The Dust Depletion and Extinction of the GRB 020813 Afterglow

The Keck optical spectrum of the GRB 020813 afterglow is the best ever obtained for GRBs. Its large spectral range and very high S/N ratio allowed for the first time the detection of a vast variety of absorption lines, associated with the circumburst medium or interstellar medium of the host. The remarkable similarity of the relative abundances of 8 elements with the dust depletion pattern seen in the Galactic ISM suggests the presence of dust. The derived visual dust extinction A_V=0.40+/-0.06 contradicts the featureless UV spectrum of the afterglow, very well described by a unreddened power law. The forthcoming Swift era will open exciting opportunities to explain similar phenomena in other GRB afterglows.Comment: To be published in "Il Nuovo Cimento", Proceedings of the 4th Rome Workshop on Gamma-Ray Bursts in the Afterglow Era, eds. L. Piro, L. Amati, S. Covino, B. Gendr

Complex Networks on a Rock Joint

A complex network approach on a rough fracture is developed. In this manner, some hidden metric spaces (similarity measurements) between apertures profiles are set up and a general evolutionary network in two directions (in parallel and perpendicular to the shear direction) is constructed. Also, an algorithm (COmplex Networks on Apertures: CONA) is proposed in which evolving of a network is accomplished using preferential detachments and attachments of edges (based on a competition and game manner) while the number of nodes is fixed. Also, evolving of clustering coefficients and number of edges display similar patterns as well as are appeared in shear stress, hydraulic conductivity and dilation changes, which can be engaged to estimate shear strength distribution of asperities.Comment: ROCKENG09: Proceedings of the 3rd CANUS Rock Mechanics Symposium, Toronto, May 2009 (Ed: M.Diederichs and G. Grasselli

WFPC2 Observations of Star Clusters in the Magellanic Clouds: I. The LMC Globular Cluster Hodge 11

We present our analysis of Hubble Space Telescope Wide Field Planetary Camera 2 observations in F555W (broadband V) and F450W (broadband B) of the globular cluster Hodge 11 in the Large Magellanic Cloud galaxy. The resulting V vs. (B-V) color-magnitude diagram reaches 2.4 mag below the main-sequence turnoff (which is at V_TO = 22.65 +- 0.10 mag or M_V^TO = 4.00 +- 0.16 mag). Comparing the fiducial sequence of Hodge 11 with that of the Galactic globular cluster M92, we conclude that, within the accuracy of our photometry, the age of Hodge 11 is identical to that of M92 with a relative age-difference uncertainty ranging from 10% to 21%. Provided that Hodge 11 has always been a part of the Large Magellanic Cloud and was not stripped from the halo of the Milky Way or absorbed from a cannibalized dwarf spheroidal galaxy, then the oldest stars in the Large Magellanic Clouds and the Milky Way appear to have the same age.Comment: 14 pages (LaTeX+aaspp4.sty), 3 tables and 4 figures (Postscript, gzipped tar file). Postscript version of paper, tables, and full-resolution figures available at http://www.astro.columbia.edu/~mighell/hodge11.html To appear in the Astronomical Journa

Paralysie flasque en début de grossesse: penser à l’hypokaliémie due aux vomissements gravidiques, à propos de deux observations dans un pays en voie de développement

Les vomissements gravidiques peuvent être responsables de rares complications neuromusculaires mais graves notamment la paralysie hypokaliémique. Nous rapportons des observations de deux jeunes femmes d'origine guinéenne, sans histoires familiales ni antécédents particuliers, admises pour paralysie flasque des quatre membres dans un contexte de vomissements incoercibles en début de grossesse. Le bilan retrouvait une hypokaliémie majeure associée à quelques troubles électro-cardiographiques. L'apport de potassium par voie parentérale avait permis une récupération motrice totale. La paralysie hypokaliémique est une complication rare des vomissements gravidiques. Une supplémentation potassique prudente avec une surveillance électro-cardiographique et biologique permet une disparition spectaculaire des troubles neuromusculaires

Bulgeless Galaxies and their Angular Momentum Problem

The specific angular momentum of Cold Dark Matter (CDM) halos in a $\Lambda$CDM universe is investigated. Their dimensionless specific angular momentum $\lambda'=\frac{j}{\sqrt{2}V_{vir} R{vir}}$ with $V_{vir}$ and $R_{vir}$ the virial velocity and virial radius, respectively depends strongly on their merging histories. We investigate a set of $\Lambda$CDM simulations and explore the specific angular momentum content of halos formed through various merging histories. Halos with a quiet merging history, dominated by minor mergers and accretion until the present epoch, acquire by tidal torques on average only 2% to 3% of the angular momentum required for their rotational support ($\lambda'=0.02$). This is in conflict with observational data for a sample of late-type bulgeless galaxies which indicates that those galaxies reside in dark halos with exceptionally high values of $\lambda' \approx 0.06-0.07$. Minor mergers and accretion preserve or slowly increase the specific angular momentum of dark halos with time. This mechanism is however not efficient enough in order to explain the observed spin values for late-type dwarf galaxies. Energetic feedback processes have been invoked to solve the problem that gas loses a large fraction of its specific angular momentum during infall. Under the assumption that dark halos hosting bulgeless galaxies acquire their mass via quiescent accretion, our results indicate yet another serious problem: the specific angular momentum gained during the formation of these objects is not large enough to explain their observed rotational properties,even if no angular momentum would be lost during gas infall.Comment: 4 pages, 3 figures. To appear in September 1, 2004, issue of ApJ Letter

Orbital Decay and Tidal Disruption of a Star Cluster: Analytical Calculation

The orbital decay and tidal disruption of a star cluster in a galaxy is studied in an analytical manner. Owing to dynamical friction, the star cluster spirals in toward the center of the galaxy. Simultaneously, the galactic tidal field strips stars from the outskirts of the star cluster. Under an assumption that the star cluster undergoes a self-similar evolution, we obtain the condition and timescale for the star cluster to reach the galaxy center before its disruption. The result is used to discuss the fate of so-called intermediate-mass black holes with >10^3 M(sun) found recently in young star clusters of starburst galaxies and also the mass function of globular clusters in galaxies.Comment: 12 pages, 1 PS file for 2 figures, to appear in The Astrophysical Journa