed to identify a possible microstructural basis for the scaling relation and the "hardness" parameter, sigma*, associated with each load relaxation curve, which Hart interpreted to represent constant "structure." They were also designed to examine the relationship between creep and load relaxation and the significance of steady-state, power-law creep within the context of the mechanical equation of state. Constant-stress creep, stress-change, and load-relaxation experiments were conducted on synthetic rock salt (NaCl) at 400C and 700C and on natural San Carlos (AZ) olivine ([Mg, Fe]2 SiO4) single crystals at 1500C and pO2 = 10-10 atm. The two minerals behaved very differently, with rock salt exhibiting classic mechanical-equation-of-state behavior and olivine, under the conditions studied, exhibiting almost no path effects. We found that in the creep of rock salt at constant stress, the material passes through a continuum of structural states during transient creep, each state represented by a constant sigma* curve measured using load-relaxation experiments. It was surmised that each load-relaxation curve corresponds to the behavior of the material at constant (or nearly constant) average subgrain diameter, and that subgrain size distributions are similar (or nearly similar) to each other. The hardness parameter is found to follow the relation sigma* ? 50Gb/DI where G is the shear modulus, b is the Burgers vector, and DI is the mean intercept diameter. In contrast, it was found that for olivine, load-relaxation data are equivalent to steady-state creep data. In olivine, as in rock salt, the density of mobile dislocations responds rapidly to changes in stress, but, unlike rock salt, subgrain formation in olivine is very slow or nonexistent under the conditions tested, resulting in the direct correspondence between creep and load relaxation.
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.
Grueneisen Relaxation Photoacoustic Microscopy
NASA Astrophysics Data System (ADS)
Wang, Lidai; Zhang, Chi; Wang, Lihong V.
2014-10-01
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 nonradiative absorption with confocal optical resolution. GR-PAM sequentially delivers two identical laser pulses with a microsecond-scale time delay. The first laser pulse generates a photoacoustic signal and thermally tags the in-focus absorbers. When the second laser pulse excites the tagged absorbers within the thermal relaxation time, a photoacoustic signal stronger than the first one is produced, owing to the temperature dependence of the Grueneisen parameter. GR-PAM detects the amplitude difference between the two colocated photoacoustic signals, confocally imaging the nonradiative absorption. We greatly improved axial resolution from 45 ?m to 2.3 ?m and, at the same time, slightly improved lateral resolution from 0.63 ?m to 0.41 ?m. In addition, the optical sectioning capability facilitates the measurement of the absolute absorption coefficient without fluence calibration.
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 m to 2.3 m and at the same time slightly improved lateral resolution from 0.63 m to 0.41 m. In addition, the optical sectioning capability facilitates the measurement of the absolute absorption coefficient without fluence calibration. PMID:25379919
Grueneisen relaxation photoacoustic microscopy.
Wang, Lidai; Zhang, Chi; Wang, Lihong V
2014-10-24
The temperature-dependent property of the Grueneisen parameter has been employed in photoacoustic imaging mainly to measure tissue temperature. Here we explore this property using a different approach and develop Grueneisen relaxation photoacoustic microscopy (GR-PAM), a technique that images nonradiative absorption with confocal optical resolution. GR-PAM sequentially delivers two identical laser pulses with a microsecond-scale time delay. The first laser pulse generates a photoacoustic signal and thermally tags the in-focus absorbers. When the second laser pulse excites the tagged absorbers within the thermal relaxation time, a photoacoustic signal stronger than the first one is produced, owing to the temperature dependence of the Grueneisen parameter. GR-PAM detects the amplitude difference between the two colocated photoacoustic signals, confocally imaging the nonradiative absorption. We greatly improved axial resolution from 45???m to 2.3???m and, at the same time, slightly improved lateral resolution from 0.63???m to 0.41???m. In addition, the optical sectioning capability facilitates the measurement of the absolute absorption coefficient without fluence calibration. PMID:25379919
Large Deviations for Two-Time-Scale Diffusions, with Delays
Kushner, Harold J.
2010-12-15
We consider the problem of large deviations for a two-time-scale reflected diffusion process, possibly with delays in the dynamical terms. The Dupuis-Ellis weak convergence approach is used. It is perhaps the most intuitive and simplest for the problems of concern. The results have applications to the problem of approximating optimal controls for two-time-scale systems via use of the averaged equation.
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.
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.
Scale-dependent intrinsic entropies of complex time series.
Yeh, Jia-Rong; Peng, Chung-Kang; Huang, Norden E
2016-04-13
Multi-scale entropy (MSE) was developed as a measure of complexity for complex time series, and it has been applied widely in recent years. The MSE algorithm is based on the assumption that biological systems possess the ability to adapt and function in an ever-changing environment, and these systems need to operate across multiple temporal and spatial scales, such that their complexity is also multi-scale and hierarchical. Here, we present a systematic approach to apply the empirical mode decomposition algorithm, which can detrend time series on various time scales, prior to analysing a signal's complexity by measuring the irregularity of its dynamics on multiple time scales. Simulated time series of fractal Gaussian noise and human heartbeat time series were used to study the performance of this new approach. We show that our method can successfully quantify the fractal properties of the simulated time series and can accurately distinguish modulations in human heartbeat time series in health and disease. PMID:26953181
Johari-Goldstein secondary relaxation in methylated alkanes
NASA Astrophysics Data System (ADS)
Ngai, K. L.
2005-06-01
Dielectric relaxation measurements of the methylated alkanes, 3-methylpentane, 3-methylheptane, 4-methylheptane, 2,3-dimethylpentane, and 2,4,6-trimethylheptane by S. Shahriari, A. Mandanici, L-M Wang, and R. Richert [J. Chem. Phys. 121, 8960 (2004)] have found a primary ? relaxation of these glass-forming liquids and a slow secondary ? relaxation that are in close proximity to each other on the frequency scale. These glass formers have one or more methyl groups individually attached to various carbons on the alkane chain. They cannot contribute to such a slow secondary relaxation. Hence the observed secondary relaxations is not intramolecular in origin and, similar to secondary relaxations found in rigid molecules by Johari and Goldstein, they are potentially important in the consideration of a mechanism for the glass transition. These secondary relaxations in the methylated alkanes are special and belong to the class of Johari-Goldstein in a generalized sense. The coupling model has predicted that its primitive relaxation time should be approximately the same as the relaxation time of the secondary relaxation if the latter is of the Johari-Goldstein kind. This prediction has been shown to hold in many other glass formers. The published data of the methylated alkanes provide an opportunity to test this prediction once more. The results of this work confirm the prediction.
Two-time-scale inverse problems: formulation and solution
NASA Astrophysics Data System (ADS)
Puel, G.; Aubry, D.
2015-11-01
The aim here is to study two-time-scale models and their associated parameter identification. When it is possible to consider two well-separated time scales, and when the fast component of the applied loading is periodic, a periodic time homogenization scheme, similar to what exists in space homogenization, can be used to derive a homogenized model. A parameter identification process for this latter is then proposed, consisting in homogenizing with respect to time a classical identification strategy based on the use of adjoint state formulations; it is then applied to an academic example showing the benefits of such a strategy.
Multi-scale description and prediction of financial time series
NASA Astrophysics Data System (ADS)
Nawroth, A. P.; Friedrich, R.; Peinke, J.
2010-08-01
A new method is proposed that allows a reconstruction of time series based on higher order multi-scale statistics given by a hierarchical process. This method is able to model financial time series not only on a specific scale but for a range of scales. The method itself is based on the general n-scale joint probability density, which can be extracted directly from given data. It is shown how based on this n-scale statistics, general n-point probabilities can be estimated from which predictions can be achieved. Exemplary results are shown for the German DAX index. The ability to model correctly the behaviour of the original process for different scales simultaneously and in time is demonstrated. As a main result it is shown that this method is able to reproduce the known volatility cluster, although the model contains no explicit time dependence. Thus a new mechanism is shown how, in a stationary multi-scale process, volatility clustering can emerge.
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.
NASA Astrophysics Data System (ADS)
Richardson, P. M.; Voice, A. M.; Ward, I. M.
2013-12-01
Longitudinal relaxation (T1) measurements of 19F, 7Li, and 1H in propylene carbonate/LiBF4 liquid electrolytes are reported. Comparison of T1 values with those for the transverse relaxation time (T2) confirm that the measurements are in the high temperature (low correlation time) limit of the T1 minimum. Using data from pulsed field gradient measurements of self-diffusion coefficients and measurements of solution viscosity measured elsewhere, it is concluded that although in general there are contributions to T1 from both translational and rotational motions. For the lithium ions, this is mainly translational, and for the fluorine ions mainly rotational.
Spatially resolved measurements of mean spin-spin relaxation time constants.
