Modeling current-voltage behaviour in oxide TFTs combining trap-limited conduction with percolation

Current-voltage behaviour of oxide TFTs is modeled based on trap-limited conduction and percolation theories. The mobility has a power-law dependence, in which percolation controls the exponent while trap states determine constant term in the power law. The proposed model, which is fully physically-based, provides a good agreement with measured transistor characteristics as well as transient operations of fabricated pixel test circuits for oxide-based OLED displays. © 2013 Society for Information Display.

A physico-chemical comparative study on extracellular carbohydrate polymers from five desert algae

Hydrodynamic properties of five newly isolated algal extracellular polysaccharides with putative adhesive properties are described, using a combination of size exclusion chromatography, total or 'multi-angle' laser light scattering and analytical ultracentrifugation. The respective polysaccharides had been extracted from four filamentous cyanobacteria: Microcoleus vaginatus, Scytonema javanicum, Phormidium tenue and Nostoc sp. and a coccoid single-cell green. algae Desmococcus olivaceus that had been separated from desert algal crusts of the Chinese Tegger Desert. SEC/MALLS experiments showed that the saccharides had, diverse-weight average molecular weights ranging from 4000 to 250,000 g/mol and all five showed either bi-modal or tri-modal molecular weight distribution profiles. Use of the Mark-Houwink-Kuhn-Sakurada (MHKS) scaling relationship between sedimentation coefficient and (weight average) molecular weight for the five samples, assuming a homologous conformation series revealed an MHKS b exponent of (0.33 +/- 0.04), suggesting a conformation between that of a stiff rod (b similar to 0.18) and a random coil (b similar to 0.4-0.5), i.e. a 'flexible rod' or 'stiff coil'. (C) 2003 Elsevier Ltd. All rights reserved.

Resting metabolism and heat increment of feeding in mandarin fish (Siniperca chuatsi) and Chinese snakehead (Channa argus)

Resting metabolism was measured in immature mandarin fish Siniperca chuatsi weighing 42.1-510.2 g and Chinese snakehead Channa argus weighing 41.5-510.3 g at 10, 15, 20, 25, 30 and 35 degreesC. Heat increment of feeding was measured in mandarin fish weighing 202.0 (+/-14.0) g and snakehead weighing 200.8 (+/-19.3) g fed swamp leach Misgurnus anguillicaudatus at 1% body weight per day at 28 degreesC. In both species, weight exponent in the power relationship between resting metabolism and body weight was not affected by temperature. The relationship between resting metabolism and temperature could be described by a power function. The temperature exponent was 1.39 in mandarin fish and 2.10 in snakehead (P < 0.05), indicating that resting metabolism in snakehead increased with temperature at a faster rate than in mandarin fish. Multiple regression models were used to describe the effects of body weight (W, g) and temperature (T, C) on the resting metabolism (R-s, mg O-2/h): In R-s = - 5.343 + 0.772 In W + 1.387 In T for the mandarin fish and In R-s = -7.863 + 0.801 ln W + 2.104 In T for the Chinese snakehead. The proportion of food energy channelled to heat increment was 8.7% in mandarin fish and 6.8% in snakehead. (C) 2000 Elsevier Science Inc. All rights reserved.

Food consumption and growth of two piscivorous fishes, the mandarin fish and the Chinese snakehead

Rates of maximum food consumption and growth were determined for immature mandarin fish Siniperca chuatsi (47.2-540.2 g) and Chinese snakehead Channa argus (45.0-546.2 g) at 10, 15, 20, 25, 30 and 35 degrees C. The relationship between maximum rate of food consumption (C-max), body weight (W) and temperature (T) was described by the multiple regression equations: lnC(max) = -4.880 + 0.597 lnW+0.284T - 0.0048T(2) for the mandarin fish, and lnC(max)= -6.718 + 0.522 lnW+0.440T-0.0077T(2) for the Chinese snakehead. The optimum temperature for consumption was 29.6 degrees C for the mandarin fish and 28.6 degrees C for the Chinese snakehead. The relationship between growth rate (G), body weight and temperature was ln(G+0.25)= - 0.439 - 0.500 lnW+0.270T - 0.0046T(2) for the mandarin fish, and ln(G+0.25)= - 6.150+ (0.175 - 0.026T) lnW+0.571T - 0.0078T(2) for the Chinese snakehead. The weight exponent in the growth-weight relationship was -0.83 for the mandarin fish, but decreased with increasing temperature for the Chinese snakehead. The optimum temperature for growth was 29.3 degrees C for the mandarin fish, but tended to decrease with increasing weight for the Chinese snakehead, being 30.3 degrees C for a 45-g fish, and 26.1 degrees C for a 550-g fish. (C) 1998 The Fisheries Society of the British Isles.

