Energy spectrum of ground state and excitation spectrum of quasi-particle for hard-core boson in optical lattices

We investigate the energy spectrum of ground state and quasi-particle excitation spectrum of hard-core bosons, which behave very much like spinless noninteracting fermions, in optical lattices by means of the perturbation expansion and Bogoliubov approach. The results show that the energy spectrum has a single band structure, and the energy is lower near zero momentum; the excitation spectrum gives corresponding energy gap, and the system is in Mott-insulating state at Tonks limit. The analytic result of energy spectrum is in good agreement with that calculated in terms of Green's function at strong correlation limit.

Electron ground state energy level determination of ZnSe self-organized quantum dots embedded in ZnS

Optical and electrical characterization of the ZnS self-organized quantum dots (QDs) embedded in ZnS by molecular beam epitaxy have been investigated using photoluminescence (PL), capacitance-voltage (C-V), and deep level transient Fourier spectroscopy (DLTFS) techniques. The temperature dependence of the free exciton emission was employed to clarify the mechanism of the PL thermal quenching processes in the ZnSe QDs. The PL experimental data are well explained by a two-step quenching process. The C-V and DLTFS techniques were used to obtain the quantitative information on the electron thermal emission from the ZnSe QDs. The correlation between the measured electron emission from the ZnSe QDs in the DLTFS and the observed electron accumulation in the C-V measurements was clearly demonstrated. The emission energy for the ground state of the ZnSe QDs was determined to be at about 120 meV below the conduction band edge of the ZnS barrier, which is in good agreement with the thermal activation energy, 130 meV, obtained by fitting the thermal quenching process of the free exciton PL peak. (C) 2003 American Institute of Physics.

Configuration-dependent diffusion can shift the kinetic transition state and barrier height of protein folding

We show that diffusion can play an important role in protein-folding kinetics. We explicitly calculate the diffusion coefficient of protein folding in a lattice model. We found that diffusion typically is configuration- or reaction coordinate-dependent. The diffusion coefficient is found to be decreasing with respect to the progression of folding toward the native state, which is caused by the collapse to a compact state constraining the configurational space for exploration. The configuration- or position-dependent diffusion coefficient has a significant contribution to the kinetics in addition to the thermodynamic free-energy barrier. It effectively changes (increases in this case) the kinetic barrier height as well as the position of the corresponding transition state and therefore modifies the folding kinetic rates as well as the kinetic routes. The resulting folding time, by considering both kinetic diffusion and the thermodynamic folding free-energy profile, thus is slower than the estimation from the thermodynamic free-energy barrier with constant diffusion but is consistent with the results from kinetic simulations. The configuration- or coordinate-dependent diffusion is especially important with respect to fast folding, when there is a small or no free-energy barrier and kinetics is controlled by diffusion.Including the configurational dependence will challenge the transition state theory of protein folding.

Controlling dispersed state and exfoliation process of clay in polymer matrix

In the present review, the authors do not try to provide a comprehensive review of researches on polymer/clay nanocomposites (PCNs), but some examples to demonstrate different exfoliation processes of the clay in various polymer matrixes and the dispersed state of clay. Interaction between polymers and layered silicates plays an important role in adjusting the exfoliation process of layered silicates and the microstructure of polymer nanocomposites. Properties of polymer/layered silicate nanocomposites mainly depend on the dispersed state of layered silicates. The authors will also address the outline of the present research in the direction of PCNs including the discussion of technical problems and their possible solutions.

Evidences of the intertidal red alga Grateloupia turuturu in turning Vibrio parahaemolyticus into non-culturable state in the presence of light

Grateloupia turuturu, previously known as Grateloupia doryphora, has been widely reported to be an invasive algal species. There are no studies to relate the impact of its existence on its surrounding environment. In this paper, we present our results to show that about 70% of individuals collected from the field could turn Vibrio parahaemolyticus into non-culturable state on both selective (TCBS) and non-selective (2216E) culture medium in 24 h in the presence of light in live algal culture. Total bacteria counts on TCBS and 2216E plates dropped from the initial 565 (174) and 1192 (60) cfu ml(-1) respectively to zero in 24 h. This effect disappeared when the alga was grown in darkness. The same effect was not found in two other intertidal macroalgae Laminaria japonica and Palmaria palmata. Further tests showed that the settlement ability of bacteria in seawater was impaired significantly in the presence of this alga in comparison with three other algal species. (c) 2006 Elsevier B.V. All rights reserved.