16,351 research outputs found
Half Quantization
A general dynamical system composed by two coupled sectors is considered. The
initial time configuration of one of these sectors is described by a set of
classical data while the other is described by standard quantum data. These
dynamical systems will be named half quantum. The aim of this paper is to
derive the dynamical evolution of a general half quantum system from its full
quantum formulation. The standard approach would be to use quantum mechanics to
make predictions for the time evolution of the half quantum initial data. The
main problem is how can quantum mechanics be applied to a dynamical system
whose initial time configuration is not described by a set of fully quantum
data. A solution to this problem is presented and used, as a guideline to
obtain a general formulation of coupled classical-quantum dynamics. Finally, a
quantization prescription mapping a given classical theory to the correspondent
half quantum one is presented.Comment: 20 pages, LaTex file, Substantially revised versio
Enhancement of the Benjamin-Feir instability with dissipation
It is shown that there is an overlooked mechanism whereby some kinds of
dissipation can enhance the Benjamin-Feir instability of water waves. This
observation is new, and although it is counterintuitive, it is due to the fact
that the Benjamin-Feir instability involves the collision of modes with
opposite energy sign (relative to the carrier wave), and it is the negative
energy perturbations which are enhanced.Comment: 15 pages, 2 figures To download more papers, go to
http://www.cmla.ens-cachan.fr/~dias. Physics of Fluids (2007) to appea
Principal components technique analysis for vegetation and land use discrimination
Automatic pre-processing technique called Principal Components (PRINCO) in analyzing LANDSAT digitized data, for land use and vegetation cover, on the Brazilian cerrados was evaluated. The chosen pilot area, 223/67 of MSS/LANDSAT 3, was classified on a GE Image-100 System, through a maximum-likehood algorithm (MAXVER). The same procedure was applied to the PRINCO treated image. PRINCO consists of a linear transformation performed on the original bands, in order to eliminate the information redundancy of the LANDSAT channels. After PRINCO only two channels were used thus reducing computer effort. The original channels and the PRINCO channels grey levels for the five identified classes (grassland, "cerrado", burned areas, anthropic areas, and gallery forest) were obtained through the MAXVER algorithm. This algorithm also presented the average performance for both cases. In order to evaluate the results, the Jeffreys-Matusita distance (JM-distance) between classes was computed. The classification matrix, obtained through MAXVER, after a PRINCO pre-processing, showed approximately the same average performance in the classes separability
Atmospheric correction analysis on LANDSAT data over the Amazon region
The Amazon Region natural resources were studied in two ways and compared. A LANDSAT scene and its attributes were selected, and a maximum likelihood classification was made. The scene was atmospherically corrected, taking into account Amazonic peculiarities revealed by (ground truth) of the same area, and the subsequent classification. Comparison shows that the classification improves with the atmospherically corrected images
A Multi-Membership Catalogue for 1876 Open Clusters using UCAC4 data
The main objective of this work is to determine the cluster members of 1876
open clusters, using positions and proper motions of the astrometric catalogue
UCAC4. For this purpose we apply three different methods, all them based on a
Bayesian approach, but with different formulations: a purely parametric method,
another completely non-parametric algorithm, and a third, recently developed by
Sampedro & Alfaro, using both formulations at different steps of the whole
process. The first and second statistical moments of the members phase-space
subspace, obtained after applying the three methods, are compared for every
cluster. Although, on average, the three methods yield similar results,
specific differences between them, as well as for some particular clusters, are
also present. The comparison with other published catalogues shows good
agreement. We have also estimated for the first time the mean proper motion for
a sample of 18 clusters. The results are organized in a single catalogue formed
by two main files, one with the most relevant information for each cluster,
partially including that in UCAC4, and the other showing the individual
membership probabilities for each star in the cluster area. The final
catalogue, with an interface design that enables an easy interaction with the
user, is available in electronic format at SSG-IAA
(http://ssg.iaa.es/en/content/sampedro-cluster-catalog) website.Comment: Accepted for publication in MNRAS. 9 pages, 3 figures, 6 table
Generation of higher derivatives operators and electromagnetic wave propagation in a Lorentz-violation scenario
We study the perturbative generation of higher-derivative operators as
