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991.
L. -E. Andersson 《Applied Mathematics and Optimization》2000,42(2):169-202
We prove the existence of a solution for an elastic frictional, quasistatic, contact problem with a Signorini non-penetration
condition and a local Coulomb friction law. The problem is formulated as a time-dependent variational problem and is solved
by the aid of an established shifting technique used to obtain increased regularity at the contact surface. The analysis is
carried out by the aid of auxiliary problems involving regularized friction terms and a so-called normal compliance penalization
technique.
\par
Accepted 15 May 2000. Online publication 6 October 2000. 相似文献
992.
Hedberg C Källström K Brandt P Hansen LK Andersson PG 《Journal of the American Chemical Society》2006,128(9):2995-3001
New chiral bidentate phoshine thiazoles have been prepared and successfully applied as ligands in the homogeneous iridium-catalyzed asymmetric hydrogenation of aryl alkenes and aryl alkene esters. The ligands are designed to be highly modular and have one common chiral intermediate, from which diversity can be introduced at a late stage in the synthetic pathway. It was found that a six-member-ring backbone of the rigid ligand structure was preferred over seven- or five-member rings. In this study it is shown that the substituent pattern of the ligands has a major influence on the stereochemical outcome of the products. By applying the selectivity model proposed in this study, it is possible to match different substrates against different catalysts. In this way, good to excellent enantioselectivity can be obtained for typically difficult substrates. Geometrically different derivatives of alpha- and beta-methyl cinnamic acid ethyl esters were hydrogenated, to demonstrate the validity of the selectivity model and to verify the importance of steric and electronic matching of the catalyst and the substrate. 相似文献
993.
994.
Mesoporous silica SBA-15 (with ~6?nm pore size and ~6?nm wall thickness) was exposed to a hydrothermal environment at 2 and 5?GPa. The p,T quenched products were investigated by powder X-ray diffraction and transmission electron microscopy. Infrared spectroscopy and thermogravimetric analysis of a sample subjected to 5?GPa at room temperature suggests functionalization of both inner and outer pore surface by silanol. Partial transformation to nano-sized (20–50?nm) coesite crystals with nonfaceted morphology was observed during short equilibration times of 2?h at 125°C, which is significantly below the melting point of water (~250°C). Untransformed SBA-15 maintained intact pore structure. At 175°C and during 8?h, SBA-15 transformed completely into faceted coesite crystals with dimensions 100–300?nm, suggesting Ostwald ripening and thus significant mass transport in the solid water environment. At 2?GPa the melting point of water is near 70°C. Partial transformation to nano-sized α-quartz was observed at 65°C and during 2?h. Untransformed SBA-15 partially pore collapsed. The reduced pore stability of SBA-15 at 2?GPa is attributed to the presence of liquid water in the pores due to melting point depression of confined water. 相似文献
995.
Thermodynamics and structure of liquid surfaces investigated directly with surface analytical tools** 下载免费PDF全文
Measuring directly the composition, the distribution of constituents as function of the depth and the orientation of molecules at liquid surfaces is essential for determining physicochemical properties of liquid surfaces. While the experimental tools that have been developed for analyzing solid surfaces can in principal be applied to liquid surfaces, it turned out that they had to be adjusted to the particular challenges imposed by liquid samples, e.g. by the unavoidable vapor pressure and by the mobility of the constituting atoms/molecules. In the present work it is shown, how electron spectroscopy and ion scattering spectroscopy have been used for analyzing liquid surfaces. The emphasis of this review is on using the structural information gained for determining the physicochemical properties of liquid surfaces. 相似文献
996.
Andersson E Calarco T Folman R Andersson M Hessmo B Schmiedmayer J 《Physical review letters》2002,88(10):100401
Atoms can be trapped and guided with electromagnetic fields, using nanofabricated structures. We describe the fundamental features of an interferometer for guided matter waves, built of two combined Y-shaped beam splitters. We find that such a device is expected to exhibit high contrast fringes even in a multimode regime, analogous to a white light interferometer. 相似文献
997.
J. -E. Andersson 《Analysis Mathematica》1988,14(1):11-25
Основной результат р аботы касается поряд ков рациональных прибли жений вН p функций типа Маркова—Стилть еса с некоторыми спец иальными условиями на меры. Как следствие, получено распростра нение на случай иррац иональных показателей а тех оце нок порядка рациональных прибли жений функцийx α вL p [0,1], 1<р <∞, которые ранее были из вестны для рациональных а. 相似文献
998.
G Gafvelin T Bergman M Andersson B Persson H J?rnvall V Mutt 《Acta chemica Scandinavica (Copenhagen, Denmark : 1989)》1991,45(1):63-67
A 28-residue N-terminal fragment of triosephosphate isomerase, TIM(1-28), has been purified from porcine upper intestine. It competes with VIP for binding to the VIP receptor on rat liver plasma membranes with an IC50 value of 2.8 mM, about 1000 times higher than that for VIP binding to the membranes. Except for a single positional identity and the number of amino acid residues, the amino acid sequences of TIM(1-28) and VIP are unrelated as regards primary structure. However, the ability to bind to the same receptor site may indicate common three-dimensional structural properties. 相似文献
999.
Magnetohydrodynamic flow of an electrically conducting power-law fluid over a stretching sheet in the presence of a uniform transverse magnetic field is investigated by using an exact similarity transformation. The effect of magnetic field on the now characteristics is explored numerically, and it is concluded that the magnetic field tends to make the boundary layer thinner, thereby increasing the wall friction. 相似文献
1000.
The influence of transverse leakage into a pressure-driven laminar flow in an infinitely long square duct is investigated.
By a simple decomposition of the resulting three-dimensional pressure field, the leakage-induced secondary flow problem decouples
from the primary flow problem. The numerical study reveals that two qualitatively different secondary flow patterns may occur,
depending on the leakage flow rate. For a given streamwise pressure gradient it is observed that the axial mass flow rate
may reduce by about 30 percent under certain leakage conditions, accompanied by a corresponding 50 percent increase in the
Darcy-Weisbach friction factor. 相似文献