Nechifor, Ruben Emanuel; Romanenko, Konstantin; Marica, Florea; Balcom, Bruce J
2014-02-01
Magnetic Resonance measurements of the T2 distribution have become very common and they are a powerful way to probe microporous fluid bearing solids. While the structure of the T2 distribution, and changes in the structure, are often very informative, it is common to reduce the T2 distribution to a mean numeric quantity in order to provide a quantitative interpretation of the distribution. Magnetic Resonance Imaging measurements of the T2 distribution have recently been introduced, but they are time consuming, especially for 2 and 3 spatial dimensions. In this paper we explore a direct MRI measurement of the arithmetic mean of 1/T2, characterizing the distribution by using the initial slope of the spatially resolved T2 decay in a CPMG prepared Centric Scan SPRITE experiment. The methodology is explored with a test phantom sample and realistic petroleum reservoir core plug samples. The arithmetic mean of 1/T2 is related to the harmonic mean of T2. The mean obtained from the early decay is explored through measurements of uniform saturated core plug samples and by comparison to other means determined from the complete T2 distribution. Complementary data were obtained using SE-SPI T2 distribution MRI measurements. The utility of the arithmetic mean 1/T2 is explored through measurements of centrifuged core plug samples where the T2 distribution varies spatially. The harmonic mean T2 obtained from the early decay was employed to estimate the irreducible water saturation for core plug samples. PMID:24361482
NASA Astrophysics Data System (ADS)
Springer, Fabian; Steidle, Gnter; Martirosian, Petros; Claussen, Claus D.; Schick, Fritz
2010-09-01
The introduction of ultrashort-echo-time-(UTE)-sequences to clinical whole-body MR scanners has opened up the field of MR characterization of materials or tissues with extremely fast signal decay. If the transverse relaxation time is in the range of the RF-pulse duration, approximation of the RF-pulse by an instantaneous rotation applied at the middle of the RF-pulse and immediately followed by free relaxation will lead to a distinctly underestimated echo signal. Thus, the regular Ernst equation is not adequate to correctly describe steady state signal under those conditions. The paper presents an analytically derived modified Ernst equation, which correctly describes in-pulse relaxation of transverse magnetization under typical conditions: The equation is valid for rectangular excitation pulses, usually applied in 3D UTE sequences. Longitudinal relaxation time of the specimen must be clearly longer than RF-pulse duration, which is fulfilled for tendons and bony structures as well as many solid materials. Under these conditions, the proposed modified Ernst equation enables adequate and relatively simple calculation of the magnetization of materials or tissues. Analytically derived data are compared to numerical results obtained by using an established Runge-Kutta-algorithm based on the Bloch equations. Validity of the new approach was also tested by systematical measurements of a solid polymeric material on a 3 T whole-body MR scanner. Thus, the presented modified Ernst equation provides a suitable basis for T1 measurements, even in tissues with T2 values as short as the RF-pulse duration: independent of RF-pulse duration, the 'variable flip angle method' led to consistent results of longitudinal relaxation time T1, if the T2 relaxation time of the material of interest is known as well.
Simulations of Bingham plastic flows with the multiple-relaxation-time lattice Boltzmann model
NASA Astrophysics Data System (ADS)
Chen, SongGui; Sun, QiCheng; Jin, Feng; Liu, JianGuo
2014-03-01
Fresh cement mortar is a type of workable paste, which can be well approximated as a Bingham plastic and whose flow behavior is of major concern in engineering. In this paper, Papanastasiou's model for Bingham fluids is solved by using the multiplerelaxation-time lattice Boltzmann model (MRT-LB). Analysis of the stress growth exponent m in Bingham fluid flow simulations shows that Papanastasiou's model provides a good approximation of realistic Bingham plastics for values of m > 108. For lower values of m, Papanastasiou's model is valid for fluids between Bingham and Newtonian fluids. The MRT-LB model is validated by two benchmark problems: 2D steady Poiseuille flows and lid-driven cavity flows. Comparing the numerical results of the velocity distributions with corresponding analytical solutions shows that the MRT-LB model is appropriate for studying Bingham fluids while also providing better numerical stability. We further apply the MRT-LB model to simulate flow through a sudden expansion channel and the flow surrounding a round particle. Besides the rich flow structures obtained in this work, the dynamics fluid force on the round particle is calculated. Results show that both the Reynolds number Re and the Bingham number Bn affect the drag coefficients C D , and a drag coefficient with Re and Bn being taken into account is proposed. The relationship of Bn and the ratio of unyielded zone thickness to particle diameter is also analyzed. Finally, the Bingham fluid flowing around a set of randomly dispersed particles is simulated to obtain the apparent viscosity and velocity fields. These results help simulation of fresh concrete flowing in porous media.
NASA Technical Reports Server (NTRS)
Desideri, J.-A.; Tannehill, J. C.
1977-01-01
An over-relaxation procedure is applied to the MacCormack finite-difference scheme in order to reduce the computation time required to obtain a steady-state solution. The implementation of this acceleration procedure to an existing computer program using the regular MacCormack method is extremely simple and does not require additional storage. The over-relaxation procedure does not alter the steady-state solution, which is second-order accurate. The method is first applied to Burgers' equation. A stability condition and an expression for the increase in the rate of convergence are derived. The method is then applied to the calculation of the hypersonic viscous flow over a flat plate, using the complete Navier-Stokes equations, and the inviscid flow over a wedge. Reductions in computing time by factors of 3 and 1.5, respectively, are obtained by over-relaxation.
NASA Astrophysics Data System (ADS)
Asaji, Tetsuo
2013-05-01
The temperature dependences of spin-lattice relaxation time T 1 of 35Cl and 37Cl NQR were studied for the co-crystal of tetramethylpyrazine (TMP) with chloranilic acid (H2ca), TMP-H2ca, in which one-dimensional hydrogen bonding is formed by alternate arrangement of TMP and H2ca. The isotope ratio 37Cl T 1 / 35Cl T 1 was determined to be 1.0 0.1 above ca. 290 K where a steep decrease of spin-lattice relaxation time T 1 with increasing temperature was observed. In this temperature range it is suggested that the relaxation is originated from the slow fluctuation of electric field gradient (EFG). Beside EFG fluctuation due to the external-charge-density fluctuation, the small angle reorientation of the quantization axis triggered by a proton transfer motion between N...H-O and N-H...O hydrogen bonding states is proposed.
Kang, Nam Lyong
2014-12-07
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 P{sub pe}=4.010{sup 22}?eV/m for InSb and P{sub pe}=1.210{sup 23}?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.
Jungmann, P.M.; Kraus, M.S.; Nardo, L.; Liebl, H.; Alizai, H.; Joseph, G.B.; Liu, F.; Lynch, J.; McCulloch, C.E.; Nevitt, M.C.; Link, T.M.
2014-01-01
Purpose To study the natural evolution of cartilage T2 relaxation times in knees with various extents of morphological cartilage abnormalities, assessed with 3T MRI from the Osteoarthritis Initiative. Materials and Methods Right knee MRIs of 245, 4560 year old individuals without radiographic OA were included. Cartilage was segmented and T2 maps were generated in five compartments (patella, medial and lateral femoral condyle, medial and lateral tibia) at baseline and two-year follow-up. We examined the association of T2 values and two-year change of T2 values with various Whole-Organ MR Imaging Scores (WORMS). Statistical analysis was performed with ANOVA and Students t-tests. Results Higher baseline T2 was associated with more severe cartilage defects at baseline and subsequent cartilage loss (P<0.001). However, longitudinal T2 change was inversely associated with both baseline (P=0.038) and follow-up (P=0.002) severity of cartilage defects. Knees that developed new cartilage defects had smaller increases in T2 than subjects without defects (P=0.045). Individuals with higher baseline T2 showed smaller T2 increases over time (P<0.001). Conclusion An inverse correlation of longitudinal T2 changes versus baseline T2 values and morphological cartilage abnormalities suggests that once morphological cartilage defects occur, T2 values may be limited for evaluating further cartilage degradation. PMID:24038491
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.
Atomic Time Scales for the 21st Century
NASA Astrophysics Data System (ADS)
Arias, E. F.
2014-06-01
The International Bureau of Weights and Measures, in coordination with international organizations and national institutes, maintains and disseminates Coordinated Universal Time (UTC). Other timescales exist for different purposes. This article describes the state-of-the-art in the elaboration of these time scales.
Scaling properties in time-varying networks with memory
NASA Astrophysics Data System (ADS)
Kim, Hyewon; Ha, Meesoon; Jeong, Hawoong
2015-12-01
The formation of network structure is mainly influenced by an individual node's activity and its memory, where activity can usually be interpreted as the individual inherent property and memory can be represented by the interaction strength between 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 time-varying networks, we propose temporal-pattern coarsening of activity-driven growing networks with memory. In particular, we focus on the relation between time-scale coarsening 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 tests.
Li, S.; Swindle, S.L.; Smith, S.K.; Nieman, R.A.; Moore, A.L.; Moore, T.A.; Gust, D. )
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.
Deelchand, Dinesh Kumar; Henry, Pierre-Gilles; Marja?ska, Ma?gorzata
2014-01-01
Purpose To investigate the effect of Carr-Purcell (CP) pulse trains on transverse relaxation times, T2, of tissue water and metabolites (both non-coupled and J-coupled spins) in the rat brain at 9.4 T using LASER, CP-LASER and T2?-LASER sequences. Methods Proton NMR spectra were measured in rat brain in vivo at 9.4 T. Spectra were acquired at multiple echo times ranging from 18 to 402 ms. All spectra were analyzed using LCModel with simulated basis sets. Signals of metabolites as a function of echo time were fitted using a mono-exponential function to determine their T2 relaxation times. Results Measured T2s for tissue water and all metabolites were significantly longer with CP-LASER and T2?-LASER compared to LASER. The T2 increased by a factor of ~1.3 for non-coupled and weakly coupled spins (e.g., N-acetylaspartate and total creatine) and by a factor of ~2 (e.g., glutamine and taurine) to ~4 (e.g., glutamate and myo-inositol) for strongly coupled spins. Conclusion Application of a CP pulse train results in a larger increase in T2 relaxation times for strongly coupled spins than for non-coupled (singlet) and weakly coupled spins. This needs to be taken into account when correcting for T2 relaxation in CP-like sequences such as LASER. PMID:24436256
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
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.
Common scaling patterns in intertrade times of U. S. stocks.
Ivanov, Plamen Ch; Yuen, Ainslie; Podobnik, Boris; Lee, Youngki
2004-05-01
We analyze the sequence of time intervals between consecutive stock trades of thirty companies representing eight sectors of the U.S. economy over a period of 4 yrs. For all companies we find that: (i) the probability density function of intertrade times may be fit by a Weibull distribution, (ii) when appropriately rescaled the probability densities of all companies collapse onto a single curve implying a universal functional form, (iii) the intertrade times exhibit power-law correlated behavior within a trading day and a consistently greater degree of correlation over larger time scales, in agreement with the correlation behavior of the absolute price returns for the corresponding company, and (iv) the magnitude series of intertrade time increments is characterized by long-range power-law correlations suggesting the presence of nonlinear features in the trading dynamics, while the sign series is anticorrelated at small scales. Our results suggest that independent of industry sector, market capitalization and average level of trading activity, the series of intertrade times exhibit possibly universal scaling patterns, which may relate to a common mechanism underlying the trading dynamics of diverse companies. Further, our observation of long-range power-law correlations and a parallel with the crossover in the scaling of absolute price returns for each individual stock, support the hypothesis that the dynamics of transaction times may play a role in the process of price formation. PMID:15244883
Observation time scale, free-energy landscapes, and molecular symmetry
Wales, David J.; Salamon, Peter
2014-01-01
When structures that interconvert on a given time scale are lumped together, the corresponding free-energy surface becomes a function of the observation time. This view is equivalent to grouping structures that are connected by free-energy barriers below a certain threshold. We illustrate this time dependence for some benchmark systems, namely atomic clusters and alanine dipeptide, highlighting the connections to broken ergodicity, local equilibrium, and “feasible” symmetry operations of the molecular Hamiltonian. PMID:24374625
Pollard, Richard; Newman, John
1980-01-01
A mathematical model of the LiAl/LiCl, KCl/FeS cell has been used to study the behavior of the system during relaxation and charging. The effects of state of charge, cell temperature, and current density are presented, and the influence of a period of relaxation on the subsequent charging operation is investigated. In addition, factors that can have a significant impact on the charging characteristics are identified.
