Dispersion-strengthened chromium alloy

Finely divided powder mixture produced by vapor deposition of CR on small ThO2 particles was hot pressed or pressure bonded. Resulting alloy has lower ductile-to-brittle transition temperature than pure chromium, and high strength and oxidation resistance at elevated temperatures, both in as-rolled condition and after annealing

The evolutionary time scale of Sakurai's object: A test of convection theory?

Sakurai's object (V4334 Sgr) is a born again AGB star following a very late thermal pulse. So far no stellar evolution models have been able to explain the extremely fast evolution of this star, which has taken it from the pre-white dwarf stage to its current appearance as a giant within only a few years. A very high stellar mass can be ruled out as the cause of the fast evolution. Instead the evolution time scale is reproduced in stellar models by making the assumption that the efficiency for element mixing in the He-flash convection zone during the very late thermal pulse is smaller than predicted by the mixing-length theory. As a result the main energy generation from fast proton capture occurs closer to the surface and the expansion to the giant state is accelerated to a few years. Assuming a mass of V4334 Sgr of 0.604Msun -- which is consistent with a distance of 4kpc -- a reduction of the mixing length theory mixing efficiency by a factor of ~ 100 is required to match its evolutionary time scale. This value decreases if V4334 Sgr has a smaller mass and accordingly a smaller distance. However, the effect does not disappear for the smallest possible masses. These findings may present a semi-empirical constraint on the element mixing in convective zones of the stellar interior.Comment: 16 pages, 3 figures, ApJ Letter, in press; some additional information as well as modifications as a result of the refereeing process, improved layout of prev. Fig.1 (now Fig.1 and Fig.2

Spitzer/MIPS Imaging of NGC 650: Probing the History of Mass Loss on the Asymptotic Giant Branch

We present the far-infrared (IR) maps of a bipolar planetary nebula (PN), NGC 650, at 24, 70, and 160 micron taken with the Multiband Imaging Photometer for Spitzer (MIPS) on-board the Spitzer Space Telescope. While the two-peak emission structure seen in all MIPS bands suggests the presence of a near edge-on dusty torus, the distinct emission structure between the 24 micron map and the 70/160 micron maps indicates the presence of two distinct emission components in the central torus. Based on the spatial correlation of these two far-IR emission components with respect to various optical line emission, we conclude that the 24 micron emission is largely due to the [O IV] line at 25.9 micron arising from highly ionized regions behind the ionization front, whereas the 70 and 160 micron emission is due to dust continuum arising from low-temperature dust in the remnant asymptotic giant branch (AGB) wind shell. The far-IR nebula structure also suggests that the enhancement of mass loss at the end of the AGB phase has occurred isotropically, but has ensued only in the equatorial directions while ceasing in the polar directions. The present data also show evidence for the prolate spheroidal distribution of matter in this bipolar PN. The AGB mass loss history reconstructed in this PN is thus consistent with what has been previously proposed based on the past optical and mid-IR imaging surveys of the post-AGB shells.Comment: 9 pages in the emulated ApJ format with 6 figures, to appear in Ap

