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A Multitechnique Study of Structure and Dynamics of Polyfluorene Cast Films and the Influence on Their Photoluminescence

FARIA, G. C.; PLIVELIC, T. S.; COSSIELLO, R. F.; SOUZA, A. A.; ATVARS, T. D. Z.; TORRIANI, I. L.; AZEVÊDO, Eduardo Ribeiro de
Fonte: AMER CHEMICAL SOC Publicador: AMER CHEMICAL SOC
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
46.03%
This article describes the microstructure and dynamics in the solid state of polyfluorene-based polymers, poly(9,)-dioctylfluorenyl-2,7-diyl) (PFO), a semicrystalline polymer, and poly [(9,9-dioctyl- 2,7-divinylene-fluorenylene)-alt-co-{2-methoxy-5-(2-ethyl-hexyloxy)- 1,4-phenylene vinylene}, a copolymer with mesomorphic phase properties. These Structures were determined by wide-angle X-ray scattering (WAXS) measurements, Assuming a packing model for the copolymer structure, where the planes of the phenyl rings are stacked and separated by an average distance of similar to 4.5 angstrom and laterally spaced by about similar to 16 angstrom, we followed the evolution of these distances as a function of temperature using WAXS and associated the changes observed to the polymer relaxation processes identified by dynamical mechanical thermal analysis. Specific molecular motions were studied by solid-state nuclear magnetic resonance. The onset of the side-chain motion at about 213 K (beta-relaxation) produced a small increase in the lateral spacing and in the stacking distance of the phenyl rings in them aggregated Structures, Besides, at about 383 K (alpha-relaxation) there occurs a significant increase in the amplitude of the torsion motion in the backbone...

Frequency-dependent capacitance of the apical membrane of frog skin: dielectric relaxation processes.

Awayda, M S; Van Driessche, W; Helman, S I
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /01/1999 EN
Relevância na Pesquisa
46.15%
Impedance analysis of the isolated epithelium of frog skin (northern Rana pipiens) was carried out in the frequency range between 0.1 Hz and 5.5 kHz while Na+ transport was abolished. Under these conditions, the impedance is determined almost completely by the dielectric properties of the apical membranes of the cells and the parallel shunt resistance. The modeling of the apical membrane impedance function required the inclusion of dielectric relaxation processes as originally described by. J. Chem. Phys. 9:341-351), where each process is characterized by a dielectric increment, relaxation frequency, and power law dependence. We found that the apical plasma membrane exhibited several populations of audio frequency dielectric relaxation processes centered at 30, 103, 2364, and 6604 Hz, with mean capacitive increments of 0.72, 1.00, 0.88, and 0.29 microF/cm2, respectively, that gave rise to dc capacitances of 1.95 +/- 0.06 microF/cm2 in 49 tissues. Capacitance was uncorrelated with large ranges of parallel shunt resistance and was not changed appreciably within minutes by K+ depolarization and hence a decrease in basolateral membrane resistance. A significant linear correlation existed between the dc capacitance and Na+ transport rates measured as short-circuit currents (Cadc = 0.028 Isc + 1.48; Isc between 4 and 35 microA/cm2) before inhibition of transport by amiloride and substitution of all Na+ with NMDG (N-methyl-D-glucamine) in the apical solution. The existence of dominant audio frequency capacitive relaxation processes complicates and precludes unequivocal interpretation of changes of capacitance in terms of membrane area alone when capacitance is measured at audio frequencies.

Topics in Present-day Science Technology and Innovation: Ultrafast Relaxation Processes in Semiconductors

Rodrigues,Clóves Gonçalves; Vasconcellos,Áurea Rosas; Luzzi,Roberto
Fonte: ABM, ABC, ABPol Publicador: ABM, ABC, ABPol
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/06/2015 EN
Relevância na Pesquisa
56.04%
The nowadays notable development of all the modern technology, fundamental for the progress and well being of world society, imposes a great deal of stress in the realm of basic Physics, more precisely on Thermo-Mechanical Statistics. In electronics and optoelectronics we face situations involving physical-chemical systems far-removed-from equilibrium, where ultrafast (in pico- and femto-second scale) and non-linear processes are present. Here we describe in an extended overview the question of ultrafast relaxation processes in the excited plasma in semiconductors.

