A contact crack problem in an infinite plate

The problem of an infinite plate with crack of length 2a loaded by the remote tensile stress P and a pair of concentrated forces Q is discussed. The value of the force Q for the initial contact of crack face is investigated and the contact length elevated, while the Q force increases. The problem is solved assuming that the stress intensity factor vanishes at the end point of the contact portion. By the Fredholm integral equation for the multiple cracks, the reduction of stress intensity factor due to Q is found. (C) 1999 Elsevier Science Ltd. All rights reserved.

Elastodynamic stress intensity factor history for a semi-infinite crack under three-dimensional transient loading

The dynamic stress intensity factor history for a semi-infinite crack in an otherwise unbounded elastic body is analyzed. The crack is subjected to a pair of suddenly-applied point loadings on its faces at a distance L away from the crack tip. The exact expression for the mode I stress intensity factor as a function of time is obtained. The method of solution is based on the direct application of integral transforms, the Wiener-Hopf technique and the Cagniard-de Hoop method. Due to the existence of the characteristic length in loading this problem was long believed a knotty problem. Some features of the solutions are discussed and graphical result for numerical computation is presented.

Compressible laminar boundary-layer flows of a dusty gas over a semi-infinite flat-plate

The compressible laminar boundary-layer flows of a dilute gas-particle mixture over a semi-infinite flat plate are investigated analytically. The governing equations are presented in a general form where more reasonable relations for the two-phase interaction and the gas viscosity are included. The detailed flow structures of the gas and particle phases are given in three distinct regions : the large-slip region near the leading edge, the moderate-slip region and the small-slip region far downstream. The asymptotic solutions for the two limiting regions are obtained by using a seriesexpansion method. The finite-difference solutions along the whole length of the plate are obtained by using implicit four-point and six-point schemes. The results from these two methods are compared and very good agreement is achieved. The characteristic quantities of the boundary layer are calculated and the effects on the flow produced by the particles are discussed. It is found that in the case of laminar boundary-layer flows, the skin friction and wall heat-transfer are higher and the displacement thickness is lower than in the pure-gas case alone. The results indicate that the Stokes-interaction relation is reasonable qualitatively but not correct quantitatively and a relevant non-Stokes relation of the interaction between the two phases should be specified when the particle Reynolds number is higher than unity.

Radical Scavenging and Antimicrobial Activities of Methanol Extracts of Two Kinds of Formicary

对两种不同的蚂蚁窝进行甲醇提取,并对提取物进行了急性毒性、抗自由基,酚含量、还原能力和抗菌活性的检测。二苯基三硝基肼(1,1-diphenyl-2-picrylhydrazyl,DPPH)自由基的清除能力的检测表明:两种蚂蚁窝甲醇提取物都具有显著的自由基清除能力,并呈现出剂量依赖性,而且,在高浓度时(5~10mg·mL-1),它们的自由基清除能力甚至显著地高于二丁基羟基甲苯(butylated hydroxyl toluene,BHT)。酚的含量和还原能力分别用福林酚试剂和铁氰化钾还原反应来测定,统计分析显示两种蚂蚁窝的抗氧化能力和其酚含量、还原能力都存在着正相关。两种蚂蚁窝甲醇提取物都具有抗革兰氏阴性菌和革兰氏阳性菌的活性,但它们却对真菌没有作用。

Frog skins keep redox homeostasis by antioxidant peptides with rapid radical scavenging ability

The question of how amphibians can protect themselves from reactive oxygen species when exposed to the sun in an oxygen-rich atmosphere is important and interesting, not only from an evolutionary viewpoint, but also as a primer for researchers interested in mammalian skin biology, in which such peptide systems for antioxidant defense are not well studied. The identification of an antioxidant peptide named antioxidin-RL from frog (Odorrana livida) skin in this report supports the idea that a peptide antioxidant system may be a widespread antioxidant strategy among amphibian skins. Its ability to eliminate most of the 2,2'-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) radical tested within 2 s, which is much faster than the commercial antioxidant factor butylated hydroxytoluene, suggests that it has a potentially large impact on redox homeostasis in amphibian skins. Cys10 is proven to be responsible for its rapid radical scavenging function and tyrosines take part in the binding of antioxidin-RL to radicals according to our nuclear magnetic resonance assay. (C) 2010 Elsevier Inc. All rights reserved.

Free radical scavenging and antioxidant enzymes activation of polysaccharide extract from Nostoc sphaeroides

Nostoc sphaeroides Kuetzing has been used as a traditional medicine in China to treat a variety of ailments. This research identified the antioxidant activities of polysaccharide extract from Nostoc sphaeroides. The extract, which contains 46.2% carbohydrates, exhibited an effective scavenging capability on superoxide radical, hydroxyl radicals in non site-specific as well as site-specific assays, and also performed lipid peroxidation inhibition in a dose-dependent manner. Polysaccharide extract had no 1,1-diphenyl-2-picrylhydrazyl radical scavenging potential at all test concentrations. Activities of superoxide dismutase, catalase, and glutathione peroxidase in human embryo kidney 293 cells were increased effectively when Nostoc sphaeroides extract was applied. These results suggested that the use of N. sphaeroides in treating ailments may be based on the antioxidant capacities of polysaccharide composition.

Spontaneous emission lifetime distribution of infinite line antennas in two-dimensional photonic crystals with finite size

The authors calculate the lifetime distribution functions of spontaneous emission from infinite line antennas embedded in two-dimensional disordered photonic crystals with finite size. The calculations indicate the coexistence of both accelerated and inhibited decay processes in disordered photonic crystals with finite size. The decay behavior of the spontaneous emission from infinite line antennas changes significantly by varying factors such as the line antennas' positions in the disordered photonic crystal, the shape of the crystal, the filling fraction, and the dielectric constant. Moreover, the authors analyze the effect of the degree of disorder on spontaneous emission. (c) 2007 American Institute of Physics.

Side radical influence on the nonlinear optical properties and thermal stability of poled polymer films

Films of polyetherketone doped with the chromophores Disperse Red 1 (DR1) and Disperse Red 13 (DR13) were prepared by spin-coating method. By the in situ Second-harmonic Generation (SHG) signal intensity measurement, the optimal poling temperatures were obtained. For the investigated polyetherketone polymer doped with DR1 (DR1/PEK-c) and polyetherketone polymer doped with DR13 (DR13/PEK-c) films, the optimal poling temperatures were 150degreesC and 140degreesC, respectively. Under the optimal poling conditions, the high second-order nonlinear optical coefficient chi(33)((2)) = 11.02 pm/V has been obtained for the DR1/PEK-c; and for DR13/PEK-c at the same conditions the coefficient is 17.9 pm/V. The SHG signal intensity DR1/PEK-c could maintain more than 80% of its initial value when the temperature was under 100degreesC, and the SHG signal intensity of the DR13/PEK-c could maintain more than 80% of its initial value when the temperature was under 135degreesC. (C) 2002 Kluwer Academic Publishers.

An algorithm of analysis tools on points distribution in high dimension space: The distance of a point and an infinite sub-space

This paper discusses the algorithm on the distance from a point and an infinite sub-space in high dimensional space With the development of Information Geometry([1]), the analysis tools of points distribution in high dimension space, as a measure of calculability, draw more attention of experts of pattern recognition. By the assistance of these tools, Geometrical properties of sets of samples in high-dimensional structures are studied, under guidance of the established properties and theorems in high-dimensional geometry.