Estimation of Turbulence Effects on Wind-Induced Suctions on the Roof of a Low-Rise Building

The effects of turbulence in the atmospheric boundary layer (ABL) on surface pressures of a typical low-rise building roof are investigated in this thesis. A 1/50 geometrically-scaled model of the Texas Tech University Wind Engineering Field Research Lab (WERFL) building model is used for pressure measurements in wind tunnel experiments. ABL wind turbulence intensities ranging from about 10% to 30%, and length scales ranging from 6 to 12 times of the building height (H) are generated. The effects of ABL turbulence on the mean roof pressures within the separated flow are explained from the time-averaged Navier-Stokes equations. The pressure fields are reconstructed by integrating the pressure gradients using an analytic interpolation approach. For high turbulence intensity levels, the maximum suction coefficient on the roof surface was found to be increased. Such increasing magnitudes are directly related to reduced sizes of mean separation bubbles, more rapid variation of the velocity magnitude near the leading edge and enhanced variation of the turbulence stresses. On the other hand, higher surface pressure recovery found in the leeward portion of the separation bubble is mainly due to the more rapid variation of the turbulence stresses. The effects of ABL turbulences on the fluctuating roof surface pressures are explained by the quasi-steady (QS) theory. Basically, the QS model assumes that the instantaneous roof surface pressure is induced by a modified local mean flow field. The selection of the mean flow pattern and the amplification of the velocity magnitudes are determined so that the resulted instantaneous velocity vector is matched to the measurement at the reference location, i.e., 1H above the roof leading edge in this thesis. The QS model is found to explain the effects of large length scale turbulences very well. Better QS-predictions are observed if vertical component of the velocities are included. A statistical method for estimating the surface pressure probability distribution, based on the assumptions from the QS model, is derived and validated. This method relates the pdf of building surface pressures to the joint pdf of wind speed, azimuth angle, and elevation angle

Permeability and volume change characeristics of bentonite-sand mixes in a contaminant environment

This research was conducted to study the characteristics of permeability and volume change of bentonite-sand mixes due to contaminants. The soil specimens consisted of clean sand, bentonite, and fly ash. Test liquids included seven diluted organic and inorganic chemicals and a landfill leachate. Index tests included liquid limit, expansion, cracking, and sedimentation tests. Expansion tests proved to be the most useful for permeability evaluation in a contaminant environment. The conventional consolidometer permeameter and flexible wall permeameter proved to be not completely satisfactory for testing soft bentonite mixes. A triple ring permeameter was developed to compensate for the limitations of these equipment and to provide a more convenient means of testing. The test results indicated that diluted chemicals showed an adverse effect on permeability. However, when the consolidation pressure increased and the void ratio decreased, this effect tends to be minimized. Consolidation pressure also restricted the adverse effect of cracking in a specimen and caused no permeability increase. The change of permeability generally agrees with the results found in the index tests and can be explained by the Gouy-Chapman theory. The fly ash from one local source mixed with bentonite did not help to reduce the permeability. The expansion of the bentonite appears to be limited in the mixtures due to the effect of ion replacements. Permeability tests conducted on bentonite-sand mixes indicated that void ratio could not be correlated well with permeability due to the effect of expanded volume of the bentonite. A four-phase soil diagram with two physical parameters, expansion ratio, er, and expansion function, ef, is proposed. It can clearly express the volumetric changes of bentonite in a mix resulting from the influence of the chemical. Permeability was found to be strongly correlated to these parameters. It decreased with an increase in er and ef. The concept of expansion appears to be very helpful in evaluating the permeability response of a bentonite mixture in a contaminant environment

Fast Response Liquid Crystal Devices

Liquid crystal (LC) has been widely used for displays, spatial light modulators, variable optical attenuators (VOAs) and other tunable photonic devices. The response time of these devices is mainly determined by the employed liquid crystal material. How to obtain fast response for the LC devices is a fundamentally important and technically challenging task. In this dissertation, we investigate several methods to improve liquid crystal response time, for examples, using dual-frequency liquid crystals, polymer stabilized liquid crystals, and sheared polymer network liquid crystals. We discover a new class of material, denoted as sheared polymer network liquid crystal (SPNLC) which exhibits a submillisecond response time. First, dual-frequency liquid crystals and polymer network methods are demonstrated as examples for the variable optical attenuators. Variable optical attenuator (VOA) is a key component in optical communications. Especially, the sheared PNLC VOA shows the best result; its dynamic range reaches 43 dB while the response time is in the submillisecond range at 1550 nm wavelength, which is 50 times faster than the commercial LC-based VOA. Second, we report a new device called axially-symmetric sheared polymer network liquid crystals (AS-SPNLC) and use it as LC devices. An axially-symmetric sheared polymer network liquid crystal has several attractive features: 1) it is polarization independent, 2) it has gradient phase change, and 3) its response time is fast. It can be used for polarization converter and divergent LC lens. In addition, a new method for simultaneously measuring the phase retardation and optic axis of a compensation film is demonstrated using an axially-symmetric sheared polymer network liquid crystal. This simple technique can be used for simultaneously measuring the optic axis and phase retardations of both A- and C-plates. These compensation films have been used extensively in wide-view LCD industry. Therefore, this method will make an important impact to the LCD industry