Vibrational origin of the fast relaxation processes in molecular glass-formers

Mossa, S.; Monaco, G.; Ruocco, G.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 14/04/2001
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46.07%
We study the interaction of the relaxation processes with the density fluctuations by molecular dynamics simulation of a flexible molecule model for o-terphenyl (oTP) in the liquid and supercooled phases. We find evidence, besides the structural relaxation, of a secondary vibrational relaxation whose characteristic time, few ps, is slightly temperature dependent. This i) confirms the result by Monaco et al. [Phys. Rev, E 62, 7595 (2000)] of the vibrational nature of the fast relaxation observed in Brillouin Light Scattering (BLS) experiments in oTP; and ii) poses a caveat on the interpretation of the BLS spectra of molecular systems in terms of a purely center of mass dynamics.; Comment: RevTeX, 5 pages, 4 eps figures

Scale properties as a basis of power law relaxation processes

Fondado, A.; Mira, J.; Rivas, J.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 07/08/2006
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46.03%
Computer simulations of first-order relaxation processes show that the spatial configurations of the system acquire an invariant shape once the stationary regime is attained. Inspired by them we find that, in any first-order relaxation process, if the interaction that governs the system fulfils a simple scale property, then the relaxation will end up by following a stationary process described by a power law. A scaling law and some invariants are obtained for the time evolution of the system in such a case.; Comment: 13 pages, 4 figures

Evidence of two viscous relaxation processes in the collective dynamics of liquid lithium

Scopigno, T.; Balucani, U.; Ruocco, G.; Sette, F.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
46.04%
New inelastic X-ray scattering experiments have been performed on liquid lithium in a wide wavevector range. With respect to the previous measurements, the instrumental resolution, improved up to 1.5 meV, allows to accurately investigate the dynamical processes determining the observed shape of the the dynamic structure factor, $S(Q,\omega)$. A detailed analysis of the lineshapes shows the co-existence of relaxation processes with both a slow and a fast characteristic timescales, and therefore that pictures of the relaxation mechanisms based on a simple viscoelastic model must be abandoned.; Comment: 5 pages, 4 .PS figures

Relaxation processes in a disordered Luttinger liquid

Bagrets, D. A.; Gornyi, I. V.; Mirlin, A. D.; Polyakov, D. G.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 30/04/2008
Relevância na Pesquisa
46.03%
The Luttinger liquid model, which describes interacting electrons in a single-channel quantum wire, is completely integrable in the absence of disorder and as such does not exhibit any relaxation to equilibrium. We consider relaxation processes induced by inelastic electron-electron interactions in a disordered Luttinger liquid, focusing on the equilibration rate and its essential differences from the electron-electron scattering rate as well as the rate of phase relaxation. In the first part of the paper, we review the basic concepts in the disordered Luttinger liquid at equilibrium. These include the elastic renormalization, dephasing, and interference-induced localization. In the second part, we formulate a conceptually important framework for systematically studying the nonequilibrium properties of the strongly correlated (non-Fermi) Luttinger liquid. We derive a coupled set of kinetic equations for the fermionic and bosonic distribution functions that describe the evolution of the nonequilibrium Luttinger liquid. Remarkably, the energy equilibration rate in the conducting disordered quantum wire (at sufficiently high temperature, when the localization effects are suppressed by dephasing) is shown to be of the order of the rate of elastic scattering off disorder...

The influence of anesthetics, neurotransmitters and antibiotics on the relaxation processes in lipid membranes

Seeger, Heiko M.; Gudmundsson, Marie L.; Heimburg, Thomas
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 02/03/2007
Relevância na Pesquisa
46.15%
In the proximity of melting transitions of artificial and biological membranes fluctuations in enthalpy, area, volume and concentration are enhanced. This results in domain formation, changes of the elastic constants, changes in permeability and slowing down of relaxation processes. In this study we used pressure perturbation calorimetry to investigate the relaxation time scale after a jump into the melting transition regime of artificial lipid membranes. This time corresponds to the characteristic rate of domain growth. The studies were performed on single-component large unilamellar and multilamellar vesicle systems with and without the addition of small molecules such as general anesthetics, neurotransmitters and antibiotics. These drugs interact with membranes and affect melting points and profiles. In all systems we found that heat capacity and relaxation times are related to each other in a simple manner. The maximum relaxation time depends on the cooperativity of the heat capacity profile and decreases with a broadening of the transition. For this reason the influence of a drug on the time scale of domain formation processes can be understood on the basis of their influence on the heat capacity profile. This allows estimations of the time scale of domain formation processes in biological membranes.; Comment: 12 pages...

