Causal Anomalies in Kaluza-Klein Gravity Theories

Causal anomalies in two Kaluza-Klein gravity theories are examined, particularly as to whether these theories permit solutions in which the causality principle is violated. It is found that similarly to general relativity the field equations of the space-time-mass Kaluza-Klein (STM-KK) gravity theory do not exclude violation of causality of G\"odel type, whereas the induced matter Kaluza-Klein (IM-KK) gravity rules out noncausal G\"odel-type models. The induced matter version of general relativity is shown to be an efficient therapy for causal anomalies that occurs in a wide class of noncausal geometries. Perfect fluid and dust G\"odel-type solutions of the STM-KK field equations are studied. It is shown that every G\"odel-type perfect fluid solution is isometric to the unique dust solution of the STM-KK field equations. The question as to whether 5-D G\"odel-type non-causal geometries induce any physically acceptable 4-D energy-momentum tensor is also addressed.Comment: 16 page. LaTex file. To appear in Int. J. Mod. Phys. A (1998

Topological Reverberations in Flat Space-times

We study the role played by multiply-connectedness in the time evolution of the energy E(t) of a radiating system that lies in static flat space-time manifolds M_4 whose t=const spacelike sections M_3 are compact in at least one spatial direction. The radiation reaction equation of the radiating source is derived for the case where M_3 has any non-trivial flat topology, and an exact solution is obtained. We also show that when the spacelike sections are multiply-connected flat 3-manifolds the energy E(t) exhibits a reverberation pattern with discontinuities in the derivative of E(t) and a set of relative minima and maxima, followed by a growth of E(t). It emerges from this result that the compactness in at least one spatial direction of Minkowski space-time is sufficient to induce this type of topological reverberation, making clear that our radiating system is topologically fragile. An explicit solution of the radiation reaction equation for the case where M_3 = R^2 x S^1 is discussed, and graphs which reveal how the energy varies with the time are presented and analyzed.Comment: 16 pages, 4 figures, REVTEX; Added five references and inserted clarifying details. Version to appear in Int. J. Mod. Phys. A (2000

Measurement errors and uncertainty estimation of an experimental set up using a 2D PIV technique

The study of the flow interaction and the heat transfer between air jets and a surface is of paramount importance in industrial processes that apply multiple air jet impingement. To ensure a good performance of the process, high heat transfer rates and uniformization of the flow over the target plate are required. To perform this analysis, a PIV technique was implemented for the measurement of the velocity fields of the flow. However, as any real experiment, the values recorded by the PIV method are subjected to several errors that compromise the reliability and accuracy of the measurements. These errors can have different sources, from the installation and alignment to the particles seeding and calibration procedure. To determine an interval that contains the measurement error, the uncertainty quantification is crucial. In that sense, this paper focus on the identification of measurement errors and uncertainty quantification of an experimental set up specially built for the analysis of the interaction between a non-isothermal jets and non-flat surfaces moving perpendicularly to the jet axis. To ensure the reliability of the results, preliminary tests were performed to guarantee a uniform and stable flow and to determine the range and conditions of operation. In addition, this work presents an analysis of the system, and the source of errors are identified, quantified and, when possible, corrected. The particle seeding, which consists of olive oil droplets, is characterized and its efficiency for the flow tracking is analysed. The test facility was tested to fully characterize the flow field in terms of mean velocity profile and turbulence intensity over a wide range of Reynolds numbers and temperature. Several velocity fields are then measured until convergence of the flow quantities is reached. The combination of these measurements with high spatial resolution and low measurement errors allow to obtain accurate and precise measurement values.Portuguese Foundation for Science and Technology (FCT) through the Research Grant PD/BD/128216/2016. This work has been supported by FCT within the Project Scope UID/CEC/00319/2019 (ALGORITMI) and Project Scope UID/EMS/04077/2019 (METRICS)

Signature for the Shape of the Universe

If the universe has a nontrivial shape (topology) the sky may show multiple correlated images of cosmic objects. These correlations can be couched in terms of distance correlations. We propose a statistical quantity which can be used to reveal the topological signature of any Robertson-Walker (RW) spacetime with nontrivial topology. We also show through computer-aided simulations how one can extract the topological signatures of flat, elliptic, and hyperbolic RW universes with nontrivial topology.Comment: 11 pages, 3 figures, LaTeX2e. This paper is a direct ancestor of gr-qc/9911049, put in gr-qc archive to make it more accessibl

Contribute to a Definition of Extensive Grazing (Mediterranean)

The subject of this paper is a definition of Extensive Grazing from Extensive Systems of Animal Production in Mediterranean environments. The edaphoclimatic characterization is essential to understand the low level of primary productivity as a consequence of irregular precipitation over the year and its absence during the long, dry and hot summer. The powerless of soils justify the limited contribution of plants and make clear the necessary recovery of the soil and storage of water naturally (soil) or artificially (irrigation). Considering the IPBES (Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services) definition of extensive grazing it has been used the National Statistics from 1999 – 2019 to calculate the Portuguese Stocking Rates related with pasture and forage production which means the potential productivity of each region. The correlations between these criterions are at the base of the definition of stocking rates. The systems of extensive animal production have been characterized in two distinct regions: the south, with larger farms and the feeding scheme of extensive animal production adapted and the north, with small farms and fluxes evolved in production system where the forage is replaced by “lameiros”(small parcels in rich/wet soils of swards of grass-legume mixtures of forage). Clearly the effects of management differed between regions. Local breeds of all domestic animal species are well adapted to these specific systems of production and higher levels of productivity can be achieved by crossing with selected pure breeds. The evaluation of environmental sustainability was calculated by C sequestration and GEE effects on global warming and finally the Balance of Energy of the system have been the indicators to use for the classification of the system. The conclusions refer that stoking rates cannot surpass 1,4 NH/ha with a feeding scheme based on natural resources and forage products. When stoking rates surpass this value, systems should have GEE balance below 0 and BE upper 1

Introdução e avaliação de forrageiras no município de Santana do Araguaia, Estado do Pará.

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pH influence on oxygen mass transfer coefficient in a bubble column. Individual characterization of kL and a

Experiments were performed in a laboratory scale bubble column (10 L), to investigate the pH influence on oxygen mass transfer coefficient, in order to achieve a better control of biological processes. The liquid-side mass transfer coefficient, kL, and the specific interfacial area, a, were studied individually. The specific interfacial area was obtained using the new automatic image analysis technique developed by Ferreira et al. (2012). The pH was changed by the addition to the system of the most common acids and base used in biological process: hydrochloric acid (HCl), phosphoric acid (H3PO4) and potassium hydroxide (KOH). The results show that aqueous systems containing HCl, H3PO4 or KOH present lower volumetric liquid side mass transfer coefficient, kLa, in relation to pure systems (distilled water), this decrease being not linear. It was found that the specific interfacial area presents higher values in KOH and HCl solutions in comparison with distilled water. However, an opposite behavior was observed in the liquid-side mass transfer coefficient values. The kL behavior on the impure systems was explained based on bubble surface contamination. Higbie's and Fröessling's equations were adapted in the present work in order to be used in bubble dispersion systems

Resposta de pastagem degradada de capim-colonião a consorciação com leguminosas e fertilização com fósforo, enxofre e micronutrientes.

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