A comparative study of ethylene oxide and diethylene dioxide adsorption on silicon (0 0 1)

The adsorption of ethylene oxide (oxirane) and diethylene dioxide (1,4-dioxane) on the Si(0 0 1) surface was investigated using the first-principles pseudopotential method within a generalised gradient approximation to the density functional theory. Our results indicate that oxirane adsorption on the silicon surface probably occurs via C-C bond. This interaction induces the breaking of the C-C bond and the formation of a Si-C-O-C-Si ring. The 1,4-dioxane interaction with the silicon (2 × 2) surface, on the other hand, results in the decomposition of the considered molecule in different radicals, depending on the original adsorbed structure. In order to disregard the possible influence of the slab considered, we suggest that high order reconstruction surfaces, i.e. (4 × 2) or (4 × 4), should be investigated.     

Radiation-induced decomposition of explosives under extreme conditions

We present high-pressure and high temperature studies of the synchrotron radiation-induced decomposition of powder secondary high explosives pentaerythritol tetranitrate (PETN) and 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) using white beam synchrotron radiation at the 16 BM-B and 16 BM-D sectors of the HP-CAT beamline at the Advanced Photon Source. The radiation-induced decomposition rate TATB showed dramatic slowing with pressure up to 26.6 GPa (the highest pressure studied), implying a positive activation volume of the activated complex. The decomposition rate of PETN varied little with pressure up to 15.7 GPa (the highest pressure studied). Diffraction line intensities were measured as a function of time using energy-dispersive methods. By measuring the decomposition rate as a function of pressure and temperature, kinetic and other constants associated with the decomposition reactions were extracted.     

Non-stoichiometry and properties of ternary semiconductor phases of variable composition based on IV-VI compounds

An overview and analysis of our experimental data on the crystal structure, mechanical, thermal, galvanomagnetic and thermoelectric properties vs composition of the ternary semiconductor phases based on IV-Te compounds in the IV-X-Te systems (IV-Ge, Sn, Pb; X-Cu, Ag, Cd, In, Ga, Bi, Sb, Mn, V) are given. The separate and joint effect of deviation from stoichiometry and cation substitution on the IV-X-Te phase properties is established using the method of ‘controlled atomic defects’. Some general regularities and new physical phenomena connected with simultaneous presence of intrinsic and impurity point defects are detected. The influence of the cation substitution on the intrinsic defect equilibrium is established. It is shown that critical phenomena of percolation nature are observed in the range of small impurity contents as well as small intrinsic defect concentrations. Principally new models of the energy band structure of IV-X-Te ternary phases, which take into consideration a high concentration of non-stoichiometric defects, are proposed. The role of long- and short-range ordering is discussed. The formation of complexes as a result of chemical interaction between impurity and host atoms is detected. The above-mentioned phenomena are common for ternary phases and should be taken into account when developing materials for different applications.     

Critical behaviour of the specific heat of La0.9Ag0.1MnO3 manganite

 For the first time the specific heat of polycrystalline La_0.9Ag_0.1MnO₃ manganite near the Curie temperature was precisely measured by AC calorimetry and its critical behaviour was studied. The critical behaviour of the specific heat was approximated by the relationship taking into account corrections to the scaling. The regularities of variations in the universal critical parameters near the critical point are determined, and their values are calculated. Detailed analysis and comparison of the received results with the theoretical predictions and other experimental results was carried out.     

Properties of then-body correlation functions near the liquid-gas critical point. Correlation inequalities

We investigate the behavior of the many-body correlation functions in the vicinity of the gas-liquid critical point. We use the framework of the liquid state theory and, accordingly, no reference to an effective Landau-Ginzburg Hamiltonian is made. The critical condition is introduced by means of the equation of state. From the Baxter equation relating the many-body correlation functionsh(n) andh(n+1), we find that the integrals of all theh(n) diverge at the critical point. Then we present strong arguments and this leads to GKS-like inequalities, under some limiting conditions: the interparticle distances must be large and the thermodynamic state of the system must be close to the critical point. In order to get these inequalities, an upper bound forh(n) is obtained. Particular attention must be paid to the fact that the usual asymptotic approximations of the liquid state theory are no longer valid.     

Photoluminescence and gamma-ray irradiation of SrAl2O4:Euand Y2O3:Eu phosphors

Y₂O₃:Eu³⁺ phosphor is a very attractive material for use as a red phosphor in many fields. SrAl₂O₄:Eu²⁺ belongs to long lasting phosphor (LLP) and it is a useful bluish-green luminescence material, which can also be a promising candidate as a simple and easy-to-use radiation detection element for visual display of two dimensional radiation distributions. In the present study, both these two kinds of phosphors were synthesized using high temperature solid state reactions. In our work, the influence of gamma-ray irradiation on the properties of these two kinds of phosphors was studied by comparing photoluminescence, brightness and the decay curve of unirradiated and gamma-ray-irradiated samples. Conclusions from the present work can be briefly summarized as follows. In irradiated samples, the brightness is decreased without sensible change in the wavelength distribution of the luminescence spectrum and in the decay kinetic upon gamma exposure. Moreover, the emission due to Eu³⁺→Eu²⁺ conversion in Y₂O₃:Eu³⁺ phosphors was not observed in our sample after irradiation to high exposure. Also the brightness of SrAl₂O₄:Eu²⁺ phosphor turned out to decrease after the exposition to ionizing radiation while the luminescence wavelength distribution remained unchanged. The reason for the effect of gamma-ray irradiation on the properties of phosphors is also discussed in the paper.     