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 networks 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 models 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
Long-time relaxation of photo-induced influence on BiFeO3 thin films
NASA Astrophysics Data System (ADS)
Gu, Jun-xing; Jin, Kui-juan; Wang, Le; He, Xu; Guo, Hai-zhong; Wang, Can; He, Meng; Yang, Guo-zhen
2015-11-01
An intuitively persistent enhancement of the local surface potential of BiFeO3 layers in both heterostructures of BiFeO3/SrRuO3/SrTiO3 and BiFeO3/Sr0.09Nb0.01TiO3 was observed by the Kelvin probe force microscopy technique after the illumination of 375 nm laser. This photo-induced enhanced surface potential can maintain as long as 15 h after the illumination. We attributed this super-long-time relaxation of photo-induced influence to a photo-induced depolarization in the BiFeO3 thin films, and our first-principles calculation of double-potential well further provides an instinct understanding on this depolarization process. Our findings provide a peculiar understanding into the photo-induced phenomena on the widely researched ferroelectric systems and offer an approach to tune their multifunctionality of the magnetization and polarization not only by applied magnetic and electric fields but also by optical filed.
Three-dimensional multi-relaxation-time lattice Boltzmann front-tracking method for two-phase flow
NASA Astrophysics Data System (ADS)
Hai-Qiong, Xie; Zhong, Zeng; Liang-Qi, Zhang
2016-01-01
We developed a three-dimensional multi-relaxation-time lattice Boltzmann method for incompressible and immiscible two-phase flow by coupling with a front-tracking technique. The flow field was simulated by using an Eulerian grid, an adaptive unstructured triangular Lagrangian grid was applied to track explicitly the motion of the two-fluid interface, and an indicator function was introduced to update accurately the fluid properties. The surface tension was computed directly on a triangular Lagrangian grid, and then the surface tension was distributed to the background Eulerian grid. Three benchmarks of two-phase flow, including the Laplace law for a stationary drop, the oscillation of a three-dimensional ellipsoidal drop, and the drop deformation in a shear flow, were simulated to validate the present model. Project supported by the National Natural Science Foundation of China (Grant No. 11572062), the Fundamental Research Funds for the Central Universities, China (Grant No. CDJZR13248801), the Program for Changjiang Scholars and Innovative Research Team in University, China (Grant No. IRT13043), and Key Laboratory of Functional Crystals and Laser Technology, TIPC, Chinese Academy of Sciences.
Fraind, Alicia M; Ryzhkov, Lev R; Tovar, John D
2016-02-11
We present a study to probe the formation of localized aromatic sextets and their effects on the charge transport properties in polymers with acene cores. Bithiophene-acene copolymers containing benzene, naphthalene, or anthracene as acene cores were synthesized using Yamamoto polymerization. Drop-casted polymer films were chemically doped and analyzed using high frequency saturation transfer EPR (HF ST-EPR), a method which has proven useful in the study of conducting polymers. The spin-spin and spin-lattice relaxation times were determined for these polymers at low temperatures (4 to 20 K) and used to obtain inter- and intrachain spin diffusion rates and conductivities. Similar interchain spin diffusion rates were seen across all polymer systems; however, anthracene containing polymer poly(hexylTTATT) was found to have the largest intrachain spin diffusion rate. The poly(hexylTTATT) intrachain spin diffusion rate may be artificially high if the anthracene ring restricts the diffusion of spin to the hexylated quaterthiophene segment in poly(hexylTTATT) whereas the spins diffuse through the acene cores in the benzene and naphthalene derivatives. Alternatively, as both the spin diffusion rates and conductivities vary unpredictably with temperature, it is possible that the π-electron localization previously seen in the anthracene core could be relieved at lower temperatures. PMID:26795133
Shear relaxations of confined liquids
Carson, G.A. Jr.
1992-01-01
Ultrathin (<40 [angstrom]) films of octamethylcyclotetrasiloxane (OMCTS), hexadecane, and dodecane were subjected to linear and non-linear oscillatory shear between flat plates. Shearing frequencies of 0.1 to 800 s[sup [minus]1] were applied at pressures from zero to 0.8 MPa using a surface rheometer only recently developed. In most cases the plates were atomically smooth mica surfaces; the role of surface interactions was examined by replacing these with alkyl chain monolayers. OMCTS and hexadecane were examined at a temperature about 5 Celcius degrees above their melting points and tended to solidify. Newtonian plateaus having enormous viscosities were observed at low shear rates. The onset of shear thinning implied relaxation times of about 0.1 s in the linear structure of the confined liquids. Large activation volumes ([approximately]80 nm[sup 3]) suggested that shear involved large-scale collective motion. Dodecane was studied at a much higher temperature relative to its melting point and showed no signs of impending solidification though it exhibited well-defined regions of Newtonian response and power law shear thinning. When treated with molecular sieves before use, dodecane had relaxation times which were short (0.02 s) compared to hexadecane, but still exhibited large-scale collective motion. When treated with silica gel, an unexplained long-time relaxation (10 s) was seen in the Newtonian viscosity of dodecane. The relaxation time of the linear structure, 0.005 s was very small, and the storage modulus was unresolvable. The small activation volume (7 nm[sup 3]) indicated a much lower level of collective motion. The activation volume remained small when dodecane was confined between tightly bound, low energy, alkyl monolayers. At low strains the storage and loss moduli became very large (>10[sup 4] Pa), probably due to interactions with flaws in the monolayers. Dramatic signs of wall slip were observed at large strains even at low pressures.
Shear Relaxations of Confined Liquids.
NASA Astrophysics Data System (ADS)
Carson, George Amos, Jr.
Ultrathin (<40 A) films of octamethylcyclotetrasiloxane (OMCTS), hexadecane, and dodecane were subjected to linear and non-linear oscillatory shear between flat plates. Shearing frequencies of 0.1 to 800 s^{-1} were applied at pressures from zero to 0.8 MPa using a surface rheometer only recently developed. In most cases the plates were atomically smooth mica surfaces; the role of surface interactions was examined by replacing these with alkyl chain monolayers. OMCTS and hexadecane were examined at a temperature about 5 Celsius degrees above their melting points and tended to solidify. Newtonian plateaus having enormous viscosities were observed at low shear rates. The onset of shear thinning implied relaxation times of about 0.1 s in the linear structure of the confined liquids. Large activation volumes (~80 nm ^3) suggested that shear involved large-scale collective motion. Dodecane was studied at a much higher temperature relative to its melting point and showed no signs of impending solidification though it exhibited well-defined regions of Newtonian response and power law shear thinning. When treated with molecular sieves before use, dodecane had relaxation times which were short (0.02 s) compared to hexadecane, but still exhibited large-scale collective motion. When treated with silica gel, an unexplained long -time relaxation (10 s) was seen in the Newtonian viscosity of dodecane. The relaxation time of the linear structure, 0.005 s was very small, and the storage modulus was unresolvable. The small activation volume (7nm^3) indicated a much lower level of collective motion. The activation volume remained small when dodecane was confined between tightly bound, low energy, alkyl monolayers. At low strains the storage and loss moduli became very large (>10^4 Pa), probably due to interactions with flaws in the monolayers. Dramatic signs of wall slip were observed at large strains even at low pressures.
On the construction of shoreline diagrams and the inference of relaxation-time spectra for the earth
NASA Astrophysics Data System (ADS)
Klemann, V.; Wolf, D.
2003-04-01
The main objective of quantifying post-glacial uplift is the inference of the earth's viscosity stratification. McConnell (1968) presented a simple method of inverting for the viscosity, which he applied to a shoreline diagram for eastern Fennoscandia. First, the spatial variation of sea level at different time epochs represented by a shoreline diagram was transformed to the spectral domain. Then, from the temporal variation of the spectral amplitudes, a relaxation-time spectrum (RTS) was derived and, finally, inverted in terms of the viscosity stratification. The main advantage of McConnell's method is that it is essentially insensitive to the ice-sheet history and mass. The remaining assumptions are: (1) The approximate radius and center of the ice sheet are known, (2) the orientation of the shorelines is roughly radial to the ice-sheet center and (3) all shorelines refer to the time after deglaciation (free decay). Recently, Wieczerkowski et al. (1999) have extended McConnell's method to spherical geometry and inverted for the viscosity using an RTS derived from an improved shoreline diagram constructed by Donner (1995) for eastern Fennoscandia. A disadvantage of the method is that only a small number of well-documented shoreline diagrams can be found in literature. To overcome this, we propose a simple method of constructing shoreline diagrams from a given set of sea-level index points (SLIs). We apply this method to SLIs in the west and south of Fennoscandia and demonstrate the robustness of the RTS inferred with respect to the SLIs considered. Furthermore, we test the technique with respect to shoreline diagrams constructed using SLIs from Scotland and Canada, for which the construction of radially oriented shorelines is more difficult than for Fennoscandia. Donner, J., 1995. The Quaternary history of Scandinavia, Cambridge University Press. McConnell, R.K., 1968. J. Geophys. Res., 73, 7089--7105. Wieczerkowski, K., Mitrovica, J.X., Wolf, D., 1999. Geophys. J. Int., 139, 69--86.
