Enhanced accretion rates of stars on Super-massive Black Holes by star-disk interactions in galactic nuclei

We investigate the dynamical interaction of a central star cluster surrounding a super-massive black hole and a central accretion disk. The dissipative force acting on stars in the disk leads to an enhanced mass flow towards the super-massive black hole and to an asymmetry in the phase space distribution due to the rotating accretion disk. The accretion disk is considered as a stationary Keplerian rotating disk, which is vertically extended in order to employ a fully self-consistent treatment of stellar dynamics including the dissipative force originating from star-gas ram pressure effects. The stellar system is treated with a direct high-accuracy N-body integration code. A star-by-star representation, desirable in N-body simulations, cannot be extended to real particle numbers yet. Hence, we carefully discuss the scaling behavior of our model with regard to particle number and tidal accretion radius. The main idea is to find a family of models for which the ratio of two-body relaxation time and dissipation time (for kinetic energy of stellar orbits) is constant, which then allows us to extrapolate our results to real parameters of galactic nuclei. Our model is derived from basic physical principles and as such it provides insight into the role of physical processes in galactic nuclei, but it should be regarded as a first step towards more realistic and more comprehensive simulations. Nevertheless, the following conclusions appear to be robust: the star accretion rate onto the accretion disk and subsequently onto the super-massive black hole is enhanced by a significant factor compared to purely stellar dynamical systems neglecting the disk. This process leads to enhanced fueling of central disks in active galactic nuclei and to an enhanced rate of tidal stellar disruptions. [Abridged]Comment: 17 pages, 6 figures (with 9 panels), 2 tables, accepted for publication in Ap

Strengthening the Case for Asteroidal Accrection: Evidence for Subtle and Diverse Disks at White Dwarfs

Spitzer Space Telescope IRAC 3-8 micron and AKARI IRC 2-4 micron photometry are reported for ten white dwarfs with photospheric heavy elements; nine relatively cool stars with photospheric calcium, and one hotter star with a peculiar high carbon abundance. A substantial infrared excess is detected at HE 2221-1630, while modest excess emissions are identified at HE 0106-3253 and HE 0307+0746, implying these latter two stars have relatively narrow (Delta r < 0.1 Rsol) rings of circumstellar dust. A likely 7.9 micron excess is found at PG 1225-079 and may represent, together with G166-58, a sub-class of dust ring with a large inner hole. The existence of attenuated disks at white dwarfs substantiates the connection between their photospheric heavy elements and the accretion of disrupted minor planets, indicating many polluted white dwarfs may harbor orbiting dust, even those lacking an obvious infrared excess.Comment: 13 pages, emulateapj, accepted to Ap

Detonation synthesis of ZrO2 by means of an ammonium nitrate-based explosive emulsion

A zirconium (IV) oxide powder was successfully synthesized from the detonation of an explosive emulsion previously mixed with zirconium sulfate tetrahydrate salt (Zr(SO4)2·4H2O) as a ceramic precursor. After detonation of the energetic mixture in a detonation tank, the as-synthesized ceramic material was purified and characterized by X-ray diffraction, transmission and scanning electron microscopy techniques, nitrogen physisorption and dynamic light scattering. The ceramic powder is made of crystalline nanosized particles exhibiting a homogeneous sphere-like morphology. An attempt to explain the oxide ceramic synthetic mechanism is discussed. The detonation synthetic route implementing high temperatures and high pressures in a short time may be seen as an encouraging method for large-scale production of nanopowder

Oscillatory activity in the infant brain and the representation of small numbers

Gamma-band oscillatory activity (GBA) is an established neural signature of sustained occluded object representation in infants and adults. However, it is not yet known whether the magnitude of GBA in the infant brain reflects the quantity of occluded items held in memory. To examine this, we compared GBA of 6–8 month-old infants during occlusion periods after the representation of two objects vs. that of one object. We found that maintaining a representation of two objects during occlusion resulted in significantly greater GBA relative to maintaining a single object. Further, this enhancement was located in the right occipital region, which is consistent with previous object representation research in adults and infants. We conclude that enhanced GBA reflects neural processes underlying infants’ representation of small numbers

Musculoskeletal injuries among operating room nurses: results from a multicenter survey in Rome, Italy

Aim: Chronic disorders of the musculoskeletal system, particularly low back pain (LBP), are increasing and represent a social and economic problem of growing importance, especially if correlated with working conditions. Health care workers are at higher risk of developing LBP during work shifts in the hospital. The aim of this study was to assess the prevalence of LBP among operating room nurses and to investigate the risk factors for musculoskeletal injuries in the operating room. Methods: We carried out a cross-sectional study that included operating room nurses from nine hospitals. Information on sociodemographic characteristics, lifestyle habits, working activity and psychological attitude of nurses was collected using an anonymous self-administered structured questionnaire. We evaluated the association of frequency, localization and intensity of LBP (FLI) with qualitative variables, making use of univariate analysis, chi-square test and Fisher's exact test. Multiple logistic regression analysis was performed to identify the variables that affected the FLI. The covariates included in the model were the variables that had a p 35 years vs. age <35 (OR = 2.68; 95% CI = 1.17–6.18) and diurnal work shift vs. diurnal/ nocturnal (OR = 4.00; 95% CI = 1.72–9.0) represent risk factors associated with FLI, while physical activity is a protective factor (OR = 0.47; 95% CI = 0.20–1.08). Conclusion: The data suggest that it is important to promote new programs of prevention based on professional training and physical activity among nurses and to improve the organization of work shifts in the hospital

Variability and Action Mechanism of a Family of Anticomplement Proteins in Ixodes ricinus

Background: Ticks are blood feeding arachnids that characteristically take a long blood meal. They must therefore counteract host defence mechanisms such as hemostasis, inflammation and the immune response. This is achieved by expressing batteries of salivary proteins coded by multigene families. Methodology/Principal Findings: We report the in-depth analysis of a tick multigene family and describe five new anticomplement proteins in ixodes ricinus. Compared to previously described Ixodes anticomplement proteins, these segregated into a new phylogenetic group or subfamily. These proteins have a novel action mechanism as they specifically bind to properdin, leading to the inhibition of C3 convertase and the alternative complement pathway. An excess of non-synonymous over synonymous changes indicated that coding sequences had undergone diversifying selection. Diversification was not associated with structural, biochemical o, functional diversity, adaptation to host species or stage specificity but rather to differences in antigenicity. Conclusion/Significance: Anticomplement proteins from I. ricinus are the first inhibitors that specifically target a positive regulator of complement, properdin. They may provide new tools for the investigation of role of properdin in physiological and pathophysiological mechanisms. They may also be useful in disorders affecting the alternative complement pathway, Looking for and detecting the different selection pressures involved will help in understanding the evolution of multigene families and hematophagy in arthropods. © 2008 Couveur et al.Journal ArticleResearch Support, Non-U.S. Gov'tSCOPUS: ar.jinfo:eu-repo/semantics/publishe

Différences entre des types de prédications dans une tâche de mémorisation de phrases

Spitzer Catherine, Brouillet Denis. Différences entre des types de prédications dans une tâche de mémorisation de phrases. In: Bulletin de psychologie, tome 52 n°442, 1999. Travaux et recherches. pp. 433-448