Structural concepts and experimental considerations for a versatile high-speed research airplane

Future aircraft may be hydrogen fueled and fly at hypersonic speeds. The resulting environments will require new structural concepts to satisfy performance goals. Large representative structures will have to be flight tested prior to commitment to a costly vehicle fleet. To perform flight tests, a versatile, economical, high-speed research airplane is defined. Results of this study including experimental considerations for a hypersonic research airplane are reported

The [alpha/Fe] Ratios in Dwarf Galaxies: Evidence for a Non-universal Stellar Initial Mass Function?

It is well established that the [alpha/Fe] ratios in elliptical galaxies increase with galaxy mass. This relation holds also for early-type dwarf galaxies, although it seems to steepen at low masses. The [alpha/Fe] vs. mass relation can be explained assuming that smaller galaxies form over longer timescales (downsizing), allowing a larger amount of Fe (mostly produced by long-living Type Ia Supernovae) to be released and incorporated into newly forming stars. Another way to obtain the same result is by using a flatter initial mass function (IMF) in large galaxies, increasing in this way the number of Type II Supernovae and therefore the production rate of alpha-elements. The integrated galactic initial mass function (IGIMF) theory predicts that the higher the star formation rate, the flatter the IMF. We have checked, by means of semi-analytical calculations, that the IGIMF theory, combined with the downsizing effect (i.e. the shorter duration of the star formation in larger galaxies), well reproduces the observed [alpha/Fe] vs. mass relation. In particular, we show a steepening of this relation in dwarf galaxies, in accordance with the available observations.Comment: 4 pages, 2 figures; to appear in the proceedings of the JENAM 2010 Symposium on Dwarf Galaxies (Lisbon, September 9-10, 2010

The structure of insulin at the air/water interface: monomers or dimers?

The hydrophobic character of the air/water interface affects the oligomeric composition of insulin. By using interface-specific vibrational sum frequency spectroscopy and calculations of insulin monomer and dimer second-order nonlinear susceptibilities chi(2), we show that insulin monomers segregate to the air/water interface

A discontinuity in the low-mass initial mass function

The origin of brown dwarfs (BDs) is still an unsolved mystery. While the standard model describes the formation of BDs and stars in a similar way recent data on the multiplicity properties of stars and BDs show them to have different binary distribution functions. Here we show that proper treatment of these uncovers a discontinuity of the multiplicity-corrected mass distribution in the very-low-mass star (VLMS) and BD mass regime. A continuous IMF can be discarded with extremely high confidence. This suggests that VLMSs and BDs on the one hand, and stars on the other, are two correlated but disjoint populations with different dynamical histories. The analysis presented here suggests that about one BD forms per five stars and that the BD-star binary fraction is about 2%-3% among stellar systems.Comment: 14 pages, 11 figures, uses emulateapj.cls. Minor corrections and 1 reference added after being accepted by the Ap

The chemical evolution of galaxies within the IGIMF theory: the [alpha/Fe] ratios and downsizing

The chemical evolution of galaxies is investigated within the framework of the star formation rate (SFR) dependent integrated galactic initial mass function (IGIMF). We study how the global chemical evolution of a galaxy and in particular how [alpha/Fe] abundance ratios are affected by the predicted steepening of the IGIMF with decreasing SFR. We use analytical and semi-analytical calculations to evaluate the mass-weighted and luminosity-weighted [alpha/Fe] ratios in early-type galaxies of different masses. The models with the variable IGIMF produce a [alpha/Fe] vs. velocity dispersion relation which has the same slope as the observations of massive galaxies, irrespective of the model parameters, provided that the star formation duration inversely correlates with the mass of the galaxy (downsizing). These models also produce steeper [alpha/Fe] vs. sigma relations in low-mass early-type galaxies and this trend is consistent with the observations. Constant IMF models are able to reproduce the [alpha/Fe] ratios in large elliptical galaxies as well, but they do not predict this change of slope for small galaxies. In order to obtain the best fit between our results and the observations, the downsizing effect (i.e. the shorter duration of the star formation in larger galaxies) must be milder than previously thought.Comment: 13 pages, 18 figures, accepted for publication in Astronomy and Astrophysic

The Influence of postpartum posttraumatic Stress Disorders on the childhood Development: a population-based Two-year follow-up Study

