CFD Modeling of Turbulent Duct Flows for Coolant Channel Analysis

The design of modern liquid rocket engines requires the analysis of chamber coolant channels to maximize the heat transfer while minimizing the coolant flow. Coolant channels often do not remain at a constant cross section or at uniform curvature. New designs require higher aspect ratio coolant channels than previously used. To broaden the analysis capability and to complement standard analysis tools an investigation on the accuracy of CFD predictions for coolant channel flow has been initiated. Validation of CFD capabilities for coolant channel analysis will enhance the capabilities for optimizing design parameters without resorting to extensive experimental testing. The eventual goal is to use CFD to determine the flow fields of unique coolant channel designs and therefore determine critical heat transfer coefficients. In this presentation the accuracy of a particular CFD code is evaluated for turbulent flows. The first part of the presentation is a comparison of numerical results to existing cold flow data for square curved ducts (NASA CR-3367, 'Measurements of Laminar and Turbulent Flow in a Curved Duct with Thin Inlet Boundary Layers'). The results of this comparison show good agreement with the relatively coarse experimental data. The second part of the presentation compares two cases of higher aspect ratio channels (AR=2.5,10) to show changes in axial and secondary flow strength. These cases match experimental work presently in progress and will be used for future validation. The comparison shows increased secondary flow strength of the higher aspect ratio case due to the change in radius of curvature. The presentation includes a test case with a heated wall to demonstrate the program's capability. The presentation concludes with an outline of the procedure used to validate the CFD code for future design analysis

BlindSignedID: Mitigating Denial-of-Service Attacks on Digital Contact Tracing

Due to the recent outbreak of COVID-19, many governments suspended outdoor activities and imposed social distancing policies to prevent the transmission of SARS-CoV-2. These measures have had severe impact on the economy and peoples' daily lives. An alternative to widespread lockdowns is effective contact tracing during an outbreak's early stage. However, mathematical models suggest that epidemic control for SARS-CoV-2 transmission with manual contact tracing is implausible. To reduce the effort of contact tracing, many digital contact tracing projects (e.g., PEPP-PT, DP-3T, TCN, BlueTrace, Google/Apple Exposure Notification, and East/West Coast PACT) are being developed to supplement manual contact tracing. However, digital contact tracing has drawn scrutiny from privacy advocates, since governments or other parties may attempt to use contact tracing protocols for mass surveillance. As a result, many digital contact tracing projects build privacy-preserving mechanisms to limit the amount of privacy-sensitive information leaked by the protocol. In this paper, we examine how these architectures resist certain classes of attacks, specifically DoS attacks, and present BlindSignedIDs, a privacy-preserving digital contact tracing mechanism, which are verifiable ephemeral identifiers to limit the effectiveness of MAC-compliant DoS attacks. In our evaluations, we showed BlindSignedID can effectively deny bogus EphIDs, mitigating DoS attacks on the local storage beyond 90% of stored EphIDs. Our example DoS attacks showed that using 4 attackers can cause the gigabyte level DoS attacks within normal working hours and days.Comment: 10 pages, 6 figure

Cost-(in)effective public good provision: an experimental exploration

This paper investigates the determinants of cost-(in)effective giving to public goods. We conduct a pre-registered experiment to elucidate how factors at the institutional and individual levels shape individual contributions and the cost-effectiveness of those contributions in a novel public good game. In particular, we examine the role of consequential uncertainty over the value of public good contributions (institutional level) as well as individual characteristics like risk and ambiguity attitudes, giving type, and demographics (individual level). We find cost-ineffective contributions in all institutions, but total contribution levels and the degree of cost-ineffectiveness are similar across institutions. Meanwhile, cost-effectiveness varies by giving type—which is a novel result that is consistent with hypotheses we generate from theory—but other individual characteristics have little influence on the cost-effectiveness of contributions. Our work has important positive and normative implications for charitable giving and public good provision in the real world, and it is particularly germane to emerging online crowdfunding and patronage platforms that confront users with a multitude of competing opportunities for giving

A Method for Photoinitating Protein Folding in a Nondenaturing Environment

The early kinetic events of protein folding are an important part of the folding pathway, yet our understanding towards the process is limited. Information from the study of these early events can allow us to distinguish between the various models that have been proposed to describe the folding of a protein in real time. Unlike “typical” chemical kinetics with well-defined initial and final states, the initial state of a denatured protein is relatively ill-defined. This uncertainty introduces ambiguity in the interpretation of the experimental data on the early events in protein folding. Toward developing a unified theory of protein folding, it is necessary to begin the observation of the refolding process from a well-defined initial state, trigger folding as rapidly as possible, and to follow the protein in real time as it samples its conformational space over its highly complex free-energy landscape

PhiC31 recombination system demonstrates heritable germinal transmission of site-specific excision from the Arabidopsis genome

<p>Abstract</p> <p>Background</p> <p>The large serine recombinase phiC31 from broad host range <it>Streptomyces </it>temperate phage, catalyzes the site-specific recombination of two recognition sites that differ in sequence, typically known as attachment sites <it>attB </it>and <it>attP</it>. Previously, we characterized the phiC31 catalytic activity and modes of action in the fission yeast <it>Schizosaccharomyces pombe</it>.</p> <p>Results</p> <p>In this work, the <it>phiC31 </it>recombinase gene was placed under the control of the <it>Arabidopsis OXS3 </it>promoter and introduced into <it>Arabidopsis </it>harboring a chromosomally integrated <it>attB </it>and <it>attP</it>-flanked target sequence. The phiC31 recombinase excised the <it>attB </it>and <it>attP</it>-flanked DNA, and the excision event was detected in subsequent generations in the absence of the <it>phiC31 </it>gene, indicating germinal transmission was possible. We further verified that the genomic excision was conservative and that introduction of a functional recombinase can be achieved through secondary transformation as well as manual crossing.</p> <p>Conclusion</p> <p>The phiC31 system performs site-specific recombination in germinal tissue, a prerequisite for generating stable lines with unwanted DNA removed. The precise site-specific deletion by phiC31 <it>in planta </it>demonstrates that the recombinase can be used to remove selectable markers or other introduced transgenes that are no longer desired and therefore can be a useful tool for genome engineering in plants.</p

Community Water Demand in Texas

Solutions to Texas water policy and planning problems will be easier to identify once the impact of price upon community water demand is better understood. Several important questions cannot be addressed in the absence of such information. This study combines monthly water use reports, Census information, weather data, and water rates for more than two hundred Texas communities. The study period is the five years for which data is most recently available, 1981-85. Descriptive and statistical results concerning community water demand are generated with this data. Notable findings are (1) a new climate variable is developed which has good performance in demand functions; (2) Texas consumers respond to water price with the average price specification being preferred over the marginal price alternative; (3) price elasticities vary during the year with the highest price sensitivity occurring in summer months; and (4) sewage rates which depend upon water consumption represent a statistically significant component of water price. The quantitative results of this study enable many potential applications for solving state and local problems