University of Vienna

About: University of Vienna is a education organization based out in Vienna, Austria. It is known for research contribution in the topics: Population & Stars. The organization has 44686 authors who have published 95840 publications receiving 2907492 citations.

Some Remarks on the Value-at-Risk and the Conditional Value-at-Risk

Abstract: The value-at-risk (VaR) and the conditional value-at-risk (CVaR) are two commonly used risk measures. We state some of their properties and make a comparison. Moreover, the structure of the portfolio optimization problem using the VaR and CVaR objective is studied.

On the Star Formation Rates in Molecular Clouds

Abstract: In this paper, we investigate the level of star formation activity within nearby molecular clouds. We employ a uniform set of infrared extinction maps to provide accurate assessments of cloud mass and structure and compare these with inventories of young stellar objects within the clouds. We present evidence indicating that both the yield and rate of star formation can vary considerably in local clouds, independent of their mass and size. We find that the surface density structure of such clouds appears to be important in controlling both these factors. In particular, we find that the star formation rate (SFR) in molecular clouds is linearly proportional to the cloud mass (M 0.8) above an extinction threshold of A K ≈ 0.8 mag, corresponding to a gas surface density threshold of Σgas ≈ 116 M ☉ pc2. We argue that this surface density threshold corresponds to a gas volume density threshold which we estimate to be n(H2) ≈ 104 cm–3. Specifically, we find SFR (M ☉ yr–1) = 4.6 ± 2.6 × 10–8 M 0.8 (M ☉) for the clouds in our sample. This relation between the rate of star formation and the amount of dense gas in molecular clouds appears to be in excellent agreement with previous observations of both galactic and extragalactic star-forming activity. It is likely the underlying physical relationship or empirical law that most directly connects star formation activity with interstellar gas over many spatial scales within and between individual galaxies. These results suggest that the key to obtaining a predictive understanding of the SFRs in molecular clouds and galaxies is to understand those physical factors which give rise to the dense components of these clouds.

GPI-anchored cell-surface molecules complexed to protein tyrosine kinases.

Abstract: Binding of ligand or antibody to certain cell-surface proteins that are anchored to the membrane by glycophosphatidylinositol (GPI) can cause activation of leukocytes. However, it is not known how these molecules, which lack intracellular domains, can transduce signals. The GPI-linked human molecules CD59, CD55, CD48, CD24, and CD14 as well as the mouse molecules Thy-1 and Ly-6 were found to associate with protein tyrosine kinases, key regulators of cell activation and signal transduction. A protein tyrosine kinase associated with the GPI-linked proteins CD59, CD55, and CD48 in human T cells, and with Thy-1 in mouse T cells was identified as p56lck, a protein tyrosine kinase related to Src. This interaction of GPI-linked molecules with protein tyrosine kinases suggests a potential mechanism of signal transduction in cells.

Optomechanical entanglement between a movable mirror and a cavity field

Abstract: In this paper we propose an experimental scheme to create and probe optomechanical entanglement between a light field and a mechanical oscillator. This is achieved using a bright laser field that resonates inside a cavity and couples to the position and momentum of a moving (micro)mirror.