2,030 research outputs found
Probing Yukawian gravitational potential by numerical simulations. I. Changing N-body codes
In the weak field limit general relativity reduces, as is well known, to the
Newtonian gravitation. Alternative theories of gravity, however, do not
necessarily reduce to Newtonian gravitation; some of them, for example, reduce
to Yukawa-like potentials instead of the Newtonian potential. Since the
Newtonian gravitation is largely used to model with success the structures of
the universe, such as for example galaxies and clusters of galaxies, a way to
probe and constrain alternative theories, in the weak field limit, is to apply
them to model the structures of the universe. In the present study, we consider
how to probe Yukawa-like potentials using N-body numerical simulations.Comment: 17 pages, 11 figures. To appear in General Relativity and Gravitatio
Multi-filter transit observations of WASP-39b and WASP-43b with three San Pedro M\'artir telescopes
Three optical telescopes located at the San Pedro M\'artir National
Observatory were used for the first time to obtain multi-filter defocused
photometry of the transiting extrasolar planets WASP-39b and WASP-43b. We
observed WASP-39b with the 2.12m telescope in the U filter for the first time,
and additional observations were carried out in the R and I filters using the
0.84m telescope. WASP-43b was observed in VRI with the same instrument, and in
the i filter with the robotic 1.50m telescope. We reduced the data using
different pipelines and performed aperture photometry with the help of custom
routines, in order to obtain the light curves. The fit of the light curves
(1.5--2.5mmag rms), and of the period analysis, allowed a revision of the
orbital and physical parameters, revealing for WASP-39b a period ( days) which is seconds larger than
previously reported. Moreover, we find for WASP-43b a planet/star radius
() which is larger in the i filter
with respect to previous works, and that should be confirmed with additional
observations. Finally, we confirm no evidence of constant period variations in
WASP-43b.Comment: 13 pages, 7 figures, accepted in PASP, scheduled for the February 1,
2015 issu
Semi-field assessment of the BG-Malaria trap for monitoring the African malaria vector, Anopheles arabiensis
Odour-baited technologies are increasingly considered for effective monitoring of mosquito populations and for the evaluation of vector control interventions. The BG-Malaria trap (BGM), which is an upside-down variant of the widely used BG-Sentinel trap (BGS), has been demonstrated to be effective to sample the Brazilian malaria vector, Anopheles darlingi. We evaluated the BGM as an improved method for sampling the African malaria vectors, Anopheles arabiensis. Experiments were conducted inside a large semi-field cage to compare trapping efficiencies of BGM and BGS traps, both baited with the synthetic attractant, Ifakara blend, supplemented with CO2. We then compared BGMs baited with either of four synthetic mosquito lures, Ifakara blend, Mbita blend, BG-lure or CO2, and an unbaited BGM. Lastly, we compared BGMs baited with the Ifakara blend dispensed via either nylon strips, BG cartridges (attractant-infused microcapsules encased in cylindrical plastic cartridge) or BG sachets (attractant-infused microcapsules encased in plastic sachets). All tests were conducted between 6P.M. and 7A.M., with 200–600 laboratory-reared An. arabiensis released nightly in the test chamber. The median number of An. arabiensis caught by the BGM per night was 83, IQR:(73.5–97.75), demonstrating clear superiority over BGS (median catch = 32.5 (25.25–37.5)). Compared to unbaited controls, BGMs baited with Mbita blend caught most mosquitoes (45 (29.5–70.25)), followed by BGMs baited with CO2 (42.5 (27.5–64)), Ifakara blend (31 (9.25–41.25)) and BG lure (16 (4–22)). BGM caught 51 (29.5–72.25) mosquitoes/night, when the attractants were dispensed using BG-Cartridges, compared to BG-Sachet (29.5 (24.75–40.5)), and nylon strips (27 (19.25–38.25)), in all cases being significantly superior to unbaited controls (p < 000.1). The findings demonstrate potential of the BGM as a sampling tool for African malaria vectors over the standard BGS trap. Its efficacy can be optimized by selecting appropriate odour baits and odour-dispensing systems
Irrigation efficiency and water-policy implications for river basin resilience
Rising demand for food, fiber, and biofuels drives
expanding irrigation withdrawals from surface water and groundwater. Irrigation
efficiency and water savings have become watchwords in response to
climate-induced hydrological variability, increasing freshwater demand for
