Due to the increased awareness of living and industrial safety, carbon monoxide detectors must be geared towards better portability and sensitivity. Metal oxide semiconductor sensors should possess advantages such as heat and corrosion resistance, low cost materials, and ease of miniaturization. This thesis applied ball milled and powdered ZnO and SnO2 to manufacture into paste, then used the screen printing method deposited ZnO and SnO2 paste film and silver electrode on glass substrate. The influence on sensing film materials, temperature, time of heat treatment, and temperature of measurement was investigated. The samples were fabricated and measured by setting up self-measurement apparatus. The data was analyzed the changes of resistance under different air and carbon monoxide environments. This is followed by analysis of both surface topography and microstructure of the sensing film under OM and SEM. Experiment reveals that samples under different annealing process yield different surface morphology and micro structure while at the beginning of the heat treatment, epoxy evaporates from the sample brought about porous structure. Annealing at higher temperature sample will have more rough surface and better sensitivity in detecting carbon monoxide. After epoxy removed, heat treatment mechanism is then switched to sinter ZnO and SnO2 powders. the longer the samples are sintered, the lower the sensitive. Sensing films composited with ZnO and SnO2 will have better carbon monoxide sensitivity at 300oC but its sensitivity decays at a faster rate than samples working at 250 oC despite the slightly weaker sensitivity. Sensing films with pure ZnO will have higher sensitivity compared to pure SnO2 one. With the increase of SnO2 proportion, carbon monoxide sensitivities of detectors decreases, however, its life time can be improve significantly.

An insulation technique has been developed which contains a single or combination of materials to help minimize heat loss in actual industrial applications. For the petroleum industry, insulation for deep sea piping is one of the greatest challenges which would prevent the industry from meeting the high demand for oil through exploration into deeper ocean environments. At current seafloor depths (5,000~10,000ft), pipeline insulation is essential in preventing pipeline blockage resulting from the solidification of paraffin waxes and / or hydrate formation which exist in crude oil. To maintain crude oil temperatures above the paraffin solidification point (68°C or 155°F), new and better insulation techniques are essential to minimize pipeline heat loss and maintain crude oil temperatures. Therefore, the objective of this investigation was to determine whether or not the thermal resistance of a new insulation concept, which involves IIT (Interstitial Insulation Technology) with screen wire, was greater than existing readily available commercial products through analytical modeling and experimentation. The model takes into account both conforming and nonconforming interfaces at the wire screen contacts within the interstitial space between coaxial pipes. In addition, confirmation was needed to determine whether or not laboratory testing of simulated coupons translate to thermal performance for a prototype pipe segment that fabricated with two layers of low conductivity wire-screen (stainless steel) as the interstitial insulation material. Both the inner and outer surface temperatures of the coaxial pipes were measured in order to evaluate the effective thermal conductivity and thermal diffusivity of the insulation concept. The predicted results from the model compared very favorably with the experimental results, confirming both the trends and magnitudes of the experimental data. In other words, whether the reduction in heat transfer observed for small laboratory samples was realistic for application to a pipeline configuration. This effort involved both analytical modeling for all thermal resistances and experimental test runs for validation of the analytical model. Finally, it was a goal of this investigation to develop a simplified model for a multilayer composite structure which will include radiation heat transfer exchange among the layers that constitute the insulation. With the developed model, feasibility and performance characteristics of the insulation concept were predicted. The thermal predictions have demonstrated the thermal competitiveness of the interstitial insulation technology.

Recently, several major incidents occurred in worldwide metro and subway systems due to inadequate or inappropriate emergency procedures. In this study, the traditional and innovative metro underground stations were analyzed utilizity the CFAST and FDS computer program. A comparative study has been conducted to evaluate the smoke descending rate, and temperature distribution, etc with addressable zoned smoke control system. Dynamic egress analysis was followed to validate the NFPA 130 which was taken as the design guidelines to evaluate the evacuation time using SIMULEX program. Finally, the smoke management design and egress system was integrated, which warrants its qpplication in actual engineering designs.