NASA Astrophysics Data System (ADS)
Lai, Ting-ing; Lim, E. C.
1981-12-01
Time-resolved fluorescence spectra and energy-resolved fluorescence decays of thioxanthone in fluid solutions are presented which demonstrate the importance of solvent relaxation in determining photophysical properties of thioxanthone via its effect on S 2 (n? *)-Si(?? *) vibronic coupling.
Carballido-Gamio, Julio; Link, Thomas M.; Majumdar, Sharmila
2010-01-01
MR relaxation time measurements of knee cartilage have shown potential to characterize knee osteoarthritis (OA). In this work, techniques that allow localized intra- and inter-subject comparisons of cartilage relaxation times, as well as cartilage flattening for texture analysis parallel and perpendicular to the natural cartilage layers, are presented. The localized comparisons are based on the registration of bone structures and the assignment of relaxation time feature vectors to each point in the bone cartilage interface. Cartilage flattening was accomplished with Bezier splines and warping, and texture analysis was performed with second-order texture measures using gray-level co-occurrence matrices (GLCM). In a cohort of five normal subjects the performance and reproducibility of the techniques were evaluated using T1? maps of femoral knee cartilage. The feasibility of creating a mean cartilage relaxation time map is also presented. Successful localized intra- and inter-subject T1? comparisons were obtained with reproducibility similar to that reported in the literature for regional T2. Improvement of the reproducibility of GLCM features was obtained by flattening the T1? maps. The results indicate that the presented techniques have potential in longitudinal and population studies of knee OA at different stages of the disease. PMID:18506807
Carballido-Gamio, Julio; Link, Thomas M; Majumdar, Sharmila
2008-06-01
MR relaxation time measurements of knee cartilage have shown potential to characterize knee osteoarthritis (OA). In this work, techniques that allow localized intra- and inter-subject comparisons of cartilage relaxation times, as well as cartilage flattening for texture analysis parallel and perpendicular to the natural cartilage layers, are presented. The localized comparisons are based on the registration of bone structures and the assignment of relaxation time feature vectors to each point in the bone-cartilage interface. Cartilage flattening was accomplished with Bezier splines and warping, and texture analysis was performed with second-order texture measures using gray-level co-occurrence matrices (GLCM). In a cohort of five normal subjects the performance and reproducibility of the techniques were evaluated using T1rho maps of femoral knee cartilage. The feasibility of creating a mean cartilage relaxation time map is also presented. Successful localized intra- and inter-subject T1rho comparisons were obtained with reproducibility similar to that reported in the literature for regional T2. Improvement of the reproducibility of GLCM features was obtained by flattening the T1rho maps. The results indicate that the presented techniques have potential in longitudinal and population studies of knee OA at different stages of the disease. PMID:18506807
Trends in Surface Radiation Budgets at Climatic Time Scales
NASA Astrophysics Data System (ADS)
Pinker, Rachel T.; Zhang, Banglin; Ma, Yingtao
2015-04-01
For assessment of variability and trends in the Earth Radiation Balance, information is needed at climatic time scales. Satellite observations have been instrumental for advancing the understanding of the radiative balance at global scale, however, due to the frequent changes in the observing systems, the length of available satellite records is limited. In this paper we report on an effort to synthesize satellite observations from independent sources to estimates shortwave, longwave and spectral surface radiative fluxes at climatic time scales and use them to learn about their variability and trends. The radiative fluxes were derived in the framework of the MEaSURES and NEWS programs; they are evaluated against ground observations and compared to independent satellite and model estimates. Attention is given to updates on the radiative balance as compared to what is known from shorter time records and from models.
Time Scales for Energy Release in Hall Magnetic Reconnection
NASA Astrophysics Data System (ADS)
Huba, J. D.; Rudakov, L. I.
2004-05-01
We present a study of the time scales for energy release in 2D Hall magnetic reconnection. We use the NRL Hall MHD code VooDoo for this study. We consider a 2D reversed field current layer with a magnetic perturbation that initiates the reconnection process. We use boundary conditions that allow inflow and outflow (i.e., not periodic) and let the system reach a steady state. We find that the system goes through three stages: a relatively long current layer thinning process, a fast reconnection phase, and a final steady state phase. We define the time scale for energy release as the fast reconnection period: from onset to steady state. Preliminary results indicate that the time for energy release scales as the initial thickness of the current layer. We apply these results to the magnetotail and magnetopause. Research supported by NASA and ONR.
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.
Improving the Geologic Time Scale (Jean Baptiste Lamarck Medal Lecture)
NASA Astrophysics Data System (ADS)
Gradstein, Felix M.
2010-05-01
The Geologic Time Scale (GTS) provides the framework for the physical, chemical and biological processes on Earth. The time scale is the tool "par excellence" of the geological trade, and insight in its construction, strength, and limitations enhances its function and its utility. Earth scientists should understand how time scales are constructed and its myriad of physical and abstract data are calibrated, rather than merely using ages plucked from a convenient chart or card. Calibration to linear time of the succession of events recorded in the rocks on Earth has three components: (1) the standard stratigraphic divisions and their correlation in the global rock record, (2) the means of measuring linear time or elapsed durations from the rock record, and (3) the methods of effectively joining the two scales, the stratigraphic one and the linear one. Under the auspices of the International Commission on Stratigraphy (ICS), the international stratigraphic divisions and their correlative events are now largely standardized, especially using the GSSP (Global Stratigraphic Section and Point) concept. The means of measuring linear time or elapsed durations from the rock record are objectives in the EARTH TIME and GTS NEXT projects, that also are educating a new generation of GTS dedicated scientists. The U/Pb, Ar/Ar and orbital tuning methods are intercalibrated, and external error analysis improved. Existing Ar/Ar ages become almost 0.5% older, and U/Pb ages stratigraphically more realistic. The new Os/Re method has potential for directly dating more GSSP's and its correlative events. Such may reduce scaling uncertainty between the sedimentary levels of an age date and that of a stage boundary. Since 1981, six successive Phanerozoic GTS have been published, each new one achieving higher resolution and more users. The next GTS is scheduled for 2011/2012, with over 50 specialists taking part. New chapters include an expanded planetary time scale, sequence stratigraphy, Osmium, Carbon and Oxygen stratigraphy, the Cryogenian period, history of the plants, hominid prehistory, and last but not least the Anthropocene. The Cambrian Period is radically improved with 10 standard stages and detailed trilobite biochronology. Ordovician now has a stable international stages and graptolites scale. The integration of a refined 100 and 400 ka sedimentary cycles scale and a truly high-resolution U/Pb ages scale for the Mississippian is a major step towards the global Carboniferous GTS. The Devonian GTS leaves to be desired with lack of firm definitions for its upper boundary, and the long Emsian stage; it also lacks age dates. Its stages scaling is disputed. The Rhaetian and Norian stages in the Triassic and the Berriasian stage in the Cretaceous urgently require lower boundary definitions, and also boundary age dates. The single ~400 ka eccentricity component is very stable and can extend orbital tuning from the Cenozoic well into the Mesozoic portion of the GTS. Jurassic and Cretaceous now have long orbitally tuned segments. A completely astronomical-tuned Geological Time Scale (AGTS) for the Cenozoic is within reach showing unprecedented accuracy, precision and resolution. Burdigalian in the Miocene, and Lutetian, Bartonian and Priabonian stages in the Eocene still require formal definition. The K/T boundary will become about 0.5 ± 0.1 Ma older. After 25 years of research and authorship in the GTS it behoves me to especially thank my colleagues James Ogg, Frits Agterberg, John McArthur and Roger Cooper for longstanding collaboration. As a final note I urge construction of more regional time scales(like developed ‘down under') calibrated to the standard global GTS, to scale regional rock units.
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 ~10(2). Calculations with specified Hurst exponent values of 0.2,0.3,...,0.9 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 (?0.03) and sharp confidential interval (standard deviation ?0.05). 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
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)
Hosoe, Yohei; Hagiwara, Tomomichi
This paper discusses the application of noncausal linear periodically time-varying (LPTV) scaling to the design of discrete-time robust stabilizing controllers. Such a new type of scaling was introduced recently through the lifting technique, and has been shown to be effective for robust stability analysis in terms of reducing conservativeness. This paper thus discusses how and why one could exploit the desirable properties of noncausal LPTV scaling in the context of robust stabilizing controller design, and provides explicit steps for such design, including the suitable selection of the structure of noncausal LPTV scaling and LMI optimization of scaling as well as the controller. Numerical examples are also studied demonstrating that the noncausal LPTV scaling approach leads to less conservative design than the conventional scaling or -synthesis approach.
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.
NASA Astrophysics Data System (ADS)
Souza Filho, N. E.; Nogueira, A. C.; Rohling, J. H.; Baesso, M. L.; Medina, A. N.; Siqueira, A. P. L.; Sampaio, J. A.; Vargas, H.; Bento, A. C.
2009-11-01
This paper discusses the use of photoacoustic models to obtain the nonradiative relaxation time (?) and characteristic diffusion time (??) for a sample showing visible absorption bands from fluorescent ion-doped low-silica calcium aluminosilicate glass. Two models allowing phase shift analyses, the thermal-expansion and thermal-diffusion models, are briefly reviewed. These models have limitations when the photoacoustic signal depends on both factors, in a coupling mechanism. An alternative model is proposed to take both thermal expansion and thermal diffusion into account with a single temperature solution for the heat-coupled differential equation. This model is simulated for absorbing samples near the thermally thick region. The model is applied to Eu-V codoped glass showing intermediate signal dependence from ?-1.0 to ?-3/2. The nonradiative time and characteristic diffusion time are derived with 33
Memory on multiple time-scales in an Abelian sandpile
NASA Astrophysics Data System (ADS)
Sokolov, Andrey; Melatos, Andrew; Kieu, Tien; Webster, Rachel
2015-06-01
We report results of a numerical analysis of the memory effects in two-dimensional Abelian sandpiles. It is found that a sandpile forgets its instantaneous configuration in two distinct stages: a fast stage and a slow stage, whose durations roughly scale as N and N2 respectively, where N is the linear size of the sandpile. We confirm the presence of the longer time-scale by an independent diagnostic based on analysing emission probabilities of a hidden Markov model applied to a time-averaged sequence of avalanche sizes. The application of hidden Markov modelling to the output of sandpiles is novel. It discriminates effectively between a sandpile time series and a shuffled control time series with the same time-averaged event statistics and hence deserves further development as a pattern-recognition tool for Abelian sandpiles.