other uses including ecosystem water needs, and low economic productivity of
irrigation compared to most other uses. We identify three classes of
unintended consequences, presented here as paradoxes. Ever-tighter cycling
of water has been shown to increase resource use, an example of the
<i>efficiency paradox</i>. In the absence of effective policy to
constrain irrigated-area expansion using "saved water", efficiency can
aggravate scarcity, deteriorate resource quality, and impair river basin
resilience through loss of flexibility and redundancy. Water scarcity and
salinity effects in the lower reaches of basins (symptomatic of the
<i>scale paradox</i>) may partly be offset over the short-term through
groundwater pumping or increasing surface water storage capacity. However,
declining ecological flows and increasing salinity have important
implications for riparian and estuarine ecosystems and for non-irrigation
human uses of water including urban supply and energy generation, examples
of the <i>sectoral paradox</i>. This paper briefly considers three
regional contexts with broadly similar climatic and water-resource
conditions – central Chile, southwestern US, and south-central
Spain – where irrigation efficiency directly influences basin resilience.
The comparison leads to more generic insights on water policy in relation to
irrigation efficiency and emerging or overdue needs for environmental protection
Enfoque multiobjetivo para determinação de Benchmarks de companhias aéreas brasileiras DEA-ineficientes.
Este trabalho usa os resultados obtidos no modelo de Análise de Envoltória de Dados que determina quais as companhias aéreas brasileiras eficientes em vendas, no triênio 1998-1999-2000. Ao invés de serem exploradas as caracterÃsticas das companhias eficientes, pretende-se mostras opções de melhora paras as companhias ineficientes, através das companhias que lhes servem de referência (benchmarks). Tal procedimento utiliza um enfoque de Programação Linear Multiobjeto, devido a algumas limitações dos modelos DEA clássicos. Este enfoque permite a escolha de uma meta dentre um conjunto possÃvel de empresas eficiente
Wide Localized Solitons in Systems with Time and Space-Modulated Nonlinearities
In this work we apply point canonical transformations to solve some classes
of nonautonomous nonlinear Schr\"{o}dinger equation namely, those which possess
specific cubic and quintic - time and space dependent - nonlinearities. In this
way we generalize some procedures recently published which resort to an ansatz
to the wavefunction and recover a time and space independent nonlinear equation
which can be solved explicitly. The method applied here allow us to find wide
localized (in space) soliton solutions to the nonautonomous nonlinear
Schr\"{o}dinger equation, which were not presented before. We also generalize
the external potential which traps the system and the nonlinearities terms.Comment: 19 pages, 5 figure
A geometrical approach for fuzzy DEA frontiers.
Interval DEA frontiers are here used in situation where one input or output is subject to uncertainty in its measurement and is presented as an interval data. We built an efficient frontier without any assumption about the probability distribution function of the imprecise variable. We take into account only the minimum and the maximum values of each imprecise variable. Two frontiers are constructed: the optimistic and the pessimistic ones. We use fuzszy relationships to introduce a new efficiency index based on a set of some Fuzzy T Norms. We will explore only the case where only on single variable presents a certain degree of uncertainty
Probing Yukawian Gravitational Potential by Numerical Simulations. II. Elliptical Galaxies
Since the Newtonian gravitation is largely used to model with success the
structures of the universe, such as galaxies and clusters of galaxies, for
example, a way to probe and constrain alternative theories, in the weak field
limit, is to apply them to model the structures of the universe. We then
modified the well known Gadget-2 code to probe alternative theories of
gravitation through galactic dynamics. In particular, we modified the Gadget-2
code to probe alternatives theories whose weak field limits have a Yukawa-like
gravitational potential. As a first application of this modified Gadget-2 code
we simulate the evolution of elliptical galaxies. These simulations show that
galactic dynamics can be used to constrain the parameters associated with
alternative theories of gravitation.Comment: 6 pages, 5 figures - To appear in General Relativity and Gravitatio
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