15,407 research outputs found
Membrane paradigm and entropy of black holes in the Euclidean action approach
The membrane paradigm approach to black holes fixes in the vicinity of the
event horizon a fictitious surface, the stretched horizon, so that the
spacetime outside remains unchanged and the spacetime inside is vacuum. Using
this powerful method, several black hole properties have been found and
settled, such as the horizon's viscosity, electrical conductivity, resistivity,
as well as other properties. On the other hand the Euclidean action approach to
black hole spacetimes has been very fruitful in understanding black hole
entropy. Combining both the Euclidean action and membrane paradigm approaches a
direct derivation of the black hole entropy is given. In the derivation it is
considered that the only fields present are the gravitational and matter
fields, with no electric field.Comment: 13 page
Magnetic Anisotropy in Quantum Hall Ferromagnets
We show that the sign of magnetic anisotropy energy in quantum Hall
ferromagnets is determined by a competition between electrostatic and exchange
energies. Easy-axis ferromagnets tend to occur when Landau levels whose states
have similar spatial profiles cross. We report measurements of integer QHE
evolution with magnetic-field tilt. Reentrant behavior observed for the QHE at high tilt angles is attributed to easy-axis anisotropy. This
interpretation is supported by a detailed calculation of the magnetic
anisotropy energy.Comment: 12 pages, 3 figures, submitted to Phys. Rev. Let
Hartree-Fock Theory of Hole Stripe States
We report on Hartree-Fock theory results for stripe states of two-dimensional
hole systems in quantum wells grown on GaAs (311)A substrates. We find that the
stripe orientation energy has a rich dependence on hole density, and on
in-plane field magnitude and orientation. Unlike the electron case, the
orientation energy is non-zero for zero in-plane field, and the ground state
orientation can be either parallel or perpendicular to a finite in-plane field.
We predict an orientation reversal transition in in-plane fields applied along
the direction.Comment: 5 pages including 4 figure
Tunneling gap of laterally separated quantum Hall states
We use a method of matched asymptotics to determine the energy gap of two
counter-propagating, strongly interacting, quantum Hall edge states. The
microscopic edge state dispersion and Coulomb interactions are used to
precisely constrain the short-distance behavior of an integrable field theory,
which then determines the low energy spectrum. We discuss the relationship of
our results to the tunneling measurements of Kang et al., Nature 403, 59
(2000).Comment: 4 pages, 1 figur
Collective excitations in double-layer quantum Hall systems
We study the collective excitation spectra of double-layer quantum-Hall
systems using the single mode approximation. The double-layer in-phase density
excitations are similar to those of a single-layer system. For out-of-phase
density excitations, however, both inter-Landau-level and intra-Landau-level
double-layer modes have finite dipole oscillator strengths. The oscillator
strengths at long wavelengths for the latter transitions are shifted upward by
interactions by identical amounts proportional to the interlayer Coulomb
coupling. The intra-Landau-level out-of-phase mode has a gap when the ground
state is incompressible except in the presence of spontaneous inter-layer
coherence. We compare our results with predictions based on the
Chern-Simons-Landau-Ginzburg theory for double-layer quantum Hall systems.Comment: RevTeX, 21 page
Electronic properties and dopant pairing behavior of manganese in boron-doped silicon
Boron-doped silicon wafers implanted with low doses of manganese have been analyzed by means of deep-level transient spectroscopy(DLTS), injection-dependent lifetime spectroscopy, and temperature-dependent lifetime spectroscopy. While DLTSmeasurements allow the defect levels and majority carrier capture cross sections to be determined, the lifetime spectroscopy techniques allow analysis of the dominant recombination levels and the corresponding ratios of the capture cross sections. Interstitialmanganese and manganese-boron pairs were found to coexist, and their defect parameters have been investigated.One of the authors T.R. gratefully acknowledges a
scholarship of the German Federal Environmental Foundation
Deutsche Bundesstiftung Umwelt. Another D.M. is
supported by an Australian Research Council QEII Fellowship
Recommended from our members
Exploration Strategies for Discovery of Interactivity in Visualizations
