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991.
C. L. J. A. Verbraak J. Van Dam A. K. Van Der Vegt 《Polymer Engineering and Science》1985,25(7):431-433
Orientation-induced crystallization of crystallizable polymer melts can occur, under certain conditions, during flow through converging channels. Attempts have been made to achieve this phenomenon in a two-phase system, i.e., during simultaneous extrusion of a continuous concentric core of polypropylene within a polystyrene matrix through a conical duct. On one occasion, using Carlona P SY6100 (MFI = 11.0) with Hostyren N2000-V-01 (MFI = 25.0), a highly oriented polypropylene thread with a modulus of 14.6 GPa and a melting point of 178°C was extruded at a die temperature of approximately 170°C and a pressure lower than 40 MPa. It is, in principle, possible to form highly oriented, fiber-like structures as reinforcing elements in a polymer matrix. 相似文献
992.
993.
The relationship between hydrogen concentration precipitated as hydride particles and ultrasonic parameters, such as velocity and attenuation, was examined in Zircaloy-4 samples for potential applications in the Non-Destructive Test Field. Different amounts of hydrogen (up to 517 ppm) were introduced in the samples by gaseous charging. Ultrasonic attenuation measurements were performed with compressive waves at frequencies of 10 and 30 MHz, and propagation velocity measurements were performed at 10 MHz. Ultrasonic velocity showed an approximately linear increase with hydrogen concentration and it could be used as an assessment parameter when the hydrogen level is high enough. Attenuation versus hydrogen concentration has been fitted by a logarithmic equation at 10 MHz. At 30 MHz a fluctuating behavior of the attenuation prevented measurement of the hydrogen concentration. 相似文献
994.
Collaborative work is an important part of tertiary education but it is very difficult to arrange and supervise for extremely large classes of students in their first year. The possibility that computer-mediated communication can be used to facilitate this type of learning is appealing from a pragmatic organisational point of view. This paper explains in detail what a ‘virtual team’ is in the educational context. It reports on an interpretive field study where students taking an introductory course were allowed to choose where and when they did the required collaborative work. The paper discusses the factors that should be taken into account when offering students the option of working as a virtual team. These include factors that influence the students’ choice. The project cannot be considered to have been successful but indicates reasons for the lack of success and suggests contexts in which it would be valuable to repeat the project. The importance of extensive preparation in terms of teaching the students necessary social and technological skills cannot be over emphasised. 相似文献
995.
Emulsification is an undesired phenomenon in the refining of highly acidic oil by alkali-washing electro-refining. In this article, a novel microwave method is applied for demulsification in the removing of naphthenic acid from diesel oil. The internal heating is attributed to molecular rotation and ionic conduction. The decrease of interface zeta-potential and the viscosity of diesel oil are responsible for the demulsification with microwave irradiation. The results exhibited that the demulsification rate is maximized when the optimum microwave irradiation power, exposure time, and irradiation pressure for Anshan and Liaohe diesel oil are deemed to be 375 W, 5/6 min and 0.05 MPa, respectively. 相似文献
996.
P.U. Sharma K.B. Modi V.K. Lakhani K.B. Zankat H.H. Joshi 《Ceramics International》2007,33(8):1543-1546
Compositional dependence of hyperfine parameters, determined through Mössbauer spectral analysis has been studied for Y3−xFe5+xO12 (x = 0.0, 0.1, 0.3 and 0.5) garnet system at 300 K. The Mössbauer spectra have been fitted with three sextets in the ferrimagnetic state corresponding to Fe3+ ions at tetrahedral (d), octahedral (a) and dodecahedral (c) sites of the crystal structure. It is observed that isormershift, quadrupole shift and hyperfine field of d-site show no significant variation with Fe3+ concentration. The change in hyperfine fields of a- and c-sites with composition (x) has been explained on the basis of strength of exchange integrals, change in isomershift can be understood due to s-electron charge distribution and asymmetric displacement of oxygen ions surrounding the a- and c-sites seems to be responsible for observable quadrupole shift. The magneton number values obtained from magnetization and Mossbauer data are in agreement to those calculated using Neel's three sublattice model of ferrimagnetism. 相似文献
997.
In this work, the filiform corrosion behaviour of powder painted aluminium profiles was studied, and the coating barrier properties together with adhesion to the substrate were analysed. Samples coated with a traditional painting procedure (one powder layer application followed by curing), and other samples coated using a special cycle to obtain wood grain effect were compared using accelerated filiform corrosion tests. Moreover, in order to better understand the degradation mechanisms of painted metal substrates, thermal stresses were applied to accelerate the natural weathering. The effects of the thermal aging were analysed by electrochemical impedance spectroscopy. 相似文献
998.
I. V. Shcherbatenko E. P. Ivanova V. I. Surikov 《Chemical and Petroleum Engineering》2007,43(5-6):335-342
A method is proposed for calculating the optimum density of lattice of blades of screw pump impeller that ensures, for a given
cavitation margin (inlet pressure), the first critical condition on the partial cavitation characteristic of the pump. The
equations obtained can be used also to calculate the permissible cavitation margin of screw centrifugal and screw mixed-flow
pumps as well as of stand-alone screw impeller, provided the geometric and operating conditions of the screw are given.
__________
Translated from Khimicheskoe i Neftegazovoe Mashinostroenie, No. 6, pp. 29–33, June, 2007. 相似文献
999.
1000.