蓝宝石衬底上生长的Ga2+xO3-x薄膜的结构分析

利用卢瑟夫背散射/沟道技术和金属有机化学气相沉积方法, 对蓝宝石衬底上 在不同温度、压强下生长的Ga_2+xO_3-x薄膜进行结构和结晶品质的测量与分析; 并结合高分辨X射线衍射分析技术, 通过对其对称(402)面的θ–2θ及ω扫描, 确定了其结构类型及结晶品质. 实验表明: 在相同的生长温度(500 ℃)下, 结晶品质随压强的下降而变好, 生长压强为15 Torr (1 Torr=133.322 Pa)的样品其结晶品质最好, 沿轴入射之比χ_min值为14.5%; 在相同的生长压强(15 Torr)下, 结晶品质受生长温度的影响不大, 所以, 生长温度不是改变结晶品质的主要因素; 此外, 在相同的生长条件下制备的样品, 分别经过700, 800和900 ℃退火后, 其结晶品质随退火温度的变化而变化. 退火温度为800 ℃的样品的结晶品质最好, χ_min值为11.1%; 当退火温度达到900 ℃时, 样品部分分解; 经热处理的样品其X射线衍射谱中有一个强的Ga₂O₃ (402)面衍射峰, 其半峰全宽为0.5°, 表明该Ga₂O₃外延膜是(402)择优取向. 关键词： 氧化镓 卢瑟夫背散射 X射线衍射 结晶品质     

Effect of side chain conjugation lengths on photovoltaic performance of two‐dimensional conjugated copolymers that contain diketopyrrolopyrrole and thiophene with side chains

Two new two‐dimensional conjugated copolymers that contain diketopyrrolopyrrole and thiophene with different π conjugation lengths as side chains, called PDPPMTD and PDPPBTD , were designed and synthesized for use in polymer solar cells (PSCs). The resulting copolymers in the thin film state displayed broad absorption in the visible range with an absorption edge at over 1000 nm, and both had relatively low‐lying HOMO levels, at ?5.20 and ?5.18 eV for PDPPMTD and PDPPBTD , respectively. The power conversion efficiency (PCE) of the PSC that was based on PDPPBTD /PC61BM (w/w = 1:2) reached 4.10 % with a Jsc of 14.5 mA/cm2, a Voc of 0.59 V and an FF of 48%, while PDPPMTD /PC61BM (w/w = 1:2) had a PCE of 2.96% with a Jsc of 12.6 mA/cm2, a Voc of 0.60 V, and an FF of 39%. These results indicate that subtle tuning of the chemical structure can significantly influence Jsc and FF. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 2878–2889     

Synthesis and characterization of miniemulsion copolymers of methyl methacrylate (or styrene) and stearyl methacrylate

The copolymers of methyl methacrylate (MMA) (or styrene (ST))/stearyl methacrylate (SMA) obtained from miniemulsion polymerization were prepared and characterized. All the miniemulsions showed satisfactory colloidal stability upon aging due to the effectively retarded Ostwald ripening by the reactive costabilizer SMA. In subsequent miniemulsion copolymerizations, monomer droplet nucleation predominated in the particle formation process, but homogeneous nucleation could not be ruled out even at such high levels of SMA (20–50 wt.%). The contact angle first increased rapidly and then leveled off when the SMA content increased from 20 to 50 wt.% for both the copolymers of MMA/SMA and ST/SMA. At constant level of SMA, the copolymer of MMA/SMA with a less hydrophobic composition showed a larger contact angle compared to the ST/SMA counterpart. The contact angle (103 ± 1°) of the copolymer MMA/SMA (50/50 w/w) was comparable to that (104°) of PSMA. A schematic model was proposed to explain the experimental results.     

Ordinal Optimization of G/G/1/K Polling Systems with <Emphasis Type="Italic">k</Emphasis>-Limited Service Discipline

In this paper, we propose an ordinal optimization theory based algorithm to solve the optimization problem of G/G/1/K polling system with k-limited service discipline for a good enough solution using limited computation time. We assume that the arrival rates do not deteriorate visibly within a very short period. Our approach consists of two stages. In the first stage, we employ a typical genetic algorithm to select N=1024 roughly good solutions from the huge discrete solution space Ω using an offline trained artificial neural network as a surrogate model for fitness evaluation. The second stage consists of several substages to select estimated good enough solutions from the previous N, and the solution obtained in the last substage is the good enough solution that we seek. Using numerous tests, we demonstrate: (i) the computational efficiency of our algorithm in the aspect that we can apply our algorithm in real-time based on the arrival rate assumption; (ii) the superiority of the good enough solution, which achieves drastic objective value reduction in comparison with other existing service disciplines. We provide a performance analysis for our algorithm based on the derived models. The results show that the good enough solution that we obtained is among the best 3.31×10⁻⁶% in the solution space with probability 0.99. This research work was supported in part by the National Science Council of Taiwan, ROC, Grant NSC95-2221-E-009-099-MY2.     