corrections to the photon effective action, which are originated from a Lorentz
violation background. Such corrections are obtained, at one-loop order, through
the proper-time method, using the zeta function regularization. We focus over
the lowest order corrections and investigate their influence in the propagation
of electromagnetic waves through the vacuum, in the presence of a strong,
constant magnetic field. This is a setting of experimental relevance, since it
bases active efforts to measure non linear electromagnetic effects. After
surprising cancellations of Lorentz violating corrections to the Maxwell's
equation, we show that no effects of the kind of Lorentz violation we consider
can be detected in such a context.Comment: v2: 13 pages, no figures, section IV considerably rewritten, main
results unchanged and are now obtained in a simpler way. To appear in PL
Fluctuating local moments, itinerant electrons and the magnetocaloric effect: the compositional hypersensitivity of FeRh
We describe an ab-initio Disordered Local Moment Theory for materials with
quenched static compositional disorder traversing first order magnetic phase
transitions. It accounts quantitatively for metamagnetic changes and the
magnetocaloric effect. For perfect stoichiometric B2-ordered FeRh, we calculate
the transition temperature of the ferromagnetic-antiferromagnetic transition to
be 495K and a maximum isothermal entropy change in 2 Tesla of J~K~kg. A large (40\%) component of is
electronic. The transition results from a fine balance of competing electronic
effects which is disturbed by small compositional changes - e.g. swapping just
2\% Fe of `defects' onto the Rh sublattice makes drop by 290K. This
hypersensitivity explains the narrow compositional range of the transition and
impurity doping effects.Comment: 11 pages, 4 figure
Metallic magnetism at finite temperatures studied by relativistic disordered moment description: Theory and applications
We develop a self-consistent relativistic disordered local moment (RDLM)
scheme aimed at describing finite temperature magnetism of itinerant metals
from first principles. Our implementation in terms of the
Korringa--Kohn--Rostoker multiple scattering theory and the coherent potential
approximation allows to relate the orientational distribution of the spins to
the electronic structure, thus a self-consistent treatment of the distribution
is possible. We present applications for bulk bcc Fe, L1-FePt and FeRh
ordered in the CsCl structure. The calculations for Fe show significant
variation of the local moments with temperature, whereas according to the mean
field treatment of the spin fluctuations the Curie temperature is
overestimated. The magnetic anisotropy of FePt alloys is found to depend
strongly on intermixing between nominally Fe and Pt layers, and it shows a
power-law behavior as a function of magnetization for a broad range of chemical
disorder. In case of FeRh we construct a lattice constant vs. temperature phase
diagram and determine the phaseline of metamagnetic transitions based on
self-consistent RDLM free energy curves.Comment: 11 pages, 8 figure
The impact of sound in people's behaviour in outdoor settings: A study using virtual reality and eye-tracking
This paper presents an analysis of space perception and how visual cues, such as landmarks and sound, are perceived and impact people's behaviour while exploring a given outdoor space. The primary goal of the research is to investigate how auditory sensations and visual stimuli influence people's behaviour in outdoor built environments. Our technique compares people's perception of the built environment in different conditions: the real world and a replicated virtual world. As a case study, a university campus was used, and four experimental conditions were designed. The study followed a between-subjects design, and the data collection included gaze data acquired from an eye-tracking device as well as self-reports. The study concludes that sound influences human behaviour in such settings. More specifically conclusions are that: i) human behaviour in virtual replications of the real space, including both visual and sound stimuli, is tendentially more similar to human behaviour in the real world than in simulations omitting sound; and ii) there is a difference in human behaviour when people explore the same virtually replicated outdoor space, by varying the presence of sound. This study is particularly useful for researchers working on the comparison between human behaviour in virtual and real environments, related to visual and sound stimuli.info:eu-repo/semantics/publishedVersio
Phase diagram of the antiferromagnetic XY model in two dimensions in a magnetic field
The phase diagram of the quasi-two-dimensional easy-plane antiferromagnetic
model, with a magnetic field applied in the easy plane, is studied using the
self-consistent harmonic approximation. We found a linear dependence of the
transition temperature as a function of the field for large values of the
field. Our results are in agreement with experimental data for the spin-1
honeycomb compound BaNi_2V_2O_3Comment: 3 page
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