Intrinsically limited critical temperatures of highly doped Ga1-xMnxAs thin films

Ga1-xMnxAs films with exceptionally high saturation magnetizations of approximate to 100 emu/cm(3) corresponding to effective Mn concentrations of x(eff)approximate to 0.10 still have a Curie temperature T-C smaller than 195 K contradicting mean-field predictions. The analysis of the critical exponent beta of the remnant magnetization-beta = 0.407(5)-in the framework of the models for disordered/amorphous ferromagnets suggests that this limit on T-C is intrinsic and due to the short range of the ferromagnetic interactions resulting from the small mean-free path of the holes. This result questions the perspective of room-temperature ferromagnetism in highly doped GaMnAs.

Band-tail shape and transport near the metal-insulator transition in Si-doped

In the present work, an infrared light-emitting diode is used to photodope molecular-beam-epitaxy-grown Si: Al0.3Ga0.7As, a well-known persistent photoconductor, to vary the effective electron concentration of samples in situ. Using this technique, we examine the transport properties of two samples containing different nominal doping concentrations of Si [1 x 10(19) cm(-3) for sample 1 (S1) and 9 x 10(17) cm(-3) for sample 2 (S2)] and vary the effective electron density between 10(14) and 10(18) cm(-3). The metal-insulator transition for S1 is found to occur at a critical carrier concentration of 5.7 x 10(16) cm(-3) at 350 mK. The mobilities in both samples are found to be limited by ionized impurity scattering in the temperature range probed, and are adequately described by the Brooks-Herring screening theory for higher carrier densities. The shape of the band tail of the density of states in Al0.3Ga0.7As is found electrically through transport measurements. It is determined to have a power-law dependence, with an exponent of -1.25 for S1 and -1.38 for S2.

Antibunching and blinking from a single colloidal CdSe quantum dot

We have investigated the optical properties of single CdSe/ZnS nanocrystals by conducting combinations of experiments on antibunching and photoluminescence intermittence under different experimental conditions. Based on photoluminescence in an antibunching experiment, we analyzed the emission lifetime of QDs by using stretched exponentials. The difference between the parameters obtained from average lifetimes and stretched exponents were analyzed by considering the effect of nonradiative emission. An Auger-assisted tunneling model was used to explain the power law exponents of off time distribution. The power law exponent under high excitation power was correlated with a higher Auger ionization rate. Using the parameters obtained from stretched exponential function and power law, the antibunching phenomena at different time and under different excitation intensity were analyzed.

Correlations between antibunching and blinking of photoluminescence from a single CdSe quantum dot

The antibunching and blinking from a single CdSe/ZnS nanocrystal with an emission wavelength of 655 nm were investigated under different excitation powers. The decay process of the photoluminescence from nanocrystal was fitted into a stretched exponential, and the small lifetime and the small stretching exponent under a high excitation power were explained by using nonradiative multi-channel model. The probability of distributions for off-times from photoluminescence intermittence was fitted into the power law, and the power exponents were explained by using a tunneling model. For higher excitation power, the Auger-assisted tunneling model takes effect, where the tunneling rate increases and the observed lifetime decreases. For weak excitation power, the electron directly tunnels between the nanocrystal and trapping state without Auger assistance. The correlation between antibunching and blinking from the same nanocrystal was analyzed.

