The mechanics and thermodynamics of edge fracture: the critical energy release rate,the compatibility constraint,and the bond potential

Following Gurtin and many others, the critical energy release rate is commonly identified as an ill-defined surface energy. The primary objectives of this paper are to clarify the definition of this surface energy and the role of the entropy inequality in the discussion of critical conditions. In view of an increasing emphasis on ab initio computations, a secondary objective is to show how the critical energy release rate and the compatibility constraint 1 Si, X, Oh, ES and Slattery, JC. 2010. Phil. Mag., 90: 655[Taylor & Francis Online] , [Google Scholar] can be used to solve a problem for which we have experimental data, using only ab initio estimates of surface tension and bond potential, both of which are increasingly available.     

测定GaAs(001)衬底上InAs的生长速率

报道了间接测定InAs生长速率的方法.通过设置不同Ga源温度,固定In源温度;和固定Ga源温度,设置不同In源温度,在GaAs(001)衬底上生长GaAs与InGaAs,用RHEED强度振荡测定GaAs与InGaAs的生长速率.验证了InGaAs的生长速率为GaAs的生长速率与InAs的生长速率之和,得到了In源温度在845～880℃时InAs的生长速率曲线.     

On limit theorems for the bivariate (magnetization,energy) variable at the critical point

The limiting (magnetization, energy) bivariate variable is studied for Ising ferromagnets at the critical point. The factorization property of the limiting bivariate moment generating function is shown to be intimately connected to critical point exponent inequalities and to the behaviour of the scaling limit near and at the critical point. The validity of this can be deduced from the study of the second and the fourth magnetization cumulants at zero external field. The limiting bivariate variable is exactly calculated at the critical point for the Curie-Weiss model (MF) and for the edge of a two-dimensional Ising ferromagnet wrapped on a cylinder. It is shown that the mean field case leads to a non-Gaussian limiting distribution in contradistinction with the particular Ising model we consider for which we obtain a product of two Gaussian probability distributions.     

The appearance of critical dimensions in regulated string theories (II)

We supply numerical evidence for the existence of critical dimensions d_c1 and d_c2 gaussian model of a discretized string, between which the mean number of vertices in the world sheet diverges, and hence a continuum limit may exist. We also discuss the possibility of non-trivial continuum limits. In particular, by introducing an additional parameter into the model, we argue that non-trivial continuum limits can possibly be obtained only between two critical dimensions d′₀ and d₀. Furthermore, we give proofs of some lower bounds on determinants of combinatorial laplacians entering the models, which were announced in a previous paper.     

Influence of the energy spectrum of structural defects on the degradation rate in AlGaAs light-emitting heterodiodes

The energy spectrum of deep levels in the depleted region of the p-n-transition of AlGaAs light-emitting heterodiodes has been investigated by the method of tunneling spectroscopy. It is shown that the rate of change of the forward current, characterizing the intensity of degradation processes in light-emitting diodes, is interrelated with electronic states of structural defects in the space-charge region (SCR) of the p-n-transition. The maximum value of this parameter is determined by the presence of donor complexes with ionization energies of 0.99 and 1.1 eV in the SCR of the p-n-transition. Institute of Electronics, National Academy of Sciences of Belarus, 22, Logoiskii Trakt, 220090, Minsk, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 2, pp. 298–302, March–April, 1998.     

An investigation of the kinetics of structural changes during the early oxidation stages of a Ni(100) surface using low energy ion scattering (LEIS)

Low energy ion scattering has been used to investigate the early stages of the oxidation of a Ni(100) surface. This technique allows simultaneous study of the oxygen uptake in the surface and the development of surface structures. Bombardment induced surface damages was minimised by performing the experiments with low ion doses, while keeping the target at 200–300°C. The measured kinetics of the oxygen uptake are in good agreement with recent work, using different techniques. It is concluded that during the early chemisorption, a two stage process takes place: an initial oxygen adsorption during which the O atoms probably reside within the fourfold surface hollows, followed by a reconstruction process, caused by the combined action of at least two nearest neighbour O atoms, trapping mobile Ni adatoms, after which the O atoms stabilise at a site in or close to the reconstructed 〈001̄〉 row. Observed structural changes at higher exposures are compatible with a transition into a (3 × 1) structure and subsequently NiO, but cannot, as yet be positively identified.     

