30,644 research outputs found
Improved semiclassical density matrix: taming caustics
We present a simple method to deal with caustics in the semiclassical
approximation to the thermal density matrix of a particle moving on the line.
For simplicity, only its diagonal elements are considered. The only ingredient
we require is the knowledge of the extrema of the Euclidean action. The
procedure makes use of complex trajectories, and is applied to the quartic
double-well potential.Comment: 20 pages, 7 figures. Revised version, accepted for publication in
Phys. Rev.
Electronic properties of curved graphene sheets
A model is proposed to study the electronic structure of slightly curved
graphene sheets with an arbitrary number of pentagon-heptagon pairs and
Stone-Wales defects based on a cosmological analogy. The disorder induced by
curvature produces characteristic patterns in the local density of states that
can be observed in scanning tunnel and transmission electron microscopy.Comment: Corrected versio
Improving the Knowledge on Seismogenic Sources in the Lower Tagus Valley for Seismic Hazard Purposes
The Lower Tagus Valley, that includes the metropolitan area of Lisbon, has been struck by several earthquakes which produced significant material damage and loss of lives. Their exact location remains unknown. Our goal is to shed some light into the seismogenic sources in the area using seismic reflection and geological data. In areas with no seismic coverage, potential-field data interpretation was carried out. Seismicity was overlaid to the potential seismogenic structures and high-resolution data was acquired in order to confirm which structures have been active into the Quaternary. Three major fault-zones affecting the Neogene were identified: V. F. Xira, Samora-Alcochete and Pinhal Novo. For the first fault, strong evidences suggest it is active. The other two fault-zones and other structures previously unknown can be correlated with several epicentres. Empirical relationships between maximum moment magnitude and fault area indicate that MW > 6.5 earthquakes can be expected for the larger structures
Number-Phase Wigner Representation for Scalable Stochastic Simulations of Controlled Quantum Systems
Simulation of conditional master equations is important to describe systems
under continuous measurement and for the design of control strategies in
quantum systems. For large bosonic systems, such as BEC and atom lasers, full
quantum field simulations must rely on scalable stochastic methods whose
convergence time is restricted by the use of representations based on coherent
states. Here we show that typical measurements on atom-optical systems have a
common form that allows for an efficient simulation using the number-phase
Wigner (NPW) phase-space representation. We demonstrate that a stochastic
method based on the NPW can converge over an order of magnitude longer and more
precisely than its coherent equivalent. This opens the possibility of realistic
simulations of controlled multi-mode quantum systems.Comment: 5 pages, 1 figur
Elastic scattering and the proton form factor
We compute the differential and the total cross sections for scattering
using the QCD pomeron model proposed by Landshoff and Nachtmann. This model is
quite dependent on the experimental electromagnetic form factor, and it is not
totally clear why this form factor gives good results even at moderate
transferred momentum. We exchange the eletromagnetic form factor by the
asymptotic QCD proton form factor determined by Brodsky and Lepage (BL) plus a
prescription for its low energy behavior dictated by the existence of a
dynamically generated gluon mass. We fit the data with this QCD inspired form
factor and a value for the dynamical gluon mass consistent with the ones
determined in the literature. Our results also provide a new determination of
the proton wave function at the origin, which appears in the BL form factor.Comment: 10 pages, 2 figures. Submitted to Physics Letters B. Submitted to
Phys. Lett.
Accessing earth observation data using JPEG2000
Applications like, change detection, global monitoring, disaster detection and management have emerging requirements that need the availability of large amounts of data. This data is currently being captured by a multiplicity of instruments and Earth Observation (EO) sensors originating large volumes of data that needs to be stored, processed and accessed in order to be useful. The authors of this paper have been involved on an ESA-founded project, called HICOD2000 to study the applicability of the new image encoding standard JPEG2000 - to EO products. This paper presents and describes the system that was developed for HICOD2000 project, which allows, not only the encoding and decoding of several EO products, but also supports some of the security requirements identified previously that allows ESA to define and apply efficient EO data access security policies and even to exploit some EO products electronic commerce over the Internet. This system was integrated with the existing ESA Ground Segment systems specifically the Services Support Environment (SSE).info:eu-repo/semantics/acceptedVersio
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