Simulations of aging and plastic deformation in polymer glasses

We study the effect of physical aging on the mechanical properties of a model polymer glass using molecular dynamics simulations. The creep compliance is determined simultaneously with the structural relaxation under a constant uniaxial load below yield at constant temperature. The model successfully captures universal features found experimentally in polymer glasses, including signatures of mechanical rejuvenation. We analyze microscopic relaxation timescales and show that they exhibit the same aging characteristics as the macroscopic creep compliance. In addition, our model indicates that the entire distribution of relaxation times scales identically with age. Despite large changes in mobility, we observe comparatively little structural change except for a weak logarithmic increase in the degree of short-range order that may be correlated to an observed decrease in aging with increasing load.Comment: 9 pages, 12 figure

Fiber Optic Telecommunications Technology and Systems – A Two-Course Sequence for a Telecommunications Engineering Technology MS Program

The continuing growth of telecommunication networks is currently dominated by two technologies: fiber optics (or optical networking) and wireless. The Telecommunications Engineering Technology program at RIT, as part of its continuous improvement program, has been developing and updating courses in these important areas. This paper describes a two-course sequence in fiber optic telecommunication technology and systems. The first course in the sequence was introduced in the spring of 2001 as an advanced undergraduate elective. It has proven to be a popular course and has run at least once per year since then. The second course has just been completed and will be offered this spring (2005). The paper begins with a brief overview of fiber optic telecommunication, including some recent forecasts of the future of optical networking. The next two sections describe each of the two courses and the last section is a short summary

Test results of the Chrysler upgraded automotive gas turbine engine: Initial design

The upgraded engine as built to the original design was deficient in power and had excessive specific fuel consumption. A high instrumented version of the engine was tested to identify the sources of the engine problems. Analysis of the data shows the major problems to be low compressor and power turbine efficiency and excessive interstage duct losses. In addition, high HC and CO emission were measured at idle, and high NOx emissions at high energy speeds

Improvements and modifications to the NASA microwave signature acquisition system

A user oriented description of the modified and upgraded Microwave Signature Acquisition System is provided. The present configuration of the sensor system and its operating characteristics are documented and a step-by-step operating procedure provides instruction for mounting the antenna truss assembly, readying the system for data acquisition, and for controlling the system during the data collection sequence. The resulting data products are also identified

Association between obesity and bacterial vaginosis as assessed by Nugent score

Background Bacterial vaginosis is one of the most common vaginal conditions in the U.S. Recent studies have suggested obese women have an abnormal microbiota reminiscent of BV; however, few studies have investigated the prevalence of bacterial vaginosis in overweight and obese populations. Moreover, despite the increased prevalence of obesity and bacterial vaginosis in black women, it is not known whether racial disparities exist in the relationship between obesity and bacterial vaginosis. Objective The objective of this study was to examine the relationship between body mass index and bacterial vaginosis as determined by Nugent score and to determine the influence of race in this context. Study Design We performed a cross-sectional study using patient data and vaginal smears from 5,918 participants of the Contraceptive CHOICE Project. Gram stained vaginal smears were scored using the Nugent method and categorized as BV-negative (Nugent score 0-3), BV-intermediate (Nugent score 4-6), or BV-positive (Nugent score 7-10). Body mass index was determined using Centers for Disease Control and Prevention guidelines and obese individuals were categorized as Class I, II, or III obese based on NIH and World Health Organization body mass index parameters. Linear regression was used to model mean differences in Nugent scores and Poisson regression with robust error variance was used to model prevalence of bacterial vaginosis. Results In our cohort, 50.7% of participants were black, 41.5% were white, and 5.1% were of Hispanic ethnicity with an average age of 25.3 years old. Overall, 28.1% of participants were bacterial vaginosis-positive. Bacterial vaginosis was prevalent in 21.3% of lean, 30.4% of overweight, and 34.5% of obese women (p<0.001). The distribution of bacterial vaginosis-intermediate individuals was similar across all body mass index categories. Compared to lean women, Nugent scores were highest among overweight and obese Class I women (adjusted mean difference; overweight 0.33 [95% CI 0.14, 0.51] and Class I obese 0.51 [95% CI 0.29, 0.72]). Consistent with this, overweight and obese women had a higher frequency of bacterial vaginosis compared to lean women, even after adjusting for variables including race. Among white women, the prevalence of BV was higher for overweight and Class I and Class II/III obese white women compared to lean white women, a phenomenon not observed among black women, suggesting an effect modification. Conclusion Overweight and obese women have higher Nugent scores and a greater occurrence of bacterial vaginosis compared to lean women. Black women have a greater prevalence of bacterial vaginosis independent of their body mass index compared to white women

