Effective schrödinger equation for a classical massless dislocation plasma

Summary The statistical behaviour of classical massless excitations finds an increasing importance in the physics of low-dimensional condensed matter. Dislocation and disclination dipole-gases and plasmas play such a relevant role in the theory of 2D melting. Here the equilibrium statistical mechanics of a system of strongly interactingparticles of this type is faced searching for the approximate stationary solution of the multivariate associated Fokker-Planck equation corresponding to zero eigenvalue. The problems, encountered in a preceding paper, involved by the nonhermiticity of Fokker-Planck operator, are evaded, following Risken, building anequivalent many-body Schr?dinger equation. This last is solved self-consistently in a Hartree-like way starting with a free-particleproduct wavefunction in the case of a uniform background whosecharge is of sign opposite to that of theparticles. Unlike thetrue quantum case, here the integral part of the equivalent Hamiltonian operator is not simply Coulomb-like and defines a more difficult novel integrodifferential problem which is solved using a convergence in mean procedure. The author of this paper has agreed to not receive the proofs for correction.     

Relaxation of protons by radicals in rotationally immobilized proteins

Proton spin-lattice relaxation by paramagnetic centers may be dramatically enhanced if the paramagnetic center is rotationally immobilized in the magnetic field. The details of the relaxation mechanism are different from those appropriate to solutions of paramagnetic relaxation agents. We report here large enhancements in the proton spin-lattice relaxation rate constants associated with organic radicals when the radical system is rigidly connected with a rotationally immobilized macromolecular matrix such as a dry protein or a cross-linked protein gel. The paramagnetic contribution to the protein-proton population is direct and distributed internally among the protein protons by efficient spin diffusion. In the case of a cross-linked-protein gel, the paramagnetic effects are carried to the water spins indirectly by chemical exchange mechanisms involving water molecule exchange with rare long-lived water molecule binding sites on the immobilized protein and proton exchange. The dramatic increase in the efficiency of spin relaxation by organic radicals compared with metal systems at low magnetic field strengths results because the electron relaxation time of the radical is orders of magnitude larger than that for metal systems. This gain in relaxation efficiency provides completely new opportunities for the design of spin-lattice relaxation based contrast agents in magnetic imaging and also provides new ways to examine intramolecular protein dynamics.     

Surface states and its influence on luminescence in ZnS nanocrystallite

In this pape,r the influence of surface effects on the self-activated (SA) luminescence in ZnS nanoparticles prepared by the wet-chemical method is presented. It is observed that the luminescence of SA decreases dramatically by rinsing with methanol. In the rinsed sample, the luminescence of SA increases more by ultraviolet (UV) light irradiation. To clarify its origin, the Raman spectra and electron paramagnetic resonance (EPR) are studied. The results demonstrate that the vibrational modes assigned to organic functional groups of -OH and -COO and -CH₃ decreases remarkably by rinsing, while the EPR signal originated from the unpaired electrons of some transition metal impurity ions including Mn²⁺ increases. It is suggested that the SA centers prefer to occupy the sites near the surface and that the donor of SA emission may be partly related to the organic functional groups of -OH and -COO adsorbed on the surface. The surface-dangling bonds caused by unpaired electrons of some transition metal impurity ions play a role of surface states, leading to the quenching of the SA emissions. The organic functional groups chemically combine with these surface-dangling bonds leading to the decrease in surface states and surface nonradiative relaxation channels and to the increase in the SA emissions.     

