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961.
Amorphous polymers are viscoelastic materials. When they are subjected to dynamical loads, their behavior can be modeled by transform functions of stress and strain in the complex plane. In our work, a model based on the fractional calculus concept is proposed in order to predict the viscoelastic behavior of polymethylmethylacrylate (PMMA) over a wide temperature range between (Tg -190°C) and (Tg +15°C). The extended fractional solid model is shown to be capable of describing experimentally observed dynamic viscoelastic behavior over a wide temperature range, including multiple relaxations, using a limited number of free parameters. Structural recovery of PMMA was studied by dynamic mechanical spectrometry, and its effect on the different parameters is also discussed. Furthermore, from the fractional differential and fractional integral formulations. most of the relevant viscoelastic functions that quantify the degree of molecular mobility of amorphous polymers, like E(t), E?(τ). and H(t), can be derived analytically. 相似文献
962.
数值地震预测的关键物理问题* 总被引:2,自引:0,他引:2
数值地震预测是地震物理研究中的一个重要课题,具有基础性的科学意义和潜在的应用价值.文章介绍了数值地震预测的三个关键物理问题——地震发生率与应力变化的关系、地震断层的摩擦函数、地球中应力的传递问题,讨论了这些问题的意义、研究现状和发展趋势. 相似文献
963.
Shan-Yang Lin 《应用光谱学评论》2013,48(1):11-63
AbstractOcular calcification is a biological mineralization. It is also a well-known human ophthalmic disease but is a complex process because the pathophysiology of calcium deposition in ocular tissues depends on site-specific factors. Calcified deposits in the eyes are asymptomatic lesions; a serious consequence of ocular plaques is the potential partial or total loss of vision in the affected eye. Therefore, a better understanding of the exact compositional components and origin of calcified plaques in different eye tissues is necessary and merits exploration. The present review article includes information on different diagnostic or analytical techniques to examine human ocular calcification collected and compiled from 2005 to 2013, together with data on the application of vibrational spectroscopy in ophthalmology studies from 1990 onwards. This overview of ocular calcification is mainly focused on two aspects: the pathogenesis and mechanism of calcification in different ocular tissues and biomedical applications of vibrational spectroscopy to spectral biodiagnosis of eye tissues. A summary of the in vitro, in situ, and in vivo spectral information that is expected to assist physicians in the diagnosis and treatment of patients or satisfy patients of the clinical competence of the diagnosis is provided. 相似文献
964.
965.
H. D. Hochheimer F. Widulle J. Th. Held G. Strehl R. T. Kotitschke A. R. Adams 《高压研究》2013,33(1-6):41-48
Abstract We present the design of a device for the simultaneous application of uniaxial stress and hydrostatic pressure. This new apparatus will for the first time allow measurements at constant strain. Results of the simultaneous application of uniaxial stress and hydrostatic pressure to a semiconductor laser are presented and discussed. 相似文献
966.
R. Otto P. Hecht H. Ulrich H. Hāntzschel 《Isotopes in environmental and health studies》2013,49(4):120-123
Bei technischen Tracerexperimenten bereitet die Markierung von Gasphasen Schwierigkeiten, wenn man auf Außenwandmessungen angewiesen ist, da die Auswahl an geeigneten Radionukliden bzw. radioaktiv markierten Verbindungen dann sehr beschrānkt ist. Eine gute Ergänzung des Radionuklidangebotes für den genannten Zweck bietet 133mXe, Halbwertszeit 2,3 d, Eγ = 0,23 MeV (16%). 133mXe erhält man mit guten Ausbeuten bei einer Reaktoraktivierung von natürlichem Xenon. Die Sälligungsaktivität fär 133mXe beträgt bei einem Fluß von 5,0 μ 1013 n/cm2s 48,5 mCi/cm3 Xenon (unter Normalbedingungen). An Veweilzeitmessungen von Gasphasen in technischen Anlagen werden die Einsatzmöglichkeiten des 133mXe dargestellt. 相似文献
967.
Wilto Kesternich 《辐射效应与固体损伤》2013,168(1-4):261-273
Helium bubble formation was observed in austenitic stainless steels by transmission electron microscopy following implantation of 30 to 1000 appm helium at room temperature and annealing at 700 to 800°C. Helium bubble distributions at dislocations and at various grain boundaries and precipitates were studied. It was found that interfacial dislocations play a dominant role in bubble nucleation at grain and interphase boundaries but not at Tic-matrix interfaces. Particularly high trapping of helium was observed at Tic precipitate-matrix interfaces which is attributed to an inhomogeneous ripening mechanism. 相似文献
968.
We consider a two-dimensional homogeneous elastic state in the arch-like region a?≤?r?≤?b, 0?≤?θ?≤?α, where (r,θ) denotes plane polar coordinates. We assume that three of the edges are traction-free, while the fourth edge is subjected to a (in plane) self-equilibrated load. The Airy stress function ‘?’ satisfies a fourth-order differential equation in the plane polar coordinates with appropriate boundary conditions. We develop a method which allows us to treat in a unitary way the two problems corresponding to the self-equilibrated loads distributed on the straight and curved edges of the region. In fact, we introduce an appropriate change for the variable r and for the Airy stress functions to reduce the corresponding boundary value problem to a simpler one which allows us to indicate an appropriate measure of the solution valuable for both the types of boundary value problems. In terms of such measures we are able to establish some spatial estimates describing the spatial behavior of the Airy stress function. In particular, our spatial decay estimates prove a clear relationship with the Saint-Venant's principle on such regions. 相似文献
969.
Manuel A.P. Segurado Margarida F.B. Silva Rita Castro 《International Journal of Mathematical Education in Science & Technology》2013,44(5):664-679
The mathematical language and its tools are complementary to the formalism in chemistry, in particular at an advanced level. It is thus crucial, for its understanding, that students acquire a solid knowledge in Calculus and that they know how to apply it. The frequent occurrence of indeterminate forms in multiple areas, particularly in Physical Chemistry, justifies the need to properly understand the limiting process in such cases. This article emphasizes the importance of the L’Hôpital's rule as a practical tool, although often neglected, to obtain the more common indeterminate limits, through the use of some specific examples as the radioactive decay, spectrophotometric error, Planck's radiation law, second-order kinetics, or consecutive reactions. 相似文献
970.