多晶薄膜屈服强度的一个模型

从位错运动的应力功和应变能关系导出了附着在基体上并有钝化层薄膜的屈服强度公式.该式表明多晶薄膜的屈服强度由两个影响因子（晶粒取向和位错类型）和三个强化因子（钝化层强化，基体强化和晶粒强化）确定.和已报道的实验结果基本一致表明了该模型的合理性. 关键词： 多晶薄膜 屈服强度     

Quantum inequivalence of different field representations

The gauge theories of antisymmetric tensor potentials A_μν and A_μν? describe 1 and 0 degrees of freedom, respectively. Yet we show the gravitational trace anomalies of A_μν and a scalar field A to be different, and that of A_μν? to be non-vanishing. Corresponding inequivalences also occur in their one-loop counterterms when the spacetime has non-trivial topology. Furthermore, the coupling of A_μν? to gravity provides a gauge principle derivation of the cosmological constant. Possible applications to supergravity are also discussed.     

Estimating the strength of single-ended dislocation sources in micron-sized single crystals

Three-dimensional (3D) discrete dislocation dynamics simulations were used to calculate the effects of anisotropy of dislocation line tension (increasing Poisson's ratio, ν) on the strength of single-ended dislocation sources in micron-sized volumes with free surfaces and to compare them with the strength of double-ended sources of equal length. Their plastic response was directly modelled within a 1?µm³ volume composed of a single crystal fcc metal. In general, double-ended sources are stronger than single-ended sources of an equal length and exhibit no significant effects from truncating the long-range elastic fields at this scale. The double-ended source strength increases with ν, exhibiting an increase of about 50% at ν?=?0.38 (value for Ni) as compared to the value at ν?=?0. Independent of dislocation line direction, for ν greater than 0.20, the strengths of single-ended sources depend upon the sense of the stress applied. The value for α in the expression for strength, τ?=?α(L)µb/L is shown to vary from 0.4 to 0.84 depending on the character of the dislocation and the direction of operation of the source at ν?=?0.38 and L?=?933b. By varying the lengths of the sources from 933 to 233b, it was shown that the scaling of the strength of single-ended and double-ended sources with their length both follow a ln(L/b)/(L/b) dependence. Surface image stresses are shown to have little effect on the critical stress of single-ended sources at a length of ～250b or greater. This suggests that for 3D discrete dislocation dynamics simulations of the plastic deformation of micron-sized crystals in the size range 0.5–20?µm, image stresses making the surface traction-free can be neglected. The relationship between these findings and a recent statistical model for the hardening of small volumes is discussed.     

Comparison of two representations of a random cut of identical sphere packing

We compare two-dimensional froths obtained by radical tessellation of random planar cuts made through disordered assemblies of monosize spheres at different packing fractions C from C=0 to C=0.64 with two-dimensional stereological cuts obtained through the three-dimensional froths made with the same packing. We have built numerically the packings using different algorithms. The study of both topological and metric properties shows significant differences between the two representations. Received 26 May 1999 and Received in final form 13 November 1999     

Statistical-thermodynamic theory of ordering in a binary film deposited on the surface of a monocrystal

The ordering of a binary monolayer deposited on the surface of a monocrystal is studied. In the case when the structure of the film is equivalent to that of the crystal surface, the ordering in the film is qualitatively similar to that in the bulk of the sample: When the ordering energy is positive there exists an order-disorder phase transition at a certain temperature and for a certain concentration interval. If the structure of the film is different from the structure of the surface, then the film is ordered at all temperatures, independently of the sign of the ordering energy. In this case, in addition to the equilibrium ordered state in the region T < T_* (T_* is a certain temperature which is determined by the composition of the alloy and by the magnitude of the energy shift of the atoms of the film in the field of the substrate), there exists a metastable ordered state in which there is a jump-like change in the ordering at the point T_*, analogous to a first-order phase transition. Possible methods of experimental study of the ordering in films are discussed.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 53–57, May, 1987.     

Developing scaling relations for the yield strength of nanoporous gold

In this work, the applicability of Gibson and Ashby’s porous scaling relations to nanoporous metals is discussed, and an updated equation is proposed for relating the yield strength of nanoporous gold to the yield strength of individual gold ligaments that form the porous structure. This new relation is derived from experimental measurements obtained by small-scale tensile testing and by nanoindentation, and incorporates the average ligament diameter. Nanoindentation data, obtained experimentally by the authors as well as reported by others in the literature, are reconciled with tensile test measurements previously reported by the present authors. The values of ligament yield strength calculated with the new scaling relation are found to agree with data reported from mechanical testing of nanowires, and the scaling relation thus represents a bridge between nanowire and nanoporous metal behaviour. In addition, calculations of yield strength for nanoporous gold samples with various ligament size and relative density are consistent with the experimentally determined values.     

