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.
Time scales and relaxation dynamics in quantum-dot lasers
Erneux, Thomas; Viktorov, Evgeny A.; Mandel, Paul
2007-08-15
We analyze a three-variable rate equation model that takes into account carrier capture and Pauli blocking in quantum dot semiconductor lasers. The exponential decay of the relaxation oscillations is analyzed from the linearized equations in terms of three key parameters that control the time scales of the laser. Depending on their relative values, we determine two distinct two-variable reductions of the rate equations in the limit of large capture rates. The first case leads to the rate equations for quantum well lasers, exhibiting relaxation oscillations dynamics. The second case corresponds to dots nearly saturated by the carriers and is characterized by the absence of relaxation oscillations.
TASEP on a Ring in Sub-relaxation Time Scale
NASA Astrophysics Data System (ADS)
Baik, Jinho; Liu, Zhipeng
2016-12-01
Interacting particle systems in the KPZ universality class on a ring of size L with O( L) number of particles are expected to change from KPZ dynamics to equilibrium dynamics at the so-called relaxation time scale t=O(L^{3/2}). In particular the system size is expected to have little effect to the particle fluctuations in the sub-relaxation time scale 1≪ t≪ L^{3/2}. We prove that this is indeed the case for the totally asymmetric simple exclusion process (TASEP) with two types of initial conditions. For flat initial condition, we show that the particle fluctuations are given by the Airy_1 process as in the infinite TASEP with flat initial condition. On the other hand, the TASEP on a ring with step initial condition is equivalent to the periodic TASEP with a certain shock initial condition. We compute the fluctuations explicitly both away from and near the shocks for the infinite TASEP with same initial condition, and then show that the periodic TASEP has same fluctuations in the sub-relaxation time scale.
Generalized dynamic scaling for quantum critical relaxation in imaginary time.
Zhang, Shuyi; Yin, Shuai; Zhong, Fan
2014-10-01
We study the imaginary-time relaxation critical dynamics of a quantum system with a vanishing initial correlation length and an arbitrary initial order parameter M0. We find that in quantum critical dynamics, the behavior of M0 under scale transformations deviates from a simple power law, which was proposed for very small M0 previously. A universal characteristic function is then suggested to describe the rescaled initial magnetization, similar to classical critical dynamics. This characteristic function is shown to be able to describe the quantum critical dynamics in both short- and long-time stages of the evolution. The one-dimensional transverse-field Ising model is employed to numerically determine the specific form of the characteristic function. We demonstrate that it is applicable as long as the system is in the vicinity of the quantum critical point. The universality of the characteristic function is confirmed by numerical simulations of models belonging to the same universality class.
Active open boundary forcing using dual relaxation time-scales in downscaled ocean models
NASA Astrophysics Data System (ADS)
Herzfeld, M.; Gillibrand, P. A.
2015-05-01
Regional models actively forced with data from larger scale models at their open boundaries often contain motion at different time-scales (e.g. tidal and low frequency). These motions are not always individually well specified in the forcing data, and one may require a more active boundary forcing while the other exert less influence on the model interior. If a single relaxation time-scale is used to relax toward these data in the boundary equation, then this may be difficult. The method of fractional steps is used to introduce dual relaxation time-scales in an open boundary local flux adjustment scheme. This allows tidal and low frequency oscillations to be relaxed independently, resulting in a better overall solution than if a single relaxation parameter is optimized for tidal (short relaxation) or low frequency (long relaxation) boundary forcing. The dual method is compared to the single relaxation method for an idealized test case where a tidal signal is superimposed on a steady state low frequency solution, and a real application where the low frequency boundary forcing component is derived from a global circulation model for a region extending over the whole Great Barrier Reef, and a tidal signal subsequently superimposed.
NASA Astrophysics Data System (ADS)
Rios, Edmilson Helton; Figueiredo, Irineu; Moss, Adam Keith; Pritchard, Timothy Neil; Glassborow, Brent Anthony; Guedes Domingues, Ana Beatriz; Bagueira de Vasconcellos Azeredo, Rodrigo
2016-07-01
The effect of the selection of different nuclear magnetic resonance (NMR) relaxation times for permeability estimation is investigated for a set of fully brine-saturated rocks acquired from Cretaceous carbonate reservoirs in the North Sea and Middle East. Estimators that are obtained from the relaxation times based on the Pythagorean means are compared with estimators that are obtained from the relaxation times based on the concept of a cumulative saturation cut-off. Select portions of the longitudinal (T1) and transverse (T2) relaxation-time distributions are systematically evaluated by applying various cut-offs, analogous to the Winland-Pittman approach for mercury injection capillary pressure (MICP) curves. Finally, different approaches to matching the NMR and MICP distributions using different mean-based scaling factors are validated based on the performance of the related size-scaled estimators. The good results that were obtained demonstrate possible alternatives to the commonly adopted logarithmic mean estimator and reinforce the importance of NMR-MICP integration to improving carbonate permeability estimates.
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.
Kokshenev, Valery B; Borges, Pablo D; Sullivan, Neil S
2005-03-15
The primary relaxation time scale tau(T) derived from the glass forming supercooled liquids (SCLs) is discussed within ergodic-cluster Gaussian statistics, theoretically justified near and above the glass-transformation temperature T(g). An analysis is given for the temperature-derivative data by Stickel et al. on the steepness and the curvature of tau(T). Near the mode-coupling-theory (MCT) crossover T(c), these derivatives separate by a kink and a jump, respectively, the moderately and strongly SCL states. After accounting for the kink and the jump, the steepness remains a piecewise conitnuous function, a material-independent equation for the three fundamental characteristic temperatures, T(g), T(c), and the Vogel-Fulcher-Tamman (VFT) T(0), is found. Both states are described within the heterostructured model of solidlike clusters parametrized in a self-consistent manner by a minimum set of observable parameters: the fragility index, the MCT slowing-down exponent, and the chemical excess potential of Adam and Gibbs model (AGM). Below the Arrhenius temperature, the dynamically and thermodynamically stabilized clusters emerge with a size of around of seven to nine and two to three molecules above and close to T(g) and T(c), respectively. On cooling, the main transformation of the moderately into the strongly supercooled state is due to rebuilding of the cluster structure, and is attributed to its rigidity, introduced through the cluster compressibility. It is shown that the validity of the dynamic AGM (dynamically equivalent to the standard VFT form) is limited by the strongly supercooled state (T(g) < T < T(c)) where the superrigid cooperative rearranging regions are shown to be well-chosen parametrized solidlike clusters. Extension of the basic parameter set by the observable kinetic and diffusive exponents results in prediction of a subdiffusion relaxation regime in SCLs that is distinct from that established for amorphous polymers.
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
Long Spin Relaxation Times in Wafer Scale Epitaxial Graphene on SiC(0001)
NASA Astrophysics Data System (ADS)
Maassen, Thomas; van den Berg, J. Jasper; Ijbema, Natasja; Fromm, Felix; Seyller, Thomas; Yakimova, Rositza; van Wees, Bart J.
2012-03-01
We developed an easy, upscalable process to prepare lateral spin-valve devices on epitaxially grown monolayer graphene on SiC(0001) and perform nonlocal spin transport measurements. We observe the longest spin relaxation times tau_S in monolayer graphene, while the spin diffusion coefficient D_S is strongly reduced compared to typical results on exfoliated graphene. The increase of tau_S is probably related to the changed substrate, while the cause for the small value of D_S remains an open question.
Lyulin, Alexey V; Michels, M A J
2007-08-24
Molecular-dynamics simulation is used to explore the influence of thermal and mechanical history of typical glassy polymers on their deformation. Polymer stress-strain and energy-strain developments have been followed for different deformation velocities, also in closed extension-recompression loops. The latter simulate for the first time the experimentally observed mechanical rejuvenation and overaging of polymers, and energy partitioning reveals essential differences between mechanical and thermal rejuvenation. All results can be qualitatively interpreted by considering the ratios of the relevant time scales: for cooling down, for deformation, and for segmental relaxation.
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.
Satoh, Katsuhiko
2013-03-07
Thermodynamic parameter Γ and thermodynamic scaling parameter γ for low-frequency relaxation time, which characterize flip-flop motion in a nematic phase, were verified by molecular dynamics simulation with a simple potential based on the Maier-Saupe theory. The parameter Γ, which is the slope of the logarithm for temperature and volume, was evaluated under various conditions at a wide range of temperatures, pressures, and volumes. To simulate thermodynamic scaling so that experimental data at isobaric, isothermal, and isochoric conditions can be rescaled onto a master curve with the parameters for some liquid crystal (LC) compounds, the relaxation time was evaluated from the first-rank orientational correlation function in the simulations, and thermodynamic scaling was verified with the simple potential representing small clusters. A possibility of an equivalence relationship between Γ and γ determined from the relaxation time in the simulation was assessed with available data from the experiments and simulations. In addition, an argument was proposed for the discrepancy between Γ and γ for some LCs in experiments: the discrepancy arises from disagreement of the value of the order parameter P2 rather than the constancy of relaxation time τ1(*) on pressure.
Pradhan, Ekadashi; Magyar, Rudolph J; Akimov, Alexey V
2016-11-30
Understanding the dynamics of electron-ion energy transfer in warm dense (WD) matter is important to the measurement of equation of state (EOS) properties and for understanding the energy balance in dynamic simulations. In this work, we present a comprehensive investigation of nonadiabatic electron relaxation and thermal excitation dynamics in aluminum under high pressure and temperature. Using quantum-classical trajectory surface hopping approaches, we examine the role of nonadiabatic couplings and electronic decoherence in electron-nuclear energy transfer in WD aluminum. The computed timescales range from 400 fs to 4.0 ps and are consistent with existing experimental studies. We have derived general scaling relationships between macroscopic parameters of WD systems such as temperature or mass density and the timescales of energy redistribution between quantum and classical degrees of freedom. The scaling laws are supported by computational results. We show that electronic decoherence plays essential role and can change the functional dependencies qualitatively. The established scaling relationships can be of use in modelling of WD matter.
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
Dai, Wei; Sengupta, Anirvan M.; Levy, Ronald M.
2015-01-01
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 mini-protein NTL9 constructed from a 2.9 millisecond simulation provided by D. E. Shaw Research. PMID:26252709
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
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.
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.
Relaxation time estimation in surface NMR
Grunewald, Elliot D.; Walsh, David O.
2017-03-21
NMR relaxation time estimation methods and corresponding apparatus generate two or more alternating current transmit pulses with arbitrary amplitudes, time delays, and relative phases; apply a surface NMR acquisition scheme in which initial preparatory pulses, the properties of which may be fixed across a set of multiple acquisition sequence, are transmitted at the start of each acquisition sequence and are followed by one or more depth sensitive pulses, the pulse moments of which are varied across the set of multiple acquisition sequences; and apply processing techniques in which recorded NMR response data are used to estimate NMR properties and the relaxation times T.sub.1 and T.sub.2* as a function of position as well as one-dimensional and two-dimension distributions of T.sub.1 versus T.sub.2* as a function of subsurface position.
Probing relaxation times in graphene quantum dots
Volk, Christian; Neumann, Christoph; Kazarski, Sebastian; Fringes, Stefan; Engels, Stephan; Haupt, Federica; Müller, André; Stampfer, Christoph
2013-01-01
Graphene quantum dots are attractive candidates for solid-state quantum bits. In fact, the predicted weak spin-orbit and hyperfine interaction promise spin qubits with long coherence times. Graphene quantum dots have been extensively investigated with respect to their excitation spectrum, spin-filling sequence and electron-hole crossover. However, their relaxation dynamics remain largely unexplored. This is mainly due to challenges in device fabrication, in particular concerning the control of carrier confinement and the tunability of the tunnelling barriers, both crucial to experimentally investigate decoherence times. Here we report pulsed-gate transient current spectroscopy and relaxation time measurements of excited states in graphene quantum dots. This is achieved by an advanced device design that allows to individually tune the tunnelling barriers down to the low megahertz regime, while monitoring their asymmetry. Measuring transient currents through electronic excited states, we estimate a lower bound for charge relaxation times on the order of 60–100 ns. PMID:23612294
An Overview on Short and Long Time Relaxations in Glass-forming Supercooled Liquids
NASA Astrophysics Data System (ADS)
Karmakar, Smarajit
2016-10-01
Density fluctuations in supercooled liquids near the glass transition relax in multiple steps. The short time relaxation is known as β-relaxation and the final long time relaxation is called α-relaxation. It is believed that the long time α-relaxation is a cooperative phenomena associated with a growing length scales, whereas the short-time β-relaxation is often attributed to spatially local processes involving the rattling motion of a particle in the transient cage formed by its neighbors. Using molecular dynamics simulations of few model glass-forming liquids, we show that the β-relaxation is also cooperative in nature and the length scale extracted from the detailed finite-size scaling analysis of β-relaxation is found to be the same as that of the length scale that describes the spatial heterogeneity of local dynamics in the long-time α-relaxation regime. These results provide a clear connection between short-time dynamics and long-time structural relaxation in glass-forming liquids.
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.
A Scale Measuring the Ability To Relax Others.
ERIC Educational Resources Information Center
Oliver, Peter V.; Boudreau, Louis A.
The present research developed and validated a self-reported instrument called the "Relaxing Others Scale" (ROS), which is designed to identify individuals who possess the ability to relax others. A second part of the study involved assessing the construct validity of the ROS. Participants in the study were male and female dormitory…
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 Cμ and the charge relaxation resistance Rq . We carry out a first principle calculation within the nonequilibrium Green’s 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.
Rotation and scale change invariant point pattern relaxation matching by the Hopfield neural network
NASA Astrophysics Data System (ADS)
Sang, Nong; Zhang, Tianxu
1997-12-01
Relaxation matching is one of the most relevant methods for image matching. The original relaxation matching technique using point patterns is sensitive to rotations and scale changes. We improve the original point pattern relaxation matching technique to be invariant to rotations and scale changes. A method that makes the Hopfield neural network perform this matching process is discussed. An advantage of this is that the relaxation matching process can be performed in real time with the neural network's massively parallel capability to process information. Experimental results with large simulated images demonstrate the effectiveness and feasibility of the method to perform point patten relaxation matching invariant to rotations and scale changes and the method to perform this matching by the Hopfield neural network. In addition, we show that the method presented can be tolerant to small random error.
Clustered continuous-time random walks: diffusion and relaxation consequences
Weron, Karina; Stanislavsky, Aleksander; Jurlewicz, Agnieszka; Meerschaert, Mark M.; Scheffler, Hans-Peter
2012-01-01
We present a class of continuous-time random walks (CTRWs), in which random jumps are separated by random waiting times. The novel feature of these CTRWs is that the jumps are clustered. This introduces a coupled effect, with longer waiting times separating larger jump clusters. We show that the CTRW scaling limits are time-changed processes. Their densities solve two different fractional diffusion equations, depending on whether the waiting time is coupled to the preceding jump, or the following one. These fractional diffusion equations can be used to model all types of experimentally observed two power-law relaxation patterns. The parameters of the scaling limit process determine the power-law exponents and loss peak frequencies. PMID:22792038
Relaxation therapy for insomnia: nighttime and day time effects.
Means, M K; Lichstein, K L; Epperson, M T; Johnson, C T
2000-07-01
We compared day time functioning in college students with and without insomnia and explored changes in day time functioning after progressive relaxation (PR) treatment for insomnia. Students with insomnia (SWI; n = 57) were compared to a control group of students not complaining of insomnia (SNI; n = 61) on self-reported sleep variables and five questionnaires: Insomnia Impact Scale (IIS), Dysfunctional Beliefs and Attitudes About Sleep Scale (DBAS), Epworth Sleepiness Scale (ESS), Fatigue Severity Scale (FSS), and Penn State Worry Questionnaire (PSWQ). SWI demonstrated significant impairment on all day time functioning and sleep measures compared to SNI. To investigate treatment effects on day time functioning, 28 SWI were randomly assigned to PR. Treated SWI were compared to untreated SWI and SNI at posttreatment. Treated participants improved sleep in comparison to untreated SWI, but failed to show significant improvements in day time functioning. Insomnia treatments focused on improving sleep may not improve day time functioning, or day time gains may emerge more slowly than sleep gains. This study documents the wide range of day time functioning complaints in young adults with insomnia and suggests that the goal of insomnia treatment should be to not only improve sleep but also to improve the subjective experience of day time functioning.
Thermodynamic scaling of relaxation: insights from anharmonic elasticity.
Bernini, S; Puosi, F; Leporini, D
2017-04-05
Using molecular dynamics simulations of a molecular liquid, we investigate the thermodynamic scaling (TS) of the structural relaxation time [Formula: see text] in terms of the quantity [Formula: see text], where T and ρ are the temperature and density, respectively. The liquid does not exhibit strong virial-energy correlations. We propose a method for evaluating both the characteristic exponent [Formula: see text] and the TS master curve that uses experimentally accessible quantities that characterise the anharmonic elasticity and does not use details about the microscopic interactions. In particular, we express the TS characteristic exponent [Formula: see text] in terms of the lattice Grüneisen parameter [Formula: see text] and the isochoric anharmonicity [Formula: see text]. An analytic expression of the TS master curve of [Formula: see text] with [Formula: see text] as the key adjustable parameter is found. The comparison with the experimental TS master curves and the isochoric fragilities of 34 glassformers is satisfying. In a few cases, where thermodynamic data are available, we test (i) the predicted characteristic exponent [Formula: see text] and (ii) the isochoric anharmonicity [Formula: see text], as drawn by the best fit of the TS of the structural relaxation, against the available thermodynamic data. A linear relation between the isochoric fragility and the isochoric anharmonicity [Formula: see text] is found and compared favourably with the results of experiments with no adjustable parameters. A relation between the increase of the isochoric vibrational heat capacity due to anharmonicity and the isochoric fragility is derived.
Effects of Stress and Relaxation on Time Perception
2003-01-01
mortality. Relaxation therapies are now commonly used to reduce negative stress consequences and were included in treatments of more than two thirds...help fine-tune relaxation therapies and allow the use of time perception as an assessment tool or outcome measure of stress management and relaxation... therapies . Self-reports of time (such as the frequency and duration of health condition symptoms) are a mainstay of diagnostic evaluation and quality of
Proton relaxation times in cancer diagnosis
Santhana Mariappan, S.V.; Subramanian, S.; Chandrakumar, N.; Rajalakshmi, K.R.; Sukumaran, S.S.
1988-10-01
Proton nuclear magnetic resonance relaxation parameters (T1, T2) were measured for over 100 malignant and normal tissue samples of various organs of the human body. The purpose of this study was to estimate the reliability of the NMR technique in discriminating normal from malignant tissues. Breast and cervix samples were analyzed by using the malignancy index concept and we were able to distinguish malignant and normal tissue in 17 out of 18 breast samples and 5 out of 7 cervix samples. Since the relaxation data of a normal control population of the other organs were not available, the data for these are reported without any further analysis. The distinction between carcinomas and sarcomas was also made by using the estimated relaxation parameters. Malignancy indices of breast tissue samples for linear least-squares and nonlinear two-parameter and three-parameter least-squares procedures were calculated and used to evaluate the relative efficiencies in discriminating malignant from normal tissues.
Cosmological relaxation and high scale inflation
NASA Astrophysics Data System (ADS)
Higaki, Tetsutaro; Takeda, Naoyuki; Yamada, Yusuke
2017-01-01
The relaxion mechanism elegantly solves the Higgs hierarchy problem, but it requires that the early Universe experiences a long inflation phase with a small energy scale since the settle down of the relaxion needs to take place during inflation. In this paper, unlike the original one, we consider another scenario in which the Higgs vacuum expectation value is determined after inflation. To accomplish the mechanism, we take into account the effects of the Hubble-induced mass and thermal one in the dynamics of the relaxion. Then, we find that for the relaxion mechanism the coupling of the relaxion with the additional mass terms should be large.
Formation of anisotropic polymer colloids by disparate relaxation times.
Kegel, Willem K; Breed, Dana; Elsesser, Mark; Pine, David J
2006-08-15
We show that coupling between a fast and a slow relaxation time causes the spontaneous formation of protrusions in colloids made of cross-linked polymers. The volume of the protrusions can be controlled by adjusting the ratio between the relaxation times. This, in principle, results in particles with levels of anisotropy that can be made "to order".
Correlation of transverse relaxation time with structure of biological tissue
NASA Astrophysics Data System (ADS)
Furman, Gregory B.; Meerovich, Victor M.; Sokolovsky, Vladimir L.
2016-09-01
Transverse spin-spin relaxation of liquids entrapped in nanocavities with different orientational order is theoretically investigated. Based on the bivariate normal distribution of nanocavities directions, we have calculated the anisotropy of the transverse relaxation time for biological systems, such as collagenous tissues, articular cartilage, and tendon. In the framework of the considered model, the dipole-dipole interaction is determined by a single coupling constant. The calculation results for the transverse relaxation time explain the angular dependence observed in MRI experiments with biological objects. The good agreement with the experimental data is obtained by adjustment of only one parameter which characterizes the disorder in fiber orientations. The relaxation time is correlated with the degree of ordering in biological tissues. Thus, microstructure of the tissues can be revealed from the measurement of relaxation time anisotropy. The clinical significance of the correlation, especially in the detection of damage must be evaluated in a large prospective clinical trials.
Correlation of transverse relaxation time with structure of biological tissue.
Furman, Gregory B; Meerovich, Victor M; Sokolovsky, Vladimir L
2016-09-01
Transverse spin-spin relaxation of liquids entrapped in nanocavities with different orientational order is theoretically investigated. Based on the bivariate normal distribution of nanocavities directions, we have calculated the anisotropy of the transverse relaxation time for biological systems, such as collagenous tissues, articular cartilage, and tendon. In the framework of the considered model, the dipole-dipole interaction is determined by a single coupling constant. The calculation results for the transverse relaxation time explain the angular dependence observed in MRI experiments with biological objects. The good agreement with the experimental data is obtained by adjustment of only one parameter which characterizes the disorder in fiber orientations. The relaxation time is correlated with the degree of ordering in biological tissues. Thus, microstructure of the tissues can be revealed from the measurement of relaxation time anisotropy. The clinical significance of the correlation, especially in the detection of damage must be evaluated in a large prospective clinical trials.
Thermodynamic scaling of relaxation: insights from anharmonic elasticity
NASA Astrophysics Data System (ADS)
Bernini, S.; Puosi, F.; Leporini, D.
2017-04-01
Using molecular dynamics simulations of a molecular liquid, we investigate the thermodynamic scaling (TS) of the structural relaxation time {τα} in terms of the quantity T{ρ-{γ\\text{ts}}}} , where T and ρ are the temperature and density, respectively. The liquid does not exhibit strong virial–energy correlations. We propose a method for evaluating both the characteristic exponent {{γ\\text{ts}} and the TS master curve that uses experimentally accessible quantities that characterise the anharmonic elasticity and does not use details about the microscopic interactions. In particular, we express the TS characteristic exponent {γ\\text{ts}} in terms of the lattice Grüneisen parameter {γL} and the isochoric anharmonicity {δL} . An analytic expression of the TS master curve of {τα} with {δL} as the key adjustable parameter is found. The comparison with the experimental TS master curves and the isochoric fragilities of 34 glassformers is satisfying. In a few cases, where thermodynamic data are available, we test (i) the predicted characteristic exponent {γ\\text{ts}} and (ii) the isochoric anharmonicity {δL} , as drawn by the best fit of the TS of the structural relaxation, against the available thermodynamic data. A linear relation between the isochoric fragility and the isochoric anharmonicity {δL} is found and compared favourably with the results of experiments with no adjustable parameters. A relation between the increase of the isochoric vibrational heat capacity due to anharmonicity and the isochoric fragility is derived.
Chemical Relaxation Times in a Hadron Gas at Finite Temperature
Goity, Jose
1993-07-01
The relaxation time of particle numbers in hot hadronic matter with vanishing baryon number are estimated using the ideal gas approximation and taking into account resonance decays and annihilation processes as the only sources of particle number fluctuations.Near the QCD critical temperature the longest relaxation times turn out to be of the order of 10 fm and grow roughly exponentially to become of the order of 10^3 fm at temperatures around 100 MeV.As a consequence of such long relaxation times, a clear departure from chemical equilibrium must be observed in the momentum distribution of secondary particles produced in high energy nuclear collisions.
Proton-nuclear magnetic resonance relaxation times in brain edema
Kamman, R.L.; Go, K.G.; Berendsen, H.J. )
1990-01-01
Proton relaxation times of protein solutions, bovine brain, and edematous feline brain tissue were studied as a function of water concentration, protein concentration, and temperature. In accordance with the fast proton exchange model for relaxation, a linear relation could be established between R1 and the inverse of the weight fraction of tissue water. This relation also applied to R2 of gray matter and of protein solutions. No straightforward relation with water content was found for R2 of white matter. Temperature-dependent studies indicated that in this case, the slow exchange model for relaxation had to be applied. The effect of macromolecules in physiological relevant concentrations on the total relaxation behavior of edematous tissue was weak. Total water content changes predominantly affected the relaxation rates. The linear relation may have high clinical potential for assessment of the status of cerebral edema on the basis of T1 and T2 readings from MR images.
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.
T2 relaxation time abnormalities in bipolar disorder and schizophrenia.
Ongür, Dost; Prescot, Andrew P; Jensen, J Eric; Rouse, Elizabeth D; Cohen, Bruce M; Renshaw, Perry F; Olson, David P
2010-01-01
There are substantial abnormalities in the number, density, and size of cortical neurons and glial cells in bipolar disorder and schizophrenia. Because molecule-microenvironment interactions modulate metabolite signals characteristics, these cellular abnormalities may impact transverse (T2) relaxation times. We measured T2 relaxation times for three intracellular metabolites (N-acetylaspartate+N-acetylaspartylglutamate, creatine+phosphocreatine, and choline-containing compounds) in the anterior cingulate cortex and parieto-occipital cortex from 20 healthy subjects, 15 patients with bipolar disorder, and 15 patients with schizophrenia at 4 T. Spectra used in T2 quantification were collected from 8-cc voxels with varying echo times (30 to 500 ms, in 10-ms steps). Both bipolar disorder and schizophrenia groups had numerically shorter T2 relaxation times than the healthy subjects group in both regions; these differences reached statistical significance for creatine+phosphocreatine and choline-containing compounds in bipolar disorder and for choline-containing compounds in schizophrenia. Metabolite T2 relaxation time shortening is consistent with reduced cell volumes and altered macromolecule structures, and with prolonged water T2 relaxation times reported in bipolar disorder and schizophrenia. These findings suggest that metabolite concentrations reported in magnetic resonance spectroscopy studies of psychiatric conditions may be confounded by T2 relaxation and highlight the importance of measuring and correcting for this variable.
Landauer’s formula with finite-time relaxation: Kramers’ crossover in electronic transport
Gruss, Daniel; Velizhanin, Kirill A.; Zwolak, Michael
2016-01-01
Landauer’s formula is the standard theoretical tool to examine ballistic transport in nano- and meso-scale junctions, but it necessitates that any variation of the junction with time must be slow compared to characteristic times of the system, e.g., the relaxation time of local excitations. Transport through structurally dynamic junctions is, however, increasingly of interest for sensing, harnessing fluctuations, and real-time control. Here, we calculate the steady-state current when relaxation of electrons in the reservoirs is present and demonstrate that it gives rise to three regimes of behavior: weak relaxation gives a contact-limited current; strong relaxation localizes electrons, distorting their natural dynamics and reducing the current; and in an intermediate regime the Landauer view of the system only is recovered. We also demonstrate that a simple equation of motion emerges, which is suitable for efficiently simulating time-dependent transport. PMID:27094206
Landauer’s formula with finite-time relaxation: Kramers’ crossover in electronic transport
Gruss, Daniel; Velizhanin, Kirill A.; Zwolak, Michael
2016-04-20
Landauer’s formula is the standard theoretical tool to examine ballistic transport in nano- and meso-scale junctions, but it necessitates that any variation of the junction with time must be slow compared to characteristic times of the system, e.g., the relaxation time of local excitations. Transport through structurally dynamic junctions is, however, increasingly of interest for sensing, harnessing fluctuations, and real-time control. Here, we calculate the steady-state current when relaxation of electrons in the reservoirs is present and demonstrate that it gives rise to three regimes of behavior: weak relaxation gives a contact-limited current; strong relaxation localizes electrons, distorting their naturalmore » dynamics and reducing the current; and in an intermediate regime the Landauer view of the system only is recovered. Lastly, we also demonstrate that a simple equation of motion emerges, which is suitable for efficiently simulating time-dependent transport.« less
Landauer’s formula with finite-time relaxation: Kramers’ crossover in electronic transport
Gruss, Daniel; Velizhanin, Kirill A.; Zwolak, Michael
2016-04-20
Landauer’s formula is the standard theoretical tool to examine ballistic transport in nano- and meso-scale junctions, but it necessitates that any variation of the junction with time must be slow compared to characteristic times of the system, e.g., the relaxation time of local excitations. Transport through structurally dynamic junctions is, however, increasingly of interest for sensing, harnessing fluctuations, and real-time control. Here, we calculate the steady-state current when relaxation of electrons in the reservoirs is present and demonstrate that it gives rise to three regimes of behavior: weak relaxation gives a contact-limited current; strong relaxation localizes electrons, distorting their natural dynamics and reducing the current; and in an intermediate regime the Landauer view of the system only is recovered. Lastly, we also demonstrate that a simple equation of motion emerges, which is suitable for efficiently simulating time-dependent transport.
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.
Relaxation Processes and Time Scale Transformation.
1982-03-01
frequency dependent susceptibility. As Ngai5 has emphasized the temperature dependence of such measurements is controlled by the temperature ...dependence of Tb or equivalently Ts . Then if EA is the activation energy of l/e value, the temperature of I is controlled by an effective activation energy E...mobility p 24 becomes non-Arrhenius, a well-known signature of small polaron hopping. Since b is constant in this temperature regime, this non-Arrhenius
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.
NASA Astrophysics Data System (ADS)
Yin, D. S.; Gao, Y. P.; Zhao, S. H.
2016-05-01
Millisecond pulsars can generate another type of time scale that is totally independent of the atomic time scale, because the physical mechanisms of the pulsar time scale and the atomic time scale are quite different from each other. Usually the pulsar timing observational data are not evenly sampled, and the internals between data points range from several hours to more than half a month. What's more, these data sets are sparse. And all these make it difficult to generate an ensemble pulsar time scale. Hence, a new algorithm to calculate the ensemble pulsar time scale is proposed. Firstly, we use cubic spline interpolation to densify the data set, and make the intervals between data points even. Then, we employ the Vondrak filter to smooth the data set, and get rid of high-frequency noise, finally adopt the weighted average method to generate the ensemble pulsar time scale. The pulsar timing residuals represent clock difference between the pulsar time and atomic time, and the high precision pulsar timing data mean the clock difference measurement between the pulsar time and atomic time with a high signal to noise ratio, which is fundamental to generate pulsar time. We use the latest released NANOGRAV (North American Nanohertz Observatory for Gravitational Waves) 9-year data set to generate the ensemble pulsar time scale. This data set is from the newest NANOGRAV data release, which includes 9-year observational data of 37 millisecond pulsars using the 100-meter Green Bank telescope and 305-meter Arecibo telescope. We find that the algorithm used in this paper can lower the influence caused by noises in timing residuals, and improve long-term stability of pulsar time. Results show that the long-term (> 1 yr) frequency stability of the pulsar time is better than 3.4×10-15.
Mindfulness meditation and relaxation training increases time sensitivity.
Droit-Volet, S; Fanget, M; Dambrun, M
2015-01-01
Two experiments examined the effect of mindfulness meditation and relaxation on time perception using a temporal bisection task. In Experiment 1, the participants performed a temporal task before and after exercises of mindfulness meditation or relaxation. In Experiment 2, the procedure was similar than that used in Experiment 1, except that the participants were trained to mediate or relax every day over a period of several weeks. The results showed that mindfulness meditation exercises increased sensitivity to time and lengthened perceived time. However, this temporal improvement with meditation exercises was primarily observed in the experienced meditators. Our results also showed the experienced meditators were less anxious than the novice participants, and that the sensitivity to time increased when the level of anxiety decreased. Our results were explained by the practice of mindfulness technique that had developed individuals' abilities in devoting more attention resources to temporal information processing.
Experimental study on relaxation time in direction changing movement
NASA Astrophysics Data System (ADS)
Liu, Chi; Song, Weiguo; Fu, Libi; Lian, Liping; Lo, Siuming
2017-02-01
Controlled experiments were conducted to clarify the movement characteristics of pedestrians in direction changing processes. We track pedestrians' trajectories and map them into real space coordinates by the direct linear transformation method. In the acceleration process, the relaxation time and free moving speed in our experiments respectively equal 0.659 s and 1.540 m/s, which are consistent with those for Chinese participants in other experiments. Meanwhile, the values of relaxation time in the direction changing process are calculated by a derived equation from the concept of the social force model. It is observed that the relaxation time is not an invariable parameter, and tends to increase with an increase in the angular difference. Furthermore, results show that pedestrians are insensitive to a tiny angular difference between instantaneous velocity and desired velocity. These experimental results presented in this work can be applied in model development and validation.
Il'in, V.G.; Llyasov, Yu.P.; Kuz'min, A.D.; Pushkin, S.B.; Palii, G.N.; Shabanova, T.V.; Shchitov, Yu.P.
1984-05-01
In this article a new time scale is proposed, that of pulsar time PT which is based on the regular sequence of time intervals between pulses of a pulsar's radio emissions. In discussing variations in the arrival times of pulsar radio emissions, three kinds of variations in the radiation periods are described. PSR 0834 + 06 is used as the basic reference pulsar. Time scales are also determined for reference pulsars PSR 0905 + 08 and 1919 + 21. The initial parameters for the three reference pulsars needed for managing a PT scale are presented. The basic PT scale is defined as the continuous sequence of time intervals between radio-emission pulses of the basic reference pulsar.
Relaxation Characteristics of 828 DGEBA Epoxy Over Long Time Periods
NASA Astrophysics Data System (ADS)
Hoo, Jasmine; Reprogle, Riley C.; Wisler, Brian; Arechederra, Gabriel K.; McCoy, John D.; Kropka, Jamie M.; Long, Kevin N.
The mechanical relaxation response in uniaxial compression of a diglycidyl ether of bisphenol-A epoxy was studied over long time periods. The epoxy, 828DEA, was Epon 828 cured with diethanolamine (DEA). A sample was compressed at constant strain rate and held at various strain levels for days to allow the sample to relax. The sample was then compressed further and held once more. The relaxation curves were fit with a stretched exponential function. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under Contract DE-AC04-94AL85000.
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 λ-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.
Subsecond pore-scale displacement processes and relaxation dynamics in multiphase flow
Armstrong, Ryan T; Ott, Holger; Georgiadis, Apostolos; Rücker, Maja; Schwing, Alex; Berg, Steffen
2014-01-01
With recent advances at X-ray microcomputed tomography (μCT) 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-μCT 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-μCT 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 μCT applications where morphological changes occur at a time scale less than that required for collecting a μCT scan. PMID:25745271
Universal and scaled relaxation of interacting magnetic nanoparticles
NASA Astrophysics Data System (ADS)
Chen, Xi; Sahoo, S.; Kleemann, W.; Cardoso, S.; Freitas, P. P.
2004-11-01
The logarithmic relaxation rate of the thermoremanent magnetic moment m(t) of interacting magnetic nanoparticles in discontinuous Co80Fe20/Al2O3 multilayers follows a universal power law, whose exponent n increases with increasing particle concentration as predicted by recent simulations [Ulrich , Phys. Rev. B 67, 024416 (2003)]. While n<1 characterizes the stretched exponential decay of the dilute superspin glass (SSG) regime, n>1 refers to algebraic decay with finite remanence for t→∞ as observed in more concentrated superferromagnets (SFM). In the crossover regime from SSG to SFM, an increase from n<1 at low temperature to n>1 at T⪅Tc violates Tln(t/τ0) scaling and seems to indicate a crossover from random-field domain state to SFM behavior.
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.
Gallavotti, G
2006-06-01
Entropy creation rate is introduced for a system interacting with thermostats (i.e., for a system subject to internal conservative forces interacting with "external" thermostats via conservative forces) and a fluctuation theorem for it is proved. As an application, a time scale is introduced, to be interpreted as the time over which irreversibility becomes manifest in a process leading from an initial to a final stationary state of a mechanical system in a general nonequilibrium context. The time scale is evaluated in a few examples, including the classical Joule-Thompson process (gas expansion in a vacuum).
Inversion of generalized relaxation time distributions with optimized damping parameter
NASA Astrophysics Data System (ADS)
Florsch, Nicolas; Revil, André; Camerlynck, Christian
2014-10-01
Retrieving the Relaxation Time Distribution (RDT), the Grains Size Distribution (GSD) or the Pore Size Distribution (PSD) from low-frequency impedance spectra is a major goal in geophysics. The “Generalized RTD” generalizes parametric models like Cole-Cole and many others, but remains tricky to invert since this inverse problem is ill-posed. We propose to use generalized relaxation basis function (for instance by decomposing the spectra on basis of generalized Cole-Cole relaxation elements instead of the classical Debye basis) and to use the L-curve approach to optimize the damping parameter required to get smooth and realistic inverse solutions. We apply our algorithm to three examples, one synthetic and two real data sets, and the program includes the possibility of converting the RTD into GSD or PSD by choosing the value of the constant connecting the relaxation time to the characteristic polarization size of interest. A high frequencies (typically above 1 kHz), a dielectric term in taken into account in the model. The code is provided as an open Matlab source as a supplementary file associated with this paper.
Hyperpolarized nanodiamond with long spin-relaxation times
Rej, Ewa; Gaebel, Torsten; Boele, Thomas; Waddington, David E.J.; Reilly, David J.
2015-01-01
The use of hyperpolarized agents in magnetic resonance, such as 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
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.
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
Relaxation Time and Conductivity at a Rural Station: Raicbur
NASA Astrophysics Data System (ADS)
Manohar, G. K.; Kandalgaonkar, S. S.; Sholapurkar, S. M.
1991-08-01
An examination of decay and growth rates of electric field near the ground during total solar eclipse of 16 February 1980 was made to study the electrical relaxation time and conductivity at Raichur. The Values obtained i.e., 1320 seconds and 67.1163 x 10-16 mhos m-1 of the two parameters were in fair agreement with the reported ones at the rural locations.
Damping effects in doped graphene: The relaxation-time approximation
NASA Astrophysics Data System (ADS)
Kupčić, I.
2014-11-01
The dynamical conductivity of interacting multiband electronic systems derived by Kupčić et al. [J. Phys.: Condens. Matter 90, 145602 (2013), 10.1088/0953-8984/25/14/145602] is shown to be consistent with the general form of the Ward identity. Using the semiphenomenological form of this conductivity formula, we have demonstrated that the relaxation-time approximation can be used to describe the damping effects in weakly interacting multiband systems only if local charge conservation in the system and gauge invariance of the response theory are properly treated. Such a gauge-invariant response theory is illustrated on the common tight-binding model for conduction electrons in doped graphene. The model predicts two distinctly resolved maxima in the energy-loss-function spectra. The first one corresponds to the intraband plasmons (usually called the Dirac plasmons). On the other hand, the second maximum (π plasmon structure) is simply a consequence of the Van Hove singularity in the single-electron density of states. The dc resistivity and the real part of the dynamical conductivity are found to be well described by the relaxation-time approximation, but only in the parametric space in which the damping is dominated by the direct scattering processes. The ballistic transport and the damping of Dirac plasmons are thus the problems that require abandoning the relaxation-time approximation.
Relaxation times and rheology in dense athermal suspensions
NASA Astrophysics Data System (ADS)
Olsson, Peter
2015-06-01
We study the jamming transition in a model of elastic particles under shear at zero temperature. The key quantity is the relaxation time τ which is obtained by stopping the shearing and letting energy and pressure decay to zero. At many different densities and initial shear rates we do several such relaxations to determine the average τ . We establish that τ diverges with the same exponent as the viscosity and determine another exponent from the relation between τ and the coordination number. Though most of the simulations are done for the model with dissipation due to the motion of particles relative to an affinely shearing substrate, we also examine a model, where the dissipation is instead due to velocity differences of disks in contact, and confirm that the above-mentioned exponent is the same for these two models. We also consider finite size effects on both τ and the coordination number.
Design of self-refocused pulses under short relaxation times.
Issa, Bashar
2009-06-01
The effect of using self-refocused RF pulses of comparable duration to relaxation times is studied in detail using numerical simulation. Transverse magnetization decay caused by short T2 and longitudinal component distortion due to short T1 are consistent with other studies. In order to design new pulses to combat short T1 and T2 the relaxation terms are directly inserted into the Bloch equations. These equations are inverted by searching the RF solution space using simulated annealing global optimization technique. A new T2-decay efficient excitation pulse is created (SDETR: single delayed excursion T2 resistive) which is also energy efficient. Inversion pulses which improve the inverted magnetization profile and achieve better suppression of the remaining transverse magnetization are also created even when both T1 and T2 are short. This is achieved, however, on the expense of a more complex B1 shape of larger energy content.
Krylov-subspace acceleration of time periodic waveform relaxation
Lumsdaine, A.
1994-12-31
In this paper the author uses Krylov-subspace techniques to accelerate the convergence of waveform relaxation applied to solving systems of first order time periodic ordinary differential equations. He considers the problem in the frequency domain and presents frequency dependent waveform GMRES (FDWGMRES), a member of a new class of frequency dependent Krylov-subspace techniques. FDWGMRES exhibits many desirable properties, including finite termination independent of the number of timesteps and, for certain problems, a convergence rate which is bounded from above by the convergence rate of GMRES applied to the static matrix problem corresponding to the linear time-invariant ODE.
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
2015-08-28
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.
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
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.
van Heeswijk, Ruud B.; Laus, Sabrina; Morgenthaler, Florence D.; Gruetter, Rolf
2007-01-01
The relaxivity of commercially available gadolinium-based contrast agents was studied for X-nuclei resonances with long intrinsic relaxation times ranging between 6 and several hundred seconds. Omniscan in pure 13C formic acid had a relaxivity of 2.9 mM-1 s-1, whereas its relaxivity on glutamate C1 and C5 in aqueous solution was ∼0.5 mM-1 s-1. Both relaxivities allow the preparation of solutions with a predetermined short T1 suggest that in vitro substantial sensitivity gains in their measurement can be achieved. 6Li has a long intrinsic relaxation time, on the order of several minutes, which was strongly affected by the contrast agents. Relaxivity ranged from ∼0.1 mM-1 s-1 for Omniscan to 0.3 for Magnevist, whereas the relaxivity of Gd-DOTP was at 11 mM-1 s-1 two orders of magnitude higher. Overall these experiments suggest that the presence of 0.1-10 μM contrast agents should be detectable, provided sufficient sensitivity is available, such as that afforded by hyperpolarization, recently introduced to in vivo imaging. PMID:17448617
Scaling vs. Vogel-Fulcher-type structural relaxation in deeply supercooled materials
NASA Astrophysics Data System (ADS)
Richert, Ranko
2000-11-01
A recent scaling-law analysis using τ∝( T- Tc) - γ with Tc< Tg has concluded that the resulting fits are superior over the Vogel-Fulcher-Tammann temperature dependence as regards the structural relaxation time of supercooled liquids (Colby, Phys. Rev. E 61 (2000) 1783). This issue is investigated based on the dielectric retardation data of poly(vinylacetate) which cover 16 decades in time, from 3 ns to over 1 year. In contrast to Colby's conclusions, the observed temperature dependence rules out a temperature-invariant exponent γ as well as a clear cut critical temperature Tc.
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.
