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排序方式: 共有137条查询结果,搜索用时 15 毫秒
51.
Fr. Müller J. Yvon V. della Cella A. Schneider und G. Vulpius 《Fresenius' Journal of Analytical Chemistry》1888,27(1):122
Ohne Zusammenfassung 相似文献
52.
New finite elements have been developed to simulate steady and unsteady two-dimensional free surface flows. The depth-averaged velocity components with the free surface elevation have been used as independent variables in the model. The differences between the various elements presented lie in the choice of velocity approximation. The Newton–Raphson method has been used to solve the non-linear system of equations. Emphasis is put on bench-mark examples to assess the accuracy and efficiency of the elements. A simple stable new element tested herein shows promising advantages for industrial finite element codes. 相似文献
53.
54.
55.
Yvon Pointud Jean Juillard Lèvon Avedikian Jean-Pierre Morel Michel Ducros 《Thermochimica Acta》1974,8(4):423-431
By using a calorimetric method, solution enthalpies of sodium, potassium, rubidium and cesium chlorides in mixtures containing from 0 to 45% by weight of alcohol are obtained. Standard enthalpies and transfer enthalpies are estimated. From previous data concerning Gibbs energies of transfer from water to the same solvent mixtures, transfer entropies are calculated. Enthalpies and entropies exhibit a maximum for molar fractions of about 0.07 of organic solvent. Results are discussed in terms of enhancement of the structuration of the aqueous network. 相似文献
56.
H. Kohlmann G. Renaudin K. Yvon B. Harbrecht 《Journal of solid state chemistry》2005,178(4):1292-1300
The hydrogenation behavior of MgPd3 has been studied by in situ X-ray powder diffraction and by neutron powder diffraction. At room temperature and p ≈500 kPa hydrogen pressure its structure is capable of incorporating up to one hydrogen atom per formula unit (α-MgPd3H≈1), thereby retaining a tetragonal ZrAl3-type metal atom arrangement. Upon heating to 750 K in a hydrogen atmosphere of 610 kPa it transforms into a cubic modification with AuCu3-type metal atom arrangement (β-MgPd3H≈0.7). Neutron diffraction on the deuteride reveals an anion deficient anti-perovskite-type structure (β-MgPd3D0.67, a=398.200(7) pm) in which octahedral sites surrounded exclusively by palladium atoms are occupied by deuterium. Complete removal of hydrogen (480 K, 1 Pa) stabilizes a new binary modification (β-MgPd3, a=391.78(2) pm) crystallizing with a primitive cubic AuCu3-type structure. Mechanical treatment (grinding) transforms both α and β modifications of MgPd3 into a cubic face-centered solid solution Mg0.25Pd0.75 showing a random distribution of magnesium and palladium atoms. 相似文献
57.
Kohlmann H Werner F Yvon K Hilscher G Reissner M Cuello GJ 《Chemistry (Weinheim an der Bergstrasse, Germany)》2007,13(15):4178-4186
Binary SmH(3) (trigonal, a=656.7(3), c=680.1(3) pm, P$\bar 3$c1, Z=6), ternary SmMg2H7 (tetragonal, a=626.47(6), c=937.2(2) pm, P4(1)2(1)2, Z=4) and the corresponding deuterides SmD3 (a=653.9(1)m, c=676.7(2) pm) and SmMg2D7 (a=624.10(1), c=934.81(2) pm) have been prepared by hydrogenation (deuteration) of elemental samarium and the Laves phase SmMg2, respectively, and investigated by X-ray and neutron powder diffraction and SQUID and vibration magnetometry. The problem of the enormous neutron absorption of the natural isotopic mixture (natSm) is circumvented by carefully choosing the neutron wavelength (approximately 50 pm) and the use of double-walled cylindrical sample holders and a high-intensity neutron diffractometer (D4c at ILL). SmD3 crystallises with a tysonite-type structure and has three independently ordered deuterium atom sites with trigonal-planar, trigonal-pyramidal and tetrahedral metal environments and Sm--D bond lengths in the range 220(1)-258(1) pm (average: 235 pm). SmMg2D7 is a new deuteride that crystallises with an LaMg2D7-type structure. It displays four fully occupied deuterium sites having triangular and tetrahedral metal environments and Sm--D bond lengths in the range 227.6(5)-246.8(8) pm (average: 239 pm). These are the first samarium-deuterium bond lengths to be reported. Both deuterides are paramagnetic down to 2 K (SmD3: mueff=0.63(1) muB, thetap approximately -4 K; SmMg2D7: mueff=0.57(2) muB, thetap approximately -4 K). Their crystal structures and chemical and physical properties suggest mainly ionic bonding according to the limiting ionic formulae Sm3+(H-)3 and Sm3+(Mg2+)2(H-)7. 相似文献
58.
Summary.
In this paper we analyze and illustrate a new "ab initio"
part design
procedure, in which, given a cost function which reflects
performance,
materials, and manufacturing considerations, the topology and the
geometry
of the part are automatically produced. The analysis is based on
demonstration
of, first, the compactness of the metric space over which the cost
function is
defined, and, second, lower semi-continuity of the cost function.
Examples include beams and
elastic supports.
Received November 15, 1993 相似文献
59.
60.
X-ray data on single crystals of the quaternary metal hydride near the composition LiB(0.33)N(0.67)H(2.67), previously identified as "Li3BN2H8", reveal that its true composition is Li4BN3H10. The structure has body-centered-cubic symmetry [space group I2(1)3, cell parameter a = 10.679(1)-10.672(1) Angstroms] and contains an ordered arrangement of BH4- and NH2- anions in the molar ratio 1:3. The borohydride anion has an almost ideal tetrahedral geometry (angleH-B-H approximately 108-114 degrees), while the amide anion has a nearly tetrahedral bond angle (angleH-N-H approximately 106 degrees). Three symmetry-independent Li atom sites are surrounded by BH4- and NH2- anions in various distorted tetrahedral configurations, one by two B and two N atoms, another by four N atoms, and the third by one B and three N atoms. The Li configuration around B is nearly tetrahedral, while that around N resembles a distorted saddlelike configuration, similar to those in LiBH4 and LiNH2, respectively. 相似文献