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

Asymptotically Stable Walking of a Five-Link Underactuated 3D Bipedal Robot

This paper presents three feedback controllers that achieve an asymptotically stable, periodic, and fast walking gait for a 3D (spatial) bipedal robot consisting of a torso, two legs, and passive (unactuated) point feet. The contact between the robot and the walking surface is assumed to inhibit yaw rotation. The studied robot has 8 DOF in the single support phase and 6 actuators. The interest of studying robots with point feet is that the robot's natural dynamics must be explicitly taken into account to achieve balance while walking. We use an extension of the method of virtual constraints and hybrid zero dynamics, in order to simultaneously compute a periodic orbit and an autonomous feedback controller that realizes the orbit. This method allows the computations to be carried out on a 2-DOF subsystem of the 8-DOF robot model. The stability of the walking gait under closed-loop control is evaluated with the linearization of the restricted Poincar\'e map of the hybrid zero dynamics. Three strategies are explored. The first strategy consists of imposing a stability condition during the search of a periodic gait by optimization. The second strategy uses an event-based controller. In the third approach, the effect of output selection is discussed and a pertinent choice of outputs is proposed, leading to stabilization without the use of a supplemental event-based controller

Gas Dispersion Modeling

Involvement of flammable or toxic materials in a process plant causes the risk of accidents. Hazard analysis and risk-based management are important to prevent escalation of dangerous event. Due to ill-defined leakage conditions, there are a few areas of uncertainty which lead to difficulty in positioning gas detectors. In industry, positioning of gas detectors has always been based on personal expertise rather than computer modeling. This method lacks of consistency and it tends to focus on locations of potential leakage but not locations of total gas accumulation. Development of gas dispersion modeling tool aids in better understanding of possible path of gas distribution and accumulation. Based on the dispersion results, possible locations of gas detector can be indicated. Gaussian plume model is being employed in this project to study dispersion of natural gas. Natural gas is a type of light gas and neutrally buoyant. Effects of meteorological parameters and gas emission rate are factors affecting dispersion pattern. After filtering the concentrations fall out of flammable range, locations where concentrations within flammable range occur are identified using top view plot and front view plot. Consequently, locations of gas detector can be determined

A study of the interlanguage of apology by Taiwanese English-Language learners

This thesis presents a study of the interlanguage of the speech act of apology by Taiwanese learners of English. It compares the way Taiwanese learners apoologize in English and how they apologize in Mandarin Chinese, as well as how native speakers of American English apologize

Moral and Legal Issues Concerning Contemporary Human Cloning Technology : Quest for Regulatory Consensus in the International Community to Safeguard Rights and Liberties Essential to the Future of Humanity

The research topic for this dissertation would focus its efforts on resolving at least two questions as follows: First, what are the major moral and legal problems in current human cloning technology and what are the intelligent choices of public policy? Second, how could respective nations, regions, and the international community corporately clarify those problems in the realm of contemporary human dignity imperative and human rights jurisprudence

The Effects of Manganese on Oxidative DNA Damage in Mesencephalic Cells.

Occupational workers who are exposed to manganese (Mn2+) manifest neural degeneration resembling Parkinson\u27s disease (PD). In the treatments of PD, the \ manipulation of dopamine (DA) concentrations is often utilized. Such manipulations seem to increase DA turnover, but increased DA may also have a deleterious effect. In several cell culture models, it has been shown that Mn2+ interacts with cellular DA and caused dopaminergic cell death. Thus, DA modulation at cellular level induced change in Mn2+and DA interaction eventually causes cell death in vulnerable brain areas. Mn2+ in cell culture model appears to induce DNA fragmentation and cell death through oxidative stress. However, DA modulation-induced change in Mn2+ and DA interaction and the underlying mechanism(s) that increased dopaminergic cell\u27s vulnerability remain unclear. In the present study, we showed that Mn2+ exposure (0-500 11M) to mesencephalic cells for 24 hrs induced minimal apoptotic cell death. However, in cell 2 cultures 2 hrs pre-exposure to DA (200 u M) potentiated Mn2+ -induced apoptotic cell death remarkably in which oxidative stress was involved. The ability of Mn2+ -induced apoptotic cell death to DA was determined by the measuring lactate dehydrogenase (LDH) and Apoptag TUNEL staining (terminaldeoxynucleotidyl transferase DNA labeling). This was further confirmed by the mitochondrial cell viability assay (MTT). This supports our hypothesis that greater level of DA interacts with Mn2+ and may cause cells to be more susceptible. The involvement of oxidative stress during Mn2+ and DA interaction was revealed through measurement of reactive oxygen species which was potentiated in the presence of DA than Mn2+ alone. DNA extraction following Mn2+ and DA treatment further revealed that DA enhanced Mn2+ induced oxidative DNA damage which was significantly prevented by various antioxidants (superoxide dismutase, catalase and vitamin E) supplementation. In addition, co-incubation of SOD, catalase or vitamin E with Mn2+ and DA significantly protected the cells from apoptotic cell death and LDH activity, which indicates the involvement of oxidative stress during Mn2+ and DA interaction induced dopaminergic cell death. These studies support our hypothesis that greater level of DA interacts with Mn2+, and causes dopaminergic cells to be more susceptible to oxidative DNA damage

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