1,337 research outputs found
Critical escape velocity of black holes from branes
In recent work we have shown that a black hole stacked on a brane escapes
once it acquires a recoil velocity. This result was obtained in the {\it
probe-brane} approximation, {\it i.e.}, when the tension of the brane is
negligibly small. Therefore, it is not clear whether the effect of the brane
tension may prevent the black hole from escaping for small recoil velocities.
The question is whether a critical escape velocity exists. Here, we analyze
this problem by studying the interaction between a Dirac-Nambu-Goto brane and a
black hole assuming adiabatic (quasi-static) evolution. By describing the brane
in a fixed black hole spacetime, which restricts our conclusions to lowest
order effects in the tension, we find that the critical escape velocity does
not exist for co-dimension one branes, while it does for higher co-dimension
branes.Comment: 10 pages, revte
Full dimensional (15D) quantum-dynamical simulation of the protonated water-dimer I: Hamiltonian setup and analysis of the ground vibrational state
Quantum-dynamical full-dimensional (15D) calculations are reported for the
protonated water dimer (H5O2+) using the multiconfiguration time-dependent
Hartree (MCTDH) method. The dynamics is described by curvilinear coordinates.
The expression of the kinetic energy operator in this set of coordinates is
given and its derivation, following the polyspherical method, is discussed. The
PES employed is that of Huang et al. [JCP, 122, 044308, (2005)]. A scheme for
the representation of the potential energy surface (PES) is discussed which is
based on a high dimensional model representation scheme (cut-HDMR), but
modified to take advantage of the mode-combination representation of the
vibrational wavefunction used in MCTDH. The convergence of the PES expansion
used is quantified and evidence is provided that it correctly reproduces the
reference PES at least for the range of energies of interest. The reported zero
point energy of the system is converged with respect to the MCTDH expansion and
in excellent agreement (16.7 cm-1 below) with the diffusion Monte Carlo result
on the PES of Huang et al. The highly fluxional nature of the cation is
accounted for through use of curvilinear coordinates. The system is found to
interconvert between equivalent minima through wagging and internal rotation
motions already when in the ground vibrational-state, i.e., T=0. It is shown
that a converged quantum-dynamical description of such a flexible, multi-minima
system is possible.Comment: 46 pages, 5 figures, submitted to J. Chem. Phy
Influence of fault geometries and mechanical anisotropies on the growth and inversion of hanging-wall synclinal basins: insights from sandbox models and natural examples
Salt is mechanically weaker than other sedimentary rocks in rift basins. It commonly acts as a strain localizer, and decouples supra- and sub-salt deformation. In the rift basins discussed in this paper, sub-salt faults commonly form wide and deep ramp synclines controlled by the thickness and strength of the overlying salt section, as well as by the shapes of the extensional faults, and the magnitudes and slip rates along the faults. Upon inversion of these rift basins, the inherited extensional architectures, and particularly the continuity of the salt section, significantly controls the later contractional deformation. This paper utilizes scaled sandbox models to analyse the interplay between sub-salt structures and supra-salt units during both extension and inversion. Series 1 experiments involved baseline models run using isotropic sand packs for simple and ramp-flat listric faults, as well as for simple planar and kinked planar faults. Series 2 experiments involved the same fault geometries but also included a pre-extension polymer layer to simulate salt in the stratigraphy. In these experiments, the polymer layer decoupled the extensional and contractional strains, and inhibited the upwards propagation of sub-polymer faults. In all Series 2 experiments, the extension produced a synclinal hanging-wall basin above the polymer layer as a result of polymer migration during the deformation. During inversion, the supra-polymer synclinal basin was uplifted, folded and detached above the polymer layer. Changes in thickness of the polymer layer during the inversion produced primary welds and these permitted the sub-polymer deformation to propagate upwards into the supra-salt layers. The experimental results are compared with examples from the Parentis Basin (Bay of Biscay), the Broad Fourteens Basin (southern North Sea), the Feda Graben (central North Sea) and the Cameros Basin (Iberian Range, Spain)
Characteristic energies, transition temperatures, and switching effects in clean SNS graphene nanostructures
We study proximity effects in clean nanoscale superconductor-normal
metal-superconductor (SNS) graphene heterostructures using a
self-consistent numerical solution to the continuum Dirac Bogoliubov-de Gennes
(DBdG) equations. We obtain results for the pair amplitude and the local
density of states (DOS), as a function of doping and of the geometrical