Calculation of the structural energy of the unreconstructed and (1 × 2) reconstructed Pt(110) surface

Describing the binding energy of both d and s valence electrons within the LCAO formalism, and by including repulsive Born-Mayer type interactions, we study the structural stability of the reconstructed and unreconstructed Pt(110) surfaces. Our main result is that amongst the various models for the (1 × 2) reconstruction the “Bonzel-Ferrer” model is unfavoured, while the “missing-row” model seems to be energetically degenerate with the unreconstructed surface. Our calculation predicts also a small surface concentration, which, however, has only a minor effect on the total energy of the system.     

Measuring the efficiency of control rods in the RBMK critical assembly using a model of RKI-1 reactimeter

The efficiency of control rods of the RBMK critical assembly is measured in a series of experiments. The aim of measurements is to determine the characteristics of the model of an RKI-1 reactimeter. The RKI-1 reactimeter is intended for measuring the efficiency of control rods when, according to conditions of operation, the metrological certification of results of an experiment is required. Complications with the metrological certification of reactimeters arise owing to the fact that usually calculated corrections to the results of measurements are required. When the RKI-1 reactimeter is used, there is no need to introduce calculated corrections; the result of measurements is given with the indication of substantiated errors. In connection with this, the metrological certification of the results of measurements using the RKI-1 reactimeter is simplified.     

Physical interpretation of the "kinetic energy release" effect in the double photoionization of H(2)

A physical interpretation is given for the variation with internuclear separation of the fully differential cross section for double photoionization of H2. This effect is analyzed in a geometry where the fourbody interaction is completely probed. Excellent agreement is found between experiment and time-dependent close-coupling theory after convoluting the latter over the relevant solid angles. We show the observed variations are purely due to the epsilon(Sigma) component of the polarization vector epsilon along the molecular axis, a conclusion which is supported through calculations of the photoionization of H2(+).     

Cation mobility and structural changes on the water removal in zeolite-like zinc hexacyanometallates (II)

The cation (A⁺) mobility and structural changes on the water molecules removal in zeolite-like zinc hexacyanometallates series, Zn₃A₂[Fe(CN)₆]₂·xH₂O with A=Na, K, Rb and Cs, were studied from X-ray diffraction data recorded for hydrated and anhydrous samples at room temperature and at 77 K. The crystal structure for the anhydrous phases were solved and refined and then compared with those corresponding to their hydrated form. On the water molecules removal the charge balancing cation (A⁺) migrates to favor a stronger interaction with the N ends of the CN bridges where the framework negative charge is located. This cation-framework interaction model is supported by the recorded IR spectra for both hydrated and anhydrous samples. The new cation position induces distortion for both the cavity shape and their windows and also leads to cavity volume reduction. This is relevant for the properties of this family of solids as porous materials and their behavior in adsorption and separation processes, among them for hydrogen storage.     

Effect of turbulence on the rate of energy loss by a test charge moving in a plasma

The energy loss rate of a charge moving in a turbulent plasma is calculated using the dielectric formalism. It is found that the net effect of the turbulence is to decrease the energy loss rate of the test charge.     

Translational energy release in the recombinative desorption of H2 from Ag(111)

We have investigated the recombinative desorption of H₂ from Ag(111) using (2 + 1) REMPI to detect the desorbing molecules. We describe a method for determining the energy released into translational motion normal to the surface over a wide range of surface temperatures. This was achieved by using a weak electric field to disperse the ions, in contrast to the usual field-free method. Calibration and analysis methods are discussed and energy distributions P(E) are reported for H₂ (v=0). Desorption from a 295 K surface shows only a single low-energy peak ( ), whereas the translational energy release is bimodal for desorption from a 580 K surface, with mean desorption energies of approximately 140 meV and 1 eV for the two pathways. Sticking functions are calculated using detailed balance, revealing a large dependence on surface temperature.     

Study of the 49Ti energy levels using the (γ, γ′) and the (γ, n) reactions

An unbound level in ⁴⁹Ti at 8884 keV was photoexcited using a γ-beam obtained from the Cr(n, γ) reaction. The γ-decay and n-decay properties of this level were studied using angular distributions and polarization measurements. Thus spin and parity assignments of some levels in ⁴⁹Ti were made. The neutron width and the total radiative widths of the 8884 keV level were determined to be: Γ_n = 0.25 ± 0.05 eV, Γ_γ = 2.55 ± 0.80 eV.     