Effective rotational correlation times of proteins from NMR relaxation interference
NASA Astrophysics Data System (ADS)
Lee, Donghan; Hilty, Christian; Wider, Gerhard; Wüthrich, Kurt
2006-01-01
Knowledge of the effective rotational correlation times, τc, for the modulation of anisotropic spin-spin interactions in macromolecules subject to Brownian motion in solution is of key interest for the practice of NMR spectroscopy in structural biology. The value of τc enables an estimate of the NMR spin relaxation rates, and indicates possible aggregation of the macromolecular species. This paper reports a novel NMR pulse scheme, [ 15N, 1H]-TRACT, which is based on transverse relaxation-optimized spectroscopy and permits to determine τc for 15N- 1H bonds without interference from dipole-dipole coupling of the amide proton with remote protons. [ 15N, 1H]-TRACT is highly efficient since only a series of one-dimensional NMR spectra need to be recorded. Its use is suggested for a quick estimate of the rotational correlation time, to monitor sample quality and to determine optimal parameters for complex multidimensional NMR experiments. Practical applications are illustrated with the 110 kDa 7,8-dihydroneopterin aldolase from Staphylococcus aureus, the uniformly 15N-labeled Escherichia coli outer membrane protein X (OmpX) in 60 kDa mixed OmpX/DHPC micelles with approximately 90 molecules of unlabeled 1,2-dihexanoyl- sn-glycero-3-phosphocholine (DHPC), and the 16 kDa pheromone-binding protein from Bombyx mori, which cover a wide range of correlation times.
NASA Astrophysics Data System (ADS)
Nonomura, Yoshihiko
2014-11-01
Nonequilibrium relaxation behaviors in the Ising model on a square lattice based on the Wolff algorithm are totally different from those based on local-update algorithms. In particular, the critical relaxation is described by the stretched-exponential decay. We propose a novel scaling procedure to connect nonequilibrium and equilibrium behaviors continuously, and find that the stretched-exponential scaling region in the Wolff algorithm is as wide as the power-law scaling region in local-update algorithms. We also find that relaxation to the spontaneous magnetization in the ordered phase is characterized by the exponential decay, not the stretched-exponential decay based on local-update algorithms.
NASA Astrophysics Data System (ADS)
Tomadakis, Manolis M.; Robertson, Teri J.
2003-07-01
We present a random walk based investigation of the pore size probability distribution and its moments, the survival probability and mean survival time, and the principal relaxation time, for random and ordered arrays of cylindrical fibers of various orientation distributions. The dimensionless mean survival time, principal relaxation time, mean pore size, and mean square pore size are found to increase with porosity, remain practically independent of the directionality of random fiber beds, and attain lower values for ordered arrays. Wide pore size distributions are obtained for random fiber structures and relatively narrow for ordered square arrays, all in very good agreement with theoretically predicted limiting values. Analytical results derived for the pore size probability and its lower moments for square arrays of fibers practically coincide with the corresponding simulation results. Earlier variational bounds on the mean survival time and principal relaxation time are obeyed by our numerical results in all cases, and are found to be quite sharp up to very high porosities. Dimensionless groups representing the deviation of such bounds from our simulation results vary in practically the same range as the corresponding values reported earlier for beds of spherical particles. A universal scaling expression of the literature relating the mean survival time to the mean pore size [S. Torquato and C. L. Y. Yeong, J. Chem. Phys. 106, 8814 (1997)] agrees very well with our results for all types of fiber structures, thus validated for the first time for anisotropic porous media.
Upper D region chemical kinetic modeling of LORE relaxation times
NASA Astrophysics Data System (ADS)
Gordillo-Vázquez, F. J.; Luque, A.; Haldoupis, C.
2016-04-01
The recovery times of upper D region electron density elevations, caused by lightning-induced electromagnetic pulses (EMP), are modeled. The work was motivated from the need to understand a recently identified narrowband VLF perturbation named LOREs, an acronym for LOng Recovery Early VLF events. LOREs associate with long-living electron density perturbations in the upper D region ionosphere; they are generated by strong EMP radiated from large peak current intensities of ±CG (cloud to ground) lightning discharges, known also to be capable of producing elves. Relaxation model scenarios are considered first for a weak enhancement in electron density and then for a much stronger one caused by an intense lightning EMP acting as an impulsive ionization source. The full nonequilibrium kinetic modeling of the perturbed mesosphere in the 76 to 92 km range during LORE-occurring conditions predicts that the electron density relaxation time is controlled by electron attachment at lower altitudes, whereas above 79 km attachment is balanced totally by associative electron detachment so that electron loss at these higher altitudes is controlled mainly by electron recombination with hydrated positive clusters H+(H2O)n and secondarily by dissociative recombination with NO+ ions, a process which gradually dominates at altitudes >88 km. The calculated recovery times agree fairly well with LORE observations. In addition, a simplified (quasi-analytic) model build for the key charged species and chemical reactions is applied, which arrives at similar results with those of the full kinetic model. Finally, the modeled recovery estimates for lower altitudes, that is <79 km, are in good agreement with the observed short recovery times of typical early VLF events, which are known to be associated with sprites.
Relaxation time prediction for a light switchable peptide by molecular dynamics.
Denschlag, Robert; Schreier, Wolfgang J; Rieff, Benjamin; Schrader, Tobias E; Koller, Florian O; Moroder, Luis; Zinth, Wolfgang; Tavan, Paul
2010-06-21
We study a monocyclic peptide called cAPB, whose conformations are light switchable due to the covalent integration of an azobenzene dye. Molecular dynamics (MD) simulations using the CHARMM22 force field and its CMAP extension serve us to sample the two distinct conformational ensembles of cAPB, which belong to the cis and trans isomers of the dye, at room temperature. For gaining sufficient statistics we apply a novel replica exchange technique. We find that the well-known NMR distance restraints are much better described by CMAP than by CHARMM22. In cAPB, the ultrafast cis/trans photoisomerization of the dye elicits a relaxation dynamics of the peptide backbone. Experimentally, we probe this relaxation at picosecond time resolution by IR spectroscopy in the amide I range up to 3 ns after the UV/vis pump flash. We interpret the spectroscopically identified decay kinetics using ensembles of non-equilibrium MD simulations, which provide kinetic data on conformational transitions well matching the observed kinetics. Whereas spectroscopy solely indicates that the relaxation toward the equilibrium trans ensemble is by no means complete after 3 ns, the 20 ns MD simulations of the process predict, independently of the applied force field, that the final relaxation into the trans-ensemble proceeds on a time scale of 23 ns. Overall our explicit solvent simulations cover more than 6 micros.
Implicit versus explicit momentum relaxation time solution for semiconductor nanowires
Marin, E. G. Ruiz, F. G. Godoy, A. Tienda-Luna, I. M.; Gámiz, F.
2015-07-14
We discuss the necessity of the exact implicit Momentum Relaxation Time (MRT) solution of the Boltzmann transport equation in order to achieve reliable carrier mobility results in semiconductor nanowires. Firstly, the implicit solution for a 1D electron gas with a isotropic bandstructure is presented resulting in the formulation of a simple matrix system. Using this solution as a reference, the explicit approach is demonstrated to be inaccurate for the calculation of inelastic anisotropic mechanisms such as polar optical phonons, characteristic of III-V materials. Its validity for elastic and isotropic mechanisms is also evaluated. Finally, the implications of the MRT explicit approach inaccuracies on the total mobility of Si and III-V NWs are studied.
Spin current relaxation time in thermally evaporated pentacene films
NASA Astrophysics Data System (ADS)
Tani, Yasuo; Kondo, Takuya; Teki, Yoshio; Shikoh, Eiji
2017-01-01
The spin current relaxation time (τ) in thermally evaporated pentacene films was evaluated with the spin-pump-induced spin transport properties and the charge current transport properties in pentacene films. Under an assumption of a diffusive transport of the spin current in pentacene films, the zero-field mobility and the diffusion constant of holes in pentacene films were experimentally obtained to be ˜8.0 × 10-7 m2/V s and ˜2.0 × 10-8 m2/s, respectively. Using those values and the previously obtained spin diffusion length in pentacene films of 42 ± 10 nm, the τ in pentacene films was estimated to be 150 ± 120 ns at room temperature. This estimated τ in pentacene films is long enough for the practical use as a spintronic material.
Chiral relaxation time at the crossover of quantum chromodynamics
NASA Astrophysics Data System (ADS)
Ruggieri, M.; Peng, G. X.; Chernodub, M.
2016-09-01
We study microscopic processes responsible for chirality flips in the thermal bath of quantum chromodynamics at finite temperature and zero baryon chemical potential. We focus on the temperature range where the crossover from chirally broken phase to quark-gluon plasma takes place, namely, T ≃(150 ,200 ) MeV . The processes we consider are quark-quark scatterings mediated by collective excitations with the quantum number of pions and σ meson; hence we refer to these processes simply as one-pion (one-σ ) exchanges. We use a Nambu-Jona-Lasinio model to compute equilibrium properties of the thermal bath, as well as the relevant scattering kernel to be used in the collision integral to estimate the chiral relaxation time τ . We find τ ≃0.1 ÷1 fm /c around the chiral crossover.
NASA Astrophysics Data System (ADS)
Shin, Kaikou; Kuroda, Mitsuru; Natsuyama, Kouichi
Advanced Planning and Scheduling (APS) has been widely recognized as a promising method for solving real production planning and scheduling problems. Based on the proposal of a real-time job shop scheduling mechanism under an APS environment, which adopts the Lagrangean relaxation method as the optimization logic, the present paper describes a feasibility study of this mechanism by evaluating its calculation speed and re-scheduling quality. Numerical experiments have been carried out for various models having different scales, as well as different densities and strengths of random events, such as the arrival of new jobs or changes to the due dates for existing jobs. The results of experiments show that the proposed scheduling mechanism has the potential to satisfy the real-time scheduling requirements, not only in terms of calculation speed and solution quality, but also with respect to predictability of the calculation load. Finally, an improvement to the Lagrangean relaxation method is proposed to improve re-scheduling quality.
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
Optical Relaxation Time Enhancement in Graphene-Passivated Metal Films
Chugh, Sunny; Mehta, Ruchit; Man, Mengren; Chen, Zhihong
2016-01-01
Due to the small skin depth in metals at optical frequencies, their plasmonic response is strongly dictated by their surface properties. Copper (Cu) is one of the standard materials of choice for plasmonic applications, because of its high conductivity and CMOS compatibility. However, being a chemically active material, it gets easily oxidized when left in ambient environment, causing an inevitable degradation in its plasmonic resonance. Here, for the first time, we report a strong enhancement in the optical relaxation time in Cu by direct growth of few-layer graphene that is shown to act as an excellent passivation layer protecting Cu surface from any deterioration. Spectroscopic ellipsometry measurements reveal a 40–50% reduction in the total scattering rate in Cu itself, which is attributed to an improvement in its surface properties. We also study the impact of graphene quality and show that high quality graphene leads to an even larger improvement in electron scattering rate. These findings are expected to provide a big push towards graphene-protected Cu plasmonics. PMID:27461968
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.
An axisymmetric multiple-relaxation-time lattice Boltzmann scheme
NASA Astrophysics Data System (ADS)
Xie, Wenjun
2015-01-01
A multiple-relaxation-time (MRT) lattice Boltzmann (LB) scheme developed for axisymmetric flows recovers the complete continuity and Navier-Stokes equations. This scheme follows the strategy of the standard D2Q9 model by using a single particle distribution function and a simple "collision-streaming" updating rule. The extra terms related to axisymmetry in the macroscopic equations are recovered by adding source terms into the LB equation, which are simple and involve no gradients. The compressible effect retained in the Navier-Stokes equations is recovered by introducing a term related to the reversed transformation matrix for MRT collision operator, so as to produce a correct bulk viscosity, making it suitable for compressible flows with high frequency and low Mach number. The validity of the scheme is demonstrated by testing the Hagen-Poiseuille flow and 3D Womersley flow, as well as the standing acoustic waves in a closed cylindrical chamber. The numerical experiments show desirable stability at low viscosities, enabling to simulate a standing ultrasound field in centimeters space.
NASA Astrophysics Data System (ADS)
Petit, G.; Murdin, P.
2000-11-01
Terrestrial time is at present derived from atomic clocks. The SI second, the unit of time of the international system of units, has been defined since 1967 in terms of a hyperfine transition of the cesium atom and the best primary frequency standards now realize it with a relative uncertainty of a few parts in 1015, which makes it the most accurately measurable physical quantity. INTERNATIONAL A...
Short relaxation times but long transient times in both simple and complex reaction networks
Henry, Adrien; Martin, Olivier C.
2016-01-01
When relaxation towards an equilibrium or steady state is exponential at large times, one usually considers that the associated relaxation time τ, i.e. the inverse of the decay rate, is the longest characteristic time in the system. However, that need not be true, other times such as the lifetime of an infinitesimal perturbation can be much longer. In the present work, we demonstrate that this paradoxical property can arise even in quite simple systems such as a linear chain of reactions obeying mass action (MA) kinetics. By mathematical analysis of simple reaction networks, we pin-point the reason why the standard relaxation time does not provide relevant information on the potentially long transient times of typical infinitesimal perturbations. Overall, we consider four characteristic times and study their behaviour in both simple linear chains and in more complex reaction networks taken from the publicly available database ‘Biomodels’. In all these systems, whether involving MA rates, Michaelis–Menten reversible kinetics, or phenomenological laws for reaction rates, we find that the characteristic times corresponding to lifetimes of tracers and of concentration perturbations can be significantly longer than τ. PMID:27411726
The time dependence of rock healing as a universal relaxation process, a tutorial
NASA Astrophysics Data System (ADS)
Snieder, Roel; Sens-Schönfelder, Christoph; Wu, Renjie
2017-01-01
The material properties of earth materials often change after the material has been perturbed (slow dynamics). For example, the seismic velocity of subsurface materials changes after earthquakes, and granular materials compact after being shaken. Such relaxation processes are associated by observables that change logarithmically with time. Since the logarithm diverges for short and long times, the relaxation can, strictly speaking, not have a log-time dependence. We present a self-contained description of a relaxation function that consists of a superposition of decaying exponentials that has log-time behaviour for intermediate times, but converges to zero for long times, and is finite for t = 0. The relaxation function depends on two parameters, the minimum and maximum relaxation time. These parameters can, in principle, be extracted from the observed relaxation. As an example, we present a crude model of a fracture that is closing under an external stress. Although the fracture model violates some of the assumptions on which the relaxation function is based, it follows the relaxation function well. We provide qualitative arguments that the relaxation process, just like the Gutenberg-Richter law, is applicable to a wide range of systems and has universal properties.
The time dependence of rock healing as a universal relaxation process, a tutorial
NASA Astrophysics Data System (ADS)
Snieder, Roel; Sens-Schönfelder, Christoph; Wu, Renjie
2016-10-01
The material properties of earth materials often change after the material has been perturbed (slow dynamics). For example, the seismic velocity of subsurface materials changes after earthquakes, and granular materials compact after being shaken. Such relaxation processes are associated by observables that change logarithmically with time. Since the logarithm diverges for short and long times, the relaxation can, strictly speaking, not have a log-time dependence. We present a self-contained description of a relaxation function that consists of a superposition of decaying exponentials that has log-time behavior for intermediate times, but converges to zero for long times, and is finite for t = 0. The relaxation function depends on two parameters, the minimum and maximum relaxation time. These parameters can, in principle, be extracted from the observed relaxation. As an example, we present a crude model of a fracture that is closing under an external stress. Although the fracture model violates some of the assumptions on which the relaxation function is based, it follows the relaxation function well. We provide qualitative arguments that the relaxation process, just like the Gutenberg-Richter law, is applicable to a wide range of systems and has universal properties.
Time scale independent signal transmission
NASA Astrophysics Data System (ADS)
Faltin, L.
1980-05-01
The paper presents a method which permits the conversion of time scale variations occurring during signal transmission into time shifts proportionally related to these variations. It is demonstrated that the method can be used to reject the adverse effects of the time scale variations (such as wow and flutter in magnetic tape recordings) and/or to determine the scale change exactly (such as would be required in Doppler signal processing). Finally, it is noted that since the system performance degrades with rising frequency of the time scale distortions, an upper bound for this frequency is derived.
NASA Astrophysics Data System (ADS)
Soroushian, Behrouz; Yang, Xinmai
2013-03-01
Most biological chromophores and molecules relax primarily through non-radiative processes; therefore, mapping of relaxation time related to non-rediative process can be a potential indicator of tissue status. In order to map relative nonradiative relaxation time, modulated tone-burst light is used to generate photoacoustic signals. Then nonradiative relaxation time is indicated by the amplitude decay rate as modulation frequency increases. The results show that although blood is an optically weak absorber at 808 nm, by using this method a significant enhancement of contrast-tonoise ratio of a blood target compared to pulsed photoacoustic imaging at this wavelength is achieved.
2006-12-01
estimates of ET, and it did not include relativistic effects. 5. ATOMIC TIME Following the appearance of the first operational Caesium beam frequency...with Wm Markowitz and R. G. Hall at the USNO, determined the frequency of the NPL Caesium standard with respect to the second of ET. Photographs of the...known UT2 determined from optical observations made at the USNO. This information was used to calibrate the Caesium beam atomic clock at NPL. The
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.
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.
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
Time-resolved X-ray measurements of energy relaxation in ultrafast laser excited semiconductors
NASA Astrophysics Data System (ADS)
Lee, Soo Heyong
In semiconductors, the properties and dynamics of photoexcited carriers and subsequent energy relaxation through lattice vibrations are quite complex and occur on a variety of time scales. Typically the transient dynamics involving transitions of electrons from lower energy states to higher ones upon photoexcitation take place almost instantaneously. The electrons eventually recombine with holes while losing most of their kinetic energy to the lattice through various routes at different time scales. The lattice relaxation processes, especially at high photoexcitation levels, have been subjected to numerous experimental and theoretical investigations during past decades. Time-resolved X-ray diffraction (TRXD) method provides a novel tool for studying these dynamics because X-rays have short wavelength, long material penetration depth and relatively strong interaction with core electrons. In my work, femtosecond laser pulses excite electrons in opaque materials, and subsequent carrier relaxation process and coherent/incoherent lattice dynamics are investigated using TRXD. My thesis covers quantitative detail of the generation and propagation of ultrafast laser induces acoustic strain waves in bulk semiconductor materials as well as at the heterostructure interface. In particular propagation of strain waves, which are comprised of broadband low wave vector phonons, is studied in an AlGaAs/GaAs multilayer structure. The spatial and temporal profiles of the acoustic waves at varying photoexcitation density are characterized. We are able to distinguish thermal from carrier-induced strain and measure the free-carrier absorption cross-section. The approximation that impulsively generated acoustic waves are uniaxial is found to break down. The research also demonstrates a novel approach to explore laser induced acoustic phonon dynamics at high wavevector, near the Brillouin zone-boundary, the details of which are inaccessible to optical pump-probe methods. Throughout this
NASA Astrophysics Data System (ADS)
Swank, J. H.
1996-12-01
A major goal of RXTE is to investigate the fastest timing signals from compact stars, especially neutron stars and black holes. Signals have now been found from many (at least nine) low mass X-ray binaries containing neutron stars in the frequency range (100-1200 Hz) expected for the rotation period of the neutron star after being spun up by accretion over a long period. The kilohertz frequency domain for these sources is simpler than the domain of oscillations below about 50 Hz in that a few isolated features can dominate over white noise. However there are three main features to consider (not all present at the same time) and at least two are quasiperiodic with varying widths and frequencies. Several models are pitting their predictions against the behavior of these features, but the bursters, especially, appear to be revealing the neutron stars's spin. It is consistent with our beliefs that no black hole candidate has shown the same complex of signals, although at least one QPO frequency of a few hundred Hz could be expected in black hole candidates by analogy to the 67 Hz observed from GRS 1915+105. The observations also provide critical tests of the interpretions of the lower frequency (5-50 Hz) QPO and the variable noise seen in both low magnetic field neutron stars and black hole candidates. The kilohertz features have not been seen from the accreting pulsars with relatively high magnetic fields, but high luminosity pulsars (such as last year's transient, GRO J1744-28) reveal signatures of the dynamic interaction between the accretion flow, the magnetic field, and perhaps the neutron star surface in addition to their coherent pulsations.
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.
NASA Astrophysics Data System (ADS)
Sobolev, Stephan; Muldashev, Iskander
2016-04-01
According to conventional view, postseismic relaxation process after a great megathrust earthquake is dominated by fault-controlled afterslip during first few months to year, and later by visco-elastic relaxation in mantle wedge. We test this idea by cross-scale thermomechanical models of seismic cycle that employs elasticity, mineral-physics constrained non-linear transient viscous rheology and rate-and-state friction plasticity. As initial conditions for the models we use thermomechanical models of subduction zones at geological time-scale including a narrow subduction channel with low static friction for two settings, similar to the Southern Chile in the region of the great Chile Earthquake of 1960 and Japan in the region of Tohoku Earthquake of 2011. We next introduce in the same models classic rate-and state friction law in subduction channels, leading to stick-slip instability. The models start to generate spontaneous earthquake sequences and model parameters are set to closely replicate co-seismic deformations of Chile and Japan earthquakes. In order to follow in details deformation process during the entire seismic cycle and multiple seismic cycles we use adaptive time-step algorithm changing integration step from 40 sec during the earthquake to minute-5 year during postseismic and interseismic processes. We show that for the case of the Chile earthquake visco-elastic relaxation in the mantle wedge becomes dominant relaxation process already since 1 hour after the earthquake, while for the smaller Tohoku earthquake this happens some days after the earthquake. We also show that our model for Tohoku earthquake is consistent with the geodetic observations for the day-to-4year time range. We will demonstrate and discuss modeled deformation patterns during seismic cycles and identify the regions where the effects of afterslip and visco-elastic relaxation can be best distinguished.
Vandewalle, S.
1994-12-31
Time-stepping methods for parabolic partial differential equations are essentially sequential. This prohibits the use of massively parallel computers unless the problem on each time-level is very large. This observation has led to the development of algorithms that operate on more than one time-level simultaneously; that is to say, on grids extending in space and in time. The so-called parabolic multigrid methods solve the time-dependent parabolic PDE as if it were a stationary PDE discretized on a space-time grid. The author has investigated the use of multigrid waveform relaxation, an algorithm developed by Lubich and Ostermann. The algorithm is based on a multigrid acceleration of waveform relaxation, a highly concurrent technique for solving large systems of ordinary differential equations. Another method of this class is the time-parallel multigrid method. This method was developed by Hackbusch and was recently subject of further study by Horton. It extends the elliptic multigrid idea to the set of equations that is derived by discretizing a parabolic problem in space and in time.
Measuring the relaxation time of the xenon atoms and the rubidium atoms
NASA Astrophysics Data System (ADS)
Jiang, Peng; Wang, Zhi-Guo; Li, Ying-Ying; Jiang, Qi-Yuan; Luo, Hui
2016-11-01
In a nuclear-magnetic-resonance gyroscope (NMRG), the polarization of nuclear spins and the detection of motional information are usually achieved by utilizing the atomic spins of alkali atoms. The parameters of the atomic spins are mainly evaluated by the relaxation time. Relaxation time is very important and can influence signal-to-noise ratio, dynamic range, start time, and other gyroscope parameters. Therefore, its accurate measurement is critical in the study of NMRG performance. In this study, we evaluate a variety of methods to measure the transverse and longitudinal relaxation times. First we examine the free-induction-decay method, which is the industry standard for measuring spin relaxation time. Second we investigate the improved free-induction-decay, fitting-ratio, and magnetic-resonance-broadening- fitting methods for measuring the transverse relaxation time, and the flipped polarization method for measuring the longitudinal relaxation time. By changing the experimental conditions, we obtain the longitudinal relaxation time using the flipped polarization method under a variety of conditions. Finally, by comparing these measurement methods, we propose the best measurement methods under different conditions.
Improved dynamical scaling analysis using the kernel method for nonequilibrium relaxation.
Echinaka, Yuki; Ozeki, Yukiyasu
2016-10-01
The dynamical scaling analysis for the Kosterlitz-Thouless transition in the nonequilibrium relaxation method is improved by the use of Bayesian statistics and the kernel method. This allows data to be fitted to a scaling function without using any parametric model function, which makes the results more reliable and reproducible and enables automatic and faster parameter estimation. Applying this method, the bootstrap method is introduced and a numerical discrimination for the transition type is proposed.
Xu, Bin; Li, Haiyue; Zhang, Yanhang
2013-01-01
This study aims to provide understanding of the macroscopic viscoelastic behavior of collagen matrices through studying the relaxation time distribution spectrum obtained from stress relaxation tests. Hydrated collagen gel and dehydrated collagen thin film was exploited as two different hydration levels of collagen matrices. Genipin solution was used to induce crosslinking in collagen matrices. Biaxial stress relaxation tests were performed to characterize the viscoelastic behavior of collagen matrices. The rate of stress relaxation of both hydrated and dehydrated collagen matrices shows a linear initial stress level dependency. Increased crosslinking reduces viscosity in collagen gel, but the effect is negligible for thin film. Relaxation time distribution spectrum was obtained from the stress relaxation data by inverse Laplace transform. For most of the collagen matrices, three peaks at the short (0.3s ~1 s), medium (3s ~90 s), and long relaxation time (> 200 s) were observed in the continuous spectrum, which likely corresponds to relaxation mechanisms involve fiber, inter-fibril, and fibril sliding. Splitting of the middle peak was observed at higher initial stress levels suggesting increased structural heterogeneity at the fibril level with mechanical loading. The intensity of the long-term peaks increases with higher initial stress levels indicating the engagement of collagen fibrils at higher levels of tissue strain.
NASA Astrophysics Data System (ADS)
Tomadakis, Manolis M.; Robertson, Teri J.
2005-03-01
Computer simulation results are presented for the mean survival time, principal relaxation time, mean pore size, and mean square pore size, for random porous structures consisting of parallel nonoverlapping or partially overlapping fibers. The numerical procedure is based on a discrete step-by-step random walk mechanism simulating the Brownian diffusion trajectories of molecules in the porous media. Numerical results on the viscous permeability of these structures are computed with a method based on electrical conduction principles and compared to a variational bound derived from the mean survival time. The results show that nonoverlapping fiber structures exhibit lower values of the dimensionless mean survival time, principal relaxation time, mean pore size, and mean square pore size than randomly overlapping fiber structures of the same porosity, while partially overlapping fiber structures show behavior intermediate to those of the two extreme cases. The mean square pore size (second moment of the pore size distribution) is found to be a very good predictor of the mean survival time for non-, partially, and randomly overlapping fiber structures. Dimensionless groups representing the deviation of variational bounds from our simulation results vary in practically the same range as the corresponding values reported earlier for beds of spherical particles. A universal scaling expression of the literature relating the mean survival time to structural properties [S. Torquato and C. L. Y. Yeong, J. Chem. Phys. 106, 8814 (1997)] agrees very well with our results for all examined fiber structures, thus validated for the first time for porous media formed by partially overlapping particles. The permeability behavior of partially overlapping fiber structures resembles that of nonoverlapping fiber structures for flow parallel to the fibers, but not for transverse flow, where percolation phenomena prevail. The permeability results for beds of unidirectional partially
Tomadakis, Manolis M; Robertson, Teri J
2005-03-01
Computer simulation results are presented for the mean survival time, principal relaxation time, mean pore size, and mean square pore size, for random porous structures consisting of parallel nonoverlapping or partially overlapping fibers. The numerical procedure is based on a discrete step-by-step random walk mechanism simulating the Brownian diffusion trajectories of molecules in the porous media. Numerical results on the viscous permeability of these structures are computed with a method based on electrical conduction principles and compared to a variational bound derived from the mean survival time. The results show that nonoverlapping fiber structures exhibit lower values of the dimensionless mean survival time, principal relaxation time, mean pore size, and mean square pore size than randomly overlapping fiber structures of the same porosity, while partially overlapping fiber structures show behavior intermediate to those of the two extreme cases. The mean square pore size (second moment of the pore size distribution) is found to be a very good predictor of the mean survival time for non-, partially, and randomly overlapping fiber structures. Dimensionless groups representing the deviation of variational bounds from our simulation results vary in practically the same range as the corresponding values reported earlier for beds of spherical particles. A universal scaling expression of the literature relating the mean survival time to structural properties [S. Torquato and C. L. Y. Yeong, J. Chem. Phys. 106, 8814 (1997)] agrees very well with our results for all examined fiber structures, thus validated for the first time for porous media formed by partially overlapping particles. The permeability behavior of partially overlapping fiber structures resembles that of nonoverlapping fiber structures for flow parallel to the fibers, but not for transverse flow, where percolation phenomena prevail. The permeability results for beds of unidirectional partially
Universal scaling, dynamic fragility, segmental relaxation, and vitrification in polymer melts.
Saltzman, Erica J; Schweizer, Kenneth S
2004-07-22
Our theory of dynamic barriers, slow relaxation, and the glass transition of polymers melts is numerically applied using parameters relevant to real materials. The numerical results are found to be in qualitative agreement with all the approximate analytic expressions previously derived with quantitative differences on the order of approximately 20-30% or much less. The analytic prediction of a universal temperature dependence of the alpha relaxation time, and its intimate connection with the idea of a nearly universal crossover time, is established. Inter-relations between the breadth of the deeply supercooled regime, two definitions of the dynamic fragility, and the magnitude of the fast local Arrhenius process at the glass transition temperature are demonstrated and system-specific limitations identified. A quantitative application to segmental relaxation over 16 orders of magnitude in a polyvinylacetate melt yields encouraging results regarding the accuracy of the theory. The theoretical relaxation time results are well fit by multiple empirical forms (generally containing an assumed singular aspect) using parameters consistent with experimental studies. No physical significance is ascribed to this finding, but it does provide additional support for the temperature dependence of the alpha relaxation process predicted by the theory.
Large lateral photovoltaic effect with ultrafast relaxation time in SnSe/Si junction
NASA Astrophysics Data System (ADS)
Wang, Xianjie; Zhao, Xiaofeng; Hu, Chang; Zhang, Yang; Song, Bingqian; Zhang, Lingli; Liu, Weilong; Lv, Zhe; Zhang, Yu; Tang, Jinke; Sui, Yu; Song, Bo
2016-07-01
In this paper, we report a large lateral photovoltaic effect (LPE) with ultrafast relaxation time in SnSe/p-Si junctions. The LPE shows a linear dependence on the position of the laser spot, and the position sensitivity is as high as 250 mV mm-1. The optical response time and the relaxation time of the LPE are about 100 ns and 2 μs, respectively. The current-voltage curve on the surface of the SnSe film indicates the formation of an inversion layer at the SnSe/p-Si interface. Our results clearly suggest that most of the excited-electrons diffuse laterally in the inversion layer at the SnSe/p-Si interface, which results in a large LPE with ultrafast relaxation time. The high positional sensitivity and ultrafast relaxation time of the LPE make the SnSe/p-Si junction a promising candidate for a wide range of optoelectronic applications.
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.
Raman, Mekala R.; Shu, Yunhong; Lesnick, Timothy G.; Jack, Clifford R.
2016-01-01
Purpose Relaxation time constants are useful as markers of tissue properties. Imaging ex vivo tissue is done for research purposes; however, T1 relaxation time constants are altered by tissue fixation in a time‐dependent manner. This study investigates regional changes in T1 relaxation time constants in ex vivo brain tissue over 6 months of fixation. Methods Five ex vivo human brain hemispheres in 10% formalin were scanned over 6 months. Mean T1 relaxation time constants were measured in regions of interest (ROIs) representing gray matter (GM) and white matter (WM) regions and analyzed as a function of fixation time. Results Cortical GM ROIs had longer T1 relaxation time constants than WM ROIs; the thalamus had T1 relaxation time constants similar to those of WM ROIs. T1 relaxation time constants showed rapid shortening within the first 6 weeks after fixation followed by a slower rate of decline. Conclusion Both GM and WM T1 relaxation time constants of fixed brain tissue show rapid decline within the first 6 weeks after autopsy and slow by 6 months. This information is useful for optimizing MR imaging acquisition parameters according to fixation time for ex vivo brain imaging studies. Magn Reson Med 77:774–778, 2017. © 2016 The Authors Magnetic Resonance in Medicine published by Wiley Periodicals, Inc. on behalf of International Society for Magnetic Resonance in Medicine. This is an open access article under the terms of the Creative Commons Attribution‐NonCommercial‐NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non‐commercial and no modifications or adaptations are made. PMID:26888162
NASA Astrophysics Data System (ADS)
Garcia-Bernabé, 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 β and γ processes. The study of the evolution of these two fast processes with temperature in the time retardation spectra shows that the β absorption is swallowed by the α in the glass-liquid transition, the γ absorption being the only relaxation that remains operative in the liquid state. In heating, a temperature is reached at which the α absorption vanishes appearing the αγ relaxation. Two characteristics of α absorptions, decrease of the dielectric strength with increasing temperature and rather high activation energy, are displayed by the αγ process. Williams' ansatz seems to hold for these topologically complex macromolecules.
Garcia-Bernabé, 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.
Goncalves; Lopez De Haro M; Taguena-Martinez; Stinchcombe
2000-02-14
The dynamic critical exponent and the frequency and wave-vector dependent susceptibility of the kinetic Ising model on an alternating isotopic chain with Glauber dynamics are examined. The analysis provides a connection between a microscopic model and the Nagel scaling curve originally proposed to describe dielectric susceptibility measurements of several glass-forming liquids. While support is given to the hypothesis relating the Nagel scaling to multiple relaxation processes, it is also found that the scaling function may exhibit plateau regions and does not hold for all temperatures.
NASA Astrophysics Data System (ADS)
Kikuchi, Yuta; Tsumura, Kyosuke; Kunihiro, Teiji
2016-05-01
We give a quantitative analysis of the dynamical properties of fermionic cold atomic gases in normal phase, such as the shear viscosity, heat conductivity, and viscous relaxation times, using the novel microscopic expressions derived by the renormalization group (RG) method, where the Boltzmann equation is faithfully solved to extract the hydrodynamics without recourse to any ansatz. In particular, we examine the quantum statistical effects, temperature dependence, and scattering-length dependence of the transport coefficients and the viscous relaxation times. The numerical calculation shows that the relation τπ = η / P, which is derived in the relaxation-time approximation (RTA) and is used in most of the literature, turns out to be satisfied quite well, while the similar relation for the viscous relaxation time τJ of the heat conductivity is satisfied only approximately with a considerable error.
Multi-scales nuclear spin relaxation of liquids in porous media
NASA Astrophysics Data System (ADS)
Korb, Jean-Pierre
2010-03-01
The magnetic field dependence of the nuclear spin-lattice relaxation rate 1/T(ω) is a rich source of dynamical information for characterizing the molecular dynamics of liquids in confined environments. Varying the magnetic field changes the Larmor frequency ω, and thus the fluctuations to which the nuclear spin relaxation is sensitive. Moreover, this method permits a more complete characterization of the dynamics than the usual measurements as a function of temperature at fixed magnetic field strength, because many common solvent liquids have phase transitions that may alter significantly the character of the dynamics over the temperature range usually studied. Further, the magnetic field dependence of the spin-lattice relaxation rate, 1/T(ω), provides a good test of the theories that relate the measurement to the microdynamical behavior of the liquid. This is especially true in spatially confined systems where the effects of reduced dimensionality may force more frequent reencounters of the studied proton spin-bearing molecules with paramagnetic impurities at the pore surfaces that may alter the correlation functions that enter the relaxation equations in a fundamental way. We show by low field NMR relaxation that changing the amount of surface paramagnetic impurities leads to striking different pore-size dependences of the relaxation times T and T of liquids in pores. Here, we focus mainly on high surface area porous materials including calibrated porous silica glasses, granular packings, heterogeneous catalytic materials, cement-based materials and natural porous materials such as clay minerals and rocks. Recent highlights NMR relaxation works are reviewed for these porous materials, like continuous characterization of the evolving microstructure of various cementitious materials and measurement of wettability in reservoir carbonate rocks. Although, the recent applications of 2-dimensional T-T and T-z-store-T correlation experiments for characterization of
Probing the Nuclear Spin-Lattice Relaxation Time at the Nanoscale
NASA Astrophysics Data System (ADS)
Wagenaar, J. J. T.; den Haan, A. M. J.; de Voogd, J. M.; Bossoni, L.; de Jong, T. A.; de Wit, M.; Bastiaans, K. M.; Thoen, D. J.; Endo, A.; Klapwijk, T. M.; Zaanen, J.; Oosterkamp, T. H.
2016-07-01
Nuclear spin-lattice relaxation times are measured on copper using magnetic-resonance force microscopy performed at temperatures down to 42 mK. The low temperature is verified by comparison with the Korringa relation. Measuring spin-lattice relaxation times locally at very low temperatures opens up the possibility to measure the magnetic properties of inhomogeneous electron systems realized in oxide interfaces, topological insulators, and other strongly correlated electron systems such as high-Tc superconductors.
Role of relaxation and time-dependent formation of x-ray spectra
NASA Astrophysics Data System (ADS)
Privalov, Timofei; Gel'mukhanov, Faris; Ågren, Hans
2001-10-01
A fundamental problem of x-ray spectroscopy is the role of relaxation of the electronic subsystem in the field of the transient core hole. The main intention of the present study is to explore the dynamics due to core-hole relaxation in the whole time domain, and to find out how it is manifested in finite molecular systems in comparison with solids. A technique is developed based on a reduction of the Noziéres-De Dominicis equation to a set of linear algebraic equations. The developed time-dependent formalism is applied to a numerical investigation of a one-dimensional tight-binding model. The formation of the x-ray profiles is explored on the real time scale, and the role of interaction with the core hole, band filling, and the final-state rule are investigated for systems of different size. The formation of spectra of the infinite translational invariant system is studied by extensions of the finite systems. We found that the dynamics of finite systems, like molecules, differs qualitatively from solids: Contrary to the latter the time lapse of the Noziéres-De Dominicis domain for finite systems is squeezed between the inverse bandwidth and the revival time, which is proportional to the system size. For small molecules this means that there is no time for a ``Mahan-Noziéres-De Dominicis singularity'' to develop. Comparison with the strict solution of the Noziéres-De Dominicis equation shows that the adiabatic approximation describes x-ray absorption and emission considerably better than the fast approximation. This explains the suppression of the relaxation effects in x-ray emission of, e.g., gas phase and surface adsorbed molecules, but also that these effects are essential for the absorption case. There is still a quantitative distinction between the adiabatic approximation and the strict approach, which becomes more important for larger systems. Adopting the so-called finite state rule by von Barth and Grossman also for molecules, an almost complete
NASA Astrophysics Data System (ADS)
Rander, D. N.; Joshi, Y. S.; Kanse, K. S.; Kumbharkhane, A. C.
2016-01-01
The measurements of complex dielectric permittivity of xylitol-water mixtures have been carried out in the frequency range of 10 MHz-30 GHz using a time domain reflectometry technique. Measurements have been done at six temperatures from 0 to 25 °C and at different weight fractions of xylitol (0 < W X ≤ 0.7) in water. There are different models to explain the dielectric relaxation behaviour of binary mixtures, such as Debye, Cole-Cole or Cole-Davidson model. We have observed that the dielectric relaxation behaviour of binary mixtures of xylitol-water can be well described by Cole-Davidson model having an asymmetric distribution of relaxation times. The dielectric parameters such as static dielectric constant and relaxation time for the mixtures have been evaluated. The molecular interaction between xylitol and water molecules is discussed using the Kirkwood correlation factor ( g eff ) and thermodynamic parameter.
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.
Convergence methods on time scales
NASA Astrophysics Data System (ADS)
Turan, Ceylan; Duman, Oktay
2013-10-01
In this paper, we introduce the concepts of lacunary statistical convergence and strongly lacunary Cesàro summability of delta measurable functions on time scales and obtain some inclusion results between them. We also display some examples containing discrete and continuous cases.
NASA Astrophysics Data System (ADS)
Ntarlagiannis, D.; Ustra, A.; Slater, L. D.; Zhang, C.; Mendonça, C. A.
2015-12-01
In this work we present an alternative formulation of the Debye Decomposition (DD) of complex conductivity spectra, with a new set of parameters that are directly related to the continuous Debye relaxation model. The procedure determines the relaxation time distribution (RTD) and two frequency-independent parameters that modulate the induced polarization spectra. The distribution of relaxation times quantifies the contribution of each distinct relaxation process, which can in turn be associated with specific polarization processes and characterized in terms of electrochemical and interfacial parameters as derived from mechanistic models. Synthetic tests show that the procedure can successfully fit spectral induced polarization (SIP) data and accurately recover the RTD. The procedure was applied to different data sets, focusing on environmental applications. We focus on data of sand-clay mixtures artificially contaminated with toluene, and crude oil-contaminated sands experiencing biodegradation. The results identify characteristic relaxation times that can be associated with distinct polarization processes resulting from either the contaminant itself or transformations associated with biodegradation. The inversion results provide information regarding the relative strength and dominant relaxation time of these polarization processes.
Time-dependent Jahn-Teller problem: phonon-induced relaxation through conical intersection.
Pae, Kaja; Hizhnyakov, Vladimir
2014-12-21
A theoretical study of time-dependent dynamical Jahn-Teller effect in an impurity center in a solid is presented. We are considering the relaxation of excited states in the E⊗e-problem through the conical intersection of the potential energy. A strict quantum-mechanical treatment of vibronic interactions with both the main Jahn-Teller active vibration and the nontotally symmetric phonons causing the energy loss is given. The applied method enables us to calculate the time-dependence of the distribution function of the basic configurational coordinate. We have performed a series of numerical calculations allowing us, among other relaxation features, to visualise the details of the relaxation through the conical intersection. In particular, we elucidate how the Slonczewski quantization of the states in the conical intersection affects the relaxation.
Time-dependent Jahn-Teller problem: Phonon-induced relaxation through conical intersection
Pae, Kaja Hizhnyakov, Vladimir
2014-12-21
A theoretical study of time-dependent dynamical Jahn-Teller effect in an impurity center in a solid is presented. We are considering the relaxation of excited states in the E⊗e-problem through the conical intersection of the potential energy. A strict quantum-mechanical treatment of vibronic interactions with both the main Jahn-Teller active vibration and the nontotally symmetric phonons causing the energy loss is given. The applied method enables us to calculate the time-dependence of the distribution function of the basic configurational coordinate. We have performed a series of numerical calculations allowing us, among other relaxation features, to visualise the details of the relaxation through the conical intersection. In particular, we elucidate how the Slonczewski quantization of the states in the conical intersection affects the relaxation.
Atomic time scales and pulsars
NASA Astrophysics Data System (ADS)
Petit, G.
2014-12-01
I review the atomic time scales generated by the BIPM, International Atomic Time TAI and the realization of Terrestrial Time TT(BIPM). TT(BIPM) is shown to be now accurate to within a few 10..16 in relative frequency and the performances of TAI and TT(BIPM) are compared. Millisecond pulsars have a very regular period of rotation and data from several pulsars may be used to realize an ensemble pulsar timescale. It is shown that a pulsar timescale may detect past instabilities in TAI. However TT(BIPM) is much more stable than TAI and should be used as a reference in pulsar analysis. Since the beginning of regular millisecond pulsar observations in the 1980s, primary standards and atomic time have gained one order of magnitude in accuracy every ~ 12 years, and this trend should continue for some time.
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
Globus, Tatiana; Sizov, Igor; Gelmont, Boris
2014-01-01
Hydrogen bonds (H-bonds) in biological macromolecules are important for the molecular structure and functions. Since interactions via hydrogen bonds are weaker than covalent bonds, it can be expected that atomic movements involving H-bonds have low frequency vibrational modes. Sub-Terahertz (sub-THz) vibrational spectroscopy that combines measurements with molecular dynamics (MD) computational prediction has been demonstrated as a promising approach for biological molecule characterization. Multiple resonance absorption lines have been reported. The knowledge of relaxation times of atomic oscillations is critical for the successful application of THz spectroscopy for hydrogen bond characterization. The purpose of this work is to use atomic oscillations in the 0.35-0.7 THz range, found from molecular dynamic (MD) simulations of E.coli thioredoxin (2TRX), to study relaxation dynamics of two intra-molecular H-bonds, OH-N and OH-C. Two different complimentary techniques are used in this study, one is the analysis of the statistical distribution of relaxation time and dissipation factor values relevant to low frequency oscillations, and the second is the analysis of the autocorrelation function of low frequency quasi-periodic movements. By studying hydrogen bond atomic displacements, it was found that the atoms are involved in a number of collective oscillations, which are characterized by different relaxation time scales ranging from 2-3 ps to more than 150 ps. The existence of long lasting relaxation processes opens the possibility to directly observe and study H-bond vibrational modes in sub-THz absorption spectra of bio-molecules if measured with an appropriate spectral resolution. The results of measurements using a recently developed frequency domain spectroscopic sensor with a spectral resolution of 1 GHz confirm the MD analysis.
