Efeito da aplicação de fungicidas no controle das ferrugens da folha e do colmo e sobre o rendimento de grãos de trigo.

bitstream/item/66142/1/CPAO-PESQ.-AND.-5-80.pd

Perturbations of spacetime: gauge transformations and gauge invariance at second order and beyond

We consider in detail the problem of gauge dependence that exists in relativistic perturbation theory, going beyond the linear approximation and treating second and higher order perturbations. We first derive some mathematical results concerning the Taylor expansion of tensor fields under the action of one-parameter families (not necessarily groups) of diffeomorphisms. Second, we define gauge invariance to an arbitrary order $n$. Finally, we give a generating formula for the gauge transformation to an arbitrary order and explicit rules to second and third order. This formalism can be used in any field of applied general relativity, such as cosmological and black hole perturbations, as well as in other spacetime theories. As a specific example, we consider here second order perturbations in cosmology, assuming a flat Robertson-Walker background, giving explicit second order transformations between the synchronous and the Poisson (generalized longitudinal) gauges.Comment: slightly revised version, accepted for publication in Classical and Quantum Gravity. 27 pages including 4 figures, latex using 2 CQG style files: ioplppt.sty, iopl10.st

Root diseases of wheat. II. Mato Grosso do Sul

O levantamento da ocorrência de doenças do sistema radicular do trigo (Triticum aestivum L.), em algumas regiões do Estado do Mato Grosso do Sul, revelou a existência da podridão comum de raízes nessas áreas tendo como principal patógeno associado à doença o fungo Cochliobolus sativus. Em geral, o grau de infecção da doença foi leve. A população de esporos desse organismo no solo foi baixa, na maioria das amostras, e maior na camada de 0-3 cm de profundidade.A survey of root diseases of wheat (Triticum aestivum L.) in some regions of the State of Mato Grosso do Sul, Brazil, showed the occurrence of common root rot in those areas. The main pathogen associated with the disease was Cochliobolus sativus. The disease incidence was slight in most of the yields sampled. In general, the spore population of this organism in the soil was low and, in most fields, it was higher in the surface layer of 0-3 cm

Interpreting doubly special relativity as a modified theory of measurement

In this article we develop a physical interpretation for the deformed (doubly) special relativity theories (DSRs), based on a modification of the theory of measurement in special relativity. We suggest that it is useful to regard the DSRs as reflecting the manner in which quantum gravity effects induce Planck-suppressed distortions in the measurement of the "true" energy and momentum. This interpretation provides a framework for the DSRs that is manifestly consistent, non-trivial, and in principle falsifiable. However, it does so at the cost of demoting such theories from the level of "fundamental" physics to the level of phenomenological models -- models that should in principle be derivable from whatever theory of quantum gravity one ultimately chooses to adopt.Comment: 18 pages, plain LaTeX2

Trapped gravitational wave modes in stars with R>3M

The possibility of trapped modes of gravitational waves appearing in stars with R>3M is considered. It is shown that the restriction to R<3M in previous studies of trapped modes, using uniform density models, is not essential. Scattering potentials are computed for another family of analytic stellar models showing the appearance of a deep potential well for one model with R>3M. However, the provided example is unstable, although it has a more realistic equation of state in the sense that the sound velocity is finite. On the other hand it is also shown that for some stable models belonging to the same family but having R<3M, the well is significantly deeper than that of the uniform density stars. Whether there are physically realistic equations of state which allow stable configurations with trapped modes therefore remains an open problem.Comment: 10 pages, 3 figures, LaTeX2

Optical geometry for gravitational collapse and Hawking radiation

The notion of optical geometry, introduced more than twenty years ago as a formal tool in quantum field theory on a static background, has recently found several applications to the study of physical processes around compact objects. In this paper we define optical geometry for spherically symmetric gravitational collapse, with the purpose of extending the current formalism to physically interesting spacetimes which are not conformally static. The treatment is fully general but, as an example, we also discuss the special case of the Oppenheimer-Snyder model. The analysis of the late time behaviour shows a close correspondence between the structure of optical spacetime for gravitational collapse and that of flat spacetime with an accelerating boundary. Thus, optical geometry provides a natural physical interpretation for derivations of the Hawking effect based on the ``moving mirror analogy.'' Finally, we briefly discuss the issue of back-reaction in black hole evaporation and the information paradox from the perspective of optical geometry.Comment: 13 pages, 10 figures, aps, revtex, To be published in PR

Holonomy in the Schwarzschild-Droste Geometry

Parallel transport of vectors in curved spacetimes generally results in a deficit angle between the directions of the initial and final vectors. We examine such holonomy in the Schwarzschild-Droste geometry and find a number of interesting features that are not widely known. For example, parallel transport around circular orbits results in a quantized band structure of holonomy invariance. We also examine radial holonomy and extend the analysis to spinors and to the Reissner-Nordstr\"om metric, where we find qualitatively different behavior for the extremal ($Q = M$) case. Our calculations provide a toolbox that will hopefully be useful in the investigation of quantum parallel transport in Hilbert-fibered spacetimes.Comment: 18 Latex pages, 3 figures. Second replacement. This version as published in CQG with some misprints correcte

Does Quantum Mechanics Clash with the Equivalence Principle - and Does it Matter?

With an eye on developing a quantum theory of gravity, many physicists have recently searched for quantum challenges to the equivalence principle of general relativity. However, as historians and philosophers of science are well aware, the principle of equivalence is not so clear. When clarified, we think quantum tests of the equivalence principle won't yield much. The problem is that the clash/not-clash is either already evident or guaranteed not to exist. Nonetheless, this work does help teach us what it means for a theory to be geometric.Comment: 12 page

Excited by a quantum field: Does shape matter?

The instantaneous transition rate of an arbitrarily accelerated Unruh-DeWitt particle detector on four-dimensional Minkowski space is ill defined without regularisation. We show that Schlicht's regularisation as the zero-size limit of a Lorentz-function spatial profile yields a manifestly well-defined transition rate with physically reasonable asymptotic properties. In the special case of stationary trajectories, including uniform acceleration, we recover the results that have been previously obtained by a regularisation that relies on the stationarity. Finally, we discuss evidence for the conjecture that the zero-size limit of the transition rate is independent of the detector profile.Comment: 7 pages, uses jpconf. Talk given at NEB XII (Nafplio, Greece, 29 June - 2 July 2006

Space--time fluctuations and the spreading of wavepackets

Using a density matrix description in space we study the evolution of wavepackets in a fluctuating space-time background. We assume that space-time fluctuations manifest as classical fluctuations of the metric. From the non-relativistic limit of a non-minimally coupled Klein-Gordon equation we derive a Schr\"odinger equation with an additive gaussian random potential. This is transformed into an effective master equation for the density matrix. The solutions of this master equation allow to study the dynamics of wavepackets in a fluctuating space-time, depending on the fluctuation scenario. We show how different scenarios alter the diffusion properties of wavepackets.Comment: 11 page