We investigate how people discover the functionality of an interactive visualization that was designed for the general public. While interactive visualizations are increasingly available for public use, we still know little about how the general public discovers what they can do with these visualizations and what interactions are available. Developing a better understanding of this discovery process can help inform the design of visualizations for the general public, which in turn can help make data more accessible. To unpack this problem, we conducted a lab study in which participants were free to use their own methods to discover the functionality of a connected set of interactive visualizations of public energy data. We collected eye movement data and interaction logs as well as video and audio recordings. By analyzing this combined data, we extract exploration strategies that the participants employed to discover the functionality in these interactive visualizations. These exploration strategies illuminate possible design directions for improving the discoverability of a visualization's functionality
An Action for Black Hole Membranes
The membrane paradigm is the remarkable view that, to an external observer, a
black hole appears to behave exactly like a dynamical fluid membrane, obeying
such pre-relativistic equations as Ohm's law and the Navier-Stokes equation. It
has traditionally been derived by manipulating the equations of motion. Here we
provide an action formulation of this picture, clarifying what underlies the
paradigm, and simplifying the derivations. Within this framework, we derive
previous membrane results, and extend them to dyonic black hole solutions. We
discuss how it is that an action can produce dissipative equations. Using a
Euclidean path integral, we show that familiar semi-classical thermodynamic
properties of black holes also emerge from the membrane action. Finally, in a
Hamiltonian description, we establish the validity of a minimum entropy
production principle for black holes.Comment: LaTeX, 30 Pages, minor editorial change
Realistic Earth escape strategies for solar sailing
With growing interest in solar sailing comes the requirement to provide a basis for future detailed planetary escape mission analysis by drawing together prior work, clarifying and explaining previously anomalies. Previously unexplained seasonal variations in sail escape times from Earth orbit are explained analytically and corroborated within a numerical trajectory model. Blended-sail control algorithms, explicitly independent of time, which providenear-optimal escape trajectories and maintain a safe minimum altitude and which are suitable as a potential autonomous onboard controller, are then presented. These algorithms are investigated from a range of initial conditions and are shown to maintain the optimality previously demonstrated by the use of a single-energy gain control law but without the risk of planetary collision. Finally, it is shown that the minimum sail characteristic acceleration required for escape from a polar orbit without traversing the Earth shadow cone increases exponentially as initial altitude is decreased
Bipartite Fluctuations as a Probe of Many-Body Entanglement
We investigate in detail the behavior of the bipartite fluctuations of
particle number and spin in many-body quantum systems,
focusing on systems where such U(1) charges are both conserved and fluctuate
within subsystems due to exchange of charges between subsystems. We propose
that the bipartite fluctuations are an effective tool for studying many-body
physics, particularly its entanglement properties, in the same way that noise
and Full Counting Statistics have been used in mesoscopic transport and cold
atomic gases. For systems that can be mapped to a problem of non-interacting
fermions we show that the fluctuations and higher-order cumulants fully encode
the information needed to determine the entanglement entropy as well as the
full entanglement spectrum through the R\'{e}nyi entropies. In this connection
we derive a simple formula that explicitly relates the eigenvalues of the
reduced density matrix to the R\'{e}nyi entropies of integer order for any
finite density matrix. In other systems, particularly in one dimension, the
fluctuations are in many ways similar but not equivalent to the entanglement
entropy. Fluctuations are tractable analytically, computable numerically in
both density matrix renormalization group and quantum Monte Carlo calculations,
and in principle accessible in condensed matter and cold atom experiments. In
the context of quantum point contacts, measurement of the second charge
cumulant showing a logarithmic dependence on time would constitute a strong
indication of many-body entanglement.Comment: 30 pages + 25 pages supplementary materia
- âŠ