Menger, Marcus; Eckstein, Fritz; Porschke, Dietmar
2000-01-01
The dynamics of a hammerhead ribozyme was analyzed by measurements of fluorescence-detected temperature jump relaxation. The ribozyme was substituted at different positions by 2-aminopurine (2-AP) as fluorescence indicator; these substitutions do not inhibit catalysis. The general shape of relaxation curves reported from different positions of the ribozyme is very similar: a fast decrease of fluorescence, mainly due to physical quenching, is followed by a slower increase of fluorescence due to conformational relaxation. In most cases at least three relaxation time constants in the time range from a few microseconds to ~200 ms are required for fitting. Although the relaxation at different positions of the ribozyme is similar in general, suggesting a global type of ribozyme dynamics, a close examination reveals differences, indicating an individual local response. For example, 2-AP in a tetraloop reports mainly the local loop dynamics known from isolated loops, whereas 2-AP located at the core, e.g. at the cleavage site or its vicinity, also reports relatively large amplitudes of slower components of the ribozyme dynamics. A variant with an A→G substitution in domain II, resulting in an inactive form, leads to the appearance of a particularly slow relaxation process (τ ≈200 ms). Addition of Mg2+ ions induces a reduction of amplitudes and in most cases a general increase of time constants. Differences between the hammerhead variants are clearly demonstrated by subtraction of relaxation curves recorded under corresponding conditions. The changes induced in the relaxation response by Mg2+ are very similar to those induced by Ca2+. The relaxation data do not provide any evidence for formation of Mg2+-inner sphere complexes in hammerhead ribozymes, because a Mg2+-specific relaxation effect was not visible. However, a Mg2+-specific effect was found for a dodeca-riboadenylate substituted with 2-AP, showing that the fluorescence of 2-AP is able to indicate inner sphere
Menger, M; Eckstein, F; Porschke, D
2000-11-15
The dynamics of a hammerhead ribozyme was analyzed by measurements of fluorescence-detected temperature jump relaxation. The ribozyme was substituted at different positions by 2-aminopurine (2-AP) as fluorescence indicator; these substitutions do not inhibit catalysis. The general shape of relaxation curves reported from different positions of the ribozyme is very similar: a fast decrease of fluorescence, mainly due to physical quenching, is followed by a slower increase of fluorescence due to conformational relaxation. In most cases at least three relaxation time constants in the time range from a few microseconds to approximately 200 ms are required for fitting. Although the relaxation at different positions of the ribozyme is similar in general, suggesting a global type of ribozyme dynamics, a close examination reveals differences, indicating an individual local response. For example, 2-AP in a tetraloop reports mainly the local loop dynamics known from isolated loops, whereas 2-AP located at the core, e.g. at the cleavage site or its vicinity, also reports relatively large amplitudes of slower components of the ribozyme dynamics. A variant with an A-->G substitution in domain II, resulting in an inactive form, leads to the appearance of a particularly slow relaxation process (tau approximately 200 ms). Addition of Mg(2+) ions induces a reduction of amplitudes and in most cases a general increase of time constants. Differences between the hammerhead variants are clearly demonstrated by subtraction of relaxation curves recorded under corresponding conditions. The changes induced in the relaxation response by Mg(2+) are very similar to those induced by Ca(2+). The relaxation data do not provide any evidence for formation of Mg(2+)-inner sphere complexes in hammerhead ribozymes, because a Mg(2+)-specific relaxation effect was not visible. However, a Mg(2+)-specific effect was found for a dodeca-riboadenylate substituted with 2-AP, showing that the fluorescence of 2
Dielectric relaxation time of bulk water at 136-140 K, background loss and crystallization effects
NASA Astrophysics Data System (ADS)
Johari, G. P.
2005-04-01
Dielectric relaxation time, τ, of ultraviscous bulk water has been determined by analyzing its loss tangent, tanδ, data, which had been measured on heating the vapor-deposited amorphous solid water and hyperquenched glassy water in our earlier studies. [Johari, Hallbrucker, and Mayer, J. Chem. Phys. 95, 2955 (1991); 97, 5851 (1992)]. As for glasses and liquids generally, the measured tanδ of water is the sum of a frequency-independent background loss and a frequency-dependent relaxational loss. A two-frequency method is provided for determining the background loss and used for obtaining the relaxational part of tanδ. After considering the structural relaxation and crystal-nuclei growth effects, τ for water has been determined. At 136±1K, it is 2.5±0.6s when a single relaxation time is (untenably) assumed, and 42±14s when a distribution of relaxation times, a characteristic of viscous liquids, is assumed, with Davidson-Cole distribution parameter of 0.75. Structural relaxation time of ˜70s for water at 136K, which was originally estimated from the DSC endotherm [Johari, Hallbrucker, and Mayer, Nature (London) 330, 552 (1987)], has been revised to ˜33s. Temperature dependence of τ could not be determined because ultraviscous water crystallizes too rapidly to cubic ice containing stacking faults and intergranular water. The study demonstrates that water is a liquid over the 136-155K range, thus removing the basis for a recent contention on its state.
Time and Temperature Dependence of Viscoelastic Stress Relaxation in Gold and Gold Alloy Thin Films
NASA Astrophysics Data System (ADS)
Mongkolsuttirat, Kittisun
Radio frequency (RF) switches based on capacitive MicroElectroMechanical System (MEMS) devices have been proposed as replacements for traditional solid-state field effect transistor (FET) devices. However, one of the limitations of the existing capacitive switch designs is long-term reliability. Failure is generally attributed to electrical charging in the capacitor's dielectric layer that creates an attractive electrostatic force between a moving upper capacitor plate (a metal membrane) and the dielectric. This acts as an attractive stiction force between them that may cause the switch to stay permanently in the closed state. The force that is responsible for opening the switch is the elastic restoring force due to stress in the film membrane. If the restoring force decreases over time due to stress relaxation, the tendency for stiction failure behavior will increase. Au films have been shown to exhibit stress relaxation even at room temperature. The stress relaxation observed is a type of viscoelastic behavior that is more significant in thin metal films than in bulk materials. Metal films with a high relaxation resistance would have a lower probability of device failure due to stress relaxation. It has been shown that solid solution and oxide dispersion can strengthen a material without unacceptable decreases in electrical conductivity. In this study, the viscoelastic behavior of Au, AuV solid solution and AuV2O5 dispersion created by DC magnetron sputtering are investigated using the gas pressure bulge testing technique in the temperature range from 20 to 80°C. The effectiveness of the two strengthening approaches is compared with the pure Au in terms of relaxation modulus and 3 hour modulus decay. The time dependent relaxation curves can be fitted very well with a four-term Prony series model. From the temperature dependence of the terms of the series, activation energies have been deduced to identify the possible dominant relaxation mechanism. The measured
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.
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.
Strange scaling and relaxation of finite-size fluctuation in thermal equilibrium
NASA Astrophysics Data System (ADS)
Yamaguchi, Yoshiyuki Y.
2016-07-01
We numerically exhibit two strange phenomena of finite-size fluctuation in thermal equilibrium of a paradigmatic long-range interacting system having a second-order phase transition. One is a nonclassical finite-size scaling at the critical point, which differs from the prediction by statistical mechanics. With the aid of this strange scaling, the scaling theory for infinite-range models conjectures the nonclassical values of critical exponents for the correlation length. The other is relaxation of the fluctuation strength from one level to another in spite of being in thermal equilibrium. A scenario is proposed to explain these phenomena from the viewpoint of the Casimir invariants and their nonexactness in finite-size systems, where the Casimir invariants are conserved in the Vlasov dynamics describing the long-range interacting systems in the limit of large population. This scenario suggests appearance of the reported phenomena in a wide class of isolated long-range interacting systems.
Deconfinement phase transition in an expanding quark system in the relaxation time approximation
NASA Astrophysics Data System (ADS)
Yang, Zhenwei; Zhuang, Pengfei
2004-03-01
We investigated the effects of nonequilibrium and collision terms on the deconfinement phase transition of an expanding quark system in Friedberg-Lee model in relaxation time approximation. By calculating the effective quark potential, the critical temperature of the phase transition is dominated by the mean field, while the collisions among quarks and mesons change the time structure of the phase transition significantly.
Option pricing during post-crash relaxation times
NASA Astrophysics Data System (ADS)
Dibeh, Ghassan; Harmanani, Haidar M.
2007-07-01
This paper presents a model for option pricing in markets that experience financial crashes. The stochastic differential equation (SDE) of stock price dynamics is coupled to a post-crash market index. The resultant SDE is shown to have stock price and time dependent volatility. The partial differential equation (PDE) for call prices is derived using risk-neutral pricing. European call prices are then estimated using Monte Carlo and finite difference methods. Results of the model show that call option prices after the crash are systematically less than those predicted by the Black-Scholes model. This is a result of the effect of non-constant volatility of the model that causes a volatility skew.
van Gemert, M J; Lucassen, G W; Welch, A J
1996-08-01
The thermal response of a semi-infinite medium in air, irradiated by laser light in a cylindrical geometry, cannot accurately be approximately by single radial and axial time constants for heat conduction. This report presents an analytical analysis of hear conduction where the thermal response is expressed in terms of distributions over radial and axial time constants. The source term for heat production is written as the product of a Gaussian shaped radial term and an exponentially shaped axial term. The two terms are expanded in integrals over eigenfunctions of the radial and axial parts of the Laplace heat conduction operator. The result is a double integral over the coupled distributions of the two time constants to compute the temperature rise as a function of time and of axial and radial positions. The distribution of axial time constants is a homogeneous slowly decreasing function of spatial frequency (v) indicating that one single axial time constant cannot reasonably characterize axial heat conduction. The distribution of radial time constants is a function centred around a distinguished maximum in the spatial frequency (lambda) close to the single radial time constant value used previously. This suggests that one radial time constant to characterize radial heat conduction may be a useful concept. Special cases have been evaluated analytically, such as short and long irradiation times, axial or radial heat conduction (shallow or deep penetrating laser beams) and, especially, thermal relaxation (cooling) of the tissue. For shallow penetrating laser beams the asymptotic cooling rate is confirmed to be proportional to [(t)0.5-(t-tL)0.5] which approaches 1/t0.5 for t > tL, where t is the time and tL is the laser pulse duration. For deep penetrating beams this is proportional to 1/(t-tL). For intermediate penetration, i.e. penetration depths about equal to spot size diameters, this is proportional to 1/(t-tL)1.5. The double integral has been evaluated
Some applications of the Lagrange identity in thermoelasticity with one relaxation time
Chirita, S.
1988-01-01
Consideration is given to the uniqueness and continuous data dependence questions appropriate to the fundamental initial/boundary-value problems in thermoelasticity with one relaxation time. On the basis of the Lagrange identity, results are obtained for bounded domains as well as for exterior unbounded domains, without definiteness conditions on the thermoelastic coefficients other than the positiveness of the product between the thermal conductivity and the relaxation time. The applicability of the Lagrange identity in order to obtain some reciprocal theorems is outlined. 24 references.
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 unified model of hysteresis and long-time relaxation in heterogeneous materials
NASA Astrophysics Data System (ADS)
Lebedev, A. V.; Ostrovsky, L. A.
2014-09-01
A physical model of stress-strain dynamics and long-time relaxation (slow time) in structured media is proposed. The model is based on the analysis of inter-grain contacts and the resulting surface force potential with a barrier. The result is a unified description of the classical acoustic nonlinearity, stress-strain hysteresis, and logarithmic relaxation law for sound velocity (and, hence, for the frequency of nonlinear resonance in samples of structured materials). Estimates of a characteristic volume of interacting contacts give close values for the variety of consolidated materials. For weak (linear) testing waves, the logarithmic relaxation occurs if a classical quadratic nonlinearity is added to the stress-strain relation.
Fragile-strong fluid crossover and universal relaxation times in a confined hard-disk fluid.
Yamchi, Mahdi Zaeifi; Ashwin, S S; Bowles, Richard K
2012-11-30
We show that a system of hard disks confined to a narrow channel exhibits a fragile-strong fluid crossover located at the maximum of the isobaric heat capacity and that the relaxation times for different channel widths fall onto a single master curve when rescaled by the relaxation times and temperatures of the crossover. Calculations of the configurational entropy and the inherent structure equation of state find that the crossover is related to properties of the jamming landscape for the model but that the Adam-Gibbs relation does not predict the relaxation behavior. We also show that a facilitated dynamics description of the system, where kinetically excited regions are identified with local packing arrangements of the disks, successfully describes the fragile-strong crossover.
Separation of Time Scales in a Quantum Newton's Cradle.
van den Berg, R; Wouters, B; Eliëns, S; De Nardis, J; Konik, R M; Caux, J-S
2016-06-03
We provide detailed modeling of the Bragg pulse used in quantum Newton's-cradle-like settings or in Bragg spectroscopy experiments for strongly repulsive bosons in one dimension. We reconstruct the postpulse time evolution and study the time-dependent local density profile and momentum distribution by a combination of exact techniques. We further provide a variety of results for finite interaction strengths using a time-dependent Hartree-Fock analysis and bosonization-refermionization techniques. Our results display a clear separation of time scales between rapid and trap-insensitive relaxation immediately after the pulse, followed by slow in-trap periodic behavior.
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 (Aβ) 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 Aβ 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 θu-4/3, where θu 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 Aβ was stabilized by the attachment of the positive Lys28 side chain to the negative phosphate of PC or 3β 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)
Suanda, Sutara H.; Kumar, Nirnimesh; Miller, Arthur J.; Di Lorenzo, Emanuele; Haas, Kevin; Cai, Donghua; Edwards, Christopher A.; Washburn, Libe; Fewings, Melanie R.; Torres, Rachel; Feddersen, Falk
2016-10-01
In upwelling regions, wind relaxations lead to poleward propagating warm water plumes that are important to coastal ecosystems. The coastal ocean response to wind relaxation around Pt. Conception, CA is simulated with a Regional Ocean Model (ROMS) forced by realistic surface and lateral boundary conditions including tidal processes. The model reproduces well the statistics of observed subtidal water column temperature and velocity at both outer and inner-shelf mooring locations throughout the study. A poleward-propagating plume of Southern California Bight water that increases shelf water temperatures by ≈ 5°C is also reproduced. Modeled plume propagation speed, spatial scales, and flow structure are consistent with a theoretical scaling for coastal buoyant plumes with both surface-trapped and slope-controlled dynamics. Plume momentum balances are distinct between the offshore (>30 m depth) region where the plume is surface-trapped, and onshore of the 30 m isobath (within 5 km from shore) where the plume water mass extends to the bottom and is slope controlled. In the onshore region, bottom stress is important in the alongshore momentum equation and generates vertical vorticity that is an order of magnitude larger than the vorticity in the plume core. Numerical experiments without tidal forcing show that modeled surface temperatures are biased 0.5°C high, potentially affecting plume propagation distance and persistence.
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.
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 α-relaxation times deep in the glassy state of the pharmaceutical, Telmisartan. Normally, deep in the glassy state τα is so long that it cannot be measured but τβ, which is usually much shorter, can be directly determined. The method basically takes advantage of the connection between the α-relaxation and the secondary β-relaxation of the Johari-Goldstein kind, including a relation between their relaxation times τα and τβ, respectively. Thus, τα of Telmisartan were determined by monitoring the change of the dielectric β-loss, ɛ'', with physical aging time at temperatures well below the vitrification temperature. The values of τα were compared with those expected by the coupling model (CM). Unequivocal comparison cannot be made in the case of Telmisartan because its β-loss peak is extremely broad, and the CM predicts only an order of magnitude agreement between the primitive relaxation frequency and the β-peak frequency. We also made an attempt to analyze all isothermal and aging susceptibility data after transformation into the electric modulus representation. The τα 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 βKWW - M = 0.51 in the electric modulus representation gives more precise fits to the aging data than in the susceptibility representation with βKWW = 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.
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.
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
Seo, Mirinae; Jahng, Geon-Ho; Sohn, Yu-Mee; Rhee, Sun Jung; Oh, Jang-Hoon; Won, Kyu-Yeoun
2017-01-01
Objective The purpose of this study was to estimate the T2* relaxation time in breast cancer, and to evaluate the association between the T2* value with clinical-imaging-pathological features of breast cancer. Materials and Methods Between January 2011 and July 2013, 107 consecutive women with 107 breast cancers underwent multi-echo T2*-weighted imaging on a 3T clinical magnetic resonance imaging system. The Student's t test and one-way analysis of variance were used to compare the T2* values of cancer for different groups, based on the clinical-imaging-pathological features. In addition, multiple linear regression analysis was performed to find independent predictive factors associated with the T2* values. Results Of the 107 breast cancers, 92 were invasive and 15 were ductal carcinoma in situ (DCIS). The mean T2* value of invasive cancers was significantly longer than that of DCIS (p = 0.029). Signal intensity on T2-weighted imaging (T2WI) and histologic grade of invasive breast cancers showed significant correlation with T2* relaxation time in univariate and multivariate analysis. Breast cancer groups with higher signal intensity on T2WI showed longer T2* relaxation time (p = 0.005). Cancer groups with higher histologic grade showed longer T2* relaxation time (p = 0.017). Conclusion The T2* value is significantly longer in invasive cancer than in DCIS. In invasive cancers, T2* relaxation time is significantly longer in higher histologic grades and high signal intensity on T2WI. Based on these preliminary data, quantitative T2* mapping has the potential to be useful in the characterization of breast cancer. PMID:28096732
Nelson, Krysta R.; Stevens, Shanlee M.; McLoon, Linda K.
2016-01-01
Purpose We tested the hypothesis that short-term treatment with brain derived neurotrophic factor (BDNF) would alter the contractile characteristics of rabbit extraocular muscle (EOM). Methods One week after injections of BDNF in adult rabbit superior rectus muscles, twitch properties were determined in treated and control muscles in vitro. Muscles were also examined for changes in mean cross-sectional areas, neuromuscular junction size, and percent of myofibers expressing specific myosin heavy chain isoforms, and sarcoendoplasmic reticulum calcium ATPases (SERCA) 1 and 2. Results Brain derived neurotrophic factor–treated muscles had prolonged relaxation times compared with control muscles. Time to 50% relaxation, time to 100% relaxation, and maximum rate of relaxation were increased by 24%, 27%, and 25%, respectively. No significant differences were seen in time to peak force, twitch force, or maximum rate of contraction. Brain derived neurotrophic factor treatment significantly increased mean cross-sectional areas of slow twitch and tonic myofibers, with increased areas ranging from 54% to 146%. Brain derived neurotrophic factor also resulted in an increased percentage of slow twitch myofibers in the orbital layers, ranging from 54% to 77%, and slow-tonic myofibers, ranging from 44% to 62%. No significant changes were seen SERCA1 or 2 expression or in neuromuscular junction size. Conclusions Short-term treatment with BDNF significantly prolonged the duration and rate of relaxation time and increased expression of both slow-twitch and slow-tonic myosin-expressing myofibers without changes in neuromuscular junctions or SERCA expression. The changes induced by BDNF treatment might have potential therapeutic value in dampening/reducing uncontrolled eye oscillations in nystagmus. PMID:27802489
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 β 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 β 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 β-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 β-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.
Relaxation of terrace-width distributions: Physical information from Fokker Planck time
NASA Astrophysics Data System (ADS)
Hamouda, Ajmi BH.; Pimpinelli, Alberto; Einstein, T. L.
2008-12-01
Recently some of us have constructed a Fokker-Planck formalism to describe the equilibration of the terrace-width distribution of a vicinal surface from an arbitrary initial configuration. However, the meaning of the associated relaxation time, related to the strength of the random noise in the underlying Langevin equation, was rather unclear. Here we present a set of careful kinetic Monte Carlo simulations that demonstrate convincingly that the time constant shows activated behavior with a barrier that has a physically plausible dependence on the energies of the governing microscopic model. Remarkably, the rate-limiting step for relaxation in the far-from-equilibrium regime is the generation of kink-antikink pairs, involving the breaking of three lateral bonds on a cubic {0 0 1} surface, in contrast to the processes breaking two bonds that dominate equilibrium fluctuations. After an initial regime, the Fokker-Planck time at least semiquantitatively tracks the actual physical time.
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.
Measurement of Ligand–Target Residence Times by 1H Relaxation Dispersion NMR Spectroscopy
2016-01-01
A ligand-observed 1H NMR relaxation experiment is introduced for measuring the binding kinetics of low-molecular-weight compounds to their biomolecular targets. We show that this approach, which does not require any isotope labeling, is applicable to ligand–target systems involving proteins and nucleic acids of variable molecular size. The experiment is particularly useful for the systematic investigation of low affinity molecules with residence times in the micro- to millisecond time regime. PMID:27933946
Godefroy, Sophie; Korb, Jean-Pierre; Creamer, Lawrence K; Watkinson, Philip J; Callaghan, Paul T
2003-11-15
Most cheeses can be considered as solid emulsions of milk fat in a matrix of water and proteins. Regions of each of the phases can be liquid during processing and maturation. Identifying these regions and monitoring changes in them is important as a prelude to controlling the structure of the final cheese. We concentrate on the behavior of water in the vicinity of proteins as a function of cheese aging. Our method utilizes nuclear magnetic relaxation dispersion (NMRD) associated with the frequency dependence of water spin-lattice relaxation rates using the field cycling NMR technique. This method provides insight into the dynamical behavior of water molecules on a very large time scale. Moreover, we can distinguish between molecular motion in bulk and motion in the vicinity of a source of relaxation, such as proteins. A fit of our dispersion data using a theory developed by J.-P. Korb and R.G. Bryant (J. Chem. Phys. 115 (2001) 23) allowed us to determine the degree of hydration of proteins as a function of aging. In particular, we find that protein hydration increases with ripening.
Determination of relaxation modulus of time-dependent materials using neural networks
NASA Astrophysics Data System (ADS)
Aulova, Alexandra; Govekar, Edvard; Emri, Igor
2016-10-01
Health monitoring systems for plastic based structures require the capability of real time tracking of changes in response to the time-dependent behavior of polymer based structures. The paper proposes artificial neural networks as a tool of solving inverse problem appearing within time-dependent material characterization, since the conventional methods are computationally demanding and cannot operate in the real time mode. Abilities of a Multilayer Perceptron (MLP) and a Radial Basis Function Neural Network (RBFN) to solve ill-posed inverse problems on an example of determination of a time-dependent relaxation modulus curve segment from constant strain rate tensile test data are investigated. The required modeling data composed of strain rate, tensile and related relaxation modulus were generated using existing closed-form solution. Several neural networks topologies were tested with respect to the structure of input data, and their performance was compared to an exponential fitting technique. Selected optimal topologies of MLP and RBFN were tested for generalization and robustness on noisy data; performance of all the modeling methods with respect to the number of data points in the input vector was analyzed as well. It was shown that MLP and RBFN are capable of solving inverse problems related to the determination of a time dependent relaxation modulus curve segment. Particular topologies demonstrate good generalization and robustness capabilities, where the topology of RBFN with data provided in parallel proved to be superior compared to other methods.
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.
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.
Fedorov, Dmitry V; Gradhand, Martin; Ostanin, Sergey; Maznichenko, Igor V; Ernst, Arthur; Fabian, Jaroslav; Mertig, Ingrid
2013-04-12
The effect of electron-impurity scattering on momentum and spin relaxation times in graphene is studied by means of relativistic ab initio calculations. Assuming carbon and silicon adatoms as natural impurities in graphene, we are able to simulate fast spin relaxation observed experimentally. We investigate the dependence of the relaxation times on the impurity position and demonstrate that C or Si adatoms act as real-space spin hot spots inducing spin-flip rates about 5 orders of magnitude larger than those of in-plane impurities. This fact confirms the hypothesis that the adatom-induced spin-orbit coupling leads to fast spin relaxation in graphene.
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.
Using Dielectric Relaxation Spectroscopy to Characterize the Glass Transition Time of Polydextrose.
Buehler, Martin G; Kindle, Michael L; Carter, Brady P
2015-06-01
Dielectric relaxation spectroscopy was used to characterize the glass transition time, tg , of polydextrose, where the glass transition temperature, Tg , and water activity, aw (relative humidity), were held constant during polydextrose relaxation. The tg was determined from a shift in the peak frequency of the imaginary capacitance spectrum with time. It was found that when the peak frequency reaches 30 mHz, polydextrose undergoes glass transition. Glass transition time, tg , is the time for polydextrose to undergo glass transition at a specific Tg and aw . Results lead to a modified state diagram, where Tg is depressed with increasing aw . This curve forms a boundary: (a) below the boundary, polydextrose does not undergo glass transition and (b) above the boundary, polydextrose rapidly undergoes glass transition. As the boundary curve is specified by a tg value, it can assist in the selection of storage conditions. An important point on the boundary curve is at aw = 0, where Tg0 = 115 °C. The methodology can also be used to calculate the stress-relaxation viscosity of polydextrose as a function of Tg and aw , which is important when characterizing the flow properties of polydextrose initially in powder form.
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.
The generalized Phillips-Twomey method for NMR relaxation time inversion
NASA Astrophysics Data System (ADS)
Gao, Yang; Xiao, Lizhi; Zhang, Yi; Xie, Qingming
2016-10-01
The inversion of NMR relaxation time involves the Fredholm integral equation of the first kind. Due to its ill-posedness, numerical solutions to this type of equations are often found much less accurate and bear little resemblance to the true solution. There has been a strong interest in finding a well-posed method for this ill-posed problem since 1950s. In this paper, we prove the existence, the uniqueness, the stability and the convergence of the generalized Phillips-Twomey regularization method for solving this type of equations. Numerical simulations and core analyses arising from NMR transverse relaxation time inversion are conducted to show the effectiveness of the generalized Phillips-Twomey method. Both the simulation results and the core analyses agree well with the model and the realities.
Kasturi, S R; Chang, D C; Hazlewood, C F
1980-01-01
The anisotropy of the spin-lattice relaxation time (T1) and the spin-spin relaxation times (T2) of water protons in skeletal muscle tissue have been studied by the spin-echo technique. Both T1 and T2 have been measured for the water protons of the tibialis anterior muscle of mature male rats for theta = 0, 55, and 90 degrees, where theta is the orientation of the muscle fiber with respect to the static field. The anisotropy in T1 and T2 has been measured at temperatures of 28, -5 and -10 degrees C. No significant anisotropy was observed in the T1 of the tissue water, while an average anisotropy of approximately 5% was observed in T2 at room temperature. The average anisotropy of T2 at -5 and -10 degrees C was found to be approximately 2 and 1.3%, respectively. PMID:6266530
The generalized Phillips-Twomey method for NMR relaxation time inversion.
Gao, Yang; Xiao, Lizhi; Zhang, Yi; Xie, Qingming
2016-10-01
The inversion of NMR relaxation time involves the Fredholm integral equation of the first kind. Due to its ill-posedness, numerical solutions to this type of equations are often found much less accurate and bear little resemblance to the true solution. There has been a strong interest in finding a well-posed method for this ill-posed problem since 1950s. In this paper, we prove the existence, the uniqueness, the stability and the convergence of the generalized Phillips-Twomey regularization method for solving this type of equations. Numerical simulations and core analyses arising from NMR transverse relaxation time inversion are conducted to show the effectiveness of the generalized Phillips-Twomey method. Both the simulation results and the core analyses agree well with the model and the realities.
Wojnarowska, Z; Ngai, K L; Paluch, M
2014-05-07
Using broadband dielectric spectroscopy we investigate the changes in the conductivity relaxation times τσ 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 τσ(Tage,tage) can be directly measured at temperatures Tage below Tg for exceedingly long aging times tage till τσ(Tage,tage) has reached the equilibrium value τσ(eq)(Tage). The dependence of τσ(Tage,tage) on tage is well described by the stretched exponential function, τσ(Tage, tage) = Aexp[-((tage)/(τage(Tage)))(β)] + τσ(eq)(Tage), where β is a constant and τage(Tage) can be taken as the structural α-relaxation time of the equilibrium liquid at T = Tage. The value of τσ(eq)(Tage) obtained after 63 days long annealing of CP, deviates from the Vogel-Fulcher-Tammann-Hesse (VFTHσ) dependence of τσ(T) determined from data taken above Tg and extrapolated down to Tage. Concurrently, τage(Tage) also deviates from the Vogel-Fulcher-Tammann-Hesse (VFTHα) dependence. The results help to answer the longstanding question of whether the VFTH dependence of τσ(T) as well as the structural α-relaxation time τα(T) holds or not in the equilibrium liquid state far below Tg.
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 τσ 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 τσ(Tage,tage) can be directly measured at temperatures Tage below Tg for exceedingly long aging times tage till τσ(Tage,tage) has reached the equilibrium value τ _σ ^{eq} ( {T_{age} } ). The dependence of τσ(Tage,tage) on tage is well described by the stretched exponential function, τ _σ ( {T_{age},t_{age} } ) = Aexp[ { - ( {{t_{age} }/{τ _{age ( {T_{age} } )}}} )^β } ] + τ _σ ^{eq} ( {T_{age} } ), where β is a constant and τage(Tage) can be taken as the structural α-relaxation time of the equilibrium liquid at T = Tage. The value of τ _σ ^{eq} ( {T_{age} } ) obtained after 63 days long annealing of CP, deviates from the Vogel-Fulcher-Tammann-Hesse (VFTHσ) dependence of τσ(T) determined from data taken above Tg and extrapolated down to Tage. Concurrently, τage(Tage) also deviates from the Vogel-Fulcher-Tammann-Hesse (VFTHα) dependence. The results help to answer the longstanding question of whether the VFTH dependence of τσ(T) as well as the structural α-relaxation time τα(T) holds or not in the equilibrium liquid state far below Tg.
Viscosity, relaxation time, and dynamics within a model asphalt of larger molecules
NASA Astrophysics Data System (ADS)
Li, Derek D.; Greenfield, Michael L.
2014-01-01
The dynamics properties of a new "next generation" model asphalt system that represents SHRP AAA-1 asphalt using larger molecules than past models is studied using molecular simulation. The system contains 72 molecules distributed over 12 molecule types that range from nonpolar branched alkanes to polar resins and asphaltenes. Molecular weights range from 290 to 890 g/mol. All-atom molecular dynamics simulations conducted at six temperatures from 298.15 to 533.15 K provide a wealth of correlation data. The modified Kohlrausch-Williams-Watts equation was regressed to reorientation time correlation functions and extrapolated to calculate average rotational relaxation times for individual molecules. The rotational relaxation rate of molecules decreased significantly with increasing size and decreasing temperature. Translational self-diffusion coefficients followed an Arrhenius dependence. Similar activation energies of ˜42 kJ/mol were found for all 12 molecules in the model system, while diffusion prefactors spanned an order of magnitude. Viscosities calculated directly at 533.15 K and estimated at lower temperatures using the Debye-Stokes-Einstein relationship were consistent with experimental data for asphalts. The product of diffusion coefficient and rotational relaxation time showed only small changes with temperature above 358.15 K, indicating rotation and translation that couple self-consistently with viscosity. At lower temperatures, rotation slowed more than diffusion.
Viscosity, relaxation time, and dynamics within a model asphalt of larger molecules.
Li, Derek D; Greenfield, Michael L
2014-01-21
The dynamics properties of a new "next generation" model asphalt system that represents SHRP AAA-1 asphalt using larger molecules than past models is studied using molecular simulation. The system contains 72 molecules distributed over 12 molecule types that range from nonpolar branched alkanes to polar resins and asphaltenes. Molecular weights range from 290 to 890 g/mol. All-atom molecular dynamics simulations conducted at six temperatures from 298.15 to 533.15 K provide a wealth of correlation data. The modified Kohlrausch-Williams-Watts equation was regressed to reorientation time correlation functions and extrapolated to calculate average rotational relaxation times for individual molecules. The rotational relaxation rate of molecules decreased significantly with increasing size and decreasing temperature. Translational self-diffusion coefficients followed an Arrhenius dependence. Similar activation energies of ∼42 kJ/mol were found for all 12 molecules in the model system, while diffusion prefactors spanned an order of magnitude. Viscosities calculated directly at 533.15 K and estimated at lower temperatures using the Debye-Stokes-Einstein relationship were consistent with experimental data for asphalts. The product of diffusion coefficient and rotational relaxation time showed only small changes with temperature above 358.15 K, indicating rotation and translation that couple self-consistently with viscosity. At lower temperatures, rotation slowed more than diffusion.
Extensional Relaxation Times and Pinch-off Dynamics of Dilute Polymer Solutions
NASA Astrophysics Data System (ADS)
Dinic, Jelena; Zhang, Yiran; Jimenez, Leidy; Sharma, Vivek
2015-11-01
We show that visualization and analysis of capillary-driven thinning and pinch-off dynamics of the columnar neck in an asymmetric liquid bridge created by dripping-onto-substrate can be used for characterizing the extensional rheology of complex fluids. Using a particular example of dilute, aqueous PEO solutions, we show the measurement of both the extensional relaxation time and extensional viscosity of weakly elastic, polymeric complex fluids with low shear viscosity η< 20 mPa .s and relatively short relaxation time, λ <1 ms. Characterization of elastic effects and extensional relaxation times in these dilute solutions is beyond the range measurable in the standard geometries used in commercially available shear and extensional rheometers (including CaBER, capillary breakup extensional rheometer). As the radius of the neck that connects a sessile drop to a nozzle is detected optically, and the extensional response for viscoelastic fluids is characterized by analyzing their elastocapillary self-thinning, we refer to this technique as optically-detected elastocapillary self-thinning dripping-onto-substrate (ODES-DOS) extensional rheometry.
NASA Astrophysics Data System (ADS)
Richert, Ranko
2017-02-01
On the basis of adiabatic calorimetry data and results obtained from dielectric relaxation studies in the presence of a high static electric field, the effects of temperature and electric field induced changes of the excess entropy are compared for the same sample: supercooled cresolphthalein dimethylether. A field induced reduction of the excess entropy by 45 mJ K-1 mol-1 at constant temperature increases the structural relaxation time by 0.75%, while the same entropy change originating from lowering the temperature at constant field increases the time constant by 3.5%. Therefore, there is no simple link connecting excess entropy and relaxation time that is independent of the control parameter that is used to modify the entropy. A consequence is that the Adam-Gibbs approach does not provide a quantitative prediction for how the dynamics of liquids depend on the electric field, and, more generally, on excess entropy. This work compares the dynamics for temperature versus field induced changes of isobaric excess entropy, thereby eliminating previous uncertainties arising from isochoric versus isobaric conditions and from unknown relations between thermodynamic, excess, and configurational entropies.
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.
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.…
Dornburg, Alex; Brandley, Matthew C; McGowen, Michael R; Near, Thomas J
2012-02-01
Various nucleotide substitution models have been developed to accommodate among lineage rate heterogeneity, thereby relaxing the assumptions of the strict molecular clock. Recently developed "uncorrelated relaxed clock" and "random local clock" (RLC) models allow decoupling of nucleotide substitution rates between descendant lineages and are thus predicted to perform better in the presence of lineage-specific rate heterogeneity. However, it is uncertain how these models perform in the presence of punctuated shifts in substitution rate, especially between closely related clades. Using cetaceans (whales and dolphins) as a case study, we test the performance of these two substitution models in estimating both molecular rates and divergence times in the presence of substantial lineage-specific rate heterogeneity. Our RLC analyses of whole mitochondrial genome alignments find evidence for up to ten clade-specific nucleotide substitution rate shifts in cetaceans. We provide evidence that in the uncorrelated relaxed clock framework, a punctuated shift in the rate of molecular evolution within a subclade results in posterior rate estimates that are either misled or intermediate between the disparate rate classes present in baleen and toothed whales. Using simulations, we demonstrate abrupt changes in rate isolated to one or a few lineages in the phylogeny can mislead rate and age estimation, even when the node of interest is calibrated. We further demonstrate how increasing prior age uncertainty can bias rate and age estimates, even while the 95% highest posterior density around age estimates decreases; in other words, increased precision for an inaccurate estimate. We interpret the use of external calibrations in divergence time studies in light of these results, suggesting that rate shifts at deep time scales may mislead inferences of absolute molecular rates and ages.
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.
2016-06-01
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 yr time span after the 2010 Mw 8.8 Maule Megathrust Earthquake (2010 February 27) over the whole South American continent. With the first 2 yr 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 100 km. 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 200 km, 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 55-135 km with viscosities below 1018 Pa s.
Phonon induced spin relaxation times of single donors and donor clusters in silicon
NASA Astrophysics Data System (ADS)
Hsueh, Yuling; Buch, Holger; Hollenberg, Lloyd; Simmons, Michelle; Klimeck, Gerhard; Rahman, Rajib
2014-03-01
The phonon induced relaxation times (T1) of electron spins bound to single phosphorous (P) donors and P donor clusters in silicon is computed using the atomistic tight-binding method. The electron-phonon Hamiltonian is directly computed from the strain dependent tight-binding Hamiltonian, and the relaxation time is computed from Fermi's Golden Rule using the donor states and the electron-phonon Hamiltonian. The self-consistent Hartree method is used to compute the multi-electron wavefunctions in donor clusters. The method takes into account the full band structure of silicon including the spin-orbit interaction, and captures both valley repopulation and single valley g-factor shifts in a unified framework. The single donor relaxation rate varies proportionally to B5, and is of the order of seconds at B =2T, both in good agreement with experimental single donor data (A. Morello et. al., Nature 467, 687 (2010)). T1 calculations in donor clusters show variations for different electron numbers and donor numbers and locations. The computed T1 in a 4P:5e donor cluster match well with a scanning tunneling microscope patterned P donor cluster (H. Buch et. al., Nature Communications 4, 2017 (2013)).
Relaxation dynamics and thermophysical properties of vegetable oils using time-domain reflectometry.
Sonkamble, Anil A; Sonsale, Rahul P; Kanshette, Mahesh S; Kabara, Komal B; Wananje, Kunal H; Kumbharkhane, Ashok C; Sarode, Arvind V
2017-04-01
Dielectric relaxation studies of vegetable oils are important for insights into their hydrogen bonding and intermolecular dynamics. The dielectric relaxation and thermo physical properties of triglycerides present in some vegetable oils have been measured over the frequency range of 10 MHz to 7 GHz in the temperature region 25 to 10 °C using a time-domain reflectometry approach. The frequency and temperature dependence of dielectric constants and dielectric loss factors were determined for coconut, peanut, soya bean, sunflower, palm, and olive oils. The dielectric permittivity spectra for each of the studied vegetable oils are explained using the Debye model with their complex dielectric permittivity analyzed using the Havriliak-Negami equation. The dielectric parameters static permittivity (ε 0), high-frequency limiting static permittivity (ε ∞), average relaxation time (τ 0), and thermodynamic parameters such as free energy (∆F τ), enthalpy (∆H τ), and entropy of activation (∆S τ) were also measured. Calculation and analysis of these thermodynamic parameters agrees with the determined dielectric parameters, giving insights into the temperature dependence of the molecular dynamics of these systems.
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
Comparative study of acoustic relaxation time of cholesteric liquid crystal and mixtures
NASA Astrophysics Data System (ADS)
Bhave, Manisha G.; Gharde, Rita; Radha, S.
2016-09-01
The present study focuses on the relaxation processes in Cholesteric Liquid Crystal and mixtures. We have dispersed two different monomers in CLC to form Polymer dispersed liquid crystals (PDCLCs). PDLC films have a remarkable electro-optical behavior since they can be switched from highly light scattering state (OFF) to transparent state (ON) simply by application of an electric field. We have also doped ferroelectric nano - powder (NP) in CLC. The phase transitions occurred at temperatures lower than those exhibited by the mesogenic component before doping. The viscosity, ultrasonic velocity and density show variation with change in the material as well as temperature. The acoustic relaxation time and ultrasonic attenuation decrease with increase in temperature for CLC and CLC+NP. The parameters of PDCLC2 in comparison with PDCLC1 are more linear in isotropic and anisotropic regions. For PDCLC2 the values reach maximum value at the Cholesteric-isotropic transition.
Multiple short time power laws in the orientational relaxation of nematic liquid crystals.
Jose, Prasanth P; Bagchi, Biman
2006-11-14
Relaxation in the nematic liquid crystalline phase is known to be sensitive to its proximity to both isotropic and smectic phases. Recent transient optical Kerr effect (OKE) studies have revealed, rather surprisingly, two temporal power laws at short to intermediate times and also an apparent absence of the expected exponential decay at longer times. In order to understand this unusual dynamics, we have carried out extensive molecular dynamics simulations of transient OKE and related orientational time correlation functions in a system of prolate ellipsoids (with aspect ratio equal to 3). The simulations find two distinct power laws, with a crossover region, in the decay of the orientational time correlation function at short to intermediate times (in the range of a few picoseconds to a few nanoseconds). In addition, the simulation results fail to recover any long time exponential decay component. The system size dependence of the exponents suggests that the first power law may originate from the local orientational density fluctuations (like in a glassy liquid). The origin of the second power law is less clear and may be related to the long range fluctuations (such as smecticlike density fluctuations)--these fluctuations are expected to involve small free energy barriers. In support of the latter, the evidence of pronounced coupling between orientational and spatial densities at intermediate wave numbers is presented. This coupling is usually small in normal isotropic liquids, but it is large in the present case. In addition to slow collective orientational relaxation, the single particle orientational relaxation is also found to exhibit slow dynamics in the nematic phase in the long time.
Relaxation times in single event electrospraying controlled by nozzle front surface modification.
Stachewicz, Urszula; Dijksman, J Frits; Burdinski, Dirk; Yurteri, Caner U; Marijnissen, Jan C M
2009-02-17
Single event electrospraying (SEE) is a method for on-demand deposition of femtoliter to picoliter volumes of fluids. To determine the influence of the size of the meniscus on the characteristics of the single event electrospraying process, glass capillaries were used with and without an antiwetting coating comprising a self-assembled 1H,1H,2H,2H-perfluorodecyltrichlorosilane-based monolayer to control the meniscus size. A large difference was found in driving single event electrospraying from a small meniscus compared to what is needed to generate a single event electrospraying from a large meniscus. Furthermore, after studying the different time constants related to the electrical and the hydrodynamic phenomena, we are able to explain the timing limitations of the deposition process from both a small and a large meniscus. The hydrodynamic relaxation time is significantly reduced in the case of the modified capillary, and the timing of SEE, which determines the deposition time, is limited by the resistor-capacitor RC time of the electrical circuit needed to drive the SEE. We have built a model that describes the almost one-dimensional motion of the liquid in the capillary during pulsing. The model has been used to estimate the hydrodynamic relaxation times related to the meniscus-to-cone and cone-to-meniscus transitions during SEE. By confining the meniscus to the inner diameter of the nozzle, we are able to deposit a volume smaller than 5 pL per SEE.
2016-01-01
Unravelling the main initial dynamics responsible for chiral recognition is a key step in the understanding of many biological processes. However, this challenging task requires a sensitive enantiospecific probe to investigate molecular dynamics on their natural femtosecond time scale. Here we show that, in the gas phase, the ultrafast relaxation dynamics of photoexcited chiral molecules can be tracked by recording time-resolved photoelectron circular dichroism (TR-PECD) resulting from the photoionization by a circularly polarized probe pulse. A large forward–backward asymmetry along the probe propagation axis is observed in the photoelectron angular distribution. Its evolution with pump–probe delay reveals ultrafast dynamics that are inaccessible in the angle-integrated photoelectron spectrum or via the usual electron emission anisotropy parameter (β). PECD, which originates from the electron scattering in the chiral molecular potential, appears as a new sensitive observable for ultrafast molecular dynamics in chiral systems. PMID:27786493
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.
Time-Resolved Torsional Relaxation of Spider Draglines by an Optical Technique
NASA Astrophysics Data System (ADS)
Emile, O.; Floch, A. Le; Vollrath, F.
