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81.
M. W. Richman C. S. Chou 《Zeitschrift für Angewandte Mathematik und Physik (ZAMP)》1988,39(6):885-901
Summary We obtain boundary conditions for two-dimensional flows of identical, nearly elastic, circular disks that interact with a flat wall to which identical, evenly spaced half-disks have been attached. Expressions for the transfer of momentum and energy from the boundary to the flow are obtained by statistical averaging over all possible wall-flow disk collisions. We improve upon the expressions derived by Jenkins and Richman [1986] by employing in the averaging process a more elaborate velocity distribution function obtained through the method of moments. In addition we expand the distribution function about a point near the flat wall that guarantees positive slip velocities. With these boundary conditions, we analyze a two-dimensional shear flow driven by parallel bumpy boundaries. The constitutive theory employed includes both the effects of particle collisions and particle transport on the transfer of momentum and energy throughout the flow. We demonstrate how the resulting profiles of velocity, granular temperature, and solid fraction are affected by changes in the geometry of the boundary. We also predict how the induced stresses vary with the geometry of the boundary and the average solid fraction within the flow.
Zusammenfassung Wir erhalten die Randbedingungen für die zweidimensionale Strömung identischer, beinahe elastischer, runder Scheiben, die sich in Wechselwirkung mit einer geraden Wand befinden, an der in gleichmäßigen Abständen Halbscheiben angebracht sind. Es werden Ausdrücke für die Übertragung von Impuls und Energie vom Rand auf den Strom aufgestellt, die durch den statisch errechneten Durchschnitt aller möglichen Scheibenkollisionen Wand-Strom erhalten werden. Wir verbessern die von Jenkins und Richman (1986) entwickelten Ausdrücke dadurch, daß bei der Berechnung der Mittelwerte eine erweiterte Geschwindigkeitsverteilung, die auf der Momentmethode beruht, einbezogen wurde. Außerdem entwickeln wir die Verteilungsfunktion an einem Punkt so nahe an der Wand, daß positive Gleitgeschwindigkeiten garantiert sind. Wir untersuchen eine zweidimensionale Scherströmung mit diesen Randbedingungen, die durch die parallelen unebenen Ränder getrieben wird. Die konstitutive Theorie, die wir anwenden, beinhaltet sowohl den Einfluß der Teilchenkollisionen als auch den des Teilchentransports auf die Übertragung von Impuls und Energie innerhalb der Strömung. Wir zeigen, wie die Profile der Geschwindigkeit, der Granu-lartemperatur und des Festkörperanteils, die sich ergeben, durch Veränderungen der Randgeometrie beeinflußt werden. Weiterhin können wir voraussagen, wie die erzeugten Spannungen sich mit der Randgeometrie und dem im Strom enthaltenen Festkörperanteil verändern.相似文献
82.
83.
A simple and rapid polyamide chromatographic method for the detection of 12 kinds of preservatives and 3 kinds of artificial sweeteners were reported. The results indicated that the method was good in sensitivity, separability and reproducibility. 相似文献
84.
A newly developed self-consistent-field molecular orbital theory is described and tested. The intermediate neglect of differential overlap (INDO) approximation is used, and all interaction integrals are differentiated according to their dependence upon 2s and 2p AO's. The bonding parameter βl is reformulated so that the model is calibrated to only one specific molecular property, namely, the ionization energy of Hi. We expect that this model will not be biased toward any special families of molecules. 相似文献
85.
[reaction: see text] Rigid U-shaped molecules containing syn-facially situated quinoxaline rings have been synthesized in three steps, by a combination of the Diels-Alder reaction, the ruthenium-catalyzed oxidation, and the Zn(OAc)(2)-catalyzed condensation of the resulting bis-alpha-diketones with benzene-1,2-diamines. The unsymmetric bis-quinoxalines, with electronically different substituents, and the quinoxaline ring-attached alpha-diketones were also prepared. Their luminescence properties were examined and described. 相似文献
86.
Nafion membranes are used as semisolid electrolytes in methanol and hydrogen fuel cells. The ion conduction takes place through those hydrophilic channels in the Nafion that can provide continuous pathways through the membrane. There is as yet limited information about the density, the size, and the shape of these channels. We have developed two electrochemical methods of visualizing the pore structure which involve the creation of metal lithographs using the membrane pores as templates. In the experiments, the membrane is supported on a flat solid surface on one side, and is in contact with an electrolyte on the other side. Using hydrogen-terminated n-doped Si(111), we deposited gold from an electrolyte containing a gold salt. The Au ions traverse the membrane through the pores, reach the silicon surface, and are spontaneously reduced. A metallic Au deposit is formed on the silicon surface, at the base of the hydrophilic channel. The Au deposits are imaged after the membrane is dissolved. Another method involves supporting the membrane on a Pt surface and depositing silver wires through the hydrophilic channels of the membrane. The scanning electron microscope pictures of these wires provide an image of the size and the shape of the hydrophilic channels. 相似文献
87.
Hydrogenation-induced metal-semiconductor transitions usually occur in simple systems based on rare earths and/or magnesium, accompanied by major reconstructions of the metal host (atom shifts >2 A). We report on the first such transition in a quaternary system based on a transition element. Metallic LaMg2Ni absorbs hydrogen near ambient conditions, forming the nonmetallic hydride LaMg2NiH7 which has a nearly unchanged metal host structure (atom shifts <0.7 A). The transition is induced by a charge transfer of conduction electrons into tetrahedral [NiH4]4- complexes having closed-shell electron configurations. 相似文献
88.
We probed the local electronic properties of the mixed-valent Co+4-x triangular lattice in NaxCoO2.yH(2)O by 59Co NMR. We observed two distinct types of Co sites for x > or =1/2, but the valence seems averaged out for x approximately 1/3. Local spin fluctuations exhibit qualitatively the same trend down to approximately 100 K regardless of the carrier concentration x, and hence the nature of the electronic ground state. A canonical Fermi-liquid behavior emerges below approximately 100 K only for x approximately 1/3. 相似文献
89.
Water surface fluctuations were analyzed using image sequences from a CCD (charge coupled device) camera. Both regular and irregular waves were used for the study. A transfer function is obtained by comparing the gray scales of the image and results of in-situ wave gauge array measurements. The effects of non-uniform illumination within the wave basin are imbedded in the transfer function. Thus, the obtained transfer function is directly applicable to all other areas of interests within the wave basin. Estimated wave heights are all in qualitative agreement with those obtained through direct measurements. It is shown that the averaged relative error between these two wave heights is less than 16%. 相似文献
90.
Alternating layer and island growth of Pb on Si by spontaneous quantum phase separation 总被引:2,自引:0,他引:2
Hong H Wei CM Chou MY Wu Z Basile L Chen H Holt M Chiang TC 《Physical review letters》2003,90(7):076104
Real-time in situ x-ray studies of continuous Pb deposition on Si(111)-(7x7) at 180 K reveal an unusual growth behavior. A wetting layer forms first to cover the entire surface. Then islands of a fairly uniform height of about five monolayers form on top of the wetting layer and grow to fill the surface. The growth then switches to a layer-by-layer mode upon further deposition. This behavior of alternating layer and island growth can be attributed to spontaneous quantum phase separation based on a first-principles calculation of the system energy. 相似文献