103 research outputs found
The operational phase space of the edge plasma and its sensitivity to magnetic topology in Alcator C-Mod
Edge Radial Electric Field Structure and its Connection to H-Mode Confinement in Alcator C-Mod
Validating the FLASH Code: Vortex-Dominated Flows
As a component of the Flash Center's validation program, we compare FLASH
simulation results with experimental results from Los Alamos National
Laboratory. The flow of interest involves the lateral interaction between a
planar Ma=1.2 shock wave with a cylinder of gaseous sulfur hexafluoride (SF_6)
in air, and in particular the development of primary and secondary
instabilities after the passage of the shock. While the overall evolution of
the flow is comparable in the simulations and experiments, small-scale features
are difficult to match. We focus on the sensitivity of numerical results to
simulation parameters.Comment: 10 pages, 5 figures, presented at the 5th International Conference on
High Energy Laboratory Astrophysics, Tucson, AZ, March 10-13, 200
Transport-driven scrape-off layer flows and the x-point dependence of the L-H power threshold in Alcator C-Mod
Endemic fungal infections in solid organ and hematopoietic cell transplant recipients enrolled in the TransplantâAssociated Infection Surveillance Network ( TRANSNET )
Background Invasive fungal infections are a major cause of morbidity and mortality among solid organ transplant ( SOT ) and hematopoietic cell transplant ( HCT ) recipients, but few data have been reported on the epidemiology of endemic fungal infections in these populations. Methods Fifteen institutions belonging to the TransplantâAssociated Infection Surveillance Network prospectively enrolled SOT and HCT recipients with histoplasmosis, blastomycosis, or coccidioidomycosis occurring between March 2001 and March 2006. Results A total of 70 patients (64 SOT recipients and 6 HCT recipients) had infection with an endemic mycosis, including 52 with histoplasmosis, 9 with blastomycosis, and 9 with coccidioidomycosis. The 12âmonth cumulative incidence rate among SOT recipients for histoplasmosis was 0.102%. Occurrence of infection was bimodal; 28 (40%) infections occurred in the first 6Â months post transplantation, and 24 (34%) occurred between 2 and 11Â years post transplantation. Three patients were documented to have acquired infection from the donor organ. Seven SOT recipients with histoplasmosis and 3 with coccidioidomycosis died (16%); no HCT recipient died. Conclusions This 5âyear multicenter prospective surveillance study found that endemic mycoses occur uncommonly in SOT and HCT recipients, and that the period at risk extends for years after transplantation.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/106980/1/tid12186.pd
On Image Contours of Projective Shapes
International audienceThis paper revisits classical properties of the outlines of solid shapes bounded by smooth surfaces, and shows that they can be established in a purely projective setting, without appealing to Euclidean measurements such as normals or curvatures. In particular, we give new synthetic proofs of Koenderink's famous theorem on convexities and concavities of the image contour, and of the fact that the rim turns in the same direction as the viewpoint in the tangent plane at a convex point, and in the opposite direction at a hyperbolic point. This suggests that projective geometry should not be viewed merely as an analytical device for linearizing calculations (its main role in structure from motion), but as the proper framework for studying the relation between solid shape and its perspective projections. Unlike previous work in this area, the proposed approach does not require an oriented setting, nor does it rely on any choice of coordinate system or analytical considerations
Non-neoclassical up/down asymmetry of impurity emission on Alcator C-Mod
We demonstrate that existing theories are insufficient to explain up/down asymmetries of argon x-ray emission in Alcator C-Mod ohmic plasmas. Instead of the poloidal variation, ñ[subscript z]/â©n[subscript z]âȘ, being of order the inverse aspect ratio, Ï”, and scaling linearly with B[subscript t][superscript _ over n][subscript e]/I[2 over p], it is observed over 0.8 < r/a < 1.0 to be of order unity and exhibits a threshold behaviour between 3.5 <B[subscript t][superscript _ over n][subscript e]/I[subscript p] < 4.0 (T10[superscript 20] m[superscript â3] MA[superscript â1]). The transition from a poloidally symmetric to asymmetric impurity distribution is shown to occur at densities just below those that trigger a reversal of the core toroidal rotation direction, thought to be linked to the transition between the linear and saturated ohmic confinement regimes. A possible drive is discussed by which anomalous radial transport might sustain the impurity density asymmetry as the ratio of the perpendicular to parallel equilibration times, Ï[subscript â„,z]/Ï[subscript â„,z], approaches unity. This explanation requires a strong up/down asymmetry in radial flux which, while not observable on C-Mod, has been measured in TEXT and Tore Supra ohmic plasmas.United States. Dept. of Energy (Contract DE-FC02-99ER54512)United States. Dept. of Energy (Fusion Research Postdoctoral Research Program
Star Formation and Dynamics in the Galactic Centre
The centre of our Galaxy is one of the most studied and yet enigmatic places
in the Universe. At a distance of about 8 kpc from our Sun, the Galactic centre
(GC) is the ideal environment to study the extreme processes that take place in
the vicinity of a supermassive black hole (SMBH). Despite the hostile
environment, several tens of early-type stars populate the central parsec of
our Galaxy. A fraction of them lie in a thin ring with mild eccentricity and
inner radius ~0.04 pc, while the S-stars, i.e. the ~30 stars closest to the
SMBH (<0.04 pc), have randomly oriented and highly eccentric orbits. The
formation of such early-type stars has been a puzzle for a long time: molecular
clouds should be tidally disrupted by the SMBH before they can fragment into
stars. We review the main scenarios proposed to explain the formation and the
dynamical evolution of the early-type stars in the GC. In particular, we
discuss the most popular in situ scenarios (accretion disc fragmentation and
molecular cloud disruption) and migration scenarios (star cluster inspiral and
Hills mechanism). We focus on the most pressing challenges that must be faced
to shed light on the process of star formation in the vicinity of a SMBH.Comment: 68 pages, 35 figures; invited review chapter, to be published in
expanded form in Haardt, F., Gorini, V., Moschella, U. and Treves, A.,
'Astrophysical Black Holes'. Lecture Notes in Physics. Springer 201
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