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41.
The fracture surfaces of single crystal [1 0 0] silicon specimens, fractured under three-point bending (3PB) and subjected to a high strain energy upon cracking, revealed exceptional surface perturbations, generated during the unstable propagation. While macroscopically the crack is propagating on the (1 1 1) low energy cleavage plane, microscopic examination revealed small angled deviations from and fluctuations along that plane. Furthermore, while the crack is propagating at a velocity of nearly 3000 m/s in the
direction, its velocity in the
direction is two orders of magnitude lower, with distinctive surface perturbations. The amplitude and complexity of the perturbations increase as the normal velocity vector changes its direction and magnitude. These perturbations were recorded with a profilometer and analyzed using non-linear dynamical analysis tools. This study provides an opportunity to interpret surface phenomena of one of the most general cases of fracture and to study the effect of major variables on the nature of the perturbations involved, such as the local crack tip velocity and the crystallographic orientations. It is shown that the surface perturbations are chaotic deterministic in nature and can be described by high order non-linear differential equations; the order of the equation varying with the variations of the local velocity and direction. 相似文献
42.
Six oligoethylene glycols were crosslinked with triphenylmethane triisocyanate, and polymers with systematically changing network chain lengths were obtained and investigated. The 10-sec. torsion moduli versus temperature, glass transition temperatures, and cohesive energy densities of the polymers were determined and studied. The 10-sec. torsion modulus versus temperature plots show that all six polymers have a glassy transition and rubbery region of rheological behavior. The front factor calculated from the equation for the torsion modulus in the rubbery region when measured values of the modulus were used was compared with the front factor computed from equations that take into consideration molecular structures of the rubbery networks. With the exception of the case of crosslinked diethylene glycol the agreement in all the other cases between the values obtained for the front factor in both ways was good. In the investigated range of temperatures the polymers have below the glass transition temperature another transition point. The solubility parameters of the polymers, calculated from swelling experiments, were with the exception of the first member in the series almost identical. 相似文献
43.
Abstract
C18 formate ester (5) [2-(6-methyl-8-(2,6,6-trimethyl-1-cyclohexen-1-yl)-3E,5E,7E-octatrienyl formate], a highly reactive analog of retinal, was synthesized and its interaction with bacterioopsin studied. The formate ester, in the absence of purple or bleached membrane, undergoes very rapid reaction (tl/2 = 0.9 min) in neutral buffer but with membrane present it diffuses more rapidly into the membrane where it reacts slowly. Incorporation of 5 in the membrane results in a 38 nm (3900 cm-1 ) red shift which remains after reconstitution with retinal. Similar experiments with the corresponding C18 alcohol (4) results in a red shift, but this absorption blue shifts upon reconstitution with retinal. Washing the formate ester-treated membrane with bovine serum albumin or the corresponding lyophilized preparation with hexane, treatments that remove retinal oxime, fails to remove the UV-visible absorption, suggesting that a covalent bond between the C18 moiety and a nucleophilic group of the protein has probably formed. 相似文献
C
44.
Thermal cyclization of β-haloalkylidenebisbenzylcarbamates (III) and subsequent hydro-genolysis of the intermediate 4-carbobenzoxyamino-2-oxazolidinones (IV) afford 4-amino-2-oxazolidinones (V). Some of the chemical properties of the aminooxazolidinones are also described. 相似文献
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47.
In the framework of dynamic programming we provide two results:
This research was supported by the fund for the promotion of research in the technion. 相似文献
| An example where uniform convergence of theT-stage value does not imply equality of the limit and the lower infinite value. |
| Generalized Tauberian theorems, that relate uniform convergence of theT-stage value to uniform convergence of values associated with a general distribution on stages. |
48.
Ulyana Shimanovich Itai Dov Tkacz Dror Eliaz Artur Cavaco‐Paulo Shulamit Michaeli Aharon Gedanken 《Advanced functional materials》2011,21(19):3659-3666
RNA was encapsulated in bovine serum albumin (BSA) microspheres using a one‐step sonochemical process from an water–oil solvent biphasic system. Confocal microcoscopy and fluorescence‐activated cell sorting indicate that a CY3‐RNA (RNA labeled with red fluorescent indocarbocyanine Cy3 dye) sphere is encapsulated in the BSA outer sphere. The diameter of the sphere depends on the number of nucleotides of the RNA, ranging from 0.63 to 2.74 μm. Total RNA (t‐RNA) was used as a prototype for the future small interfering RNA (siRNA) delivery. A very broad size distribution characterizes the RNA spheres and therefore, among the loaded BSA spheres, there were sufficiently small spheres to be successfully introduced into trypanosoma brucei parasites and human osteosarcoma U2OS cancer cells. 相似文献
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50.
Processes of collimation of electrically charged particles near a rotating black hole are discussed. It is assumed that the black hole is immersed in a weak magnetic field aligned with rotation axis. This situation is relevant for understanding pre-collimation of astrophysical jets. The magnetic field affects the motion of material and restricts the validity of various scenarios which use the test-particle (cold plasma) approximation. A simplified criterion to estimate the relevance of this approximation is discussed in connection with the mechanism of the dissipative collimation, as proposed by de Felice and Curir. 相似文献