Background. Against the background of very limited evidence, the present study aimed to prospectively examine the impact of maternal postpartum PTSD symptoms on four important areas of child development, i.e. gross motor, fine motor, communication, and social-emotional development. Methods. This study is part of the large, population based Akershus Birth Cohort. Data from the hospital’s birth record as well as questionnaire data from 8 weeks and 2 years postpartum were used (n=1,472). The domains of child development that were significantly correlated with PTSD symptoms were entered into regression analyses. Interaction analyses were run to test whether the influence of postpartum PTSD symptoms on child development was moderated by child sex or infant temperament. Results. Postpartum PTSD symptoms had a prospective relationship with poor child social-emotional development two years later. This relationship remained significant even when adjusting for confounders such as maternal depression and anxiety or infant temperament. Both child sex and infant temperament moderated the association between maternal PTSD symptoms and child socialemotional development, i.e. with increasing maternal PTSD symptom load, boys and children with a difficult temperament showed to have comparatively higher levels of social-emotional problems. Conclusions. Examining four different domains of child development, we found a prospective impact of postpartum PTSD symptoms on children’s social-emotional development at two years of age. Our findings suggest that both boys and children with an early difficult temperament may be particularly susceptible to the adverse impact of postpartum PTSD symptoms. Additional studies are needed to further investigate the mechanisms at work

Chemo-Archaeological Downsizing in a Hierarchical Universe: Impact of a Top Heavy IGIMF

We make use of a semi-analytical model of galaxy formation to investigate the origin of the observed correlation between [a/Fe] abundance ratios and stellar mass in elliptical galaxies. We implement a new galaxy-wide stellar initial mass function (Top Heavy Integrated Galaxy Initial Mass Function, TH-IGIMF) in the semi-analytic model SAG and evaluate its impact on the chemical evolution of galaxies. The SFR-dependence of the slope of the TH-IGIMF is found to be key to reproducing the correct [a/Fe]-stellar mass relation. Massive galaxies reach higher [a/Fe] abundance ratios because they are characterized by more top-heavy IMFs as a result of their higher SFR. As a consequence of our analysis, the value of the minimum embedded star cluster mass and of the slope of the embedded cluster mass function, which are free parameters involved in the TH-IGIMF theory, are found to be as low as 5 solar masses and 2, respectively. A mild downsizing trend is present for galaxies generated assuming either a universal IMF or a variable TH-IGIMF. We find that, regardless of galaxy mass, older galaxies (with formation redshifts > 2) are formed in shorter time-scales (< 2 Gyr), thus achieving larger [a/Fe] values. Hence, the time-scale of galaxy formation alone cannot explain the slope of the [a/Fe]-galaxy mass relation, but is responsible for the big dispersion of [a/Fe] abundance ratios at fixed stellar mass.We further test the hyphothesis of a TH-IGIMF in elliptical galaxies by looking into mass-to-light ratios, and luminosity functions. Models with a TH-IGIMF are also favoured by these constraints. In particular, mass-to-light ratios agree with observed values for massive galaxies while being overpredicted for less massive ones; this overprediction is present regardless of the IMF considered.Comment: 24 pages, 15 figures, 2 tables. (Comments most welcome). Summited to MNRA

Analysis of Scramjet Flight Trajectories with Oxygen Enrichment

Scramjets are proposed as a second stage for a multi-stage access-to-space system. At present the upper limit of scramjet operation is expected to be Mach 12-14. Use of oxygen enrichment is a possible method for increasing the speed and altitude of scramjet operation. This paper involves mission analysis of scramjets using oxygen enrichment. It follows on from Smart & Tetlow [5], in which trajectory studies of a threestage rocket-scramjet-rocket access-to-space system were conducted. These calculations indicated that the net thrust (scramjet thrust - vehicle drag) of a hypersonic vehicle with three scramjet engine modules was reduced to very low levels above Mach 12. The current work examines the use of oxygen enrichment in the scramjet to increase net thrust above Mach 10. Results of the study indicate that an important effect of oxygen enrichment is to allow scramjet powered vehicle operation at higher altitude

Testing the universal stellar IMF on the metallicity distribution in the bulges of the Milky Way and M31

We test whether the universal initial mass function (UIMF) or the integrated galaxial IMF (IGIMF) can be employed to explain the metallicity distribution (MD) of giants in the Galactic bulge. We make use of a single-zone chemical evolution model developed for the Milky Way bulge in the context of an inside-out model for the formation of the Galaxy. We checked whether it is possible to constrain the yields above 80 M_{\sun} by forcing the UIMF and required that the resulting MD matches the observed ones. We also extended the analysis to the bulge of M31 to investigate a possible variation of the IMF among galactic bulges. Several parameters that have an impact on stellar evolution (star-formation efficiency, gas infall timescale) are varied. We show that it is not possible to satisfactorily reproduce the observed metallicity distribution in the two galactic bulges unless assuming a flatter IMF ($x \leq 1.1$) than the universal one. We conlude that it is necessary to assume a variation in the IMF among the various environments.Comment: 9 pages, 4 figures, accepted for publication in A&