Thermal-conductivity of periodic composite media with spherical inclusions

The thermal conductivity of periodic composite media with spherical inclusions embedded in a homogeneous matrix is discussed. Using Green's function, we show that the Rayleigh identity can be generalized to deal with the thermal properties of these systems. A technique for calculating effective thermal conductivities is proposed. Systems with cubic symmetries (including simple cubic, body centered cubic and face centered cubic symmetry) are investigated in detail, and useful formulae for evaluating effective thermal conductivities are derived.

Alterations of immune functions induced by 12C6+ion irradiation in mice

Purpose: To estimate the biological risks to the immune system of the type of space radiation, 12C6+, encountered by cosmonauts during long-term travel in space. Materials and methods: The Kun-Ming strain mice were whole-body irradiated by 12C6+ ion with 0, 0.01, 0.05, 0.075, 0.2, 0.3, 0.5, 0.75, 1 or 2 Gy, at a dose rate of 1 Gy/min. At 35 days after irradiation, the thymus and spleen weights were measured, the natural killer (NK) cells activity of spleen was determined by 3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyl tetrazolium bromide (MTT), and the interferon-gamma (IFN-gamma) levels in serum and thymus were detected with enzyme-linked immunosorbent assays (ELISA). Results: The results showed that the thymus weight, IFN-gamma levels in serum and the activity of splenic NK-cells had significantly increased at a dose of 0.05 Gy. With further dose increase, the weight of spleen continued to increase but the weight of thymus, IFN-gamma level and NK-cells activity declined. Conclusions: These results suggest that the dose of 0.05 Gy irradiation has a stimulatory effect on mouse immunity; this effect declined with increasing dose.

Hierarchy of structure functions for passive scalars advected by turbulent flows

A hierarchical model is proposed for the joint moments of the passive scalar dissipation and the velocity dissipation in fluid turbulence. This model predicts that the joint probability density function (PDF) of the dissipations is a bivariate log-Poisson. An analytical calculation of the scaling exponents of structure functions of the passive scalar is carried out for this hierarchical model, showing a good agreement with the results of direct numerical simulations and experiments.

The Effect of Periodic Segmentation Cracks on the Interfacial Debonding: Study on Interfacial Stresses

Hard coatings on relatively soft substrate always face the danger of debonding along the interface. Interfacial stresses are considered to be the initial driving force for the interfacial debonding of the relatively strong bonded coatings. Interfacial stresses due to the mismatch of strain between the coating and substrate are simulated with FEM firstly. The distribution of the interfacial stresses is achieved, which confirms an excessive stresses concentration near the interface end. Subsequently, the redistribution of interfacial stresses is calculated for a coating with periodic segmentation cracks. Results indicate that the distribution of interfacial stresses is altered greatly with the periodic segmentation cracks. To reveal the effect of the spacing of the periodic segmentation cracks on the distribution of interfacial stresses, different crack density is modeled within the coating. It is found that that the peak values of the interfacial stresses decrease with the increase of crack density, i.e. with reduction of spacing of segmentation cracks.

On the Formation of Periodic Segmentation Cracks in a Coating Plated on a Substrate with Periodic Subsurface Inclusions

The mechanism of the formation of periodic segmentation cracks of a coating plated on a substrate with periodic subsurface inclusions (PSI) is investigated. The internal stress in coating and subsequently the strain energy release rate (SERR) of the segmentation cracks are computed with finite element method (FEM). And the effect of the geometrical parameters of the PSI is studied. The results indicate that the ratio of the width of the inclusion to the period of the repeated structure has an optimum value, at which the maximum internal tensile stress and SERR arise. On the other hand, the ratio of the max-thickness of the inclusion to the thickness of the coating has a threshold value, above which the further increase of this ratio should seldom influence the internal stress or the SERR.

Traces of nonsmooth functions on polyhedral domains

introduced in this paper are the definitions of the traces for a class of nonsmooth functions on polyhedral domains. By analyzing their properties we get the structures of these traces.

