10,345 research outputs found
On the duality in four-dimensional Lorentz-breaking field theories
We consider new issues of duality in four-dimensional Lorentz-breaking field
theories. In particular, we demonstrate that the arising of the aether-like
Lorentz-breaking term is necessary in order for the 4D models to display the
duality analog between the MCS and self-dual models in 3D. We further study the
dispersion relations in both theories and discuss the physical contents of the
models involved in this new dualilty.Comment: 16 page
Seeing colors in real scenes
Color perception in real conditions is determined by the spectral and spatial properties of objects and illumination. These
properties are best evaluated by spectral imaging, a technique that records the reflecting spectral profile for each point of
the scene. Using this technique on a set of natural scenes it was found that the color gamut expressed in the CIELAB
color space is much smaller than the theoretical limits defined for the object colors. Moreover, the colors more frequent
are those around the white point and their frequency of occurrence can be well described by a power law. Spatial
variations of the spectral composition of the illumination across natural scenes were also quantified by placing small
reflecting spheres in different locations of the scenes. The extent of these variations across scenes was found to be large
and of the same order of magnitude as the variations of daylight along the day. These findings show that colors in nature
are considerable constrained and that constancy mechanisms must be efficient over a wide range of stimuli variations to
compensate for large natural variations of illumination
Single and Double Photoionization and Photodissociation of Toluene by Soft X-rays in Circumstellar Environment
The formation of polycyclic aromatic hydrocarbons (PAHs) and their methyl
derivatives occurs mainly in the dust shells of asymptotic giant branch (AGB)
stars. The bands at 3.3 and 3.4 m, observed in infrared emission spectra
of several objects, are attributed C-H vibrational modes in aromatic and
aliphatic structures, respectively. In general, the feature at 3.3 m is
more intense than the 3.4 m. Photoionization and photodissociation
processes of toluene, the precursor of methylated PAHs, were studied using
synchrotron radiation at soft X-ray energies around the carbon K edge with
time-of-flight mass spectrometry. Partial ion yields of a large number of ionic
fragments were extracted from single and 2D-spectra, where electron-ion
coincidences have revealed the doubly charged parent-molecule and several
doubly charged fragments containing seven carbon atoms with considerable
abundance. \textit{Ab initio} calculations based on density functional theory
were performed to elucidate the chemical structure of these stable dicationic
species. The survival of the dications subjected to hard inner shell ionization
suggests that they could be observed in the interstellar medium, especially in
regions where PAHs are detected. The ionization and destruction of toluene
induced by X-rays were examined in the T Dra conditions, a carbon-rich AGB
star. In this context, a minimum photodissociation radius and the half-life of
toluene subjected to the incidence of the soft X-ray flux emitted from a
companion white dwarf star were determined.Comment: 11 pages, 4 figures, accept for publication in Ap
Valor nutritivo de palha de carnaúba tratada com uréia.
bitstream/item/131478/1/circular-33-Valor-nutritivo-da-palha-de-carnauba.pd
Tratamento de resÃduos agroindustriais com uréia.
Bagaço de cana, casca de arroz e bagana de carnauba (Copernicia prunifera) foram tratados com uréia liquida, visando-se melhorar o seu valor nutritivo para utilização na alimentação animal. Foi utilizada a uréia liquida ( a 5%) na proporção de 100 l da solução para 100 kg de resÃduo. Os materiais foram incubados em silos durante 10, 20 e 30 dias. 0 delineamento foi inteiramente casualisado, com três repetições. Os três resÃduos tiveram seus percentuais de proteÃna aumentados pela amoniação, sendo que os aumentos foram relativamente maiores nos materiais de menor teor proteico. Antes da incubação os percentuais de proteÃna eram de. 2,78; 4,43 e 10,03, respectivamente em bagaço de cana, casca de arroz, e bagana de carnauba, aumentando para 5,20; 7,56 e 13,97% após dez dias de incubação. Os perÃodos de incubação superiores a 10 dias não tiveram efeito benéfico (P>0,05), ocorrendo até mesmo decréscimo nos percentuais de proteÃna, com o alongamento do perÃodo de incubação
Color diversity index : the effect of chromatic adaptation
Common descriptors of light quality fail to predict the chromatic diversity produced by the same illuminant in different
contexts. The aim of this paper was to study the influence of the chromatic adaptation in the context of the development
of the color diversity index, a new index capable of predicting illuminant-induced variations in several types of images.
The spectral reflectance obtained from hyperspectral images of natural, indoor and artistic paintings, and the spectral
reflectance of 1264 Munsell surfaces were converted into the CIELAB color space for each of the 55 CIE illuminants
and 5 light sources tested. The influence of the CAT02 chromatic adaptation was estimated for each illuminant and for
each scene. The CIELAB volume was estimated by the convex hull method and the number of discernible colors was
estimated by segmenting the CIELAB color volume into unitary cubes and by counting the number of non-empty cubes.
High correlation was found between the CIELAB volume occupied by the Munsell surfaces and the number of
discernible colors and the CILEAB color volume of the colors in all images analyzed. The effects of the chromatic
adaptation were marginal and did not change the overall result. These results indicate that the efficiency of the new
illuminant chromatic diversity index is not influenced by chromatic adaptation
Five-Dimensional QED, Muon Pair Production and Correction to the Coulomb Potential
We consider QED in five dimensions in a configuration where matter is
localized on a 3-brane while foton propagates in the bulk. The idea is to
investigate the effects of the Kaluza-Klein modes of the photon in the
relativistic regime, but in low energy, and in the nonrelativistic regime. In
the relativistic regime, we calculate the cross section for the reaction . We compare our theoretical result with a precise
measurement of this cross section at GeV. As result, we
extract a lower bound on the size of the extra dimension. In the
nonrelativistic regime, we derive the contribution for the Coulomb potential
due to the whole tower of the Kaluza-Klein excited modes of the photon. We use
the modified potential to calculate the Rutherford scattering differential
cross section.Comment: minor changes, three new refs. added, to appear in IJMP
A Framework for Efficient Adaptively Secure Composable Oblivious Transfer in the ROM
Oblivious Transfer (OT) is a fundamental cryptographic protocol that finds a
number of applications, in particular, as an essential building block for
two-party and multi-party computation. We construct a round-optimal (2 rounds)
universally composable (UC) protocol for oblivious transfer secure against
active adaptive adversaries from any OW-CPA secure public-key encryption scheme
with certain properties in the random oracle model (ROM). In terms of
computation, our protocol only requires the generation of a public/secret-key
pair, two encryption operations and one decryption operation, apart from a few
calls to the random oracle. In~terms of communication, our protocol only
requires the transfer of one public-key, two ciphertexts, and three binary
strings of roughly the same size as the message. Next, we show how to
instantiate our construction under the low noise LPN, McEliece, QC-MDPC, LWE,
and CDH assumptions. Our instantiations based on the low noise LPN, McEliece,
and QC-MDPC assumptions are the first UC-secure OT protocols based on coding
assumptions to achieve: 1) adaptive security, 2) optimal round complexity, 3)
low communication and computational complexities. Previous results in this
setting only achieved static security and used costly cut-and-choose
techniques.Our instantiation based on CDH achieves adaptive security at the
small cost of communicating only two more group elements as compared to the
gap-DH based Simplest OT protocol of Chou and Orlandi (Latincrypt 15), which
only achieves static security in the ROM
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