Relaxation dispersion in MRI induced by fictitious magnetic fields

A new method entitled Relaxation Along a Fictitious Field (RAFF) was recently introduced for investigating relaxations in rotating frames of rank ≥ 2. RAFF generates a fictitious field (E) by applying frequency-swept pulses with sine and cosine amplitude and frequency modulation operating in a sub-adiabatic regime. In the present work, MRI contrast is created by varying the orientation of E, i.e. the angle ε between E and the z″ axis of the second rotating frame. When ε > 45°, the amplitude of the fictitious field E generated during RAFF is significantly larger than the RF field amplitude used for transmitting the sine/cosine pulses. Relaxation during RAFF was investigated using an invariant-trajectory approach and the Bloch-McConnell formalism. Dipole-dipole interactions between identical (like) spins and anisochronous exchange (e.g., exchange between spins with different chemical shifts) in the fast exchange regime were considered. Experimental verifications were performed in vivo in human and mouse brain. Theoretical and experimental results demonstrated that changes in ε induced a dispersion of the relaxation rate constants. The fastest relaxation was achieved at ε ≈ 56°, where the averaged contributions from transverse components during the pulse are maximal and the contribution from longitudinal components are minimal. RAFF relaxation dispersion was compared with the relaxation dispersion achieved with off-resonance spin lock T(?ρ) experiments. As compared with the off-resonance spin lock T(?ρ) method, a slower rotating frame relaxation rate was observed with RAFF, which under certain experimental conditions is desirable.     

Relaxation intensity in some polyacrylates

Empirical formula suggested by Kita and Koizumi for evaluation of relaxation intensity in a limited range of frequency around the relaxation frequency for the Cole-Cole type distribution has been tested for poly butyl acrylate (PBA), Poly butyl methacrylate (PBMA) and poly isobutyl methacrylate (PiBMA). The relaxation intensity Δε is expressed in terms ofε″ _M , the dielectric loss maxima andW, the frequency separation for half, two thirds or three quarters ofε″ _M , in the form Δε=ε″ _M /[(C ₁/W)+C ₂+C ₃ W], where the numerical constantsC ₁,C ₂,C ₃ are given for the respective type of relaxation.     

Inhomogeneous Relaxation in Vibrated Granular Media: Consolidation Waves

We investigate the spatial dependence of the density of vibrated granular beds, using simulations based on a hybrid Monte Carlo algorithm. We find that the initial consolidation is typically inhomogeneous, both in the presence of a constant shaking intensity and when the granular bed is subjected to "annealed shaking". We also present a theoretical model which explains such inhomogeneous relaxation in terms of a "consolidation wave", in good qualitative agreement with our simulations. Our results are also in qualitative agreement with recent experiments.     

Relaxation properties of weakly coupled classical systems

The relaxation properties of a small classical system weakly coupled to a large classical system which acts as a heat bath are described using a generalized Fokker-Planck equation. The Fokker-Planck equation is derived in general using a modification of the elimination of fast variables techniques previously described. The specific example in which the small system is a harmonic oscillator linearly coupled to the heat bath is treated in detail and it is demonstrated that there is a dynamic frequency shift as well as a statistical shift of the oscillator frequency.     

Relaxation, crystallization, and glass transition in supercooled liquid Ni

In this Letter, molecular dynamics (MD) simulations based on EAM many-body potential have been performed to investigate the differences of dynamical heterogeneity in the course of crystallization and glass transition, respectively. The crystallization of liquid, detected at a cooling rate of , is characterized by the appearances of the second plateau in mean square displacement (MSD) and the nonzero plateau in non-Gaussian parameter (NGP). It implies that the non-diffusive rearrangement of atoms occurring at a certain temperature and relaxation time leads to nucleus forming. The glass phase forms as the cooling rate increases to . There is no second plateau in MSD appearing in the formation of metallic glass, indicating the diffusive motion of atoms. The non-Gaussian characteristic in NGP is more obvious at low temperatures.     