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.
Femtosecond excited state relaxation of dye molecules in solution
NASA Astrophysics Data System (ADS)
Weiner, A. M.; Ippen, E. P.
1985-03-01
The bleaching dynamics of organic dye molecules in solution have been investigated using 70 fs pulses from a colliding pulse mode-locked ring dye laser. In addition to ground state relaxation on a nanosecond time scale, a fast partial recovery is observed. For the dyes Nile blue, oxazine 720, cresyl violet and rhodamine 640, this recovery is exponential, with relaxation times in the range 190-480 fs.
Dynamics symmetries of Hamiltonian system on time scales
Peng, Keke Luo, Yiping
2014-04-15
In this paper, the dynamics symmetries of Hamiltonian system on time scales are studied. We study the symmetries and quantities based on the calculation of variation and Lie transformation group. Particular focus lies in: the Noether symmetry leads to the Noether conserved quantity and the Lie symmetry leads to the Noether conserved quantity if the infinitesimal transformations satisfy the structure equation. As the new application of result, at end of the article, we give a simple example of Noether symmetry and Lie symmetry on time scales.
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.
The development and relaxation of growth strains in thermally grown Al{sub 2}O{sub 3} scales.
Hou, P. Y.; Paulikas, A. P.; Veal, B. W.; LBNL
2009-01-01
The strains in alumina thin films growing on high-temperature alloys at 1,000-1,100 C and during cooling have been successfully measured in-situ using a novel x-ray technique, exploiting synchrotron radiation at the Advanced Photon Source at Argonne National Laboratory. This paper summarizes results obtained from model alloys, with or without the presence of a reactive element, such as Zr, Hf, and Y, to show the importance of the dynamic nature of the stress evolution process and the effects of alloy composition on the generation and relaxation of these stresses.
Time-scale modification of complex acoustic signals in noise
NASA Astrophysics Data System (ADS)
Quatieri, Thomas F.; Dunn, Robert B.; McAulay, Robert J.; Hanna, Thomas E.
1994-02-01
A new approach is introduced for time-scale modification of short-duration complex acoustic signals to improve their audibility. The method preserves an approximate time-scaled temporal envelope of a signal, thus capitalizing on the perceptual importance of the signal's temporal structure, while also maintaining the character of a noise background. The basis for the approach is a subband signal representation, derived from a filter bank analysis/synthesis, the channel phases of which are controlled to shape the temporal envelope of the time-scaled signal. Channel amplitudes and filter bank inputs are selected to shape the spectrum and correlation of the time-scaled background. The phase, amplitude, and input control are derived from locations of events that occur within filter bank outputs. A frame-based generalization of the method imposes phase consistency and background noise continuity across consecutive synthesis frames. The approach and its derivatives are applied to synthetic and actual complex acoustic signals consisting of closely spaced sequential time components.
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).
Deoni, Sean C.L.; Dean, Douglas C.; O'Muircheartaigh, Jonathan; Dirks, Holly; Jerskey, Beth A.
2012-01-01
The elaboration of the myelinated white matter is essential for normal neurodevelopment, establishing and mediating rapid communication pathways throughout the brain. These pathways facilitate the synchronized communication required for higher order behavioral and cognitive functioning. Altered neural messaging (or ‘disconnectivity’) arising from abnormal white matter and myelin development may underlie a number of neurodevelopmental psychiatric disorders. Despite the vital role myelin plays, few imaging studies have specifically examined its maturation throughout early infancy and childhood. Thus, direct investigations of the relationship(s) between evolving behavioral and cognitive functions and the myelination of the supporting neural systems have been sparse. Further, without knowledge of the ‘normative’ developmental time-course, identification of early abnormalities associated with developmental disorders remains challenging. In this work, we examined the use of longitudinal (T1) and transverse (T2) relaxation time mapping, and myelin water fraction (MWF) imaging to investigate white matter and myelin development in 153 healthy male and female children, 3 months through 60 months in age. Optimized age-specific acquisition protocols were developed using the DESPOT and mcDESPOT imaging techniques; and mean T1, T2 and MWF trajectories were determined for frontal, temporal, occipital, parietal and cerebellar white matter, and genu, body and splenium of the corpus callosum. MWF results provided a spatio-temporal pattern in-line with prior histological studies of myelination. Comparison of T1, T2 and MWF measurements demonstrates dissimilar sensitivity to tissue changes associated with neurodevelopment, with each providing differential but complementary information. PMID:22884937
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.
Multiple-Time-Scale Concepts in Turbulent Transport Modeling
NASA Technical Reports Server (NTRS)
Hanjalic, K.; Launder, B. E.; Schiestel, R.
1980-01-01
Progress in developing a turbulence closure employing two or more independently calculated time scales with which to characterize the rates of progress of different turbulent interactions is reported. The energy containing part of the spectrum is divided into two regions which respond at different rates and in different ways to changes in the environment. The scheme may be regarded as providing an intermediate level of approximation between the relatively simple, but fallible, single-point closures and the vastly more elaborate two-point closures which have so far been applied only to simulating homogeneous flows. The proposed approach requires only slightly more computational effort than single-scale schemes. 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.
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 Baados-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.
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
Separation of time scales in the HCA model for sand
NASA Astrophysics Data System (ADS)
Niemunis, Andrzej; Wichtmann, Torsten
2014-10-01
Separation of time scales is used in a high cycle accumulation (HCA) model for sand. An important difficulty of the model is the limited applicability of the Miner's rule to multiaxial cyclic loadings applied simultaneously or in a combination with monotonic loading. Another problem is the lack of simplified objective HCA formulas for geotechnical settlement problems. Possible solutions of these problems are discussed.
NASA Astrophysics Data System (ADS)
Hamasaki, Tatsuichi; Zenmyo, Kazuko; Kubo, Hidenori
2013-08-01
The mixed transition metal dichloride dihydrates A1- x B x Cl22H2O (A, B=Co, Mn, Ni) have been prepared in order to understand the specificity of the Mn spins in the mixtures. The temperature dependences of the spin lattice relaxation times T 1 of proton nuclear magnetic resonance (NMR) on these mixed crystals have been measured. In Ni1- x B x Cl22H2O (B=Co, Mn), Mn substitution increased the relaxation rates 1/ T 1 more than Co substitution, even when the amounts of substitution were almost the same. In Co1- x B x Cl22H2O (B=Mn, Ni), Mn has a significant impact on the relaxation rates in comparison with Ni. In Mn1- x B x Cl22H2O (B=Ni, Co), the relaxation rates are much increased by a slight substitution of Co and exhibit a minimum in the temperature range of observation. This appearance of a minimum in the relaxation rates at low temperatures is believed to reflect an instability due to the occurrence of a reentrant spin-glass transition. A similar trend is seen at low temperatures in the case of Ni substitution, too. A Co1- x Fe x Cl22H2O ( x = 0.1) sample has been prepared, too. In this sample, a minimum of the relaxation rate is seen in the temperature range of observation. This may reflect an instability due to the occurrence of an oblique antiferromagnetic transition.
NASA Astrophysics Data System (ADS)
Odelius, Michael; Ribbing, Carl; Kowalewski, Jozef
1996-03-01
A method of calculating the time correlation functions for electron spin is proposed, based on solving the time-dependent Schrdinger equation for a spin Hamiltonian that contains a term varying randomly in discrete time steps. It is applied to the study of electron spin relaxation in aqueous solution of nickel(II) ions with S=1. The random term in the spin Hamiltonian in this case is the zero-field splitting (ZFS) interaction. The method is evaluated by an application to a model system (the pseudorotation model) for which an analytical solution to the electron spin relaxation problem is known. The same method is then employed to study the electron and nuclear spin dynamics in a system where the time variation of the zero-field splitting is obtained by a combination of ab initio quantum chemistry and molecular dynamics simulations.
Spectral decomposition of time-scales in hyporheic exchange
NASA Astrophysics Data System (ADS)
Wrman, 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 (?) data as ? ? ?e/(2?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.
Stellar differential rotation and coronal time-scales
NASA Astrophysics Data System (ADS)
Gibb, G. P. S.; Jardine, M. M.; Mackay, D. H.
2014-10-01
We investigate the time-scales of evolution of stellar coronae in response to surface differential rotation and diffusion. To quantify this, we study both the formation time and lifetime of a magnetic flux rope in a decaying bipolar active region. We apply a magnetic flux transport model to prescribe the evolution of the stellar photospheric field, and use this to drive the evolution of the coronal magnetic field via a magnetofrictional technique. Increasing the differential rotation (i.e. decreasing the equator-pole lap time) decreases the flux rope formation time. We find that the formation time is dependent upon the lap time and the surface diffusion time-scale through the relation ?_Form ? ?{?_Lap?_Diff}. In contrast, the lifetimes of flux ropes are proportional to the lap time (?Life??Lap). With this, flux ropes on stars with a differential rotation of more than eight times the solar value have a lifetime of less than 2 d. As a consequence, we propose that features such as solar-like quiescent prominences may not be easily observable on such stars, as the lifetimes of the flux ropes which host the cool plasma are very short. We conclude that such high differential rotation stars may have very dynamical coronae.
Time Scales of Conformational Gating in a Lipid-Binding Protein.