2007-04-01
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.
Intracellular sodium and lithium NMR relaxation times in the perfused frog heart.
Burstein, D; Fossel, E T
1987-03-01
We have used a combination of a shift reagent and mathematical filtering or presaturation of the extracellular sodium resonance for the quantitative investigation of the intracellular sodium and lithium relaxation times in the perfused frog heart. While the T1 of the intracellular sodium was found to consist of a single-exponential time constant (approximately 23 ms), the T2 was better fit as a double-exponential decay with time constants of approximately 2 and 17 ms. However, the relative amplitudes of the two time constants in the T2 decay were found to be inconsistent with those which would be expected from a homogeneous pool of nuclei undergoing quadrupolar interactions. The relaxation times were not changed by a fivefold increase in the intracellular sodium level (due to perfusion with a ouabain-containing buffer). The T1 and T2 of the intracellular lithium (after perfusion with lithium-containing buffer) were both well fit by single exponentials (700- and 31-ms time constants, respectively).
NASA Astrophysics Data System (ADS)
Bradley, T. D.; Ilinova, E.; McFerran, J. J.; Jouin, J.; Debord, B.; Alharbi, M.; Thomas, P.; Gérôme, F.; Benabid, F.
2016-09-01
We report on the measurement of ground-state atomic polarization relaxation time of Rb vapor confined in five different hypocycloidal core-shape Kagome hollow-core photonic crystal fibers made with uncoated silica glass. We are able to distinguish between wall-collision and transit-time effects in an optical waveguide and deduce the contribution of the atom’s dwell time at the core wall surface. In contrast with conventional macroscopic atomic cell configuration, and in agreement with Monte Carlo simulations, the measured relaxation times were found to be at least one order of magnitude longer than the limit set by atom-wall collisional from thermal atoms. This extended relaxation time is explained by the combination of a stronger contribution of the slow atoms in the atomic polarization build-up, and of the relatively significant contribution of dwell time to the relaxation process of the ground state polarization.
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.
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
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 < 20τ_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 Alfvén 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, 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 (Bθ ≤ 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 / Bθ > 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 τ 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 Alfvén 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.
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.
Energy and temperature dependence of relaxation time and Wiedemann-Franz law on PbTe
NASA Astrophysics Data System (ADS)
Ahmad, Salameh; Mahanti, S. D.
2010-04-01
Recent revival of interest in high-temperature (T) thermoelectrics has made it necessary to understand in detail the T dependence of different transport coefficients, and different processes contributing to this temperature dependence. Since PbTe is a well-studied prototypical high-temperature thermoelectric, we have carried out theoretical studies to analyze how different physical sources contribute to electronic transport coefficients in this system over a wide T and concentration (n) range; 300K
NASA Astrophysics Data System (ADS)
Margetis, Dionisios; Aziz, Michael J.; Stone, Howard A.
2005-04-01
The morphological relaxation of axisymmetric crystal surfaces with a single facet below the roughening transition temperature is studied analytically for diffusion-limited (DL) and attachment-detachment-limited (ADL) kinetics with inclusion of the Ehrlich-Schwoebel barrier. The slope profile F(r,t) , where r is the polar distance and t is time, is described via a nonlinear, fourth-order partial differential equation (PDE) that accounts for step line-tension energy g1 and step-step repulsive interaction energy g3 ; for ADL kinetics, an effective surface diffusivity that depends on the step density is included. The PDE is derived directly from the step-flow equations and, alternatively, via a continuum surface free energy. The facet evolution is treated as a free-boundary problem where the interplay between g1 and g3 gives rise to a region of rapid variations of F , a boundary layer, near the expanding facet. For long times and g3/g1
An iterative linear method for calculation of spin-lattice relaxation times
NASA Astrophysics Data System (ADS)
Crouch, Ronald; Hurlbert, Stuart; Ragouzeos, Aris
A simple algorithm for the calculation of spin-lattice relaxation times which can be run in a programmable calculator is presented. As was suggested by H. Hanssum et al., an experimentally determined inhomogeneity parameter ( I) can be used with this procedure to compensate for imperfections in the RF field. The effects of variation of pulse width and repetition rate on both I and T1 are investigated with simulated and experimental data sets. The superiority of this approach over three-parameter nonlinear fitting methods is demonstrated by comparisons between data sets generated with different pulse flip angles and sample volumes.
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.
Time scale in quasifission reactions
Back, B.B.; Paul, P.; Nestler, J.
1995-08-01
The quasifission process arises from the hindrance of the complete fusion process when heavy-ion beams are used. The strong dissipation in the system tends to prevent fusion and lead the system towards reseparation into two final products of similar mass reminiscent of a fission process. This dissipation slows down the mass transfer and shape transformation and allows for the emission of high energy {gamma}-rays during the process, albeit with a low probability. Giant Dipole {gamma} rays emitted during this time have a characteristic spectral shape and may thus be discerned in the presence of a background of {gamma} rays emitted from the final fission-like fragments. Since the rate of GDR {gamma} emission is very well established, the strength of this component may therefore be used to measure the timescale of the quasifission process. In this experiment we studied the reaction between 368-MeV {sup 58}Ni and a {sup 165}Ho target, where deep inelastic scattering and quasifission processes are dominant. Coincidences between fission fragments (detected in four position-sensitive avalanche detectors) and high energy {gamma} rays (measured in a 10{close_quotes} x 10{close_quotes} actively shielded NaI detector) were registered. Beams were provided by the Stony Brook Superconducting Linac. The {gamma}-ray spectrum associated with deep inelastic scattering events is well reproduced by statistical cooling of projectile and target-like fragments with close to equal initial excitation energy sharing. The y spectrum associated with quasifission events is well described by statistical emission from the fission fragments alone, with only weak evidence for GDR emission from the mono-nucleus. A 1{sigma} limit of t{sub ss} < 11 x 10{sup -21} s is obtained for the mono-nucleus lifetime, which is consistent with the lifetime obtained from quasifission fragment angular distributions. A manuscript was accepted for publication.
Relaxation and dissipation in time-dependent current-density functional theory
NASA Astrophysics Data System (ADS)
D'Agosta, Roberto
2005-03-01
In a typical relaxation problem a many-particle system evolves from an initial excited state under the action of its own hamiltonian plus a ``thermal bath", until equilibrium (or the ground-state at T=0) is reached. Due to the presence of the thermal bath the time evolution of the system is not unitary, and an initially pure state will evolve into a statistical mixture of states. Here we show that the time-dependent current density functional theory^1 allows a hamiltonian description of the relaxation process, whereby the quantum state of the system undergoes a unitary time evolution without becoming entangled with a thermal bath. The essential feature that causes the system to eventually settle into a stationary state of the ground-state Kohn-Sham hamiltonian is the presence of an effective electric field, which is determined by the instantaneous values of the current and the density. Our theory is consistent with recent numerical results by Wijewardane and Ullrich^ 2.1. G. Vignale, C. A. Ullrich, and S. Conti, PRL 79, 4878 (1997)2. H. O. Wijewardane and C. A. Ullrich, cond-mat/0411157
Correlation between T2∗ (T2 star) relaxation time and cervical intervertebral disc degeneration
Huang, Minghua; Guo, Yong; Ye, Qiong; Chen, Lei; Zhou, Kai; Wang, Qingjun; Shao, Lixin; Shi, Qinglei; Chen, Chun
2016-01-01
Abstract Purpose: To demonstrate the potential benefits of T2∗ relaxation time of intervertebral discs (IVDs) regarding the detection and grading of degenerative disc disease using 3.0-T magnetic resonance imaging (MRI) in a clinical setting. Materials and Methods: Cervical sagittal T2-weighted, T2∗ relaxation MRI was performed at 3.0-T in 61 subjects, covering discs C2–3 to C6–7. All discs were morphologically assessed based on the Pfirrmann grade, and regions of interests (ROIs) were drawn over the T2∗ mapping. Receiver operating characteristic (ROC) analysis was performed among grades to determine the cut-off values. Results: Cervical intervertebral discs (IVDs) of patients were commonly determined to be at Pfirrmann grades III to V. The nucleus pulposus (NP) values did not differ significantly between sexes at the same anatomic level (P > 0.05). In the NP, the T2∗ values tended to decrease with increasing grade (P < 0.000), and a significant difference was found in the T2 values between grades I to V (P < 0.05). T2∗ values based on disc degeneration level classification were as follows: grade I (>30 milliseconds), grade II (24.55–29.99 milliseconds), grade III (21.65–24.54 milliseconds), grade IV (18.35–21.64 milliseconds), and grade V (<18.34 milliseconds). Conclusion: Our standardized method of region-specific quantitative T2∗ relaxation time evaluation seems capable of characterizing different degrees of disc degeneration quantitatively. The T2∗ values obtained in these cervical IVDs may serve as baseline values for future T2∗ measurements in both healthy and degenerated cervical discs. PMID:27893652
NASA Astrophysics Data System (ADS)
Moraes, Tiago Bueno; Monaretto, Tatiana; Colnago, Luiz Alberto
2016-09-01
Longitudinal (T1) and transverse (T2) relaxation times have been widely used in time-domain NMR (TD-NMR) to determine several physicochemical properties of petroleum, polymers, and food products. The measurement of T2 through the CPMG pulse sequence has been used in most of these applications because it denotes a rapid, robust method. On the other hand, T1 has been occasionally used in TD-NMR due to the long measurement time required to collect multiple points along the T1 relaxation curve. Recently, several rapid methods to measure T1 have been proposed. Those methods based upon single shot, known as Continuous Wave Free Precession (CWFP) pulse sequences, have been employed in the simultaneous measurement of T1 and T2 in a rapid fashion. However, these sequences can be used exclusively in instrument featuring short dead time because the magnitude of the signal at thermal equilibrium is required. In this paper, we demonstrate that a special CWFP sequence with a low flip angle can be a simple and rapid method to measure T1 regardless of instruments dead time. Experimental results confirmed that the method called CWFP-T1 may be used to measure both single T1 value and T1 distribution in heterogeneous samples. Therefore, CWFP-T1 sequence can be a feasible alternative to CPMG in the determination of physicochemical properties, particularly in processes where fast protocols are requested such as industrial applications.
NASA Astrophysics Data System (ADS)
Mahmoud, Sami; Trochet, Mickaël; Restrepo, Oscar; Mousseau, Normand
The microscopic mechanisms associated with the evolution of metallic materials are still a matter of debate as both experimental and numerical approaches fail to provide a detailed atomic picture of their time evolution. Here, we use the kinetic activation-relaxation technique (k-ART), an unbiased off-lattice kinetic Monte Carlo method with on-the-fly catalog building to overcome these limitations and follow the atomistic evolution of a 10.000-atom grain boundary Ni system over macroscopic time scales. We first characterize the kinetic properties of four different empirical potentials, the embedded atom method (EAM), the first and second modified embedded atom method (MEAM1NN and MEAM2NN respectively) and the Reax force field (ReaxFF) potentials. Comparing the energetics, the elastic effects and the diffusion mechanisms for systems with one to three vacancies and one to three self-interstitials in nickel simulated over second time scale, we conclude that ReaxFF and EAM potentials are closest to experimental values. We then proceed to study the long-time evolution of a grain boundary with the Reax forcefield and to offer a detailed description of its energy landscape, including the exact description of short and long-range effects on self-diffusion along the interface
NASA Astrophysics Data System (ADS)
Valente, Pedro C.; da Silva, Carlos B.; Pinho, Fernando T.
2013-11-01
We report a numerical study of statistically steady and decaying turbulence of FENE-P fluids for varying polymer relaxation times ranging from the Kolmogorov dissipation time-scale to the eddy turnover time. The total turbulent kinetic energy dissipation is shown to increase with the polymer relaxation time in both steady and decaying turbulence, implying a ``drag increase.'' If the total power input in the statistically steady case is kept equal in the Newtonian and the viscoelastic simulations the increase in the turbulence-polymer energy transfer naturally lead to the previously reported depletion of the Newtonian, but not the overall, kinetic energy dissipation. The modifications to the nonlinear energy cascade with varying Deborah/Weissenberg numbers are quantified and their origins investigated. The authors acknowledge the financial support from Fundação para a Ciência e a Tecnologia under grant PTDC/EME-MFE/113589/2009.
In Vivo Measurements of T2 Relaxation Time of Mouse Lungs during Inspiration and Expiration
Hockings, Paul D.
2016-01-01
Purpose The interest in measurements of magnetic resonance imaging relaxation times, T1, T2, T2*, with intention to characterize healthy and diseased lungs has increased recently. Animal studies play an important role in this context providing models for understanding and linking the measured relaxation time changes to the underlying physiology or disease. The aim of this work was to study how the measured transversal relaxation time (T2) in healthy lungs is affected by normal respiration in mouse. Method T2 of lung was measured in anaesthetized freely breathing mice. Image acquisition was performed on a 4.7 T, Bruker BioSpec with a multi spin-echo sequence (Car-Purcell-Meiboom-Gill) in both end-expiration and end-inspiration. The echo trains consisted of ten echoes of inter echo time 3.5 ms or 4.0 ms. The proton density, T2 and noise floor were fitted to the measured signals of the lung parenchyma with a Levenberg-Marquardt least-squares three-parameter fit. Results T2 in the lungs was longer (p<0.01) at end-expiration (9.7±0.7 ms) than at end-inspiration (9.0±0.8 ms) measured with inter-echo time 3.5 ms. The corresponding relative proton density (lung/muscle tissue) was higher (p<0.001) during end-expiration, (0.61±0.06) than during end-inspiration (0.48±0.05). The ratio of relative proton density at end-inspiration to that at end-expiration was 0.78±0.09. Similar results were found for inter-echo time 4.0 ms and there was no significant difference between the T2 values or proton densities acquired with different interecho times. The T2 value increased linearly (p< 0.001) with proton density. Conclusion The measured T2 in-vivo is affected by diffusion across internal magnetic susceptibility gradients. In the lungs these gradients are modulated by respiration, as verified by calculations. In conclusion the measured T2 was found to be dependent on the size of the alveoli. PMID:27936061
Eugene, M.; Lechat, P.; Hadjiisky, P.; Teillac, A.; Grosgogeat, Y.; Cabrol, C.
1986-01-01
It should be possible to detect heart transplant rejection by nuclear magnetic resonance (NMR) imaging if it induces myocardial T1 and T2 proton relaxation time alterations or both. We studied 20 Lewis rats after a heterotopic heart transplantation. In vitro measurement of T1 and T2 was performed on a Minispec PC20 (Bruker) 3 to 9 days after transplantation. Histologic analysis allowed the quantification of rejection process based on cellular infiltration and myocardiolysis. Water content, a major determinant of relaxation time, was also studied. T1 and T2 were significantly prolonged in heterotopic vs orthotopic hearts (638 +/- 41 msec vs 606 +/- 22 msec for T1, p less than 0.01 and 58.2 +/- 8.4 msec vs 47.4 +/- 1.9 msec for T2, p less than 0.001). Water content was also increased in heterotopic hearts (76.4 +/- 2.3 vs 73.8 +/- 1.0, p less than 0.01). Most importantly, we found close correlations between T1 and especially T2 vs water content, cellular infiltration, and myocardiolysis. We conclude that rejection reaction should be noninvasively detected by NMR imaging, particularly with pulse sequences emphasizing T2.
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.
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 σdc of an ultraviscous liquid varies nonlinearly with the dielectric relaxation time τ, and the slope of the logσdc against logτ 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(σdcτ )=constant+logα, where α 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 σdc-τ 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.
Niu, Xiao-Dong; Hyodo, Shi-Aki; Munekata, Toshihisa; Suga, Kazuhiko
2007-09-01
It is well known that the Navier-Stokes equations cannot adequately describe gas flows in the transition and free-molecular regimes. In these regimes, the Boltzmann equation (BE) of kinetic theory is invoked to govern the flows. However, this equation cannot be solved easily, either by analytical techniques or by numerical methods. Hence, in order to efficiently maneuver around this equation for modeling microscale gas flows, a kinetic lattice Boltzmann method (LBM) has been introduced in recent years. This method is regarded as a numerical approach for solving the BE in discrete velocity space with Gauss-Hermite quadrature. In this paper, a systematic description of the kinetic LBM, including the lattice Boltzmann equation, the diffuse-scattering boundary condition for gas-surface interactions, and definition of the relaxation time, is provided. To capture the nonlinear effects due to the high-order moments and wall boundaries, an effective relaxation time and a modified regularization procedure of the nonequilibrium part of the distribution function are further presented based on previous work [Guo et al., J. Appl. Phys. 99, 074903 (2006); Shan et al., J. Fluid Mech. 550, 413 (2006)]. The capability of the kinetic LBM of simulating microscale gas flows is illustrated based on the numerical investigations of micro Couette and force-driven Poiseuille flows.
Temperature dependence of relaxation times in proton components of fatty acids.
Kuroda, Kagayaki; Iwabuchi, Taku; Obara, Makoto; Honda, Masatoshi; Saito, Kensuke; Imai, Yutaka
2011-01-01
We examined the temperature dependence of relaxation times in proton components of fatty acids in various samples in vitro at 11 tesla as a standard calibration data for quantitative temperature imaging of fat. The spin-lattice relaxation time, T(1), of both the methylene (CH(2)) chain and terminal methyl (CH(3)) was linearly related to temperature (r>0.98, P<0.001) in samples of animal fat. The temperature coefficients for the 2 primary proton components differed significantly; in 5 bovine fat samples, the coefficient at 30 °C was 1.79±0.07 (%/°C) for methylene and 2.98±0.38 (%/°C) for methyl. Numerical simulations based on such a difference demonstrated the possibility of considerable error from inconsistent ratios in fatty acid components when calibrating and estimating temperature. The error reached 3.3 °C per 15 °C in temperature elevation when we used a pure CH(2) signal for calibration and observed the signal with 18% of CH(3) to estimate temperature. These findings suggested that separating the fatty acid components would significantly improve accuracy in quantitative thermometry for fat. Use of the T(1) of CH(2) seems promising in terms of reliability and reproducibility in measuring temperature of fat.
Enhancing Web applications in radiology with Java: estimating MR imaging relaxation times.
Dagher, A P; Fitzpatrick, M; Flanders, A E; Eng, J
1998-01-01
Java is a relatively new programming language that has been used to develop a World Wide Web-based tool for estimating magnetic resonance (MR) imaging relaxation times, thereby demonstrating how Java may be used for Web-based radiology applications beyond improving the user interface of teaching files. A standard processing algorithm coded with Java is downloaded along with the hypertext markup language (HTML) document. The user (client) selects the desired pulse sequence and inputs data obtained from a region of interest on the MR images. The algorithm is used to modify selected MR imaging parameters in an equation that models the phenomenon being evaluated. MR imaging relaxation times are estimated, and confidence intervals and a P value expressing the accuracy of the final results are calculated. Design features such as simplicity, object-oriented programming, and security restrictions allow Java to expand the capabilities of HTML by offering a more versatile user interface that includes dynamic annotations and graphics. Java also allows the client to perform more sophisticated information processing and computation than is usually associated with Web applications. Java is likely to become a standard programming option, and the development of stand-alone Java applications may become more common as Java is integrated into future versions of computer operating systems.
Direct measurement of dipole-dipole/CSA cross-correlated relaxation by a constant-time experiment
Liu, Yizhou; Prestegard, James H.
2008-01-01
Relaxation rates in NMR are usually measured by intensity modulation as a function of a relaxation delay during which the relaxation mechanism of interest is effective. Other mechanisms are often suppressed during the relaxation delay by pulse sequences which eliminate their effects, or cancel their effects when two data sets with appropriate combinations of relaxation rate effects are added. Cross-correlated relaxation (CCR) involving dipole-dipole and CSA interactions differ from auto-correlated relaxation (ACR) in that the signs of contributions can be changed by inverting the state of one spin involved in the dipole-dipole interaction. This property has been exploited previously using CPMG sequences to refocus CCR while ACR evolves. Here we report a new pulse scheme that instead eliminates intensity modulation by ACR and thus allows direct measurement of CCR. The sequence uses a constant time relaxation period for which the contribution of ACR does not change. An inversion pulse is applied at various points in the sequence to effect a decay that depends on CCR only. A 2-D experiment is also described in which chemical shift evolution in the indirect dimension can share the same constant period. This improves sensitivity by avoiding the addition of a separate indirect dimension acquisition time. We illustrate the measurement of residue specific CCR rates on the non-myristoylated yeast ARF1 protein and compare the results to those obtained following the conventional method of measuring the decay rates of the slow and fast-relaxing 15N doublets. The performances of the two methods are also quantitatively evaluated by simulation. The analysis shows that the shared constant-time CCR (SCT-CCR) method significantly improves sensitivity. PMID:18406649
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.
Going up in time and length scales in modeling polymers
NASA Astrophysics Data System (ADS)
Grest, Gary S.
Polymer properties depend on a wide range of coupled length and time scales, with unique macroscopic viscoelastic behavior stemming from interactions at the atomistic level. The need to probe polymers across time and length scales and particularly computational modeling is inherently challenging. Here new paths to probing long time and length scales including introducing interactions into traditional bead-spring models and coarse graining of atomistic simulations will be compared and discussed. Using linear polyethylene as a model system, the degree of coarse graining with two to six methylene groups per coarse-grained bead derived from a fully atomistic melt simulation were probed. We show that the degree of coarse graining affects the measured dynamic. Using these models we were successful in probing highly entangled melts and were able reach the long-time diffusive regime which is computationally inaccessible using atomistic simulations. We simulated the relaxation modulus and shear viscosity of well-entangled polyethylene melts for scaled times of 500 µs. Results for plateau modulus are in good agreement with experiment. The long time and length scale is coupled to the macroscopic viscoelasticity where the degree of coarse graining sets the minimum length scale instrumental in defining polymer properties and dynamics. Results will be compared to those obtained from simple bead-spring models to demonstrate the additional insight that can be gained from atomistically inspired coarse grained models. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.
Average-atom treatment of relaxation time in x-ray Thomson scattering from warm dense matter
NASA Astrophysics Data System (ADS)
Johnson, W. R.; Nilsen, J.
2016-03-01
The influence of finite relaxation times on Thomson scattering from warm dense plasmas is examined within the framework of the average-atom approximation. Presently most calculations use the collision-free Lindhard dielectric function to evaluate the free-electron contribution to the Thomson cross section. In this work, we use the Mermin dielectric function, which includes relaxation time explicitly. The relaxation time is evaluated by treating the average atom as an impurity in a uniform electron gas and depends critically on the transport cross section. The calculated relaxation rates agree well with values inferred from the Ziman formula for the static conductivity and also with rates inferred from a fit to the frequency-dependent conductivity. Transport cross sections determined by the phase-shift analysis in the average-atom potential are compared with those evaluated in the commonly used Born approximation. The Born approximation converges to the exact cross sections at high energies; however, differences that occur at low energies lead to corresponding differences in relaxation rates. The relative importance of including relaxation time when modeling x-ray Thomson scattering spectra is examined by comparing calculations of the free-electron dynamic structure function for Thomson scattering using Lindhard and Mermin dielectric functions. Applications are given to warm dense Be plasmas, with temperatures ranging from 2 to 32 eV and densities ranging from 2 to 64 g/cc.
Spin-drag relaxation time in one-dimensional spin-polarized Fermi gases
NASA Astrophysics Data System (ADS)
Rainis, Diego; Polini, Marco; Tosi, M. P.; Vignale, G.
2008-01-01
Spin propagation in systems of one-dimensional interacting fermions at finite temperature is intrinsically diffusive. The spreading rate of a spin packet is controlled by a transport coefficient termed “spin drag” relaxation time τsd . In this paper we present both numerical and analytical calculations of τsd for a two-component spin-polarized cold Fermi gas trapped inside a tight atomic waveguide. At low temperatures we find an activation law for τsd , in agreement with earlier calculations of Coulomb drag between slightly asymmetric quantum wires, but with a different and much stronger temperature dependence of the prefactor. Our results provide a fundamental input for microscopic time-dependent spin-density functional theory calculations of spin transport in one-dimensional inhomogeneous systems of interacting fermions.
Dynamical theory of spin noise and relaxation: Prospects for real-time NMR measurements.
Field, Timothy R
2014-11-01
Recent developments in theoretical aspects of spin noise and relaxation and their interrelationship reveal a modified spin density, distinct from the density matrix, as the necessary object to describe fluctuations in spin systems. These fluctuations are to be viewed as an intrinsic quantum mechanical property of such systems immersed in random magnetic environments and are observed as "spin noise" in the absence of any radio frequency excitation. With the prospect of ultrafast digitization, the role of spin noise in real-time parameter extraction for (NMR) spin systems, and the advantage over standard techniques, is of essential importance, especially for systems containing a small number of spins. In this article we outline prospects for harnessing the recent dynamical theory in terms of spin-noise measurement, with attention to real-time properties.
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.
Temperature dependence of proton NMR relaxation times at earth's magnetic field
NASA Astrophysics Data System (ADS)
Niedbalski, Peter; Kiswandhi, Andhika; Parish, Christopher; Ferguson, Sarah; Cervantes, Eduardo; Oomen, Anisha; Krishnan, Anagha; Goyal, Aayush; Lumata, Lloyd
The theoretical description of relaxation processes for protons, well established and experimentally verified at conventional nuclear magnetic resonance (NMR) fields, has remained untested at low fields despite significant advances in low field NMR technology. In this study, proton spin-lattice relaxation (T1) times in pure water and water doped with varying concentrations of the paramagnetic agent copper chloride have been measured from 6 to 92oC at earth's magnetic field (1700 Hz). Results show a linear increase of T1 with temperature for each of the samples studied. Increasing the concentration of the copper chloride greatly reduced T1 and reduced dependence on temperature. The consistency of the results with theory is an important confirmation of past results, while the ability of an ultra-low field NMR system to do contrast-enhanced magnetic resonance imaging (MRI) is promising for future applicability to low-cost medical imaging and chemical identification. This work is supported by US Dept of Defense Award No. W81XWH-14-1-0048 and the Robert A. Welch Foundation Grant No. AT-1877.
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.
Adolescent Time Attitude Scale: Adaptation into Turkish
ERIC Educational Resources Information Center
Çelik, Eyüp; Sahranç, Ümit; Kaya, Mehmet; Turan, Mehmet Emin
2017-01-01
This research is aimed at examining the validity and reliability of the Turkish version of the Time Attitude Scale. Data was collected from 433 adolescents; 206 males and 227 females participated in the study. Confirmatory factor analysis performed to discover the structural validity of the scale. The internal consistency method was used for…
Ngai, K L; Capaccioli, Simone; Paluch, Marian; Prevosto, Daniele
2014-05-22
When the thickness is reduced to nanometer scale, freestanding high molecular weight polymer thin films undergo large reduction of degree of cooperativity and coupling parameter n in the Coupling Model (CM). The finite-size effect together with the surfaces with high mobility make the α-relaxation time of the polymer in nanoconfinement, τ(α)(nano)(T), much shorter than τ(α)(bulk)(T) in the bulk. The consequence is avoidance of vitrification at and below the bulk glass transition temperature, T(g)(bulk), on cooling, and the freestanding polymer thin film remains at thermodynamic equilibrium at temperatures below T(g)(bulk). Molecular dynamics simulations have shown that the specific volume of the freestanding film is the same as the bulk glass-former at equilibrium at the same temperatures. Extreme nanoconfinement renders total or almost total removal of cooperativity of the α-relaxation, and τ(α)(nano)(T) becomes the same or almost the same as the JG β-relaxation time τ(β)(bulk)(T) of the bulk glass-former at equilibrium and at temperatures below T(g)(bulk). Taking advantage of being able to obtain τ(β)(bulk)(T) at equilibrium density below T(g)(bulk) by extreme nanoconfinement of the freestanding films, and using the CM relation between τ(α)(bulk)(T) and τ(β)(bulk)(T), we conclude that the Vogel-Fulcher-Tammann-Hesse (VFTH) dependence of τ(α)(bulk)(T) cannot hold for glass-formers in equilibrium at temperatures significantly below T(g)(bulk). In addition, τ(α)(bulk)(T) does not diverge at the Vogel temperature, T₀, as suggested by the VFTH-dependence and predicted by some theories of glass transition. Instead, τ(α)(bulk)(T) of the glass-former at equilibrium has a much weaker temperature dependence than the VFTH-dependence at temperature below T(g)(bulk) and even below T₀. This conclusion from our analysis is consistent with the temperature dependence of τ(α)(bulk)(T) found experimentally in polymers aged long enough time to attain the
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
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
Van Rossom, Sam; Smith, Colin Robert; Zevenbergen, Lianne; Thelen, Darryl Gerard; Vanwanseele, Benedicte; Van Assche, Dieter; Jonkers, Ilse
2017-01-01
Cartilage is responsive to the loading imposed during cyclic routine activities. However, the local relation between cartilage in terms of thickness distribution and biochemical composition and the local contact pressure during walking has not been established. The objective of this study was to evaluate the relation between cartilage thickness, proteoglycan and collagen concentration in the knee joint and knee loading in terms of contact forces and pressure during walking. 3D gait analysis and MRI (3D-FSE, T1ρ relaxation time and T2 relaxation time sequence) of fifteen healthy subjects were acquired. Experimental gait data was processed using musculoskeletal modeling to calculate the contact forces, impulses and pressure distribution in the tibiofemoral joint. Correlates to local cartilage thickness and mean T1ρ and T2 relaxation times of the weight-bearing area of the femoral condyles were examined. Local thickness was significantly correlated with local pressure: medial thickness was correlated with medial condyle contact pressure and contact force, and lateral condyle thickness was correlated with lateral condyle contact pressure and contact force during stance. Furthermore, average T1ρ and T2 relaxation time correlated significantly with the peak contact forces and impulses. Increased T1ρ relaxation time correlated with increased shear loading, decreased T1ρ and T2 relaxation time correlated with increased compressive forces and pressures. Thicker cartilage was correlated with higher condylar loading during walking, suggesting that cartilage thickness is increased in those areas experiencing higher loading during a cyclic activity such as gait. Furthermore, the proteoglycan and collagen concentration and orientation derived from T1ρ and T2 relaxation measures were related to loading. PMID:28076431
Equilibrium distributions and relaxation times in gaslike economic models: an analytical derivation.
Calbet, Xavier; López, José-Luis; López-Ruiz, Ricardo
2011-03-01
A step-by-step procedure to derive analytically the exact dynamical evolution equations of the probability density functions (PDFs) of well-known kinetic wealth exchange economic models is shown. This technique gives a dynamical insight into the evolution of the PDF, for example, allowing the calculation of its relaxation times. Their equilibrium PDFs can also be calculated by finding its stationary solutions. This gives as a result an integro-differential equation, which can be solved analytically in some cases and numerically in others. This should provide some guidance into the type of PDFs that can be derived from particular economic agent exchange rules or, for that matter, any other kinetic model of gases with particular collision physics.
Senra Filho, Antonio Carlos da S; Barbosa, Jeam Haroldo O; Salmon, Carlos E G; Murta, Luiz O
2014-01-01
Relaxometry mapping is a quantitative modality in magnetic resonance imaging (MRI) widely used in neuroscience studies. Despite its relevance and utility, voxel measurement of relaxation time in relaxometry MRI is compromised by noise that is inherent to MRI modality and acquisition hardware. In order to enhance signal to noise ratio (SNR) and quality of relaxometry mapping we propose application of anisotropic anomalous diffusion (AAD) filter that is consistent with inhomogeneous complex media. Here we evaluated AAD filter in comparison to two usual spatial filters: Gaussian and non local means (NLM) filters applied to real and simulated T2 relaxometry image sequences. The results demonstrate that AAD filter is comparatively more efficient in noise reducing and maintaining the image structural edges. AAD shows to be a robust and reliable spatial filter for brain image relaxometry.
A multiple relaxation time extension of the constant speed kinetic model
NASA Astrophysics Data System (ADS)
Zadehgol, Abed; Ashrafizaadeh, Mahmud
2016-02-01
In this work, a multiple relaxation time (MRT) extension of the recently introduced constant speed kinetic model (CSKM) is proposed. The CSKM, which is an entropic kinetic model and based on unconventional entropies of Burg and Tssalis, was introduced in [A. Zadehgol and M. Ashrafizaadeh, J. Comput. Phys. 274, 803 (2014)]; [A. Zadehgol Phys. Rev. E 91, 063311 (2015)] as an extension of the model of Boghosian et al. [Phys. Rev. E 68, 025103 (2003)] in the limit of fixed speed continuous velocities. The present extension improves the stability of the previous models at very high Reynolds numbers, while allowing for a more convenient orthogonal lattice. The model is verified by solving the following benchmark problems: (i) the lid driven square cavity and (ii) the Kelvin-Helmholtz instability of thin shear layers in a doubly periodic square domain.
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.
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.
Modified scaling principle for rotational relaxation in a model for suspensions of rigid rods
NASA Astrophysics Data System (ADS)
Tse, Ying-Lung Steve; Andersen, Hans C.
2013-07-01
We have performed simulations of the model of infinitely thin rigid rods undergoing rotational and translational diffusion, subject to the restriction that no two rods can cross one another, for various concentrations well into the semidilute regime. We used a modification of the algorithm of Doi et al. [J. Phys. Soc. Jpn. 53, 3000 (1984)], 10.1143/JPSJ.53.3000 that simulates diffusive dynamics using a Monte Carlo method and a nonzero time step. In the limit of zero time step, this algorithm is an exact description of diffusive dynamics subject to the noncrossing restriction. For a wide range of concentrations in the semidilute regime, we report values of the long time rotational diffusion constant of the rods, extrapolated to the limit of zero time step, for various sets of values of the infinite dilution (bare) diffusion constants. These results are compared with the results of a previous simulation of the model by Doi et al. and of previous simulations of rods with finite aspect ratio by Fixman and by Cobb and Butler that had been extrapolated to the limit of infinitely thin rods. The predictions of the Doi-Edwards (DE) scaling law do not hold for this model for the concentrations studied. The simulation data for the model display two deviations from the predictions of the DE theory that have been observed in experimental systems in the semidilute regime, namely, the very slow approach toward DE scaling behavior as the concentration is increased and the large value of the prefactor in the DE scaling law. We present a modified scaling principle for this model that is consistent with the simulation results for a broad range of concentrations in the semidilute regime. The modified scaling principle takes into account two physical effects, which we call "leakage" and "drift," that were found to be important for the transport properties of a simpler model of nonrotating rods on a lattice [Y.-L. S. Tse and H. C. Andersen, J. Chem. Phys. 136, 024904 (2012)], 10.1063/1.3673791.
NASA Astrophysics Data System (ADS)
Balaev, D. A.; Dubrovskiy, A. A.; Shaykhutdinov, K. A.; Popkov, S. I.; Petrov, M. I.
2009-03-01
In order to clarify the mechanism of hysteretic behavior of magnetoresistance of granular HTSC the magnetoresistance curves R(H) and time evolution of the resistance in constant applied magnetic fields have been studied in granular YBCO at T=77 K. It was found that on ascending branch of R(H) dependence the resistance at H=const decreased with time while on the descending branch the resistance increased with time in applied constant magnetic field. For the range of low magnetic fields (below the minimum point of the descending branch of R(H) dependence) the resistance at H=const decreased again. The behavior observed is well described by the model of granular HTSC, where the intergrain space is in effective magnetic field which is the superposition of the applied field and the field induced by superconducting grains. The time evolution of resistance reflects processes of time relaxation of magnetization of HTSC grains due to the intragrain flux creep.
RKKY oscillations in the spin relaxation rates of atomic-scale nanomagnets
NASA Astrophysics Data System (ADS)
Delgado, F.; Fernández-Rossier, J.
2017-02-01
Exchange interactions with itinerant electrons are known to act as a relaxation mechanism for individual local spins. The same exchange interactions induce the so-called RKKY indirect exchange interaction between two otherwise decoupled local spins. Here, we show that both the spin relaxation and the RKKY coupling can be seen as the dissipative and reactive response to the coupling of the local spins with the itinerant electrons. We thereby predict that the spin relaxation rates of magnetic nanostructures of exchanged coupled local spins, such as nanoengineered spin chains, have an oscillatory dependence on kFd , where kF is the Fermi wave number and d is the interspin distance, very much like the celebrated oscillations in the RKKY interaction. We demonstrate that both T1 and T2 can be enhanced or suppressed, compared to the single-spin limit, depending on the interplay between the Fermi surface and the nanostructure geometrical arrangement. Our results open a route to engineer spin relaxation and decoherence in atomically designed spin structures.
Time-dependent pseudo Jahn-Teller effect: Phonon-mediated long-time nonadiabatic relaxation
Vaikjärv, 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.
Nuclear Spin-Lattice Relaxation Times from Continuous Wave NMR Spectroscopy.
ERIC Educational Resources Information Center
Wooten, Jan B.; And Others
1979-01-01
The experiment described, suitable for undergraduate physical chemistry laboratories, illustrates the general principles of relaxation and introduces the nmr concepts of saturation and spin-inversion. (BB)
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.
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.
Time scales involved in emergent market coherence
NASA Astrophysics Data System (ADS)
Kwapień, J.; Drożdż, S.; Speth, J.
2004-06-01
In addressing the question of the time scales characteristic for the market formation, we analyze high-frequency tick-by-tick data from the NYSE and from the German market. By using returns on various time scales ranging from seconds or minutes up to 2 days, we compare magnitude of the largest eigenvalue of the correlation matrix for the same set of securities but for different time scales. For various sets of stocks of different capitalization (and the average trading frequency), we observe a significant elevation of the largest eigenvalue with increasing time scale. Our results from the correlation matrix study can be considered as a manifestation of the so-called Epps effect. There is no unique explanation of this effect and it seems that many different factors play a role here. One of such factors is randomness in transaction moments for different stocks. Another interesting conclusion to be drawn from our results is that in the contemporary markets the emergence of significant correlations occurs on time scales much smaller than in the more distant history.
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
Scaling and Multiscaling in Financial Time Series
2007-11-02
Prescribed by ANSI Std Z39-18 Outline 1/ A brief overview of financial markets • Basic definitions and problems related to finance • Scaling in finance 2...quantitative finance • Rational investment and risk management - Price dynamics - Risk quantification and control - Financial instruments: derivatives... finance • Supported by empirical observations • Practical interests. - Stability over time scales (by aggregation) - The same model is valid over a wide
Structural relaxation and aging scaling in the Coulomb and Bose glass models
NASA Astrophysics Data System (ADS)
Assi, Hiba; Chaturvedi, Harshwardhan; Pleimling, Michel; Täuber, Uwe Claus
2016-11-01
We employ Monte Carlo simulations to study the relaxation properties of the two-dimensional Coulomb glass in disordered semiconductors and the three-dimensional Bose glass in type-II superconductors in the presence of extended linear defects. We investigate the effects of adding non-zero random on-site energies from different distributions on the properties of the correlation-induced Coulomb gap in the density of states (DOS) and on the non-equilibrium aging kinetics highlighted by the density autocorrelation functions. We also probe the sensitivity of the system's equilibrium and non-equilibrium relaxation properties to instantaneous changes in the density of charge carriers in the Coulomb glass or flux lines in the Bose glass.
NASA Astrophysics Data System (ADS)
de Lima, Isabel; Lovejoy, Shaun
2016-04-01
The characterization of precipitation scaling regimes represents a key contribution to the improved understanding of space-time precipitation variability, which is the focus here. We conduct space-time scaling analyses of spectra and Haar fluctuations in precipitation, using three global scale precipitation products (one instrument based, one reanalysis based, one satellite and gauge based), from monthly to centennial scales and planetary down to several hundred kilometers in spatial scale. Results show the presence - similarly to other atmospheric fields - of an intermediate "macroweather" regime between the familiar weather and climate regimes: we characterize systematically the macroweather precipitation temporal and spatial, and joint space-time statistics and variability, and the outer scale limit of temporal scaling. These regimes qualitatively and quantitatively alternate in the way fluctuations vary with scale. In the macroweather regime, the fluctuations diminish with time scale (this is important for seasonal, annual, and decadal forecasts) while anthropogenic effects increase with time scale. Our approach determines the time scale at which the anthropogenic signal can be detected above the natural variability noise: the critical scale is about 20 - 40 yrs (depending on the product, on the spatial scale). This explains for example why studies that use data covering only a few decades do not easily give evidence of anthropogenic changes in precipitation, as a consequence of warming: the period is too short. Overall, while showing that precipitation can be modeled with space-time scaling processes, our results clarify the different precipitation scaling regimes and further allow us to quantify the agreement (and lack of agreement) of the precipitation products as a function of space and time scales. Moreover, this work contributes to clarify a basic problem in hydro-climatology, which is to measure precipitation trends at decadal and longer scales and to
Vugmeyster, Liliya; Ostrovsky, Dmitry; Lipton, Andrew S
2013-05-23
In order to examine the origin of the abrupt change in the temperature dependence of (2)H NMR longitudinal relaxation times observed previously for methyl groups of L69 in the hydrophobic core of villin headpiece protein at around 90 K (Vugmeyster et al. J. Am. Chem. Soc. 2010, 132, 4038-4039), we extended the measurements to several other methyl groups in the hydrophobic core. We show that, for all methyl groups, relaxation times experience a dramatic jump several orders of magnitude around this temperature. Theoretical modeling supports the conclusion that the origin of the apparent transition in the relaxation times is due to the existence of the distribution of conformers distinguished by their activation energy for methyl three-site hops. It is also crucial to take into account the differential contribution of individual conformers into overall signal intensity. When a particular conformer approaches the regime at which its three-site hop rate constant is on the order of the quadrupolar coupling interaction constant, the intensity of the signal due to this conformer experiences a sharp drop, thus changing the balance of the contributions of different conformers into the overall signal. As a result, the observed apparent transition in the relaxation rates can be explained without the assumption of an underlying transition in the rate constants. This work in combination with earlier results also shows that the model based on the distribution of conformers explains the relaxation behavior in the entire temperature range between 300 and 70 K.
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.
Hoad, Caroline L; Palaniyappan, Naaventhan; Kaye, Philip; Chernova, Yulia; James, Martin W; Costigan, Carolyn; Austin, Andrew; Marciani, Luca; Gowland, Penny A; Guha, Indra N; Francis, Susan T; Aithal, Guruprasad P
2015-06-01
Liver biopsy is the standard test for the assessment of fibrosis in liver tissue of patients with chronic liver disease. Recent studies have used a non-invasive measure of T1 relaxation time to estimate the degree of fibrosis in a single slice of the liver. Here, we extend this work to measure T1 of the whole liver and investigate the effects of additional histological factors such as steatosis, inflammation and iron accumulation on the relationship between liver T1 and fibrosis. We prospectively enrolled patients who had previously undergone liver biopsy to have MR scans. A non-breath-holding, fast scanning protocol was used to acquire MR relaxation time data (T1 and T2*), and blood serum was used to determine the enhanced liver fibrosis (ELF) score. Areas under the receiver operator curves (AUROCs) for T1 to detect advanced fibrosis and cirrhosis were derived in a training cohort and then validated in a second cohort. Combining the cohorts, the influence of various histology factors on liver T1 relaxation time was investigated. The AUROCs (95% confidence interval (CI)) for detecting advanced fibrosis (F ≥ 3) and cirrhosis (F = 4) for the training cohort were 0.81 (0.65-0.96) and 0.92 (0.81-1.0) respectively (p < 0.01). Inflammation and iron accumulation were shown to significantly alter T1 in opposing directions in the absence of advanced fibrosis; inflammation increasing T1 and iron decreasing T1. A decision tree model was developed to allow the assessment of early liver disease based on relaxation times and ELF, and to screen for the need for biopsy. T1 relaxation time increases with advanced fibrosis in liver patients, but is also influenced by iron accumulation and inflammation. Together with ELF, relaxation time measures provide a marker to stratify patients with suspected liver disease for biopsy.