AN ECONOMY-WIDE ANALYSIS OF GM FOOD LABELING POLICIES IN TAIWAN

The development of agricultural biotechnology offers the opportunity to increase crop production, lowers farming costs, improves food quality and could reduce costs to consumers. For the food importing economies, the import quantities as well as prices will be affected through world market as the production technology of GM crops is adopted by the exporting countries. Many sectors will be affected by the use of these crops through vertical (or backward) and horizontal (or forward) linkages. The purpose of this paper is to develop an economy-wide quantitative assessment of the economic impacts of the introduction of GM products with and without labeling. The modeling framework used in this analysis is TAIGEM (Taiwan General Equilibrium Model), a multi-sectoral computable general equilibrium (CGE) model of the Taiwan¡¦s economy which is derived from ORANI model (Dixon, Parmenter, Sutton and Vincent, 1982). TAIGEM is amended by splitting corn and soybeans into GM and non-GM varieties. It also endogenizes the decision of producers and consumers to use GM vs. non-GM corn and soybeans in their intermediate uses and consumption, respectively. We also consider the consumers¡¦ acceptance of GM food so that the mandatory labeling policy can be examined. Our simulation results indicate that the most extreme import ban on GM crops would be very costly in terms of total production values, ranging from NT$ 40 to 90 billions per year.Research and Development/Tech Change/Emerging Technologies,

Transflective Liquid Crystal Display Using Separate Transmissive and Reflective Liquid Crystal Cells and Materials with Single Cell Gap

A transflective liquid crystal display (TLCD) using separate transmissive (T) and reflective (R) cells in which two liquid crystal materials with different birefringence changes are used. The birefringence change of the R region is half of the birefringence change of the T region. In this case, a single cell gap is possible and identical transmittance and reflectance for R and T is obtained. It is applicable to various reflective LC modes, and the fabrication methods are simple

AN ONTOLOGY-BASED DOCUMENT RECOMMENDATION SYSTEM: DESIGN, IMPLEMENTATION, AND EVALUATION

With the explosion of information, more and more people are embarrassed to manage information effectively. How to search and retrieve accurate information match to people\u27s requirements has been an important issue in information management research. Although search engine can solve this problem partly, the support of manage information is still limited. To use search engine, the users should input precise keywords by themselves first and this stage might cause much confusion to users. For that reason, we need a recommendation system that can catch users\u27 preferences to help users to obtain information more quickly and conveniently without copious process. In our research, a recommendation system is designed based on users\u27 profile. We use ontology technology to be the core of our recommendation system, because ontology can describe the concepts and relations of individual\u27s domain knowledge. Formal Concept Analysis (FCA) algorithm is one of the most popular methods to build ontology, and we apply it to construct our experimental system to recommend master theses to subjects. In order to evaluate our recommendation system, we developed a FCA-based system and another Scoring FCA-based system as treatments, and a Keyword-based system as a control group. We focus on both users\u27 satisfaction on information quality and system quality of our systems. The results show that users have higher information satisfaction on Scoring FCA-based system and FCA-based system than Keyword-based system. This study contributes to research and practice in information recommendation system

The Influence of Short-Range Correlation on the Phonon Confinement of a Single ZnO Nanowire

Abstract Plenty of researches have been performed to probe the diverse properties of ZnO nanowires, but only a few have focused on the physical properties of a single nanowire since to analyze the optical confinement and their correlation lengths along a single nanowire is difficult. In this study, a single ZnO nanowire was synthesized using a Ti-assisted chemical vapor deposition (CVD) method to avoid the appearance of catalytic contamination. Confocal Raman spectroscopy is a powerful tool for probing the phonon confinement effect in a single ZnO nanowire. A confinement model was used to calculate the correlation lengths along the growth direction. The Raman mapping of ZnO nanowires was obtained by a confocal Raman spectrometer. A phonon confinement model was used to fit the Raman curves of the E2 mode and to obtain the correlation lengths along the growth direction of the ZnO nanowire. The correlation lengths are related to the phonon confined region by boundaries and/or defects

Effect of fare and travel time on the demand for domestic air transportation

April 1979Includes bibliographical references (p. 80)Introduction: One of the axioms in the air transportation industry is that advances in technology have led to a greater amount of passenger travel by air. Improvements in airframe and engine design have increased range, speed and payload and have decreased seat-mile costs (in constant dollars), while simultaneously introducing more comfortable and safer travel. The resultant lower ticket prices have made pleasure travel steadily more attractive in the competition for the consumer's disposable income, while the availability of comfortable, high speed travel has increased the air mode's share of business travel. However, it has not been a trivial matter to determine the magnitude of travel that can be attributed to advanced aircraft technology. NASA, as the U.S. government agency responsible for research and technology in commercial aviation, has a natural interest in the applications of the technological improvements it has helped to create. Thus NASA has sponsored research analyzing the economic and operational impact of technological innovations; some of these studies have attempted to quantify the demand for air transportation that improvements in technology have brought about. This report presents the final results of an econometric demand model developed by the MIT Flight Transportation Laboratory under NASA sponsorship over the course of the last three years. During the first two years the conceptual framework for the model was developed and the initial calibration was undertaken.* Preliminary results were encouraging and validation and refinement of the model continued under Langley sponsorship during 1978. The model that was finally developed is useful for analyzing long haul domestic passenger markets in the United States. Specifically, it was used to show the sensitivities of passenger demand to changes in fares and speed reflecting technology through more efficient designs of aircraft; and to analyze, through the year 2000, the impact of selected changes in fares, speeds, and frequencies on passenger demand.Supported by NAS