Evolution and propagation of density waves on galactic disk .2. An approximation of the thin transition layer

In this part of the present work, a simplified model—the thin transition layer theory is proposed. The comparison of this model with the G-L sheet model is made.

An extension of the Quasicontinuum Treatment of Multiscale Solid Systems to Nonzero Temperature

Covering the solid lattice with a finite-element mesh produces a coarse-grained system of mesh nodes as pseudoatoms interacting through an effective potential energy that depends implicitly on the thermodynamic state. Use of the pseudoatomic Hamiltonian in a Monte Carlo simulation of the two-dimensional Lennard-Jones crystal yields equilibrium thermomechanical properties (e.g., isotropic stress) in excellent agreement with ``exact'' fully atomistic results.

Direct numerical test of the B-G-K model equation by the DSMC method

In the present paper the rarefied gas how caused by the sudden change of the wall temperature and the Rayleigh problem are simulated by the DSMC method which has been validated by experiments both in global flour field and velocity distribution function level. The comparison of the simulated results with the accurate numerical solutions of the B-G-K model equation shows that near equilibrium the BG-K equation with corrected collision frequency can give accurate result but as farther away from equilibrium the B-G-K equation is not accurate. This is for the first time that the error caused by the B-G-K model equation has been revealed.

Towards an Understanding of the Influence of Sedimentation on Colloidal Aggregation by Peclet Number

The Peclet number is a useful index to estimate the importance of sedimentation as compared to the Brownian motion. However, how to choose the characteristic length scale for the Peclet number evaluation is rather critical because the diffusion length increases as the square root of the time whereas the drifting length is linearly related to time. Our Brownian dynamics simulation shows that the degree of sedimentation influence on the coagulation decreases when the dispersion volume fraction increases. Therefore using a fixed length, such as the diameter of particle, as the characteristic length scale for Peclet number evaluation is not a good choice when dealing with the influence of sedimentation on coagulation. The simulations demonstrated that environmental factors in the coagulation process, such as dispersion volume fraction and size distribution, should be taken into account for more reasonable evaluation of the sedimentation influence.

Toward an understanding of the turbidity measurement of fleterocoagulation rate constants of dispersions containing particles of different sizes

Our previous studies have shown that the determination of coagulation rate constants by turbidity measurement becomes impossible for a certain operating wavelength (that is, its blind point) because at this wavelength the change in the turbidity of a dispersion completely loses its response to the coagulation process. Therefore, performing the turbidity measurement in the wavelength range near the blind point should be avoided. In this article, we demonstrate that the turbidity measurement of the rate constant for coagulation of a binary dispersion containing particles of two different sizes (heterocoagulation) presents special difficulties because the blind point shifts with not only particle size but also with the component fraction. Some important aspects of the turbidity measurement for the heterocoagulation rate constant are discussed and experimentally tested. It is emphasized that the T-matrix method can be used to correctly evaluate extinction cross sections of doublets formed during the heterocoagulation process, which is the key data determining the rate constant from the turbidity measurement, and choosing the appropriate operating wavelength and component fraction are important to achieving a more accurate rate constant. Finally, a simple scheme in experimentally determining the sensitivity of the turbidity changes with coagulation over a wavelength range is proposed.

An analysis of the effects of symmetrical tilt grain boundaries on the plastic deformation

A numerical investigation on the simple polycrystals containing three symmetrical tilt grain boundaries (GBs) is carried out within the framework of crystal plasticity which precisely considers the finite deformation and finite lattice rotation as well as elastic anisotropy. The calculated results show that the slip geometry and the redistribution of stresses arising from the anisotropy and boundary constraint play an important role in the plastic deformation in the simple polycrystals. The stress level along GB is sensitive to the load level and misorientation, and the stresses along QB are distributed nonuniformly. The GB may exhibit a softening or strengthening feature, which depends on the misorientation angle. The localized deformation bands usually develop accompanying the GB plastic deformation, the impingement of the localized band on the GB may result in another localized deformation band. The yield stresses with different misorientation angles are favorably compared with the experimental results.

