Modeling the Dust Spectral Energy Distributions of Dwarf Galaxies

Recent efforts on the modeling of the infrared spectral energy distributions (SEDs) of dwarf galaxies are summarised here. The characterisation of the dust properties in these low metallicity environments is just unfolding, as a result of recently available mid-infrared to millimetre observations. From the limited cases we know to date, it appears that the hard radiation fields that are present in these star-bursting dwarf galaxies, as well as the rampent energetics of supernovae shocks and winds have modified the dust properties, in comparison with those in the Galaxy, or other gas and dust rich galaxies. The sophistication of the SED models is limited by the availability of detailed data in the mid infrared and particularly in the submillimetre to millimetre regime, which will open up in the near future with space-based missions, such as Herschel.Comment: 8 pages presented at "The Spectral Energy Distribution of Gas-Rich Galaxies: Confronting Models with Data" Heidelberg (Germany), October 2004. To be published in The Spectral Energy Distribution of Gas-Rich Galaxies, ed. C. Popescu & R. Tuffs (Melville:AIP) in pres

Interstellar Gas in Low Mass Virgo Cluster Spiral Galaxies

We have measured the strengths of the [C II] 158 micron, [N II] 122 micron, and CO (1 - 0) lines from five low blue luminosity spiral galaxies in the Virgo Cluster, using the Infrared Space Observatory and the NRAO 12m millimeter telescope. Two of the five galaxies have high L([C II)]/L(CO) and L(FIR)/L(CO) ratios compared to higher mass spirals. These two galaxies, NGC 4294 and NGC 4299, have L([C II])/L(CO) ratios of >14,300 and 15,600, respectively, which are similar to values found in dwarf irregular galaxies. This is the first time that such enhanced L([C II])/L(CO) ratios have been found in spiral galaxies. This result may be due to low abundances of dust and heavy elements, which can cause the CO (1 - 0) measurements to underestimate the molecular gas content. Another possibility is that radiation from diffuse HI clouds may dominate the [C II] emission from these galaxies. Less than a third of the observed [C II] emission arises from HII regions.Comment: 24 pages, Latex, 2 Figures, 6 Tables To appear in the Astronomical Journal, July 199

Formation of offshore tidal sandbanks triggered by a gasmined bed subsidence

Offshore gasmining is an example of a human intervention with a morphological impact. On land, it is usually attended with a dish-like bed depression. We show that, if located at sea, such a bed depression can become morphodynamically active by triggering mechanisms related to tidal sand bank formation. To that end, a simple morphological model is considered which describes an erodible bed subject to a tidal wave in a shallow sea. The continuous subsidence is modelled by a sink term in the sediment balance. Then, a linear approximation is carried out to describe the bed evolution after the onset of subsidence. The results, presented in physical space, show that the subsidence triggers the formation of a sand bank pattern that gradually spreads around the centre of subsidence, at a rate that may go up to 160 m year¿1, depending on the tidal transport rate and the tidal eccentricity. The dimension of the depression does not affect the spreading rate nor the orientation of the sand banks, but it does influence their spacing. The main conclusion is that the horizontal extent of the area influenced by the bed depression by far exceeds that of the direct subsidence, thus showing that bed depressions on land and at sea indeed behave in fundamentally different ways. The results suggest that nonlinear effects are worthwhile to be investigated in order to describe finite amplitude development of sand banks as well as the interaction between subsidence and bed forms

Constraints on crustal rheology and age of deformation from models of gravitational spreading in Ishtar Terra, Venus

Gravitational spreading is expected to lead to rapid relaxation of high relief due to the high surface temperature and associated weak crust on Venus. In this study, we use new Magellan radar and altimetry data to determine the extent of gravitational relaxation in Ishtar Terra, which contains the highest relief on Venus as well as areas of extremely high topographic slope. Within Ishtar Terra the only mountain belts found on Venus, Akna, Danu, Freyja, and Maxwell Montes, nearly encircle the smooth, high (3-4 km) plateau of Lakshmi Planum. Finite-element models of this process give expected timescales for relaxation of relief and failure at the surface. From these modeling results we attempt to constrain the strength of the crust and timescales of deformation in Ishtar Terra. Below we discuss observational evidence for gravitational spreading in Ishtar Terra, results from the finite-element modeling, independent age constraints, and implications for the rheology and timing of deformation