<p>Railway track and ground vibrations are considered, with anemphasis on methods of mitigation ("countermeasures"), forapplication to wayside disturbance problems.</p><p>Original field measurements from two sites in Sweden, aswell as borrowed measurements from Norway, provide vibrationresults at many points on the track, on and underneath theground surface, for a variety of trains, both with and withoutcountermeasures in-place.</p><p>Infinite periodic system theory is the basis of track-onlyand track-ground interaction models presented. The repeatingelement includes the sleeper, pad-fastener, rail, and either alocally-reacting ballast or a continuous ballast-soilwaveguide. The track-only model is even refined for nonlinearand high-frequency cases. The models are suitable for studyingcountermeasures in the track, or in the foundation(soil-stabilization). This latter countermeasure is shown to beeffective at low frequencies (of geotechnical interest), butsometimes counterproductive at audible frequencies (disturbanceproblems).</p><p>An analytical model for hard seismic screens is alsopresented, to complement the treatment of ground vibrationcountermeasures; this is based on physical approximations whichare favored by "high" (i.e, audible)frequencies and softsoils. Notably, experimentally observed resonant behavior isexplained.</p><p><b>Keywords:</b>ground vibration, vibration screen, trackvibration, railway vibration</p>

Human pluripotent stem cells (hPSCs) hold the potential to revolutionize cardiac tissue engineering. Because of their ability to proliferate and differentiate into all cardiomyocyte subtypes they represent an opportunity to regenerate virtually any tissue lost from the over 1 million cardiac disease patients in the United States alone. Studies have shown, however, that hPSCs which are not terminally differentiated pose a variety of risks including teratoma formation and lack of appropriate cell engraftment. It is therefore important to ensure that only well characterized cardiac subtypes are implanted into patients or used for research purposes. Current differentiation protocols generate a mixture of cardiac subtypes, and research on cardiac subtype specification is hampered by the lack of a high throughput method to distinguish cardiac subtypes. This thesis establishes the ability to identify, enrich and characterize cardiac subtypes using MBs. This will provide a robust tool for clinical use of hPSCs in cardiac cell therapy and for analysis of differentiation protocol effects on cardiac subtype formation.

Particle-laden flows occur in a variety of natural and industrial situations. As particulate suspensions flow through a medium, particles are often retained at constrictions such as pore throats, outlets or orifices. This occurs not only with oversized particles, but also with particles smaller than the constriction. For instance, jams are caused by the formation of particle bridges/arches when several particles attempt to flow through a constriction simultaneously. In many instances the success of an operation depends on our ability to either ensure or stop the flow of particles in the flow stream. Managing the flow of sand into wellbores during hydrocarbon production from poorly consolidated sandstone reservoirs, also referred to as sand control, is one such application in the oil and gas industry. This dissertation presents a multi-pronged effort at modeling the flow of granular suspensions of different concentrations, and through pore openings of different shapes, with two main objectives: (1) predicting the mass and size-distribution of the particles that are produced before jamming, and (2) investigating the underlying factors that influence the onset and stability of particle arches. Since, the dominant interactions and retention mechanisms are concentration dependent, we divided particulate suspensions into three groups based on the volumetric particle concentration ([phi]). High-concentration suspension flows ([phi]>~50%) are dominated by particle-particle interactions. We modeled polydisperse sand packs flowing through screens with rectangular and woven-square openings using 3D discrete element method (DEM). Simulations were validated against experimental data for a wide range of screen opening and sand size distributions. From the experiments and DEM simulations, a new scaling relation is identified, in which the number of different sized particles produced before retention follows a power-law correlation with the particle-to-outlet size ratio. This correlation is explained with a simple probabilistic model of bridging in polydisperse systems and a particle-size dependent jamming probability calculated from experimental data. A new method is presented to estimate the mass and size distribution of the produced solids through screens. The method uses the entire particle size distribution (PSD) of the formation sand, is validated with experimental data and numerical simulations, and provides more quantitative and accurate predictions of screen performance compared to past methods. It is also found that the stability of particle arches is compromised when adjacent outlets are less than three particle diameters away from each other. Low-concentration suspension flows ([phi]<~1%) are dominated by particle-fluid interactions. They were modeled using analytical and stochastic methods to predict sand production through screens with slot and woven-square openings. Analytical expressions were derived for screens with a constant outlet size or with a known outlet size distribution. Monte Carlo simulations showed excellent agreement with the analytical solutions. Based on experiments, we have demonstrated that the models presented here are predictive, provided that an accurate representation of the formation sand PSD and the screen pore size distribution are available. In the intermediate-concentration regime (~1%<[phi]<~50%), the particle trajectories and the flow field are both influenced by each other. The onset of particle bridging due to hydrodynamic forces was studied for monodisperse systems, in a rectangular channel with a single constriction, using coupled computational fluid dynamics (CFD) and DEM simulations. It is shown that the probability of jamming increases with [phi], and there is a critical particle concentration ([phi, superscript asterisk]) for spontaneous bridging. The outlet-to-particle size ratio is the most critical parameter affecting [phi, superscript asterisk]. The effect of inlet-to-particle size ratio, fluid velocity, particle stiffness, particle-to-fluid density ratio, and the effect of convergence in flow geometry were also studied quantitatively. Finally, the application of micro-tomography images in constructing accurate 3D representations and calculating the pore size distribution of complex filter media is demonstrated. A simulation tool is presented that allows one to evaluate the performance of different screens without running expensive and sometimes inconclusive experiments, and enhances our understanding of screen performance. This helps to improve sand screen selection to meet performance criteria under a wide variety of conditions. / text

