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71.
72.
The paper presents a numerical study of the propagation of plane waves in a half-space occupied by a granular material, with periodic boundary conditions for velocity or stresses prescribed at the boundary of the half-space. The constitutive behaviour of the material is described by a simplified hypoplastic equation which takes into account different values of the stiffness for different directions of deformation, and the coupling between shear and volumetric strains owing to dilatancy. These two features are responsible for a nonlinear character of longitudinal waves and for the generation of longitudinal motion by transverse disturbances. It is shown that longitudinal and transverse boundary disturbances produce qualitatively the same longitudinal waves at large distances from the boundary. As a longitudinal wave propagates, the amplitude of oscillations decreases and eventually vanishes, resulting in a single non-oscillating wave.Received: 10 September 2002, Accepted: 31 March 2003
Correspondence to: Y. A. Berezin 相似文献
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Hughes JM Hutter MC Reimers JR Hush NS 《Journal of the American Chemical Society》2001,123(35):8550-8563
Site-directed mutagenesis has been employed by a number of groups to produce mutants of bacterial photosynthetic reaction centers, with the aim of tuning their operation by modifying hydrogen-bond patterns in the close vicinity of the "special pair" of bacteriochlorophylls P identical with P(L)P(M). Direct X-ray structural measurements of the consequences of mutation are rare. Attention has mostly focused on effects on properties such as carbonyl stretching frequencies and midpoint potentials to infer indirectly the induced structural modifications. In this work, the structures of 22 mutants of Rhodobacter sphaeroides have been calculated using a mixed quantum-mechanical molecular-mechanical method by modifying the known structure of the wild type. We determine (i) the orientation of the 2a-acetyl groups in the wild type, FY(M197), and FH(M197) series mutants of the neutral and oxidized reaction center, (ii) the structure of the FY(M197) mutant and possible water penetration near the special pair, (iii) that significant protein chain distortions are required to assemble some M160 series mutants (LS(M160), LN(M160), LQ(M160), and LH(M160) are considered), (iv) that there is competition for hydrogen-bonding between the 9-keto and 10a-ester groups for the introduced histidine in LH(L131) mutants, (v) that the observed midpoint potential of P for HL(M202) heterodimer mutants, including one involving also LH(M160), can be correlated with the change of electrostatic potential experienced at P(L), (vi) that hydrogen-bond cleavage may sometimes be induced by oxidation of the special pair, (vii) that the OH group of tyrosine M210 points away from P(M), and (viii) that competitive hydrogen-bonding effects determine the change in properties of NL(L166) and NH(L166) mutants. A new technique is introduced for the determination of ionization energies at the Koopmans level from QM/MM calculations, and protein-induced Stark effects on vibrational frequencies are considered. 相似文献
76.
A. R. Hutter 《Journal of Radioanalytical and Nuclear Chemistry》2001,249(1):203-207
Joint Russian-American field studies have been conducted within theframework of a Memorandum of Cooperation between the Ministry of Atomic Energyfor the Russian Federation and the U.S. Department of Energy and managed bythe Joint Coordinating Committee on Environmental Restoration and Waste Management(JCCEM). We conducted the field studies discussed in this report in 1996 nearthe Mayak Production Association in the South Urals, Russia. The primary purposeof the research was to apply new methods to study the distribution of a contaminantplume originating from Lake Karachai, an unlined radioactive waste repository,which is currently migrating into the Mishelyak River valley. This researchwas conducted within the frontal part of the contaminant water plume. Thestudies from this work include: surface water and soil moisture sampling within situ radiometric measurements. The data from the radiometric measurementsobtained in the field were then compared to laboratory measurements of fieldsamples. Due to the possible inflow of the radionuclides from the groundwaterto the Mishelyak River, this paper also describes the study of river bottomsediments and water contamination. 相似文献
77.
Alexander V. Wilchinsky Kolumban Hutter 《Theoretical and Computational Fluid Dynamics》2001,15(1):23-33
The problem of the implementation of the second law of thermodynamics for the determination of the thermodynamic consistency
of solutions determined by turbulent closures is considered for incompressible fluids. The possibility of the application
of the methods of thermodynamics to constraining constitutive laws describing turbulent flow features, but not material behaviour,
is discussed. It is shown that the ordinary realizability conditions requiring non-negative values of the averaged squared
fluctuations are necessary and sufficient conditions determining the thermodynamic consistency of a process governed by a
closure model. Because turbulent closures are not universal, using the second law of thermodynamics to constrain them can
impose unnecessary restrictions on the models, when the turbulent entropy is considered as a constitutive quantity. The notion
and validity of different forms of the turbulent entropy is discussed. It is found that the form of the turbulent entropy
originating from the analogy between the turbulent kinetic energy and absolute temperature contradicts the principle of irreversibility.
In a particular case of small temperature fluctuations, the second law yields correct constraints, if the turbulent entropy
is assumed not to be a constitutive quantity, but a variable governed by an evolution equation of special form generated by
the balance equation for internal energy.
Received 14 October 2000 and accepted 30 May 2001 相似文献
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79.
Vacuum deposited films of immiscible metal–metal systems can be applied as tribological coatings for plain bearings in high
performance diesel engines. These industrially manufactured coatings show higher lifetimes than conventional electroplated
coatings. For our investigations we used aluminum-tin coatings of 1 μm thickness on a glass substrate produced by sequential
deposition from two separate targets under working gas pressure of 0.4 Pa. The tough Al matrix takes high mechanical loads
and the soft inclusions of Sn act as solid lubricant. While Sn is deposited it migrates on the Al surface and grows as islands.
We characterized the conformation and the distribution of the Sn islands on the surface and to the interstitial area between
the islands with 3-D secondary ion mass spectroscopy (SIMS). The existence of a Sn layer between the islands (“wetting layer”)
has been detected by SIMS and verified by measurements with Auger electron spectroscopy (AES). 相似文献
80.
We consider a viscoelastic–viscoplastic continuum damage model for polycrystalline ice. The focus lies on the thermodynamics particularities of such a constitutive model and restrictions on the constitutive theory which are implied by the entropy principle. We use Müller’s formulation of the entropy principle, together with Liu’s method of exploiting it with the aid of Lagrange multipliers. 相似文献