NASA Astrophysics Data System (ADS)
Dinh, Thanh-Chung; Renger, Thomas
2016-07-01
In pigment-protein complexes, often the excited states are partially delocalized and the exciton-vibrational coupling in the basis of delocalized states contains large diagonal and small off-diagonal elements. This inequality may be used to introduce potential energy surfaces (PESs) of exciton states and to treat the inter-PES coupling in Markov and secular approximations. The resulting lineshape function consists of a Lorentzian peak that is broadened by the finite lifetime of the exciton states caused by the inter-PES coupling and a vibrational sideband that results from the mutual displacement of the excitonic PESs with respect to that of the ground state. So far analytical expressions have been derived that relate the exciton relaxation-induced lifetime broadening to the Redfield [T. Renger and R. A. Marcus, J. Chem. Phys. 116, 9997 (2002)] or modified Redfield [M. Schröder, U. Kleinekathöfer, and M. Schreiber, J. Chem. Phys. 124, 084903 (2006)] rate constants of exciton relaxation, assuming that intra-PES nuclear relaxation is fast compared to inter-PES transfer. Here, we go beyond this approximation and provide an analytical expression, termed Non-equilibrium Modified Redfield (NeMoR) theory, for the lifetime broadening that takes into account the finite nuclear relaxation time. In an application of the theory to molecular dimers, we find that, for a widely used experimental spectral density of the exciton-vibrational coupling of pigment-protein complexes, the NeMoR spectrum at low-temperatures (T < 150 K) is better approximated by Redfield than by modified Redfield theory. At room temperature, the lifetime broadening obtained with Redfield theory underestimates the NeMoR broadening, whereas modified Redfield theory overestimates it by a similar amount. A fortuitous error compensation in Redfield theory is found to explain the good performance of this theory at low temperatures. Since steady state spectra of PPCs are often measured at low temperatures
Dinh, Thanh-Chung; Renger, Thomas
2016-07-21
In pigment-protein complexes, often the excited states are partially delocalized and the exciton-vibrational coupling in the basis of delocalized states contains large diagonal and small off-diagonal elements. This inequality may be used to introduce potential energy surfaces (PESs) of exciton states and to treat the inter-PES coupling in Markov and secular approximations. The resulting lineshape function consists of a Lorentzian peak that is broadened by the finite lifetime of the exciton states caused by the inter-PES coupling and a vibrational sideband that results from the mutual displacement of the excitonic PESs with respect to that of the ground state. So far analytical expressions have been derived that relate the exciton relaxation-induced lifetime broadening to the Redfield [T. Renger and R. A. Marcus, J. Chem. Phys. 116, 9997 (2002)] or modified Redfield [M. Schröder, U. Kleinekathöfer, and M. Schreiber, J. Chem. Phys. 124, 084903 (2006)] rate constants of exciton relaxation, assuming that intra-PES nuclear relaxation is fast compared to inter-PES transfer. Here, we go beyond this approximation and provide an analytical expression, termed Non-equilibrium Modified Redfield (NeMoR) theory, for the lifetime broadening that takes into account the finite nuclear relaxation time. In an application of the theory to molecular dimers, we find that, for a widely used experimental spectral density of the exciton-vibrational coupling of pigment-protein complexes, the NeMoR spectrum at low-temperatures (T < 150 K) is better approximated by Redfield than by modified Redfield theory. At room temperature, the lifetime broadening obtained with Redfield theory underestimates the NeMoR broadening, whereas modified Redfield theory overestimates it by a similar amount. A fortuitous error compensation in Redfield theory is found to explain the good performance of this theory at low temperatures. Since steady state spectra of PPCs are often measured at low temperatures
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 μs 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
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.
Structure of Student Time Management Scale (STMS)
ERIC Educational Resources Information Center
Balamurugan, M.
2013-01-01
With the aim of constructing a Student Time Management Scale (STMS), the initial version was administered and data were collected from 523 standard eleventh students. (Mean age = 15.64). The data obtained were subjected to Reliability and Factor analysis using PASW Statistical software version 18. From 42 items 14 were dropped, resulting in the…
Fu, Riqiang; Li, Jun; Cui, Jingyu; Peng, Xinhua
2016-07-01
Numerous nuclear magnetic resonance (NMR) measurements of spin-lattice relaxation times (T1S) for dilute spins such as (13)C have led to investigations of the motional dynamics of individual functional groups in solid materials. In this work, we revisit the Solomon equations and analyze how the heteronuclear cross relaxation between the dilute S (e.g. (13)C) and abundant I (e.g. (1)H) spins affects the measured T1S values in solid-state NMR in the absence of (1)H saturation during the recovery time. It is found theoretically that at the beginning of the S spin magnetization recovery, the existence of non-equilibrium I magnetization introduces the heteronuclear cross relaxation effect onto the recovery of the S spin magnetization and confirmed experimentally that such a heteronuclear cross relaxation effect results in the recovery overshoot phenomena for the dilute spins when T1S is on the same order of T1H, leading to inaccurate measurements of the T1S values. Even when T1S is ten times larger than T1H, the heteronuclear cross relaxation effect on the measured T1S values is still noticeable. Furthermore, this cross relaxation effect on recovery trajectory of the S spins can be manipulated and even suppressed by preparing the initial I and S magnetization, so as to obtain the accurate T1S values. A sample of natural abundance l-isoleucine powder has been used to demonstrate the T1S measurements and their corresponding measured T1C values under various experimental conditions.
NASA Astrophysics Data System (ADS)
Clay, M. P.; Yeung, P. K.; Warhaft, Z.
2015-11-01
Turbulence subjected to axisymmetric strain is a fundamental problem which is common in engineering equipment with variable cross-section, but is not yet fully understood. We have performed direct numerical simulations on a deforming domain with grids up to 10243 and a time-dependent strain history designed to mimic spatial gradients in wind-tunnel experiments. Isotropic turbulence with a specified energy spectrum is allowed to decay and then passed through a numerical conduit of 4:1 contraction ratio. The Reynolds stress tensor, velocity gradient variances, and longitudinal and transverse one-dimensional (1D) spectra are studied during both the contraction and subsequent relaxation. Contraction leads to amplification of energy in the compressed directions and departures from local isotropy. When the strain is removed local isotropy returns quickly while the energy decays with a power law exponent smaller than for decaying isotropic turbulence. The evolution of 1D spectra including changes in shape is consistent with experiments, but a large solution domain is important. Supported by NSF Grant CBET-1510749 (Fluid Dynamics Program).
[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.
NASA Astrophysics Data System (ADS)
Socratous, Josephine; Watanabe, Shun; Banger, Kulbinder K.; Warwick, Christopher N.; Branquinho, Rita; Barquinha, Pedro; Martins, Rodrigo; Fortunato, Elvira; Sirringhaus, Henning
2017-01-01
Despite the success of exploiting the properties of amorphous oxide semiconductors for device applications, the charge transport in these materials is still not clearly understood. The observation of a definite Hall voltage suggests that electron transport in the conduction band is free-electron-like. However, the temperature dependence of the Hall and field-effect mobilities cannot be explained using a simple bandlike model. Here, we perform gated Hall effect measurements in field-effect transistors, which allow us to make two independent estimates of the charge carrier concentration and determine the Hall factor providing information on the energy dependence of the relaxation time. We demonstrate that the Hall factor in a range of sputtered and solution-processed quaternary amorphous oxides, such as a-InGaZnO, is close to two, while in ternary oxides, such as InZnO, it is near unity. This suggests that quaternary elements like Ga act as strong ionized impurity scattering centers in these materials.
Role of band-index-dependent transport relaxation times in anomalous Hall effect
NASA Astrophysics Data System (ADS)
Xiao, Cong; Li, Dingping; Ma, Zhongshui
2017-01-01
We revisit model calculations of the anomalous Hall effect (AHE) and show that, in isotropic Rashba-coupled two-dimensional electron gas with pointlike potential impurities, the full solution of the semiclassical Boltzmann equation (SBE) may differ from the widely used 1 /τ|| and 1 /τ⊥ solution [Schliemann and Loss, Phys. Rev. B 68, 165311 (2003), 10.1103/PhysRevB.68.165311]. Our approach to solving the SBE is consistent with the integral equation approach [Vyborny et al., Phys. Rev. B 79, 045427 (2009), 10.1103/PhysRevB.79.045427] but in the present case, we reduce the description to band-index-dependent transport relaxation times. When both Rashba bands are partially occupied, these are determined by solving a system of linear equations. Detailed calculations show that, for intrinsic and hybrid skew scatterings the difference between 1 /τ|| and 1 /τ⊥ and the full solution of SBE is notable for large Fermi energies. For coordinate-shift effects, the side-jump velocity acquired in the interband elastic-scattering process is shown to be more important for larger Rashba coupling and may even exceed the intraband one for the outer Rashba band. The coordinate-shift contribution to AHE in the considered case notably differs from that in the limit of smooth disorder potential analyzed before.
Tighten after Relax: Minimax-Optimal Sparse PCA in Polynomial Time
Wang, Zhaoran; Lu, Huanran; Liu, Han
2014-01-01
We provide statistical and computational analysis of sparse Principal Component Analysis (PCA) in high dimensions. The sparse PCA problem is highly nonconvex in nature. Consequently, though its global solution attains the optimal statistical rate of convergence, such solution is computationally intractable to obtain. Meanwhile, although its convex relaxations are tractable to compute, they yield estimators with suboptimal statistical rates of convergence. On the other hand, existing nonconvex optimization procedures, such as greedy methods, lack statistical guarantees. In this paper, we propose a two-stage sparse PCA procedure that attains the optimal principal subspace estimator in polynomial time. The main stage employs a novel algorithm named sparse orthogonal iteration pursuit, which iteratively solves the underlying nonconvex problem. However, our analysis shows that this algorithm only has desired computational and statistical guarantees within a restricted region, namely the basin of attraction. To obtain the desired initial estimator that falls into this region, we solve a convex formulation of sparse PCA with early stopping. Under an integrated analytic framework, we simultaneously characterize the computational and statistical performance of this two-stage procedure. Computationally, our procedure converges at the rate of 1∕t within the initialization stage, and at a geometric rate within the main stage. Statistically, the final principal subspace estimator achieves the minimax-optimal statistical rate of convergence with respect to the sparsity level s*, dimension d and sample size n. Our procedure motivates a general paradigm of tackling nonconvex statistical learning problems with provable statistical guarantees. PMID:25620858
Grain boundary effects on the optical constants and Drude relaxation times of silver films
NASA Astrophysics Data System (ADS)
Jiang, Yajie; Pillai, Supriya; Green, Martin A.
2016-12-01
Silver demonstrates the unique optical properties that make it suitable for various plasmonic applications. Determining the accurate optical constants for silver and investigating its dependence on grain structures are necessary for reliable theoretical predictions. This work investigates the effects of different deposition conditions and the resultant variable grain sizes, upon the optical properties of the silver films in conjunction with ellipsometry and optical characterization. Annealing conditions of substrate SiNx films were also studied to ensure good quality of deposited polycrystalline silver films. The effects of grain sizes of silver on its electronic relaxation times were studied and shown to be consistent with the theoretical electrical resistivity model. This study shows that voids and surface layers can affect the optical constant values and that reproducible results can be obtained by avoiding such artefacts. The results will have implications on the analysis of different silver based nanostructures like nanowires and nanorods where grain boundary scattering can affect the optical and electrical properties like reflection and resistivity.
Kendall, William L.; Hines, James E.; Nichols, James D.; Grant, Evan H. Campbell
2013-01-01
Occupancy statistical models that account for imperfect detection have proved very useful in several areas of ecology, including species distribution and spatial dynamics, disease ecology, and ecological responses to climate change. These models are based on the collection of multiple samples at each of a number of sites within a given season, during which it is assumed the species is either absent or present and available for detection while each sample is taken. However, for some species, individuals are only present or available for detection seasonally. We present a statistical model that relaxes the closure assumption within a season by permitting staggered entry and exit times for the species of interest at each site. Based on simulation, our open model eliminates bias in occupancy estimators and in some cases increases precision. The power to detect the violation of closure is high if detection probability is reasonably high. In addition to providing more robust estimation of occupancy, this model permits comparison of phenology across sites, species, or years, by modeling variation in arrival or departure probabilities. In a comparison of four species of amphibians in Maryland we found that two toad species arrived at breeding sites later in the season than a salamander and frog species, and departed from sites earlier.
Long Spin Relaxation and Coherence Times of Electrons In Gated Si/SiGe Quantum Dots
NASA Astrophysics Data System (ADS)
He, Jianhua; Tyryshkin, A. M.; Lyon, S. A.; Lee, C.-H.; Huang, S.-H.; Liu, C. W.
2012-02-01
Single electron spin states in semiconductor quantum dots are promising candidate qubits. We report the measurement of 250 μs relaxation (T1) and coherence (T2) times of electron spins in gated Si/SiGe quantum dots at 350 mK. The experiments used conventional X-band (10 GHz) pulsed electron spin resonance (pESR), on a large area (3.5 x 20 mm^2) dual-gate undoped high mobility Si/SiGe heterostructure sample, which was patterned with 2 x 10^8 quantum dots using e-beam lithography. Dots having 150 nm radii with a 700 nm period are induced in a natural Si quantum well by the gates. The measured T1 and T2 at 350 mK are much longer than those of free 2D electrons, for which we measured T1 to be 10 μs and T2 to be 6.5 μs in this gated sample. The results provide direct proof that the effects of a fluctuating Rashba field have been greatly suppressed by confining the electrons in quantum dots. From 0.35 K to 0.8 K, T1 of the electron spins in the quantum dots shows little temperature dependence, while their T2 decreased to about 150 μs at 0.8 K. The measured 350 mK spin coherence time is 10 times longer than previously reported for any silicon 2D electron-based structures, including electron spins confined in ``natural quantum dots'' formed by potential disorder at the Si/SiO2ootnotetextS. Shankar et al., Phys. Rev. B 82, 195323 (2010) or Si/SiGe interface, where the decoherence appears to be controlled by spin exchange.
Hu, Lili; Song, Tao; Yang, Wenhui; Wang, Ming; Zhang, Fang; Tao, Chunjing
2007-06-01
To research on the effect of three different magnetic nanoparticles upon relaxation time of proton. The detection by magnetic resonance imaging (MRI) indicates that there is the effect of marked difference to right control experiment and to analyze the difference from theory. The result discloses that will be able to perform the experiment of molecular recognition using magnetic nanoparticles later.
NASA Astrophysics Data System (ADS)
Carpenter, B. M.; Ikari, M. J.; Marone, C.
2016-02-01
Interseismic recovery of fault strength (healing) following earthquake failure is a fundamental requirement of the seismic cycle and likely plays a key role in determining the stability and slip behavior of tectonic faults. We report on laboratory measurements of time- and slip-dependent frictional strengthening for natural and synthetic gouges to evaluate the role of mineralogy in frictional strengthening. We performed slide-hold-slide (SHS) shearing experiments on nine natural fault gouges and eight synthetic gouges at conditions of 20 MPa normal stress, 100% relative humidity (RH), large shear strain (~15), and room temperature. Phyllosilicate-rich rocks show the lowest rates of frictional strengthening. Samples rich in quartz and feldspar exhibit intermediate rates of frictional strengthening, and calcite-rich gouges show the largest values. Our results show that (1) the rates of frictional strengthening and creep relaxation scale with frictional strength, (2) phyllosilicate-rich fault gouges have low strength and healing characteristics that promote stable, aseismic creep, (3) most natural fault gouges exhibit intermediate rates of frictional strengthening, consistent with a broad range of fault slip behaviors, and (4) calcite-rich fault rocks show the highest rates of frictional strengthening, low values of dilation upon reshear, and high frictional strengths, all of which would promote seismogenic behavior.
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.
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.
Electrochemical properties and relaxation times of the hematite/water interface.
Shimizu, Kenichi; Boily, Jean-François
2014-08-12
Electric double layer properties and protonation rates at the surface of a mechanically and chemically polished (001) surface of hematite (α-Fe2O3) contacted with aqueous solutions of NaCl were extracted by electrochemical impedance spectroscopy (EIS). Effects of pH (4-12) and ionic strength (10-1000 mM) on the EIS response of the electrode were predicted using an electrical equivalent circuit model accounting for hematite bulk and interfacial processes. These efforts generated diffuse layer as well as compact layer capacitances and resistance values pertaining to interfacial processes. Diffuse layer capacitance values lie in the 0.5-0.6 μF cm(-2) region and are about 1.5 times smaller than those obtained on a roughened hematite surface. Compact layer capacitances are strongly pH dependent as they pertain to the transfer of ions (charge carriers) from the diffuse layer onto surface (hydr)oxo groups. These values, alongside those of resistance adsorption, pointed a 50% decrease in proton adsorption/desorption resistance under acidic and alkaline conditions relative to that of the point of zero charge (pH 8-9). Increasing ionic strength generally induces larger diffuse layer capacitances, larger adsorption capacitances, and lower resistance values. Such a response is in line with the concept for thinner electric double layers and facilitated proton adsorption reactions by solutions of high ionic strengths. Relaxation times pertaining to the transfer of charge carriers across the compact plane induced by the EIS experiments lie in the 0.7-4.2 s range and become larger under acidic conditions. Decreases in site availability and increases in electrostatic repulsion are two possible contributing factors impeding reaction rates below the point of zero charge. Collectively, these finding are underpinning important relationships between classical views on mineral surface complexation reactions and electrochemical views of semiconductor/water interfaces.
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.
KUMAR, DEEPAK; SUBBURAJ, KARUPPPASAMY; LIN, WILSON; KARAMPINOS, DIMITRIOS C.; MCCULLOCH, CHARLES E.; LI, XIAOJUAN; LINK, THOMAS M.; SOUZA, RICHARD B.; MAJUMDAR, SHARMILA
2015-01-01
STUDY DESIGN Controlled laboratory study using a cross-sectional design. OBJECTIVES To analyze the relationship of quadriceps-hamstrings and medial-lateral quadriceps anatomical cross-sectional area (ACSA) ratios with knee loads during walking and articular and meniscal cartilage composition in young, healthy subjects. BACKGROUND Muscle forces affect knee loading during walking, but it is not known if muscle morphology is associated with walking mechanics and cartilage composition in young subjects. METHODS Forty-two knees from 27 young, healthy, active volunteers (age, 20-35 years; body mass index, <28 kg/m2) underwent 3-T magnetic resonance imaging (MRI) and 3-D motion capture. Standard MRI sequences were used for articular and meniscal cartilage T1rho and T2 relaxation times and for quadriceps and hamstrings muscle ACSA. Frontal plane kinetics during the stance phase of walking was calculated. Generalized estimating equation models were used to identify muscle variables that predicted MRI and gait parameters. RESULTS Quadriceps-hamstrings and medial-lateral quadriceps ACSA ratios were positively related to frontal plane loading (β = .27-.54, P≤.006), global articular cartilage relaxation times (β = .22-.28, P≤.041), and the medial-lateral ratio of meniscus T1rho relaxation time (β = .26-.36, P≤.049). The medial-lateral quadriceps ACSA ratio was positively related to global meniscus T1rho relaxation times (β = .30, P = .046). CONCLUSION Higher quadriceps-hamstrings and medial-lateral quadriceps ACSA ratios were associated with higher frontal plane loading during walking and with articular and meniscal cartilage T1rho and T2 relaxation times. These findings highlight the relationships between different knee tissues and knee mechanics in young, healthy individuals. PMID:24175607
Boddy, A M; McGowen, M R; Sherwood, C C; Grossman, L I; Goodman, M; Wildman, D E
2012-05-01
There is a well-established allometric relationship between brain and body mass in mammals. Deviation of relatively increased brain size from this pattern appears to coincide with enhanced cognitive abilities. To examine whether there is a phylogenetic structure to such episodes of changes in encephalization across mammals, we used phylogenetic techniques to analyse brain mass, body mass and encephalization quotient (EQ) among 630 extant mammalian species. Among all mammals, anthropoid primates and odontocete cetaceans have significantly greater variance in EQ, suggesting that evolutionary constraints that result in a strict correlation between brain and body mass have independently become relaxed. Moreover, ancestral state reconstructions of absolute brain mass, body mass and EQ revealed patterns of increase and decrease in EQ within anthropoid primates and cetaceans. We propose both neutral drift and selective factors may have played a role in the evolution of brain-body allometry.
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.
Special Issue on Time Scale Algorithms
2008-01-01
unclassified Standard Form 298 (Rev. 8-98) Prescribed by ANSI Std Z39-18 IOP PUBLISHING METROLOGIA Metrologia 45 (2008) doi:10.1088/0026-1394/45/6/E01...special issue of Metrologia presents selected papers from the Fifth International Time Scale Algorithm Symposium (VITSAS), including some of the...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
Time Scales, Coherency, and Weak Coupling.
1980-10-01
U. S. Department of Energy, Electric Energy Systems Division, under Contract EX-76-C-01-2088; in part by the National Science Foundation under Grant...for the degree of Doctor of Philosophy in Electrical Engineering in the Graduate College of the University of Illinois at Urbana-Champaign, 1980... Electrical Engineering University of Illinois at Urbana-Champaign, 1980 In this thesis we study a relation between time scales and structural properties of
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.
Liquidity crises on different time scales.
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.
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)
Monthus, Cécile
2014-08-01
We consider the long-ranged Ising spin-glass with random couplings decaying as a power-law of the distance, in the region of parameters where the spin-glass phase exists with a positive droplet exponent. For the Metropolis single-spin-flip dynamics near zero temperature, we construct via real-space renormalization the full hierarchy of relaxation times of the master equation for any given realization of the random couplings. We then analyze the probability distribution of dynamical barriers as a function of the spatial scale. This real-space renormalization procedure represents a simple explicit example of the droplet scaling theory, where the convergence towards local equilibrium on larger and larger scales is governed by a strong hierarchy of activated dynamical processes, with valleys within valleys.
Multidimensional scaling of musical time estimations.
Cocenas-Silva, Raquel; Bueno, José Lino Oliveira; Molin, Paul; Bigand, Emmanuel
2011-06-01
The aim of this study was to identify the psycho-musical factors that govern time evaluation in Western music from baroque, classic, romantic, and modern repertoires. The excerpts were previously found to represent variability in musical properties and to induce four main categories of emotions. 48 participants (musicians and nonmusicians) freely listened to 16 musical excerpts (lasting 20 sec. each) and grouped those that seemed to have the same duration. Then, participants associated each group of excerpts to one of a set of sine wave tones varying in duration from 16 to 24 sec. Multidimensional scaling analysis generated a two-dimensional solution for these time judgments. Musical excerpts with high arousal produced an overestimation of time, and affective valence had little influence on time perception. The duration was also overestimated when tempo and loudness were higher, and to a lesser extent, timbre density. In contrast, musical tension had little influence.
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.
Zakharov, Anatoly I.; Adzhemyan, Loran Ts.; Shchekin, Alexander K.
2015-09-28
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.
Biller, Joshua R.; Meyer, Virginia; Elajaili, Hanan; Rosen, Gerald M.; Kao, Joseph P.Y.; Eaton, Sandra S.; Eatona, Gareth R.
2011-01-01
Optimization of nitroxides as probes for EPR imaging requires detailed understanding of spectral properties. Spin lattice relaxation times, spin packet line widths, nuclear hyperfine splitting, and overall lineshapes were characterized for six low molecular weight nitroxides in dilute deoxygenated aqueous solution at X-band. The nitroxides included 6-member, unsaturated 5-member, or saturated 5-member rings, most of which were isotopically labeled. The spectra are near the fast tumbling limit with T1 ~ T2 in the range of 0.50 to 1.1 μs at ambient temperature. Both spin-lattice relaxation T1 and spin-spin relaxation T2 are longer for 15N- than for 14N-nitroxides. The dominant contributions to T1 are modulation of nitrogen hyperfine anisotropy and spin rotation. Dependence of T1 on nitrogen nuclear spin state mI was observed for both 14N and 15N. Unresolved hydrogen/deuterium hyperfine couplings dominate overall line widths. Lineshapes were simulated by including all nuclear hyperfine couplings and spin packet line widths that agreed with values obtained by electron spin echo. Line widths and relaxation times are predicted to be about the same at 250 MHz as at X-band. PMID:21843961
Harsh Corporal Punishment Is Associated With Increased T2 Relaxation Time in Dopamine-Rich Regions
Sheu, Yi-Shin; Polcari, Ann; Anderson, Carl M.; Teicher, Martin H.
2010-01-01
Harsh corporal punishment (HCP) was defined as frequent parental administration of corporal punishment (CP) for discipline, with occasional use of objects such as straps, or paddles. CP is linked to increased risk for depression and substance abuse. We examine whether long-term exposure to HCP acts as sub-traumatic stressor that contributes to brain alterations, particularly in dopaminergic pathways, which may mediate their increased vulnerability to drug and alcohol abuse. Nineteen young adults who experienced early HCP but no other forms of maltreatment and twenty-three comparable controls were studied. T2 relaxation time (T2-RT) measurements were performed with an echo planar imaging TE stepping technique and T2 maps were calculated and analyzed voxel-by-voxel to locate regional T2-RT differences between groups. Previous studies indicated that T2-RT provides an indirect index of resting cerebral blood volume. Region of interest (ROI) analyses were also conducted in caudate, putamen, nucleus accumbens, anterior cingulate cortex, dorsolateral prefrontal cortex, thalamus, globus pallidus and cerebellar hemispheres. Voxel-based relaxometry showed that HCP was associated with increased T2-RT in right caudate and putamen. ROI analyses also revealed increased T2-RT in dorsolateral prefrontal cortex, substantia nigra, thalamus and accumbens but not globus pallidus or cerebellum. There were significant associations between T2-RT measures in dopamine target regions and use of drugs and alcohol, and memory performance. Alteration in the paramagnetic or hemodynamic properties of dopaminergic cell body and projection regions were observed in subjects with HCP, and these findings may relate to their increased risk for drug and alcohol abuse. PMID:20600981
Harsh corporal punishment is associated with increased T2 relaxation time in dopamine-rich regions.
Sheu, Yi-Shin; Polcari, Ann; Anderson, Carl M; Teicher, Martin H
2010-11-01
Harsh corporal punishment (HCP) was defined as frequent parental administration of corporal punishment (CP) for discipline, with occasional use of objects such as straps, or paddles. CP is linked to increased risk for depression and substance abuse. We examine whether long-term exposure to HCP acts as sub-traumatic stressor that contributes to brain alterations, particularly in dopaminergic pathways, which may mediate their increased vulnerability to drug and alcohol abuse. Nineteen young adults who experienced early HCP but no other forms of maltreatment and twenty-three comparable controls were studied. T2 relaxation time (T2-RT) measurements were performed with an echo planar imaging TE stepping technique and T2 maps were calculated and analyzed voxel-by-voxel to locate regional T2-RT differences between groups. Previous studies indicated that T2-RT provides an indirect index of resting cerebral blood volume. Region of interest (ROI) analyses were also conducted in caudate, putamen, nucleus accumbens, anterior cingulate cortex, dorsolateral prefrontal cortex, thalamus, globus pallidus and cerebellar hemispheres. Voxel-based relaxometry showed that HCP was associated with increased T2-RT in right caudate and putamen. ROI analyses also revealed increased T2-RT in dorsolateral prefrontal cortex, substantia nigra, thalamus and accumbens but not globus pallidus or cerebellum. There were significant associations between T2-RT measures in dopamine target regions and use of drugs and alcohol, and memory performance. Alteration in the paramagnetic or hemodynamic properties of dopaminergic cell body and projection regions were observed in subjects with HCP, and these findings may relate to their increased risk for drug and alcohol abuse.
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
Time ephemeris and general relativistic scale factor
NASA Astrophysics Data System (ADS)
Fukushima, Toshio
2010-01-01
Time ephemeris is the location-independent part of the transformation formula relating two time coordinates such as TCB and TCG (Fukushima 1995). It is computed from the corresponding (space) ephemerides providing the relative motion of two spatial coordinate origins such as the motion of geocenter relative to the solar system barycenter. The time ephemerides are inevitably needed in conducting precise four dimensional coordinate transformations among various spacetime coordinate systems such as the GCRS and BCRS (Soffel et al. 2003). Also, by means of the time average operation, they are used in determining the information on scale conversion between the pair of coordinate systems, especially the difference of the general relativistic scale factor from unity such as LC. In 1995, we presented the first numerically-integrated time ephemeris, TE245, from JPL's planetary ephemeris DE245 (Fukushima 1995). It gave an estimate of LC as 1.4808268457(10) × 10-8, which was incorrect by around 2 × 10-16. This was caused by taking the wrong sign of the post-Newtonian contribution in the final summation. Four years later, we updated TE245 to TE405 associated with DE405 (Irwin and Fukushima 1999). This time the renewed vale of LC is 1.48082686741(200) × 10-8 Another four years later, by using a precise technique of time average, we improved the estimate of Newtonian part of LC for TE405 as 1.4808268559(6) × 10-8 (Harada and Fukushima 2003). This leads to the value of LC as LC = 1.48082686732(110) × 10-8. If we combine this with the constant defining the mean rate of TCG-TT, LG = 6.969290134 × 10-10 (IAU 2001), we estimate the numerical value of another general relativistic scale factor LB = 1.55051976763(110) × 10-8, which has the meaning of the mean rate of TCB-TT. The main reasons of the uncertainties are the truncation effect in time average and the uncertainty of asteroids' perturbation. The former is a natural limitation caused by the finite length of numerical
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.
Deciphering Time Scale Hierarchy in Reaction Networks.
Nagahata, Yutaka; Maeda, Satoshi; Teramoto, Hiroshi; Horiyama, Takashi; Taketsugu, Tetsuya; Komatsuzaki, Tamiki
2016-03-03
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.
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.
NASA Astrophysics Data System (ADS)
Vazina, A. A.; Gadzhiev, A. M.; Gerasimov, V. S.; Gorbunova, N. P.; Sergienko, P. M.; Korneev, V. N.; Aulchenko, V. M.; Baru, S. E.
1995-02-01
The use of the modern time-resolved X-ray diffraction and sample technique has played an important role in studying muscle structures during contraction at various physiological conditions. We represent time-resolved X-ray data on equatorial diffraction and tension response of the frog sartorius muscle during relaxation. The measurements of the time-course of the intensity change of reflections (1,0), (1,1) and the background under them give a possibility to study the effect of potentiation of contraction by repetitive stimulation in fresh and tired muscles. Model calculations of meridional diffraction patterns for various configurations of cross-bridges in the relaxation phase were carried out.
Relaxation of liquid bridge after droplets coalescence
NASA Astrophysics Data System (ADS)
Zheng, Jiangen; Shi, Haiyang; Chen, Guo; Huang, Yingzhou; Wei, Hua; Wang, Shuxia; Wen, Weijia
2016-11-01
We investigate the relaxation of liquid bridge after the coalescence of two sessile droplets resting on an organic glass substrate both experimentally and theoretically. The liquid bridge is found to relax to its equilibrium shape via two distinct approaches: damped oscillation relaxation and underdamped relaxation. When the viscosity is low, damped oscillation shows up, in this approach, the liquid bridge undergoes a damped oscillation process until it reaches its stable shape. However, if the viscous effects become significant, underdamped relaxation occurs. In this case, the liquid bridge relaxes to its equilibrium state in a non-periodic decay mode. In depth analysis indicates that the damping rate and oscillation period of damped oscillation are related to an inertial-capillary time scale τc. These experimental results are also testified by our numerical simulations with COMSOL Multiphysics.
NASA Astrophysics Data System (ADS)
Iyengar, Shruthi S.; Parthasarathi, Praveen; Selvan, Rekha; Bhattacharya, Sarbari; Ananthamurthy, Sharath
2016-04-01
Optical Tweezers are capable of trapping individual particles of sizes that range from micrometers to sub micrometers. One can compute the trap strength experienced by a particle by analyzing the fluctuations in the position of the trapped particle with time. It is reported that the trap strength of a dielectric bead increases linearly with increase in the power of the trapping laser. The situation with metallic particles, however, is strongly dependent on the particle size. Available literature shows that metallic Rayleigh particles experience enhanced trap strengths when compared to dielectric particles of similar sizes due to a larger polarizability. On the contrary, micrometer sized metallic particles are poor candidates for trapping due to high reflectivity. We report here that commercially available micrometer sized metal oxide core - dielectric shell (core - shell) beads are trapped in a single beam optical tweezer in a manner similar to dielectric beads. However as the laser power is increased these core - shell beads are trapped with a reduced corner frequency, which represents a lowered trap strength, in contrast to the situation with ordinary dielectric beads. We attribute this anomaly to an increase in the temperature of the medium in the vicinity of the core - shell bead due to an enhanced dissipation of the laser power as heat. We have computed autocorrelation functions for both types of beads at various trapping laser powers and observe that the variation in the relaxation times with laser power for core - shell beads is opposite in trend to that of ordinary dielectric beads. This supports our claim of an enhanced medium temperature about the trapped core - shell bead. Since an increase in temperature should lead to a change in the local viscosity of the medium, we have estimated the ratio of viscosity to temperature for core - shell and dielectric beads of the same size. We observe that while for ordinary dielectric beads this ratio remains a
SU-E-T-531: Large--Scale DVH Quality Study: Correlated Aims Lead Relaxations
Nohadani, O; Roy, A; Das, I
2015-06-15
Purpose: Intensity modulated radiation therapy plans are designed to optimally target a tumor while sparing surrounding tissue. Desired dose distributions are iteratively approached via inverse planning. This leads to tradeoffs between clinical objectives for the planning target volume (PTV), organs at risk, and normal tissues. Dose volume histogram (DVHs) related aims are followed that are either institutional or internationally recommended. We analyze common goals and identify potential reasons that often lead to tradeoffs. Methods: 524 IMRT plans for various tumor sites were analyzed based on the main institutional DVH goal for PTV (D95) and the recommendations by ICRU-83 (D2, D50, and D98). Robust statistical tools are developed and applied to ensure that the results are immune to data uncertainties. The probability of violation was measured for each of the DVH goals based on the frequency of not meeting recommended doses. Conditional probabilities for satisfying and/or violating DVH aims were computed to test the hypothesized pair-wise relations between DVH aims. For example, for plans that satisfied D50, the probability of violating D98 was computed via P(D98 < 95% | 98% ≤ D50 ≤ 102%). The equality constraint D50 = 100% was relaxed to encompass the range [98,102]%. Results: A large majority of cases (88%) satisfied the institutional goal for PTV of D95 ≤ 95%. Similar consensus existed for D98. 51% of cases satisfied D2 ≥ 107%. However, only 18% of cases satisfied D50. The conditional probability showed correlations amongst the studied DVH goals. In fact, a negative correlation was revealed between D50 and D95 (and D98), suggesting that these competing goals cannot be satisfied concurrently. Conclusion: The majority of plans followed the institutional guidelines. The reason for their deviation from international recommendations seems to be that the latter goals are competing and cannot be satisfied concurrently in clinical practice.
Kumar, Deepak; Schooler, Joseph; Zuo, Jin; McCulloch, Charles E.; Nardo, Lorenzo; Link, Thomas M.; Li, Xiaojuan; Majumdar, Sharmila
2012-01-01
Objective To analyze knee trabecular bone structure and spatial cartilage T1ρ and T2 relaxation times using 3-T MRI in subjects with and without tears of posterior horn of medial meniscus (PHMM). Design 3-T MRI from 59 subjects (> 18 years), were used to evaluate PHMM tears based on modified WORMS scoring; and to calculate apparent trabecular bone - volume over total bone volume fraction (app. BV/TV), number (app. Tb.N), separation (app. Tb.Sp) and thickness (app. Tb.Th) for overall femur/tibia and medial/lateral femur/tibia; and relaxation times for deep and superficial layers of articular cartilage. A repeated measures analysis using GEE was performed to compare trabecular bone and cartilage relaxation time parameters between people with (n = 35) and without (n= 24) PHMM tears, while adjusting for age and knee OA presence. Results Subjects with PHMM tears had lower app. BV./TV and app. Tb.N, and greater app. Tb.Th, and app. Tb.Sp. They also had higher T1ρ times in the deep cartilage layer for lateral tibia and medial femur and higher T2 relaxation times for the deep cartilage layer across all compartments. Conclusions PHMM tears are associated with differences in underlying trabecular bone and deep layer of cartilage. Overload of subchondral bone can lead to its sclerosis and stress shielding of trabecular bone leading to the resorptive changes observed in this study. The results underline the importance of interactions of trabecular bone and cartilage in the pathogenesis of knee OA in people with PHMM tears. PMID:23047010
Cratering time scales for the Galilean satellites
NASA Technical Reports Server (NTRS)
Shoemaker, E. M.; Wolfe, R. F.
1982-01-01
An attempt is made to estimate the present cratering rate for each Galilean satellite within the correct order of magnitude and to extend the cratering rates back into the geologic past on the basis of evidence from the earth-moon system. For collisions with long and short period comets, the magnitudes and size distributions of the comet nuclei, the distribution of their perihelion distances, and the completeness of discovery are addressed. The diameters and masses of cometary nuclei are assessed, as are crater diameters and cratering rates. The dynamical relations between long period and short period comets are discussed, and the population of Jupiter-crossing asteroids is assessed. Estimated present cratering rates on the Galilean satellites are compared and variations of cratering rate with time are considered. Finally, the consistency of derived cratering time scales with the cratering record of the icy Galilean satellites is discussed.
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.
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.
Papaleo, R. M.; Leal, R.; Carreira, W. H.; Barbosa, L. G.; Bello, I.; Bulla, A.
2006-09-01
We report on measurements of relaxation times of nanometer-sized deformations resulting from the impact of individual energetic ions on poly(methyl methacrylate) surfaces at temperatures close to and below the glass transition T{sub g}. The temporal evolution of the dimensions of the deformations is well described by a stretched exponential function, but with relaxation times {tau}(T) many orders of magnitude smaller than bulk values at the same T. The local T{sub g} was around 86 deg. C, roughly 30 deg. C below the conventional bulk T{sub g}. At the vicinity of the local T{sub g}, {tau}(T) follows the Vogel-Fulcher type of T dependence, but at lower T a transition towards a less steep behavior is seen.
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)
Marzola, Luca; Raidal, Martti
2016-11-01
Motivated by natural inflation, we propose a relaxation mechanism consistent with inflationary cosmology that explains the hierarchy between the electroweak scale and Planck scale. This scenario is based on a selection mechanism that identifies the low-scale dynamics as the one that is screened from UV physics. The scenario also predicts the near-criticality and metastability of the Standard Model (SM) vacuum state, explaining the Higgs boson mass observed at the Large Hadron Collider (LHC). Once Majorana right-handed neutrinos are introduced to provide a viable reheating channel, our framework yields a corresponding mass scale that allows for the seesaw mechanism as well as for standard thermal leptogenesis. We argue that considering singlet scalar dark matter extensions of the proposed scenario could solve the vacuum stability problem and discuss how the cosmological constant problem is possibly addressed.
SU-E-I-64: Transverse Relaxation Time in Methylene Protons of Non-Alcoholic Fatty Liver Disease Rats
Song, K-H; Lee, D-W; Choe, B-Y
2015-06-15
Purpose: The aim of this study was to evaluate transverse relaxation time of methylene resonance compared to other lipid resonances. Methods: The examinations were performed using a 3.0 T scanner with a point — resolved spectroscopy (PRESS) sequence. Lipid relaxation time in a lipid phantom filled with canola oil was estimated considering repetition time (TR) as 6000 msec and echo time (TE) as 40 — 550 msec. For in vivo proton magnetic resonance spectroscopy ({sup 1}H — MRS), eight male Sprague — Dawley rats were given free access to a normal - chow (NC) and eight other male Sprague-Dawley rats were given free access to a high — fat (HF) diet. Both groups drank water ad libitum. T{sub 2} measurements in the rats’ livers were conducted at a fixed TR of 6000 msec and TE of 40 – 220 msec. Exponential curve fitting quality was calculated through the coefficients of determination (R{sup 2}). Results: A chemical analysis of phantom and liver was not performed but a T{sub 2} decay curve was acquired. The T{sub 2} relaxation time of methylene resonance was estimated as follows: NC rats, 37.07 ± 4.32 msec; HF rats, 31.43 ± 1.81 msec (p < 0.05). The extrapolated M0 values were higher in HF rats than in NC rats (p < 0.005). Conclusion: This study of {sup 1}H-MRS led to sufficient spectral resolution and signal — to — noise ratio differences to characterize all observable resonances for yielding T{sub 2} relaxation times of methylene resonance. {sup 1}H — MRS relaxation times may be useful for quantitative characterization of various liver diseases, including fatty liver disease. This study was supported by grant (2012-007883 and 2014R1A2A1A10050270) from the Mid-career Researcher Program through the NRF funded by Ministry of Science. In addition, this study was supported by the Industrial R&D of MOTIE/KEIT (10048997, Development of the core technology for integrated therapy devices based on real-time MRI-guided tumor tracking)
NASA Astrophysics Data System (ADS)
Lafarge, Denis
1993-02-01
Recently, Avellaneda and Torquato [Phys. Fluids A 3, 2529 (1991)] derived several expressions for both the static and dynamic permeability for flow through porous media, in terms of the characteristic viscous relaxation times. In this Brief Communication the focus is on the physical interpretation, Darcy's law is explicitly obtained, and a slightly misleading statement (which has no effect on the mathematics but may induce erroneous interpretations) is corrected.
NASA Astrophysics Data System (ADS)
Hess, C.; Herick, J.; Berlin, A.; Meyer, W.; Reicherz, G.
2012-12-01
The electron spin-lattice relaxation time (T1e) of TEMPO- and trityl-doped butanol samples at 2.5 T and temperatures between 0.95 K and 2.17 K was studied by pulsed nuclear magnetic resonance (NMR) using the nuclear-electron double resonance (NEDOR) method. This method is based on the idea to measure the NMR lineshift produced by the local field of paramagnetic impurities, whose polarization can be manipulated. This is of technical advantage as measurements can be performed under conditions typically used for the dynamic nuclear polarization (DNP) process - in our case 2.5 T and temperatures around 1 K - where a direct measurement on the electronic spins would be far more complicated to perform. As T1e is a crucial parameter determining the overall efficiency of DNP, the effect of the radical type, its spin concentration, the temperature and the oxygen content on T1e has been investigated. For radical concentrations as used in DNP (several 1019 spins/cm3) the relaxation rate (T1e-1) has shown a linear dependence on the paramagnetic electron concentration for both radicals investigated. Experiments with perdeuterated and ordinary butanol have given no indication for any influence of the host materials isotopes. The measured temperature dependence has shown an exponential characteristic. It is further observed that the oxygen content in the butanol samples has a considerable effect on the electron relaxation time and thus influences the nuclear relaxation time and polarization rate during the DNP. The experiments also show a variation in the NMR linewidth, leading to comparable time constants as determined by the lineshift. NEDOR measurements were also performed on irradiated, crystal grains of 6LiD. These samples exhibited a linewidth behavior similar to that of the cylindrically shaped butanol samples.
Measurement of T1/T2 relaxation times in overlapped regions from homodecoupled 1H singlet signals
NASA Astrophysics Data System (ADS)
Castañar, Laura; Nolis, Pau; Virgili, Albert; Parella, Teodor
2014-07-01
The implementation of the HOmodecoupled Band-Selective (HOBS) technique in the conventional Inversion-Recovery and CPMG-based PROJECT experiments is described. The achievement of fully homodecoupled signals allows the distinction of overlapped 1H resonances with small chemical shift differences. It is shown that the corresponding T1 and T2 relaxation times can be individually measured from the resulting singlet lines using conventional exponential curve-fitting methods.
In vivo Protein Dynamics on the Nanometer Length Scale and Nanosecond Time Scale.
Anunciado, Divina B; Nguyen, Vyncent P; Hurst, Gregory Blake; Doktycz, Mitchel J; Urban, Volker S; Langan, Paul; Mamontov, Eugene; O'Neill, Hugh M
2017-04-07
Selectively-labeled GroEL protein was produced in living deuterated bacterial cells to enhance its neutron scattering signal above that of the intra-cellular milieu. Quasi-elastic neutron scattering shows that the in-cell diffusion coefficient of GroEL was (0.047 ± 0.003)10-10 m2/s, a factor of 4 slower than its diffusion coefficient in buffer solution. Internal protein dynamics showed a relaxation time of (65 ± 6) ps, a factor of 2 slower compared to the protein in solution. Comparison to literature suggests that the effective diffusivity of proteins depends on the length scale being probed. Retardation of in-cell diffusion compared to the buffer becomes more significant with the increasing probe length scale suggesting that intra-cellular diffusion of biomolecules is non-uniform over the cellular volume. The approach outlined here enables investigation of protein dynamics within living cells to open up new lines of research using "in-cell neutron scattering" to study the dynamics of complex biomolecular systems.