Preferred growth of nanocrystalline silicon in boron-doped nc-Si : H Films

Preferred growth of nanocrystalline silicon (nc-Si) was first found in boron-doped hydrogenated nanocrystalline (nc-Si:H) films prepared using plasma-enhanced chemical vapor deposition system. The films were characterized by high-resolution transmission electron microscope, X-ray diffraction (XRD) spectrum and Raman Scattering spectrum. The results showed that the diffraction peaks in XRD spectrum were at 2theta approximate to 47degrees and the exponent of crystalline plane of nc-Si in the film was (220). A considerable reason was electric field derived from dc bias made the bonds of Si-Si array according to a certain orient. The size and crystalline volume fraction of nc-Si in boron-doped films were intensively depended on the deposited parameters: diborane (B2H6) doping ratio in silane (SiH4), silane dilution ratio in hydrogen (H-2), rf power density, substrate's temperature and reactive pressure, respectively. But preferred growth of nc-Si in the boron-doped nc-Si:H films cannot be obtained by changing these parameters. (C) 2004 Elsevier Ltd. All rights reserved.

Time-resolved photoluminescence studies of AlInGaN alloys

We study the two samples of AIInGaN, i.e., 1-mum GaN grown at 1030degreesC on the buffer and followed by a 0.6-mum-thick epilayer of AIInGaN under the low pressure of 76 Torr and the AIInGaN layer deposited directly on the buffer layer without the high-temperature GaN layer, by temperature-dependent photoluminescence (PL) spectroscopy and picosecond time-resolved photoluminescence (TRPL) spectroscopy. The TRPL signals of both the samples were fitted well as a stretched exponential decay at all temperatures, indicating significant disorder in the material. We attribute the disorder to nanoscale quantum dots or discs of high indium concentration. Temperature dependence of dispersive exponent beta shows that the stretched exponential decay of the two samples comes from different mechanisms. The different depths of the localization potential account for the difference, which is illustrated by the results of temperature dependence of radiative recombination lifetime and PL peak energy.

Localized exciton dynamics in AlInGaN alloy

Carrier recombination dynamics in AlInGaN alloy has been studied by photoluminescence (PL) and time-resolved PL (TRPL) at various temperatures. The fast red-shift of PL peak energy is observed and well fitted by a physical model considering the thermal activation and transfer processes. This result provides evidence for the exciton localization in the quantum dot (QD)-like potentials in our AlInGaN alloy. The TRPL signals are found to be described by a stretched exponential function of exp[(-t/,tau)13], indicating the presence of a significant disorder in the material. The disorder is attributed to a randomly distributed QDs or clusters caused by indium fluctuations. By studying the dependence of the dispersive exponent beta on temperature and emission energy, we suggest that the exciton hopping dominate the diffusion of carriers localized in the disordered QDs. Furthermore, the localized states are found to have 0D density of states up to 250 K, since the radiative lifetime remains almost unchanged with increasing temperature. (C) 2003 Elsevier Science Ltd. All rights reserved.

An adaptive controller for a class of nonlinear system using direction basis function

For a class of nonlinear dynamical systems, the adaptive controllers are investigated using direction basis function (DBF) in this paper. Based on the criterion of Lyapunov' stability, DBF is designed which guarantees that the output of the controlled system asymptotically tracks the reference signals. Finally, the simulation shows the good tracking effectiveness of the adaptive controller.

Set invariance in control

The properties of positively invariant sets are involved in many different problems in control theory, such as constrained control, robustness analysis, synthesis and optimization. In this paper we provide an overview of the literature concerning positively invariant sets and their application to the analysis and synthesis of control systems.

土丘陵沟壑区植被恢复过程中的土壤抗蚀与细沟侵蚀演变

对黄土丘陵沟壑区安塞纸坊沟和县南沟、延安燕沟3个流域不同恢复年限的植物群落的土壤抗蚀性和侵蚀程度进行了研究。对12个土壤抗蚀性指标进行主成分分析表明,土壤抗蚀性(主成分综合指数)强弱为灌木群落阶段>多年生草本和蒿类群落阶段>一二年生草本群落阶段,与一二年生草本群落阶段相比,灌木群落阶段与多年生草本和蒿类群落阶段的土壤抗蚀性分别增加了362.29%～673.33%和574.71%～930.00%;野外调查结果分析表明,随着植被的恢复演替,土壤侵蚀量呈现明显的下降趋势,灌木群落阶段的土壤侵蚀量仅为演替初期的1.42%～5.59%;通过回归分析,土壤侵蚀量和水稳性团聚类因子,以及有机质含量之间分别存在极显著与显著相关关系,鉴于土壤分析的易获性,可选择>0.5mm水稳性团聚体与有机质含量作为反映土壤侵蚀程度的指标。