Monte Carlo evidence for a cusp in the uniform susceptibility of the site-diluted simple cubic Ising antiferromagnet

Monte Carlo simulations are performed for pure and site-diluted Ising antiferromagnets on a simple cubic lattice with up to 40³ sites and impurity concentrationx=0, 0.2. and 0.5. Forx=0.5 a cusp emerges for the temperature dependence of the uniform susceptibility at the critical temperature which is contrasted with the smooth behavior for a pure antiferromagnet, in agreement with the theoretical prediction of Fishman and Aharony.     

ZrO2/ SiO2多层膜的化学法制备研究

 分别以ZrOCl₂·8H₂O 和正硅酸乙酯为原料,采用溶胶-凝胶工艺制备了性能稳定的ZrO₂和SiO₂溶胶。用旋转镀膜法分别在K9玻璃和单晶硅片上制备了ZrO₂/ SiO₂多层膜。采用溶剂替换和紫外光处理等手段,有效地解决了ZrO₂/SiO₂多层膜中膜层开裂和膜间渗透等问题。应用扫描电子显微镜观测了薄膜的表面和剖面微观形貌,并用椭偏仪测得薄膜的厚度和折射率,研究了薄膜厚度、折射率与热处理温度、紫外光处理时间的关系,对所获得薄膜的紫外-可见、红外光谱进行了分析。用输出波长1064nm ,脉宽15ns 的电光调Q光系统产生的强激光进行了单层膜的辐照实验,结果发现溶剂替换后激光损伤阈值有所提高。     

Onset of superfluidity far from equilibrium: dynamical effects on the correlation length

Nonlinear heat conduction has recently been measured near the superfluid transition in pure ⁴He at very low heat flux Q. Since both dynamic effects and gravity limit the divergence of the superfluid correlation length near the transition at low-Q, these measurements must be repeated in the microgravity environment in order to observe the dynamic effects in isolation. Comparison of the microgravity data to similar data obtained on Earth will provide experimental insight into the effect of gravity on this nonlinear conduction region at low heat flux where theoretical predictions are lacking. While some measurement advantages exist in the microgravity laboratory, it is the study of the direct effect of gravity on the nonlinear conduction measurements that motivate the microgravity need.     

Soft X-ray induced chemical modification of polysaccharides in vascular plant cell walls

Scanning transmission X-ray microscopy and micro carbon X-ray Absorption Near Edge Spectroscopy (C-XANES) can provide quantitative information regarding the distribution of the biopolymers cellulose, hemicellulose, and lignin in vascular plant cell walls. In the case of angiosperms, flowering plants, C-XANES may also be able to distinguish variations in lignin monomer distributions throughout the cell wall. Polysaccharides are susceptible to soft X-ray irradiation induced chemical transformations that may complicate spectral analysis. The stability of a model polysaccharide, cellulose acetate, to variable doses of soft X-rays under conditions optimized for high quality C-XANES spectroscopy was investigated. The primary chemical effect of soft X-ray irradiation on cellulose acetate involves mass loss coincident with de-acetylation. A lesser amount of vinyl ketone formation also occurs. Reduction in irradiation dose via defocusing does enable high quality pristine spectra to be obtained. Radiation induced chemical modification studies of oak cell wall reveals that cellulose and hemicellulose are less labile to chemical modification than cellulose acetate. Strategies for obtaining pristine C-XANES spectra of polysaccharides are presented.     

Phase diagrams of noisy traffic states in the presence of a bottleneck

The traffic states are investigated for the noisy traffic flow in the presence of a bottleneck under the open boundary condition. The phase diagrams of the different kinds of congested traffic are presented for different values of sensitivity (the inverse of delay time). It is shown that the five different types of traffic states appear below the critical point: the free traffic with a pinned localized cluster, the weak standing shock, the moving localized cluster, the oscillatory congested traffic, and the strong standing shock. Above the critical point, the moving localized cluster and oscillatory congested traffic do not occur. Also, in the traffic flow without noise, the moving localized cluster and oscillatory congested traffic do not appear.     