Theoretical description of slow non-monotonic relaxation processes in Al-Y melts

Vasin, M. G.; Menshikova, S. G.; Ivshin, M. D.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 21/11/2015
Relevância na Pesquisa
46.04%
The slow non-monotonic relaxation processes, which have been recently fixed in Al-Y melts, are described theoretically. The theoretical description is based on the Cahn-Hilliard theory and functional methods of non-equilibrium dynamics. In terms of the suggested approach the reasons of this relaxation kinetics are non-linearity of the system near to the liquidus line, which sharply increases with Y concentration, and strong initial heterogeneity of the melt on the concentration of Y atoms. According to our analysis one can conclude that the non-monotonic temporal dependence of viscosity is caused by the Ostwald ripening processes in the rich in yttrium areas.; Comment: Submitted in Physica A

Linear Relaxation Processes Governed by Fractional Symmetric Kinetic Equations

Chechkin, A. V.; Gonchar, V. Yu.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 07/10/1999
Relevância na Pesquisa
46.04%
We get fractional symmetric Fokker - Planck and Einstein - Smoluchowski kinetic equations, which describe evolution of the systems influenced by stochastic forces distributed with stable probability laws. These equations generalize known kinetic equations of the Brownian motion theory and contain symmetric fractional derivatives over velocity and space, respectively. With the help of these equations we study analytically the processes of linear relaxation in a force - free case and for linear oscillator. For a weakly damped oscillator we also get kinetic equation for the distribution in slow variables. Linear relaxation processes are also studied numerically by solving corresponding Langevin equations with the source which is a discrete - time approximation to a white Levy noise. Numerical and analytical results agree quantitatively.; Comment: 30 pages, LaTeX, 13 figures PostScript

Fast Algorithm for Relaxation Processes in Big-data Systems

Hwang, S.; Lee, D. -S.; Kahng, B.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
46.07%
Relaxation processes driven by a Laplacian matrix can be found in many real-world big-data systems, for example, in search engines on the World-Wide-Web and the dynamic load balancing protocols in mesh networks. To numerically implement such processes, a fast-running algorithm for the calculation of the pseudo inverse of the Laplacian matrix is essential. Here we propose an algorithm which computes fast and efficiently the pseudo inverse of Markov chain generator matrices satisfying the detailed-balance condition, a general class of matrices including the Laplacian. The algorithm utilizes the renormalization of the Gaussian integral. In addition to its applicability to a wide range of problems, the algorithm outperforms other algorithms in its ability to compute within a manageable computing time arbitrary elements of the pseudo inverse of a matrix of size millions by millions. Therefore our algorithm can be used very widely in analyzing the relaxation processes occurring on large-scale networked systems.; Comment: 11 pages, 3 figures

Effects of relaxation processes during deposition of anisotropic grains on a flat substrate

Trojan, Kamil; Ausloos, Marcel
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 29/11/2004
Relevância na Pesquisa
46.09%
The ballistic deposition on a one dimensional substrate of grains with one degree of freedom, called spin, is studied with respect to relaxation processes during deposition. The "spin" represents the grain anisotropy, e.g. its longest axis with respect to the vertical. The grains interact through some contact energy (J) and are allowed to flip with a probability q during deposition and relaxation. Different relaxation processes are investigated. The pile structure is investigated, i.e. the density and "magnetisation", as a function of q and J. A percolation transition is found across which the cluster size changes from exponential-like to a power law-like dependence. The differences between "ferromagnetic" and "anti-ferromagnetic"-like contact energies are emphasized as a function of q.; Comment: 7 pages, 8 fig., submitted to Physica A

Stellar Relaxation Processes Near the Galactic Massive Black Hole

Alexander, Tal
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 05/08/2007
Relevância na Pesquisa
46.15%
The massive black hole (MBH) in the Galactic Center and the stars around it form a unique stellar dynamics laboratory for studying how relaxation processes affect the distribution of stars and compact remnants and lead to close interactions between them and the MBH. Recent theoretical studies suggest that processes beyond "minimal" two-body relaxation may operate and even dominate relaxation and its consequences in the Galactic Center. I describe loss-cone refilling by massive perturbers, strong mass segregation and resonant relaxation; review observational evidence that these processes play a role in the Galactic Center; and discuss some cosmic implications for the rates of gravitational wave emission events from compact remnants inspiraling into MBHs, and the coalescence timescales of binary MBHs.; Comment: Invited talk. To appear in "2007 STScI spring symposium: Black Holes", eds, M. Livio & A. M. Koekemoer, Cambridge University Press, in press. 25 pages, 13 figures

