Swollen-collapsed transition in random hetero-polymers

A lattice model of a hetero-polymer with random hydrophilic-hydrophobic charges interacting with the solvent is introduced, whose continuum counterpart has been proposed by Garel, Leibler and Orland [#!GLO!#]. The transfer matrix technique is used to study various constrained annealed systems which approximate at various degrees of accuracy the original quenched model. For highly hydrophobic chains an ordinary -point transition is found from a high temperature swollen phase to a low temperature compact phase. Depending on the type of constrained averages, at very low temperatures a swollen phase or a coexistence between compact and swollen phases are found. The results are carefully compared with the corresponding ones obtained in the continuum limit, and various improvements in the original calculations are discussed. Received: 10 April 1998 / Revised: 4 June 1998 / Accepted: 1st July 1998     

Magneto-optical spectroscopy of Yb ions in huntite structure

We report the first measurements of magnetic circular dichroism (MCD) and magneto-optical activity (ratio of zero moments of MCD and absorption bands) of Yb³⁺ ion in the trigonal single crystals Yb_xTm_1−xAl₃(BO₃)₄ as a function of temperature in the range of 100-293 K. Magneto-optical activity follows the Curie-Weiss law with the Weiss constant θ=−55 K for Yb_0.1Tm_0.9Al₃(BO₃)₄ crystal. The value and origin of the magneto-optical activity is theoretically analyzed.     

Conservative force fields in non-Gaussian statistics

In this Letter, we determine the κ-distribution function for a gas in the presence of an external field of force described by a potential U(r). In the case of a dilute gas, we show that the κ-power law distribution including the potential energy factor term can rigorously be deduced in the framework of kinetic theory with basis on the Vlasov equation. Such a result is significant as a preliminary to the discussion on the role of long range interactions in the Kaniadakis thermostatistics and the underlying kinetic theory.     

First passage time of multiple Brownian particles on networks with applications

In this article, we study some theoretical and technological problems with relation to multiple Brownian particles on networks. We are especially interested in the behavior of the first arriving Brownian particle when all the Brownian particles start out from the source s simultaneously and head to the destination h randomly. We analyze the first passage time (FPT) Y_sh(z) and the mean first passage time (MFPT) 〈Y_sh(z)〉 of multiple Brownian particles on complex networks. Equations of Y_sh(z) and 〈Y_sh(z)〉 are obtained. On a variety of commonly encountered networks, we observe first passage properties of multiple Brownian particles from different aspects. We find that 〈Y_sh(z)〉 drops substantially when particle number z increases at the first stage, and converges to d_sh, the distance between the source and the destination when z→∞. The distribution of FPT Prob{Y_sh(z)=t},t=0,1,2,… is also analyzed in these networks. The distribution curve peaks up towards t=d_sh when z increases. Consequently, if particle number z is set appropriately large, the first arriving Brownian particle will go along the shortest or near shortest paths between the source and the destination with high probability. Simulations confirm our analysis. Based on theoretical studies, we also investigate some practical problems using multiple Brownian particles, such as communication on P2P networks, optimal routing in small world networks, phenomenon of asymmetry in scale-free networks, information spreading in social networks, pervasion of viruses on the Internet, and so on. Our analytic and experimental results on multiple Brownian particles provide useful evidence for further understanding and properly tackling these problems.     

The microscopic interaction parameters for Er/Ho energy transfer in tellurite glasses

We investigate the energy transfer between Er³⁺/Ho³⁺ in tellurite glasses. The main channels of energy transfer between Er³⁺/Ho³⁺ are analyzed in detail. The microscopic interaction parameters of resonant and non-resonant (phonon-assisted) energy transfer parameters via Er³⁺→Ho³⁺ are calculated. The result shows that the resonant energy transfers Er³⁺(²H_11/2(⁴S_3/2))→Ho³⁺(⁵F₄(⁵S₂)) and Er³⁺(⁴F_9/2)→Ho³⁺(⁵F₅) are very efficient and non-resonant energy transfers Er³⁺(⁴I_13/2)→Ho³⁺(⁵I₇) and Er³⁺(⁴I_11/2)→Ho³⁺(⁵I₆), which are a phonon-assisted energy transfer process because of energy mismatch are also existed and cannot be neglected.     

Charge dynamics and optical properties of layered cobaltates

We study the charge dynamics and electronic structure by optical spectroscopy technique. Here we focus on the following four issues: (1) the evolution of optical spectra with Na content; (2) the spectral features specific to different regions in the phase diagram; (3) the c-axis optical response for crystal at the A-type antiferromagnetic region; (4) the optical response of misfit-layered Bi₂M₂Co₂O_y (M=Ba, Sr, Ca) and Ca₃Co₄O_y single crystals.     

Optimal design of multimode interference couplers using an improved self-imaging theory

Self-imaging theory is widely accepted as a good method in designing 1 × N multimode interference (MMI) couplers, but it is also true that self-imaging theory is not suitable for low-contrast structures. An improved self-imaging theory is proposed in this paper for the optimal design of low-contrast 1 × N MMI couplers. The average effective width of MMI waveguide and the average effective propagation constant of MMI waveguide are used as the basis to modify the conventional self-imaging theory. A direct calculation of the average effective width of low-contrast MMIs is presented. We use this approach in the optimal design of a 1 × 4 silica MMI coupler, and the results show that the improved self-imaging theory is more accurate than conventional self-imaging theory for low-contrast structures, the results also show that if the material parameters and the width of an MMI waveguide are fixed, the average effective width of the MMI waveguide will increase with the decrease of the height of the core layer.     

Photoreflectance study of energy level structure of self-assembled InAs/GaAs quantum dots emitting at 1.3 μm

Photoreflectance and photoluminescence measurements were performed on the ensemble of self assembled InAs/GaAs quantum dots designed to emit at 1.3 μm. As many as six QDs-related optical transitions were observed in PR spectra, the energies of which were confirmed by high-excitation PL results. Numerical calculations allowed estimating the average size of the dots, which is larger than for standard InAs/GaAs QDs. This result is in agreement with structural data. Additionally, the energy level structure for such QDs was derived and compared with the electronic structure of standard InAs/GaAs dots. It was shown that the energy level structure of such large dots qualifies them for the active region of a laser emitting at 1.3 μm.     

Fast computation of observed cross section for ψ′ → PP decays

It has been conjectured that the relative phase between strong and electromagnetic amplitudes is universally -90° in charmonium decays. ψ′ decaying into a pseudoscalar pair provides a possibility to test this conjecture. However, the experimentally observed cross section for such a process is depicted by the two-fold integral, which takes into account the initial state radiative (ISR) correction and energy spread effect. Using the generalized linear regression approach, a complex energy-dependent factor is ...