Mechanical properties,thermal stability,sound absorption,and flame retardancy of rigid PU foam composites containing a fire‐retarding agent: Effect of magnesium hydroxide and aluminum hydroxide

Isocyanate, polyether polyol, a flame retardant (10 wt%), and aluminum hydroxide/magnesium hydroxide (0, 5, 10, 15, and 20 wt%) are used to form the rigid polyurethane (PU) foam, while nylon nonwoven fabrics and a polyester aluminum foil are combined to serve as the panel. The rigid PU foam and panel are combined to form the rigid foam composites. The cell structure, compressive stress, combustion resistance, thermal stability, sound absorption, and electromagnetic interference shielding effectiveness (EMI SE) of the rigid foam composites are evaluated, examining the effects of using aluminum hydroxide and magnesium hydroxide. Compared with magnesium hydroxide, aluminum hydroxide exhibits superior performance to the rigid foam composites. When aluminum hydroxide is 20 wt%, the rigid foam composite has an optimal density of 0.153 g/cm³, an average cell size of 0.2466 mm, a maximum compressive stress of 546.44 Kpa, an optimal limiting oxygen index (LOI) of 29.5%, an optimal EMI SE of 40 dB, and excellent thermal stability and sound absorption.     

Possible competing order-induced Fermi arcs in cuprate superconductors

We investigate the scenario of competing order (CO) induced Fermi arcs and pseudogap in cuprate superconductors. For hole-type cuprates, both phenomena as functions of temperature and doping level can be accounted for if the CO vanishes at $T^1$ above the superconducting transition $T_c$ and the CO wave-vector Q is parallel to the antinodal direction. In contrast, the absence of these phenomena and the non-monotonic $d$-wave gap in electron-type cuprates may be attributed to $T^1<T_c$ and a CO wave-vector Q parallel to the nodal direction.     

A work-hardening rule for finite elastic-plastic deformation of metals at elevated temperatures

An extension of Prager-Ziegler's work-hardening rule for infinitesimal elastic-plastic deformation to a work-hardening rule for finite elastic-plastic deformation of polycrystalline metals at elevated temperatures is developed. Attention is given to the development to satisfy certain invariant, continuity and thermodynamic requirements.     

Determination of urinary lead, cadmium and nickel in steel production workers

The determination of toxic metals in urine is an important clinical screening procedure. In this study, the aim of our investigation was to determine the concentrations of Pb, Cd, and Ni in urine samples under routine clinical laboratory conditions. To assess the reliability of these methods, critical factors such as detection limit(s), calibration range(s), cost, accuracy and precision were studied. The method was employed for the quantitative determination of lead, cadmium and nickel in urine samples from steel production and quality control (QC) workers and healthy unexposed controls. After pre-treatment with acids, the samples were digested via a microwave oven and the samples were determined by a graphite furnace atomic absorption spectrometry (GFAAS). Quality control for these procedures was established with the concurrent analysis of Standard Trace Metals 7879 Level II and NIST SRM 2670 (Toxic Elements in Freeze Dried Urine). The results indicate that urinary lead, cadmium and nickel levels of the exposed workers are significantly higher those of the controls. The possible connection of these elements with the etiology of disease is discussed. The results also show the need for immediate improvements in workplace ventilation and industrial hygiene practices.     

Low-conductivity buffers for high-sensitivity NMR measurements

The sensitivity of nuclear magnetic resonance (NMR) probes, especially the recently introduced cryogenic probes, can be substantially reduced by the electrical noise generated by conductive samples. In particular, samples of biological macromolecules, which usually contain salts to keep the pH constant and to prevent aggregation, can experience a significant reduction in sensitivity. So far this dependence has forced researchers to minimize the salt concentrations in their samples. Here we demonstrate that the decisive factor is not the salt concentration itself but the conductivity which is a function of both the concentration and the mobility of the ions in solution. We show that by choosing buffers with low ionic mobility, the sample conductivity can be dramatically reduced and the sensitivity substantially enhanced compared to the same measurement with an equal concentration of a standard NMR buffer such as phosphate. We further show that the highest sensitivity gain of one buffer over another buffer is equal to the square root of the ratio of their ion mobilities and describe a simple method to evaluate the effect of a certain buffer on the sensitivity.