1,155 research outputs found
A Smooth Transition from Powerlessness to Absolute Power
We study the phase transition of the coalitional manipulation problem for
generalized scoring rules. Previously it has been shown that, under some
conditions on the distribution of votes, if the number of manipulators is
, where is the number of voters, then the probability that a
random profile is manipulable by the coalition goes to zero as the number of
voters goes to infinity, whereas if the number of manipulators is
, then the probability that a random profile is manipulable
goes to one. Here we consider the critical window, where a coalition has size
, and we show that as goes from zero to infinity, the limiting
probability that a random profile is manipulable goes from zero to one in a
smooth fashion, i.e., there is a smooth phase transition between the two
regimes. This result analytically validates recent empirical results, and
suggests that deciding the coalitional manipulation problem may be of limited
computational hardness in practice.Comment: 22 pages; v2 contains minor changes and corrections; v3 contains
minor changes after comments of reviewer
Magnetic Monopole in Noncommutative Space-Time and Wu-Yang Singularity-Free Gauge Transformations
We investigate the validity of the Dirac Quantization Condition (DQC) for
magnetic monopoles in noncommutative space-time. We use an approach which is
based on an extension of the method introduced by Wu and Yang. To study the
effects of noncommutativity of space-time, we consider the gauge
transformations of gauge fields and use the corresponding deformed
Maxwell's equations. Using a perturbation expansion in the noncommutativity
parameter , we show that the DQC remains unmodified up to the first
order in the expansion parameter. The result is obtained for a class of
noncommutative source terms, which reduce to the Dirac delta function in the
commutative limit.Comment: 18 pages. Relation to relevant literature clarified in the
conclusions, 6 references adde
Differential freezeout and pion interferometry at RHIC from covariant transport theory
Puzzling discrepancies between recent pion interferometry data on Au+Au
reactions at s^1/2 = 130 and 200 AGeV from RHIC and predictions based on ideal
hydrodynamics are analyzed in terms of covariant parton transport theory. The
discrepancies of out and longitudinal radii are significantly reduced when the
finite opacity of the gluon plasma is taken into account.Comment: 4 pages, 3 EPS figures. Submitted to PR
Vaginal Repair of Cystocele with Anterior Wall Mesh via Transobturator Route: Efficacy and Complications with Up to 3-Year Followup
Study Objective. The objective of this study was to report on the safety and efficacy of cystocele repair with anterior wall mesh placed via a transobturator route (Perigee system, AMS, Minnetonka, MN). Design. Single center retrospective study. Setting. Single center hospital setting and Urogynecology practice in the United States. Patients. 77 women presenting with symptomatic anterior wall prolapse. Intervention. Repair of cystocele with an anterior wall Type I soft-polypropylene mesh placed via a transobturator approach. Concomitant procedures in other compartment were also completed as indicated. Measurements and Main Results. 77 women underwent the Perigee procedure at our institution over a 2-year period. The mesh was attached to the pelvic sidewalls at the level of the bladder neck and near the ischial spine apically with needles passed through the groins and obturator space. Mean follow-up was 18.2 months (range 3–36 months). Objective cure rate was 93%. Subjectively only two patients have had recurrent symptoms of prolapse, and only 1 of these has required repeat surgery for cystocele. Mesh exposure vaginally occurred in 5 patients (6.5%); however all were treated with estrogen and/or local excision of exposed mesh and had no further sequelae. There were no incidences of chronic pain, infection, or abscess, and no patient required complete mesh removal for infection, pain, or extrusion.