Kaieda, Shuji; Halle, Bertil
2015-06-25
Lipid-binding proteins sequester amphiphilic molecules in a large internal cavity occupied by ?30 water molecules, some of which are displaced by the ligand. The role of these internal water molecules in lipid binding and release is not understood. We use magnetic relaxation dispersion (MRD) to directly monitor internal-water dynamics in apo and palmitate-bound rat intestinal fatty acid-binding protein (rIFABP). Specifically, we record the water (2)H and (17)O MRD profiles of the apo and holo forms of rIFABP in solution or immobilized by covalent cross-links. A global analysis of this extensive data set identifies three internal-water classes with mean survival times of ?1 ns, ?100 ns, and ?6 ?s. We associate the two longer time scales with conformational fluctuations of the gap between ?-strands D and E (?6 ?s) and of the portal at the helix-capped end of the ?-barrel (?100 ns). These fluctuations limit the exchange rates of a few highly ordered structural water molecules but not the dissociation rate of the fatty acid. The remaining 90% (apo) or 70% (holo) of cavity waters exchange among internal hydration sites on a time scale of ?1 ns but exhibit substantial orientational order, particularly in the holo form. PMID:26012957
Multi-time-scale heat transfer modeling of turbid tissues exposed to short-pulsed irradiations.
Kim, Kyunghan; Guo, Zhixiong
2007-05-01
A combined hyperbolic radiation and conduction heat transfer model is developed to simulate multi-time-scale heat transfer in turbid tissues exposed to short-pulsed irradiations. An initial temperature response of a tissue to an ultrashort pulse irradiation is analyzed by the volume-average method in combination with the transient discrete ordinates method for modeling the ultrafast radiation heat transfer. This response is found to reach pseudo steady state within 1 ns for the considered tissues. The single pulse result is then utilized to obtain the temperature response to pulse train irradiation at the microsecond/millisecond time scales. After that, the temperature field is predicted by the hyperbolic heat conduction model which is solved by the MacCormack's scheme with error terms correction. Finally, the hyperbolic conduction is compared with the traditional parabolic heat diffusion model. It is found that the maximum local temperatures are larger in the hyperbolic prediction than the parabolic prediction. In the modeled dermis tissue, a 7% non-dimensional temperature increase is found. After about 10 thermal relaxation times, thermal waves fade away and the predictions between the hyperbolic and parabolic models are consistent. PMID:17335934
Characterization of a binary karst aquifer using process time scales
NASA Astrophysics Data System (ADS)
Birk, Steffen; Wagner, Thomas
2013-04-01
Within "a theoretical framework for the interpretation of karst spring signals" (Covington, EGU2012-853-1) process length scales that characterize the travel distances required for damping pulses of physicochemical parameters of spring waters such as electrical conductivity and temperature were derived (Covington et al., J. Geophys. Res., 2012). These length scales can be converted to corresponding process time scales characterizing the travel times needed for damping the pulses. This is particularly convenient if the travel distance is unknown. In this case the time lag between the increase of spring discharge and subsequent physicochemical responses at the spring may provide an estimate of the travel time. In binary karst aquifers with localized recharge from a sinking stream, the recharge pulse can be directly observed and thus travel times are readily obtained from the time delay of the physicochemical spring responses. If the spring response is strongly damped travel times can be inferred from artificial tracer testing. In this work, time scales for carbonate dissolution and heat transport were used for characterizing the binary Lurbach-Tanneben karst aquifer (Austria). This aquifer receives allogenic recharge from the sinking stream Lurbach and is drained by two springs, namely the Hammerbach and the Schmelzbach. The two springs show different thermal responses to two recharge events in December 2008: Whereas the temperature of the Schmelzbach responds within one day after the flood pulse in the Lurbach, the temperature signal is strongly damped at the Hammerbach. The evaluation based on the thermal time scale thus suggests that the Schmelzbach spring is fed by conduits with hydraulic diameters at least in the order of decimetres. In contrast, the damping of the thermal responses at the Hammerbach may be due to lower hydraulic diameters and/or longer residence times. Interestingly, the Hammerbach did show thermal responses in the time before a flood event in August 2005. This suggests that this flood event may have caused a change of the properties of the Hammerbach aquifer such that temperature pulses are more strongly damped than before. As opposed to the thermal responses the electrical conductivity appears to be less affected by this change, which suggests that the hydraulic diameters are still sufficiently large to permit the propagation of chemical signals.
Konrat, R; Tollinger, M
1999-03-01
A novel NMR experiment comprising adiabatic fast passage techniques for the measurement of heteronuclear self-relaxation rates in fully 15N-enriched proteins is described. Heteronuclear self-relaxation is monitored by performing adiabatic fast passage (AFP) experiments at variable adiabaticity (e.g., variation of RF spin-lock field intensity). The experiment encompasses gradient- selection and sensitivity-enhancement. It is shown that transverse relaxation rates derived with this method are in good agreement with the ones measured by the classical Carr-Purcell-Meiboom-Gill (CPMG) sequences. An application of this method to the study of the carboxyl-terminal LIM domain of quail cysteine and glycine-rich protein qCRP2(LIM2) is presented. PMID:20700818
Dyakin, Victor V.; Chen, Yuanxin; Branch, Craig A.; Veeranna; Yuan, Aidong; Rao, Mala; Kumar, Asok; Peterhoff, Corrinne M.; Nixon, Ralph. A
2010-01-01
White matter disorders can involve injury to myelin or axons but the respective contribution of each to clinical course is difficult to evaluate non-invasively. Here, to develop a paradigm for further investigations of axonal pathology by MRI, we compared two genetic mouse models exhibiting relatively selective axonal or myelin deficits using quantitative MRI relaxography of the transverse relaxation times (T2) in vivo and ultrastructural morphometry. In HM-DKO mice, which lack genes encoding the heavy (NF-H) and medium (NF-M) subunits of neurofilaments, neurofilament content of large myelinated axons of the central nervous system (CNS) is markedly reduced in the absence of changes in myelin thickness and volume. In shiverer mutant mice, which lack functional myelin basic protein, CNS myelin sheath formation is markedly reduced but neurofilament content is normal. We observed increases in T2 in nearly all white matter in Shiverer mice compared to their wild type, while more subtle increases in T2 were observed in HM-DKO in the corpus callosum. White matter T2 was generally greater in Shiverer mice than HM-DKO mice. Ultrastructural morphometry of the corpus callosum, which exhibited the greatest T2 differences, confirmed that total cross sectional area occupied by axons was similar in the two mouse models and that the major ultrastructural differences, determined by morphometry, were an absence of myelin and larger unmyelinated axons in shiverer mice and absence of neurofilaments in HM-DKO mice. Our findings indicate that T2 is strongly influenced by myelination state and axonal volume, while neurofilament structure within the intra-axonal compartment has a lesser effect upon single compartment T2 estimates. PMID:20226865
BeiDou Navigation Satellite System and its time scales
NASA Astrophysics Data System (ADS)
Han, Chunhao; Yang, Yuanxi; Cai, Zhiwu
2011-08-01
The development and current status of BeiDou Navigation Satellite System are briefly introduced. The definition and realization of the system time scales are described in detail. The BeiDou system time (BDT) is an internal and continuous time scale without leap seconds. It is maintained by the time and frequency system of the master station. The frequency accuracy of BDT is superior to 2 × 10-14 and its stability is better than 6 × 10-15/30 days. The satellite synchronization is realized by a two-way time transfer between the uplink stations and the satellite. The measurement uncertainty of satellite clock offsets is less than 2 ns. The BeiDou System has three modes of time services: radio determination satellite service (RDSS) one-way, RDSS two-way and radio navigation satellite service (RNSS) one-way. The uncertainty of the one-way time service is designed to be less than 50 ns, and that of the two-way time service is less than 10 ns. Finally, some coordinate tactics of UTC from the viewpoint of global navigation satellite systems (GNSS) are discussed. It would be helpful to stop the leap second, from our viewpoint, but to keep the UTC name, the continuity and the coordinate function unchanged.
Time scale controversy: Accurate orbital calibration of the early Paleogene
NASA Astrophysics Data System (ADS)
Roehl, U.; Westerhold, T.; Laskar, J.
2012-12-01
Timing is crucial to understanding the causes and consequences of events in Earth history. The calibration of geological time relies heavily on the accuracy of radioisotopic and astronomical dating. Uncertainties in the computations of Earth's orbital parameters and in radioisotopic dating have hampered the construction of a reliable astronomically calibrated time scale beyond 40 Ma. Attempts to construct a robust astronomically tuned time scale for the early Paleogene by integrating radioisotopic and astronomical dating are only partially consistent. Here, using the new La2010 and La2011 orbital solutions, we present the first accurate astronomically calibrated time scale for the early Paleogene (47-65 Ma) uniquely based on astronomical tuning and thus independent of the radioisotopic determination of the Fish Canyon standard. Comparison with geological data confirms the stability of the new La2011 solution back to 54 Ma. Subsequent anchoring of floating chronologies to the La2011 solution using the very long eccentricity nodes provides an absolute age of 55.530 0.05 Ma for the onset of the Paleocene/Eocene Thermal Maximum (PETM), 54.850 0.05 Ma for the early Eocene ash -17, and 65.250 0.06 Ma for the K/Pg boundary. The new astrochronology presented here indicates that the intercalibration and synchronization of U/Pb and 40Ar/39Ar radioisotopic geochronology is much more challenging than previously thought.
Characterizing Complex Time Series from the Scaling of Prediction Error.
NASA Astrophysics Data System (ADS)
Hinrichs, Brant Eric
This thesis concerns characterizing complex time series from the scaling of prediction error. We use the global modeling technique of radial basis function approximation to build models from a state-space reconstruction of a time series that otherwise appears complicated or random (i.e. aperiodic, irregular). Prediction error as a function of prediction horizon is obtained from the model using the direct method. The relationship between the underlying dynamics of the time series and the logarithmic scaling of prediction error as a function of prediction horizon is investigated. We use this relationship to characterize the dynamics of both a model chaotic system and physical data from the optic tectum of an attentive pigeon exhibiting the important phenomena of nonstationary neuronal oscillations in response to visual stimuli.
Time-frequency and time-scale analyses for structural health monitoring.
Staszewski, Wies?aw J; Robertson, Amy N
2007-02-15
Signal processing is one of the most important elements of structural health monitoring. This paper documents applications of time-variant analysis for damage detection. Two main approaches, the time-frequency and the time-scale analyses are discussed. The discussion is illustrated by application examples relevant to damage detection. PMID:17255047
The Available Time Scale: Measuring Foster Parents' Available Time to Foster
ERIC Educational Resources Information Center
Cherry, Donna J.; Orme, John G.; Rhodes, Kathryn W.
