Large size LYSO crystals for future high energy physics experiments

Because of their high stopping power and fast bright scintillation, cerium doped silicate based heavy crystal scintillators, such as GSO, LSO, and LYSO, have been developed for medical instruments. Their applications in high energy and nuclear physics, however, are limited by lacking high quality crystals in sufficiently large size. The optical and scintillation properties, including the transmittance, emission and excitation spectra and the light output, decay kinetics and light response uniformity, as well as their degradation under /spl gamma/-ray irradiation were measured for two long (2.5/spl times/2.5/spl times/20 cm) LYSO samples from CPI and Saint-Gobain, and were compared to a BGO sample of the same size from SIC. Possible applications for crystal calorimetry in future high energy and nuclear physics experiments are discussed

A Radiation Damage and Recovery Study for Lead Tungstate Crystals from BTCP and SIC

This paper presents result of a study on radiation damage and recovery for lead tungstate crystals produced at BTCP and SIC. Correlations were observed between initial light output and initial longitudinal transmittance at 360 nm, between the loss of longitudinal transmittance at 440 nm and the loss of light output, and between radiation damages levels at different dose rates. No correlations, however, were found between crystal’s initial optical properties and radiation hardness. Excellent linearity was observed between the variations of crystal’s light output and its longitudinal transmittance at 440 nm in several cycles of irradiation followed by recovery, indicating these PWO crystals can be monitored in situ at LHC

华南与东南亚华人社会的互动关系--以潮人侨批网络为中心 (1911-1949) = Interactions between South China and the Chinese Communities in Southeast Asia : A study of the Teochew remittance networks, 1911-1949

Ph.DDOCTOR OF PHILOSOPH

Facial Expression Recognition Based on SVM in E-learning

AbstractFacial expression is one of the most powerful channels of nonverbal communication which contains plenty of affective information. Recognition of facial expression and sending them back to the teacher is potentially helpful in E-learning. In this paper, we differentiate between person-relevant and person-irrelevant situations. Our goal is to extract powerful features used for facial expression recognition system in real-time and person-irrelevant situation. Previous work suggests that both facial shape features and appearance features could be used to recognize facial expressions. The first type is shape features calculated from positions on a face. The second type is a set of multi-scale and multi-orientation Gabor wavelet coefficients. The classifier is based on Support Vector Machines (SVM) and our expriments cover both person-relevant and person-irrelevant situations. The result shows that in person-irrelevant situation, using facial shape features outperforms using Gabor wavelet and it is faster. Furthermore, the radial basis function of SVM is more suitable for person-associated situation and the linear function describes person-irrelevant problems better

Essays on Portfolio Optimization, Volatility Modelling and Risk Measurement

This study comprises of three essays on the subject of financial risk management with applications in the fields of portfolio optimization, continuous and discrete time stochastic volatility (SV) modelling. We jointly consider two risk measures: Value-at-Risk (VaR) and conditional Value-at-Risk (CVaR) to measure the financial market risk. In order to model the distribution of financial asset returns which is characterized by skewness, heavy tails and leptokurtosis, we employ the Asymmetric Laplace distribution (ALD) in the first and third essay while constructing the risk model on the basis of the Heston stochastic volatility (SV) model in the second essay. Specifically, in the first essay, we provide a comprehensive empirical examination of the viability of the new proposed Mean-CVaR-Skewness optimization model under ALD by Zhao et al. (2015). In addition, we propose the Mean-VaR-Skewness model under ALD by employing VaR as risk measure. The closed-form solution of the two optimization models is shown to be consistent and is obtainable by using the Lagrange Multiplier approach. In the second essay, we construct the VaR and CVaR models for the financial dynamics that do not have a closed-form probability density function. The only input required in our approach is the knowledge of the characteristic function of the underlying asset. In the numerical analysis, we investigate the elements that could impact the VaR and CVaR approximations in the Heston model. The third essay contributes to the existing literature by extending the ALD (Kotz et al., 2001) to the return error term of a standard discrete time SV model. We give the closed-form VaR and CVaR formulas for oil supply and demand. As additional contribution, we propose a new scale mixture of uniform (SMU) representation for the AL density so that the model can be implemented efficiently within the Bayesian Markov Chain Monte Carlo framework

Effect of counter-rotating fan’s speed matching on stall inception and characteristics of tip clearance flow

In order to study the effect of speed matching on behavior of tip clearance flow and its possible link to stall inception in counter-rotating fan, the Reynolds-averaged Navier-Stokes equations are solved by the numerical method in conjunction with a SST turbulence model, the effect of speed matching on performance and stability margin are investigated, so are the difference of the tip clearance flow in different speed matching. Furthermore, the effect of speed matching on behavior of tip clearance flow and its possible link to stall inception are investigated. Research results show that: when the rotational speed of Rotor 2 is less than that of Rotor 1, with the decrease of rotational speed of Rotor 2 has no notable effect on tip clearance flow fields of the two rotors, therefore offset of stalling boundary is minor and strong blockage effect is observed in Rotor 1; when the rotational speed of Rotor 1 is less than that of Rotor 2, decrease of rotational speed of Rotor 1 show significant effect on the two rotors, which leads to major offset of stalling boundary, tip leakage flow performance of Rotor 1 improved, while that of Rotor 2 weakened and large blockage area occurs. By comparison, speed variation of Rotor 1 has more effect on stalling boundary of counter-rotating fan

A neural network-based direct adaptive fault tolerance flight control for control surface damage

AbstractIn order to enhance the reliability of flight control systems, a new neural network-based direct adaptive fault tolerance control was proposed for flight control system in the presence of control surface damage. Based on the accuracy approach of neural network, a fault parameter identification models were built to constitute hybrid compensator in order to ensure the strictly positive real of the failure flight control systems in the inner control loop. In the outer loop, a common direct adaptive controller was designed. The scheme was illustrated through simulations using an aircraft. The results show that an aircraft has also good dynamic performance in the control surface damage

Wetting and Drying of Colloidal Droplets: Physics and Pattern Formation

When a colloidal droplet is deposited on a solid substrate at ambient condition, it will experience the processes of wetting and drying spontaneously. These ostensibly simple and ubiquitous processes involve numerous physics: droplet spreading and wetting, three-phase contact line motion, flow fields inside droplets, and mass transportation within droplets during drying. Meanwhile, the continuous evaporation of liquid produces inter- and/or intra-molecular interactions among suspended materials and builds up the internal stress within droplets. After drying, interesting and complex desiccation patterns form in the dried droplets. These desiccation patterns are believed to have wide applications, e.g., medical diagnosis. However, many potential applications are limited by the current understanding of wetting and drying of colloidal droplets. This chapter focuses on the complex physics associated with these processes and the pattern formation in the dried colloidal droplets. Moreover, potential applications of these desiccation patterns and prospective works of wetting and drying of the colloidal droplets are outlined in this chapter