7,052 research outputs found
Vortex interaction with a leading-edge of finite thickness
Vortex interaction with a thick elliptical leading-edge at zero relative offset produces a pronounced secondary vortes of opposite sense that travels with the same phase speed as the primaty vortex along the lower surface of the edge. The edge thickness (scale) relative to the incident vorticity field has a strong effect on the distortion of the incident primary vortex during the impingement processs. When the thickness is sufficiently small, there is a definite severing of the incident vortex and the portion of the incident vortex that travels along the upper part of the elliptical surface has a considerably larger phase speed than that along the lower surface; this suggests that the integrated loading along the upper surface is more strongly correlated. When the thickness becomes too large, then most, if not all, of the incident vortex passes below the leading-edge. On the other hand, the relative tranverse offset of the edge with respect to the center of the incident vortex has a significant effect on the secondary vortex formation
Free vorticity field-boundary layer conversions: Effect of boundary configuration and scale
Progress was made on further flow visualization of vortex-leading edge interaction, in conjunction with characterization of the unsteady pressure field. The range of scale of an elliptical leading edge, relative to the incident primary vortex, was determined. The scale of the incident vortex was characterized in terms of mean shear layer parameters. An overview of the interaction mechanism for the range of thin to thick leading-edges is given. The interaction mechanism corresponding to the case where the incident vortex is above the leading-edge is given for hydrogen bubble wires well upstream of and at the tip of the leading edge. A sample of the instantaneous pressure distribution for the case where the incident vortex dives beneath the edge is presented. The effect of scale of the incident vortex relative to that of the leading-edge was examined. The circulation and length scale of the incident vortices in the street are being characterized
DMRG evaluation of the Kubo formula -- Conductance of strongly interacting quantum systems
In this paper we present a novel approach combining linear response theory
(Kubo) for the conductance and the Density Matrix Renormalization Group (DMRG).
The system considered is one-dimensional and consists of non-interacting tight
binding leads coupled to an interacting nanostructure via weak links. Electrons
are treated as spinless fermions and two different correlation functions are
used to evaluate the conductance.
Exact diagonalization calculations in the non-interacting limit serve as a
benchmark for our combined Kubo and DMRG approach in this limit. Including both
weak and strong interaction we present DMRG results for an extended
nanostructure consisting of seven sites. For the strongly interacting structure
a simple explanation of the position of the resonances is given in terms of
hard-core particles moving freely on a lattice of reduced size.Comment: 7 pages, 2 figures. Minor typos correcte
Prediction of airfoil stall using Navier-Stokes equations in streamline coordinates
A Navier-Stokes procedure to calculate the flow about an airfoil at incidence was developed. The parabolized equations are solved in the streamline coordinates generated for an arbitrary airfoil shape using conformal mapping. A modified k-epsilon turbulence model is applied in the entire domain, but the eddy viscosity in the laminar region is suppressed artificially to simulate the region correctly. The procedure was applied to airfoils at various angles of attack, and the results are quite satisfactory for both laminar and turbulent flows. It is shown that the present choice of the coordinate system reduces the error due to numerical diffusion, and that the lift is accurately predicted for a wide range of incidence
Diagnostic and therapeutic considerations in idiopathic hypereosinophilia with warm autoimmune hemolytic anemia.