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.
Measurements of T1 and T2 relaxation times of colon cancer metastases in rat liver at 7 T.
Gambarota, G; Veltien, A; van Laarhoven, H; Philippens, M; Jonker, A; Mook, O R; Frederiks, W M; Heerschap, A
2004-12-01
The purpose of this study was to investigate the magnetic resonance imaging (MRI) characteristics of colon cancer metastases in rat liver at 7 T. A dedicated RF microstrip coil of novel design was built in order to increase the signal-to-noise ratio and, in combination with respiratory triggering, to minimize motion artifacts. T1- and T2-weighted MR imaging was performed to follow tumor growth. T1-weighted images provided a good anatomical delineation of the liver structure, while the best contrast between metastases and normal liver tissue was achieved with T2-weighted images. Measurements of T1 and T2 relaxation times were performed with inversion recovery FLASH and Carr-Purcell-Meiboom-Gill and inversion recovery FLASH imaging sequences, respectively, for quantitative MR characterization of metastases. Both the T1 and T2 of the metastases were significantly higher than those of normal liver tissue. Further, an increase in the T1 relaxation time of the metastases was observed with tumor growth. These findings suggest that quantitative in vivo MR characterization provides information on tumor development and possibly response to therapy, though additional studies are needed to elucidate the correlation between the changes in relaxation times and tumor microenvironment.
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
Liu, Y H; Hawk, R M; Ramaprasad, S
1995-01-01
RIF tumors implanted on mice feet were investigated for changes in relaxation times (T1 and T2) after photodynamic therapy (PDT). Photodynamic therapy was performed using Photofrin II as the photosensitizer and laser light at 630 nm. A home-built proton solenoid coil in the balanced configuration was used to accommodate the tumors, and the relaxation times were measured before, immediately after, and up to several hours after therapy. Several control experiments were performed untreated tumors, tumors treated with Photofrin II alone, or tumors treated with laser light alone. Significant increases in T1s of water protons were observed after PDT treatment. In all experiments, 31P spectra were recorded before and after the therapy to study the tumor status and to confirm the onset of PDT. These studies show significant prolongation of T1s after the PDT treatment. The spin-spin relaxation measurements, on the other hand, did not show such prolongation in T2 values after PDT treatment.
Hu, Jian Zhi; Wind, Robert A.; Rommereim, Donald N.
2006-03-01
Methods suitable for measuring 1H relaxation times such as T1, T2 and T1p, in small sized biological objects including live cells, excised organs and tissues, oil seeds etc., were developed in this work. This was achieved by combining inversion-recovery, spin-echo, or spin lock segment with the phase-adjusted spinning sideband (PASS) technique that was applied at slow sample spinning rate. Here, 2D-PASS was used to produce a high-resolution 1H spectrum free from the magnetic susceptibility broadening so that the relaxation parameters of individual metabolite can be determined. Because of the slow spinning employed, tissue and cell damage due to sample spinning is minimized. The methodologies were demonstrated by measuring 1H T1, T2 and T1p of metabolites in excised rat livers and sesame seeds at spinning rates of as low as 40 Hz.
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
Relaxing the electroweak scale: the role of broken dS symmetry
NASA Astrophysics Data System (ADS)
Patil, Subodh P.; Schwaller, Pedro
2016-02-01
Recently, a novel mechanism to address the hierarchy problem has been proposed [1], where the hierarchy between weak scale physics and any putative `cutoff' M is translated into a parametrically large field excursion for the so-called relaxion field, driving the Higgs mass to values much less than M through cosmological dynamics. In its simplest incarnation, the relaxion mechanism requires nothing beyond the standard model other than an axion (the relaxion field) and an inflaton. In this note, we critically re-examine the requirements for successfully realizing the relaxion mechanism and point out that parametrically larger field excursions can be obtained for a given number of e-folds by simply requiring that the background break exact de Sitter invariance. We discuss several corollaries of this observation, including the interplay between the upper bound on the scale M and the order parameter ɛ associated with the breaking of dS symmetry, and entertain the possibility that the relaxion could play the role of a curvaton. We find that a successful realization of the mechanism is possible with as few as O(1{0}^3) e-foldings, albeit with a reduced cutoff M ˜ 106 GeV for a dark QCD axion and outline a minimal scenario that can be made consistent with CMB observations.
NASA Astrophysics Data System (ADS)
Bolinger, Joshua C.; Bixby, Teresa J.; Reid, Philip J.
2005-08-01
We report a series of time-resolved infrared absorption studies on chlorine dioxide (OClO) dissolved in H2O, D2O, and acetonitrile. Following the photoexcitation at 401 nm, the evolution in optical density for frequencies corresponding to asymmetric stretch of OClO is measured with a time resolution of 120±50fs. The experimentally determined optical-density evolution is compared with theoretical models of OClO vibrational relaxation derived from collisional models as well as classical molecular-dynamics (MD) studies. The vibrational relaxation rates in D2O are reduced by a factor of 3 relative to H2O consistent with the predictions of MD. This difference reflects modification of the frequency-dependent solvent-solute coupling accompanying isotopic substitution of the solvent. Also, the geminate-recombination quantum yield for the primary photofragments resulting in the reformation of ground-state OClO is reduced in D2O relative to H2O. It is proposed that this reduction reflects enhancement of the dissociation rate accompanying vibrational excitation along the asymmetric-stretch coordinate. In contrast to H2O and D2O, the vibrational-relaxation dynamics in acetonitrile are not well described by the theoretical models. Reproduction of the optical-density evolution in acetonitrile requires significant modification of the frequency-dependent solvent-solute coupling derived from MD. It is proposed that this modification reflects vibrational-energy transfer from the asymmetric stretch of OClO to the methyl rock of acetonitrile. In total, the results presented here provide a detailed description of the solvent-dependent geminate-recombination and vibrational-relaxation dynamics of OClO in solution.
Bolinger, Joshua C.; Bixby, Teresa J.; Reid, Philip J.
2005-08-22
We report a series of time-resolved infrared absorption studies on chlorine dioxide (OClO) dissolved in H{sub 2}O, D{sub 2}O, and acetonitrile. Following the photoexcitation at 401 nm, the evolution in optical density for frequencies corresponding to asymmetric stretch of OClO is measured with a time resolution of 120{+-}50 fs. The experimentally determined optical-density evolution is compared with theoretical models of OClO vibrational relaxation derived from collisional models as well as classical molecular-dynamics (MD) studies. The vibrational relaxation rates in D{sub 2}O are reduced by a factor of 3 relative to H{sub 2}O consistent with the predictions of MD. This difference reflects modification of the frequency-dependent solvent-solute coupling accompanying isotopic substitution of the solvent. Also, the geminate-recombination quantum yield for the primary photofragments resulting in the reformation of ground-state OClO is reduced in D{sub 2}O relative to H{sub 2}O. It is proposed that this reduction reflects enhancement of the dissociation rate accompanying vibrational excitation along the asymmetric-stretch coordinate. In contrast to H{sub 2}O and D{sub 2}O, the vibrational-relaxation dynamics in acetonitrile are not well described by the theoretical models. Reproduction of the optical-density evolution in acetonitrile requires significant modification of the frequency-dependent solvent-solute coupling derived from MD. It is proposed that this modification reflects vibrational-energy transfer from the asymmetric stretch of OClO to the methyl rock of acetonitrile. In total, the results presented here provide a detailed description of the solvent-dependent geminate-recombination and vibrational-relaxation dynamics of OClO in solution.
NASA Astrophysics Data System (ADS)
Bauer, S. H.; Lazaar, K. I.
1983-09-01
The usually quoted expression for the second order rate constant, for a unimolecular reaction at the low pressure limit, is valid only for strictly irreversible processes. Its application to isomerization reactions (which are to some extent reversible) is demonstrably in error; corrected expressions have been published. Attention is directed to intramolecular conversions over low barriers, for which the inappropriateness of the unidirectional expression becomes obvious. For such isomerizations we propose a model which incorporates only operationally observable states, so that an essential conceptual ambiguity is avoided. Use of this model is illustrated for the syn⇄anti conversions of methyl nitrite, derived from a gas phase NMR coalescence curve (Mc:Tc). The present data suggest that during isomerization the alkyl nitrites may not be completely ergodic on a time scale of 10-9 s. A regional phase-space model is proposed which has the appropriate formalism to account for this behavior.
NASA Astrophysics Data System (ADS)
Bretón, J.; Hardisson, A.; Mauricio, F.; Velasco, S.
1984-07-01
Given a quantum system of a few degrees of freedom in weak interaction with a bath, the expressions which connect its total-time-ordering-cumulant and partial-time-ordering-cumulant relaxation with the corresponding spectral line shapes of dipolar absorption are deduced. For simplicity we consider a system with a nondegenerate and nonequidistant energy spectrum. A special study in the cases of isolated resonances and of a weak interference effect between resonances is made.
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 τ between the two pulses. In conventional acquisition, the two pulses have a mutual phase shift of π. 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 π 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
Yoshioka, Sumie; Aso, Yukio; Kojima, Shigeo
2003-11-01
Laboratory- and rotating- frame spin-lattice relaxation times (T(1) and T(1rho)) of (1)H and (13)C in lyophilized poly(vinylpyrrolidone) (PVP) and methylcellulose (MC) are determined to examine feasibility of using T(1) and T(1rho) as a measure of molecular motions on large time scales related to the storage stability of lyophilized formulations. The T(1rho) of proton and carbon was found to reflect the mobility of PVP and MC backbones, indicating that it is useful as a measure of large-time-scale molecular motions. In contrast to the T(1rho), the T(1) of proton measured in the same temperature range reflected the mobility of PVP and MC side chains. The T(1) of proton may be useful as a measure of local molecular motions on a smaller-time-scale, although the measurement is interfered by moisture under some conditions. The temperature dependence of T(1) and T(1rho) indicated that methylene in the MC molecule had much higher mobility than that in the dextran molecule, also indicated that methylene in the PVP side chain had a higher mobility than that in the MC side chain.
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.
Fluctuations of a surface relaxation model in interacting scale free networks
NASA Astrophysics Data System (ADS)
Torres, M. F.; La Rocca, C. E.; Braunstein, L. A.
2016-12-01
Isolated complex networks have been studied deeply in the last decades due to the fact that many real systems can be modeled using these types of structures. However, it is well known that the behavior of a system not only depends on itself, but usually also depends on the dynamics of other structures. For this reason, interacting complex networks and the processes developed on them have been the focus of study of many researches in the last years. One of the most studied subjects in this type of structures is the Synchronization problem, which is important in a wide variety of processes in real systems. In this manuscript we study the synchronization of two interacting scale-free networks, in which each node has ke dependency links with different nodes in the other network. We map the synchronization problem with an interface growth, by studying the fluctuations in the steady state of a scalar field defined in both networks. We find that as ke slightly increases from ke = 0, there is a really significant decreasing in the fluctuations of the system. However, this considerable improvement takes place mainly for small values of ke, when the interaction between networks becomes stronger there is only a slight change in the fluctuations. We characterize how the dispersion of the scalar field depends on the internal degree, and we show that a combination between the decreasing of this dispersion and the integer nature of our growth model are the responsible for the behavior of the fluctuations with ke.
NASA Astrophysics Data System (ADS)
Buehler, Martin G.; Campbell, Zachary J.; Carter, Brady P.
2017-02-01
Dielectric relaxation methods are applicable to powdery materials such as carbohydrates. These materials have relaxations that occur in the milli-Hz range while samples are held at fixed temperatures and fixed water activities, a w, (relativity humidity). Under proper conditions these materials undergo physical changes where the initially glassy powder transitions to an amorphous equilibrium state at the glass transition temperature, T g. Determining this transition involves characterizing the boundary curve (T g versus a w) which determines T g and a w conditions where materials are stable with long-shelf life or unstable with very a short shelf-life. This paper serves to illustrate multiple methodologies which can be used to characterize glass transition from frequency-spectra. Three methodologies are described: peak-broadening, peak-shift, and single-frequency. The new single frequency method not only provides results that identical to those of the peak-shift method but increases the data acquisition speeds by a factor of 5. This method is illustrated on polydextrose, a common sugar substitute. The information gathered can then be used to construct the boundary curve which is used to characterize the shelf-life of a material at various conditions.
Time Scales, Bedforms and Bedload Transport
NASA Astrophysics Data System (ADS)
Dhont, B.
2015-12-01
Bedload transport rates in mountain streams may exhibit wide fluctuations even under constant flow conditions. A better understanding of bedload pulses is key to predict natural hazards induced by torrential activity and sediment issues in mountainous areas. Several processes such as bedforms migration, grain sorting and random particles' trajectories are evoked as the driving agents of pulse formation and development. Quantifying the effects of these processes is a difficult task. This work aims to investigate the interactions between bedload transport and bedform dynamics in steep gravel-bed rivers. Experiments are carried out in a 17-m long 60-cm wide flume inclined at an angle of 2.7%. The bed is initially flat and made of homogenous natural gravel with a mean diameter of 6 mm. We imposed 200 identical hydrographs (of 1 hr duration) at the flume inlet (the bed surface was not flattened out during these cycling floods). The input hydrograph and the input sediment discharge are nearly triangular. Bed topography is measured after each flood using ultrasound sensors while the bedload transport rate is steadily monitored at the outlet using accelerometers (accelerometers fixed on metallic plates record the impacts of the grains flowing out of the flume). For the sake of comparison, a similar experiment consisting of 19 floods of 10 hours is carried out under constant supply conditions. We show that accelerometers are a cost effective technique to obtain high-frequency bedload discharge data. Spectral analysis of the bedload timeseries is used to highlight the different time scales corresponding to different bedload transport processes. We show that long timeseries are necessary to capture the different processes that drive bedload transport, including the resilience time after a perturbation of the bed. The alternate bars that develop and migrate along the flume are found to significantly influence bedload transport rate fluctuations.
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.
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.
Ultra-Slow Dielectric Relaxation Process in Polyols
NASA Astrophysics Data System (ADS)
Yomogida, Yoshiki; Minoguchi, Ayumi; Nozaki, Ryusuke
2004-04-01
Dielectric relaxation processes with relaxation times larger than that for the structural α process are reported for glycerol, xylitol, sorbitol and their mixtures for the first time. Appearance of this ultra-slow process depends on cooling rate. More rapid cooling gives larger dielectric relaxation strength. However, relaxation time is not affected by cooling rate and shows non-Arrhenius temperature dependence with correlation to the α process. It can be considered that non-equilibrium dynamic structure causes the ultra-slow process. Scale of such structure would be much larger than that of the region for the cooperative molecular orientations for the α process.
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.
Yoshioka, Sumie; Aso, Yukio; Kojima, Shigeo
2002-10-01
The spin-lattice relaxation times in the laboratory and rotating frame (T(1) and T(1rho)) of protons and carbons in lyophilized bovine serum gamma-globulin formulation containing dextran were determined by (1)H solid-state pulsed nuclear magnetic resonance (NMR) and high-resolution (13)C solid-state NMR. The temperature dependence of T(1) and T(1rho) of dextran protons in the lyophilized formulation suggests that the correlation time, tau(c), of the methylene protons in dextran is approximately 10(-6) s at -100 degrees C and 60% relative humidity, and decreases to 10(-7) s at 0 degrees C. When temperature is increased from 0 degrees C, the increased motion of the methylene groups is reflected in T(1), but is too fast to be observed by changes in T(1rho). Thus, the motion of the methine groups rather than the methylene groups begins to be reflected in T(1rho). The correlation time of the methine protons as determined by T(1rho) was of the same order as that of the methine carbons as determined by T(1rho). As the temperature is increased past the glass/rubber transition temperature, both the methylene and methine motions are greatly enhanced, resulting in much shorter T(1) and T(1rho) relaxation times.
PARAMAGNETIC RELAXATION IN CRYSTALS.
CRYSTALS, PARAMAGNETIC RESONANCE, RELAXATION TIME , CRYSTAL DEFECTS, QUARTZ, GLASS, STRAIN(MECHANICS), TEMPERATURE, NUCLEAR SPINS, HYDROGEN, CALCIUM COMPOUNDS, FLUORIDES, COLOR CENTERS, PHONONS, OXYGEN.
Wehrenberg, C. E.; Comley, A. J.; Barton, N. R.; ...
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
Time-optimal control of spin 1/2 particles in the presence of radiation damping and relaxation.
Zhang, Y; Lapert, M; Sugny, D; Braun, M; Glaser, S J
2011-02-07
We consider the time-optimal control of an ensemble of uncoupled spin 1/2 particles in the presence of relaxation and radiation damping effects, whose dynamics is governed by nonlinear equations generalizing the standard linear Bloch equations. For a single spin, the optimal control strategy can be fully characterized analytically. However, in order to take into account the inhomogeneity of the static magnetic field, an ensemble of isochromats at different frequencies must be considered. For this case, numerically optimized pulse sequences are computed and the dynamics under the corresponding optimal field is experimentally demonstrated using nuclear magnetic resonance techniques.
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.
Kim, Kang; Saito, Shinji
2013-03-28
We report an extensive and systematic investigation of the multi-point and multi-time correlation functions to reveal the spatio-temporal structures of dynamic heterogeneities in glass-forming liquids. Molecular dynamics simulations are carried out for the supercooled states of various prototype models of glass-forming liquids such as binary Kob-Andersen, Wahnström, soft-sphere, and network-forming liquids. While the first three models act as fragile liquids exhibiting super-Arrhenius temperature dependence in their relaxation times, the last is a strong glass-former exhibiting Arrhenius behavior. First, we quantify the length scale of the dynamic heterogeneities utilizing the four-point correlation function. The growth of the dynamic length scale with decreasing temperature is characterized by various scaling relations that are analogous to the critical phenomena. We also examine how the growth of the length scale depends upon the model employed. Second, the four-point correlation function is extended to a three-time correlation function to characterize the temporal structures of the dynamic heterogeneities based on our previous studies [K. Kim and S. Saito, Phys. Rev. E 79, 060501(R) (2009); and J. Chem. Phys. 133, 044511 (2010)]. We provide comprehensive numerical results obtained from the three-time correlation function for the above models. From these calculations, we examine the time scale of the dynamic heterogeneities and determine the associated lifetime in a consistent and systematic way. Our results indicate that the lifetime of the dynamical heterogeneities becomes much longer than the α-relaxation time determined from a two-point correlation function in fragile liquids. The decoupling between the two time scales is remarkable, particularly in supercooled states, and the time scales differ by more than an order of magnitude in a more fragile liquid. In contrast, the lifetime is shorter than the α-relaxation time in tetrahedral network-forming strong
Time scales in Galveston Bay: An unsteady estuary
NASA Astrophysics Data System (ADS)
Rayson, Matthew D.; Gross, Edward S.; Hetland, Robert D.; Fringer, Oliver B.
2016-04-01
Estuarine time scales including the turnover, particle e-folding time, the age (calculated with a passive tracer), and residence time (calculated with Lagrangian particles) were computed using a three-dimensional hydrodynamic model of Galveston Bay, a low-flow, partially stratified estuary. Time scales were computed during a time period when river flow varied by several orders of magnitude and all time scales therefore exhibited significant temporal variability because of the unsteadiness of the system. The spatial distributions of age and residence time were qualitatively similar and increased from 15 days in a shipping channel to >45 days in the upper estuary. Volume-averaged age and residence time decreased during high-flow conditions. Bulk time scales, including the freshwater and salinity turnover times, were far more variable due to the changing river discharge and salt flux through the estuary mouth. A criterion for calculating a suitable averaging time is discussed to satisfy a steady state assumption and to estimate a more representative bulk time scale. When scaled with a freshwater advective time, all time scales were approximately equal to the advective time scale during high-flow conditions and many times higher during low-flow conditions. The mean age, Lagrangian residence, and flushing times exhibited a relationship that was weakly dependent on the freshwater advective time scale demonstrating predictability even in an unsteady, realistic estuary.
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)
Rastogi, Abhishek; Yadav, Siddharth; Suresh, S. J.
2011-08-01
We recently proposed a theory [Suresh, J. Chem. Phys. 113, 9727 (2000)], 10.1063/1.1320822, based on the principles of statistical mechanics, for describing the temperature variation of static dielectric constant of water and the average number of H-bonds per molecule in the liquid phase. The theoretical model contains three parameters; two of them pertain to the energy and entropy changes accompanying bond-formation, and the third (ɛ∞) represents the dielectric constant at a frequency that is sufficiently low for atomic and electronic polarization, but sufficiently high for intermolecular relaxation processes involving the movement of permanent dipole moments to be inoperative. In the absence of a consensus in the literature for the value of ɛ∞ to be used in dielectric constant calculations, it was arbitrarily set to a commonly accepted value of 1.77 (corresponding to refractive index of 1.33). Values for H-bond parameters were then estimated by best fitting model calculations to experimental data for dielectric constant across temperatures ranging from melting to the critical point of water. It is the purpose of the present Note to eliminate the ambiguity on the choice of ɛ∞ and propose refined values for the H-bond parameters.
NASA Astrophysics Data System (ADS)
Harabech, Mariem; Leliaert, Jonathan; Coene, Annelies; Crevecoeur, Guillaume; Van Roost, Dirk; Dupré, Luc
2017-03-01
Magnetic nanoparticle hyperthermia is a cancer treatment in which magnetic nanoparticles (MNPs) are subjected to an alternating magnetic field to induce heat in the tumor. The generated heat of MNPs is characterized by the specific loss power (SLP) due to relaxation phenomena of the MNP. Up to now, several models have been proposed to predict the SLP, one of which is the Linear Response Theory. One parameter in this model is the relaxation time constant. In this contribution, we employ a macrospin model based on the Landau-Lifshitz-Gilbert equation to investigate the relation between the Gilbert damping parameter and the relaxation time constant. This relaxation time has a pre-factor τ0 which is often taken as a fixed value ranging between 10-8 and 10-12 s. However, in reality it has small size dependence. Here, the influence of this size dependence on the calculation of the SLP is demonstrated, consequently improving the accuracy of this estimate.
NASA Astrophysics Data System (ADS)
Hu, Yan; Bürgmann, Roland; Uchida, Naoki; Banerjee, Paramesh; Freymueller, Jeffrey T.
2016-01-01
Understanding of postseismic deformation following great subduction zone earthquakes is complicated by the combined effects of viscoelastic relaxation of earthquake-induced stresses in the upper mantle and time-dependent afterslip on the megathrust. We integrate geodetic observations and constraints on afterslip from small repeating earthquakes on the megathrust to better distinguish contributions from these two postseismic processes. We have developed a three-dimensional, spherical viscoelastic finite element model to study the postseismic deformation of the 2011 Mw9.0 Tohoku earthquake that has been recorded at unprecedented high resolution in space and time. We model stress-driven afterslip in a 2 km thick weak shear zone away from historic rupture zones on the megathrust. We model both the viscoelastic relaxation of the upper mantle and shear zone deformation with a transient Burgers body rheology. The transient Kelvin viscosity is assumed to be one order of magnitude lower than that of the Maxwell viscosity. Viscoelastic relaxation of the mantle wedge alone causes postseismic uplift and seaward motion in the upper plate, opposite to the pattern from relaxation of just the oceanic upper mantle. Afterslip on the fault produces uplift updip of the afterslip zone and subsidence over its downdip edge and mostly seaward motion above the afterslip zone. The best fit Maxwell viscosity of the shear zone at depths ≤50 km is 1017 Pa s, constrained by afterslip estimates from repeating earthquakes. The optimal viscosities of the deep weak shear zone, continental mantle wedge, and oceanic upper mantle are determined to be 5 × 1017 Pa s, 3 × 1019 Pa s, and 5 × 1019 Pa s, respectively. The stress-driven afterslip in the shear zone is up to ~3.5 m in the first 2 years after the earthquake, equivalent to an Mw8.4. Our model reproduces the first-order pattern of the GPS observations both in horizontal and in vertical directions. Seafloor geodetic observations of subsidence
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
NASA Astrophysics Data System (ADS)
Wers, E.; Oudadesse, H.; Lefeuvre, B.; Merdrignac-Conanec, O.; Barroug, A.
2015-10-01
Chitosan scaffolds, combined with bioactive glass 46S6, were prepared to serve as gentamicin sulfate delivery in situ systems for bone biomaterials. This work presents a study about the effect of the ratio chitosan/bioactive glass (CH/BG) on the release of gentamicin sulfate and on the bioactivity during in vitro experiments. SEM observations allowed understanding the bond between the glass grains and the chitosan matrix. In vitro results showed that scaffolds form a hydroxyapatite (HA) Ca10(PO4)6(OH)2 after 15 days of immersion in a simulated body fluid (SBF).The interest of this study is to see that the increase of the content of bioactive glass in the chitosan matrix slows the release of gentamicin sulfate in the liquid medium. Starting concentration of gentamicin sulfate has an influence on the relaxation time of the scaffolds. Indeed, an increasing concentration delays the return to a new equilibrium. Contents of chitosan and bioactive glass do not affect the relaxation time. Synthesized scaffolds could be adapted to a clinical situation: severity and type of infection, weight and age of the patient.
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.
Müller, Andreas; Hochrath, Katrin; Stroeder, Jonas; Hittatiya, Kanishka; Schneider, Günther; Lammert, Frank; Buecker, Arno
2017-01-01
Recently, clinical studies demonstrated that magnetic resonance relaxometry with determination of relaxation times T1 and T2⁎ may aid in staging and management of liver fibrosis in patients suffering from viral hepatitis and steatohepatitis. In the present study we investigated T1 and T2⁎ in different models of liver fibrosis to compare alternate pathophysiologies in their effects on relaxation times and to further develop noninvasive quantification methods of liver fibrosis. MRI was performed with a fast spin echo sequence for measurement of T1 and a multigradient echo sequence for determination of T2⁎. Toxic liver fibrosis was induced by injections of carbon tetrachloride (1.4 mL CCl4 per kg bodyweight and week, for 3 or 6 weeks) in BALB/cJ mice. Chronic sclerosing cholangitis was mimicked using the ATP-binding cassette transporter B4 knockout (Abcb4 −/−) mouse model. Untreated BALB/cJ mice served as controls. To assess hepatic fibrosis, we ascertained collagen contents and fibrosis scores after Sirius red staining. T1 and T2⁎ correlate differently to disease severity and etiology of liver fibrosis. T2⁎ shows significant decrease correlating with fibrosis in CCl4 treated animals, while demonstrating significant increase with disease severity in Abcb4 −/− mice. Measurements of T1 and T2⁎ may therefore facilitate discrimination between different stages and causes of liver fibrosis. PMID:28194423
Li, Xiaojuan; Pai, Alex; Blumenkrantz, Gabrielle; Carballido-Gamio, Julio; Link, Thomas; Ma, Benjamin; Ries, Michael; Majumdar, Sharmila
2009-01-01
T1ρ and T2 relaxation time constants have been proposed to probe biochemical changes in osteoarthritic cartilage. This study aimed to evaluate the spatial correlation and distribution of T1ρ and T2 values in osteoarthritic cartilage. Ten patients with osteoarthritis (OA) and 10 controls were studied at 3T. The spatial correlation of T1ρ and T2 values was investigated using Z-scores. The spatial variation of T1ρ and T2 values in patellar cartilage was studied in different cartilage layers. The distribution of these relaxation time constants was measured using texture analysis parameters based on gray-level co-occurrence matrices (GLCM). The mean Z-scores for T1ρ and T2 values were significantly higher in OA patients vs. controls (P < 0.05). Regional correlation coefficients of T1ρ and T2 Z-scores showed a large range in both controls and OA patients (0.2– 0.7). OA patients had significantly greater GLCM contrast and entropy of T1ρ values than controls (P < 0.05). In summary, T1ρ and T2 values are not only increased but are also more heterogeneous in osteoarthritic cartilage. T1ρ and T2 values show different spatial distributions and may provide complementary information regarding cartilage degeneration in OA. PMID:19319904
Müller, Andreas; Hochrath, Katrin; Stroeder, Jonas; Hittatiya, Kanishka; Schneider, Günther; Lammert, Frank; Buecker, Arno; Fries, Peter
2017-01-01
Recently, clinical studies demonstrated that magnetic resonance relaxometry with determination of relaxation times T1 and T2(⁎) may aid in staging and management of liver fibrosis in patients suffering from viral hepatitis and steatohepatitis. In the present study we investigated T1 and T2(⁎) in different models of liver fibrosis to compare alternate pathophysiologies in their effects on relaxation times and to further develop noninvasive quantification methods of liver fibrosis. MRI was performed with a fast spin echo sequence for measurement of T1 and a multigradient echo sequence for determination of T2(⁎). Toxic liver fibrosis was induced by injections of carbon tetrachloride (1.4 mL CCl4 per kg bodyweight and week, for 3 or 6 weeks) in BALB/cJ mice. Chronic sclerosing cholangitis was mimicked using the ATP-binding cassette transporter B4 knockout (Abcb4 (-/-)) mouse model. Untreated BALB/cJ mice served as controls. To assess hepatic fibrosis, we ascertained collagen contents and fibrosis scores after Sirius red staining. T1 and T2(⁎) correlate differently to disease severity and etiology of liver fibrosis. T2(⁎) shows significant decrease correlating with fibrosis in CCl4 treated animals, while demonstrating significant increase with disease severity in Abcb4 (-/-) mice. Measurements of T1 and T2(⁎) may therefore facilitate discrimination between different stages and causes of liver fibrosis.
Hyperpolarized 13C NMR lifetimes in the liquid-state: relating structures and T1 relaxation times
NASA Astrophysics Data System (ADS)
Parish, Christopher; Niedbalski, Peter; Hashami, Zohreh; Fidelino, Leila; Kovacs, Zoltan; Lumata, Lloyd
Among the various attempts to solve the insensitivity problem in nuclear magnetic resonance (NMR), the physics-based technique dissolution dynamic nuclear polarization (DNP) is probably the most successful method of hyperpolarization or amplifying NMR signals. Using this technique, liquid-state NMR signal enhancements of several thousand-fold are expected for low-gamma nuclei such as carbon-13. The lifetimes of these hyperpolarized 13C NMR signals are directly related to their 13C spin-lattice relaxation times T1. Depending upon the 13C isotopic location, the lifetimes of hyperpolarized 13C compounds can range from a few seconds to minutes. In this study, we have investigated the hyperpolarized 13C NMR lifetimes of several 13C compounds with various chemical structures from glucose, acetate, citric acid, naphthalene to tetramethylallene and their deuterated analogs at 9.4 T and 25 deg C. Our results show that the 13C T1s of these compounds can range from a few seconds to more than 60 s at this field. Correlations between the chemical structures and T1 relaxation times will be discussed and corresponding implications of these results on 13C DNP experiments will be revealed. US Dept of Defense Award No. W81XWH-14-1-0048 and Robert A. Welch Foundation Grant No. AT-1877.
NASA Astrophysics Data System (ADS)
Shim, Yunsic; Amar, Jacques G.; Uberuaga, B. P.; Voter, A. F.
2007-11-01
We present a method for performing parallel temperature-accelerated dynamics (TAD) simulations over extended length scales. In our method, a two-dimensional spatial decomposition is used along with the recently proposed semirigorous synchronous sublattice algorithm of Shim and Amar [Phys. Rev. B 71, 125432 (2005)]. The scaling behavior of the simulation time as a function of system size is studied and compared with serial TAD in simulations of the early stages of Cu/Cu(100) growth as well as for a simple case of surface relaxation. In contrast to the corresponding serial TAD simulations, for which the simulation time tser increases as a power of the system size N (tser˜Nx) with an exponent x that can be as large as three, in our parallel simulations the simulation time increases only logarithmically with system size. As a result, even for relatively small system sizes our parallel TAD simulations are significantly faster than the corresponding serial TAD simulations. The significantly improved scaling behavior of our parallel TAD simulations over the corresponding serial simulations indicates that our parallel TAD method may be useful in performing simulations over significantly larger length scales than serial TAD, while preserving all the atomistic details provided by the TAD method.
Subburaj, Karupppasamy; Souza, Richard B.; Wyman, Bradley T.; Le Graverand-Gastineau, Marie-Pierre Hellio; Li, Xiaojuan; Link, Thomas M.; Majumdar, Sharmila
2014-01-01
Purpose To prospectively evaluate changes in T1ρ and T2 relaxation times in the meniscal body with acute loading using MRI in osteoarthritic knees and to compare these findings with those of age-matched healthy controls. Materials and Methods Female subjects above 40 years of age with (N1 = 20) and without osteoarthritis (OA) (N2 = 10) were imaged on a 3 Tesla MR scanner using a custom made loading device. MR images were acquired, with the knee flexed at 20°, with and without a compressive load of 50% of the subject's bodyweight. The subjects were categorized based on the radiographic evidence of OA. Three different zones (outer, middle, and inner) of meniscus body were defined (each occupying 1/3rd the width). After adjusting for age and body mass index in the general linear regression model, repeated measures analysis of variance was used to detect significant differences in T1ρ and T2 with and without loading. Results In the unloaded condition, the average T1ρ and T2 times were elevated in the outer and middle zones of the medial meniscus in OA subjects compared with the controls. In the loaded condition, T1ρ and T2 times of the outer zone of the medial meniscus was significantly elevated in OA subjects compared with controls. Finally the change (from unloaded to loaded) was significantly higher in controls than OA subjects (15.1% versus 8.3%; P = 0.039 for ΔT1ρ, and 11.5% versus 6.9%, P = 0.049 for ΔT2). Conclusion These findings suggest that while the OA process appears to affect the relaxation times of all regions within the meniscus, it may affect some regions sooner or to a greater degree. Furthermore, the differences in the change in relaxation times between unloaded and loaded conditions may reveal evidence about load transmission failure of the outer zone of the medial meniscus in subjects with knee OA. It is possible that these metrics (ΔT1ρ and ΔT2) may be valuable as an early biomechanical biomarker, which could be used to predict load
Linking Response-Time Parameters onto a Common Scale
ERIC Educational Resources Information Center
van der Linden, Wim J.
2010-01-01
Although response times on test items are recorded on a natural scale, the scale for some of the parameters in the lognormal response-time model (van der Linden, 2006) is not fixed. As a result, when the model is used to periodically calibrate new items in a testing program, the parameter are not automatically mapped onto a common scale. Several…
NASA Astrophysics Data System (ADS)
Nagasawa, Sh
2017-02-01
Paperboards are recognized to be important raw materials for packaging industry due to their advantages such as high strength-to-weight ratio, recyclability. Regarding the development of advanced packaging materials and the requirement of smart formed products, a study of sheet’s response behaviour is necessary for expanding the advanced converting industry. After introducing a couple of past research works concerned crease technologies, a fundamental mechanisms of crease deformation is reviewed using the scoring depth and the folding angle of a paperboard. Since one of important forming characteristics is a time-dependent stress relaxation or time-delayed strain during a fold/unfold process, the author’s experimental approaches for estimating a short term (less than 10 seconds) dynamic deformation behaviour of creased paperboard are discussed.
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)
Guo, Xixiong; Zhong, Chengwen; Zhuo, Congshan; Cao, Jun
2014-04-01
As a fundamental subject in fluid mechanics, sophisticated cavity flow patterns due to the movement of multi-lids have been routinely analyzed by the computational fluid dynamics community. Unlike those reported computational studies that were conducted using more conventional numerical methods, this paper features employing the multiple-relaxation-time (MRT) lattice Boltzmann method (LBM) to numerically investigate the two-dimensional cavity flows generated by the movements of two adjacent lids. The obtained MRT-LBM results reveal a number of important bifurcation flow features, such as the symmetry and steadiness of cavity flows at low Reynolds numbers, the multiplicity of stable cavity flow patterns when the Reynolds number exceeds its first critical value, as well as the periodicity of the cavity flow after the second critical Reynolds number is reached. Detailed flow characteristics are reported that include the critical Reynolds numbers, the locations of the vortex centers, and the values of stream function at the vortex centers. Through systematic comparison against the simulation results obtained elsewhere by using the lattice Bhatnagar-Gross-Krook model and other numerical schemes, not only does the MRT-LBM approach exhibit fairly satisfactory accuracy, but also demonstrates its remarkable flexibility that renders the adjustment of its multiple relaxation factors fully manageable and, thus, particularly accommodates the need of effectively investigating the multiplicity of flow patterns with complex behaviors.
Oliveira, Patrícia D.; Michel, Ricardo C.; McBride, Alan J. A.; Moreira, Angelita S.; Lomba, Rosana F. T.; Vendruscolo, Claire T.
2013-01-01
The aim of this work was to evaluate the utilization of analysis of the distribution of relaxation time (DRT) using a dynamic light back-scattering technique as alternative method for the determination of the concentration regimes in aqueous solutions of biopolymers (xanthan, clairana and tara gums) by an analysis of the overlap (c*) and aggregation (c**) concentrations. The diffusion coefficients were obtained over a range of concentrations for each biopolymer using two methods. The first method analysed the behaviour of the diffusion coefficient as a function of the concentration of the gum solution. This method is based on the analysis of the diffusion coefficient versus the concentration curve. Using the slope of the curves, it was possible to determine the c* and c** for xanthan and tara gum. However, it was not possible to determine the concentration regimes for clairana using this method. The second method was based on an analysis of the DRTs, which showed different numbers of relaxation modes. It was observed that the concentrations at which the number of modes changed corresponded to the c* and c**. Thus, the DRT technique provided an alternative method for the determination of the critical concentrations of biopolymers. PMID:23671627
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 ɛ of the small and large scales. We illustrate the implications of the resonantly enhanced O(ɛ2) 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.
Liao, Shu-Hsien; Chen, Kuen-Lin; Wang, Chun-Min; Chieh, Jen-Jie; Horng, Herng-Er; Wang, Li-Min; Wu, C H; Yang, Hong-Chang
2014-11-12
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.
Sagnella, Diane E.; Straub, John E.; Jackson, Timothy A.; Lim, Manho; Anfinrud, Philip A.
1999-01-01
The vibrational energy relaxation of carbon monoxide in the heme pocket of sperm whale myoglobin was studied by using molecular dynamics simulation and normal mode analysis methods. Molecular dynamics trajectories of solvated myoglobin were run at 300 K for both the δ- and ɛ-tautomers of the distal His-64. Vibrational population relaxation times of 335 ± 115 ps for the δ-tautomer and 640 ± 185 ps for the ɛ-tautomer were estimated by using the Landau–Teller model. Normal mode analysis was used to identify those protein residues that act as the primary “doorway” modes in the vibrational relaxation of the oscillator. Although the CO relaxation rates in both the ɛ- and δ-tautomers are similar in magnitude, the simulations predict that the vibrational relaxation of the CO is faster in the δ-tautomer with the distal His playing an important role in the energy relaxation mechanism. Time-resolved mid-IR absorbance measurements were performed on photolyzed carbonmonoxy hemoglobin (Hb13CO). From these measurements, a T1 time of 600 ± 150 ps was determined. The simulation and experimental estimates are compared and discussed. PMID:10588704
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 T1ρ 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 35.8±5.4 years, BMI 23.5±2.5 kg/m2) participated 1.5±0.8 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. T1ρ 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 T1ρ 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
NASA Astrophysics Data System (ADS)
Lidorikis, Elefterios; Bachlechner, Martina E.; Kalia, Rajiv K.; Nakano, Aiichiro; Vashishta, Priya
2005-09-01
A hybrid atomistic-continuum simulation approach has been implemented to study strain relaxation in lattice-mismatched Si/Si3N4 nanopixels on a Si(111) substrate. We couple the molecular-dynamics (MD) and finite-element simulation approaches to provide an atomistic description near the interface and a continuum description deep into the substrate, increasing the accessible length scales and greatly reducing the computational cost. The results of the hybrid simulation are validated against full multimillion-atom MD simulations. We find that strain relaxation in Si/Si3N4 nanopixels may occur through the formation of a network of interfacial domain boundaries reminiscent of interfacial misfit dislocations. They result from the nucleation of domains of different interfacial bonding at the free edges and corners of the nanopixel, and subsequent to their creation they propagate inwards. We follow the motion of the domain boundaries and estimate a propagation speed of about ˜2.5×103m/s . The effects of temperature, nanopixel architecture, and film structure on strain relaxation are also investigated. We find: (i) elevated temperature increases the interfacial domain nucleation rates; (ii) a thin compliant Si layer between the film and the substrate plays a beneficial role in partially suppressing strain relaxation; and (iii) additional control over the interface morphology may be achieved by varying the film structure.
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 τ. In the density scaling regime, we argue that the decoupling between τ and S is a consequence of different values of the scaling exponents γ and γ(S) in the density scaling laws, τ=f(ρ(γ)/T) and S=h(ρ(γ(S))/T), where ρ and T denote density and temperature, respectively. It implies that the proper relation between τ and S requires supplementing with a density factor, u(ρ), i.e., τ=g(u(ρ)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 τ 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 τ(T,ρ), 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.
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 τ. In the density scaling regime, we argue that the decoupling between τ and S is a consequence of different values of the scaling exponents γ and γS in the density scaling laws, τ =f (ργ/T ) and S =h (ργS/T ) , where ρ and T denote density and temperature, respectively. It implies that the proper relation between τ and S requires supplementing with a density factor, u (ρ), i.e., τ =g ( u (ρ )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 τ 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 τ(T ,ρ), 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 .
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.
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.
Timing signatures of large scale solar eruptions
NASA Astrophysics Data System (ADS)
Balasubramaniam, K. S.; Hock-Mysliwiec, Rachel; Henry, Timothy; Kirk, Michael S.
2016-05-01
We examine the timing signatures of large solar eruptions resulting in flares, CMEs and Solar Energetic Particle events. We probe solar active regions from the chromosphere through the corona, using data from space and ground-based observations, including ISOON, SDO, GONG, and GOES. Our studies include a number of flares and CMEs of mostly the M- and X-strengths as categorized by GOES. We find that the chromospheric signatures of these large eruptions occur 5-30 minutes in advance of coronal high temperature signatures. These timing measurements are then used as inputs to models and reconstruct the eruptive nature of these systems, and explore their utility in forecasts.
An Adaptive Fourier Filter for Relaxing Time Stepping Constraints for Explicit Solvers
Gelb, Anne; Archibald, Richard K
2015-01-01
Filtering is necessary to stabilize piecewise smooth solutions. The resulting diffusion stabilizes the method, but may fail to resolve the solution near discontinuities. Moreover, high order filtering still requires cost prohibitive time stepping. This paper introduces an adaptive filter that controls spurious modes of the solution, but is not unnecessarily diffusive. Consequently we are able to stabilize the solution with larger time steps, but also take advantage of the accuracy of a high order filter.
Macías-Hernández, Salvador Israel; Miranda-Duarte, Antonio; Ramírez-Mora, Isabel; Cortés-González, Socorro; Morones-Alba, Juan Daniel; Olascoaga-Gómez, Andrea; Coronado-Zarco, Roberto; Soria-Bastida, María de Los Angeles; Nava-Bringas, Tania Inés; Cruz-Medina, Eva
2016-08-01
The objective of this study is to correlate T2 relaxation time (T2RT), measured by magnetic resonance imaging (MRI) with quadriceps and hamstring strength in young participants with risk factors for knee osteoarthritis (OA). A descriptive cross-sectional study was conducted with participants between 20 and 40 years of age, without diagnosis of knee OA. Their T2 relaxation time was measured through MRI, and their muscle strength (MS) was measured with an isokinetic dynamometer. Seventy-one participants were recruited, with an average age of 28.3 ± 5.5 years; 39 (55 %) were females. Negative correlations were found between T2RT and quadriceps peak torque (QPT) in males in the femur r = -0.46 (p = 0.01), tibia r = -0.49 (p = 0.02), and patella r = -0.44 (p = 0.01). In women, correlations were found among the femur r = -0.43 (p = 0.01), tibia r = -0.61 (p = 0.01), and patella r = -0.32 (p = 0.05) and among hamstring peak torque (HPT), in the femur r = -0.46 (p = 0.01), hamstring total work (HTW) r = -0.42 (p = 0.03), and tibia r = -0.33 (p = 0.04). Linear regression models showed good capacity to predict T2RT through QPT in both genders. The present study shows that early changes in femoral, tibial, and patellar cartilage are significantly correlated with MS, mainly QPT, and that these early changes might be explained by MS, which could play an important role in pre-clinical phases of the disease.
