Fracture Paths from Front Kinetics: Relaxation and Rate Independence

Crack fronts play a fundamental role in engineering models for fracture: they are the location of both crack growth and the energy dissipation due to growth. However, there has not been a rigorous mathematical definition of crack front, nor rigorous mathematical analysis predicting fracture paths using these fronts as the location of growth and dissipation. Here, we give a natural weak definition of crack front and front speed, and consider models of crack growth in which the energy dissipation is a function of the front speed, that is, the dissipation rate at time t is of the form

长杆弹超高速侵彻半无限混凝土靶实验研究及开坑分析

随着超高速动能武器的发展,长杆弹超高速侵彻混凝土靶机理成为当前的研究热点。为了探究长杆弹超高速侵彻混凝土靶的侵彻机理和开坑规律,本文中开展了TU1铜、Q235钢两类长杆弹以初速度1.8～2.4 km/s正侵彻强度26.5、42.1 MPa混凝土靶的超高速实验。结合文献和本文中的实验数据,对开坑直径和开坑体积进行量纲分析,基于开坑截面的弓形形貌几何关系,得到了开坑深度预测公式。结果表明：靶面开坑尺寸明显大于中低速侵彻时的靶面开坑尺寸,在分析侵彻机理的过程中不能忽略开坑阶段;弹体发生严重的长度缩短,直至最后完全侵蚀,弹洞半径明显大于弹体半径,说明长杆弹超高速侵彻半无限混凝土靶属于半流体侵彻机制。另外,在超高速侵彻条件下：弹体长度是影响侵彻深度的最主要参数;侵彻深度随弹体长度和密度的增大而增大,受弹体强度影响不大。

     

Thermodynamics of the Dimer Formation of 2I,3I-O-(o-Xylylene)-per-O-Me-γ-cyclodextrin: Fluorescence, Molecular Mechanics and Molecular Dynamics

The thermodynamics of the dimer formation of 2^I,3^I-O-(o-xylylene)-per-O-Me-γ-cyclodextrin (XmγCD) in aqueous solution was studied by fluorescence techniques, Molecular Mechanics and Molecular Dynamics. Lifetime averages á t ñ \left\langle \tau \right\rangle , obtained from fluorescence decay profiles upon excitation of the xylylene appended group, were used as the property sensitive to the association process. The dimerization equilibrium constants (K _D) were obtained from non-linear regression analysis of the plots of á t ñ \left\langle \tau \right\rangle against [XmγCD] at several temperatures and they were compared with the values obtained for the counterparts Xmα- and XmβCDs. The van’t Hoff plot allows us to obtain the ΔH and ΔS showing that the dimerization process was also entropically disfavoured. Molecular Mechanics as well as Molecular Dynamics calculations in the presence of water were also employed to study the conformational behaviour of isolated XmγCDs, the possible structure of the dimers formed and the driving forces involved in such association processes. Results indicate that those conformations where Xy moiety does not block the cavity entrance are favoured. Dimers are preferably formed by head-to-head CD approaching. However, the formation of stable head-to-tail is not dismissed.     

Elastic scattering of neutrons on natPb at forward angles

Angular distributions were measured for neutron elastically scattered by ^natPb at 2.9, 3.0, 3.1, 3.2 and 3.4MeV at very forward angles. The mono-energetic neutron flux was produced at the tandem accelerator facility of the National Institute of Nuclear Research (ININ), Mexico, using the Associated Particle Technique (APT) in the D(d, n)³He reaction. Optical model predictions with best potential systematic show a fairly good agreement with our data, and also the need for a better understanding of the neutron scattering process at very small angles from the theoretical point of view.     

Two-Parameter Stochastic Resonance in a Model of Electrodissolution of Fe in H_2SO_4

IntroductionStochastic resonance (SR) is a nonlinear effect which describes the optimal detection of a weak periodic signal by the action of external noise in nonlinear systems. SR was originally proposed to account for periodicity in the Earth's ice ages1, and it has been observed in a wide range of biological2-4 , physical5 and chemical6 systems. The systems mentioned above which may give rise to SR have a denominator despite many examples of SR in different scientific areas. It is noted…     

工科物理实验教学改革的实践与探索

介绍了近年来华中科技大学物理实验中心教学改革的历程及构建物理实验创新基地的思路和体会．     

New triazole antifungal agents derived from mercaptomethylisoxazoles

Several new triazole antifungal agents derived from mercaptomethylisoxazoles of general structure 2(2,4-dihalogenophenyl)-3-((X-isoxazolyl)methylthio)-(1,2,4-triazol-1-yl)-2-propanol, as well as some selected sulfoxides and sulfones derived thereof, have been synthesized and tested for antifungal activity. Some of these compounds showed good activity against yeasts and dermatophytes.     

Elucidating a particulate matter deposition episode by combining scanning electron microscopy and X-ray fluorescence spectrometry.

Multielemental composition and morphology of particulate matter samples were examined to detect the presence of two potential responsible pollutant emitters at four sites impacted during a pollution episode in the City of Campana, Argentina. Coke and smoke black are the main constituents associated to the industrial plants that were considered, a priori, as responsible pollutant emitters. Wavelength dispersive X-ray fluorescence (WDXRF) was employed for the analysis of metals in samples coming from both, suspected sources and four sites. On the basis of multielemental composition profiles, a screening analysis was undertaken for exploring similarities among sources and sample sites adopting the average concentration profile of the crustal rock as soil surrogate. Particle morphology was studied by scanning electron microscopy (SEM) in source samples and in those environmental samples selected through the screening analysis. Two types of collected samples were analyzed: 1) those with composition profiles closer to the potential sources and 2) those closer to the cluster rock. This strategy was adequate to identify the responsible source of the contamination episode.