Monte Carlo study of the magnetic properties of Fe0.9−qMn0.1Alq-disordered alloys

Within the framework of a random site-diluted Ising model with nearest-neighbor interactions, and using the Metropolis algorithm for equilibration and energy minimization, we have computed the ensemble and configurational averages for magnetization per site, magnetic susceptibility and specific heat of Fe_0.9−qMn_0.1Al_q-disordered alloys with 0.1q0.55. In the model, atoms have been randomly distributed on a body-centered cubic lattice in order to simulate the disorder and structure as that obtained in arc-melted Fe_0.9−qMn_0.1Al_q alloys treated at high temperatures during long periods of time and followed by fast quenching. Competitive interactions coming from Fe–Fe ferromagnetic bonds and Fe–Mn and Mn–Mn antiferromagnetic couplings, as well as the Al dilutor effect, have been taken into account in our study. Results allow us to conclude that, in agreement with previous Mössbauer data of the average hyperfine field, for which a comparison is also carried out, the Fe_0.9−qMn_0.1Al_q-disordered alloys are well characterized by a critical concentration at room temperature at around 40 at% Al, for which the system undergoes a transition from a ferromagnetic state to a paramagnetic one. The finite size scaling analysis to obtain the critical Al concentration in the thermodynamic limit, as well as the critical exponents, is also presented and discussed.     

Empirical determination of the random fraction in disordered channel

A new method of deriving the random fraction in a disordered channel : rom dechanneling experiments is described. In this method backscattering spectra obtained at two different doses are employed, with an assumption on the dose dependence of the defect concentration. The method is applied to the experimental data for B-implanted Si and it is found that the obtained random fraction is similar to the result of the diffusion calculation made by the present authors. The depth profiles of defects are also obtained and compared with the result of theoretical calculations.     

Applying the Mises-Hill criterion to modeling the dynamic loading of highly anisotropic materials

The effect of averaging the properties of a target material on the results from calculations of target deformation and destruction by means of numerical modeling and the possibility of applying such averaging to the properties of elastic and strength constant materials of targets made of orthotropic composite materials are investigated. Numerical investigations are performed for materials with high degrees of anisotropy in their mechanical properties using the example of an organoplastic.     

Relating tracer and chemical diffusion coefficients in intermetallic compounds taking the DO3 and A15 structures

In this article we employ computer simulation to explore the validity of the Darken/Manning relation between the chemical diffusion coefficient and the tracer diffusion coefficients of the components in stoichiometric intermetallic compounds A₃B taking the DO₃ and A15 structures at vanishingly small vacancy contents. The analysis centres on the validity of Manning’s random alloy expression for the vacancy wind factor. The models for both the DO₃ and A15 structures use eight atom-vacancy exchange frequencies. For the DO₃ structure it is found that the actual vacancy wind factor is usually somewhat larger than that predicted by Manning but overall the agreement is good. At worst the use of Manning’s expression would underestimate this factor by about 30 or 40%. For the A15 structure a similar result is found except when diffusion along the chains in the structure is rapid. Then Manning’s expression fails badly when a constant geometrical tracer correlation factor is employed. In both the structures if the geometrical correlation factor is varied to reflect the structure actually explored by the atoms (mainly the majority atoms A) the agreement is improved very dramatically.     

Swelling and structure of radiation induced near-surface damage in CR-39 and its chemical etching

Systematic measurements of swelling of CR-39 nuclear track detector (NTD) due to irradiation with fission fragments and alpha particles over a wide range of fluences from ²⁵²Cf are presented here. Precisely designed and optimized exposure and chemical etching experiments were employed to unfold the structure of radiation induced surface damage. Delays in the startup of the chemical etching of latent tracks in low radiation fluence detectors are measured and are found to contain important information about structure of the surface damage. Simple atomic scale pictures of radiation induced surface damage and its chemical etching are developed using measurements of radiation induced swelling of CR-39 detectors and nuclear track parameters. The computer code SRIM2010 was utilized for the calculations of basic features of latent tracks of fission fragments and alpha particles in CR-39. Another computer code TRACK_VISION was used to compute parameters of etched tracks. Computations and experimental findings in the paper coherently compose a realistic picture of radiation damage.     

Anomaly in electric resistance of binary liquids near the critical point

Electric resistance in critical solutions of nitrobenzene inn-hexane,n-heptane andn-octane was measured. The resistance near the critical point was studied and divergence in the temperature derivative measured.     

Impurity effects on the critical behaviour of the electrical resistance of binary liquid mixtures

The electrical resistance of the binary liquid system cyclohexane + acetic anhydride is measured, in the critical region, both in the pure mixture and when the mixture is doped with small amounts (≈ 100 ppm) of H₂O/D₂O impurities.T _c was approached to aboutt=3×10⁻⁶ wheret=(T −T _c )/T _c . The critical exponentb ≈ 0.35 in the fit of the resistance data to the equationdR/dT ∼t ^−b does not seem to be affected appreciably by the impurities. There is a sign reversal ofdR/dt in the non-critical region. Binary liquid systems seem to violate the universality of the critical resistivity.     

Critical Exponents of the Diluted Ising Model between Dimensions 2 and 4

Within the massive field-theoretic renormalization-group approach the expressions for the and functions of the anisotropic mn-vector model are obtained for general space dimension d in three-loop approximation. Resumming corresponding asymptotic series, critical exponents for the case of the weakly diluted quenched Ising model (m = 1, n = 0), as well as estimates for the marginal order parameter component number m _c of the weakly diluted quenched m-vector model, are calculated as functions of d in the region 2 d < 4. Conclusions concerning the effectiveness of different resummation techniques are drawn.