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221.
S.E.-S. Abd El-Ghany 《Optics Communications》2009,282(2):284-290
The two-dimensional integral Laplace transform technique has been applied to get the temperature distributions in the molten layer, the solid part and in the backward surface of a finite target irradiated with a pulsed laser. Formulas for the time dependence of the evaporated part and the molten layer thicknesses of the target were found. This is accomplished by considering the temperature dependence of the absorption coefficient of the irradiated surface as well as the chemical reaction. As an illustrative example computations were carried out on an aluminum (Al) target. 相似文献
222.
NMR cryoporometry: Principles, applications and potential 总被引:3,自引:0,他引:3
Oleg V. Petrov 《Progress in Nuclear Magnetic Resonance Spectroscopy》2009,54(2):97-122
223.
Weiping Li Yuejin Zhu Dayin Hua Peiqing Wang Xiaorong Chen Jie Shen 《Applied Surface Science》2008,254(22):7321-7325
To further understand the crystallization behavior from melts of P(VDF-TrFE) (70/30) copolymer, the morphologies of P(VDF-TrFE) copolymer thin and ultra-thin films are studied by AFM. It is found that P(VDF-TrFE) (70/30) copolymer films exhibit morphologic transition from big grains to fiber-like rods above melting point. And this may be on account of the molecule chains plastic flow and self-organization, corresponding to polymer homoepitaxy. 相似文献
224.
225.
技术考试项目的设计对科学全面地评价学生技能的掌握程度以及教师的教学水平起着重要作用.本文运用聚类分析方法详细分析了篮球技术考试项目的设计问题,为客观反映评价教学质量提供了科学依据. 相似文献
226.
A statistical approach has been developed for modeling the dynamic response of brittle materials by superimposing the effects of a myriad of microcracks, including opening, shear, growth and coalescence, taking as a starting point the well-established theory of penny-shaped cracks. This paper discusses the general approach, but in particular an application to the sensitivity of explosives and propellants, which often contain brittle constituents. We examine the hypothesis that the intense heating by frictional sliding between the faces of a closed crack during unstable growth can form a hot spot, causing localized melting, ignition, and fast burn of the reactive material adjacent to the crack. Opening and growth of a closed crack due to the pressure of burned gases inside the crack and interactions of adjacent cracks can lead to violent reaction, with detonation as a possible consequence.This approach was used to model a multiple-shock experiment by Mulford et al. [1993. Initiation of preshocked high explosives PBX-9404, PBX-9502, PBX-9501, monitored with in-material magnetic gauging. In: Proceedings of the 10th International Detonation Symposium, pp. 459-467] involving initiation and subsequent quenching of chemical reactions in a slab of PBX 9501 impacted by a two-material flyer plate. We examine the effects of crack orientation and temperature dependence of viscosity of the melt on the response. Numerical results confirm our theoretical finding [Zuo, Q.H., Dienes, J.K., 2005. On the stability of penny-shaped cracks with friction: the five types of brittle behavior. Int. J. Solids Struct. 42, 1309-1326] that crack orientation has a significant effect on brittle behavior, especially under compressive loading where interfacial friction plays an important role. With a reasonable choice of crack orientation and a temperature-dependent viscosity obtained from molecular dynamics calculations, the calculated particle velocities compare well with those measured using embedded velocity gauges. 相似文献
227.
Y. Okano T. Suzumura S. Sakai Y. Hayakawa M. Kumagawa A. Hirata S. Dost 《Mechanics Research Communications》2004,31(5):605-610
The effect of coexistence of Marangoni and natural convections was studied numerically in melting of a GaSb/InSb/GaSb sandwich sample. Fluid flow and concentration fields are oscillatory when the solutal natural convection coexists with the thermal Marangoni convection. The coexistence of solutal and thermal natural convections, without Marangoni convection, however, does not lead to fluid flow oscillations in spite of the existence of two flow cells in opposite directions. The conclusion is that not the presence of two opposite flow cells but the flow structure itself, due to the presence of a free surface, is responsible for such an oscillatory behaviour. 相似文献
228.
用Voronoi图进行新型自然邻居插值的几何学方法与特性 总被引:2,自引:0,他引:2
新的基于Voronoi图的Natural Neighbour插值是自然单元法的数学基础,也是一种新型的几何插值方法,具有与其他传统常用插值不同的构造方法,并表现出一定的优越性。本文介绍了基于Natural Noighbour关系的Sibson插值和non-Sibsonian插值,并与有限元法和无单元法所用的插值方法,就离散插值方案和网格总体特性、形函数支撑域、本征边界条件、空间维数扩展与计算工作量等诸问题进行了比较分析。 相似文献
229.
Mismatch binding molecules (MBLs), strongly and selectively bound to the mismatched base pair in duplex DNA, were immobilized
on Sepharose. Three MBL–Sepharose columns were prepared with three MBLs, naphthyridine dimer (ND), naphthyridine–azaquinolone (NA), and aminonaphthyridine dimer (amND), which exhibited different binding profiles to the mismatched base pairs. These three MBL–Sepharose columns showed characteristic
elution profiles for DNA duplexes containing mismatched base pairs. The ND–Sepharose column separated the G–G and G–A mismatched DNA from fully matched duplexes. The NA–Sepharose column separated the A–A and G–A mismatched DNA from other DNA duplexes. The amND–Sepharose column separated the C–C mismatched DNA. These chromatographic profiles were very consistent with the binding preference
of each MBL. By changing the elution conditions from sodium hydroxide to sodium chloride, MBL–Sepharose columns were also
able to separate the mismatched DNA that weakly bound to the MBL from fully matched DNA duplex.
Figure MBL-Sepharose affinity chromatography successfully separates the mismatched duplex DNA from fully matched duplex. 相似文献
230.
The changes in crystallite orientation during melting of oriented ultra-high-molecular-weight polyethylene (UHMW PE) were
investigated by means of wide-angle X-ray scattering. The orientation distribution of crystallites in drawn UHMW PE is composed
of two components differing in width. The narrow and broad components revealed in this study indicate the existence of two
classes of crystallites with different orientability. Some of the crystallites are oriented almost perfectly even at low-draw
ratios, while the others do not orient so effectively. The analysis of melting behaviour of such a texture composed of orthorhombic
crystals indicates that highly oriented crystallites are formed by taut molecules and transform first to the hexagonal phase,
while the molecules constituting low-oriented crystallites melt directly to the typical amorphous phase. The increase in orientation
of highly oriented crystallites during their partial melting, observed in the samples kept at constant length and even those
allowed to shrink under constant load, can be explained by the kinetic factor proposed by Ziabicki.
Received: 11 September 1998 Accepted in revised form: 18 February 1999 相似文献