parameters determining the width of the structures. The superconducting
correlations are found to penetrate the normal graphene layers even when there
is extreme mismatch in the normal and superconducting doping levels, where
specular Andreev reflection dominates. The local DOS exhibits peculiar
features, which we discuss, arising from the Dirac cone dispersion relation and
from the interplay between the superconducting and Thouless energy scales. The
corresponding characteristic energies emerge in the form of resonant peaks in
the local DOS, that depend strongly on the doping level, as does the energy
gap, which declines sharply as the relative difference in doping between the S
and N regions is reduced. We also linearize the DBdG equations and develop an
essentially analytical method that determines the critical temperature of
an \sns nanostructure self-consistently. We find that for S regions that occupy
a fraction of the coherence length, can undergo substantial variations as
a function of the relative doping. At finite temperatures and by manipulating
the doping levels, the self consistent pair amplitudes reveal dramatic
transitions between a superconducting and resistive normal state of the
structure. Such behavior suggests the possibility of using the proposed system
as a carbon-based superconducting switch, turning superconductivity on or off
by tuning the relative doping levels.Comment: 13 pages, figures include
Distributions of Conductance and Shot Noise and Associated Phase Transitions
For a chaotic cavity with two indentical leads each supporting N channels, we
compute analytically, for large N, the full distribution of the conductance and
the shot noise power and show that in both cases there is a central Gaussian
region flanked on both sides by non-Gaussian tails. The distribution is weakly
singular at the junction of Gaussian and non-Gaussian regimes, a direct
consequence of two phase transitions in an associated Coulomb gas problem.Comment: 5 pages, 3 figures include
Separable Measurement Estimation of Density Matrices and its Fidelity Gap with Collective Protocols
We show that there exists a gap between the performance of separable and
collective measurements in qubit mixed-state estimation that persists in the
large sample limit. We characterize such gap in terms of the corresponding
bounds on the mean fidelity. We present an adaptive protocol that attains the
separable-measurement bound. This (optimal separable) protocol uses von Neumann
measurements and can be easily implemented with current technology.Comment: version published in PR
Adolescent Bullying Victimization and Life Satisfaction: Can Family and School Adult Support Figures Mitigate this Effect?
Indexación: Scopus.Existen pocos estudios que vinculen la victimización sufrida por bullying con la satisfacción con la vida. Por ello, este estudio tiene como objetivo evaluar el efecto mitigador del apoyo de figuras adultas (padres, madres y adultos de la escuela) sobre la relación de la victimización por bullying y la satisfacción con la vida en adolescentes. Con este fin, se evalúa una muestra de 5774 adolescentes provenientes de 71 escuelas públicas ubicadas en barrios violentos de Lima, Perú. Para ello, se realiza un análisis de moderación para evaluar el rol de las figuras adultas de apoyo en la casa y la escuela. Los resultados muestran que el apoyo de los adultos en casa mitiga la relación negativa entre la victimización y la satisfacción con la vida. Este efecto es mayor en el caso del apoyo adulto en la casa. El apoyo brindado por los adultos, tanto en la casa como en la escuela, favorece que los adolescentes que padecen de una alta prevalencia de victimización puedan mantener niveles superiores de satisfacción con la vida respecto a los adolescentes que perciben bajo apoyo de los adultos. Finalmente, se discute la necesidad de que adultos en la escuela y padres realicen acciones coordinadas para prevenir y disminuir la prevalencia de este tipo de violencia entre compañeros/as.There are still few studies relating bullying victimization and life satisfaction. This study aimed to assess the mitigating effect of adult figures support (at school and home) on the relationship between bullying victimization and life satisfaction experienced by adolescents. To this end, a sample of 5774 adolescents from 71 public schools located throughout the violent neighborhoods of Lima (Perú) was evaluated. A moderation analysis was performed to assess the moderating role of support adult figures from home and school. The results show that the support of adults at home and school mitigate the negative effect of bullying victimization on life satisfaction, and this effect is larger in the case of adult home support. Adult support at home and school help students with high prevalence of bullying victimization maintain high levels of life satisfaction compared to adolescents with low support from adults. Finally, the need for adults at school and home to take joint measures to prevent and reduce the prevalence of this type of peer violence is discussed.https://www.sciencedirect.com/science/article/pii/S1136103417302332?via%3Dihu
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