Conclusion. In select patients with anterior wall prolapse, repair with mesh augmentation via the transobturator route is a safe and effective procedure with up to 3 years of follow-up
Development of an Experimental Data Base to Validate Compressor-Face Boundary Conditions Used in Unsteady Inlet Flow Computations
The ability to predict the dynamics of integrated inlet/compressor systems is an important part of designing high-speed propulsion systems. The boundaries of the performance envelope are often defined by undesirable transient phenomena in the inlet (unstart, buzz, etc.) in response to disturbances originated either in the engine or in the atmosphere. Stability margins used to compensate for the inability to accurately predict such processes lead to weight and performance penalties, which translate into a reduction in vehicle range. The prediction of transients in an inlet/compressor system requires either the coupling of two complex, unsteady codes (one for the inlet and one for the engine) or else a reliable characterization of the inlet/compressor interface, by specifying a boundary condition. In the context of engineering development programs, only the second option is viable economically. Computations of unsteady inlet flows invariably rely on simple compressor-face boundary conditions (CFBC's). Currently, customary conditions include choked flow, constant static pressure, constant axial velocity, constant Mach number or constant mass flow per unit area. These conditions are straightforward extensions of practices that are valid for and work well with steady inlet flows. Unfortunately, it is not at all likely that any flow property would stay constant during a complex system transient. At the start of this effort, no experimental observation existed that could be used to formulate of verify any of the CFBC'S. This lack of hard information represented a risk for a development program that has been recognized to be unacceptably large. The goal of the present effort was to generate such data. Disturbances reaching the compressor face in flight may have complex spatial structures and temporal histories. Small amplitude disturbances may be decomposed into acoustic, vorticity and entropy contributions that are uncoupled if the undisturbed flow is uniform. This study is focused on the response of an inlet/compressor system to acoustic disturbances. From the viewpoint of inlet computations, acoustic disturbances are clearly the most important, since they are the only ones capable of moving upstream. Convective and entropy disturbances may also produce upstream-moving acoustic waves, but such processes are outside the scope of the present study
Universal Flow-Driven Conical Emission in Ultrarelativistic Heavy-Ion Collisions
The double-peak structure observed in soft-hard hadron correlations is
commonly interpreted as a signature for a Mach cone generated by a supersonic
jet interacting with the hot and dense medium created in ultrarelativistic
heavy-ion collisions. We show that it can also arise due to averaging over many
jet events in a transversally expanding background. We find that the
jet-induced away-side yield does not depend on the details of the
energy-momentum deposition in the plasma, the jet velocity, or the system size.
Our claim can be experimentally tested by comparing soft-hard correlations
induced by heavy-flavor jets with those generated by light-flavor jets.Comment: 4 pages, 3 figure
Near Zone Navier-Stokes Analysis of Heavy Quark Jet Quenching in an =4 SYM Plasma
The near zone energy-momentum tensor of a supersonic heavy quark jet moving
through a strongly-coupled SYM plasma is analyzed in terms of
first-order Navier-Stokes hydrodynamics. It is shown that the hydrodynamical
description of the near quark region worsens with increasing quark velocities.
For realistic quark velocities, , the non-hydrodynamical region is
located at a narrow band surrounding the quark with a width of approximately
in the direction parallel to the quark's motion and with a length of
roughly in the perpendicular direction. Our results can be
interpreted as an indication of the presence of coherent Yang-Mills fields
where deviation from hydrodynamics is at its maximum. In the region where
hydrodynamics does provide a good description of the system's dynamics, the
flow velocity is so small that all the nonlinear terms can be dropped. Our
results, which are compatible with the thermalization timescales extracted from
elliptic flow measurements, suggest that if AdS/CFT provides a good description
of the RHIC system, the bulk of the quenched jet energy has more than enough
time to locally thermalize and become encoded in the collective flow. The
resulting flow pattern close to the quark, however, is shown to be considerably
different than the superposition of Mach cones and diffusion wakes observed at
large distances.Comment: new revised version, 11 figures, as published in PR
Convex Constraint Decomposition of Circular Dichroism Curves of Proteins
A new algorithm, called convex analysis, has been developed
to deduce the chiral contribution of the common secondary structures
directly from experimental circular dichroism (CD) curves
of a large number of proteins. The analysis is based on CD data
reported by Yang et aU Test runs were performed on sets of artificial
protein spectra created by the Monte Carlo technique using
poly-u-Iysine based component spectra. Application of the decomposition algorithm for the created sets of spectra resulted in
component spectra [B (2, i)] and weights [C (i, k)] with excellent
Pearson correlation coefficients (r).2 The algori thm, independent
of X-ray data, revealed that the CD spectrum of a given protein
is composed of at least four independent sources of chirality. Three
of the computed component curves show remarkable resemblance
to the CD spectra of known protein secondary structures. This
approach yields a significant improvement compared to the eigenvector analysis of Hennessey and Johnson." The new method is a useful tool not only in analyzing CD spectra but also in treating
other decomposition problems where an additivity constraint is
valid
Editorial: the role of heat shock proteins in neuroprotection
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