119. [Rule for finding the number of quarts not greater than a given number N (a quart being a number which cannot be expressed a the sum of one, two, or three squares).]

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Massive star formation via high accretion rates and early disk-driven outflows

We present an investigation of massive star formation that results from the gravitational collapse of massive, magnetized molecular cloud cores. We investigate this by means of highly resolved, numerical simulations of initial magnetized Bonnor-Ebert-Spheres that undergo collapse and cooling. By comparing three different cases - an isothermal collapse, a collapse with radiative cooling, and a magnetized collapse - we show that massive stars assemble quickly with mass accretion rates exceeding 10^-3 Msol/yr. We confirm that the mass accretion during the collapsing phase is much more efficient than predicted by selfsimilar collapse solutions, i.e. dM/dt ~ c^3/G. We find that during protostellar assembly the mass accretion reaches 20 - 100 c^3/G. Furthermore, we determined the self-consistent structure of bipolar outflows that are produced in our three dimensional magnetized collapse simulations. These outflows produce cavities out of which radiation pressure can be released, thereby reducing the limitations on the final mass of massive stars formed by gravitational collapse. Moreover, we argue that the extraction of angular momentum by disk-threaded magnetic fields and/or by the appearance of bars with spiral arms significantly enhance the mass accretion rate, thereby helping the massive protostar to assemble more quickly.Comment: 22 pages, 12 figures, aastex style, accepted for publication in ApJ, see http://www.ita.uni-heidelberg.de/~banerjee/publications/MassiveStars.pdf for high resolution figure

Assessing the association between oral hygiene and preterm birth by quantitative light-induced fluorescence

The aim of this study was to investigate the purported link between oral hygiene and preterm birth by using image analysis tools to quantify dental plaque biofilm. Volunteers (η = 91) attending an antenatal clinic were identified as those considered to be “at high risk” of preterm delivery (i.e., a previous history of idiopathic preterm delivery, case group) or those who were not considered to be at risk (control group). The women had images of their anterior teeth captured using quantitative light-induced fluorescence (QLF). These images were analysed to calculate the amount of red fluorescent plaque (ΔR%) and percentage of plaque coverage. QLF showed little difference in ΔR% between the two groups, 65.00% case versus 68.70% control, whereas there was 19.29% difference with regard to the mean plaque coverage, 25.50% case versus 20.58% control. A logistic regression model showed a significant association between plaque coverage and case/control status (Ρ = 0.031), controlling for other potential predictor variables, namely, smoking status, maternal age, and body mass index (BMI)

Cost efficient operations for Discovery class missions

The Near Earth Asteroid Rendezvous (NEAR) program at The Johns Hopkins University Applied Physics Laboratory is scheduled to launch the first spacecraft in NASA's Discovery program. The Discovery program is to promote low cost spacecraft design, development, and mission operations for planetary space missions. The authors describe the NEAR mission and discuss the design and development of the NEAR Mission Operations System and the NEAR Ground System with an emphasis on those aspects of the design that are conducive to low-cost operations

Global Nonradial Instabilities of Dynamically Collapsing Gas Spheres

Self-similar solutions provide good descriptions for the gravitational collapse of spherical clouds or stars when the gas obeys a polytropic equation of state, $p=K\rho^\gamma$ (with $\gamma\le 4/3$). We study the behaviors of nonradial perturbations in the similarity solutions of Larson, Penston and Yahil, which describe the evolution of the collapsing cloud prior to core formation. Our global stability analysis reveals the existence of unstable bar-modes ($l=2$) when $\gamma\le 1.09$. In particular, for the collapse of isothermal spheres, which applies to the early stages of star formation, the $l=2$ density perturbation relative to the background, $\delta\rho({\bf r},t)/\rho(r,t)$, increases as $(t_0-t)^{-0.352}\propto \rho_c(t)^{0.176}$, where $t_0$ denotes the epoch of core formation, and $\rho_c(t)$ is the cloud central density. Thus, the isothermal cloud tends to evolve into an ellipsoidal shape (prolate bar or oblate disk, depending on initial conditions) as the collapse proceeds. In the context of Type II supernovae, core collapse is described by the $\gamma\simeq 1.3$ equation of state, and our analysis indicates that there is no growing mode (with density perturbation) in the collapsing core before the proto-neutron star forms, although nonradial perturbations can grow during the subsequent accretion of the outer core and envelope onto the neutron star. We also carry out a global stability analysis for the self-similar expansion-wave solution found by Shu, which describes the post-collapse accretion (``inside-out'' collapse) of isothermal gas onto a protostar. We show that this solution is unstable to perturbations of all $l$'s, although the growth rates are unknown.Comment: 28 pages including 7 ps figures; Minor changes in the discussion; To be published in ApJ (V.540, Sept.10, 2000 issue