Study of the spectral properties of spin ladders in different representations via a renormalization procedure

We implement an algorithm which is aimed to reduce the dimensions of the Hilbert space of quantum many-body systems by means of a renormalization procedure. We test the role and importance of different representations on the reduction process by working out and analyzing the spectral properties of strongly interacting frustrated quantum spin systems.     

Relations between different representations of stochastic adiabatic solutions

We present ESR-data for Gd³⁺-impurities in the heavy fermion compound CeAl₃ under hydrostatic pressure up to 17kbar. At ambient pressure andT<4K the Gd-resonance shows a strongly enhanced thermal broadening with respect to isostructural LaAl₃. With increasing pressure this slope decreases from at least 138 Oe/K (p=0) to 18 Oe/K (p=17kbar) which is almost the Korringa slope of LaAl₃. These results support the idea of an increasing Ce-spin fluctuation rate as a function of pressure.     

Effect of source strength on dislocation pileups in the presence of stress gradients

The behaviour of a dislocation pileup with a finite-strength source is investigated in the presence of various stress gradients within a continuum model where a free-dislocation region exists around the source. Expressions for dislocation density and stress field within the pileup are derived for the situation where there are first and second spatial gradients in applied stress. For a pileup configuration under an applied stress, yielding occurs when the force acting on the leading dislocations at the pileup tips reaches the obstacle strength, and at the same time, it is required that the source be at the threshold stress for dislocation production. A numerical methodology is presented to solve the underlying equations that represent the yielding conditions. The yield stress calculated for a pileup configuration is found to depend on stress gradients, obstacle spacing and source/obstacle strengths. It increases with increasing the first stress gradient, yet dependent on the second stress gradient. Furthermore, while the dependency of yield stress on the obstacle spacing intensifies with increasing the first stress gradient, it diminishes with an increase of second stress gradient. Therefore, the second stress gradient, as a newly introduced parameter, can provide a new physical insight into the size-dependent plasticity phenomena at small length scales.     

On the yield strength of single-crystal zinc under uniaxial compression in a plane shock wave

The shock wave pattern in zinc single crystals compressed in the direction normal to the basal plane of the crystal is traced with a high time resolution. In this geometry of the experiment, plastic deformation of the zinc is found to begin at a shock compression pressure above 15 GPa and is not accompanied by splitting of the shock wave into an elastic precursor and a plastic compression wave.     

Dependence of the yield stress of filamentary sodium chloride crystals on the starting dislocation structure

The onset of plastic flow of filamentary NaCl crystals with the simplest types of starting dislocation structure was studied under conditions which completely exclude the effect of stress concentration in the clamps of the microdeformation machine. It was established that the growth dislocations, having an outlet to the side boundaries, do not exclude the appearance of a sharp projection of the flow on the stretching diagram, though they reduce its height. The flow projection remains in samples with traces of microdeformation, formed by random effects during manipulation; in addition, the behavior of the filamentary crystals at the yield stress depends on the nature of these traces.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 20–24, April, 1986.     

The occurrence of negative Barkhausen jumps during the magnetization of a Fe-Si frame monocrystal

The paper describes an experimental investigation into the character and occurrence rate of negative Barkhausen jumps (B. j.) accompanying the magnetization process in a Fe-Si frame monocrystal. It has been ascertained that parallel with positive B. j., negative B. j. are unambiguously present during the magnetization process. The obtained experimental results seem to support the theorem published in [5] that negative B. j. appear as a rule in tandem with preceding positive B. j.The authors would like to express their thanks to V. Kavetschanský for determining the domain structure shown in Fig. 1 and to Z. Kubanyi for his valuable help in designing the experimental set-up and carrying out the experiments.     

Temperature shift of the maximum of critical X-ray scattering in a BaTiO3 monocrystal

The temperature shift of the maximum of critical scattering in BaTiO₃ monocrystal was found to depend on the direction of the scattering vector with respect to the crystalline axes.     

Comparison of the roex and gammachirp filters as representations of the auditory filter

Although the rounded-exponential (roex) filter has been successfully used to represent the magnitude response of the auditory filter, recent studies with the roex(p, w, t) filter reveal two serious problems: the fits to notched-noise masking data are somewhat unstable unless the filter is reduced to a physically unrealizable form, and there is no time-domain version of the roex(p, w, t) filter to support modeling of the perception of complex sounds. This paper describes a compressive gammachirp (cGC) filter with the same architecture as the roex(p, w, t) which can be implemented in the time domain. The gain and asymmetry of this parallel cGC filter are shown to be comparable to those of the roex(p, w, t) filter, but the fits to masking data are still somewhat unstable. The roex(p, w, t) and parallel cGC filters were also compared with the cascade cGC filter [Patterson et al., J. Acoust. Soc. Am. 114, 1529-1542 (2003)], which was found to provide an equivalent fit with 25% fewer coefficients. Moreover, the fits were stable. The advantage of the cascade cGC filter appears to derive from its parsimonious representation of the high-frequency side of the filter. It is concluded that cGC filters offer better prospects than roex filters for the representation of the auditory filter.