13,288 research outputs found
Cerca elétrica: alternativa viável e econômica para manejo de pastagens.
bitstream/item/65421/1/COT-48-Cerca-eletrica-alternativa.pd
Lattice calculations on the spectrum of Dirac and Dirac-K\"ahler operators
We present a matrix technique to obtain the spectrum and the analytical index
of some elliptic operators defined on compact Riemannian manifolds. The method
uses matrix representations of the derivative which yield exact values for the
derivative of a trigonometric polynomial. These matrices can be used to find
the exact spectrum of an elliptic operator in particular cases and in general,
to give insight into the properties of the solution of the spectral problem. As
examples, the analytical index and the eigenvalues of the Dirac operator on the
torus and on the sphere are obtained and as an application of this technique,
the spectrum of the Dirac-Kahler operator on the sphere is explored.Comment: 11 page
Tratamento e reciclagem de águas residuárias em sistema intensivo de produção de leite.
bitstream/item/65245/1/CT-75-Tratamento-e-reciclagem-de-aguas.pd
Stabilization of Extra Dimensions and The Dimensionality of the Observed Space
We present a simple model for the late time stabilization of extra
dimensions. The basic idea is that brane solutions wrapped around extra
dimensions, which is allowed by string theory, will resist expansion due to
their winding mode. The momentum modes in principle work in the opposite way.
It is this interplay that leads to dynamical stabilization. We use the idea of
democratic wrapping \cite{art5}-\cite{art6}, where in a given decimation of
extra dimensions, all possible winding cases are considered. To simplify the
study further we assumed a symmetric decimation in which the total number of
extra dimensions is taken to be where N can be called the order of the
decimation. We also assumed that extra dimensions all have the topology of
tori. We show that with these rather conservative assumptions, there exists
solutions to the field equations in which the extra dimensions are stabilized
and that the conditions do not depend on . This fact means that there exists
at least one solution to the asymmetric decimation case. If we denote the
number of observed space dimensions (excluding time) by , the condition for
stabilization is for pure Einstein gravity and for dilaton
gravity massaged by string theory parameters.Comment: Final versio
Particle production in the outflow of a midlatitude storm
The concentrations of atmospheric gases and condensation nuclei (CN) or aerosol in the outflow of a storm were measured aboard a NASA DC-8 aircraft, as described in a companion paper [Twohy et al., 2002]. The data are used here to study the production of the aerosol. Major fluctuations in CN concentration are observed, in correlation with gas-phase species, but these are shown to arise as the result of the mixing of two distinct air masses. It is deduced that the CN originated in a storm outflow air mass and that its concentration before mixing was approximately uniform over a flight distance of about 200 km. The formation of the aerosol by nucleation followed by growth and coagulation is analyzed assuming that it consists of water and sulphuric acid produced locally by the oxidation of SO2. The analysis uses analytic models, and it is concluded that a 5 min burst of nucleation was followed by growth and coagulation over a period of about 5 hours. Both the mass and number concentrations of the observed aerosol can be reproduced by this analysis within a timescale consistent with that of the storm. The final number concentration is very insensitive to the initial SO2 concentration
Dynamics of radiating braneworlds
If the observable universe is a braneworld of Randall-Sundrum type, then
particle interactions at high energies will produce 5-dimensional gravitons
that escape into the bulk. As a result, the Weyl energy density on the brane
does not behave like radiation in the early universe, but does so only later,
in the low energy regime. Recently a simple model was proposed to describe this
modification of the Randall-Sundrum cosmology. We investigate the dynamics of
this model, and find the exact solution of the field equations. We use a
dynamical systems approach to analyze global features of the phase space of
solutions.Comment: error in figures corrected, reference adde
Vibrating Winding Branes, Wrapping Democracy and Stabilization of Extra Dimensions in Dilaton Gravity
We show that, in the context of dilaton gravity, a recently proposed
democratic principle for intersection possibilities of branes winding around
extra dimensions yield stabilization, even with the inclusion of momentum modes
of the wrapped branes on top of the winding modes. The constraints for
stabilization massaged by string theory inputs forces the number of observed
dimensions to be three. We also discuss consequences of adding ordinary matter
living in the observed dimensions.Comment: Added a section discussing the linear and non-linear stability of the
equilibrium point of the scale factors of the extra dimensions. Corrected a
typo in the original field equations and other typos. Added and changed
references. Final version appeared in JHE
Cerebral and cardiovascular effects of analgesic doses of ketamine during a target controlled general anesthesia: a prospective randomized study
Introduction: Ketamine is increasingly being used in various pain settings. The purpose of this study was to
assess the effect of an analgesic dose of ketamine in the bispectral index (BIS), spectral edge frequency (SEF-95), density spectral array (DSA), cerebral oximetry (rSO2) and mean arterial pressure (MAP) during general
anaesthesia with a target controlled infusion.
Methods: A prospective, single-blinded and randomized study on adult patients scheduled for elective spine
surgery was carried out. After anaesthesia induction with propofol, remifentanil and rocuronium, when a stable BIS
value (45-55) was achieved, an automatic recording of BIS, SEF-95, rSO2 and MAP values during 9 min was
performed to establish patients baseline values. Subsequently, patients were randomly assigned to receive a
ketamine bolus dose of 0.2 mg/kg, 0.5 mg/kg or 1 mg/kg; all variables were recorded for additional 9 min after the
ketamine bolus, in the absence of any surgical stimulus. A p-value <0.05 was considered significant in the statistical
analysis.
Results and discussion: Thirty-nine patients were enrolled in the study. Our results show a dose-related
increase of SEF-95 and BIS values. DSA demonstrate a shift in the frequency range and power distribution towards
higher frequencies. Our results do not show significant differences in MAP and rSO2 values.
Conclusion: When ketamine is used intraoperatively in analgesic doses, the anaesthetist should anticipate an
increase in SEF-95 and BIS values which will not be associated with the level of anaesthesia.info:eu-repo/semantics/publishedVersio
Polarization tailored novel vector beams based on conical refraction
Coherent vector beams with involved states of polarization (SOP) are
widespread in the literature, having applications in laser processing,
super-resolution imaging and particle trapping. We report novel vector beams
obtained by transforming a Gaussian beam passing through a biaxial crystal, by
means of the conical refraction phenomenon. We analyze both experimentally and
theoretically the SOP of the different vector beams generated and demonstrate
that the SOP of the input beam can be used to control both the shape and the
SOP of the transformed beam. We also identify polarization singularities of
such beams for the first time and demonstrate their control by the SOP of an
input beam
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