3,564 research outputs found
Nut-charged black holes in matter-coupled N=2, D=4 gauged supergravity
Using the results of arXiv:0804.0009, where all timelike supersymmetric
backgrounds of N=2, D=4 matter-coupled supergravity with Fayet-Iliopoulos
gauging were classified, we construct genuine nut-charged BPS black holes in
AdS_4 with nonconstant moduli. The calculations are exemplified for the
SU(1,1)/U(1) model with prepotential F=-iX^0X^1. The resulting supersymmetric
black holes have a hyperbolic horizon and carry two electric, two magnetic and
one nut charge, which are however not all independent, but are given in terms
of three free parameters. We find that turning on a nut charge lifts the flat
directions in the effective black hole potential, such that the horizon values
of the scalars are completely fixed by the charges. We also oxidize the
solutions to eleven dimensions, and find that they generalize the geometry
found in hep-th/0105250 corresponding to membranes wrapping holomorphic curves
in a Calabi-Yau five-fold. Finally, a class of nut-charged Nernst branes is
constructed as well, but these have curvature singularities at the horizon.Comment: 21 pages, no figures, uses JHEP3.cl
Overspinning a Kerr black hole: the effect of self-force
We study the scenario in which a massive particle is thrown into a rapidly
rotating Kerr black hole in an attempt to spin it up beyond its extremal limit,
challenging weak cosmic censorship. We work in black-hole perturbation theory,
and focus on non-spinning, uncharged particles sent in on equatorial orbits. We
first identify the complete parameter-space region in which overspinning occurs
when back-reaction effects from the particle's self-gravity are ignored. We
find, in particular, that overspinning can be achieved only with particles sent
in from infinity. Gravitational self-force effects may prevent overspinning by
radiating away a sufficient amount of the particle's angular momentum
("dissipative effect"), and/or by increasing the effective centrifugal
repulsion, so that particles with suitable parameters never get captured
("conservative effect"). We analyze the full effect of the self-force, thereby
completing previous studies by Jacobson and Sotiriou (who neglected the
self-force) and by Barausse, Cardoso and Khanna (who considered the dissipative
effect on a subset of orbits). Our main result is an inequality, involving
certain self-force quantities, which describes a necessary and sufficient
condition for the overspinning scenario to be overruled. This "censorship"
condition is formulated on a certain one-parameter family of geodesics in an
extremal Kerr geometry. We find that the censorship condition is insensitive to
the dissipative effect (within the first-order self-force approximation used
here), except for a subset of perfectly fine-tuned orbits, for which a separate
censorship condition is derived. We do not obtain here the self-force input
needed to evaluate either of our two conditions, but discuss the prospects for
producing the necessary data using state-of-the-art numerical codes.Comment: 25 pages, 4 figure
Why Would the Rise of Social Media Increase the Influence of Traditional Media on Collective Judgments?
3reservedrestrictedRavasi, Davide; Etter, Michael; Colleoni, ElanorRavasi, Davide; Etter, Michael; Colleoni, Elano
Measuring Skill level integrating Administratrive Dataset and National Collective Agreement Archive
Given the group job classification and collective agreement identification code, we extracted from the national bargaining archive the skill level definition and we created a skill grades classification for the workers. We added this information to Workers History Italian Panel -Whip-, and we created a new variable which allow us to identify whether a worker is skilled or unskilled. The new skill level variable increase the possibility for a better comprehension of labour market issues as well as for new studies in the field of job risk evaluation. The sections are organized as follow: 1. creation of skill level classification from national collective agreements archive; 2. short explanation of Whip archives; 3. adding informations to Whip archives; 4. checking the consistency and coverage of the skill level variable in Whip; 5. a first interpretation of the resulting skill distribution.
Milanâs pollution charge : sustainable transport and the politics of evidence
Non peer reviewedPostprin
Modeling sea level changes and geodetic variations by glacial isostasy: the improved SELEN code
We describe the basic features of SELEN, an open source Fortran 90 program
for the numerical solution of the so-called "Sea Level Equation" for a
spherical, layered, non-rotating Earth with Maxwell viscoelastic rheology. The
Sea Level Equation was introduced in the 70s to model the sea level variations
in response to the melting of late-Pleistocene ice-sheets, but it can be also
employed for predictions of geodetic quantities such as vertical and horizontal
surface displacements and gravity variations on a global and a regional scale.
SELEN (acronym of SEa Level EquatioN solver) is particularly oriented to
scientists at their first approach to the glacial isostatic adjustment problem
and, according to our experience, it can be successfully used in teaching. The
current release (2.9) considerably improves the previous versions of the code
in terms of computational efficiency, portability and versatility. In this
paper we describe the essentials of the theory behind the Sea Level Equation,
the purposes of SELEN and its implementation, and we provide practical
guidelines for the use of the program. Various examples showing how SELEN can
be configured to solve geodynamical problems involving past and present sea
level changes and current geodetic variations are also presented and discussed
Self-force as a cosmic censor in the Kerr overspinning problem
It is known that a near-extremal Kerr black hole can be spun up beyond its
extremal limit by capturing a test particle. Here we show that overspinning is
always averted once back-reaction from the particle's own gravity is properly
taken into account. We focus on nonspinning, uncharged, massive particles
thrown in along the equatorial plane, and work in the first-order self-force
approximation (i.e., we include all relevant corrections to the particle's
acceleration through linear order in the ratio, assumed small, between the
particle's energy and the black hole's mass). Our calculation is a numerical
implementation of a recent analysis by two of us [Phys.\ Rev.\ D {\bf 91},
104024 (2015)], in which a necessary and sufficient "censorship" condition was
formulated for the capture scenario, involving certain self-force quantities
calculated on the one-parameter family of unstable circular geodesics in the
extremal limit. The self-force information accounts both for radiative losses
and for the finite-mass correction to the critical value of the impact
parameter. Here we obtain the required self-force data, and present strong
evidence to suggest that captured particles never drive the black hole beyond
its extremal limit. We show, however, that, within our first-order self-force
approximation, it is possible to reach the extremal limit with a suitable
choice of initial orbital parameters. To rule out such a possibility would
require (currently unavailable) information about higher-order self-force
corrections.Comment: 13 pages, 3 figure
Murine models of human neuropathic pain
AbstractNeuropathic pain refers to pain that originates from pathology of the nervous system. Diabetes, infection (herpes zoster), nerve compression, nerve trauma, and autoimmune diseases are examples of diseases that may cause neuropathic pain. Unfortunately no satisfactory treatment is yet available for this type of pain. This consideration has led to an explosion of interest for the underlying mechanisms, accompanied by a growing number of animal models. In recent years, most of the neuropathic pain models initially developed in the rat have been translated to mice in order to exploit the resource represented by genetically modified mice. Obviously the most useful animal models of pain would be ones in which the etiology of the pain would be endogenous and not induced by the experimenters: together with the classic models based on peripheral nerve ligation, in the last years other techniques are being developed that mimic more closely clinical pain syndromes, often by attempting to induce the disease associated to neuropathic pain. Although several variables must be taken into account when using animal models for mimicking clinical neuropathic pain, the huge number of models that are now reproducible and well characterized should help to reach important goals in the comprehension of mechanisms and to discover novel therapeutic target for this disease
- âŠ