2,183 research outputs found
A non-singular black hole model as a possible end-product of gravitational collapse
In this paper we present a non-singular black hole model as a possible
end-product of gravitational collapse. The depicted spacetime which is type
[II,(II)], by Petrov classification, is an exact solution of the Einstein
equations and contains two horizons. The equation of state in the radial
direction, is a well-behaved function of the density and smoothly reproduces
vacuum-like behavior near r=0 while tending to a polytrope at larger r, low
density, values. The final equilibrium configuration comprises of a de
Sitter-like inner core surrounded by a family of 2-surfaces of matter fields
with variable equation of state. The fields are all concentrated in the
vicinity of the radial center r=0. The solution depicts a spacetime that is
asymptotically Schwarzschild at large r, while it becomes de Sitter-like for
vanishing r. Possible physical interpretations of the macro-state of the black
hole interior in the model are offered. We find that the possible state admits
two equally viable interpretations, namely either a quintessential intermediary
region or a phase transition in which a two-fluid system is in both dynamic and
thermodynamic equilibrium. We estimate the ratio of pure matter present to the
total energy and in both (interpretations) cases find it to be virtually the
same, being 0.83. Finally, the well-behaved dependence of the density and
pressure on the radial coordinate provides some insight on dealing with the
information loss paradox.Comment: 12 Pages, 1 figure. Accepted for publication in Phys. Rev.
Adsorption Way of the Loss of Moon's Atmosphere
Theory on gas adsorption by lunar surface to explain loss of lunar atmospher
Minimal Universal Two-qubit Quantum Circuits
We give quantum circuits that simulate an arbitrary two-qubit unitary
operator up to global phase. For several quantum gate libraries we prove that
gate counts are optimal in worst and average cases. Our lower and upper bounds
compare favorably to previously published results. Temporary storage is not
used because it tends to be expensive in physical implementations.
For each gate library, best gate counts can be achieved by a single universal
circuit. To compute gate parameters in universal circuits, we only use
closed-form algebraic expressions, and in particular do not rely on matrix
exponentials. Our algorithm has been coded in C++.Comment: 8 pages, 2 tables and 4 figures. v3 adds a discussion of asymetry
between Rx, Ry and Rz gates and describes a subtle circuit design problem
arising when Ry gates are not available. v2 sharpens one of the loose bounds
in v1. Proof techniques in v2 are noticeably revamped: they now rely less on
circuit identities and more on directly-computed invariants of two-qubit
operators. This makes proofs more constructive and easier to interpret as
algorithm
Zel'dovich states with very small mass and charge in nonlinear electrodynamics coupled to gravity
It is shown that in non-linear electrodynamics (in particular, Born-Infeld
one) in the framework of general relativity there exist "weakly singular"
configurations such that (i) the proper mass M is finite in spite of
divergences of the energy density, (ii) the electric charge q and Schwarzschild
mass m ~ q can be made as small as one likes, (iv) all field and energy
distributions are concentrated in the core region. This region has an almost
zero surface area but a finite longitudinal size L=2M. Such configurations can
be viewed as a new version of a classical analogue of an elementary particle.Comment: 11 pages. 1 reference added. To appear in Grav. Cosm
Temperature Dependence of Exciton Diffusion in Conjugated Polymers
The temperature dependence of the exciton dynamics in a conjugated polymer is studied using time-resolved spectroscopy. Photoluminescence decays were measured in heterostructured samples containing a sharp polymer-fullerene interface, which acts as an exciton quenching wall. Using a 1D diffusion model, the exciton diffusion length and diffusion coefficient were extracted in the temperature range of 4-293 K. The exciton dynamics reveal two temperature regimes: in the range of 4-150 K, the exciton diffusion length (coefficient) of ~3 nm (~1.5 × 10-4 cm2/s) is nearly temperature independent. Increasing the temperature up to 293 K leads to a gradual growth up to 4.5 nm (~3.2 × 10-4 cm2/s). This demonstrates that exciton diffusion in conjugated polymers is governed by two processes: an initial downhill migration toward lower energy states in the inhomogenously broadened density of states, followed by temperature activated hopping. The latter process is switched off below 150 K.
Synthesis and Optimization of Reversible Circuits - A Survey
Reversible logic circuits have been historically motivated by theoretical
research in low-power electronics as well as practical improvement of
bit-manipulation transforms in cryptography and computer graphics. Recently,
reversible circuits have attracted interest as components of quantum
algorithms, as well as in photonic and nano-computing technologies where some
switching devices offer no signal gain. Research in generating reversible logic
distinguishes between circuit synthesis, post-synthesis optimization, and
technology mapping. In this survey, we review algorithmic paradigms ---
search-based, cycle-based, transformation-based, and BDD-based --- as well as
specific algorithms for reversible synthesis, both exact and heuristic. We
conclude the survey by outlining key open challenges in synthesis of reversible
and quantum logic, as well as most common misconceptions.Comment: 34 pages, 15 figures, 2 table
The Boltzmann equation for colourless plasmons in hot QCD plasma. Semiclassical approximation
Within the framework of the semiclassical approximation, we derive the
Boltzmann equation describing the dynamics of colorless plasmons in a hot QCD
plasma. The probability of the plasmon-plasmon scattering at the leading order
in the coupling constant is obtained. This probability is gauge-independent at
least in the class of the covariant and temporal gauges. It is noted that the
structure of the scattering kernel possesses important qualitative difference
from the corresponding one in the Abelian plasma, in spite of the fact that we
focused our study on the colorless soft excitations. It is shown that
four-plasmon decay is suppressed by the power of relative to the process of
nonlinear scattering of plasmons by thermal particles at the soft momentum
scale. It is stated that the former process becomes important in going to the
ultrasoft region of the momentum scale.Comment: 41, LaTeX, minor changes, identical to published versio
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