Age-related alterations of relaxation processes and non-Markov effects in stochastic dynamics of R-R intervals variability from human ECGs

Yulmetyev, Renat M.; Demin, Sergey A.; Panischev, Oleg Yu.; Hänggi, Peter
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 05/03/2006
Relevância na Pesquisa
46.07%
In this paper we consider the age-related alterations of heart rate variability on the basis of the study of non-Markovian effects. The age dynamics of relaxation processes is quantitatively described by means of local relaxation parameters, calculated by the specific localization procedure. We offer a quantitative informational measure of non-Markovity to evaluate the change of statistical effects of memory. Local relaxation parameters for young and elderly people differ by 3.3 times, and quantitative measures of non-Markovity differ by 4.2 times. The comparison of quantitative parameters allows to draw conclusions about the reduction of relaxation rate with ageing and the higher degree of the Markovity of heart rate variability of elderly people.; Comment: 22 pages, 7 figures, 2 tables

The RARE model: a generalized approach to random relaxation processes in disordered systems

Eliazar, Iddo; Metzler, Ralf
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 27/11/2012
Relevância na Pesquisa
46.17%
This paper introduces and analyses a general statistical model, termed the RARE model, of random relaxation processes in disordered systems. The model considers excitations, that are randomly scattered around a reaction center in a general embedding space. The model's input quantities are the spatial scattering statistics of the excitations around the reaction center, and the chemical reaction rates between the excitations and the reaction center as a function of their mutual distance. The framework of the RARE model is robust, and a detailed stochastic analysis of the random relaxation processes is established. Analytic results regarding the duration and the range of the random relaxation processes, as well as the model's thermodynamic limit, are obtained in closed form. In particular, the case of power-law inputs, which turn out to yield stretched exponential relaxation patterns and asymptotically Paretian relaxation ranges, is addressed in detail.; Comment: 10 pages, REVTeX4

Relaxation Processes in Solar Wind Turbulence

Servidio, S.; Gurgiolo, C.; Carbone, V.; Goldstein, M. L.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 16/06/2014
Relevância na Pesquisa
46.03%
Based on global conservation principles, magnetohydrodynamic (MHD) relaxation theory predicts the existence of several equilibria, such as the Taylor state or global dynamic alignment. These states are generally viewed as very long-time and large-scale equilibria, which emerge only after the termination of the turbulent cascade. As suggested by hydrodynamics and by recent MHD numerical simulations, relaxation processes can occur during the turbulent cascade that will manifest themselves as local patches of equilibrium-like configurations. Using multi-spacecraft analysis techniques in conjunction with Cluster data, we compute the current density and flow vorticity and for the first time demonstrate that these localized relaxation events are observed in the solar wind. Such events have important consequences for the statistics of plasma turbulence.

Evolution of spin relaxation processes in LiY$_{1-x}$Ho$_x$F$_4$ with increasing x studied via AC-susceptibility and muon spin relaxation

Johnson, R. C.; Malkin, B. Z.; Lord, J. S.; Giblin, S. R.; Amato, A.; Baines, C.; Lascialfari, A.; Barbara, B.; Graf, M. J.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 12/07/2012
Relevância na Pesquisa
46.07%
We present measurements of magnetic field and frequency dependences of the low temperature (T = 1.8 K) AC-susceptibility, and temperature and field dependences of the longitudinal field positive muon spin relaxation ({\mu}SR) for LiY$_{1-x}$Ho$_x$F$_4$ with x = 0.0017, 0.0085, 0.0408, and 0.0855. The fits of numerical simulations to the susceptibility data for the x = 0.0017, 0.0085 and 0.0408 show that Ho-Ho cross-relaxation processes become more important at higher concentrations, signaling the crossover from single-ion to correlated behavior. We simulate the muon spin depolarization using the parameters extracted from the susceptibility, and the simulations agree well with our data for samples with x = 0.0017 and 0.0085. The {\mu}SR data for samples with x = 0.0408 and 0.0855 at low temperatures (T < 10 K) cannot be described within a single-ion picture of magnetic field fluctuations and give evidence for additional mechanisms of depolarization due to Ho$^{3+}$ correlations. We also observe an unusual peak in the magnetic field dependence of the muon relaxation rate in the temperature interval 10 - 20 K that we ascribe to a modification of the Ho$^{3+}$ fluctuation rate due to a field induced shift of the energy gap between the ground and the first excited doublet crystal field states relative to a peak in the phonon density of states centered near 63 cm$^{-1}$.; Comment: 33 pages...