Generation of periodic ultrashort electron bunches and strongly asymmetric ion Coulomb explosion in nanometer foils interacting with ultra-intense laser pulse

The interaction of a linearly polarized intense laser pulse with an ultrathin nanometer plasma layer is investigated to understand the physics of the ion acceleration. It is shown by the computer simulation that the plasma response to the laser pulse comprises two steps. First, due to the vxB effect, electrons in the plasma layer are extracted and periodic ultrashort relativistic electron bunches are generated every half of a laser period. Second, strongly asymmetric Coulomb explosion of ions in the foil occurs due to the strong electrostatic charge separation, once the foil is burnt through. Followed by the laser accelerated electron bunch, the ion expansion in the forward direction occurs along the laser beam that is much stronger as compared to the backward direction. (c) 2008 American Institute of Physics.

Coherent linking of periodic nano-ripples on a ZnO crystal surface induced by femtosecond laser pulses

We demonstrate the coherent linking of periodic nano-ripples formed on the surface of ZnO crystals induced by femtosecond laser pulses. By adjusting the distance between two laser scanning zones, the periodic nano-ripples induced by two separated laser writing processes can be coherently linked and the ZnO nanograting with much longer grooves is therefore produced. The length limitation of this kind of nanograting previously set by the laser focus size is thus overcome. The micro-Raman mapping technique is used to evaluate the quality of coherent linking, and the underlying physics is discussed. The demonstrated scheme is promising for producing large-size self-organized nanogratings induced by femtosecond laser pulses.

Formation mechanisms of uniform arrays of periodic nanoparticles and nanoripples on 6H-SiC crystal surface induced by femtosecond laser ablation

Uniform arrays of periodic nanoparticles with 80-nm period are formed on 6H-SiC crystal irradiated by circularly polarized 400-nm femtosecond laser pulses. In order to understand the formation mechanism, the morphology evolvement as a function of laser pulse energy and number is studied. Periodic nanoripples are also formed on the sample surface irradiated by linearly polarized 400-, 510- and 800-nm femtosecond laser pulses. All these results support well the mechanism that second-harmonic generation plays an important role in the formation of periodic nanostructures.

Optical transfer of periodic microstructures by interfering femtosecond laser beams

We report on an optical interference method for transferring periodic microstructures of metal film from a supporting substrate to a receiving substrate by means of five-beam interference of femtosecond laser pulses. Scanning electron microscopy and optical microscopy revealed microstructures with micrometer-order were transferred to the receiving substrate. In the meanwhile, a negative copy of the transferred structures was induced in the metal film on the supporting substrate. The diffraction characteristics of the transferred structures were also evaluated. The present technique allows one-step realization of functional optoelectronic devices. (C) 2005 Optical Society of America.

Characterize dynamic conformational space of human CCR5 extracellular domain by molecular modeling and molecular dynamics simulation

The chemokine receptor CCR5 is the receptor for several chemokines and major coreceptor for R5 human immunodeficiency virus type-1 strains entry into cell. Three-dimensional models of CCR5 were built by using homology modeling approach and 1 ns molecular dynamics (MD) simulation, because studies of site-directed mutagenesis and chimeric receptors have indicated that the N-terminus (Nt) and extracellular loops (ECLs) of CCR5 are important for ligands binding and viral fusion and entry, special attention was focused on disulfide bond function, conformational flexibility, hydrogen bonding, electrostatic interactions, and solvent-accessible surface area of Nt and ECLs of this protein part. We found that the extracellular segments of CCR5 formed a well-packet globular domain with complex interactions occurred between them in a majority of time of MID simulation, but Nt region could protrude from this domain sometimes. The disulfide bond Cys20-Cys269 is essential in controlling specific orientation of Nt region and maintaining conformational integrity of extracellular domain. RMS comparison analysis between conformers revealed the ECL1 of CCR5 stays relative rigid, whereas the ECL2 and Nt are rather flexible. Solvent-accessible surface area calculations indicated that the charged residues within Nt and ECL2 are often exposed to solvent. Integrating these results with available experimental data, a two-step gp120-CCR5 binding mechanism was proposed. The dynamic interaction of CCR5 extracellular domain with gp120 was emphasized. (C) 2004 Elsevier B.V. All rights reserved.