A theoretical model of the linear electro-optic effect

A simple theoretical study of the linear electro-optic effect is presented. This semiclassical approach is based on the single-energy-gap model, the dielectric theory and the concepts of bond charge and effective ionic charge. A general expression is obtained for the electro-optic coefficient of a crystal and is applied to a wide variety of diatomic and ternary compounds including zincblende (GaAs, GaP, ZnSe, ZnS, ZnTe, CuCl), wurtzite (ZnS, CdS, CdSe), quartz (SiO2), lithium niobate (LiNbO3, LiTaO3), KDP (KH2PO4, KD2PO4, NH4H2PO4), chalcopyrite (AgGaS2, CuGaS2) and proustite (Ag3AsS3). The calculated results are generally in good agreement with experiment

Relationships among student attitudes, motivation, learning styles, learning strategies, patterns of learning and achievement: a formative evaluation of distance education via Web-based courses

The World Wide Web (WWW) is the latest in a long line of educational technologies, and the list of courses on it is growing daily. Formative evaluations would help educators enhance teaching and learning in Web-based courses. This study analyzed the relationships between student achievement and the following variables: attitudes, motivation, learning strategies, patterns of learning, learning styles, and selected demographics. It was a population study that included 99 students taking two non-major introductory biology courses offered over the WWW by Iowa State University in the fall of 1997. Seventy-four (75%) students completed a learning style test, an on-line questionnaire, and received a grade by the end of the semester. The learning style test was the Group Embedded Figures Test (GEFT), which classified students as either field-dependent or field-independent. The on-line questionnaire consisted of four scales (attitude, motivation, learning strategies, and patterns of learning), whose pilot-test reliabilities ranged from .71 to .91. The selected demographic variables were gender, class level, previous experience in subject area, hours per week studying and working, computer access, and types of students as off-campus, on-campus, or adult students. Over two-thirds of the students taking the Web-based courses were field-independent learners; however, there were no significant differences (.05 level) in achievement by learning style. Also, different backgrounds of students with different learning styles learned equally well in Web-based courses. The students enjoyed the convenience and self-controlled learning pace and were motivated by competition and high expectations in Web-based learning. They used most the learning strategies of finding important ideas from lectures and memorizing key words of important concepts and least the learning strategy of making charts or tables to organize the material. They seemed more interested in checking their grades than in communicating with the class and instructors via e-mail, discussion netforum or chat netforum. Motivation and learning strategies were the two significant factors that explained more than one-third of student achievement measured by class grade. Educators should assist students in mastering different motivational and learning strategies to help them become self-regulated learners

The Potential Economic Impact of Avian Flu Pandemic on Taiwan

This study analyzes the potential consequences of an outbreak of avian influenza (H5N1) on Taiwan¡¦s macro economy and individual industries. Both the Input-Output (IO) Analysis Model and Computable General Equilibrium (CGE) Model are used to simulate the possible damage brought by lowering domestic consumption, export, and labor supply. The simulation results indicates that if the disease is confined within the poultry sector, then the impact on real GDP is around -0.1%~-0.4%. Once it becomes a human-to-human pandemic, the IO analysis suggests that the potential impacts on real GDP would be as much as -4.2%~-5.9% while labor demand would decrease 4.9%~6.4%. In the CGE analysis, which allows for resource mobility and substitutions through price adjustments, the real GDP and labor demand would contract 2.0%~2.4% and 2.2%~2.4%, respectively, and bringing down consumer prices by 3%. As for the individual sector, the outbreak will not only damage the poultry sector and its upstream and downstream industries, but also affect the service sectors including wholesale, retail, trade, air transportation, restaurants, as well as healthcare services. These results can be used to support public investment in animal disease control measures.Avian Flu Pandemic, Input-output Model, Computable General Equilibrium Model, Livestock Production/Industries,

Caffeamide 36-13 Regulates the Antidiabetic and Hypolipidemic Signs of High-Fat-Fed Mice on Glucose Transporter 4, AMPK Phosphorylation, and Regulated Hepatic Glucose Production

This study was to investigate the antidiabetic and antihyperlipidemic effects of (E)-3-[3, 4-dihydroxyphenyl-1-(piperidin-1-yl)prop-2-en-1-one] (36-13) (TS), one of caffeic acid amide derivatives, on high-fat (HF-) fed mice. The C57BL/6J mice were randomly divided into the control (CON) group and the experimental group, which was firstly fed a HF diet for 8 weeks. Then, the HF group was subdivided into four groups and was given TS orally (including two doses) or rosiglitazone (Rosi) or vehicle for 4 weeks. Blood, skeletal muscle, and tissues were examined by measuring glycaemia and dyslipidemia-associated events. TS effectively prevented HF diet-induced increases in the levels of blood glucose, triglyceride, insulin, leptin, and free fatty acid (FFA) and weights of visceral fa; moreover, adipocytes in the visceral depots showed a reduction in size. TS treatment significantly increased the protein contents of glucose transporter 4 (GLUT4) in skeletal muscle; TS also significantly enhanced Akt phosphorylation in liver, whereas it reduced the expressions of phosphoenolpyruvate carboxykinase (PEPCK) and glucose-6-phosphatase (G6Pase). Moreover, TS enhanced phosphorylation of AMP-activated protein kinase (phospho-AMPK) both in skeletal muscle and liver tissue. Therefore, it is possible that the activation of AMPK by TS resulted in enhanced glucose uptake in skeletal muscle, contrasting with diminished gluconeogenesis in liver. TS exhibits hypolipidemic effect by decreasing the expressions of fatty acid synthase (FAS). Thus, antidiabetic properties of TS occurred as a result of decreased hepatic glucose production by PEPCK and G6Pase downregulation and improved insulin sensitization. Thus, amelioration of diabetic and dyslipidemic state by TS in HF-fed mice occurred by regulation of GLUT4, G6Pase, and FAS and phosphorylation of AMPK

Two-element free-electron lasers

The interaction between the electrons and the radiation in a free-electron laser leads to a shift and a spread of the electron velocity distribution. The electron dynamics of a two-element system are studied in the small signal region. It is found that the efficiency and gain can be increased through introduction of an adjustable drift distance between two identical wigglers

Single-electron analysis of the space-charge effect in free-electron lasers

An exact treatment of the space-charge effect in the single-electron analysis of a free-electron laser is presented to calculate its small-signal gain. With the inclusion of the repulsive force between electrons, it is found that the trajectory of an electron can be solved from a generalized equation which includes a space-charge term. The results show the gain is saturated with decreasing growth rate due to high electron density. The radiation frequency is found to increase with the electron density and approach the value at plasma resonance. The condition ωpL/c = π clearly defines the boundary between the noninteracting and the collective regime of an electron beam, where ωp is the plasma frequency, L is the device length, and c is the light velocity in vacuum

Quantitative Calculation of Electro-Optic Coefficients of Diatomic Crystals

The bond-charge dielectric theory of Phillips and Van Vechten is applied to the calculation of the electro-optic tensor coefficients. The agreement of the theoretical predictions with experimental values in the case of zinc blende and wurtzite crystals is very good