Correlated X-ray and Optical Variability in Mkn 509

We present results of a 3 year monitoring campaign of the Seyfert 1 galaxy Markarian 509, using X-ray data from the Rossi X-ray Timing Explorer (RXTE) and optical data taken by the SMARTS consortium. Both light curves show significant variations, and are strongly correlated with the optical flux leading the X-ray flux by 15 days. The X-ray power spectrum shows a steep high-frequency slope of -2.0, breaking to a slope of -1.0 at at timescale of 34 days. The lag from optical to X-ray emission is most likely caused by variations in the accretion disk propagating inward.Comment: 13 pages, 3 figures. Accepted for publication in the Astrophysical Journa

Rapid Circumstellar Disk Evolution and an Accelerating Star Formation Rate in the Infrared Dark Cloud M17 SWex

We present a catalog of 840 X-ray sources and first results from a 100 ks Chandra X-ray Observatory imaging study of the filamentary infrared dark cloud G014.225$-$00.506, which forms the central regions of a larger cloud complex known as the M17 southwest extension (M17 SWex). In addition to the rich population of protostars and young stellar objects with dusty circumstellar disks revealed by Spitzer Space Telescope archival data, we discover a population of X-ray-emitting, intermediate-mass pre--main-sequence stars (IMPS) that lack infrared excess emission from circumstellar disks. We model the infrared spectral energy distributions of this source population to measure its mass function and place new constraints on the inner dust disk destruction timescales for 2-8 $M_{\odot}$ stars. We also place a lower limit on the star formation rate (SFR) and find that it is quite high ($\dot{M}\ge 0.007~M_{\odot}$ yr$^{-1}$), equivalent to several Orion Nebula Clusters in G14.225$-$0.506 alone, and likely accelerating. The cloud complex has not produced a population of massive, O-type stars commensurate with its SFR. This absence of very massive (${\ge}20~M_{\odot}$) stars suggests that either (1) M17 SWex is an example of a distributed mode of star formation that will produce a large OB association dominated by intermediate-mass stars but relatively few massive clusters, or (2) the massive cores are still in the process of accreting sufficient mass to form massive clusters hosting O stars.Comment: 29 pages, 9 figures, accepted to Ap

Vitamin D Deficiency and Long-Term Cognitive Impairment Among Older Adult Emergency Department Patients

Introduction: Approximately 16% of acutely ill older adults develop new, long-term cognitive impairment (LTCI), many of whom initially seek care in the emergency department (ED). Currently, no effective interventions exist to prevent LTCI after an acute illness. Identifying early and modifiable risk factors for LTCI is the first step toward effective therapy. We hypothesized that Vitamin D deficiency at ED presentation was associated with LTCI in older adults.Methods: This was an observational analysis of a prospective cohort study that enrolled ED patients ≥ 65 years old who were admitted to the hospital for an acute illness. All patients were enrolled within four hours of ED presentation. Serum Vitamin D was measured at enrollment and Vitamin D deficiency was defined as serum concentrations <20 mg/dL. We measured pre-illness and six-month cognition using the short form Informant Questionnaire on Cognitive Decline in the Elderly (IQCODE), which ranges from 1 to 5 (severe cognitive impairment). Multiple linear regression was performed to determine whether Vitamin D deficiency was associated with poorer six-month cognition adjusted for pre-illness IQCODE and other confounders. We incorporated a two-factor interaction into the regression model to determine whether the relationship between Vitamin D deficiency and six-month cognition was modified by pre-illness cognition.Results: We included a total of 134 older ED patients; the median (interquartile range [IQR]) age was 74 (69, 81) years old, 61 (46%) were female, and 14 (10%) were nonwhite race. The median (IQR) vitamin D level at enrollment was 25 (18, 33) milligrams per deciliter and 41 (31%) of enrolled patients met criteria for vitamin D deficiency. Seventy-seven patients survived and had a six-month IQCODE. In patients with intact pre-illness cognition (IQCODE of 3.13), Vitamin D deficiency was significantly associated with worsening six-month cognition (β-coefficient: 0.43, 95% CI, 0.07 to 0.78, p = 0.02) after adjusting for pre-illness IQCODE and other confounders. Among patients with pre-illness dementia (IQCODE of 4.31), no association with Vitamin D deficiency was observed (β-coefficient: -0.1;, 95% CI, [-0.50-0.27], p = 0.56).Conclusion: Vitamin D deficiency was associated with poorer six-month cognition in acutely ill older adult ED patients who were cognitively intact at baseline. Future studies should determine whether early Vitamin D repletion in the ED improves cognitive outcomes in acutely ill older patients.

