612 research outputs found

    Correlations among global photometric properties of disk galaxies

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    Using a two-dimensional galaxy image decomposition technique, we extract global bulge and disk parameters for a complete sample of early type disk galaxies in the near infrared K band. We find significant correlation of the bulge parameter n with the central bulge surface brightness μb(0)\mu_b(0) and with effective radius r_e. Using bivar iate analysis techniques, we find that logn\log n, logre\log r_e and μb(0)\mu_b(0) are distributed in a plane with small scatter. We do not find a strong correlation of n with bulge-to-disk luminosity ratio, contrary to earlier reports. r_e and the disk scale length r_d are well correlated for these early type disk galaxies, but with large scatter. We examine the implications of our results to various bulge formation scenarios in disk galaxies.Comment: 14 pages, LaTeX including 14 figures. To appear in the Astrophysical Journa

    Goal-directed fluid management based on pulse pressure variation monitoring during high-risk surgery: a pilot randomized controlled trial

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    Abstract\ud \ud \ud \ud Introduction\ud \ud Several studies have shown that maximizing stroke volume (or increasing it until a plateau is reached) by volume loading during high-risk surgery may improve post-operative outcome. This goal could be achieved simply by minimizing the variation in arterial pulse pressure (ΔPP) induced by mechanical ventilation. We tested this hypothesis in a prospective, randomized, single-centre study. The primary endpoint was the length of postoperative stay in hospital.\ud \ud \ud \ud Methods\ud \ud Thirty-three patients undergoing high-risk surgery were randomized either to a control group (group C, n = 16) or to an intervention group (group I, n = 17). In group I, ΔPP was continuously monitored during surgery by a multiparameter bedside monitor and minimized to 10% or less by volume loading.\ud \ud \ud \ud Results\ud \ud Both groups were comparable in terms of demographic data, American Society of Anesthesiology score, type, and duration of surgery. During surgery, group I received more fluid than group C (4,618 ± 1,557 versus 1,694 ± 705 ml (mean ± SD), P < 0.0001), and ΔPP decreased from 22 ± 75 to 9 ± 1% (P < 0.05) in group I. The median duration of postoperative stay in hospital (7 versus 17 days, P < 0.01) was lower in group I than in group C. The number of postoperative complications per patient (1.4 ± 2.1 versus 3.9 ± 2.8, P < 0.05), as well as the median duration of mechanical ventilation (1 versus 5 days, P < 0.05) and stay in the intensive care unit (3 versus 9 days, P < 0.01) was also lower in group I.\ud \ud \ud \ud Conclusion\ud \ud Monitoring and minimizing ΔPP by volume loading during high-risk surgery improves postoperative outcome and decreases the length of stay in hospital.\ud \ud \ud \ud Trial registration\ud \ud NCT00479011The authors thank Maria De Amorim (Paris, France) and Julia Fukushima (São Paulo, SP, Brazil) for help in data analysis, Dr Julia Wendon (London, UK) for reviewing the manuscript, and Dixtal (Sao Paulo, SP, Brazil) for providing the software for the automatic calculation of ?PP.The authors thank Maria De Amorim (Paris, France) and Julia Fukushima (São Paulo, SP, Brazil) for help in data analysis, Dr Julia Wendon (London, UK) for reviewing the manuscript, and Dixtal (Sao Paulo, SP, Brazil) for providing the software for the automatic calculation of ?PP

    Flexible n-i-p thin film silicon solar cells on polyimide foils with textured ZnO:Ga back reflector

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    In thin film silicon solar cells on opaque substrates in n-i-p deposition sequence where the textured transparent conductive oxide (TCO) layer serves as a back reflector, one can independently optimize the morphology of the TCO layer without compromise on transparency and conductivity of this layer and further adjust the electro-optical properties of the back contact by using additional layers on top of the textured TCO. In the present work, we use this strategy to obtain textured back reflectors for solar cells in n-i-p deposition sequence on non-transparent flexible plastic foils. Gallium doped ZnO (ZnO:Ga) films were deposited on polyimide substrates by DC magnetron sputtering at a temperature of 200 °C. A wet-chemical etching step was performed by dipping the ZnO:Ga covered foil into a diluted HCl solution. The textured ZnO:Ga is then coated with a highly reflective Ag/ZnO double layer. On this back reflector, we develop thin film silicon solar cells with a microcrystalline silicon absorber layer. The current density for the cell with the textured ZnO:Ga layer is ~ 23 mA/cm2, 4 mA/cm2 higher than the one without such layer, and a maximum efficiency of 7.5% is obtained for a 1 cm2 cell.Fundação para a Ciência e a Tecnologia (FCT