A PPMAP analysis of the filamentary structures in Ophiuchus L1688 and L1689

We use the PPMAP (Point Process MAPping) algorithm to re-analyse the \textit{Herschel} and SCUBA-2 observations of the L1688 and L1689 sub-regions of the Ophiuchus molecular cloud. PPMAP delivers maps with high resolution (here $14''$, corresponding to $\sim 0.01\,{\rm pc}$ at $\sim 140\,{\rm pc}$), by using the observations at their native resolutions. PPMAP also delivers more accurate dust optical depths, by distinguishing dust of different types and at different temperatures. The filaments and prestellar cores almost all lie in regions with $N_{\rm H_2}\gtrsim 7\times 10^{21}\,{\rm cm}^{-2}$ (corresponding to $A_{_{\rm V}}\gtrsim 7$). The dust temperature, $T$, tends to be correlated with the dust opacity index, $\beta$, with low $T$ and low $\beta$ tend concentrated in the interiors of filaments. The one exception to this tendency is a section of filament in L1688 that falls -- in projection -- between the two B stars, S1 and HD147889; here $T$ and $\beta$ are relatively high, and there is compelling evidence that feedback from these two stars has heated and compressed the filament. Filament {\sc fwhm}s are typically in the range $0.10\,{\rm pc}$ to $0.15\,{\rm pc}$. Most filaments have line densities in the range $25\,{\rm M_{_\odot}\,pc^{-1}}$ to $65\,{\rm M_{_\odot}\,pc^{-1}}$. If their only support is thermal gas pressure, and the gas is at the canonical temperature of $10\,{\rm K}$, the filaments are highly supercritical. However, there is some evidence from ammonia observations that the gas is significantly warmer than this, and we cannot rule out the possibility of additional support from turbulence and/or magnetic fields. On the basis of their spatial distribution, we argue that most of the starless cores are likely to disperse (rather than evolving to become prestellar).Comment: 22 pages, 18 figures, Accepted for publication by MNRAS March 202

Spatial-Distance Cues Influence Economic Decision-Making in a Social Context

Social distance (i.e., the degree of closeness to another person) affects the way humans perceive and respond to fairness during financial negotiations. Feeling close to someone enhances the acceptance of monetary offers. Here, we explored whether this effect also extends to the spatial domain. Specifically, using an iterated version of the Ultimatum Game in a within-subject design, we investigated whether different visual spatial distance-cues result in different rates of acceptance of otherwise identical monetary offers. Study 1 found that participants accepted significantly more offers when they were cued with spatial closeness than when they were cued with spatial distance. Study 2 replicated this effect using identical procedures but different spatial- distance cues in an independent sample. Importantly, our results could not be explained by feelings of social closeness. Our results demonstrate that mere perceptions of spatial closeness produce analogous–but independent–effects to those of social closeness

Naturally occurring Ehrlichia chaffeensis infection in coyotes from Oklahoma.

A nested polymerase chain reaction assay was used to determine the presence of Ehrlichia chaffeensis, E. canis, and E. ewingii DNA in blood samples of free-ranging coyotes from central and northcentral Oklahoma. Of the 21 coyotes examined, 15 (71%) were positive for E. chaffeensis DNA; none was positive for E. canis or E. ewingii. Results suggest that E. chaffeensis infections are common in free-ranging coyotes in Oklahoma and that these wild canids could play a role in the epidemiology of human monocytotropic ehrlichiosis

Structure and Evolution of Hot Gas in 30 Dor

We have investigated the structure and evolution of hot gas in the 30 Dor nebula, based on recent X-ray observations. Our deep ROSAT HRI image shows that diffuse X-ray emission arises in blister-shaped regions outlined by loops of HII gas. X-ray spectroscopic data from ASCA confirm the thermal nature of the emission and indicate that hot gas temperature decreases from the core to the halo of the nebula. The structure of the nebula can be understood as outflows of hot and HII gases from the parent giant molecular cloud of the central OB association. The dynamic mixing between the two gas phases is likely responsible for the mass loading to the hot gas, as required to explain the observed thermal structure and X-ray luminosity of the nebula. Such processes should also be important in the formation of similar giant HII regions and in their subsequent evolution into supergiant bubbles or galactic chimneys.Comment: 9 page text plus 4 color figures. To appear in ApJ