No-horizon theorem for spacetimes with spacelike G1 isometry groups

We consider four-dimensional spacetimes $(M,{\mathbf g})$ which obey the Einstein equations ${\mathbf G}={\mathbf T}$, and admit a global spacelike $G_{1}={\mathbb R}$ isometry group. By means of dimensional reduction and local analyis on the reduced (2+1) spacetime, we obtain a sufficient condition on ${\mathbf T}$ which guarantees that $(M,{\mathbf g})$ cannot contain apparent horizons. Given any (3+1) spacetime with spacelike translational isometry, the no-horizon condition can be readily tested without the need for dimensional reduction. This provides thus a useful and encompassing apparent horizon test for $G_{1}$-symmetric spacetimes. We argue that this adds further evidence towards the validity of the hoop conjecture, and signals possible violations of strong cosmic censorship.Comment: 8 pages, LaTeX, uses IOP package; published in Class. Quantum Gra

One-loop effective potential for scalar and vector fields on higher dimensional noncommutative flat manifolds

The effective potentials for massless scalar and vector quantum field theories on D dimensional manifolds with p compact noncommutative extra dimensions are evaluated by means of dimensional regularization implemented by zeta function techniques. It is found that the zeta function associated with the one-loop operator may not be regular at the origin. Thus, the related heat-kernel trace has a logarithmic term in the short t asymptotics expansion. Consequences of this fact are briefly discussed.Comment: 9 pages, Latex AMS style, typos corrected, numerical coefficients corrected, references adde

Vacuum energy for the supersymmetric twisted D-brane in constant electromagnetic field

We calculate vacuum energy for twisted SUSY D-brane on toroidal background with constant magnetic or constant electric field. Its behaviour for toroidal D-brane (p=2) in constant electric field shows the presence of stable minimum for twisted versions of the theory. That indicates such a background maybe reasonable groundstate.Comment: LaTeX, 10 page

Hysteretic Optimization For Spin Glasses

The recently proposed Hysteretic Optimization (HO) procedure is applied to the 1D Ising spin chain with long range interactions. To study its effectiveness, the quality of ground state energies found as a function of the distance dependence exponent, $\sigma$, is assessed. It is found that the transition from an infinite-range to a long-range interaction at $\sigma=0.5$ is accompanied by a sharp decrease in the performance . The transition is signaled by a change in the scaling behavior of the average avalanche size observed during the hysteresis process. This indicates that HO requires the system to be infinite-range, with a high degree of interconnectivity between variables leading to large avalanches, in order to function properly. An analysis of the way auto-correlations evolve during the optimization procedure confirm that the search of phase space is less efficient, with the system becoming effectively stuck in suboptimal configurations much earlier. These observations explain the poor performance that HO obtained for the Edwards-Anderson spin glass on finite-dimensional lattices, and suggest that its usefulness might be limited in many combinatorial optimization problems.Comment: 6 pages, 9 figures. To appear in JSTAT. Author website: http://www.bgoncalves.co

Controle integrado de plantas invasoras em pastagens cultivadas no município de Terra Alta, Nordeste paraense.

bitstream/item/48597/1/Boletim-PD-25-AMAZ-ORIENTAL.pd

Competição de gramíneas forrageiras em relação a ervas invasoras de pastagens em Porto Velho-RO.

O presente trabalho teve por finalidade testar métodos de controle e gramíneas mais competitivas com as ervas invasoras, visando minimizar os custos de seu controle em sistemas integrados.bitstream/item/56193/1/COT1602-0001.pd

Measured and perceived physical responses in multidimensional fitness training through exergames in older adults

Exergames have been used to increase physical activity levels to produce health benefits in older adults. However, only a small number of studies have quantified the physical activity levels produced by custom-made Exergames and their capacity to elicit recommended levels of exercise. This study investigates the effectiveness of custom-made Exergames, designed for multidimensional fitness training, in eliciting recommended levels of exercise. We rely on both objective (accelerometry) and subjective (perceived exertion) information collected in two different modalities of exercise, consisting of 40- minutes sessions: Exergaming and conventional training (Control). A between-subjects analysis was done involving two groups of active older adults (n=33). Participants in the Control Between condition performed physical activity in conventional group fitness training, while the intervention group used individualized Exergaming as training modality. In addition, a sub-group of the Exergaming participants also performed a conventional training session (Control-Within), which enabled a within-subjects comparison. Results show that participants spent significantly more time in moderate-to-vigorous intensities during Exergaming, interestingly, perceiving significantly lower exertion levels. The between-subjects analysis only presented statistically significant differences for the perceived exertion scale. This study helps to unveil the impact of custom-made Exergames in physical activity levels during training when compared to conventional training for the older adult population.info:eu-repo/semantics/publishedVersio

CORRELATION BETWEEN LEIDENFROST TEMPERATURE, COOLING CAPACITY AND MACHINING TEMPERATURE: AN EXPERIMENTAL STUDY OF CUTTING FLUIDS

Much of the energy consumed by machining materials is converted into heat, which causes several technical and economic problems for the process. The cutting fluid application by the conventional method forms a vapor film of low thermal conductivity, which prevents direct contact between the fluid and the heated surface; the so-called Leidenfrost effect, which reduces cooling efficiency. Studies of this phenomenon applied to the machining of materials are still very restricted and scarce. In this sense, the present work experimentally studied the correlation of parameters Leidenfrost temperature, cooling capacity and machining temperatures, applied to the SAE 52100 steel turning process with conventional lubri-coolant, with different cutting fluids. The thermal properties of the studied cutting fluids were taken from the technical-scientific literature. An experimental apparatus was developed for measuring and acquiring machining temperatures. Synthetic cutting fluids were shown to have a better cooling capacity, followed by semi-synthetic fluids and emulsions. There is no relationship between Leidenfrost temperature, cooling capacity, and machining temperatures for the different types of cutting fluids studied

Automating senior fitness testing through gesture detection with depth sensors

Sedentarism has a negative impact on health, life expectancy and quality of life, especially in older adults. The assessment of functional fitness helps evaluating the effects of ageing and sedentarism, and this assessment is typically done through validated battery tests such as the Senior Fitness Test (SFT). In this paper we present a computer-based system for assisting and automating SFT administration and scoring in the elderly population. Our system assesses lower body strength, agility and dynamic balance, and aerobic endurance making use of a depth sensor for body tracking and multiple gesture detectors for the evaluation of movement execution. The system was developed and trained with optimal data collected in laboratory conditions and its performance was evaluated in a real environment with 22 elderly end-users, and compared to traditional SFT administered by an expert. Results show a high accuracy of our system in identifying movement patterns (>95%) and consistency with the traditional fitness assessment method. Our results suggest that this technology is a viable low cost option to assist in the fitness assessment of elderly that could be deployed for at home use in the context of fitness programs.info:eu-repo/semantics/publishedVersio