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1.
Cavitation erosion is caused in solids exposed to strong pressure waves developing in an adjacent fluid field. The knowledge of the transient distribution of stresses in the solid is important to understand the cause of damaging by comparisons with breaking points of the material. The modeling of this problem requires the coupling of the models for the fluid and the solid. For this purpose, we use a strategy based on the solution of coupled Riemann problems that has been originally developed for the coupling of 2 fluids. This concept is exemplified for the coupling of a linear elastic structure with an ideal gas. The coupling procedure relies on the solution of a nonlinear equation. Existence and uniqueness of the solution is proven. The coupling conditions are validated by means of quasi‐1D problems for which an explicit solution can be determined. For a more realistic scenario, a 2D application is considered where in a compressible single fluid, a hot gas bubble at low pressure collapses in a cold gas at high pressure near an adjacent structure. 相似文献
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High-precision sub-pixel interpolation in particle image velocimetry image processing 总被引:4,自引:0,他引:4
The task of image interpolation and re-sampling for particle image velocimetry (PIV) is investigated, which is used for window shifting with sub-pixel accuracy and image or window deformation. A new interpolation scheme based on a Gaussian filter is introduced and compared with commonly used and widely accepted interpolation techniques in terms of the achievable root mean square deviation of the displacement estimates. 相似文献
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P. E. M. Siegbahn 《Theoretical chemistry accounts》1994,88(6):413-424
Summary The ground state structures and bond energies have been obtained for the triatomic MHX systems where M is the entire sequence of second row transition metal atoms and X is a halide. The most interesting results of this study appear when these systems are compared to the triatomic MH2 and MX2 systems. It turns out that the structure of the MHX systems are quite similar to the corresponding MH2 systems in general. Most of the MHX systems to the right thus have bent low-spin ground states, indicating large covalent contributions to the bonding. RuHX is a special case and has a high-spin linear ground state. For the systems to the left ionicity dominates the bonding. An important result, with implications for halide ligand effects on carbonyl and olefin insertion into M-H and M-R bonds, is that the M-H bonds for the systems to the right have a different character and are significantly weaker for the MHX than for the MH2 systems. A similar effect is noted when the M-Cl bond strengths of MCl2 are compared to the ones in MHCl. Both these effects can be explained by a more cationic metal with mores
0-state character when halide ligands are present. 相似文献
7.
CAS SCF and CCI calculations have been performed in order to establish the existence or non-existence of the HO3 radical. The potential surface for the dissociation reaction, HO3 → O2(3Σ) + OH, along one chosen coordinate has been calculated. The calculations show that although the wavefunctions describing the short-distance and long-distance states are of different character, the energies are the same and the curve connecting the states is very flat. There is probably no barrier towards dissociation of the radical. However, the existence of HO3 can still not be excluded. 相似文献
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Nils G. A. Ekelund Christer Sundqvist Peter H. Quail Richard D. Vierstra 《Photochemistry and photobiology》1985,41(2):221-223
Abstract— From light-induced changes in linear dichroism, we have calculated the rotation of the long-wavelength-absorbing transition moment that occurs during phototransformation of 124-kilodalton Avena sativa phytochrome. Phytochrome was purified to homogeneity and immobilized onto Sepharose beads covalently coated with antibodies against A. sativa phytochrome. Changes in linear dichroism were induced by plane-polarized red or far-red light and measured by the absorbance differences at 660 and 730 nm using a dual-wavelength spectrophotometer equipped with polarizing filters in the measuring beams. From such measurements, we calculate a rotation angle of 31o (or 149o ) during photoconversion of Pr to Pfr and 30o (or 150o ) during photoconversion of Pfr to Pr. These values are similar to the value of 32o (or 148o ) reported earlier for the rotation of the transition moment of "large" A. sativa phytochrome (∽ 120 kilodalton) isolated under conditions that did not preclude post homogenization proteolysis of the 124 kilodalton molecule. 相似文献
9.
Pelmenschikov V Blomberg MR Siegbahn PE Crabtree RH 《Journal of the American Chemical Society》2002,124(15):4039-4049
The mechanism for methane formation in methyl-coenzyme M reductase (MCR) has been investigated using the B3LYP hybrid density functional method and chemical models consisting of 107 atoms. The experimental X-ray crystal structure of the enzyme in the inactive MCR(ox1)(-)(silent) state was used to set up the initial model structure. The calculations suggest a mechanism not previously proposed, in which the most remarkable feature is the formation of an essentially free methyl radical at the transition state. The reaction cycle suggested starts from a Michaelis complex with CoB and methyl-CoM coenzymes bound and with a squareplanar coordination of the Ni(I) center in the tetrapyrrole F(430) prosthetic group. In the rate-limiting step the methyl radical is released from methyl-CoM, induced by the attack of Ni(I) on the methyl-CoM thioether sulfur. In this step, the metal center is oxidized from Ni(I) to Ni(II). The resulting methyl radical is rapidly quenched by hydrogen-atom transfer from the CoB thiol group, yielding the methane molecule and the CoB radical. The estimated activation energy is around 20 kcal/mol, which includes a significant contribution from entropy due to the formation of the free methyl. The mechanism implies an inversion of configuration at the reactive carbon. The size of the inversion barrier is used to explain the fact that CF(3)-S-CoM is an inactive substrate. Heterodisulfide CoB-S-S-CoM formation is proposed in the final step in which nickel is reduced back to Ni(I). The suggested mechanism agrees well with experimental observations. 相似文献
10.
Bassan A Blomberg MR Siegbahn PE Que L 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(2):692-705
The reactivity of [HO-(tpa)Fe(V)=O] (TPA=tris(2-pyridylmethyl)amine), derived from O-O bond heterolysis of its [H(2)O-(tpa)Fe(III)-OOH] precursor, was explored by means of hybrid density functional theory. The mechanism for alkane hydroxylation by the high-valent iron-oxo species invoked as an intermediate in Fe(tpa)/H(2)O(2) catalysis was investigated. Hydroxylation of methane and propane by HO-Fe(V)=O was studied by following the rebound mechanism associated with the heme center of cytochrome P450, and it is demonstrated that this species is capable of stereospecific alkane hydroxylation. The mechanism proposed for alkane hydroxylation by HO-Fe(V)=O accounts for the experimentally observed incorporation of solvent water into the products. An investigation of the possible hydroxylation of acetonitrile (i.e., the solvent used in the experiments) shows that the activation energy for hydrogen-atom abstraction by HO-Fe(V)=O is rather high and, in fact, rather similar to that of methane, despite the similarity of the H-CH(2)CN bond strength to that of the secondary C-H bond in propane. This result indicates that the kinetics of hydrogen-atom abstraction are strongly affected by the cyano group and rationalizes the lack of experimental evidence for solvent hydroxylation in competition with that of substrates such as cyclohexane. 相似文献