Characterization of 10-ft. Diameter Aluminum Alloy 2219 Integrally Stiffened Cylinders

The integrally stiffened cylinder (ISC) process, pioneered by NASA Langley Research Center, offers significant savings for launch vehicle structures. The ISC process is a near net shape, advanced manufacturing method for fabrication of single-piece, thin-walled barrels with internal longitudinal stiffeners, eliminating the need for longitudinal welding and machining. A cost-benefit analysis of the ISC process estimated a 50 % reduction in manufacturing costs and a 10% weight savings over the current multi-piece, machined and welded construction approach for stiffened barrels. In 2017, commercial-scale manufacturing trials were pursued, leading to a successful manufacturing demonstration of 10-ft. diameter ISC barrels fabricated from Al alloy 2219. Some cracking was observed in the stiffeners during fabrication. Optical metallography was performed to evaluate the as-formed microstructures to identify potential causes of cracking, along with mechanical testing to evaluate formability. Results revealed that cracking in the stiffeners was attributed to three likely causes: 1) large Al-Cu stringer particles, 2) stick-slip friction between the mandrel and ISC due to non-optimized lubrication, and 3) differences in material flow rate between the wall and stiffener locations. Testing to gauge formability revealed a significant decrease in ductility in the longitudinal directional for the as-formed condition, attributed to reduced ductility due to the large Al-Cu stringer particles. These results provide guidance toward materials and processing modifications for future ISC forming trials

Thermal and Dynamical Equilibrium in Two-Component Star Clusters

We present the results of Monte Carlo simulations for the dynamical evolution of star clusters containing two stellar populations with individual masses m1 and m2 > m1, and total masses M1 and M2 < M1. We use both King and Plummer model initial conditions and we perform simulations for a wide range of individual and total mass ratios, m2/m1 and M2/M1. We ignore the effects of binaries, stellar evolution, and the galactic tidal field. The simulations use N = 10^5 stars and follow the evolution of the clusters until core collapse. We find that the departure from energy equipartition in the core follows approximately the theoretical predictions of Spitzer (1969) and Lightman & Fall (1978), and we suggest a more exact condition that is based on our results. We find good agreement with previous results obtained by other methods regarding several important features of the evolution, including the pre-collapse distribution of heavier stars, the time scale on which equipartition is approached, and the extent to which core collapse is accelerated by a small subpopulation of heavier stars. We briefly discuss the possible implications of our results for the dynamical evolution of primordial black holes and neutron stars in globular clusters.Comment: 31 pages, including 13 figures, to appear in Ap

Risky Business? Entrepreneurship in the New Independent-Power Sector

Building on sociological research on institutions and organizations and psychological research on risk and decision making, we propose that the development of institutions that reduce the risks of entering new sectors has a stronger effect on the founding rates of firms using novel technologies than on firms using established technologies. In an analysis of the independent-power sector of the electricity industry from 1980 to 1992, we found that the development of regulative and cognitive institutions legitimated the entire sector and provided incentives for all sector entrants; thus, foundings of all kinds of firms multiplied rapidly but had a stronger impact on those using risky novel technologies. In contrast, the central normative institutions that developed in this sector, state-level trade associations, provided greater support for particular forms (those using established technologies) and thus increased foundings of those favored forms more than foundings of less favored forms (those using novel technologies). Our study demonstrates how institutional forces can alter the mix of organizations entering a new industry and thus contribute to diversity, as well as similarity, among organizations

EBSD and Nanoindentation-Correlated Study of Delamination Fracture in Al-Li Alloy 2090

Al-Li alloys offer attractive combinations of high strength and low density. However, a tendency for delamination fracture has limited their use. A better understanding of the delamination mechanisms may identify methods to control delaminations through processing modifications. A combination of new techniques has been used to evaluate delamination fracture in Al-Li alloys. Both high quality electron backscattered diffraction (EBSD) information and valid nanoindentation measurements were obtained from fractured test specimens. Correlations were drawn between nano-scale hardness variations and local texture along delaminating boundaries. Intriguing findings were observed for delamination fracture through the combined analysis of grain orientation, Taylor factor, and kernel average misorientation