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.
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.
Assessment of Nanosecond Time Scale Motions in Native and Non-Native States of Ubiquitin.
Morozova, Olga B; Yurkovskaya, Alexandra V
2015-10-01
The paramagnetic relaxation times of the aromatic and β protons of Tyr59 and His68 residues of the native ubiquitin and of Tyr59 residue of the non-native ubiquitin were determined from an analysis of chemically induced dynamic nuclear polarization (CIDNP) kinetics obtained during the photoreaction of the protein and 2,2'-dipyridyl excited in the triplet state. Using the paramagnetic relaxation times determined earlier for the radicals of free amino acids as an internal standard and assuming that the hyperfine interaction (HFI) anisotropy is very similar for the radicals of free amino acids and the corresponding radicals of amino acid residues in the proteins, we determined parameters that characterize the intramolecular mobility of different protons in native and two non-native states of ubiquitin. The latter are denatured at pH 2 and 57 °C, and the A-state at pH 2 in a 60%/40% methanol/water mixture. The determination of the two parameters of intramolecular mobility (i.e., the correlation time of internal motion, τ(e), and the order parameter, S(2)) was only possible by analyzing paramagnetic relaxation data obtained at two magnetic fields (4.7 and 9.4 T) using nuclear magnetic resonance (NMR) spectrometry. Intramolecular correlation times fall into the submicrosecond-microsecond time scale. Longer correlation times and higher order parameters were found for the less accessible Tyr59 residue than for the His68 residue, as well as for the more buried β protons than for the aromatic protons for both of the protein residues in the native state. For Tyr59, intramolecular mobility increases following the loss of the tertiary structure of ubiquitin. These findings strongly support the reliability of the obtained data.
2016-01-01
Over recent years, several alternative relaxed clock models have been proposed in the context of Bayesian dating. These models fall in two distinct categories: uncorrelated and autocorrelated across branches. The choice between these two classes of relaxed clocks is still an open question. More fundamentally, the true process of rate variation may have both long-term trends and short-term fluctuations, suggesting that more sophisticated clock models unfolding over multiple time scales should ultimately be developed. Here, a mixed relaxed clock model is introduced, which can be mechanistically interpreted as a rate variation process undergoing short-term fluctuations on the top of Brownian long-term trends. Statistically, this mixed clock represents an alternative solution to the problem of choosing between autocorrelated and uncorrelated relaxed clocks, by proposing instead to combine their respective merits. Fitting this model on a dataset of 105 placental mammals, using both node-dating and tip-dating approaches, suggests that the two pure clocks, Brownian and white noise, are rejected in favour of a mixed model with approximately equal contributions for its uncorrelated and autocorrelated components. The tip-dating analysis is particularly sensitive to the choice of the relaxed clock model. In this context, the classical pure Brownian relaxed clock appears to be overly rigid, leading to biases in divergence time estimation. By contrast, the use of a mixed clock leads to more recent and more reasonable estimates for the crown ages of placental orders and superorders. Altogether, the mixed clock introduced here represents a first step towards empirically more adequate models of the patterns of rate variation across phylogenetic trees. This article is part of the themed issue ‘Dating species divergences using rocks and clocks’. PMID:27325829
Lartillot, Nicolas; Phillips, Matthew J; Ronquist, Fredrik
2016-07-19
Over recent years, several alternative relaxed clock models have been proposed in the context of Bayesian dating. These models fall in two distinct categories: uncorrelated and autocorrelated across branches. The choice between these two classes of relaxed clocks is still an open question. More fundamentally, the true process of rate variation may have both long-term trends and short-term fluctuations, suggesting that more sophisticated clock models unfolding over multiple time scales should ultimately be developed. Here, a mixed relaxed clock model is introduced, which can be mechanistically interpreted as a rate variation process undergoing short-term fluctuations on the top of Brownian long-term trends. Statistically, this mixed clock represents an alternative solution to the problem of choosing between autocorrelated and uncorrelated relaxed clocks, by proposing instead to combine their respective merits. Fitting this model on a dataset of 105 placental mammals, using both node-dating and tip-dating approaches, suggests that the two pure clocks, Brownian and white noise, are rejected in favour of a mixed model with approximately equal contributions for its uncorrelated and autocorrelated components. The tip-dating analysis is particularly sensitive to the choice of the relaxed clock model. In this context, the classical pure Brownian relaxed clock appears to be overly rigid, leading to biases in divergence time estimation. By contrast, the use of a mixed clock leads to more recent and more reasonable estimates for the crown ages of placental orders and superorders. Altogether, the mixed clock introduced here represents a first step towards empirically more adequate models of the patterns of rate variation across phylogenetic trees.This article is part of the themed issue 'Dating species divergences using rocks and clocks'.
Lee, Casey Y; Thompson, R Terry; Prato, Frank S; Goldhawk, Donna E; Gelman, Neil
2015-01-01
Reporter gene-based labeling of cells with iron is an emerging method of providing magnetic resonance imaging contrast for long-term cell tracking and monitoring cellular activities. This report investigates 9.4 T nuclear magnetic resonance properties of mammalian cells overexpressing MagA, a putative iron transport protein from magnetotactic bacteria. MagA-expressing MDA-MB-435 cells were cultured in the presence and absence of iron supplementation and compared to the untransfected control. The relationship between the transverse relaxation rate (R2) and interecho time was investigated using the Carr-Purcell-Meiboom-Gill sequence. This relationship was analyzed using a model based on water diffusion in weak magnetic field inhomogeneities (Jensen-Chandra model) as well as a fast-exchange model (Luz-Meiboom model). Increases in R2 with increasing interecho time were larger in the iron-supplemented, MagA-expressing cells compared to other cells. The dependence of R2 on interecho time in these iron-supplemented, MagA-expressing cells was better represented by the Jensen-Chandra model compared to the Luz-Meiboom model, whereas the Luz-Meiboom model performed better for the remaining cell types. Our findings provide an estimate of the distance scale of microscopic magnetic field variations in MagA-expressing cells, which is thought to be related to the size of iron-containing vesicles.
Scaling the Martian Walls of Time
NASA Astrophysics Data System (ADS)
Thornton, Nikki; Yagloski, Joseph; Fledderman, Joe; OMarr, Gregg; Weber, Ben; Carlins, Chris; Krishna, Shubh; Sloan, Kevin; Merriman, Taite; Borowski, David
2000-01-01
On Earth, when scientists want to investigate planetary history they take a core sample, with deeper fragments corresponding to older materials. In essence, descending through sedimentary layers is like going back in time. But creating a robot capable of taking samples more than a few meters below the planetary surface is still beyond the current available technology. The cliffhanger idea takes advantage of the natural surface features of Mars to explore the history of the planet without digging. So interesting and difficult questions can be answered not with the brute force of a drill, but with creative mission design. Penn State University HEDS-UP team has designed a novel Mars mission approach. A main Lander with a Rover and a Cliffhanger will land near cliffs of Valles Mariners. Especially design cannon (gas, guided munitions or rocket) will deploy a long rope into the canyon. The rover will carry the cliffhanger to the edge of Valles Marineris following the rope, attach the cliffhanger to the rope. The Cliffhanger will then climb a 2 km down the rope and will allow the team to study sedimentary layers of rock on the side of the cliff. Samples and high-resolution images will be taken and delivered to the Lander for further investigation (optical multispectral imaging microscope, spectrometry) and sending the results to Earth. The robot has been designed to have the capability for locomotion at any angle (including somewhat uphill slopes) but maximum effective After the mission of rope-climbing is completed, the Rover am Lander will embark on another long-term mission to provide meteorological and geological data over a long period of time (long-term Mars Observatory), and perform acoustic and seismic experiments on the surface of Mars in preparation for human arrival.
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 (ππ*) 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 (πσ*) 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.
Langer, S F J; Habazettl, H; Kuebler, W M; Pries, A R
2005-01-01
The left ventricular isovolumic pressure decay, obtained by cardiac catheterization, is widely characterized by the time constant tau of the exponential regression p(t)=Pomega+(P0-Pomega)exp(-t/tau). However, several authors prefer to prefix Pomega=0 instead of coestimating the pressure asymptote empirically; others present tau values estimated by both methods that often lead to discordant results and interpretation of lusitropic changes. The present study aims to clarify the relations between the tau estimates from both methods and to decide for the more reliable estimate. The effect of presetting a zero asymptote on the tau estimate was investigated mathematically and empirically, based on left ventricular pressure decay data from isolated ejecting rat and guinea pig hearts at different preload and during spontaneous decrease of cardiac function. Estimating tau with preset Pomega=0 always yields smaller values than the regression with empirically estimated asymptote if the latter is negative and vice versa. The sequences of tau estimates from both methods can therefore proceed in reverse direction if tau and Pomega change in opposite directions between the measurements. This is exemplified by data obtained during an increasing preload in spontaneously depressed isolated hearts. The estimation of the time constant of isovolumic pressure fall with a preset zero asymptote is heavily biased and cannot be used for comparing the lusitropic state of the heart in hemodynamic conditions with considerably altered pressure asymptotes.
Livingstone, Ruth A; Thompson, James O F; Iljina, Marija; Donaldson, Ross J; Sussman, Benjamin J; Paterson, Martin J; Townsend, Dave
2012-11-14
Time-resolved photoelectron imaging was used to investigate the dynamical evolution of the initially prepared S(1) (ππ*) 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 S(1) potential surface. In catechol, the overall S(1) 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 S(1) state and the close lying S(2) (πσ*) state, which is dissociative along the O-H stretching coordinate. Further evidence of this S(1)/S(2) 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.
On stabilisability of nonlinear systems on time scales
NASA Astrophysics Data System (ADS)
Bartosiewicz, Zbigniew; Piotrowska, Ewa
2013-01-01
In this article, stabilisability of nonlinear finite-dimensional control systems on arbitrary time scales is studied. The classical results on stabilisation of nonlinear continuous-time and discrete-time systems are extended to systems on arbitrary time scales with bounded graininess function. It is shown that uniform exponential stability of the linear approximation of a nonlinear system implies uniform exponential stability of the nonlinear system. Then this result is used to show a similar implication for uniform exponential stabilisability.
Time scales of tunneling decay of a localized state
Ban, Yue; Muga, J. G.; Sherman, E. Ya.; Buettiker, M.
2010-12-15
Motivated by recent time-domain experiments on ultrafast atom ionization, we analyze the transients and time scales that characterize, aside from the relatively long lifetime, the decay of a localized state by tunneling. While the tunneling starts immediately, some time is required for the outgoing flux to develop. This short-term behavior depends strongly on the initial state. For the initial state, tightly localized so that the initial transients are dominated by over-the-barrier motion, the time scale for flux propagation through the barrier is close to the Buettiker-Landauer traversal time. Then a quasistationary, slow-decay process follows, which sets ideal conditions for observing diffraction in time at longer times and distances. To define operationally a tunneling time at the barrier edge, we extrapolate backward the propagation of the wave packet that escaped from the potential. This extrapolated time is considerably longer than the time scale of the flux and density buildup at the barrier edge.
Springer, Fabian; Steidle, Günter; 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 3T 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.
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}=4.0×10{sup 22} eV/m for InSb and P{sub pe}=1.2×10{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.
NASA Astrophysics Data System (ADS)
Fragiadakis, D.; Roland, C. M.
2014-05-01
Molecular dynamics simulations were carried out on a series of Lennard-Jones binary mixtures of rigid, asymmetric, dumbbell-shaped molecules. Below an onset temperature, the rotational and translational dynamics split into the slow structural α relaxation and a higher-frequency Johari-Goldstein β relaxation. Both processes are dynamically heterogeneous, having broad distributions of relaxation times. However, only the α relaxation shows strong dynamic correlations; correlations at the β time scale are weak, in particular for molecules having shorter bonds. Despite the close connection between the two processes, we find no correlation between the α and β relaxation times of individual molecules; that is, a molecule exhibiting slow β motion does not necessarily undergo slow α dynamics and likewise for fast molecules. However, the single-molecule α relaxation times do correlate with both the α and β relaxation strengths.
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.
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.
Relaxation of magnetotail plasmas
NASA Technical Reports Server (NTRS)
Bhattacharjee, A.
1987-01-01
A quasi-thermodynamic model is presented for the relaxation of magnetotail plasmas during substorms, followed by quiet times. It is proposed that the plasma relaxes to a state of low-potential energy subject to a small number of global constraints. The constraints are exactly preserved by all ideal motions and, approximately, by a wide class of motions of the plasma undergoing magnetic reconnection. A variational principle which minimizes the free energy predicts the relaxed state. Exact, two-dimensional solutions of the relaxed state are obtained. A universal feature of the exact solutions is a chain of magnetic islands along the tail axis. Sufficient conditions for the stability of relaxed states are obtained from the second variation of the free-energy functional.
Bouhrara, Mustapha; Spencer, Richard G
2017-02-15
A number of central nervous system (CNS) diseases exhibit changes in myelin content and magnetic resonance longitudinal, T1, and transverse, T2, relaxation times, which therefore represent important biomarkers of CNS pathology. Among the methods applied for measurement of myelin water fraction (MWF) and relaxation times, the multicomponent driven equilibrium single pulse observation of T1 and T2 (mcDESPOT) approach is of particular interest. mcDESPOT permits whole brain mapping of multicomponent T1 and T2, with data acquisition accomplished within a clinically realistic acquisition time. Unfortunately, previous studies have indicated the limited performance of mcDESPOT in the setting of the modest signal-to-noise range of high-resolution mapping, required for the depiction of small structures and to reduce partial volume effects. Recently, we showed that a new Bayesian Monte Carlo (BMC) analysis substantially improved determination of MWF from mcDESPOT imaging data. However, our previous study was limited in that it did not discuss determination of relaxation times. Here, we extend the BMC analysis to the simultaneous determination of whole-brain MWF and relaxation times using the two-component mcDESPOT signal model. Simulation analyses and in-vivo human brain studies indicate the overall greater performance of this approach compared to the stochastic region contraction (SRC) algorithm, conventionally used to derive parameter estimates from mcDESPOT data. SRC estimates of the transverse relaxation time of the long T2 fraction, T2,l, and the longitudinal relaxation time of the short T1 fraction, T1,s, clustered towards the lower and upper parameter search space limits, respectively, indicating failure of the fitting procedure. We demonstrate that this effect is absent in the BMC analysis. Our results also showed improved parameter estimation for BMC as compared to SRC for high-resolution mapping. Overall we find that the combination of BMC analysis and mcDESPOT, BMC
Kolev, N; Cserhalmi, L; Palik, I; Romoda, T
1981-01-01
To determine the usefulness of the time intervals obtained from the first derivative of apexcardiogram (dA/dt) in assessing contraction and relaxation in cardiomyopathy, 11 patients with hypertrophic obstructive cardiomyopathy (HOCM) and 9 patients with congestive cardiomyopathy (COCM) with hemodynamically and angiographically documented diagnosis were studied. As a control group 50 normal subjects were used. Since contraction and relaxation is dependent on preload and afterload, the time interval from R wave of electrocardiogram to the positive peak of dA/dt (R to dA/dt) and 2 relaxation parameters derived from negative peak dA/dt, early relaxation index (ERI) and total relaxation index (TRI) were investigated. In HOCM the R to dA/dt were shortened (55 +/- 13 msec versus 76 +/- 14 msec in controls, P less than 0.01) and both ERI and TRI were augmented (ERI: 12.5 +/- 9 versus 4.3 +/- 5 in controls, p less than 0.001; TRI: 147 +/- 29 versus 70 +/- 18 in controls, p less than 0.02). In COCM the R to dA/dt were elongated (124 +/- 14 msec versus 76 +/- 14 msec in controls, P less than 09.001) and both ERI and TRI were decreased (ERI: 2.1 +/- 4 versus 4.3 +/- 5 in controls, p less than 0.005; TRI: 41 +/- 17 versus 70 +/- 18 in controls, p less than 0.002)., Significant correlation between these indices and some internal parameters of myocardial performance were observed. These findings indicate that systolic and diastolic time intervals measured from the first derivative of apexcardiogram may be used as a reliable indices for evaluation of contraction and relaxation independently of preload and afterload.
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.
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
Multiple time scale complexity analysis of resting state FMRI.
Smith, Robert X; Yan, Lirong; Wang, Danny J J
2014-06-01
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.
Song, Kyu-Ho; Baek, Hyeon-Man; Lee, Do-Wan; Choe, Bo-Young
2015-10-01
The aim of this study was to evaluate the transverse relaxation time of methylene resonance as compared to other lipid resonances. The examinations were performed using a 3.0 T scanner with a point-resolved spectroscopy (PRESS) sequence. Lipid relaxation time in a lipid phantom filled with canola oil was estimated with a repetition time (TR) of 6000ms and echo time (TE) of 40-550ms. For in vivo proton magnetic resonance spectroscopy ((1)H-MRS), eight male Sprague-Dawley rats were given free access to a normal-chow (NC) and another eight male Sprague-Dawley rats were given free access to a high-fat (HF) diet. Both groups drank water ad libitum. T2 measurements in the rats' livers were conducted at a fixed TR of 6000ms and TE of 40-220ms. Exponential curve fitting quality was calculated through the coefficients of determination (R(2)). Chemical analyses of the phantom and livers were not performed, but T2 decay curves were acquired. The T2 relaxation time of methylene resonance was estimated as follows: NC rats, 37.1±4.3ms; HF rats, 31.4±1.8ms (p<0.05). The extrapolated M0 values were higher in HF rats than in NC rats (p<0.005). This study of (1)H MRS led to sufficient spectral resolution and signal-to-noise ratio differences to characterize the T2 relaxation times of methylene resonance. (1)H MRS relaxation times may be useful for quantitative characterization of various liver diseases, including fatty liver disease.
Extreme reaction times determine fluctuation scaling in human color vision
NASA Astrophysics Data System (ADS)
Medina, José M.; Díaz, José A.
2016-11-01
In modern mental chronometry, human reaction time defines the time elapsed from stimulus presentation until a response occurs and represents a reference paradigm for investigating stochastic latency mechanisms in color vision. Here we examine the statistical properties of extreme reaction times and whether they support fluctuation scaling in the skewness-kurtosis plane. Reaction times were measured for visual stimuli across the cardinal directions of the color space. For all subjects, the results show that very large reaction times deviate from the right tail of reaction time distributions suggesting the existence of dragon-kings events. The results also indicate that extreme reaction times are correlated and shape fluctuation scaling over a wide range of stimulus conditions. The scaling exponent was higher for achromatic than isoluminant stimuli, suggesting distinct generative mechanisms. Our findings open a new perspective for studying failure modes in sensory-motor communications and in complex networks.
NASA Astrophysics Data System (ADS)
Mannstadt, W.; Freeman, A. J.
1997-03-01
The chemisorption of alkali atoms on metals still remains a challenging topic after almost sixty years of study. Recently, a novel type of experiment, β-decay NMR, was developed and applied to investigate Li atoms chemisorbed on a Ru(001) surface( H. J. Jänsch et al., Phys.Rev.Lett. 25, 120 (1995)). Such measurements of the spin lattice relaxation time provide information about the local density of states (LDOS) at EF and at the Li nucleus. Through the LDOS, the very local electronic properties of the chemisorbed alkali atom is determined, which provides new physical insight into the chemisorption process. One striking result is a constancy of the LDOS at low coverage, Θ=0 - 0.15, while the work function changes by about 2 eV. We present the first ab initio LDA calculations of the LDOS, using our full potential linearized augmented plane wave (FLAPW) method for thin films(E.Wimmer,H.Krakauer,M.Weinert, A.J.Freeman, Phys.Rev.B 24, 864 (1981)), to determine the Li chemisorption on Ru(001) for three coverages, Θ=1.0, 0.25 and 0.11, including a structure optimization for each. The calculations show a constant value of the LDOS at Θ= 0.25 and 0.11 which increases at high coverage by about a factor of two. * Supported by A.v.Humboldt Foundation
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.
Baranowski, M; Woźniak-Braszak, A; Jurga, K
2011-01-01
This paper reports on design and construction of a double coil high-homogeneity ensuring Nuclear Magnetic Resonance Probe for off-resonance relaxation time measurements. NMR off-resonance experiments pose unique technical problems. Long irradiation can overheat the sample, dephase the spins because of B(1) field inhomogeneity and degrade the signal received by requiring the receiver bandwidth to be broader than that needed for normal experiment. The probe proposed solves these problems by introducing a separate off-resonance irradiation coil which is larger than the receiver coil and is wound up on the dewar tube that separates it from the receiver coil thus also thermally protects the sample from overheating. Large size of the irradiation coil also improves the field homogeneity because as a ratio of the sample diameter to the magnet (coil) diameter increases, the field inhomogeneity also increases (Blümich et al., 2008) [1]. The small receiver coil offers maximization of the filling factor and a high signal to the noise ratio.
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.
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.
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.
NEA Scout Solar Sail: Half-scale Fold Time Lapse
In this time lapse, the Near-Earth Asteroid Scout (NEA Scout) CubeSat team rolls a half-scale prototype of the small satellite's solar sail in preparation for a deployment test. During its mission,...
Stress-relaxation behavior in gels with ionic and covalent crosslinks.
Zhao, Xuanhe; Huebsch, Nathaniel; Mooney, David J; Suo, Zhigang
2010-03-15
Long-chained polymers in alginate hydrogels can form networks by either ionic or covalent crosslinks. This paper shows that the type of crosslinks can markedly affect the stress-relaxation behavior of the gels. In gels with only ionic crosslinks, stress relaxes mainly through breaking and subsequent reforming of the ionic crosslinks, and the time scale of the relaxation is independent of the size of the sample. By contrast, in gels with only covalent crosslinks, stress relaxes mainly through migration of water, and the relaxation slows down as the size of the sample increases. Implications of these observations are discussed.
Kolev, N; Cserhalmi, L; Palik, I; Romoda, T
1981-01-01
To determine the usefulness of the time intervals obtained from the first derivative of apex cardiogram (dA/dt) in assessing contraction and relaxation in cardiomyopathy, 11 patients with hypertrophic obstructive cardiomyopathy (HOCM) and 9 with congestive cardiomyopathy (COCM) with hemodynamically and angiographically documented diagnosis were studied. The control group numbered 50 normal subjects. Since contraction and relaxation are dependent on preload and afterload, the time interval from R wave of the electrocardiogram to the positive peak of dA/dt (R to dA/dt) and two relaxation parameters derived from the negative peak dA/dt, as well as early apex cardiographic relaxation index EARI) and total apex cardiographic relaxation index (TARI) were determined in all the subjects investigated. In HOCM the R to dA/dt were shortened (55 +/- 13 msec vs. 76 + 14 msec for controls, p less than 0.01) and both EARI and TARI were augmented (EARI: 11.5 +/- 9 vs. 4.3 +/- 5 in controls, p less than 0.001; TARI: 127 +/- 29 vs. 70 +/- 18 in controls p less than 0.02). In COCM the R to dA/dt were elongated (124 +/- 14 msec vs. 76 +/- 14 msec in controls, p less than 0.001) and both EARI and TARI were decreased (EARI: 2.4 +/- 4 vs. 4.3 +/- 5 in controls, p less than 0.005; TARI; 43 + 17 vs. 70 +/- 18 for controls, p less than 0.02). A significant correlation between these indices and some internal indices of myocardial performances was demonstrated. These findings indicate that the interval R to dA/dt, EARI and TARI may be used as reliable indices for the evaluation of contraction and relaxation in cardiomyopathy, independently of preload and afterload.
Dynamics in entangled polyethylene melts [Multi time scale dynamics in entangled polyethylene melts
Salerno, K. Michael; Agrawal, Anupriya; Peters, Brandon L.; Perahia, Dvora; Grest, Gary S.
2016-10-10
Polymer dynamics creates distinctive viscoelastic behavior as a result of a coupled interplay of motion at the atomic length scale and motion of the entire macromolecule. Capturing the broad time and length scales of polymeric motion however, remains a challenge. Using linear polyethylene as a model system, we probe the effects of the degree of coarse graining on polymer dynamics. Coarse-grained (CG) potentials are derived using iterative Boltzmann inversion with λ methylene groups per CG bead (denoted CGλ) with λ = 2,3,4 and 6 from a fully-atomistic polyethylene melt simulation. By rescaling time in the CG models by a factor α, the chain mobility for the atomistic and CG models match. We show that independent of the degree of coarse graining, all measured static and dynamic properties are essentially the same once the dynamic scaling factor α and a non-crossing constraint for the CG6 model are included. The speedup of the CG4 model is about 3 times that of the CG3 model and is comparable to that of the CG6 model. Furthermore, using these CG models we were able to reach times of over 500 μs, allowing us to measure a number of quantities, including the stress relaxation function, plateau modulus and shear viscosity, and compare directly to experiment.
Dynamics in entangled polyethylene melts [Multi time scale dynamics in entangled polyethylene melts
Salerno, K. Michael; Agrawal, Anupriya; Peters, Brandon L.; ...
2016-10-10
Polymer dynamics creates distinctive viscoelastic behavior as a result of a coupled interplay of motion at the atomic length scale and motion of the entire macromolecule. Capturing the broad time and length scales of polymeric motion however, remains a challenge. Using linear polyethylene as a model system, we probe the effects of the degree of coarse graining on polymer dynamics. Coarse-grained (CG) potentials are derived using iterative Boltzmann inversion with λ methylene groups per CG bead (denoted CGλ) with λ = 2,3,4 and 6 from a fully-atomistic polyethylene melt simulation. By rescaling time in the CG models by a factormore » α, the chain mobility for the atomistic and CG models match. We show that independent of the degree of coarse graining, all measured static and dynamic properties are essentially the same once the dynamic scaling factor α and a non-crossing constraint for the CG6 model are included. The speedup of the CG4 model is about 3 times that of the CG3 model and is comparable to that of the CG6 model. Furthermore, using these CG models we were able to reach times of over 500 μs, allowing us to measure a number of quantities, including the stress relaxation function, plateau modulus and shear viscosity, and compare directly to experiment.« less
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.
Characteristic Time Scales of Characteristic Magmatic Processes and Systems
NASA Astrophysics Data System (ADS)
Marsh, B. D.
2004-05-01
Every specific magmatic process, regardless of spatial scale, has an associated characteristic time scale. Time scales associated with crystals alone are rates of growth, dissolution, settling, aggregation, annealing, and nucleation, among others. At the other extreme are the time scales associated with the dynamics of the entire magmatic system. These can be separated into two groups: those associated with system genetics (e.g., the production and transport of magma, establishment of the magmatic system) and those due to physical characteristics of the established system (e.g., wall rock failure, solidification front propagation and instability, porous flow). The detailed geometry of a specific magmatic system is particularly important to appreciate; although generic systems are useful, care must be taken to make model systems as absolutely realistic as possible. Fuzzy models produce fuzzy science. Knowledge of specific time scales is not necessarily useful or meaningful unless the hierarchical context of the time scales for a realistic magmatic system is appreciated. The age of a specific phenocryst or ensemble of phenocrysts, as determined from isotopic or CSD studies, is not meaningful unless something can be ascertained of the provenance of the crystals. For example, crystal size multiplied by growth rate gives a meaningful crystal age only if it is from a part of the system that has experienced semi-monotonic cooling prior to chilling; crystals entrained from a long-standing cumulate bed that were mechanically sorted in ascending magma may not reveal this history. Ragged old crystals rolling about in the system for untold numbers of flushing times record specious process times, telling more about the noise in the system than the life of typical, first generation crystallization processes. The most helpful process-related time scales are those that are known well and that bound or define the temporal style of the system. Perhaps the most valuable of these
Time Scales of Ion Transport in Imidazolium-based Polymers
NASA Astrophysics Data System (ADS)
Choi, U. Hyeok; Ye, Yuesheng; Lee, Minjae; Gibson, Harry; Elabd, Yossef; Runt, James; Colby, Ralph
2011-03-01
We synthesize and characterize ionic polymers with imidazolium cations covalently attached to the polymer chain and various ionic liquid counterions for ionic actuators. The imidazolium cations are attached to the polymers with flexible alkyl spacer chains and also have a variety of alkyl and alkyl ether termini. The anionic counterions are also varied; tetrafluoroborate (BF4) , hexafluorophosphate (PF6) and bis(trifluoromethanesulfonyl)imide (TFSI) were mainly used in this study. Dielectric relaxation spectroscopy (DRS) is utilized to measure the dielectric constant and conductivity, as a function of temperature. The 1953 Macdonald model is applied to estimate the number density of conducting ions and their mobility, from electrode polarization at low frequencies in DRS. The 1988 Dyre model is used to determine ion hopping times from the frequency-dependent conductivity at higher frequencies. The consequence of polymer structural variations will be elucidated for these vital characteristics.
Whole brain MP2RAGE-based mapping of the longitudinal relaxation time at 9.4T.
Hagberg, G E; Bause, J; Ethofer, T; Ehses, P; Dresler, T; Herbert, C; Pohmann, R; Shajan, G; Fallgatter, A; Pavlova, M A; Scheffler, K
2017-01-01
Mapping of the longitudinal relaxation time (T1) with high accuracy and precision is central for neuroscientific and clinical research, since it opens up the possibility to obtain accurate brain tissue segmentation and gain myelin-related information. An ideal, quantitative method should enable whole brain coverage within a limited scan time yet allow for detailed sampling with sub-millimeter voxel sizes. The use of ultra-high magnetic fields is well suited for this purpose, however the inhomogeneous transmit field potentially hampers its use. In the present work, we conducted whole brain T1 mapping based on the MP2RAGE sequence at 9.4T and explored potential pitfalls for automated tissue classification compared with 3T. Data accuracy and T2-dependent variation of the adiabatic inversion efficiency were investigated by single slice T1 mapping with inversion recovery EPI measurements, quantitative T2 mapping using multi-echo techniques and simulations of the Bloch equations. We found that the prominent spatial variation of the transmit field at 9.4T (yielding flip angles between 20% and 180% of nominal values) profoundly affected the result of image segmentation and T1 mapping. These effects could be mitigated by correcting for both flip angle and inversion efficiency deviations. Based on the corrected T1 maps, new, 'flattened', MP2RAGE contrast images were generated, that were no longer affected by variations of the transmit field. Unlike the uncorrected MP2RAGE contrast images acquired at 9.4T, these flattened images yielded image segmentations comparable to 3T, making bias-field correction prior to image segmentation and tissue classification unnecessary. In terms of the T1 estimates at high field, the proposed correction methods resulted in an improved precision, with test-retest variability below 1% and a coefficient-of-variation across 25 subjects below 3%.
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 (T(1)(-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, T(1)(-1) can be used as a convenient quantitative measure of membrane fluidity that reflects local membrane dynamics. T(1)(-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 T(1)(-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).
NASA Astrophysics Data System (ADS)
Kim, Kang; Saito, Shinji
2013-03-01
We report an extensive and systematic investigation of the multi-point and multi-time correlation functions to reveal the spatio-temporal structures of dynamic heterogeneities in glass-forming liquids. Molecular dynamics simulations are carried out for the supercooled states of various prototype models of glass-forming liquids such as binary Kob-Andersen, Wahnström, soft-sphere, and network-forming liquids. While the first three models act as fragile liquids exhibiting super-Arrhenius temperature dependence in their relaxation times, the last is a strong glass-former exhibiting Arrhenius behavior. First, we quantify the length scale of the dynamic heterogeneities utilizing the four-point correlation function. The growth of the dynamic length scale with decreasing temperature is characterized by various scaling relations that are analogous to the critical phenomena. We also examine how the growth of the length scale depends upon the model employed. Second, the four-point correlation function is extended to a three-time correlation function to characterize the temporal structures of the dynamic heterogeneities based on our previous studies [K. Kim and S. Saito, Phys. Rev. E 79, 060501-R (2009), 10.1103/PhysRevE.79.060501; K. Kim and S. Saito, J. Chem. Phys. 133, 044511 (2010), 10.1063/1.3464331]. We provide comprehensive numerical results obtained from the three-time correlation function for the above models. From these calculations, we examine the time scale of the dynamic heterogeneities and determine the associated lifetime in a consistent and systematic way. Our results indicate that the lifetime of the dynamical heterogeneities becomes much longer than the α-relaxation time determined from a two-point correlation function in fragile liquids. The decoupling between the two time scales is remarkable, particularly in supercooled states, and the time scales differ by more than an order of magnitude in a more fragile liquid. In contrast, the lifetime is shorter
Galaxy merger time-scales in the Illustris Simulation
NASA Astrophysics Data System (ADS)
Rojas, Areli; Rodriguez-Gomez, Vicente; Hernquist, Lars E.; Wellons, Sarah; Moreno, Jorge
2017-01-01
In this project we are investigate merger time-scales, define as the time delays from dark matter halo viral crossing to galaxy-galaxy coalescence. Our project uses merger history trees drawn from the Illustris Simulation, a cosmological hydrodynamic run that follows the formation and evolution of galaxies across cosmic time. Preliminary results indicate that merger time-scales are not sensitive to stellar mass or mass ratio, in stark contrast to what has been found earlier with cosmological dark-matter-only simulations. Work towards understanding the source of this disagreement is currently in progress.
Vorticity statistics and the time scales of turbulent strain.
Moriconi, L; Pereira, R M
2013-07-01
Time scales of turbulent strain activity, denoted as the strain persistence times of first and second order, are obtained from time-dependent expectation values and correlation functions of Lagrangian rate-of-strain eigenvalues taken in particularly defined statistical ensembles. Taking into account direct numerical simulation data, our approach relies on heuristic closure hypotheses which allow us to establish a connection between the statistics of vorticity and strain. It turns out that softly divergent prefactors correct the usual "1/s" strain time-scale estimate of standard turbulence phenomenology, in a way which is consistent with the phenomenon of vorticity intermittency.
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 Technical Reports Server (NTRS)
Moshchalcov, V. V.; Zhukov, A. A.; Kuznetzov, V. D.; Metlushko, V. V.; Leonyuk, L. I.
1990-01-01
At the initial time intervals, preceding the thermally activated flux creep regime, fast nonlogarithmic relaxation is found. The fully magnetic moment Pm(t) relaxation curve is shown. The magnetic measurements were made using SQUID-magnetometer. Two different relaxation regimes exist. The nonlogarithmic relaxation for the initial time intervals may be related to the viscous Abrikosov vortices flow with j is greater than j(sub c) for high enough temperature T and magnetic field induction B. This assumption correlates with Pm(t) measurements. The characteristic time t(sub O) separating two different relaxation regimes decreases as temperature and magnetic field are lowered. The logarithmic magnetization relaxation curves Pm(t) for fixed temperature and different external magnetic field inductions B are given. The relaxation rate dependence on magnetic field, R(B) = dPm(B, T sub O)/d(1nt) has a sharp maximum which is similar to that found for R(T) temperature dependences. The maximum shifts to lower fields as temperature goes up. The observed sharp maximum is related to a topological transition in shielding critical current distribution and, consequently, in Abrikosov vortices density. The nonlogarithmic magnetization relaxation for the initial time intervals is found. This fast relaxation has almost an exponentional character. The sharp relaxation rate R(B) maximum is observed. This maximum corresponds to a topological transition in Abrikosov vortices distribution.
Exponentials and Laplace transforms on nonuniform time scales
NASA Astrophysics Data System (ADS)
Ortigueira, Manuel D.; Torres, Delfim F. M.; Trujillo, Juan J.
2016-10-01
We formulate a coherent approach to signals and systems theory on time scales. The two derivatives from the time-scale calculus are used, i.e., nabla (forward) and delta (backward), and the corresponding eigenfunctions, the so-called nabla and delta exponentials, computed. With these exponentials, two generalised discrete-time Laplace transforms are deduced and their properties studied. These transforms are compatible with the standard Laplace and Z transforms. They are used to study discrete-time linear systems defined by difference equations. These equations mimic the usual continuous-time equations that are uniformly approximated when the sampling interval becomes small. Impulse response and transfer function notions are introduced. This implies a unified mathematical framework that allows us to approximate the classic continuous-time case when the sampling rate is high or to obtain the standard discrete-time case, based on difference equations, when the time grid becomes uniform.
The scaling of time series size towards detrended fluctuation analysis
NASA Astrophysics Data System (ADS)
Gao, Xiaolei; Ren, Liwei; Shang, Pengjian; Feng, Guochen
2016-06-01
In this paper, we introduce a modification of detrended fluctuation analysis (DFA), called multivariate DFA (MNDFA) method, based on the scaling of time series size N. In traditional DFA method, we obtained the influence of the sequence segmentation interval s, and it inspires us to propose a new model MNDFA to discuss the scaling of time series size towards DFA. The effectiveness of the procedure is verified by numerical experiments with both artificial and stock returns series. Results show that the proposed MNDFA method contains more significant information of series compared to traditional DFA method. The scaling of time series size has an influence on the auto-correlation (AC) in time series. For certain series, we obtain an exponential relationship, and also calculate the slope through the fitting function. Our analysis and finite-size effect test demonstrate that an appropriate choice of the time series size can avoid unnecessary influences, and also make the testing results more accurate.
Universal scaling function in discrete time asymmetric exclusion processes
NASA Astrophysics Data System (ADS)
Chia, Nicholas; Bundschuh, Ralf
2005-03-01
In the universality class of the one dimensional Kardar-Parisi-Zhang surface growth, Derrida and Lebowitz conjectured the universality of not only the scaling exponents, but of an entire scaling function. Since Derrida and Lebowitz' original publication this universality has been verified for a variety of continuous time systems in the KPZ universality class. We study the Derrida-Lebowitz scaling function for multi-particle versions of the discrete time Asymmetric Exclusion Process. We find that in this discrete time system the Derrida-Lebowitz scaling function not only properly characterizes the large system size limit, but even accurately describes surprisingly small systems. These results have immediate applications in searching biological sequence databases.
Trends in Surface Radiation Budgets at Climatic Time Scales
NASA Astrophysics Data System (ADS)
Pinker, R. T.; Zhang, B.; Ma, Y.
2015-12-01
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 radiative balance at global scale, however, the length of available satellite records is limited due to the frequent changes in the observing systems. In this paper we report on an effort to synthesize satellite observations from independent sources to estimates shortwave and longwave surface radiative fluxes at climatic time scales and use them to learn about their variability and trends at global scale with a focus on the tropics. An attempt will be made to learn from the comparison about possible causes of observed 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 updated knowledge on radiative balance as compared to what is known from shorter time records.
Controllability of multiplex, multi-time-scale networks
NASA Astrophysics Data System (ADS)
Pósfai, Márton; Gao, Jianxi; Cornelius, Sean P.; Barabási, Albert-László; D'Souza, Raissa M.
2016-09-01
The paradigm of layered networks is used to describe many real-world systems, from biological networks to social organizations and transportation systems. While recently there has been much progress in understanding the general properties of multilayer networks, our understanding of how to control such systems remains limited. One fundamental aspect that makes this endeavor challenging is that each layer can operate at a different time scale; thus, we cannot directly apply standard ideas from structural control theory of individual networks. Here we address the problem of controlling multilayer and multi-time-scale networks focusing on two-layer multiplex networks with one-to-one interlayer coupling. We investigate the practically relevant case when the control signal is applied to the nodes of one layer. We develop a theory based on disjoint path covers to determine the minimum number of inputs (Ni) necessary for full control. We show that if both layers operate on the same time scale, then the network structure of both layers equally affect controllability. In the presence of time-scale separation, controllability is enhanced if the controller interacts with the faster layer: Ni decreases as the time-scale difference increases up to a critical time-scale difference, above which Ni remains constant and is completely determined by the faster layer. We show that the critical time-scale difference is large if layer I is easy and layer II is hard to control in isolation. In contrast, control becomes increasingly difficult if the controller interacts with the layer operating on the slower time scale and increasing time-scale separation leads to increased Ni, again up to a critical value, above which Ni still depends on the structure of both layers. This critical value is largely determined by the longest path in the faster layer that does not involve cycles. By identifying the underlying mechanisms that connect time-scale difference and controllability for a simplified
Inferring Patterns in Network Traffic: Time Scales and Variations
2014-10-21
2014 Carnegie Mellon University Inferring Patterns in Network Traffic : Time Scales and Variation Soumyo Moitra smoitra@sei.cmu.edu...number. 1. REPORT DATE 21 OCT 2014 2. REPORT TYPE N/A 3. DATES COVERED 4. TITLE AND SUBTITLE Inferring Patterns in Network Traffic : Time...method and metrics for Situational Awareness • SA Monitoring trends and changes in traffic • Analysis over time Time series data analysis • Metrics
Levin, E M; Cui, J-F; Schmidt-Rohr, K
2016-09-01
(125)Te NMR spectra and spin-lattice relaxation times, T1, have been measured for several GeTe-based materials with Te excess. The spectra show inhomogeneous broadening by several thousand ppm and a systematic variation in T1 relaxation time with resonance frequency. The quadratic dependence of the spin-lattice relaxation rate, 1/T1, on the Knight shift in the Korringa relation is found to be valid over a wide range of Knight shifts. This result confirms that T1 relaxation in GeTe-based materials is mostly dominated by hyperfine interaction between nuclei and free charge carriers. In GeTe with 2.5% excess of Te, about 15% of the material exhibits a Knight shift of ≥4500ppm and a T1 of only 0.3ms, indicating a high hole concentration that could correspond to close to 50% vacancies on the Ge sublattice in this component. Our findings provide a basis for determining the charge carrier concentration and its distribution in complex thermoelectric and phase-change tellurides, which should lead to a better understanding of electronic and thermal transport properties as well as chemical bonding in these materials.
Multiple-time scales analysis of physiological time series under neural control.
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.
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.
Broken scale invariance in time-dependent trapping potentials
NASA Astrophysics Data System (ADS)
Gharashi, Seyed Ebrahim; Blume, D.
2016-12-01
The response of a cold atom gas with contact interactions to a smoothly varying external harmonic confinement in the nonadiabatic regime is studied. The time variation of the angular frequency is varied such that the system is, for vanishing or infinitely strong contact interactions, scale invariant. The time evolution of the system with broken scale invariance (i.e., the time evolution of the system with finite interaction strength) is contrasted with that for a scale invariant system, which exhibits Efimovian-like expansion dynamics that is characterized by log-periodic oscillations with unique period and amplitude. It is found that the breaking of the scale invariance by the finiteness of the interactions leads to a time dependence of the oscillation period and amplitude. It is argued, based on analytical considerations for atomic gases of arbitrary size and numerical results for two one-dimensional particles, that the oscillation period approaches that of the scale-invariant system at large times. The role of the time-dependent contact in the expansion dynamics is analyzed.
Time scale bias in erosion rates of glaciated landscapes.
Ganti, Vamsi; von Hagke, Christoph; Scherler, Dirk; Lamb, Michael P; Fischer, Woodward W; Avouac, Jean-Philippe
2016-10-01
Deciphering erosion rates over geologic time is fundamental for understanding the interplay between climate, tectonic, and erosional processes. Existing techniques integrate erosion over different time scales, and direct comparison of such rates is routinely done in earth science. On the basis of a global compilation, we show that erosion rate estimates in glaciated landscapes may be affected by a systematic averaging bias that produces higher estimated erosion rates toward the present, which do not reflect straightforward changes in erosion rates through time. This trend can result from a heavy-tailed distribution of erosional hiatuses (that is, time periods where no or relatively slow erosion occurs). We argue that such a distribution can result from the intermittency of erosional processes in glaciated landscapes that are tightly coupled to climate variability from decadal to millennial time scales. In contrast, we find no evidence for a time scale bias in spatially averaged erosion rates of landscapes dominated by river incision. We discuss the implications of our findings in the context of the proposed coupling between climate and tectonics, and interpreting erosion rate estimates with different averaging time scales through geologic time.