Characterization of Proteostasis Mechanisms in Chlamydia trachomatis

Chlamydia trachomatis is a gram negative, obligate intracellular pathogen with a highly reduced genome of ~1 Mbp. It is the leading cause of the reportable sexually transmitted infection known as chlamydia in the United States and is the leading cause of preventable blindness (trachoma) worldwide. While treatment of infections is possible, weaknesses of current approaches include treatment failure, antibiotic-induced dysbiosis, and resistance development of bystander bacteria during chlamydial treatment. These weaknesses support the need for improved therapeutic approaches. C. trachomatis undergoes a biphasic developmental cycle with two forms, the infectious elementary body (EB) and replicative reticulate body (RB), that have unique protein profiles. Due to the differing proteomes of each developmental form, we hypothesized that mechanisms that facilitate protein turnover will be essential for progression of C. trachomatis through the developmental cycle making them ideal drug targets. This study focused on characterization of two caseinolytic protease (Clp) systems: the ClpX/P2/P1 system and the ClpC/P1/P2 / McsAB system. We predicted that ClpP1 and ClpP2 come together to form the proteolytic component, that ClpX and ClpC are unfoldases that unfold and linearize large substrates in an ATP dependent manner for ClpP-dependent proteolysis, and that McsAB are adaptor proteins with McsA activating the kinase McsB to tag proteins for degradation by the ClpC/P1/P2 complex. The Clp system has been the focus of numerous studies as a target for novel antimicrobials and we hypothesized that the chlamydial Clp system would also be a druggable target. To assess the functionality of the Clp system, we successfully purified all components except McsB for use in vitro assays. Using oligomerization, peptide and protein degradation assays, and ATP hydrolysis assays, we characterized the activity of the ClpP1, ClpP2, and ClpX components individually and in complexes. We also measured the activity of a collection of ClpX mutants. In addition, we assessed the activity of ClpP-targeted activating compounds that were potent in vivo inhibitors of C. trachomatis. We demonstrated that ClpP2/P1 can form hetero-oligomers and degrade peptides and that ClpX has ATPase activity, can oligomerize, and can degrade an SsrA-tagged GFP when complexed with ClpP2/P1. While the activator studies did not support interactions with ClpP2/P1 under the conditions tested, assays were developed for further analysis of Clp-targeted compounds. Our in vitro results support that C. trachomatis possesses a functional Clp system. In addition, in vivo expression of ClpX mutants confirmed to lack activity in our in vitro assays led to reduced chlamydial fitness and alterations in development supporting our hypothesis that the Clp system is required for chlamydial development. Collectively, our results indicate that the Clp system is critical to C. trachomatis survival in cells and suggests that drugs altering Clp-function could be a novel approach for anti-chlamydial therapeutics

3-D Photoionization Structure and Distances of Planetary Nebulae III. NGC 6781

Continuing our series of papers on the three-dimensional (3-D) structures of and accurate distances to Planetary Nebulae (PNe), we present our study of the planetary nebula NGC6781. For this object we construct a 3-D photoionization model and, using the constraints provided by observational data from the literature we determine the detailed 3-D structure of the nebula, the physical parameters of the ionizing source and the first precise distance. The procedure consists in simultaneously fitting all the observed emission line morphologies, integrated intensities and the 2-D density map from the [SII] line ratios to the parameters generated by the model, and in an iterative way obtain the best fit for the central star parameters and the distance to NGC6781, obtaining values of 950+-143pc and 385 Lsun for the distance and luminosity of the central star respectively. Using theoretical evolutionary tracks of intermediate and low mass stars, we derive the mass of the central star of NGC6781 and its progenitor to be 0.60+-0.03 Msun and 1.5+-0.5 Msun respectively.Comment: 16 pp, 6 figues, 2 tables, submitted to the Ap

Life Products of Stars

We attempt to document complete energetic transactions of stars in their life. We calculate photon and neutrino energies that are produced from stars in their each phase of evolution from 1 to 8 M_sun, using the state-of-the-art stellar evolution code, tracing the evolution continuously from pre-main sequence gravitational contraction to white dwarfs. We also catalogue gravitational and thermal energies and helium, and heavier elements that are stored in stars and those ejected into interstellar space in each evolutionary phase.Comment: 26 pages, including 8 figures and 3 tables. Submitted to ApJ

A Possible Hidden Population of Spherical Planetary Nebulae

We argue that relative to non-spherical planetary nebulae (PNs), spherical PNs are about an order of magnitude less likely to be detected, at distances of several kiloparsecs. Noting the structure similarity of halos around non-spherical PNs to that of observed spherical PNs, we assume that most unobserved spherical PNs are also similar in structure to the spherical halos around non-spherical PNs. The fraction of non-spherical PNs with detected spherical halos around them, taken from a recent study, leads us to the claim of a large (relative to that of non-spherical PNs) hidden population of spherical PNs in the visible band. Building a toy model for the luminosity evolution of PNs, we show that the claimed detection fraction of spherical PNs based on halos around non-spherical PNs, is compatible with observational sensitivities. We use this result to update earlier studies on the different PN shaping routes in the binary model. We estimate that ~30% of all PNs are spherical, namely, their progenitors did not interact with any binary companion. This fraction is to be compared with the ~3% fraction of observed spherical PNs among all observed PNs. From all PNs, ~15% owe their moderate elliptical shape to the interaction of their progenitors with planets, while \~55% of all PNs owe their elliptical or bipolar shapes to the interaction of their progenitors with stellar companions.Comment: AJ, in pres