Researchers have learned much about how sighted individuals seek information on Web sites - for example, users follow "information scent" as they move from page to page, and individual differences may impact successful information seeking on the Web. While it is possible that individuals with disabilities, especially those with severe visual impairments, perform information-seeking activities in a similar manner, little is known about how individuals who use screen readers to navigate actually seek information on the Web. In this study, we used both qualitative and quantitative measures to investigate the Web navigation techniques of four screen-reader users and how a user’s experience affects these navigation techniques and his or her ability to successfully complete an information-finding task. We compared metrics for between-page and within-page navigation to studies of sighted users. We also considered how a Web site’s compliance with Section 508 guidelines affects the overall information-finding experience of a visually-impaired individual. We discovered that among the four individuals in this study, user experience was not necessarily indicative of a successful information-finding experience. As individuals, the participants' navigation techniques varied widely; as a group, they generally searched more frequently and used the back button less frequently than has been reported for sighted individuals. Screen-reader users in this study followed a more flimsy, linear navigation style and generally used scrolling actions rather than searching actions. When using a Web site that has a Section 508 compliant home page, we found that the screen-reader users in this study completed information-finding tasks significantly more quickly, used significantly fewer actions, and reported a more satisfying information-finding experience. They were also more successful at finding the information goal and encountered fewer impasses. Using both quantitative and qualitative measures was critical in this study. The quantitative metrics allowed us to compare values and the qualitative data provided additional insight into individual differences as well as allowing a deeper understanding of the quantitative data. The information from this study contributes to the growing body of research knowledge about screen-reader users. It also contributes a new understanding of screen-reader users that can be used by the worldwide community of Web developers, designers, and users. / text

Repair of DNA double-strand breaks is critical to the maintenance of genomic stability, and failure to repair these DNA lesions can cause loss of chromosome telomeric regions, complex translocations, or cell death. In humans this can lead to severe developmental abnormalities and cancer. A central pathway for double-strand break repair is homologous recombination (HR), a mechanism that operates during the S and G2 phases of the cell cycle and primarily utilizes the replicated sister chromatid as a template for repair. Most knowledge of HR is derived from work carried out in prokaryotic and eukaryotic model organisms. To probe the HR pathway in human cells, we performed a genome-wide siRNA-based screen; and through this screen, we uncovered cellular functions required for HR and identified proteins that localize to sites of DNA damage. Among positive regulators of HR, we identified networks of pre-mRNA-processing factors and canonical DNA damage response effectors. Within the former, we found RBMX, a heterogeneous nuclear ribonucleoprotein (hnRNP) that associates with the spliceosome, binds RNA, and influences alternative splicing. We found that RBMX is required for cellular resistance to genotoxic stress, accumulates at sites of DNA damage in a poly(ADP-ribose) polymerase 1-dependent manner and through multiple domains, and promotes HR by facilitating proper BRCA2 expression. Screen data also revealed that the mammalian recombinase RAD51 is commonly off-targeted by siRNAs, presenting a cautionary note to those studying HR with RNAi and highlighting the vulnerability of RNAi screens to off-target effects in general. Candidate validation through secondary screening with independent reagents successfully circumvented the effects of off-targeting and set a new standard for reagent redundancy in RNAi screens.

