Characterization of SiC and Si<Subscript>3</Subscript>N<Subscript>4</Subscript> nanoparticles and their aqueous dispersions

Nanoparticles of SiC and Si₃N₄ were previously used to obtain electroless NiP/particles nanocomposites. The incorporation process was very different, depending on the particle: SiC tended to agglomerate and had a high incorporation level; Si₃N₄ particles were not aggregated, but their incorporation level was very low. To try to explain these differences, the particles and their aqueous dispersions were characterized. Although the as-received products were both oxidized and of the identical mean size, results showed that the size distributions and the surface oxidation products were rather different. The zeta potential in water dispersions was similar and negative for both particles but, as the electrolyte ions were introduced, it showed a different evolution: nitride particles retained a small negative charge and carbide was almost uncharged. The overall results obtained in this study explain the different behavior of both ceramic particles and provide possible solutions to improve their co-deposition with nickel.     

Marginal Distributions of Wigner Function in a Mesoscopic L-C Circuit at Finite Temperature and Thermal Wigner Operator

Wigner function in phase space has its physical meaning as marginal probability distribution in coordinate space and momentum space respectively, here we endow the Wigner function with a new physical meaning, i.e., its marginal distributions’ statistical average for q ²/(2C) and p ²/(2L) are the energy stored in capacity and in inductance of a mesoscopic L-C circuit at finite temperature, respectively. PACS numbers: 03.65.-w, 73.21.-b     

Calculation of conformations and vibrational spectra of a monomeric fragment of the 2,6-carboxymethyl cellulose molecule

A theoretical conformational analysis has been carried out for the side substituents of a fragment of the molecule for 2,6-carboxymethyl cellulose (a water-soluble cellulose ether), and the frequencies and the potential energy distribution of the normal vibrations have been calculated for the most stable conformers of the ether groups of this fragment in the approximation of the molecular mechanics method. It has been shown that the most stable conformers are those that have the conformations gg, t, g⁻, g⁻, g⁻-for the groups of atoms on the bonds C5-C6, C6-O6, C13-O6, C10-C13, C10-O9 and the conformations g⁺g⁻, g⁺, g⁻, g⁻; g⁺g⁻, g⁻, g⁻, g⁻; g⁺g⁻, g⁻, g⁺, t for the groups of atoms on the bonds C2-O2, C11-O2, C7-C11, C7-O8. Comparative analysis of the calculated frequencies and the potential energy distribution of the normal vibrations for 13 of the most stable conformers showed, as in the case of the 2,6-hydroxyethyl cellulose molecule, that the frequencies and modes of the normal vibrations are highly sensitive to conformational transitions in the analyzed spectral region (800–1500 cm⁻¹). The characteristic patterns for the change in the frequencies and modes of the normal vibrations have been established in connection with conformational transitions within both side substituents. The observed conformational lability of the bulky substituents in the cellulose ether molecules and its manifestations in the vibrational spectrum provide a basis for hypothesizing that one of the major mechanisms for the process of their thermal gelation in aqueous solutions is conformational transitions within these substituents. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 1, pp. 5–15, January–February, 2007.     

Planar Line Processes for Void and Density Statistics in Thin Stochastic Fibre Networks

Using results for the distribution of perimeters of random polygons arising from random lines in a plane, we obtain new analytic approximations to the distributions of areas and local line densities for random polygons and compute various limiting properties of random polygons. Using simulation, we show that the lengths of adjacent sides of polygons generated by random line processes in the plane are correlated with ρ=0.616±0.001.     

Network formed by traces of random walks

We propose a model of time evolving networks in which a kind of transport between vertices generates new edges in the graph. We call the model “Network formed by traces of random walks”, because the transports are represented abstractly by random walks. Our numerical calculations yield several important properties observed commonly in complex networks, although the graph at initial time is only a one-dimensional lattice. For example, the distribution of vertex degree exhibits various behaviors such as exponential, power law like, and bi-modal distribution according to change of probability of extinction of edges. Another property such as strong clustering structure and small mean vertex–vertex distance can also be found. The transports represented by random walks in a framework of strong links between regular lattice is a new mechanisms which yields biased acquisition of links for vertices.     