Hypereosinophilic syndrome (HES) encompasses numerous diverse conditions resulting in peripheral hypereosinophilia that cannot be explained by hypersensitivity, infection, or atopy and that is not associated with known systemic diseases with specific organ involvement. HES is often attributed to neoplastic or reactive causes, such as chronic eosinophilic leukemia, although a majority of cases remains unexplained and are considered idiopathic. Here, we review the current diagnosis and management of HES and present a unique case of profound hypereosinophilia associated with warm autoimmune hemolytic anemia requiring intensive management. This case clearly illustrates the limitations of current knowledge with respect to hypereosinophilia syndrome as well as the challenges associated with its classification and management
Multi-community command and control systems in law enforcement: An introductory planning guide
A set of planning guidelines for multi-community command and control systems in law enforcement is presented. Essential characteristics and applications of these systems are outlined. Requirements analysis, system concept design, implementation planning, and performance and cost modeling are described and demonstrated with numerous examples. Program management techniques and joint powers agreements for multicommunity programs are discussed in detail. A description of a typical multi-community computer-aided dispatch system is appended
Exploratory analysis of high-resolution power interruption data reveals spatial and temporal heterogeneity in electric grid reliability
Modern grid monitoring equipment enables utilities to collect detailed
records of power interruptions. These data are aggregated to compute publicly
reported metrics describing high-level characteristics of grid performance. The
current work explores the depth of insights that can be gained from public
data, and the implications of losing visibility into heterogeneity in grid
performance through aggregation. We present an exploratory analysis examining
three years of high-resolution power interruption data collected by archiving
information posted in real-time on the public-facing website of a utility in
the Western United States. We report on the size, frequency and duration of
individual power interruptions, and on spatio-temporal variability in aggregate
reliability metrics. Our results show that metrics of grid performance can vary
spatially and temporally by orders of magnitude, revealing heterogeneity that
is not evidenced in publicly reported metrics. We show that limited access to
granular information presents a substantive barrier to conducting detailed
policy analysis, and discuss how more widespread data access could help to
answer questions that remain unanswered in the literature to date. Given open
questions about whether grid performance is adequate to support societal needs,
we recommend establishing pathways to make high-resolution power interruption
data available to support policy research.Comment: Journal submission (in review), 22 pages, 8 figures, 1 tabl
Mesoscopic Capacitance Oscillations
We examine oscillations as a function of Fermi energy in the capacitance of a
mesoscopic cavity connected via a single quantum channel to a metallic contact
and capacitively coupled to a back gate. The oscillations depend on the
distribution of single levels in the cavity, the interaction strength and the
transmission probability through the quantum channel. We use a Hartree-Fock
approach to exclude self-interaction. The sample specific capacitance
oscillations are in marked contrast to the charge relaxation resistance, which
together with the capacitance defines the RC-time, and which for spin polarized
electrons is quantized at half a resistance quantum. Both the capacitance
oscillations and the quantized charge relaxation resistance are seen in a
strikingly clear manner in a recent experiment.Comment: 9 pages, 2 figure
Arp 65 interaction debris: massive HI displacement and star formation
Context: Pre-merger interactions between galaxies can induce significant
changes in the morphologies and kinematics of the stellar and ISM components.
Large amounts of gas and stars are often found to be disturbed or displaced as
tidal debris. This debris then evolves, sometimes forming stars and
occasionally tidal dwarf galaxies. Here we present results from our HI study of
Arp 65, an interacting pair hosting extended HI tidal debris. Aims: In an
effort to understand the evolution of tidal debris produced by interacting
pairs of galaxies, including in situ star and tidal dwarf galaxy formation, we
are mapping HI in a sample of interacting galaxy pairs. The Arp 65 pair is one
of them. Methods: Our resolved HI 21 cm line survey is being carried out using
the Giant Metrewave Radio Telescope (GMRT). We used our HI survey data as well
as available SDSS optical, Spitzer infra-red and GALEX UV data to study the
evolution of the tidal debris and the correlation of HI with the star-forming
regions within it. Results: In Arp 65 we see a high impact pre-merger
interaction involving a pair of massive galaxies (NGC 90 and NGC 93) that have
a stellar mass ratio of ~ 1:3. The interaction, which probably occurred ~ 1.0
-- 2.5 10 yr ago, appears to have displaced a large fraction of
the HI in NGC 90 (including the highest column density HI) beyond its optical
disk. We also find extended ongoing star formation in the outer disk of NGC 90.
In the major star-forming regions, we find the HI column densities to be ~ 4.7
10 cm or lower. But no signature of star formation was
found in the highest column density HI debris, SE of NGC 90. This indicates
conditions within the highest column density HI debris remain hostile to star
formation and it reaffirms that high HI column densities may be a necessary but
not sufficient criterion for star formation.Comment: Accepted in A&
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