Effects of a burst of formation of first-generation stars on the evolution of galaxies

First-generation (Population III) stars in the universe play an important role inearly enrichment of heavy elements in galaxies and intergalactic medium and thus affect the history of galaxies. The physical and chemical properties of primordial gas clouds are significantly different from those of present-day gas clouds observed in the nearby universe because the primordial gas clouds do not contain any heavy elements which are important coolants in the gas. Previous theoretical considerations have suggested that typical masses of the first-generation stars are between several $M_\odot$ and $\approx 10 M_\odot$ although it has been argued that the formation of very massive stars (e.g., $> 100 M_\odot$) is also likely. If stars with several $M_\odot$ are most popular ones at the epoch of galaxy formation, most stars will evolve to hot (e.g., $\gtrsim 10^5$ K), luminous ($\sim 10^4 L_\odot$) stars with gaseous and dusty envelope prior to going to die as white dwarf stars. Although the duration of this phase is short (e.g., $\sim 10^5$ yr), such evolved stars could contribute both to the ionization of gas in galaxies and to the production of a lot of dust grains if the formation of intermediate-mass stars is highly enhanced. We compare gaseous emission-line properties of such nebulae with some interesting high-redshift galaxies such asIRAS F10214+4724 and powerful radio galaxies.Comment: 25 pages, 7 figures, ApJ, in pres

ALTERING BARRIERS TO PHYSICAL ACTIVITY AND EXERCISE IN RURAL KANSAS THROUGH EDUCATION AND EXERCISE INTERVENTIONS

Rural Americans (RA) report significantly higher percentages of obesity, chronic disease, and cognitive decline than urban-dwelling Americans. However, rural individuals face different barriers to physical activity and exercise than their urban counterparts. PURPOSE: The purpose of this study was to increase physical activity among middle-aged and older adults living in rural Kansas, increase Alzheimer’s disease knowledge through risk reduction education, and determine the unique barriers to physical activity and exercise in this rural Kansas cohort. METHODS: Sixty-nine rural dwelling adults (17 male, 52 female; mean age 63.9±7.95 years) participated in a 10-week community-based education and exercise intervention program in rural Kansas. Baseline physical fitness (Queen’s College Step Test, blood pressure), balance and muscular endurance (30-second chair sit and stand), quality of life (OPQOL), healthy lifestyle survey (HLPLII), and Alzheimer’s disease knowledge (ADKS) assessments were collected prior to participation. Subjects were randomly assigned to one of three groups and participated in either 10 weeks of education (ED), education and exercise (EDEX), or were assigned to the control group (CON). Sixty-nine (69) participants completed the 10-week study and completed follow-up assessments. A cohort of subjects (N=23) participated in interviews throughout the course of the study. Repeated measures ANCOVAs were conducted to determine differences, if any, in the dependent variables before and after interventions (p<.05). Small group interviews were conducted throughout the study period to assess views and attitudes toward exercise and physical activity and determine perceived and actual barriers faced by rural Kansas adults. Interview response frequencies and differences, if any, were determined for barriers to, benefits of and opportunities to participate in exercise and physical activity. RESULTS: The EDEX group acquired significantly more steps on average throughout the study period than the CON group, but not significantly more than the ED group (p<.05). Chair test scores improved significantly for the EDEX group compared to both the ED and CON group (p<.05). Weight and waist to hip ratio improvements did not differ significantly between groups. Scores on the HLPLII, both overall and the physical activity component alone, improved significantly for the EDEX group compared to both ED and CON groups, p<.05). Quality of life scores (OPQOL) were significantly higher for the CON group than the ED and EDEX group (p<.05). Time, lack of motivation and injury or illness were the most commonly reported barriers to exercise, while brain health and overall health were the most commonly reported benefits of exercise. Rural Kansas adults were able to successfully distinguish between physical activity and exercise and identify numerous opportunities for exercise and physical within the surrounding rural communities. Response frequencies did not differ significantly between groups (p<.05)