Sputtering of compound semiconductor surfaces. II. Compositional changes and radiation-induced topography and damage

Ion bombardment often leads to compositional changes in the surface layers of multicomponent targets. Such changes due to noble gas ion sputtering are discussed for InP and GaAs. The analyses show that the compositional change in InP (i.e., indium enrichment) is mainly due to preferential sputtering. In the case of GaAs. the changes are due to radiation-induced diffusion and segregation effects. Brief mention is made of compositional changes in a few other systems. The discussion on sputter-induced topography development deals mainly with InP because ion bombardment leads to dramatic topographical effects in this material. Ripple development on GaAs is also briefly discussed. Radiation damage has been well researched, and its mechanism and effects usually differ substantially when going from one semiconductor group to another. Bombardment-induced damage is briefly discussed for InP, GaAs, SiC, some II-VI semiconductors, and HgCdTe.     

用新局域模型计算高Z靶的溅射产额

用ACAT模拟程序计算了不同离子碰撞在单原子材料上的溅射产额。计算中采用山村等人提出的包括壳效应的新电子能量损失局域模型 ,原子间作用势使用Moli啨ｒｅ势?扑愕玫降慕峁胧笛槭莺蜕酱宓鹊木楣浇斜冉?,符合得很好     

Optimal harvesting for a stochastic regime-switching logistic diffusion system with jumps

The optimization problem of fishing for a stochastic logistic model is studied in this paper. Besides a standard geometric Brownian motion, another two driving processes are taken into account: a stationary Poisson point process and a continuous-time finite-state Markov chain. The classical harvesting problem for this model is a big difficult puzzle since the corresponding Fokker–Planck equations with three types of noise are very difficult to solve. Our main goal of this paper is to work out the optimization problem with respect to stationary probability density. One of the main contributions is to provide a new equivalent approach to overcome this problem. More precisely, an ergodic method is used to show the almost surely equivalency between the time averaging yield and sustainable yield. Results show that the optimal strategy changes with environment. An interesting thing is that the optimal strategy for each state is equivalent to the global optimality.     

Average 2p subshells fluorescence yield values of some elements in the atomic number range 60 ≤ Z ≤ 90

The average 2p (L_2,3) subshells fluorescence yield (?_2,3) in 11 elements with Z ranging from 60 to 90 were measured with corporation of total L_2,3 X-ray production cross-sections. Measurements were carried out exciting L₂ and L₃ subshells of relevant elements that were exposed to beam of selected K X-rays from secondary sources. The measured values were compared with theoretical and semi-empirical values. It is clear that the present values of experimental ?_2,3 are generally smaller than the calculated and semi-empirical values for some elements in the atomic number range 60–90.     

Rational Perturbation of the Fluorescence Quantum Yield in Emission‐Tunable and Predictable Fluorophores (Seoul‐Fluors) by a Facile Synthetic Method Involving CH Activation

Fluorescence imaging enables the uniquely sensitive observation of functional‐ and molecular‐recognition events in living cells. However, only a limited range of biological processes have been subjected to imaging because of the lack of a design strategy and difficulties in the synthesis of biosensors. Herein, we report a facile synthesis of emission‐tunable and predictable Seoul‐Fluors, 9‐aryl‐1,2‐dihydrolopyrrolo[3,4‐b]indolizin‐3‐ones, with various R¹ and R² substituents by coinage‐metal‐catalyzed intramolecular 1,3‐dipolar cycloaddition and subsequent palladium‐mediated C? H activation. We also showed that the quantum yields of Seoul‐Fluors are controlled by the electronic nature of the substituents, which influences the extent of photoinduced electron transfer. On the basis of this understanding, we demonstrated our design strategy by the development of a Seoul‐Fluor‐based chemosensor 20 for reactive oxygen species that was not accessible by a previous synthetic route.     

Iodination of Aromatic Compounds Using Potassium Iodide and Hydrogen Peroxide

A simple, efficient, regioselective, and ecofriendly method for oxyiodination of aromatic compounds is presented. In this method, the electrophilic substitutions of iodine generated in situ from KI as an iodine source and hydrogen peroxide as an oxygen source have been employed without any catalyst/mineral acid for the first time.     

Flow behaviour of titanium dioxide dispersions in the presence of 2-hydroxyethyl cellulose

 The effects of 2-hydroxyethyl cellulose (HEC) of weight-average molecular weight 15,000, 90,000 and 7,20,000 on the rheological properties of TiO₂ dispersions were evaluated. For all three HECs, the maximum yield stress, τ_ymax, (occurred at zero zeta potential), decreased with increasing HEC concentration. Interestingly, the largest reduction in τ_ymax was observed with the HEC with the highest molecular weight. This reduction was attributed to steric interaction arising from adsorbed HEC. Adsorbed high-molecular-weight HEC formed an effectively thicker steric barrier because of its larger size and higher adsorption capacity. Bridging interactions that were expected to be important for the high-molecular-weight HEC were found to be unimportant here. In the flocculated regime, HEC enhanced the shear-thinning characteristics of the TiO₂ dispersions. Received: 8 November 1999 Accepted: 20 December 1999     

遗传算法结合神经网络在油气产量预测中的应用

基于遗传算法的全局搜索能力和BP算法的局部精确搜索特性,通过采用遗传算法优化神经网络的方法,将遗传算法和BP算法有机结合,做到优势互补,在提高油气产量预测精度的研究中得到了很好的应用.在对国内某中小型气田油气产量的预测中,以历史产量资料进行检验,其结果表明,提出的预测方法,预测精度明显优于BP算法,证明了这种方法的有效性和可靠性.     

On parabolic equations with gauge function term and applications to the multidimensional Leland equation

This paper studies the effect of introducing stochastic volatility in the first‐passage structural approach to default risk. The impact of volatility time scales on the yield spread curve is analyzed. In particular it is shown that the presence of a short time scale in the volatility raises the yield spreads at short maturities. It is argued that combining first passage default modelling with multiscale stochastic volatility produces more realistic yield spreads. Moreover, this framework enables the use of perturbation techniques to derive explicit approximations which facilitate the complicated issue of calibration of parameters.     

Diglycidylphenylphosphate based fire retardant liquid crystalline thermosets

Organophosphorus liquid crystalline thermosets (LCTs) were developed using diglycidylphenylphosphate (DGPP) and various aromatic diamines. DGPP was prepared by the esterification of phenylphosphorodichloridate with glycidol. 2,5-Bis(p-aminophenyl)-1,3,4-oxadiazole (BPOD) was synthesized and three different commercial diamines, 4,4′-diaminodiphenyl sulphone (DDS), 4,4′-diaminodiphenyl methane (DDM) and biphenyl diamine (BPD) were used as curing agents. The mesomorphic behaviour of DGPP/diamine mixtures and their curing kinetics were monitored by differential scanning calorimetry and hot stage optical polarized microscopy. The thermogravimetric analysis data showed that the LCTs are stable in the range 261-292 °C and afford 36-48% char yield. The limiting oxygen index values are between 35 and 47 proving fire retardance. The mechanical properties of the cured LCTs were characterized by dynamic mechanical analysis.