Investigating carbonization and graphitization using electron energy loss spectroscopy (EELS) in the transmission electron microscope (TEM)

Electron energy loss spectroscopy (EELS) in the transmission electron microscope (TEM) is explored as a useful characterization technique in the study of carbonization and graphitization of organic precursors. A model series of carbon materials was prepared from highly graphitizable petroleum pitch heat treated in the range 200–2730°C. Initial characterization was performed using the established techniques of X-ray diffraction (XRD), He pycnometry, TEM, electron diffraction and high-resolution lattice imaging (HREM). EELS in the TEM was then examined. Two routes are presented to quantify the change in the proportion of sp ² type hybridization accompanying the heat treatment as the material transforms to the graphitic state. Both routes suggest an initial relative sp ² content of ～70%, rapidly increasing to ～90% during mesophase development and carbonization, and then slowly increasing to 100% during graphitization. The peak position of the bulk valence plasmon (π?+?σ) is shown to be an excellent measure of the degree of graphitic character, and its fundamental dependence upon sample density (ρ) is confirmed. The appearance and definition of features within the core loss region representing the density of unoccupied σ* states are demonstrated to be an excellent measure of the extent of order. Finally, a method is established by which to extract the C–C bond length from core loss EELS spectra with an accuracy of ±0.1?pm. This method suggests an average bond length of 1.44?Å in samples with low heat treatment temperatures, decreasing to the theoretical length of 1.42?Å as both the heteroatom content and proportion of non-sp ²-type hybridized carbon atoms decrease.     

用双原子分子离子XY+的能量自洽法研究卤化氢离子HX+(X=F,Cl,Br,I)基态的势能函数

利用研究双原子分子离子XY 解析势能函数的能量自洽法(ECMI)研究了四个卤化氢离子HX (X=F,Cl,Br,I)基态X2∏的势能函数.得到的势能函数表明,ECMI势能很好与Rydberg-Klein-Rees(RKR)数据相符合,而且在离子的渐进区和离解区域,ECMI势比常用的中性分子的势能函数的Morse势和Huxley-Murrell-Sorbie(HMS)等的结果更可靠,并能得到RKR方法在渐进区和离解区可能缺乏的势能数据,并且表明将能量自洽法从中性分子XY推广到一价双原子分子离子XY 是可行的.     

Measuring the Soret coefficient of binary hydrocarbon mixtures in packed thermogravitational columns (contribution of Toulouse University to the benchmark test)

Within the framework of an international benchmark test, our group which researches packed thermogravitational columns has measured the porous medium thermodiffusion coefficient of two hydrocarbon binary mixtures: tetrahydronaphthalene-dodecane and tetrahydronaphthalene-isobutylbenzene. The weight fraction of each component was near 50 wt%.     

Effect of laser incident energy on the structural,morphological and optical properties of Cu2ZnSnS4 (CZTS) thin films

The polycrystalline Cu₂ZnSnS₄ (CZTS) thin films have been prepared by pulsed laser deposition (PLD) method at room temperature. The laser incident energy was varied from 1.0 at the interval of 0.5–3.0 J/cm². The effect of laser incident energy on the structural, morphological and optical properties of CZTS thin films was studied by means of X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), and optical absorption. The studies reveal that an improvement in the structural, morphological and optical properties of CZTS thin films with increasing laser incident energy up to 2.5 J/cm². However, when the laser incident energy was further increased to 3.0 J/cm², leads to degrade the structural, morphological and optical properties of the CZTS thin films.     

InSb(110)表面S,O原子吸附的第一性原理研究

基于第一性原理方法, 采用广义梯度近似的交换关联势, 对InSb材料(110)表面的硫吸附和氧吸附之后体系性质的差异进行了分析. 讨论了两种吸附下的键长、键角、能带结构和态密度的变化, 从理论上论证了硫吸附比氧吸附对InSb红外探测器表面态的钝化有优越性, 有利于工艺上在钝化时的选择. 关键词： 第一性原理 InSb 硫吸附 氧吸附