    Quantitative Morphology of Galaxies in the Hubble Deep Field

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    We measure quantitative structural parameters of galaxies in the Hubble Deep Field (HDF) on the drizzled F814W images. Our structural parameters are based on a two-component surface brightness made up of a S\'ersic profile and an exponential profile. We compare our results to the visual classification of van den Bergh et al. (1996) and the CAC-A classification of Abraham et al. (1996a). Our morphological analysis of the galaxies in the HDF indicates that the spheroidal galaxies, defined here as galaxies with a dominant bulge profile, make up for only a small fraction, namely 8% of the galaxy population down to mF814W(AB)_{F814W}(AB) = 26.0. We show that the larger fraction of early-type systems in the van den Bergh sample is primarily due to the difference in classification of 40% of small round galaxies with half-light radii < 0\arcsecpoint 31. Although these objects are visually classified as elliptical galaxies, we find that they are disk-dominated with bulge fractions < 0.5. Given the existing large dataset of HDF galaxies with measured spectroscopic redshifts, we are able to determine that the majority of distant galaxies (z>2z>2) from this sample are disk-dominated. Our analysis reveals a subset of HDF galaxies which have profiles flatter than a pure exponential profile.Comment: 35 pages, LaTeX, 18 Postscript Figures, Tables available at http://astro.berkeley.edu/~marleau/. Accepted for Publication in The Astrophysical Journa

    Ising model with memory: coarsening and persistence properties

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    We consider the coarsening properties of a kinetic Ising model with a memory field. The probability of a spin-flip depends on the persistence time of the spin in a state. The more a spin has been in a given state, the less the spin-flip probability is. We numerically studied the growth and persistence properties of such a system on a two dimensional square lattice. The memory introduces energy barriers which freeze the system at zero temperature. At finite temperature we can observe an apparent arrest of coarsening for low temperature and long memory length. However, since the energy barriers introduced by memory are due to local effects, there exists a timescale on which coarsening takes place as for the Ising model. Moreover the two point correlation functions of the Ising model with and without memory are the same, indicating that they belong to the same universality class.Comment: 10 pages, 7 figures; some figures and some comments adde

    M32+/-1

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    WFPC-2 images are used to study the central structure of M31, M32, and M33. The dimmer peak, P2, of the M31 double nucleus is centered on the bulge to 0.1", implying that it is the dynamical center of M31. P2 contains a compact source discovered by King et al. (1995) at 1700 A. This source is resolved, with r_{1/2} approx0.2 pc. It dominates the nucleus at 3000 A, and is consistent with late B-early A stars. This probable cluster may consist of young stars and be an older version of the cluster of hot stars at the center of the Milky Way, or it may consist of heavier stars built up from collisions in a possible cold disk of stars orbiting P2. In M32, the central cusp rises into the HST limit with gamma approx0.5, and the central density rho_0>10^7M_sol pc^-3. The V-I and U-V color profiles are flat, and there is no sign of an inner disk, dust, or any other structure. This total lack of features seems at variance with a nominal stellar collision time of 2 X 10^10 yr, which implies that a significant fraction of the light in the central pixel should come from blue stragglers. InM33, the nucleus has an extremely steep gamma=1.49 power-law profile for 0.05"<r<0.2" that becomes shallower as the HST resolution limit is approached. The profile for r<0.04" has either a gamma approx 0.8 cusp or a small core with r_c ~<0.13 pc. The central density is rho_0 > 2 10^6M_sol pc^-3, and the implied relaxation time is only ~3 X 10^6 yr, indicating that the nucleus is highly relaxed. The accompanying short collision time of 7 X 10^9 yr predicts a central blue straggler component quantitatively consistent with the strong V-I and B-R color gradients seen with HST and from the ground.Comment: 44 pages, 22 figures (7 as separate JPEG images), submitted to The Astronomical Journal. Full postscript image available at http://www.noao.edu/noao/staff/lauer/lauer_paper
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