Gain–loss asymmetry for emerging stock markets

Stock indexes for some European emerging markets are analyzed using an investment-horizon approach. Austrian ATX index and Dow Jones have been studied and compared with several emerging European markets. The optimal investment horizons are plotted as a function of an absolute return value. Gain–loss asymmetry, originally found for American DJIA index, is observed for all analyzed data. It is shown, that this asymmetry has different character for emerging and for established markets. For established markets, gain curve lies typically above loss curve, whereas in the case of emerging markets the situation is just the opposite. We propose a measure quantifying the gain–loss asymmetry that clearly exhibits a difference between emerging and established markets.     

Quantitative, dynamic fuel distribution measurements in combustion-related devices using laser-induced fluorescence imaging of biacetyl in iso-octane

Knowledge of in-situ fuel distributions in practical combustion devices, such as internal combustion engines, is crucial for research and devlopment purposes. Numerous imaging techniques, mostly based on laser-induced fluorescence (LIF), have been developed and yield high levels of 2-D spatial information, but generally lack the temporal resolution (frame rates) necessary to resolve important timescales at sub-millisecond levels for sustained times. A planar LIF technique for quantitatively visualizing fuel distribution is presented which gives not only high spatial resolution, but also high temporal resolution. Using a high-speed CMOS camera, a lens-coupled image intensifier, and frequency-tripled diode-pumped Nd:YAG laser allows for capturing LIF images of biacetyl that is used as a fluorescence tracer at 12 kHz (one crank-angle resolution at 2000 RPM) for hundreds of consecutive engine cycles. The LIF signal strength of biacetyl doped in iso-octane is shown to vary substantially over a wide range of temperatures and pressures. The low absorption coefficient at 355 nm and a longpass filter in the detection path exclude bias errors due to laser beam attenuation and fluorescence trapping. An intensifier gate time of 350 ns is shown to suppress the detection of phosphorescence signals under practical conditions. An example for a quantitative high-speed measurement of fuel concentration at varying pressure and temperature conditions is presented. Quantitative equivalence ratio maps are shown for the fuel injection event within a single cycle in a spark-ignition direct-injected engine, showing the ability of the technique to not only reveal static fuel concentration maps, but also the motion of the fuel cloud along with very steep gradients. Spray velocities determined from the moving fuel cloud are in agreement with previous particle image velocimetry measurements.     

低能N+注入植物种子射程分布的模拟计算

伴随着离子束生物技术的广泛应用, 国内许多单位开展了低能离子注入植物种子的实验研究. 其中关于低能离子注入植物种子诱变的物理机理, 集中在离子注入的深度-浓度分布上. 一些单位直接使用纵向非静态(LSS)理论和TRIM程序来计算低能离子注入植物种子的深度-浓度分布, 却发现计算结果与实验测量结果相差甚远. 所以在对植物种子靶材料进行处理和对LSS理论进行修正的基础上, 在二维近似情况下, 用蒙特卡罗方法分别模拟计算了200keV V⁺和20keV Ti⁺注入花生和棉花种子的射程分布, 得到了与实验结果较符合的曲线. 在此模型基础上, 计算了同样初始条件和理论计算模型下无法从实验上测量的N⁺注入植物种子的射程分布, 初步地为低能N⁺注入植物种子射程分布提供了一种理论计算方法.     

Exact results in modeling planetary atmospheres—I. Gray atmospheres

An exact model is proposed for a gray, isotropically scattering planetary atmosphere in radiative equilibrium. The slab is illuminated on one side by a collimated beam and is bounded on the other side by an emitting and partially reflecting ground. We provide expressions for the incident and reflected fluxes on both boundary surfaces, as well as the temperature of the ground and the temperature distribution in the atmosphere, assuming the latter to be in local thermodynamic equilibrium. Tables and curves of the temperature distribution are included for various values of the optical thickness. Finally, semi-infinite atmospheres illuminated from the outside or by sources at infinity is dealt with.