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

Fonte: AMER CHEMICAL SOC
Publicador: AMER CHEMICAL SOC

Tipo: Artigo de Revista Científica

ENG

Relevância na Pesquisa

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#LIGHT-EMITTING-DIODES#SOLID-STATE NMR#MAGIC-ANGLE#CRYSTALLINE POLYMERS#RELAXATION PROCESSES#MOLECULAR-DYNAMICS#MEH-PPV#TEMPERATURE#COPOLYMER#EMISSION#Chemistry, Physical

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...

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

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.

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

Fonte: ABM, ABC, ABPol
Publicador: ABM, ABC, ABPol

Tipo: Artigo de Revista Científica
Formato: text/html

Publicado em 01/06/2015
EN

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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.

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

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 14/04/2001

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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

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## Scale properties as a basis of power law relaxation processes

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 07/08/2006

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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

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

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Relevância na Pesquisa

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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

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## Relaxation processes in a disordered Luttinger liquid

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 30/04/2008

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#Condensed Matter - Mesoscale and Nanoscale Physics#Condensed Matter - Strongly Correlated Electrons

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...

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

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 02/03/2007

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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...

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

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 21/11/2015

Relevância na Pesquisa

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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

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## Linear Relaxation Processes Governed by Fractional Symmetric Kinetic Equations

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 07/10/1999

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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

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## Fast Algorithm for Relaxation Processes in Big-data Systems

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

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

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 29/11/2004

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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

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## Stellar Relaxation Processes Near the Galactic Massive Black Hole

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

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

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 05/03/2006

Relevância na Pesquisa

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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

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

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 27/11/2012

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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

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## Relaxation Processes in Solar Wind Turbulence

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.

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

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 12/07/2012

Relevância na Pesquisa

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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...

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

Fonte: John Wiley & Sons
Publicador: John Wiley & Sons

Tipo: Artículo
Formato: 22195 bytes; application/pdf

ENG

Relevância na Pesquisa

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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

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

Fonte: American Chemical Society
Publicador: American Chemical Society

Tipo: Article; published version

EN

Relevância na Pesquisa

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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...

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

Fonte: American Chemical Society
Publicador: American Chemical Society

Tipo: Artigo de Revista Científica

Relevância na Pesquisa

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#Keywords: Enzymes#Oxidation#Paramagnetic resonance#Relaxation processes#Photosystems#Biochemistry#cytochrome c oxidase#iron dehydrogenase#manganese#membrane enzyme#nickel dehydrogenase

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...

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