Classical limit of the Casimir entropy for scalar massless field

We study the Casimir effect at finite temperature for a massless scalar field in the parallel plates geometry in N spatial dimensions, under various combinations of Dirichlet and Neumann boundary conditions on the plates. We show that in all these cases the entropy, in the limit where energy equipartitioning applies, is a geometrical factor whose sign determines the sign of the Casimir force.     

Decay rate with coordinate-dependent diffusion coefficients

Using a master equation for the reduced density matrix of open quantum system, the influence of coordinate-dependent microscopical diffusion coefficients on the decay rate from a potential well is studied. For different temperatures, frictions, heights of barrier and ratios of stiffnesses of the potential in the minimum and on the top of the barrier, the quasistationary decay rates are obtained with the sets of coordinate-dependent and -independent microscopical diffusion coefficients, and coordinate-dependent phenomenological diffusion coefficients.     

Nanoscale observations of the operational failure for phase-change-type nonvolatile memory devices using Ge2Sb2Te5 chalcogenide thin films

In this study, a phase-change memory device was fabricated and the origin of device failure mode was examined using transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDS). Ge₂Sb₂Te₅ (GST) was used as the active phase-change material in the memory device and the active pore size was designed to be 0.5 m. After the programming signals of more than 2×10⁶ cycles were repeatedly applied to the device, the high-resistance memory state (reset) could not be rewritten and the cell resistance was fixed at the low-resistance state (set). Based on TEM and EDS studies, Sb excess and Ge deficiency in the device operating region had a strong effect on device reliability, especially under endurance-demanding conditions. An abnormal segregation and oxidation of Ge also was observed in the region between the device operating and inactive peripheral regions. To guarantee an data endurability of more than 1×10¹⁰ cycles of PRAM, it is very important to develop phase-change materials with more stable compositions and to reduce the current required for programming.     

Discrimination of photoblinking and photobleaching on the single molecule level

Wide field observation of individual dye molecules have been performed to study fluorescence intermittency. We demonstrate a data analysis scheme, which enables us to quantify the decay of the ensemble intensity which is due to on/off-blinking of the molecules (photophysical bleaching) by getting rid of the effects of photochemical degradation of the dye (photochemical bleaching). Under the conditions of our experiments, photophysical and thus reversible bleaching is the dominant of the two bleaching mechanisms.     

Zipf distribution in top Chinese firms and an economic explanation

By analyzing the data of top 500 Chinese firms from the year 2002 to 2007, we reveal that their revenues and ranks obey the Zipf’s law with exponent of 1 for each year. This result confirms the universality of firm size character which has been presented in many other empirical works, since China possesses a unique ideological and political system. We offer an explanation of it based on a simple economic model which takes production and capital accumulation into account.     

Frequency-dependent linear and non-linear response properties of single carrier quantum dots: Role of effective mass and anharmonicity in the confinement potential

We explore the pattern of frequency-dependent linear and non-linear optical (NLO) response of one electron quantum dots harmonically confined in two dimensions. For some fixed values of transverse magnetic field strength (ω_c), and harmonic confinement potential (ω₀), the influence of effective mass (m^*) of the system and the symmetry breaking anharmonic interaction on the frequency-dependent linear (α), and the first (β), and second (γ) NLO responses of the dot is computed through linear variational route. The investigation reveals interesting roles played by the anharmonic interaction and effective mass in modulating the response properties.     

The first measured Mn I Stark widths

The shapes of the astrophysically interesting neutral manganese (Mn I) resonance spectral lines (403.075, 403.306, 403.448, 279.481, 279.826 and 280.108 nm) have been observed together with six other prominent Mn I lines in the laboratory helium plasma at a 47 000 K electron temperature and electron density. With these plasma parameters the Stark broadening has been found to be an important mechanism in the Mn I line shape formation. Our measured Mn I Stark widths (W) are the first data in the literature. Stark widths are compared with line hyperfine structure splittings (Δ_hfs). At above mentioned helium plasma conditions the line broadening due to hyperfine structure splitting of the lines is less than that of the Stark and Doppler broadening for the case of the Mn I lines under investigation. We estimate that at electron densities below and electron temperatures below 4000 K the components in the hyperfine structure play an important role in the mentioned Mn I line shape formation.     

Tsallis, Rényi and nonextensive Gaussian entropy derived from the respective multinomial coefficients

We explore the generalization of the ordinary multinomial coefficient, based on the deformed q-multiplication and q-division. Aim of this study is to construct the appropriate multinomial coefficients, from which one can obtain the Tsallis, Rényi and nonextensive Gaussian entropy, respectively. We show that for all three above entropies there are two possible ways to define the generalized multinomial coefficient. Its consequence is discussed.     

Changes in the shapes of self-organized PbSe quantum dots during PbEuTe overgrowth investigated by anomalous X-ray diffraction

Anomalous X-ray diffraction was used for the investigation of shape and chemical composition of self-organized PbSe quantum dots covered by PbEuTe capping layers. From reciprocal-space maps of diffracted intensities measured at two energies of the primary radiation, we discriminated the contributions of the dot volumes and the surrounding crystal lattice to the diffracted intensity. We have found that the presence of Eu atoms suppresses the flattening of the dots during their overgrowth.     

Submillimeter measurements of N2 and air broadening of hypochlorous acid

The pressure induced broadening of a several pure rotational transitions of hypochlorous acid, HOCl, have been measured as a function of temperature. This set of rotational transitions is the dominant feature of the submillimeter spectrum in the range where several remote sensing instruments currently operate. Additional features throughout the submillimeter spectrum have been recorded at the full-resolution of the room temperature Doppler linewidth using multiplier chains in the 110- wavelengths.     