Inorganic phosphate \((P_i)\) is an essential nutrient whose intracellular levels are maintained by the PHO pathway in Saccharomyces cerevisiae. \(P_i\) limitation triggers upregulation of the PHO genes whose gene products primarily function to counterbalance the \(P_i\) deficiency. Despite a growing catalogue of genes that are involved in signaling of the PHO pathway, little is known about how cells actually sense \(P_i\) limitation. To better characterize the \(P_i\) sensing mechanism, I exploited two comprehensive and orthogonal approaches: 1) genome-wide genetic screening to identify novel genes involved in signaling \(P_i\) limitation through the PHO pathway and characterization of genetic interactions among these genes and 2) liquid chromatography /mass spectrometry (LC/MS)-based metabolic profiling to characterize the metabolomic response to changes in \(P_i\) availability. In genome-wide screening, I found that the aah1 mutant constitutively activated the PHO pathway and showed that AAH1 is involved in regulating PHO pathway activity. Moreover, I identified several novel genetic interactions of genes involved in inositol polyphosphate metabolism with those involved in purine metabolism and mitochondrial fatty acid biosynthesis.Through metabolomic profiling, I showed that all adenine nucleotides were downregulated in the constitutively induced ado1, adk1, and aah1 mutants in high \(P_i\) as well as in the wild type strain in low \(P_i\). These observations led to the hypothesis that downregulation of adenine nucleotides triggers activation of the PHO pathway. However, I find that decreases in adenine nucleotides appear to be the consequence of downregulation of glycolysis and of the pentose phosphate pathway rather than an activation signal for the PHO pathway.Among all the detected metabolites, S-adenosyl-L-homocysteine (SAH) responded the most quickly and significantly to changes in \(P_i\) concentration. It was known that SAH is an inhibitor of de novo synthesis of phosphatidylcholine (PC). I showed that overall PC levels were downregulated in low \(P_i\), suggesting that phospholipid metabolism is downregulated in low \(P_i\) conditions. Furthermore, I observed that exogenous SAH induces activation of the PHO pathway in high \(P_i\) implying a possible role of SAH as an initiating activation signal of the PHO pathway. / Chemistry and Chemical Biology

The EQ-VAS, a measure of self-reported health status, has been operationalized in ways that depart from the original format. The primary purpose of the study was to examine the equivalence of the original paper-based vertical format with a touch screenbased horizontal format. Non-probability sampling was used to recruit 314 subjects intended to reflect the primary socio-demographic characteristics of the general adult population. A two-part questionnaire completed roughly 10 minutes apart was administered in a randomized crossover design. One part was the original paper-based 20cm vertical EQ-VAS; the other part was touch screen computer-based (designed by Assist Technologies) and included, among other items/scales, a horizontal EQ-VAS, the SF-36, and socio-demographic items. A mean difference of ± eight points between the two versions was specified as the minimally important difference (MID). Almost a third (30.1%) of the respondents reported identical scores on both formats and 80.1% of the respondents had difference scores within ± 8 points. The 95% confidence intervals for both samples indicated that the difference in scores was relatively small and below our equivalence threshold. In addition, data collected via touch screen may be more reliable since 22% of subjects did not complete the EQ-VAS paper format as instructed. These results provided evidence for the measurement equivalence of the touch screen EQ-VAS with the original paper format. A secondary purpose was to examine the psychometric properties of an electronic version of the SF-36. Floor and ceiling effects were comparable to that observed in other studies using the paper SF-36 in the general population. All reliability coefficients exceeded 0.70; the range was from 0.75 to 0.93. There was support for the construct validity of the touch screen SF-36, as the direction and strength of the correlations between the SF-36 scales and the EQ-5D domains were as hypothesized. Overall, there was a high level of correspondence between the touch screen SF-36 scores and previously reported paper based SF-36 scores in the general population. The comparable psychometric properties and low level of missing data make touch screen questionnaires a very viable alternative to their paper-based formats.