An extension of the two dimensional JKR theory to the case with a large contact width

In the Hertz and JKR theories, parabolic assumptions for the rounded profiles of the sphere or cylinder are adopted under the condition that the contact radius (width) should be very small compared to the radius of the sphere or cylinder. However, a large contact radius (width) is often found in experiments even under a zero external loading. We aim at extending the plane strain JKR theory to the case with a large contact width. The relation between the external loading and the contact width is given. Solutions for the Hertz, JKR and rounded-profile cases are compared and analyzed. It is found that when the ratio of a/R is approximately larger than about 0.4, the parabolic assumptions in the Hertz and JKR theories are no longer valid and the exact rounded profile function should be used.

Toward an understanding of the molecular mechanism for successful blood feeding by coupling proteomics analysis with pharmacological testing of horsefly salivary glands

Horseflies are economically important blood-feeding arthropods and also a nuisance for humans and vectors for filariasis. They rely heavily on the pharmacological properties of their saliva to get a blood meal and suppress immune reactions of hosts. Little information is available on antihemostatic substances in horsefly salivary glands; especially no horsefly immune suppressants have been reported. By proteomics or peptidomics and coupling transcriptome analysis with pharmacological testing, several families of proteins or peptides, which act mainly on the hemostatic system or immune system of the host, were identified and characterized from 30,000 pairs salivary glands of the horsefly Tabanus yao (Diptera, Tabanidae). They are: (i) a novel family of inhibitors of platelet aggregation including two members, which possibly inhibit platelet aggregation by a novel mechanism and act on platelet membrane, (ii) a novel family of immunosuppressant peptides including 12 members, which can inhibit interferon-gamma production and increase interleukin-10 secretion, (iii) a serine protease inhibitor with 56 amino acid residues containing anticoagulant activity, (iv) a serine protease with anticoagulant activity, (v) a protease with fibrinogenolytic activity, (vi) three families of antimicrobial peptides including six members, (vii) a hyaluronidase, (viii) a vasodilator peptide, which is an isoform of vasotab identified from Hybomitra bimaculata, and interestingly (ix) two metallothioneins, which are the first metallothioneins reported from invertebrate salivary glands. The current work will facilitate the understanding of the molecular mechanisms of the ectoparasite-host relationship and help in identifying novel vaccine targets and novel leading pharmacological compounds.

Diving behaviour of freshwater finless porpoises (Neophocaena phocaenoides) in an oxbow of the Yangtze River, China

Dive-depth and swim-speed of a juvenile and an adult free-ranging, Yangtze finless porpoises (Neophocaena phocaenoides) were observed using velocity-time-depth recorders in an oxbow of the Yangtze River. In total, 8222 individual dives were recorded over 59 hours. Two dive types, deep-dive (greater than or equal to 2.7 m) and shallow-dive. were recognized. Horizontal travel distances of two finless pot-poises in a day were 94.4 km and 90.3 km, which were longer than those of oceanic relative species (harbor porpoises, Phocoena phocoena). Although the shallow water limited the maximum dive-depth, dive-duration, and bottom-time of finless porpoises were similar to the harbor porpoises. A sudden drop of swim-speed below 0.25 m s(-1) was frequently observed nearby the maximum dive-depth. This seemed to indicate "turning, around" behaviour, possibly during prey pursuit. (C) 2002 Published by Elsevier science Ltd on behalf of International Council for the Exploration of the Sea.

An investigation of the mode characteristics of SOI submicron rib waveguides using the film mode matching method

The mode characteristics of SOI (silicon-on-insulator) submicron rib waveguides are very different from those of micrometer-sized ones. Using the full-vector film mode matching method, we propose a simple criterion to determine whether a waveguide mode is guided or not. The single-mode condition for deep-etched waveguides is obtained using this criterion. We also obtain the inherent TM mode leakage and sharp cancelation effects due to TE-TM mode coupling in shallow-etched rib waveguides from numerical simulations, which agree well with the analytical results based on total internal reflection and interference theories.