2009-01-01
This article presents a new measure of available time specific to fostering, the Available Time Scale (ATS). It was tested with a national sample of 304 foster mothers and is designed to measure the amount of time foster parents are able to devote to fostering activities. The ATS has excellent reliability, and good support exists for its validity.
Constraints on the Heating Time Scale in Active Regions
NASA Astrophysics Data System (ADS)
Brooks, D. H.; Warren, H. P.
2012-08-01
Understanding the heating time scale is important for constraining models of active region emission. Hinode observations of moss at the bases of high temperature active region core loops are allowing us to study this problem in unprecedented detail. Here we discuss some of our recent results studying the variability of moss properties such as intensity, magnetic flux, Doppler and non-thermal velocity. We find that most of these quantities are relatively constant. One interpretation is that the heating is therefore effectively steady , i.e., heating events occur with a rapid repetition rate. Alternatively, the heating could be low frequency, but only if it occurs on sub-resolution spatial scales.
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.
RELAXATION PROCESSES IN SOLAR WIND TURBULENCE
Servidio, S.; Carbone, V.; Gurgiolo, C.; Goldstein, M. L.
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.
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)
Miyazaki, Yasunori; Inokuchi, Yoshiya; Ebata, Takayuki; Petković, Milena
2013-06-01
A comparative study of vibrational energy relaxation (VER) between the monohydrated complexes of phenol-d0 and phenol-d1 is investigated in a supersonic molecular beam. The direct time-resolved measurement of energy redistribution from the phenolic OH/OD stretching mode of the phenol-d0-H2O/phenol-d1-D2O is performed by picosecond IR-UV pump-probe spectroscopy. Two complexes follow the same relaxation process that begins with the intramolecular vibrational energy redistribution (IVR) and the intermolecular vibrational energy redistribution (IVR), which is followed by the vibrational predissociation (VP). The difference in the relaxation lifetimes between them is discussed by anharmonic force field and RRKM calculations. Anharmonic analysis implies that intra- (IVR) and intermolecular (IVR) relaxations occur in parallel in the complexes. The RRKM-predicted dissociation (VP) lifetimes show qualitative agreement with the observed results, suggesting that VP takes place after the statistical energy distribution in the complexes.
Sublinear scaling for time-dependent stochastic density functional theory
Gao, Yi; Neuhauser, Daniel; Baer, Roi; Rabani, Eran
2015-01-21
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.
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
Statistical Analysis of Sensor Network Time Series at Multiple Time Scales
NASA Astrophysics Data System (ADS)
Granat, R. A.; Donnellan, A.
2013-12-01
Modern sensor networks often collect data at multiple time scales in order to observe physical phenomena that occur at different scales. Whether collected by heterogeneous or homogenous sensor networks, measurements at different time scales are usually subject to different dynamics, noise characteristics, and error sources. We explore the impact of these effects on the results of statistical time series analysis methods applied to multi-scale time series data. As a case study, we analyze results from GPS time series position data collected in Japan and the Western United States, which produce raw observations at 1Hz and orbit corrected observations at time resolutions of 5 minutes, 30 minutes, and 24 hours. We utilize the GPS analysis package (GAP) software to perform three types of statistical analysis on these observations: hidden Markov modeling, probabilistic principle components analysis, and covariance distance analysis. We compare the results of these methods at the different time scales and discuss the impact on science understanding of earthquake fault systems generally and recent large seismic events specifically, including the Tohoku-Oki earthquake in Japan and El Mayor-Cucupah earthquake in Mexico.
Assestment of correlations and crossover scale in electroseismic time series
NASA Astrophysics Data System (ADS)
Guzman-Vargas, L.; Ramrez-Rojas, A.; Angulo-Brown, F.
2009-04-01
Evaluating complex fluctuations in electroseismic time series is an important task not only for earthquake prediction but also for understanding complex processes related to earthquake preparation. Previous studies have reported alterations, as the emergence of correlated dynamics in geoelectric potentials prior to an important earthquake (EQ). In this work, we apply the detrended fluctuation analysis and introduce a statistical procedure to characterize the presence of crossovers in scaling exponents, to analyze the fluctuations of geoelectric time series monitored in two sites located in Mexico. We find a complex behavior characterized by the presence of a crossover in the correlation exponents in the vicinity of a M=7.4 EQ occurred on Sept. 14, 1995. Finally, we apply the t-student test to evaluate the level of significance between short and large scaling exponents.
HMC algorithm with multiple time scale integration and mass preconditioning
NASA Astrophysics Data System (ADS)
Urbach, C.; Jansen, K.; Shindler, A.; Wenger, U.
2006-01-01
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 ?=5.6 and at pion masses ranging from 380 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.
Cieszanowski, Andrzej; Podgórska, Joanna; Rosiak, Grzegorz; Maj, Edyta; Grudziński, Ireneusz P.; Kaczyński, Bartosz; Szeszkowski, Wojciech; Milczarek, Krzysztof; Rowiński, Olgierd
2016-01-01
Summary Background To investigate the effect of gadoxetic acid disodium (Gd-EOB-DTPA) on T2 relaxation times and apparent diffusion coefficient (ADC) values of the liver and focal liver lesions on a 1.5-T system. Material/Methods Magnetic resonance (MR) studies of 50 patients with 35 liver lesions were retrospectively analyzed. All examinations were performed at 1.5T and included T2-weighted turbo spin-echo (TSE) and diffusion-weighted (DW) images acquired before and after intravenous administration of Gd-EOB-DTPA. To assess the effect of this hepatobiliary contrast agent on T2-weighted TSE images and DW images T2 relaxation times and ADC values of the liver and FLLs were calculated and compared pre- and post-injection. Results The mean T2 relaxation times of the liver and focal hepatic lesions were lower on enhanced than on unenhanced T2-weighted TSE images (decrease of 2.7% and 3.6% respectively), although these differences were not statistically significant. The mean ADC values of the liver showed statistically significant decrease (of 4.6%) on contrast-enhanced DW images, compared to unenhanced images (P>0.05). The mean ADC value of liver lesions was lower on enhanced than on unenhanced DW images, but this difference (of 2.9%) did not reach statistical significance. Conclusions The mean T2 relaxation times of the liver and focal liver lesions as well as the mean ADC values of liver lesions were not significantly different before and after administration of Gd-EOB-DTPA. Therefore, acquisition of T2-weighted and DW images between the dynamic contrast-enhanced examination and hepatobiliary phase is feasible and time-saving.
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.
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.
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.
Time scale interactions and the coevolution of humans and water
NASA Astrophysics Data System (ADS)
Sivapalan, Murugesu; Blschl, Gnter
2015-09-01
We present a coevolutionary view of hydrologic systems, revolving around feedbacks between environmental and social processes operating across different time scales. This brings to the fore an emphasis on emergent phenomena in changing water systems, such as the levee effect, adaptation to change, system lock-in, and system collapse due to resource depletion. Changing human values play a key role in the emergence of these phenomena and should therefore be considered as internal to the system. Guidance is provided for the framing and modeling of these phenomena to test alternative hypotheses about how they arose. A plurality of coevolutionary models, from stylized to comprehensive system-of-system models, may assist strategic water management for long time scales through facilitating stakeholder participation, exploring the possibility space of alternative futures, and helping to synthesize the observed dynamics in a wide range of case studies. Future research opportunities lie in exploring emergent phenomena arising from time scale interactions through historical, comparative, and process studies of human-water feedbacks.
NASA Astrophysics Data System (ADS)
Amatya, J. M.; Floro, J. A.
2015-12-01
Chemical ordering in semiconductor alloys could modify thermal and electronic transport, with potential benefits to thermoelectric properties. Here, metastable ordering that occurs during heteroepitaxial growth of Si1-xGex thin film alloys on Si(001) and Ge(001) substrates is investigated. A parametric study was performed to study how strain, surface roughness, and growth parameters affect the order parameter during the alloy growth. The order parameter for the alloy films was carefully quantified using x-ray diffraction, taking into account an often-overlooked issue associated with the presence of multiple spatial variants associated with ordering along equivalent <111> directions. Optimal ordering was observed in the films having the smoothest surfaces. Extended strain relaxation is suggested to reduce the apparent order through creation of anti-phase boundaries. Ordering surprisingly persists even when the film surface extensively roughens to form {105} facets. Growth on deliberately miscut Si(001) surfaces does not affect the volume-averaged order parameter but does impact the relative volume fractions of the equivalent ordered variants in a manner consistent with geometrically necessary changes in step populations. These results provide somewhat self-contradictory implications for the role of step edges in controlling the ordering process, indicating that our understanding is still incomplete.
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 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
Scaling Laws, Shell Effects, and Transient Times in Fission Probabilities
Moretto, L.G.; Jing, K.X.; Gatti, R.; Wozniak, G.J.; Schmitt, R.P.
1995-12-04
The fission excitation functions for 14 compound nuclei covering a mass range from {ital A}=186 to 213 are shown to scale exactly according to the transition state prediction once shell effects are accounted for. The extracted shell effects correlate closely with those obtained from the ground state masses. No effects of transient times longer than 3{times}10{sup {minus}20} sec are visible. Pairing effects are noticeable at excitation energies at few MeV above the barrier. {copyright} {ital 1995} {ital The} {ital American} {ital Physical} {ital Society}.
Scale dependence of the directional relationships between coupled time series
NASA Astrophysics Data System (ADS)
Shirazi, Amir Hossein; Aghamohammadi, Cina; Anvari, Mehrnaz; Bahraminasab, Alireza; Rahimi Tabar, M. Reza; Peinke, Joachim; Sahimi, Muhammad; Marsili, Matteo
2013-02-01
Using the cross-correlation of the wavelet transformation, we propose a general method of studying the scale dependence of the direction of coupling for coupled time series. The method is first demonstrated by applying it to coupled van der Pol forced oscillators and coupled nonlinear stochastic equations. We then apply the method to the analysis of the log-return time series of the stock values of the IBM and General Electric (GE) companies. Our analysis indicates that, on average, IBM stocks react earlier to possible common sector price movements than those of GE.
