Evidence against a simple two-component model for the far-infrared emission from galaxies

Two of the first Infrared Astronomy Satellite (IRAS) results were that galaxies have a wide range of values for the ratio of 60 micron to 100 micron flux density (0.2 less than or equal to S sub 60/S sub 100 less than or equal to 1.0) and that this ratio is correlated with L sub fir, L sub b, L sub fir being the total far-infrared luminosity and L sub b being the luminosity at visible wavelengths (de Jong et al. 1984; Soifer et al. 1984). From these results arose the following simple model for the far-infrared emission from galaxies (de Jong et al. 1984), which has remained the standard model ever since. In this model, the far-infrared emission comes from two dust components: warm dust (T approx. equals 50 K) intermingled with, and heated by, young massive OB stars in molecular clouds and HII regions, and colder dust (T approx. equals 20 K) associated with the diffuse atomic hydrogen in the interstellar medium and heated by the general interstellar radiation field. As the number of young stars in a galaxy increases, S sub 60/S sub 100 increases, because there is a greater proportion of warm dust, and so does L sub fir/L sub b, because most of the radiation from the young stars is absorbed by the dust, leading to a swifter increase in far-infrared emission than in visible light. Although this model explains the basic IRAS results, it is inelegant. It uses two free parameters to fit two data (the 60 and 100 micron flux densities)-and there are now several observations that contradict it. Despite these major problems with the two-component model, it is not clear what should be put in its place. When considering possible models for the far-infrared emission from galaxies, the observational evidence for our own galaxy must be considered. Researchers suspect that the study by Boulanger and Perault (1988) of the far-infrared properties of the local interstellar medium may be particularly relevant. They showed that molecular clouds are leaky - that most of the light from OB stars in molecular clouds does not heat the dust in the clouds, but instead leaks out. The consequence of this is that that while most of the far-infrared emission from the solar neighborhood is from dust associated with diffuse HI, this dust is mostly heated by young stars

Rapid Mass Segregation in Massive Star Clusters

Several dynamical scenarios have been proposed that can lead to prompt mass segregation on the crossing time scale of a young cluster. They generally rely on cool and/or clumpy initial conditions, and are most relevant to small systems. As a counterpoint, we present a novel dynamical mechanism that can operate in relatively large, homogeneous, cool or cold systems. This mechanism may be important in understanding the assembly of large mass-segregated clusters from smaller clumps.Comment: 2 pages, 2 figures; Invited talk presented as Special Session 1 "Origin and Complexity of Massive Star Clusters" at IAU General Assembly XXVIII, Beijing 2012. To appear in Highlights of Astronom

An Indicator Measuring Underlying Economic Activity in Greece

Using a state space formulation developed by Stock and Watson and Garratt and Hall we construct an indicator, which then is interpreted as a measure of the underlying economic activity of the Greek economy. The chief novelty of the paper is that the underlying model is calibrated, rather than estimated, using sample information. Our approach is more flexible than the original one, in that it provides the possibility to cope with outlying observations and to evaluate particular shocks affecting the economy using judgmental interventions. The new indicator could be very helpful for short run policy analysis signalling emerging economic problems.Economic Activity; Coincident Indicator; Kalman Filter

On the instability of hypersonic flow past a flat plate

The instability of hypersonic boundary-layer flows over flat plates is considered. The viscosity of the fluid is taken to be governed by Sutherland's law, which gives a much more accurate representation of the temperature dependence of fluid viscosity at hypersonic speeds than Chapman's approximate linear law; although at lower speeds the temperature variation of the mean state is less pronounced so that the Chapman law can be used with some confidence. Attention is focussed on the so-called (vorticity) mode of instability of the viscous hypersonic boundary layer. This is thought to be the fastest growing inviscid disturbance at hypersonic speeds; it is also believed to have an asymptotically larger growth rate than any viscous or centrifugal instability. As a starting point the instability of the hypersonic boundary layer which exists far downstream from the leading edge of the plate is investigated. In this regime the shock that is attached to the leading edge of the plate plays no role, so that the basic boundary layer is non-interactive. It is shown that the vorticity mode of instability of this flow operates on a significantly different lengthscale than that obtained if a Chapman viscosity law is assumed. In particular, it is found that the growth rate predicted by a linear viscosity law overestimates the size of the growth rate by O(M(exp 2). Next, the development of the vorticity mode as the wavenumber decreases is described, and it is shown that acoustic modes emerge when the wavenumber has decreased from it's O(1) initial value to O(M (exp -3/2). Finally, the inviscid instability of the boundary layer near the leading edge in the interaction zone is discussed and particular attention is focussed on the strong interaction region which occurs sufficiently close to the leading edge. It is found that the vorticity mode in this regime is again unstable, and that it is concentrated in the transition layer at the edge of the boundary layer where the temperature adjusts from its large, O(M(exp 2), value in the viscous boundary layer, to its O(1) free stream value. The existence of the shock indirectly, but significantly, influences the instability problem by modifying the basic flow structure in this layer

Incidence of Gunshot Wounds: Before and After Implementation of a Shall Issue Conceal Carry Law

Introduction. This study examined the incidence of gunshot wounds before and after enacting a conceal carry (CC) law in a predominately rural state. Methods. A retrospective review was conducted of all patients who were admitted with a gunshot injury to a Level I trauma center. Patient data collected included demographics, injury details, hospital course, and discharge destination. Results. Among the 238 patients included, 44.6% (n = 107) were admitted during the pre-CC period and 55.4% (n = 131) in the post-CC period. No demographic differences were noted between the two periods except for an increase in uninsured patients from 43.0% vs 61.1% (p = 0.020). Compared to pre-CC patients, post-CC patients experienced a trend toward increased abdominal injury (11.2% vs 20.6%, p = 0.051) and increased vascular injuries (11.2% vs 22.1%, p = 0.026) while lower extremity injuries decreased significantly (38.3% vs 26.0%, p = 0.041). Positive focused assessment with sonography in trauma (FAST) exams (2.2% vs 16.8, p < 0.001), intensive care unit admission (26.2% vs 42.0%, p = 0.011) and need for ventilator support (11.2% vs 22.1%, p = 0.026) all increased during the post-CC period. In-hospital mortality more than doubled (8.4% vs 18.3%, p = 0.028) across the pre- and post-CC time periods. Conclusion. Implementation of a CC law was not associated with a decrease in the overall number of penetrating injuries or a decrease in mortality

A Short Proof of Increased Parabolic Regularity

We present a new, short proof of the increased regularity obtained by solutions to uniformly parabolic partial differential equations. Though this setting is fairly introductory, our new method of proof, which uses a priori estimates, can be extended to prove analogous results for problems with time-dependent coefficients, transport equations, and nonlinear equations even when other tools, such as semigroup methods or the use of explicit fundamental solutions, are unavailable.Comment: 8 page