Gravitational spreading of Danu, Freyja and Maxwell Montes, Venus

The potential energy of elevated terrain tends to drive the collapse of the topography. This process of gravitational spreading is likely to be more important on Venus than on Earth because the higher surface temperature weakens the crust. The highest topography on Venus is Ishtar Terra. The high plateau of Lakshmi Planum has an average elevation of 3 km above mean planetary radius, and is surrounded by mountain belts. Freyja, Danu, and Maxwell Montes rise, on average, an additional 3, 0.5, and 5 km above the plateau, respectively. Recent high resolution Magellan radar images of this area, east of approx. 330 deg E, reveal widespread evidence for gravity spreading. Some observational evidence is described for gravity spreading and the implications are discussed in terms of simple mechanical models. Several simple models predict that gravity spreading should be an important process on Venus. One difficulty in using remote observations to infer interior properties is that the observed features may not have formed in response to stresses which are still active. Several causes of surface topography are briefly examined

A comparison of refined models for flexible subassemblies

Interactions between structure response and control of large flexible space systems have challenged current modeling techniques and have prompted development of new techniques for model improvement. Due to the geometric complexity of envisioned large flexible space structures, finite element models (FEM's) will be used to predict the dynamic characteristics of structural components. It is widely accepted that these models must be experimentally 'validated' before their acceptance as the basis for final design analysis. However, predictions of modal properties (natural frequencies, mode shapes, and damping ratios) are often in error when compared to those obtained from Experimental Modal Analysis (EMA). Recent research efforts have resulted in the development of algorithmic approaches for model improvement, also referred to as system or structure identification

Competition between Pressure and Gravity Confinement in Lyman-Alpha Forest Observations

A break in the distribution function of Ly$\alpha$ clouds (at a typical redshift of $2.5$) has been reported by Petitjean et al. (1993). This feature is what would be expected from a transition between pressure confinement and gravity confinement (as predicted in Charlton, Salpeter, and Hogan (1993)). The column density at which the feature occurs has been used to determine the external confining pressure, $\sim 10 {\rm cm}^{-3} {\rm K}$, which could be due to a hot, intergalactic medium. For models that provide a good fit to the data, the contribution of the gas in clouds to $\Omega$ is small. The specific shape of the distribution function at the transition (predicted by models to have a non-monotonic slope) can serve as a diagnostic of the distribution of dark matter around Ly$\alpha$ forest clouds, and the present data already eliminate certain models.Comment: 10 pages plain TeX, 2 figures available upon request, submitted to ApJ Letters, PSU-jc-

An Exploration of Racial/Ethnic Differences in the Association between Perfectionism and Disordered Eating in College Students

Perfectionism is a robust risk factor for eating disorders (EDs). Although individually-oriented dimensions of perfectionism are strongly related to eating pathology, less is known about the contribution of parent-oriented dimensions, specifically parental expectations (PE) and parental criticisms (PC). Further, few studies have investigated these effects within racially/ethnically diverse samples. However, PE and PC might be particularly relevant to eating pathology among certain cultural groups, such as those from collectivistic and interdependent societies. This study examined associations among PE, PC, and ED symptoms across racial/ethnic groups. Undergraduates (N=706; 74.8% Female; 48% White, 19.8% Black, 7.1% Latinx, 16% Asian, 9.1% multiracial) completed online surveys assessing perfectionism and ED symptoms. Multiple and logistic regressions examined the association between parent-oriented perfectionism, global eating pathology, loss-of-control (LOC) eating, purging behaviors, and ED risk status (EDE-Q global \u3c 4.0). Analyses were conducted by racial/ethnic group, controlling for gender. Both PE and PC were related to greater ED pathology in students identifying as White (pp=.03), Asian (p=.02), and multiracial (pp=.19). Higher PC was related to a greater likelihood of endorsing LOC eating in White (p=.004) and Black students (p=.05) and purging behaviors in White (p=.004), Asian (p=.04), and multiracial students (p=.03). Greater PC was also associated with ED risk in Asian (p=.03) and multiracial participants (p=.01). Findings indicate that the relations between specific aspects of parent-oriented perfectionism differ among cultural groups and are associated with ED symptoms in college students. PC seemed more relevant to ED pathology than did PE overall. Findings suggest that parent-oriented perfectionism, particularly PC, might be important to include in clinical assessment and treatment with students at-risk of EDs.https://scholarscompass.vcu.edu/gradposters/1039/thumbnail.jp