Relaxation processes in poled electro-optic polymer films
NASA Astrophysics Data System (ADS)
Dureiko, Rick Dean
1998-06-01
Combining several experimental techniques for monitoring chromophore orientational relaxation in dye doped nonlinear optical polymer films within the theoretical framework of the Dissado-Hill and Adam-Gibbs relaxation models, we have developed a method for characterizing the useful lifetime of devices based on nonlinear optical polymers. In order to monitor the chromophore relaxation process over 13 orders of magnitude in time, it was necessary to perform both time and frequency domain relaxation experiments. In the time domain experiments both the linear and second order nonlinear optical susceptibilities of nonlinear optical polymer films were monitored. The linear susceptibility was probed by monitoring the depolarization current created from the reorientation of the dipolar chromophore molecules, while the second order susceptibility was probed by monitoring the decay of the second harmonic light generated from the relaxing chromophores. In the frequency domain, the linear and second order nonlinear optical susceptibilities of nonlinear optical polymer films were monitored, using dielectric relaxation and dielectric spectroscopy respectively. Dielectric spectroscopy, which is frequency domain electric field induced second harmonic generation, was developed to study the nonlinear optical response near the glass transition temperature at short time scales. These measurements, along with polymer structural relaxation measurements, which were performed using differential scanning calorimetry, were used to characterize the decay of poling-induced electro-optic properties of guest-host and side-chain methacrylate polymers having glass transition temperatures in the range of 90 < [Tg] < 125o C. The temperature dependence of the relaxation time constants, ?, from the polymeric systems were then compared and a scaling model for predicting useful lifetimes of poled electro-optic media is discussed within the framework of the Adam-Gibbs entropic model. We have also verified that chromophore relaxation is coupled primarily to the /alpha, or main chain relaxation of the host polymer. In addition, after scaling the temperature to the glass transition temperature, Tg, and the relaxation time constant, /tau, to the glass transition temperature time constant, ?g, the calculated values for ? for all three types of polymeric systems in this study, seem to have the same reduced temperature dependence which indicates chromophore orientational relaxation behavior may be universal.
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…
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.
Dardzinski, BJ; Schneider, E
2013-01-01
Introduction T2 (spin-spin) relaxation time is frequently used for compositional assessment of articular cartilage. However little is known about the influence of MR system components on these measurements. The reproducibility and range of cartilage T2 values were evaluated using different extremity radiofrequency (RF) coils with potential differences in flip angle uniformity and SNR. Method Ten knees underwent 3 Tesla MR exams using RF coils with different signal-to-noise (SNR): quadrature transmit/receive (QTR); quadrature transmit/eight-channel phased-array receive (QT8PAR). Each knee was scanned twice per coil (4 exams total). T2 values were calculated for the central medial and lateral femoral (cMF, cLF) and medial and lateral tibial (MT, LT) cartilage. Results The flip angle varied across a central 40mm diameter region-of-interest of each coil by <1.5%. However SNR was significantly higher using QT8PAR than QTR (p<0.001). T2 values for cMF (50.7msec/45.9msec) and MT (48.2msec/41.6msec) were significantly longer with QT8PAR than QTR (p<0.05). T2 reproducibility was improved using QT8PAR for cMF and cLF (4.8%/5.8% and 4.1%/6.5%; p<0.001), similar for LT (3.8%/3.6%; p=1.0), and worse for MT (3.7%/3.3%; p<0.001). T2 varied spatially, with cLF having the longest (52.0msec) and the LT having the shortest (40.6msec) values. All deep cartilage had significantly longer, and less variable, T2 values using QT8PAR (higher SNR; p<0.03). Conclusions SNR varied spatially depending upon coil, but refocusing flip angle did not. With higher SNR, significantly longer T2 values were measured for deep (all plates) and global (MT, cMF) cartilage. T2 values varied by depth and plate, in agreement with prior studies. PMID:23376528
Two-time-scale population evolution on a singular landscape
NASA Astrophysics Data System (ADS)
Xu, Song; Jiao, Shuyun; Jiang, Pengyao; Ao, Ping
2014-01-01
Under the effect of strong genetic drift, it is highly probable to observe gene fixation or gene loss in a population, shown by singular peaks on a potential landscape. The genetic drift-induced noise gives rise to two-time-scale diffusion dynamics on the bipeaked landscape. We find that the logarithmically divergent (singular) peaks do not necessarily imply infinite escape times or biological fixations by iterating the Wright-Fisher model and approximating the average escape time. Our analytical results under weak mutation and weak selection extend Kramers's escape time formula to models with B (Beta) function-like equilibrium distributions and overcome constraints in previous methods. The constructed landscape provides a coherent description for the bistable system, supports the quantitative analysis of bipeaked dynamics, and generates mathematical insights for understanding the boundary behaviors of the diffusion model.
5nsec Dead time multichannel scaling system for Mssbauer spectrometer
NASA Astrophysics Data System (ADS)
Verrastro, C.; Trombetta, G.; Pita, A.; Saragovi, C.; Duhalde, S.
1991-11-01
A PC programmable and fast multichannel scaling module has been designed to use a commercial Mssbauer spectrometer. This module is based on a 10 single chip 8 bits microcomputer (MC6805) and on a 35 fast ALU, which allows a high performance and low cost system. The module can operate in a stand-alone mode. Data analysis are performed in real time display, on XT/AT IBM PC or compatibles. The channels are ranged between 256 and 4096, the maximum number of counts is 232-1 per channel, the dwell time is 3 ?sec and the dead time between channels is 5 nsec. A friendly software display the real time spectrum and offers menues with different options at each state.
Gao, Ying; Erokwu, Bernadette O; DeSantis, David A; Croniger, Colleen M; Schur, Rebecca M; Lu, Lan; Mariappuram, Jose; Dell, Katherine M; Flask, Chris A
2016-01-01
Autosomal recessive polycystic kidney disease (ARPKD) is a potentially lethal multi-organ disease affecting both the kidneys and the liver. Unfortunately, there are currently no non-invasive methods to monitor liver disease progression in ARPKD patients, limiting the study of potential therapeutic interventions. Herein, we perform an initial investigation of T1 relaxation time as a potential imaging biomarker to quantitatively assess the two primary pathologic hallmarks of ARPKD liver disease: biliary dilatation and periportal fibrosis in the PCK rat model of ARPKD. T1 relaxation time results were obtained for five PCK rats at 3?months of age using a Look-Locker acquisition on a Bruker BioSpec 7.0?T MRI scanner. Six three-month-old Sprague-Dawley (SD) rats were also scanned as controls. All animals were euthanized after the three-month scans for histological and biochemical assessments of bile duct dilatation and hepatic fibrosis for comparison. PCK rats exhibited significantly increased liver T1 values (mean??standard deviation?=?935??39?ms) compared with age-matched SD control rats (847??26?ms, p?=?0.01). One PCK rat exhibited severe cholangitis (mean T1 ?=?1413?ms), which occurs periodically in ARPKD patients. The observed increase in the in vivo liver T1 relaxation time correlated significantly with three histological and biochemical indicators of biliary dilatation and fibrosis: bile duct area percent (R?=?0.85, p?=?0.002), periportal fibrosis area percent (R?=?0.82, p?=?0.004), and hydroxyproline content (R?=?0.76, p?=?0.01). These results suggest that hepatic T1 relaxation time may provide a sensitive and non-invasive imaging biomarker to monitor ARPKD liver disease. Copyright 2015 John Wiley & Sons, Ltd. PMID:26608869
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
Hamido, Aliou; Frapiccini, Ana Laura; Piraux, Bernard; Eiglsperger, Johannes; Madronero, Javier; Mota-Furtado, Francisca; O'Mahony, Patrick
2011-07-15
We present an ab initio approach to solving the time-dependent Schroedinger equation to treat electron- and photon-impact multiple ionization of atoms or molecules. It combines the already known time-scaled coordinate method with a high-order time propagator based on a predictor-corrector scheme. In order to exploit in an optimal way the main advantage of the time-scaled coordinate method, namely, that the scaled wave packet stays confined and evolves smoothly toward a stationary state, of which the squared modulus is directly proportional to the electron energy spectra in each ionization channel, we show that the scaled bound states should be subtracted from the total scaled wave packet. In addition, our detailed investigations suggest that multiresolution techniques like, for instance, wavelets are the most appropriate ones to represent the scaled wave packet spatially. The approach is illustrated in the case of the interaction of a one-dimensional model atom as well as atomic hydrogen with a strong oscillating field.
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.
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 β is between 0.1 and 0.3 up to millennial time scales, where a deviation is observed and a seemingly higher value of β 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.
Relaxation Kinetics in Nano-Structured Thin Polymer Films
NASA Astrophysics Data System (ADS)
Duerig, Urs; Gotsmann, Bernd; Knoll, Armin; King, William P.; Cross, Graham
2004-03-01
We have studied the temperature dependent relaxation characteristics of periodic surface corrugations fabricated by means of electron beam lithography in poly-methyl-metacrylate films of molecular weight Mn 300 kg/mol corresponding to a radius of gyration of Rg 40 nm. Experiments are conducted for film thicknesses ranging from 35 nm to 130 nm. Heating induces a surface-tension driven relaxation that results in a decay of the surface wave amplitude, observed through measurement of the scattering signal from an incident laser beam. Atomic force microscopy snap shot images of the polymer surface recorded at various stages of the relaxation process aid interpretation of the scattering signal evolution. We observe a rapid elastic relaxation response at the glass transition temperature which enhances the fundamental Fourier component of the grating structure. Viscous flow relaxation of the surface corrugation to a flat equilibrium state occurs on a much slower time scale whose temperature dependence obeys a time-temperature superposition principle. In addition we find that the relaxation kinetics depends on film thickness, being more than one order of magnitude slower for the thinnest films investigated. This relaxation slow down can be understood in terms of a hydrodynamic boundary interaction which is accentuated by a dramatic reduction of the effective hydrodynamic film thickness due to correlation effects as the physical film thickness becomes comparable to Rg. The results also show that in contrast to conventional fluids, relaxation flow of our polymer films involves substantial slip flow at the substrate surface.