366,619 research outputs found
Asymptotically Universal Crossover in Perturbation Theory with a Field Cutoff
We discuss the crossover between the small and large field cutoff (denoted
x_{max}) limits of the perturbative coefficients for a simple integral and the
anharmonic oscillator. We show that in the limit where the order k of the
perturbative coefficient a_k(x_{max}) becomes large and for x_{max} in the
crossover region, a_k(x_{max}) is proportional to the integral from -infinity
to x_{max} of e^{-A(x-x_0(k))^2}dx. The constant A and the function x_0(k) are
determined empirically and compared with exact (for the integral) and
approximate (for the anharmonic oscillator) calculations. We discuss how this
approach could be relevant for the question of interpolation between
renormalization group fixed points.Comment: 15 pages, 11 figs., improved and expanded version of hep-th/050304
Uniqueness and stability of time and space-dependent conductivity in a hyperbolic cylindrical domain
This paper is devoted to the reconstruction of the time and space-dependent
coefficient in an infinite cylindrical hyperbolic domain. Using a local
Carleman estimate we prove the uniqueness and a H\"older stability in the
determining of the conductivity by a single measurement on the lateral
boundary. Our numerical examples show good reconstruction of the location and
contrast of the conductivity function in three dimensions.Comment: arXiv admin note: text overlap with arXiv:1501.0138
Lipschitz stability for an inverse hyperbolic problem of determining two coefficients by a finite number of observations
We consider an inverse problem of reconstructing two spatially varying
coefficients in an acoustic equation of hyperbolic type using interior data of
solutions with suitable choices of initial condition. Using a Carleman
estimate, we prove Lipschitz stability estimates which ensures unique
reconstruction of both coefficients. Our theoretical results are justified by
numerical studies on the reconstruction of two unknown coefficients using noisy
backscattered data
The Behaviour of Finely Ground Bottom Ash in Portland Cement
The aim of this project was to assess the effects of finely ground MSWI bottom ash in Portland cement. Mortar mixes were prepared with 10% and 40% replacement of cement by ground IBA and then tested with regards to their material composition and engineering behaviour. IBA was found not to be inert, but showed some degree of reactivity. Replacement of cement with IBA was found to have no detrimental effects at low concentrations. This was not the case for 40% replacement, where cement replacement greatly affected strength, creep and drying shrinkage
Darwinian Data Structure Selection
Data structure selection and tuning is laborious but can vastly improve an
application's performance and memory footprint. Some data structures share a
common interface and enjoy multiple implementations. We call them Darwinian
Data Structures (DDS), since we can subject their implementations to survival
of the fittest. We introduce ARTEMIS a multi-objective, cloud-based
search-based optimisation framework that automatically finds optimal, tuned DDS
modulo a test suite, then changes an application to use that DDS. ARTEMIS
achieves substantial performance improvements for \emph{every} project in
Java projects from DaCapo benchmark, popular projects and uniformly
sampled projects from GitHub. For execution time, CPU usage, and memory
consumption, ARTEMIS finds at least one solution that improves \emph{all}
measures for () of the projects. The median improvement across
the best solutions is , , for runtime, memory and CPU
usage.
These aggregate results understate ARTEMIS's potential impact. Some of the
benchmarks it improves are libraries or utility functions. Two examples are
gson, a ubiquitous Java serialization framework, and xalan, Apache's XML
transformation tool. ARTEMIS improves gson by \%, and for
memory, runtime, and CPU; ARTEMIS improves xalan's memory consumption by
\%. \emph{Every} client of these projects will benefit from these
performance improvements.Comment: 11 page
The pointer basis and the feedback stabilization of quantum systems
The dynamics for an open quantum system can be `unravelled' in infinitely
many ways, depending on how the environment is monitored, yielding different
sorts of conditioned states, evolving stochastically. In the case of ideal
monitoring these states are pure, and the set of states for a given monitoring
forms a basis (which is overcomplete in general) for the system. It has been
argued elsewhere [D. Atkins et al., Europhys. Lett. 69, 163 (2005)] that the
`pointer basis' as introduced by Zurek and Paz [Phys. Rev. Lett 70,
1187(1993)], should be identified with the unravelling-induced basis which
decoheres most slowly. Here we show the applicability of this concept of
pointer basis to the problem of state stabilization for quantum systems. In
particular we prove that for linear Gaussian quantum systems, if the feedback
control is assumed to be strong compared to the decoherence of the pointer
basis, then the system can be stabilized in one of the pointer basis states
with a fidelity close to one (the infidelity varies inversely with the control
strength). Moreover, if the aim of the feedback is to maximize the fidelity of
the unconditioned system state with a pure state that is one of its conditioned
states, then the optimal unravelling for stabilizing the system in this way is
that which induces the pointer basis for the conditioned states. We illustrate
these results with a model system: quantum Brownian motion. We show that even
if the feedback control strength is comparable to the decoherence, the optimal
unravelling still induces a basis very close to the pointer basis. However if
the feedback control is weak compared to the decoherence, this is not the case
Electronic properties of bilayer phosphorene quantum dots in the presence of perpendicular electric and magnetic fields
Using the tight-binding approach, we investigate the electronic properties of
bilayer phosphorene (BLP) quantum dots (QDs) in the presence of perpendicular
electric and magnetic fields. Since BLP consists of two coupled phosphorene
layers, it is of interest to examine the layer-dependent electronic properties
of BLP QDs, such as the electronic distributions over the two layers and the
so-produced layer-polarization features, and to see how these properties are
affected by the magnetic field and the bias potential. We find that in the
absence of a bias potential only edge states are layer-polarized while the bulk
states are not, and the layer-polarization degree (LPD) of the unbiased edge
states increases with increasing magnetic field. However, in the presence of a
bias potential both the edge and bulk states are layer-polarized, and the LPD
of the bulk (edge) states depends strongly (weakly) on the interplay of the
bias potential and the interlayer coupling. At high magnetic fields, applying a
bias potential renders the bulk electrons in a BLP QD to be mainly distributed
over the top or bottom layer, resulting in layer-polarized bulk Landau levels
(LLs). In the presence of a large bias potential that can drive a
semiconductor-to-semimetal transition in BLP, these bulk LLs exhibit different
magnetic-field dependences, i.e., the zeroth LLs exhibit a linear-like
dependence on the magnetic field while the other LLs exhibit a square-root-like
dependence.Comment: 11 pages, 6 figure
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