Racial Credit Steering as a Discriminatory Credit Practice Under the Equal Credit Opportunity Act

This article will explore the possible application of the Equal Credit Opportunity Act with its multiple remedies and enforcement methods to racial credit steering practices as described above

pH-Independent, 520 mV Open-Circuit Voltages of Si/Methyl Viologen^(2+/+) Contacts Through Use of Radial n^+p-Si Junction Microwire Array Photoelectrodes

The effects of introducing an n^+-doped emitter layer have been evaluated for both planar Si photoelectrodes and for radial junction Si microwire-array photoelectrodes. In contact with the pH-independent, one-electron, outer-sphere, methyl viologen redox system (denoted MV^(2+/+)), both planar and wire array p-Si photoelectrodes yielded open-circuit voltages, V_(oc), that varied with the pH of the solution. The highest V_(oc) values were obtained at pH = 2.9, with V_(oc) = 0.53 V for planar p-Si electrodes and V_(oc) = 0.42 V for vapor−liquid−solid catalyzed p-Si microwire array samples, under 60 mW cm^(−2) of 808 nm illumination. Increases in the pH of the electrolyte produced a decrease in V_(oc) by approximately −44 mV/pH unit for planar electrodes, with similar trends observed for the Si microwire array electrodes. In contrast, introduction of a highly doped, n^+ emitter layer produced V_(oc) = 0.56 V for planar Si electrodes and V_(oc) = 0.52 V for Si microwire array electrodes, with the photoelectrode properties in each system being essentially independent of pH over six pH units (3 < pH < 9). Hence, formation of an n^+ emitter layer not only produced nearly identical photovoltages for planar and Si microwire array photoelectrodes, but decoupled the band energetics of the semiconductor (and hence the obtainable photovoltage) from the value of the redox potential of the solution. The formation of radial junctions on Si microwire arrays thus provides an approach to obtaining Si-based photoelectrodes with high-photovoltages that can be used for a variety of photoelectrochemical processes, including potentially the hydrogen evolution reaction, under various pH conditions, regardless of the intrinsic barrier height and flat-band properties of the Si/liquid contact

Methodology for urban rail and construction technology research and development planning

A series of transit system visits, organized by the American Public Transit Association (APTA), was conducted in which the system operators identified the most pressing development needs. These varied by property and were reformulated into a series of potential projects. To assist in the evaluation, a data base useful for estimating the present capital and operating costs of various transit system elements was generated from published data. An evaluation model was developed which considered the rate of deployment of the research and development project, potential benefits, development time and cost. An outline of an evaluation methodology that considered benefits other than capital and operating cost savings was also presented. During the course of the study, five candidate projects were selected for detailed investigation; (1) air comfort systems; (2) solid state auxiliary power conditioners; (3) door systems; (4) escalators; and (5) fare collection systems. Application of the evaluation model to these five examples showed the usefulness of modeling deployment rates and indicated a need to increase the scope of the model to quantitatively consider reliability impacts

Void Statistics in Large Galaxy Redshift Surveys: Does Halo Occupation of Field Galaxies Depend on Environment?

We use measurements of the projected galaxy correlation function w_p and galaxy void statistics to test whether the galaxy content of halos of fixed mass is systematically different in low density environments. We present new measurements of the void probability function (VPF) and underdensity probability function (UPF) from Data Release Four of the Sloan Digital Sky Survey, as well as new measurements of the VPF from the full data release of the Two-Degree Field Galaxy Redshift Survey. We compare these measurements to predictions calculated from models of the Halo Occupation Distribution (HOD) that are constrained to match both w_p and the space density of galaxies. The standard implementation of the HOD assumes that galaxy occupation depends on halo mass only, and is independent of local environment. For luminosity-defined samples, we find that the standard HOD prediction is a good match to the observations, and the data exclude models in which galaxy formation efficiency is reduced in low-density environments. More remarkably, we find that the void statistics of red and blue galaxies (at L ~ 0.4L_*) are perfectly predicted by standard HOD models matched to the correlation function of these samples, ruling out "assembly bias" models in which galaxy color is correlated with large-scale environment at fixed halo mass. We conclude that the luminosity and color of field galaxies are determined predominantly by the mass of the halo in which they reside and have little direct dependence on the environment in which the host halo formed. In broader terms, our results show that the sizes and emptiness of voids found in the distribution of L > 0.2L_* galaxies are in excellent agreement with the predictions of a standard cosmological model with a simple connection between galaxies and dark matter halos. (abridged)Comment: 20 emulateapj pages, 9 figures. submitted to Ap