Influence of leather stretching to gain area yield on its stress-relaxation behavior

Manich, Albert M.; Castellar Bertrán, María Dolors; González, Berania; Ussman, M.; Marsal, Agustí
Fonte: John Wiley & Sons Publicador: John Wiley & Sons
Tipo: Artículo Formato: 22195 bytes; application/pdf
ENG
Relevância na Pesquisa
46.11%
9 pages, 10 figures.-- Printed version published Dec 15, 2006.; Four bovine leathers subjected to five stretching procedures in water at different temperatures between 60 and 80ºC and drawing ratios between 1.20 and 1.40 were analyzed to demonstrate the suitability of the generalized Maxwell model to fit the different stress-relaxation processes related to the structural hierarchy of leather. This consists of a set of three Maxwell units connected in parallel to represent the high-rate, the medium-rate, and the low-rate stress-relaxation processes, and a Hookean spring in parallel to represent the residual stress at the equilibrium. The high-rate, the medium-rate and the low-rate relaxation times were approximately of 0.6, 10, and 200 s, respectively. Stretching of leather under different conditions to gain area yield in addition to a reduction in thickness also produces a decrease in leather density but not always induce hardening of leather. Leather stretching increases the initial stress when leather is strained 20% for stress-relaxation tests. The effect of stretching on the residual stress depends on the level of stretching. The hardening effect of stretching measured by relative softness showed a good relationship with the medium-rate relaxed stress. The harder the stretched leather the higher the decrease in the medium-rate relaxed stress. Softness also showed a good relationship with the low-rate relaxation time.; Peer reviewed

Thermal Decoupling of Molecular-Relaxation Processes from the Vibrational Density of States at Terahertz Frequencies in Supercooled Hydrogen-Bonded Liquids

Sibik, Juraj; Elliott, Stephen R.; Zeitler, J. Axel
Fonte: American Chemical Society Publicador: American Chemical Society
Tipo: Article; published version
EN
Relevância na Pesquisa
46.04%
This is the final published version, which can also be viewed on the publisher's website at: http://pubs.acs.org/doi/pdf/10.1021/jz5007302; At terahertz frequencies, the libration-vibration motions couple to the dielectric relaxations in disordered hydrogen-bonded solids. The interplay between these processes is still poorly understood, in particular at temperatures below the glass transition temperature, Tg, yet this behavior is of vital importance for the molecular mobility of such materials to remain in the amorphous phase. A series of polyhydric alcohols were studied at temperatures between 80 and 310 K in the frequency range of 0.2?3 THz using terahertz time-domain spectroscopy. Three universal features were observed in the dielectric losses, ??(?): (a) At temperatures well below the glass transition, ??(?) comprises a temperature-independent microscopic peak, which persists into the liquid phase and which is identi?ed as being due to librational/torsional modes. For 0.65 Tg < T < Tg, additional thermally dependent contributions are observed, and we found strong evidence for its relation to the Johari?Goldstein secondary ?-relaxation process. (b) Clear spectroscopic evidence is found for a secondary ? glass transition at 0.65 Tg...

Flash-induced relaxation changesd of the EPR signals from the manganese cluster and Yd reveal a light-adaptation process of photosystem II

Peterson Arskold, Sindra; Ahrling, Karin; Hogblom, Joakim; Styring, Stenbjorn
Fonte: American Chemical Society Publicador: American Chemical Society
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
46.11%
By exposing photosystem II (PSII) samples to an incrementing number of excitation flashes at room temperature, followed by freezing, we could compare the Mn-derived multiline EPR signal from the S2 oxidation state as prepared by 1, 5, 10, and 25 flashes of light. While the S2 multiline signals exhibited by these samples differed very little in spectral shape, a significant increase of the relaxation rate of the signal was detected in the multiflash samples as compared to the S2-state produced by a single oxidation. A similar relaxation rate increase was observed for the EPR signal from YD*. The temperature dependence of the multiline spin-lattice relaxation rate is similar after 1 and 5 flashes. These data are discussed together with previously reported phenomena in terms of a light-adaptation process of PSII, which commences on the third flash after dark-adaptation and is completed after 10 flashes. At room temperature, the fast-relaxing, light-adapted state falls back to the slow-relaxing, dark-adapted state with t1/2 = 80 s. We speculate that light-adaptation involves changes necessary for efficient continuous water splitting. This would parallel activation processes found in many other large redox enzymes, such as Cytochrome c oxidase and Ni-Fe hydrogenase. Several mechanisms of light-adaptation are discussed...