15,629 research outputs found
Regularity at infinity of real mappings and a Morse-Sard theorem
We prove a new Morse-Sard type theorem for the asymptotic critical values of
semi-algebraic mappings and a new fibration theorem at infinity for
mappings. We show the equivalence of three different types of regularity
conditions which have been used in the literature in order to control the
asymptotic behaviour of mappings. The central role of our picture is played by
the -regularity and its bridge toward the -regularity which implies
topological triviality at infinity
SP mountain data analysis
An analysis of synthetic aperture radar data of SP Mountain was undertaken to demonstrate the use of digital image processing techniques to aid in geologic interpretation of SAR data. These data were collected with the ERIM X- and L-band airborne SAR using like- and cross-polarizations. The resulting signal films were used to produce computer compatible tapes, from which four-channel imagery was generated. Slant range-to-ground range and range-azimuth-scale corrections were made in order to facilitate image registration; intensity corrections were also made. Manual interpretation of the imagery showed that L-band represented the geology of the area better than X-band. Several differences between the various images were also noted. Further digital analysis of the corrected data was done for enhancement purposes. This analysis included application of an MSS differencing routine and development of a routine for removal of relief displacement. It was found that accurate registration of the SAR channels is critical to the effectiveness of the differencing routine. Use of the relief displacement algorithm on the SP Mountain data demonstrated the feasibility of the technique
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
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
School through the eyes of children... are we just bricks in the wall?
Over the years it has been debated what should be the role of school, which is the best teaching practices, and the most appropriate methods in primary education. However, rarely we are available to hear who is at the center of any education system... The student, the child within… We may wonder what children really think. What are their needs and aspirations? Listening to children, we can better understand their ideas, feelings, desires and dreams, about teaching and the school they attend, and how this is reflected in their behavior and development. Their representations of school allow us to rethink education and school itself. So, in this study, we were guided by the eyes of children aged between 8 and 11 years, of both sexes, attending elementary school, in Lisbon. What do they think and how they feel about school? What are their wishes and how they imagine school should be? These were the main objectives. The data was gathered using free associations of words, from questions individually made, and examined through Factorial Correspondence Analysis. Children link school both to playful and learning dimensions. In fact the most important for all of them is the playful side of school, a place where they can meet peers and establish important relations, also with teachers. They care about each other, they wish to learn and feel free. They yearn for a better school… Remembering Pink Floyd, we hope we are not just contributing for more 'bricks in the wall'.info:eu-repo/semantics/publishedVersio
Axion Like Particles and the Inverse Seesaw Mechanism
Light pseudoscalars known as axion like particles (ALPs) may be behind
physical phenomena like the Universe transparency to ultra-energetic photons,
the soft -ray excess from the Coma cluster, and the 3.5 keV line. We
explore the connection of these particles with the inverse seesaw (ISS)
mechanism for neutrino mass generation. We propose a very restrictive setting
where the scalar field hosting the ALP is also responsible for generating the
ISS mass scales through its vacuum expectation value on gravity induced
nonrenormalizable operators. A discrete gauge symmetry protects the theory from
the appearance of overly strong gravitational effects and discrete anomaly
cancellation imposes strong constraints on the order of the group. The
anomalous U symmetry leading to the ALP is an extended lepton number and
the protective discrete symmetry can be always chosen as a subgroup of a
combination of the lepton number and the baryon number.Comment: 29pp. v4: published version with erratum. Conclusions unchange
School through the eyes of children... are we just bricks in the wall?
Over the years it has been debated what should be the role of school, which is the best teaching practices, and the most appropriate methods in primary education. However, rarely we are available to hear who is at the center of any education system... The student, the child within… We may wonder what children really think. What are their needs and aspirations? Listening to children, we can better understand their ideas, feelings, desires and dreams, about teaching and the school they attend, and how this is reflected in their behavior and development. Their representations of school allow us to rethink education and school itself. So, in this study, we were guided by the eyes of children aged between 8 and 11 years, of both sexes, attending elementary school, in Lisbon. What do they think and how they feel about school? What are their wishes and how they imagine school should be? These were the main objectives. The data was gathered using free associations of words, from questions individually made, and examined through Factorial Correspondence Analysis. Children link school both to playful and learning dimensions. In fact the most important for all of them is the playful side of school, a place where they can meet peers and establish important relations, also with teachers. They care about each other, they wish to learn and feel free. They yearn for a better school… Remembering Pink Floyd, we hope we are not just contributing for more 'bricks in the wall'.info:eu-repo/semantics/publishedVersio
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
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