Microscopic modeling of photoluminescence of strongly disordered semiconductors

A microscopic theory for the luminescence of ordered semiconductors is modified to describe photoluminescence of strongly disordered semiconductors. The approach includes both diagonal disorder and the many-body Coulomb interaction. As a case study, the light emission of a correlated plasma is investigated numerically for a one-dimensional two-band tight-binding model. The band structure of the underlying ordered system is assumed to correspond to either a direct or an indirect semiconductor. In particular, luminescence and absorption spectra are computed for various levels of disorder and sample temperature to determine thermodynamic relations, the Stokes shift, and the radiative lifetime distribution.     

The Gaussian effective potential and stochastic partial differential equations

We investigate arbitrary stochastic partial differential equations subject to translation invariant and temporally white noise correlations from a nonperturbative framework. The method that we expose first casts the stochastic equations into a functional integral form, then it makes use of the Gaussian effective potential approach, which is an useful tool for describing symmetry breaking. We apply this method to the Kardar-Parisi-Zhang equation and find that the system exhibits spontaneous symmetry breaking in and (3+1) Euclidean dimensions, providing insight into the evolution of the system configuration due to the presence of noise correlations. A simple and systematic approach to the renormalization, without explicit regularization, is employed.     

Tsallis’ statistics in the variability of El Niño/Southern Oscillation during the Holocene epoch

Analysis of the Tsallis q-triplet for the variability of El Niño Southern Oscillation (ENSO) index during the Holocene epoch (last 11,000 years) is presented. Three periods are analyzed, 0-7000, 7000-9700, 9700-11,000 years before the present. During the first and the third periods, the q-index values have the expected usual relations between them (q_sens<1<q_stat<q_rel), and in the second one there is an inversion between q_stat and q_rel (q_stat>q_rel).     

Intermediate statistics as a consequence of deformed algebra

We present a formulation of deformed oscillator algebra which leads to intermediate statistics as a continuous interpolation between Bose-Einstein and Fermi-Dirac statistics. It is deduced that a generalized permutation or exchange symmetry leads to the introduction of the basic number and it is then established that this in turn leads to the deformed algebra of oscillators. We obtain the mean occupation number describing the particles obeying intermediate statistics which thus establishes the interpolating statistics and describe boson-like and fermion-like particles obeying intermediate statistics. We also obtain an expression for the mean occupation number in terms of an infinite continued fraction, thus clarifying successive approximations.     

The magnetoresistance effect in a nanostructure with the periodic magnetic barriers

The magnetoresistance (MR) effect is theoretically investigated in a periodic magnetically modulated nanostructure, which can be realized experimentally by depositing periodic parallel ferromagnetic strips on the top of a heterostructure. We find that there exists a significant conductance difference for electrons through the parallel (P) and antiparallel (AP) magnetization configurations, which results in a considerable magnetoresistance effect. We also find that the magnetoresistance effect depends not only on the temperature but also on the number of the periodic magnetic barriers.     

Partial equivalence of statistical ensembles and kinetic energy

The phenomenon of partial equivalence of statistical ensembles is illustrated by discussing two examples, the mean-field XY and the mean-field spherical model. The configurational parts of these systems exhibit partial equivalence of the microcanonical and the canonical ensemble. Furthermore, the configurational microcanonical entropy is a smooth function, whereas a nonanalytic point of the configurational free energy indicates the presence of a phase transition in the canonical ensemble. In the presence of a standard kinetic energy contribution, partial equivalence is removed and a nonanalyticity arises also microcanonically. Hence in contrast to the common belief, kinetic energy, even though a quadratic form in the momenta, has a nontrivial effect on the thermodynamic behaviour. As a by-product we present the microcanonical solution of the mean-field spherical model with kinetic energy for finite and infinite system sizes.     

Complex turing patterns in non-linearly coupled systems

Recently pattern formation in layered structures, showing complicated superimposed patterns, has been modeled by coupling two Turing systems linearly, i.e., passively, such that the characteristic length scales of the independent systems are well separated. Here we propose a model of two non-linearly coupled Turing systems to study pattern formation in layered membrane-like structures, where the coupling plays an active role and changes the kinetics of the uncoupled systems. Extensive numerical simulations show that non-linear coupling generates a number of new regular patterns different from the ones observed earlier with linearly coupled systems. Some of them turn out to be superimposed patterns with different length scales, but many are not. Also, contrary to the linear coupling case, the strength of the non-linear coupling is found to play an important role in the formation and selection of patterns.     

Multifractal detrended fluctuation analysis of derivative and spot markets

We investigate the multifractal properties of price increments in the cases of derivative and spot markets. Through the multifractal detrended fluctuation analysis, we estimate the generalized Hurst and the Renyi exponents for price fluctuations. By deriving the singularity spectrum from the above exponents, we quantify the multifractality of a financial time series and compare the multifractal properties of two different markets. The different behavior of each agent-group in transactions is also discussed. In order to identify the nature of the underlying multifractality, we apply the method of surrogate data to both sets of financial data. It is shown that multifractality due to a fat-tailed distribution is significant.     

Transport of waves in disordered waveguides: A potential model

We study the statistical properties of wave transport in a disordered waveguide. We first derive the properties of a “building block” (BB) of length δL starting from a potential model consisting of thin potential slices. We then find a diffusion equation—in the space of transfer matrices that describe our system—which governs the evolution with the length L of the disordered waveguide of the transport properties of interest. The latter depend only on the mean free paths and on no other property of the slice distribution. The universality that arises demonstrates the existence of a generalized central-limit theorem. We have developed a numerical simulation in which the universal statistical properties of the BB found analytically are first implemented numerically, and then the various BBs are combined to construct the full waveguide. The reported results thus obtained are in good agreement with microscopic calculations, for both bulk and surface disorder.