Relaxation of interstitials in spherical colloidal crystals

Spherical colloidal crystals (CCs) self-assemble on the interface between two liquids. These 2D structures unconventionally combine local hexagonal order and spherical geometry. Nowadays CCs are actively studied by altering their structures. However, the statistical analysis of such experiments results is limited by uniqueness of self-assembled structures and their short lifetime. Here we perform numerical experiments to investigate pathways of CC structure relaxation after the intrusion of interstitial. The process is simulated in the frames of overdamped molecular dynamics method. The relaxation occurs due to interaction with extended topological defects (ETDs) mandatory induced in spherical CCs by their intrinsic Gaussian curvature. Types of relaxation pathways are classified and their probabilities are estimated in the low-temperature region. To analyze the structural changes during the relaxation we use a parent phase approach allowing us to describe the global organization of spherical order. This organization is preserved by only the most typical relaxation pathway resulting in filling one of vacancies integrated inside the ETD areas. In contrast with this pathway the other ones shift the ETDs centers and can strongly reconstruct the internal structure of ETDs. Temperature dependence of the relaxation processes and the mechanism of dislocation unbinding are discussed. Common peculiarities in relaxation of spherical structures and particular fragments of planar hexagonal lattice are found.     

Relaxation and decoherence of orbital and spin degrees of freedom in quantum dots

The phonon induced mechanisms of relaxation/decoherence in quantum dots are analysed. A non-perturbative technique - a modification of the Davydov transformation appropriate to the localised particles is applied for solving the electron-phonon eigenvalue problem in a quantum dot at magnetic field presence. The decay rates for polaron relaxation via the anharmonicity induced channel are analysed in details. In particular, it is indicated that previous, of perturbative type, estimations of the anharminicity induced relaxation rates were too severe and after including the coherence effects they are of, at least, one order longer. The process of exciton dressing with phonons is also analysed as the unavoidable source of picosecond scale decoherence in optically driven nanostructures. A break-down of an instant Pauli spin blocking mechanism and a large enhancement of the Fröhlich constant for confined electrons are also addressed.     

Relaxation dynamics of the Kuramoto model with uniformly distributed natural frequencies

The Kuramoto model describes a system of globally coupled phase-only oscillators with distributed natural frequencies. The model in the steady state exhibits a phase transition as a function of the coupling strength, between a low-coupling incoherent phase in which the oscillators oscillate independently and a high-coupling synchronized phase. Here, we consider a uniform distribution for the natural frequencies, for which the phase transition is known to be of first order. We study how the system close to the phase transition in the supercritical regime relaxes in time to the steady state while starting from an initial incoherent state. In this case, numerical simulations of finite systems have demonstrated that the relaxation occurs as a step-like jump in the order parameter from the initial to the final steady state value, hinting at the existence of metastable states. We provide numerical evidence to suggest that the observed metastability is a finite-size effect, becoming an increasingly rare event with increasing system size.     

Relaxation time for a charge carrier due to its scattering from other charge carriers in superlattices

A calculation of relaxation time for (i) electron–electron scattering in a modulation-doped superlattice of type-I and (ii) electron–electron, hole–hole and electron–hole scattering processes in a compositional superlattice of type-II has been performed, using Fermi's golden rule. As compared to a two-dimensional electron gas system, both intralayer and interlayer interactions, between charge carriers in a superlattice, contribute to relaxation time. It is found that scattering processes at all possible value of momentum transfer contribute to relaxation time, for a given value of temperature and carrier density. We further find interlayer interactions in a superlattice make a significant contribution to relaxation time. Relaxation time is found to decrease on increasing temperature, carrier density and single particle energy, in a superlattice. The computed relaxation time for an electron (hole) in a superlattice enhances on increasing the width of layer consisting of electrons (holes). The electron–hole (hole–electron) scattering process in a type-II superlattice yields maximum contribution to the relaxation time when a hole layer lies exactly in between two consecutive electron layers.     

Experimental examination of displacement field in an edge dislocation core in aluminum

The displacement field of an edge dislocation in aluminum was experimentally investigated. Three typical theoretical models were discussed. High-resolution transmission electron microscopy (HRTEM) and geometric phase analysis (GPA) were used to map the displacement field of an edge dislocation. The displacement field near the dislocation core was determined. The experimental show that Peierls-Nabarro model is the most appropriate theoretical model for displacement field of dislocation in aluminum.     