Time scale bias in erosion rates of glaciated landscapes
Ganti, Vamsi; von Hagke, Christoph; Scherler, Dirk; Lamb, Michael P.; Fischer, Woodward W.; Avouac, Jean-Philippe
2016-01-01
Deciphering erosion rates over geologic time is fundamental for understanding the interplay between climate, tectonic, and erosional processes. Existing techniques integrate erosion over different time scales, and direct comparison of such rates is routinely done in earth science. On the basis of a global compilation, we show that erosion rate estimates in glaciated landscapes may be affected by a systematic averaging bias that produces higher estimated erosion rates toward the present, which do not reflect straightforward changes in erosion rates through time. This trend can result from a heavy-tailed distribution of erosional hiatuses (that is, time periods where no or relatively slow erosion occurs). We argue that such a distribution can result from the intermittency of erosional processes in glaciated landscapes that are tightly coupled to climate variability from decadal to millennial time scales. In contrast, we find no evidence for a time scale bias in spatially averaged erosion rates of landscapes dominated by river incision. We discuss the implications of our findings in the context of the proposed coupling between climate and tectonics, and interpreting erosion rate estimates with different averaging time scales through geologic time. PMID:27713925
Auroral Substorm Time Scales: Seasonal and IMF Variations
NASA Technical Reports Server (NTRS)
Chua, D.; Parks, G. K.; Brittnacher, M.; Germany, G. A.; Spann, J. F.; Six, N. Frank (Technical Monitor)
2002-01-01
The time scales and phases of auroral substorm, activity are quantied in this study using the hemispheric power computed from Polar Ultraviolet Imager (UVI) images. We have applied this technique to several hundred substorm events and we are able to quantify how the characterist act, of substorms vary with season and IMF Bz orientation. We show that substorm time scales vary more strongly with season than with IMF Bz orientation. The recovery time for substorm. activity is well ordered by whether or not the nightside oral zone is sunlit. The recovery time scales for substorms occurring in the winter and equinox periods are similar and are both roughly a factor of two longer than in summer when the auroral oval is sunlit. Our results support the hypothesis that the ionosphere plays an active role in governing the dynamics of the aurora.
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.
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
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
Toptygin, Dmitri; Gronenborn, Angela M; Brand, Ludwig
2006-12-28
The B1 domain of Streptococcal protein G (GB1) is a small, thermostable protein containing a single tryptophan residue. We recorded time-resolved fluorescence of the wild-type GB1 and its 5-fluorotryptophan (5FTrp) variant at more than 30 emission wavelengths between 300 and 470 nm. The time-resolved emission spectra reveal no signs of heterogeneity, but show a time-dependent red shift characteristic of microscopic dielectric relaxation. This is true for both 5FTrp and unmodified Trp in GB1. The time-dependent red shifts in the fluorescence of 5FTrp and unmodified Trp are essentially identical, confirming that the shift is caused by the relaxation of the protein matrix rather than by the fluorophore itself. The total amplitude (but not the rate) of the time-dependent red shift depends on the fluorophore, specifically, on the magnitude of the vector difference between its excited state and ground state electric dipole moments; for 5FTrp this is estimated to be about 88% of that for the unmodified Trp. The decay of the excited state fluorophore population is not monoexponential for either fluorophore; however, the deviation from the monoexponential decay law is larger in the case of unmodified Trp. The relaxation dynamics of GB1 was found to be considerably faster than that of other proteins studied previously, consistent with the small size, tightly packed core, and high thermodynamic stability of GB1.
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.
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…
A methane-based time scale for Vostok ice
NASA Astrophysics Data System (ADS)
Ruddiman, William F.; Raymo, Maureen E.
2003-02-01
Tuning the Vostok methane signal to mid-July 30°N insolation yields a new ice-core gas time scale. This exercise has two rationales: (1) evidence supporting Kutzbach's theory that low-latitude summer insolation in the northern hemisphere controls the strength of tropical monsoons, and (2) interhemispheric CH 4 gradients showing that the main control of orbital-scale CH 4 variations is tropical (monsoonal) sources. The immediate basis for tuning CH 4 to mid-July insolation is the coincident timing of the most recent (pre-anthropogenic) CH 4 maximum at 11,000-10,500 calendar years ago and the most recent July 30°N insolation maximum (all ages in this paper are in calendar years unless specified as 14C years). The resulting CH 4 gas time scale diverges by as much as 15,000 years from the GT4 gas time scale (Petit et al., Nature 399 (1999) 429) prior to 250,000 years ago, but it matches fairly closely a time scale derived by tuning ice-core δ18O atm to a lagged insolation signal (Shackleton, Science 289 (2000) 1897). Most offsets between the CH 4 and δ18O atm time scales can be explained by assuming that tropical monsoons and ice sheets alternate in controlling the phase of the δ18O atm signal. The CH 4 time scale provides an estimate of the timing of the Vostok CO 2 signal against SPECMAP marine δ18O, often used as an index of global ice volume. On the CH 4 time scale, all CO 2 responses are highly coherent with SPECMAP δ18O at the orbital periods. CO 2 leads δ18O by 5000 years at 100,000 years (eccentricity), but the two signals are nearly in-phase at 41,000 years (obliquity) and 23,000 years (precession). The actual phasing between CO 2 and ice volume is difficult to infer because of likely SST overprints on the SPECMAP δ18O signal. CO 2 could lead, or be in phase with, ice volume, but is unlikely to lag behind the ice response.
Segregation time-scales in model granular flows
NASA Astrophysics Data System (ADS)
Staron, Lydie; Phillips, Jeremy C.
2016-04-01
Segregation patterns in natural granular systems offer a singular picture of the systems evolution. In many cases, understanding segregation dynamics may help understanding the system's history as well as its future evolution. Among the key questions, one concerns the typical time-scales at which segregation occurs. In this contribution, we present model granular flows simulated by means of the discrete Contact Dynamics method. The granular flows are bi-disperse, namely exhibiting two grain sizes. The flow composition and its dynamics are systematically varied, and the segregation dynamics carefully analyzed. We propose a physical model for the segregation that gives account of the observed dependence of segregation time scales on composition and dynamics. References L. Staron and J. C. Phillips, Stress partition and micro-structure in size-segregating granular flows, Phys. Rev. E 92 022210 (2015) L. Staron and J. C. Phillips, Segregation time-scales in bi-disperse granular flows, Phys. Fluids 26 (3), 033302 (2014)
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.
Time-dependent scaling patterns in high frequency financial data
NASA Astrophysics Data System (ADS)
Nava, Noemi; Di Matteo, Tiziana; Aste, Tomaso
2016-10-01
We measure the influence of different time-scales on the intraday dynamics of financial markets. This is obtained by decomposing financial time series into simple oscillations associated with distinct time-scales. We propose two new time-varying measures of complexity: 1) an amplitude scaling exponent and 2) an entropy-like measure. We apply these measures to intraday, 30-second sampled prices of various stock market indices. Our results reveal intraday trends where different time-horizons contribute with variable relative amplitudes over the course of the trading day. Our findings indicate that the time series we analysed have a non-stationary multifractal nature with predominantly persistent behaviour at the middle of the trading session and anti-persistent behaviour at the opening and at the closing of the session. We demonstrate that these patterns are statistically significant, robust, reproducible and characteristic of each stock market. We argue that any modelling, analytics or trading strategy must take into account these non-stationary intraday scaling patterns.
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
Two-spin relaxation of P dimers in silicon
NASA Astrophysics Data System (ADS)
Borhani, Massoud; Hu, Xuedong
2010-12-01
We study two-electron singlet-triplet relaxation of donor-bound electrons in Silicon. Hyperfine interaction of the electrons with the phosphorus (P) nuclei, in combination with the electron-phonon interaction, lead to relaxation of the triplet states. Within the Heitler-London and effective-mass approximations, we calculate the triplet relaxation rates in the presence of an applied magnetic field. This relaxation mechanism affects the resonance peaks in current electron-spin-resonance experiments on P dimers. Moreover, the estimated time scales for the spin decay put an upper bound on the gate pulses needed to perform fault-tolerant two-qubit operations in donor-spin-based quantum computers. We have found the optimal regimes though, which mitigate this relaxation mechanism, yet permit sufficiently fast two-qubit operations.
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
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.
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.
Time scales of crystal mixing in magma mushes
NASA Astrophysics Data System (ADS)
Schleicher, Jillian M.; Bergantz, George W.; Breidenthal, Robert E.; Burgisser, Alain
2016-02-01
Magma mixing is widely recognized as a means of producing compositional diversity and preconditioning magmas for eruption. However, the processes and associated time scales that produce the commonly observed expressions of magma mixing are poorly understood, especially under crystal-rich conditions. Here we introduce and exemplify a parameterized method to predict the characteristic mixing time of crystals in a crystal-rich magma mush that is subject to open-system reintrusion events. Our approach includes novel numerical simulations that resolve multiphase particle-fluid interactions. It also quantifies the crystal mixing by calculating both the local and system-wide progressive loss of the spatial correlation of individual crystals throughout the mixing region. Both inertial and viscous time scales for bulk mixing are introduced. Estimated mixing times are compared to natural examples and the time for basaltic mush systems to become well mixed can be on the order of 10 days.
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.
NASA Technical Reports Server (NTRS)
1987-01-01
Environ Corporation's relaxation system is built around a body lounge, a kind of super easy chair that incorporates sensory devices. Computer controlled enclosure provides filtered ionized air to create a feeling of invigoration, enhanced by mood changing aromas. Occupant is also surrounded by multidimensional audio and the lighting is programmed to change colors, patterns, and intensity periodically. These and other sensory stimulators are designed to provide an environment in which the learning process is stimulated, because research has proven that while an individual is in a deep state of relaxation, the mind is more receptive to new information.
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.
Dynamics symmetries of Hamiltonian system on time scales
NASA Astrophysics Data System (ADS)
Peng, Keke; Luo, Yiping
2014-04-01
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.
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. PMID:27026795
NASA Astrophysics Data System (ADS)
Nagel, Hannes; Janke, Wolfhard
2016-05-01
Driven diffusive systems such as the zero-range process (ZRP) and the pair-factorized steady states (PFSS) stochastic transport process are versatile tools that lend themselves to the study of transport phenomena on a generic level. While their mathematical structure is simple enough to allow significant analytical treatment, they offer a variety of interesting phenomena. With appropriate dynamics, the ZRP and PFSS models feature a condensation transition where, for a supercritical density, the translational symmetry breaks spontaneously and excess particles form a single-site or spatially extended condensate, respectively. In this paper we numerically study the typical time scales of the two stages of this condensation process: Nucleation and coarsening. Nucleation is the first stage of condensation where the bulk system relaxes to its stationary distribution and droplet nuclei form in the system. These droplets then gradually grow or evaporate in the coarsening regime to coalesce in a single condensate when the system finally relaxes to the stationary state. We use the ZRP condensation model to discuss the choice of the estimation method for the nucleation time scale and present scaling exponents for the ZRP and PFSS condensation models with respect to the choice of the typical droplet nuclei mass. We then proceed to present scaling exponents in the coarsening regime of the ZRP for partially asymmetric dynamics and the PFSS model for symmetric and asymmetric dynamics.
Improved jet noise modeling using a new time-scale.
Azarpeyvand, M; Self, R H
2009-09-01
To calculate the noise emanating from a turbulent flow using an acoustic analogy knowledge concerning the unsteady characteristics of the turbulence is required. Specifically, the form of the turbulent correlation tensor together with various time and length-scales are needed. However, if a Reynolds Averaged Navier-Stores calculation is used as the starting point then one can only obtain steady characteristics of the flow and it is necessary to model the unsteady behavior in some way. While there has been considerable attention given to the correct way to model the form of the correlation tensor less attention has been given to the underlying physics that dictate the proper choice of time-scale. In this paper the authors recognize that there are several time dependent processes occurring within a turbulent flow and propose a new way of obtaining the time-scale. Isothermal single-stream flow jets with Mach numbers 0.75 and 0.90 have been chosen for the present study. The Mani-Gliebe-Balsa-Khavaran method has been used for prediction of noise at different angles, and there is good agreement between the noise predictions and observations. Furthermore, the new time-scale has an inherent frequency dependency that arises naturally from the underlying physics, thus avoiding supplementary mathematical enhancements needed in previous modeling.
NASA Astrophysics Data System (ADS)
Lim, Ae Ran
2017-04-01
To better elucidate the structural properties of Rb2CoBr4 in paraelectric, incommensurate, and ferroelectric phases, we studied the 87Rb nuclear magnetic resonance (NMR) spectra and spin-lattice relaxation times in laboratory frame T1 and in rotating frame T1ρ. The resonance frequency and the chemical shift do not change abruptly near the phase transition temperature of Ti = 333 K and TC = 192 K, whereas T1 and T1ρ display discontinuous changes near Ti and TC. The abrupt changes in the relaxation times near these temperatures seem to be a result of the structural phase transitions. The results are distinctly different from those reported for Rb2CoCl4.
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.
Parry, A; Clare, S; Jenkinson, M; Smith, S; Palace, J; Matthews, P M
2002-09-01
Previous studies have established the clinical relevance of hypointense lesions ("black holes") on T1-weighted MRI as a surrogate marker for pathological change [36]. In contrast to measuring the volume of "black holes", the direct measurement of T1 values allows an objective assessment of the changes contributing to hypointensity both in the focal lesions and in the normal appearing white matter (NAWM). The aims of this study were first, to determine the relationship between T1 values in the NAWM and in discrete lesions, second, to test the relationship between white matter T1 changes and measures of disability and third, to determine whether pathology leading to T1 change occurred in thalamic grey matter of patients with multiple sclerosis. 24 patients with clinically definite multiple sclerosis (13 with relapsing-remitting multiple sclerosis and 11 with secondary progressive multiple sclerosis) and 11 controls participated. White matter T1 histograms and mean T1 values for the thalamus were generated from whole brain T1 relaxation time maps measured using a novel echo-planar imaging based MRI sequence at 3Tesla. Tissue segmentation based on T2- and T1-weighted images allowed independent study of changes in lesions and NAWM. White matter T1 histograms from the patient group showed a reduced peak height and a shift towards higher T1 values (p = 0.028) relative to controls. The mean thalamic T1 was greater for secondary progressive patients than for healthy controls (p = 0.03). Mean white matter T1 values correlated significantly with disability (r = 0.48, p = 0.02). The mean T1 value in the T1-hypointense lesions correlated strongly with the mean T1 value in the NAWM (r = 0.80, p < 0.001). No significant relationship was found between mean white matter T1 value and cerebral volume (r = -0.23, p = 0.31). The T1 measurements extend previous observations suggesting that changes in the NAWM occur in parallel with pathology in lesions of MS. T1 measurements of either
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.
Satellite attitude prediction by multiple time scales method
NASA Technical Reports Server (NTRS)
Tao, Y. C.; Ramnath, R.
1975-01-01
An investigation is made of the problem of predicting the attitude of satellites under the influence of external disturbing torques. The attitude dynamics are first expressed in a perturbation formulation which is then solved by the multiple scales approach. The independent variable, time, is extended into new scales, fast, slow, etc., and the integration is carried out separately in the new variables. The theory is applied to two different satellite configurations, rigid body and dual spin, each of which may have an asymmetric mass distribution. The disturbing torques considered are gravity gradient and geomagnetic. Finally, as multiple time scales approach separates slow and fast behaviors of satellite attitude motion, this property is used for the design of an attitude control device. A nutation damping control loop, using the geomagnetic torque for an earth pointing dual spin satellite, is designed in terms of the slow equation.
Speech Compensation for Time-Scale-Modified Auditory Feedback
ERIC Educational Resources Information Center
Ogane, Rintaro; Honda, Masaaki
2014-01-01
Purpose: The purpose of this study was to examine speech compensation in response to time-scale-modified auditory feedback during the transition of the semivowel for a target utterance of /ija/. Method: Each utterance session consisted of 10 control trials in the normal feedback condition followed by 20 perturbed trials in the modified auditory…
Gott time machines, BTZ black hole formation, and choptuik scaling
Birmingham; Sen
2000-02-07
We study the formation of Banados-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.
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 τ_Form ∝ √{τ_Lapτ_Diff}. In contrast, the lifetimes of flux ropes are proportional to the lap time (τLife∝τLap). 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.
Relaxation dynamics in correlated quantum dots
Andergassen, S.; Schuricht, D.; Pletyukhov, M.; Schoeller, H.
2014-12-04
We study quantum many-body effects on the real-time evolution of the current through quantum dots. By using a non-equilibrium renormalization group approach, we provide analytic results for the relaxation dynamics into the stationary state and identify the microscopic cutoff scales that determine the transport rates. We find rich non-equilibrium physics induced by the interplay of the different energy scales. While the short-time limit is governed by universal dynamics, the long-time behavior features characteristic oscillations as well as an interplay of exponential and power-law decay.
Chakraborty, Anjan; Seth, Debabrata; Chakrabarty, Debdeep; Setua, Palash; Sarkar, Nilmoni
2005-12-15
The dynamics of solvent and rotational relaxation of Coumarin 153 (C-153) in ionic liquid (IL) 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF6]) and in the ionic liquid confined in Brij-35 micellar aggregates have been investigated using steady-state and time-resolved fluorescence spectroscopy. We observed slower dynamics in the presence of micellar aggregates as compared to the pure IL. However, the slowing down in the solvation time on going from neat IL to IL-confined micelles is much smaller compared to that on going from water to water-confined micellar aggregates. The increase in solvation and rotational time in micelles is attributed to the increase in viscosity of the medium. The slow component is assumed to be dependent on the viscosity of the solution and involves large-scale rearrangement of the anions and cations while fast component is assumed to originate from the initial response of the anions during excitation. The slow component increases due to the increase in the viscosity of the medium and increase in fast component is probably due to the hydrogen bonding between the anions and polar headgroup of the surfactant. The dynamics of solvent relaxation was affected to a small extent due to the micelle formation.
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.
Energy and time determine scaling in biological and computer designs.
Moses, Melanie; Bezerra, George; Edwards, Benjamin; Brown, James; Forrest, Stephanie
2016-08-19
Metabolic rate in animals and power consumption in computers are analogous quantities that scale similarly with size. We analyse vascular systems of mammals and on-chip networks of microprocessors, where natural selection and human engineering, respectively, have produced systems that minimize both energy dissipation and delivery times. Using a simple network model that simultaneously minimizes energy and time, our analysis explains empirically observed trends in the scaling of metabolic rate in mammals and power consumption and performance in microprocessors across several orders of magnitude in size. Just as the evolutionary transitions from unicellular to multicellular animals in biology are associated with shifts in metabolic scaling, our model suggests that the scaling of power and performance will change as computer designs transition to decentralized multi-core and distributed cyber-physical systems. More generally, a single energy-time minimization principle may govern the design of many complex systems that process energy, materials and information.This article is part of the themed issue 'The major synthetic evolutionary transitions'.
NASA Astrophysics Data System (ADS)
Shiwakoti, N.; Bobby, A.; Asokan, K.; Antony, Bobby
2017-01-01
The in-situ capacitance-frequency and conductance-frequency measurements of 100 MeV Au8+ swift heavy ion irradiated Ni/n-GaP Schottky structure at a constant bias voltage have been carried out in the frequency range 1 kHz-1 MHz at room temperature. The interface states density and the relaxation time of the charge carriers have been calculated from Nicollian and Brews method. Various dielectric parameters such as dielectric constant, dielectric loss, loss tangent, series resistance, ac conductivity, real and imaginary parts of electric modulus have been extracted and analyzed under complex permittivity and complex electric modulus formalisms. The capacitance and conductance characteristics are found to exhibit complex behaviors at lower frequency region (1-20 kHz) for all the samples. The observed peaks and dips at low frequency region are attributed to the relaxation mechanisms of charge carriers and the interface or dipolar polarization at the interface. The dielectric properties are found to be effectively changed by the ion fluence which is attributed to the variation in interface states density and their relaxation time.
Wavelet analysis and scaling properties of time series
NASA Astrophysics Data System (ADS)
Manimaran, P.; Panigrahi, Prasanta K.; Parikh, Jitendra C.
2005-10-01
We propose a wavelet based method for the characterization of the scaling behavior of nonstationary time series. It makes use of the built-in ability of the wavelets for capturing the trends in a data set, in variable window sizes. Discrete wavelets from the Daubechies family are used to illustrate the efficacy of this procedure. After studying binomial multifractal time series with the present and earlier approaches of detrending for comparison, we analyze the time series of averaged spin density in the 2D Ising model at the critical temperature, along with several experimental data sets possessing multifractal behavior.
Anomalous multiphoton photoelectric effect in ultrashort time scales.
Kupersztych, J; Raynaud, M
2005-09-30
In a multiphoton photoelectric process, an electron needs to absorb a given number of photons to escape the surface of a metal. It is shown for the first time that this number is not a constant depending only on the characteristics of the metal and light, but varies with the interaction duration in ultrashort time scales. The phenomenon occurs when electromagnetic energy is transferred, via ultrafast excitation of electron collective modes, to conduction electrons in a duration less than the electron energy damping time. It manifests itself through a dramatic increase of electron production.
The Importance of Rotational Time-scales in Accretion Variability
NASA Astrophysics Data System (ADS)
Costigan, Gráinne; Vink, Joirck; Scholz, Aleks; Testi, Leonardo; Ray, Tom
2013-07-01
For the first few million years, one of the dominant sources of emission from a low mass young stellar object is from accretion. This process regulates the flow of material and angular moments from the surroundings to the central object, and is thought to play an important role in the definition of the long term stellar properties. Variability is a well documented attribute of accretion, and has been observed on time-scales of from days to years. However, where these variations come from is not clear. Th current model for accretion is magnetospheric accretion, where the stellar magnetic field truncates the disc, allowing the matter to flow from the disc onto the surface of the star. This model allows for variations in the accretion rate to come from many different sources, such as the magnetic field, the circumstellar disc and the interaction of the different parts of the system. We have been studying unbiased samples of accretors in order to identify the dominant time-scales and typical magnitudes of variations. In this way different sources of variations can be excluded and any missing physics in these systems identified. Through our previous work with the Long-term Accretion Monitoring Program (LAMP), we found 10 accretors in the ChaI region, whose variability is dominated by short term variations of 2 weeks. This was the shortest time period between spectroscopic observations which spanned 15 months, and rules out large scale processes in the disk as origins of this variability. On the basis of this study we have gone further to study the accretion signature H-alpha, over the time-scales of minutes and days in a set of Herbig Ae and T Tauri stars. Using the same methods as we used in LAMP we found the dominant time-scales of variations to be days. These samples both point towards rotation period of these objects as being an important time-scale for accretion variations. This allows us to indicate which are the most likely sources of these variations.
NASA Astrophysics Data System (ADS)
Wang, Nian; Xia, Yang
2013-10-01
A number of experimental issues in the measurement of multi-component T2 and T1ρ relaxations in native and enzymatically digested articular cartilage were investigated by microscopic MRI (μMRI). The issues included the bath solutions (physiological saline and phosphate buffered saline (PBS)), the imaging resolution (35-140 μm), the specimen orientations (0° and 55°), and the strength of spin-lock frequencies (0.5-2 kHz) in the T1ρ experiments. In addition to cartilage, the samples of agar gel and doped water solution were also used in the investigation. Two imaging sequences were used: CPMG-SE and MSME. All raw data were analyzed by the non-negative least square (NNLS) method. The MSME sequence was shown to result in the observation of multi-component T2, even in the gel and liquid samples, demonstrating the artificial uncleanness of this sequence in the multi-component measurements. The soaking of cartilage in PBS reduced the observable T2 components to one at both 0° and 55°, suggesting the effect of phosphate ions on proton exchange between different pools of water molecules. The cartilage orientation with respect to the external magnetic field and the spin-lock strengths in the T1ρ experiment both affected the quantification of the multi-component relaxation. The transitions between a mono-component and multi-components in cartilage under various experimental conditions call for the extra caution in interpreting the relaxation results.
Wang, Nian; Xia, Yang
2013-10-01
A number of experimental issues in the measurement of multi-component T2 and T1ρ relaxations in native and enzymatically digested articular cartilage were investigated by microscopic MRI (μMRI). The issues included the bath solutions (physiological saline and phosphate buffered saline (PBS)), the imaging resolution (35-140 μm), the specimen orientations (0° and 55°), and the strength of spin-lock frequencies (0.5-2 kHz) in the T1ρ experiments. In addition to cartilage, the samples of agar gel and doped water solution were also used in the investigation. Two imaging sequences were used: CPMG-SE and MSME. All raw data were analyzed by the non-negative least square (NNLS) method. The MSME sequence was shown to result in the observation of multi-component T2, even in the gel and liquid samples, demonstrating the artificial uncleanness of this sequence in the multi-component measurements. The soaking of cartilage in PBS reduced the observable T2 components to one at both 0° and 55°, suggesting the effect of phosphate ions on proton exchange between different pools of water molecules. The cartilage orientation with respect to the external magnetic field and the spin-lock strengths in the T1ρ experiment both affected the quantification of the multi-component relaxation. The transitions between a mono-component and multi-components in cartilage under various experimental conditions call for the extra caution in interpreting the relaxation results.
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.
Tailored real-time scaling of heteronuclear couplings.
Schilling, Franz; Glaser, Steffen J
2012-10-01
Heteronuclear couplings are a valuable source of molecular information, which is measured from the multiplet splittings of an NMR spectrum. Radiofrequency irradiation on one coupled nuclear spin allows to modify the effective coupling constant, scaling down the multiplet splittings in the spectrum observed at the resonance frequency of the other nuclear spin. Such decoupling sequences are often used to collapse a multiplet into a singlet and can therefore simplify NMR spectra significantly. Continuous-wave (cw) decoupling has an intrinsic non-linear offset dependence of the scaling of the effective J-coupling constant. Using optimal control pulse optimization, we show that virtually arbitrary off-resonance scaling of the J-coupling constant can be achieved. The new class of tailored decoupling pulses is named SHOT (Scaling of Heteronuclear couplings by Optimal Tracking). Complementing cw irradiation, SHOT pulses offer an alternative approach of encoding chemical shift information indirectly through off-resonance decoupling, which however makes it possible for the first time to achieve linear J scaling as a function of offset frequency. For a simple mixture of eight aromatic compounds, it is demonstrated experimentally that a 1D-SHOT {(1)H}-(13)C experiment yields comparable information to a 2D-HSQC and can give full assignment of all coupled spins.
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.
Time-average based on scaling law in anomalous diffusions
NASA Astrophysics Data System (ADS)
Kim, Hyun-Joo
2015-05-01
To solve the obscureness in measurement brought about from the weak ergodicity breaking appeared in anomalous diffusions, we have suggested the time-averaged mean squared displacement (MSD) /line{δ 2 (τ )}τ with an integral interval depending linearly on the lag time τ. For the continuous time random walk describing a subdiffusive behavior, we have found that /line{δ 2 (τ )}τ ˜ τ γ like that of the ensemble-averaged MSD, which makes it be possible to measure the proper exponent values through time-average in experiments like a single molecule tracking. Also, we have found that it has originated from the scaling nature of the MSD at an aging time in anomalous diffusion and confirmed them through numerical results of the other microscopic non-Markovian model showing subdiffusions and superdiffusions with the origin of memory enhancement.
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.
Snoddy (1926) revisited: time scales of motor learning.
Stratton, Shannon M; Liu, Yeou-Teh; Hong, Siang Lee; Mayer-Kress, Gottfried; Newell, Karl M
2007-11-01
The authors investigated the time scales of the learning of a mirror-tracing task to reexamine G. S. Snoddy's (1926) original claim and the received theoretical view (A. Newell & P. S. Rosenbloom, 1981) that motor learning follows a power law. Adult participants (N = 16) learned the tracing task in either a normal or a reversed visual-image condition over 5 consecutive days of practice and then performed 1 day of practice 1 week later and again 1 month later. The reversed-image group's performance was poorer than that of the normal-image group throughout the practice. An exponential was the best fitting function on individual data, but the power-law function was the best fit on the group-averaged data. The findings provided preliminary evidence that 2 characteristic time scales, (a) fast, dominated by warm-up, and (b) slow, dominated by persistent change, capture individuals' performance in the learning of the mirror-tracing task.
A study of Venus rotation at short time scale
NASA Astrophysics Data System (ADS)
Cottereau, L.; Souchay, J.
2009-12-01
Venus which can be considered as the twin sister of the Earth in view of its global characteristics (size, density) has been the subject of many investigations to understand its slow retrograde rotation (243d) and its rather small obliquity (2°.63). Many of these studies concern the evolution of Venus rotation at very long time scales. Here we present a complete model of Venus precession and nutation based on Hamiltonian formalism for short times scales. We apply a theoretical framework already used by Kinoshita (1977) for the rigid Earth. After calculating the effects due to the gravitational tide exerted by the Sun, we also evaluate the indirect planetary effects due to the perturbation of the planets. We compare our results with those obtained by Souchay et al. (1999) on the Earth. At last we present the prospect for future studies among which are the polhody, the effects of the atmosphere and of the core-mantle interaction.
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 β=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.
Assestment of correlations and crossover scale in electroseismic time series
NASA Astrophysics Data System (ADS)
Guzman-Vargas, L.; Ramírez-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.
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.
Adaptive Haar transforms with arbitrary time and scale splitting
NASA Astrophysics Data System (ADS)
Egiazarian, Karen O.; Astola, Jaakko T.
2001-05-01
The Haar transform is generalized to the case of an arbitrary time and scale splitting. To any binary tree we associate an orthogonal system of Haar-type functions - tree-structured Haar (TSH) functions. Unified fast algorithm for computation of the introduced tree-structured Haar transforms is presented. It requires 2(N - 1) additions and 3N - 2 multiplications, where N is transform order or, equivalently, the number of leaves of the binary tree.
Solar Irradiance Variations on Active Region Time Scales
NASA Technical Reports Server (NTRS)
Labonte, B. J. (Editor); Chapman, G. A. (Editor); Hudson, H. S. (Editor); Willson, R. C. (Editor)
1984-01-01
The variations of the total solar irradiance is an important tool for studying the Sun, thanks to the development of very precise sensors such as the ACRIM instrument on board the Solar Maximum Mission. The largest variations of the total irradiance occur on time scales of a few days are caused by solar active regions, especially sunspots. Efforts were made to describe the active region effects on total and spectral irradiance.
Time-scale and branching ratios in sequential multifragmentation
Moretto, L.G.; Phair, L.; Tso, K.; Jing, K.; Wozniak, G.J.
1994-04-01
Experimental intermediate-mass-fragment multiplicity distributions are shown to be binomial at all excitation energies. From these distributions a single binary event probability can be extracted that has the thermal dependence p= exp[{minus}B/T]. Thus, it is inferred that multi fragmentation is a sequence of thermal binary events. The increase of p with excitation energy implies a corresponding contraction of the time-scale and explains recently observed fragment-fragment and fragment-spectator Coulomb correlations.
NASA Astrophysics Data System (ADS)
Furman, Gregory B.; Goren, Shaul D.; Meerovich, Victor M.; Sokolovsky, Vladimir L.
2016-02-01
Spin-spin and spin-lattice relaxations in liquid or gas entrapped in nanosized ellipsoidal cavities with different orientation ordering are theoretically investigated. The model is flexible in order to be applied to explain experimental results in cavities with various forms, from very prolate up to oblate ones, and different degree of ordering of nanocavities. In the framework of the considered model, the dipole-dipole interaction is determined by a single coupling constant, which depends on the form, size, and orientation of the cavity and number of nuclear spins in the cavity. It was shown that the transverse and longitudinal relaxation rates differently depend on the angle between the external magnetic field and cavity main axis. The calculation results for the local dipolar field, transverse and longitudinal relaxation times explain the angular dependencies observed in MRI experiments with biological objects: cartilage and tendon. Microstructure of these tissues can be characterized by the standard deviation of the Gaussian distribution of fibril orientations. The comparison of the theoretical and experimental results shows that the value of the standard deviation obtained at the matching of the calculation to experimental results can be used as a parameter characterizing the disorder in the biological sample.
Furman, Gregory B; Goren, Shaul D; Meerovich, Victor M; Sokolovsky, Vladimir L
2016-02-01
Spin-spin and spin-lattice relaxations in liquid or gas entrapped in nanosized ellipsoidal cavities with different orientation ordering are theoretically investigated. The model is flexible in order to be applied to explain experimental results in cavities with various forms, from very prolate up to oblate ones, and different degree of ordering of nanocavities. In the framework of the considered model, the dipole-dipole interaction is determined by a single coupling constant, which depends on the form, size, and orientation of the cavity and number of nuclear spins in the cavity. It was shown that the transverse and longitudinal relaxation rates differently depend on the angle between the external magnetic field and cavity main axis. The calculation results for the local dipolar field, transverse and longitudinal relaxation times explain the angular dependencies observed in MRI experiments with biological objects: cartilage and tendon. Microstructure of these tissues can be characterized by the standard deviation of the Gaussian distribution of fibril orientations. The comparison of the theoretical and experimental results shows that the value of the standard deviation obtained at the matching of the calculation to experimental results can be used as a parameter characterizing the disorder in the biological sample.
In situ determination of surface relaxivities for unconsolidated sediments
NASA Astrophysics Data System (ADS)
Duschl, Markus; Galvosas, Petrik; Brox, Timothy I.; Pohlmeier, Andreas; Vereecken, Harry
2015-08-01
NMR relaxometry has developed into a method for rapid pore-size determination of natural porous media. Nevertheless, it is prone to uncertainties because of unknown surface relaxivities which depend mainly on the chemical composition of the pore walls as well as on the interfacial dynamics of the pore fluid. The classical approach for the determination of surface relaxivities is the scaling of NMR relaxation times by surface to volume ratios measured by gas adsorption or mercury intrusion. However, it is preferable that a method for the determination of average pore sizes uses the same substance, water, as probe molecule for both relaxometry and surface to volume measurements. One should also ensure that in both experiments the dynamics of the probe molecule takes place on similar length scales, which are in the order of some microns. Therefore, we employed NMR diffusion measurements with different observation times using bipolar pulsed field gradients and applied them to unconsolidated sediments (two purified sands, two natural sands, and one soil). The evaluation by Mitra's short-time model for diffusion in restricted environments yielded information about the surface to volume ratios which is independent of relaxation mechanisms. We point out that methods based on NMR diffusometry yield pore dimensions and surface relaxivities consistent with a pore space as sampled by native pore fluids via the diffusion process. This opens a way to calibrate NMR relaxation measurements with other NMR techniques, providing information about the pore-size distribution of natural porous media directly from relaxometry.
Time scale interactions and the coevolution of humans and water
NASA Astrophysics Data System (ADS)
Sivapalan, Murugesu; Blöschl, Günter
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.
Garnov, Nikita; Linder, Nicolas; Schaudinn, Alexander; Blüher, Matthias; Karlas, Thomas; Schütz, Tatjana; Dietrich, Arne; Kahn, Thomas; Busse, Harald
2014-09-01
Subcutaneous (SAT) and visceral adipose tissue (VAT) differ in composition, endocrine function and localization in the body. VAT is considered to play a role in the pathogenesis of insulin resistance, type 2 diabetes, fatty liver disease, and other obesity-related disorders. It has been shown that the amount, distribution, and (cellular) composition of adipose tissue (AT) correlate well with metabolic conditions. In this study, T1 relaxation times of AT were measured in severely obese subjects and compared with those of healthy lean controls. Here, we tested the hypothesis that T1 relaxation times of AT differ between lean and obese individuals, but also between VAT and SAT as well as superficial (sSAT) and deep SAT (dSAT) in the same individual. Twenty severely obese subjects (BMI 41.4 ± 4.8 kg/m(2) ) and ten healthy lean controls matched for age (BMI 21.5 ± 1.9 kg/m(2) ) underwent MRI at 1.5 T using a single-shot fast spin-echo sequence (short-tau inversion recovery) at six different inversion times (TI range 100-1000 ms). T1 relaxation times were computed for all subjects by fitting the TI -dependent MR signal intensities of user-defined regions of interest in both SAT and VAT to a model function. T1 times in sSAT and dSAT were only measured in obese patients. For both obese patients and controls, the T1 times of SAT (275 ± 14 and 301 ± 12 ms) were significantly (p < 0.01) shorter than the respective values in VAT (294 ± 20 and 360 ± 35 ms). Obese subjects also showed significant (p < 0.01) T1 differences between sSAT (268 ± 11 ms) and dSAT (281 ± 19 ms). More important, T1 differences in both SAT and VAT were highly significant (p < 0.001) between obese patients and healthy subjects. The results of our pilot study suggest that T1 relaxation times differ between severely obese patients and lean controls, and may potentially provide an additional means for the non-invasive assessment of AT
Scaling brain size, keeping timing: evolutionary preservation of brain rhythms.
Buzsáki, György; Logothetis, Nikos; Singer, Wolf
2013-10-30
Despite the several-thousand-fold increase of brain volume during the course of mammalian evolution, the hierarchy of brain oscillations remains remarkably preserved, allowing for multiple-time-scale communication within and across neuronal networks at approximately the same speed, irrespective of brain size. Deployment of large-diameter axons of long-range neurons could be a key factor in the preserved time management in growing brains. We discuss the consequences of such preserved network constellation in mental disease, drug discovery, and interventional therapies.
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
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.
Challenges of Integrated Modeling Across Space and Time Scales
NASA Astrophysics Data System (ADS)
Jagers, B.; Donchyts, G.; Baart, F.; Schellekens, J.; Winsemius, H.
2015-12-01
New data collection methods combined with rapid advances in processing technologies enabled by increases in data processing and storage capabilities are causing an significant shift in our modeling capabilities. Freely available global data sets allow us to build more quickly models for bigger areas. By linking the right data, models, and tools we gain significant insight at scales that hadn't considered possible a few decades ago. However, by increasing the spatial extent of our models, we risk missing regionally important critical elements by limitations of model resolution, processes selected, or blind spots in our big data world. At the same time we are pushing the time scales of our models from events and seasonal scale out to decades, centuries, or millennia to simulate the dynamics of the earth surface under varying external conditions. Also here we simplify and ignore to gain performance to resolve bigger time and space domains; are we including all the relevant elements in our models? These elements are often easy to spot from the right perspective. However, what is that perspective when you try to comprehend the results of baffling integrated global models and the amount of data is overwhelming? At the same time we want to know results with an ever increasing accuracy and detail: Will my house flood? Can we reduce flood risk, increase shipping capacity here, and at the same time reduce the maintenance costs by optimizing our dredging strategy? Can we build a number of interoperable cyberinfrastructures that when combined address all these questions? This presentation gives an overview of our work in this field at Deltares, and the main challenges that we foresee.
NASA Astrophysics Data System (ADS)
Jakobsen, Bo; Maggi, Claudio; Christensen, Tage; Dyre, Jeppe C.
2008-11-01
Shear-mechanical and dielectric measurements on the two monohydroxy (monoalcohol) molecular glass formers 2-ethyl-1-hexanol and 2-butanol close to the glass-transition temperature are presented. The shear-mechanical data are obtained using the piezoelectric shear-modulus gauge method covering frequencies from 1 mHz to 10 kHz. The shear-mechanical relaxation spectra show two processes, which follow the typical scenario of a structural (alpha) relaxation and an additional (Johari-Goldstein) beta relaxation. The dielectric relaxation spectra are dominated by a Debye-type peak with an additional non-Debye peak visible. This Debye-type relaxation is a common feature peculiar to monoalcohols. The time scale of the non-Debye dielectric relaxation process is shown to correspond to the mechanical structural (alpha) relaxation. Glass-transition temperatures and fragilities are reported based on the mechanical alpha relaxation and the dielectric Debye-type process, showing that the two glass-transition temperatures differ by approximately 10 K and that the fragility based on the Debye-type process is a factor of 2 smaller than the structural fragility. If a mechanical signature of the Debye-type relaxation exists in these liquids, its relaxation strength is at most 1% and 3% of the full relaxation strength of 2-butanol and 2-ethyl-1-hexanol, respectively. These findings support the notion that it is the non-Debye dielectric relaxation process that corresponds to the structural alpha relaxation in the liquid.
Multiple time scale behaviors and network dynamics in liquid methanol.
Sharma, Ruchi; Chakravarty, Charusita; Milotti, Edoardo
2008-07-31
Canonical ensemble molecular dynamics simulations of liquid methanol, modeled using a rigid-body, pair-additive potential, are used to compute static distributions and temporal correlations of tagged molecule potential energies as a means of characterizing the liquid state dynamics. The static distribution of tagged molecule potential energies shows a clear multimodal structure with three distinct peaks, similar to those observed previously in water and liquid silica. The multimodality is shown to originate from electrostatic effects, but not from local, hydrogen bond interactions. An interesting outcome of this study is the remarkable similarity in the tagged potential energy power spectra of methanol, water, and silica, despite the differences in the underlying interactions and the dimensionality of the network. All three liquids show a distinct multiple time scale (MTS) regime with a 1/ f (alpha) dependence with a clear positive correlation between the scaling exponent alpha and the diffusivity. The low-frequency limit of the MTS regime is determined by the frequency of crossover to white noise behavior which occurs at approximately 0.1 cm (-1) in the case of methanol under standard temperature and pressure conditions. The power spectral regime above 200 cm (-1) in all three systems is dominated by resonances due to localized vibrations, such as librations. The correlation between alpha and the diffusivity in all three liquids appears to be related to the strength of the coupling between the localized motions and the larger length/time scale network reorganizations. Thus, the time scales associated with network reorganization dynamics appear to be qualitatively similar in these systems, despite the fact that water and silica both display diffusional anomalies but methanol does not.
Abdolmohammadi, Jamil; Shafiee, Mohsen; Faeghi, Fariborz; Arefan, Douman; Zali, Alireza; Motiei-Langroudi, Rouzbeh; Farshidfar, Zahra; Nazarlou, Ali Kiani; Tavakkoli, Ali; Yarham, Mohammad
2016-01-01
Introduction Timely diagnosis of brain tumors could considerably affect the process of patient treatment. To do so, para-clinical methods, particularly MRI, cannot be ignored. MRI has so far answered significant questions regarding tumor characteristics, as well as helping neurosurgeons. In order to detect the tumor cellularity, neuro-surgeons currently have to sample specimens by biopsy and then send them to the pathology unit. The aim of this study is to determine the tumor cellularity in the brain. Methods In this cross-sectional study, 32 patients (18 males and 14 females from 18–77 y/o) were admitted to the neurosurgery department of Shohada-E Tajrish Hospital in Tehran, Iran from April 2012 to February 2014. In addition to routine pulse sequences, T2W Multi echo pulse sequences were taken and the images were analyzed using the MATLAB software to determine the brain tumor cellularity, compared with the biopsy Results These findings illustrate the need for more T2 relaxation time decreases, the higher classes of tumors will stand out in the designed table. In this study, the results show T2 relaxation time with a 85% diagnostic weight, compared with the biopsy, to determine the brain tumor cellularity (p<0.05). Conclusion Our results indicate that the T2 relaxation time feature is the best method to distinguish and present the degree of intra-axial brain tumors cellularity (85% accuracy compared to biopsy). The use of more data is recommended in order to increase the percent accuracy of this techniques. PMID:27757181
NASA Astrophysics Data System (ADS)
de Jong, Saskia; van Vliet, Ton; de Jongh, Harmen H. J.
2015-11-01
The recoverable energy (RE), defined as the ratio of the work exerted on a test specimen during compression and recovered upon subsequent decompression, has been shown to correlate to sensory profiling of protein-based food products. Understanding the mechanism determining the time-dependency of RE is primordial. This work aims to identify the protein-specific impact on the recoverable energy by stress dissipation via relaxation of (micro)structural rearrangements within protein gels. To this end, caseinate and gelatin gels are studied for their response to time-dependent mechanical deformation as they are known to develop structurally distinct network morphologies. This work shows that in gelatin gels no significant stress relaxation occurs on the seconds timescale, and consequently no time-dependency of the amount of en