Relaxation and localization in interacting quantum maps

Quantum relaxation is studied in coupled quantum baker's maps. The classical systems are exactly solvable Kolmogorov systems, for which the exponential decay to equilibrium is known. They model the fundamental processes of transport in classically chaotic phase space. The quantum systems, in the absence of global symmetry, show a marked saturation in the level of transport, as the suppression of diffusion in the quantum kicked rotor, and eigenfunction localization in the position basis. In the presence of a global symmetry we study another model that has classically an identical decay to equilibrium, but-quantally shows resonant transport, no saturation, and large fluctuations around equilibrium. We generalize the quantization to finite multibaker maps. As a byproduct we introduce some simple models of quantal tunneling between classically chaotic regions of phase space.     

Relaxation oscillation studies in Nd: YAG laser—Some new results

The study of transient behaviour of a pulse pumped solid state laser system has assumed importance on account of SLM generation by self-seeding with the pre-lase signal. This paper reports on the observations of seed pulses for two different Nd: YAG laser rods, one with anti-reflection coating (AR) on end faces and the other without. The latter displays single longitudinal mode behaviour in each of the relaxation pulse train while the former displays multimode behaviour. Our observations are well explained by the ‘active etalon concept’ introduced earlier.     

Relaxation phenomena of polar non-polar liquid mixtures under low and high frequency electric field

Simultaneous calculation of the dipole moment μ_j and the relaxation time τ_j of a certain number of non-spherical rigid aliphatic polar liquid molecules (j) in non-polar solvents (i) under 9.8 GHz electric field is possible from real ε′_ij and imaginary ε″_ij parts of the complex relative permittivity ε*_ij. The low frequency and infinite frequency permittivities ε_0ij and ε_∞ij measured by Purohitet al [1,2] and Srivastava and Srivastava [3] at 25, 35 and 30°C respectively are used to obtain static μ_s. The ratio of the individual slopes of imaginary σ″_ij and real σ′_ij parts of high frequency (hf) complex conductivity σ*_ij with weight fractionsw _jatw _j → 0 and the slopes of σ″_ij— σ′_ij curves for differentw _js [4] are employed to obtain τ_js. The former method is better in comparison to the existing one as it eliminates polar-polar interaction. The hf μ_js in Coulomb metre (C m) when compared with static and reported μs indicate that μ_s s favour the monomer formations which combine to form dimers in the hf electric field. The comparison among μs shows that a part of the molecule is rotating under X-band electric field [5]. The theoretical μ_theos from available bond angles and bond moments of the substituent polar groups attached to the parent molecules differ from the measured μ_js and μs to establish the possible existence of mesomeric, inductive and electromeric effects in polar liquid molecules.     

Relaxation modes in glassy polymers: A temporal analysis by the simplex method of isothermal depolarisation current measurements

Molecular dynamics associated to relaxation phenomena in the glass transition temperature domain is often investigated by means of thermostimulated depolarisation current TSDC technique. It is a very sensitive method and the data are traditionally obtained according to two protocols leading to the well known complex spectra and elementary spectra. The aim of this work is to use a new TSDC protocol which analyses the relaxation current kinetics obtained after submitting the sample to an electrical field pulse at a constant temperature. A new temporal analysis of the return equilibrium isothermal transient current I(T) is proposed. The signal fitting is obtained by a simplex optimisation method. The entire signal recorded for all the temperatures can be fitted with a sum of two exponentials allowing the definition of two different relaxation times called τ₁ and τ₂. This new protocol has been used to analyse the glass transition domain of amorphous PET.     

金原子的放大自发辐射脉冲的弛豫振荡

首次报道了由金原子发出的波长627.8nm的放大自发辐射脉冲具有弛豫振荡.得出其在时间域和频率域的规律.这种振荡可能是高增益脉冲辐射系统的一种普遍现象.