457 research outputs found
Technical solutions to prevent heat stress induced crop growth reduction for three climatic regions in Mexico
In the last 15 years a significant increase in greenhouse area has occurred in Mexico, from a modest 50 hectares in 1990 to over 2,000 hectares in 2004. The rapid increase in greenhouse area is a result of an attractive export market, USA. Mexican summer midday temperatures are well above crop optimum and cooling is needed if heat stress induced crop growth reduction is to be prevented. The objective of this study was to determine the effectiveness and feasibility of greenhouse cooling systems for tomato culture under desert, humid tropic and temperate Mexican weather conditions. These climate regions are represented by Mexicali, Merida and Huejutla respectively. The cooling systems included a variety of passive and active systems, which through an engineering design methodology were combined to suit the climate conditions of the 3 regions. The evaluation was conducted via simulation, taking into account the most important temperature effects on crop growth and yield. The results showed that the cooling systems were effective in decreasing heat stress to plants. Investment costs of greenhouse with cooling equipment were under USD 50 m-2 and operational costs were under USD 10 m-2 for all equipment combinations and treatments except for the humid tropic climate of Merida. Solutions for Merida were both economically and physically not feasible due to too high humidity levels. This model study clearly indicates that cooling is feasible in desert and moderate climate regions of Mexico but in humid tropic climate regions feasibility is a problem. Application of design methodology and design evaluation with help of simulation greatly contributed to pointing out effective and non-effective solutions to reduce heat stress in hot climates
Near-Horizon geometry from flux compactification
We study the conditions an arbitrary flux configuration must fulfill in order
to construct a 4d space-time of the type from a type IIB
supergravity flux compactification in which NS-NS fluxes are included. We
present a solution consisting on a compactification in the presence of 3-form
NS-NS and RR fluxes. The internal manifold is a SU(3) structure six-dimensional
manifold, with null curvature and with torsion. By preserving two
supersymmetries in the four-dimensional low energy theory, we find a way to
obtain the geometry as a near-horizon solution by
compactification in non-Calabi-Yau manifolds.Comment: Version accepted for publication in Physical Review
ABC-based Forecasting in State Space Models
Approximate Bayesian Computation (ABC) has gained popularity as a method for
conducting inference and forecasting in complex models, most notably those
which are intractable in some sense. In this paper we use ABC to produce
probabilistic forecasts in state space models (SSMs). Whilst ABC-based
forecasting in correctly-specified SSMs has been studied, the misspecified case
has not been investigated, and it is that case which we emphasize. We invoke
recent principles of 'focused' Bayesian prediction, whereby Bayesian updates
are driven by a scoring rule that rewards predictive accuracy; the aim being to
produce predictives that perform well in that rule, despite misspecification.
Two methods are investigated for producing the focused predictions. In a
simulation setting, 'coherent' predictions are in evidence for both methods:
the predictive constructed via the use of a particular scoring rule predicts
best according to that rule. Importantly, both focused methods typically
produce more accurate forecasts than an exact, but misspecified, predictive. An
empirical application to a truly intractable SSM completes the paper
Interferometry with Photon-Subtracted Thermal Light
We propose and implement a quantum procedure for enhancing the sensitivity
with which one can determine the phase shift experienced by a weak light beam
possessing thermal statistics in passing through an interferometer. Our
procedure entails subtracting exactly one (which can be generalized to m)
photons from the light field exiting an interferometer containing a
phase-shifting element in one of its arms. As a consequence of the process of
photon subtraction, and somewhat surprisingly, the mean photon number and
signal-to-noise ratio of the resulting light field are thereby increased,
leading to enhanced interferometry. This method can be used to increase
measurement sensitivity in a variety of practical applications, including that
of forming the image of an object illuminated only by weak thermal light
Utilizing optical transition edge sensors and superconducting nanowire single photon detectors in quantum optics
We present the current state-of-the art of single-photon detection in quantum optics using high-efficiency superconducting single photon detectors, the implementation of highefficiency sources and the measurement of large photon number squeezing in waveguides
Carbon sequestration and ecosystem services potential in a fragmented landscape in the Atlantic forest, Rio de Janeiro.
Magnetic characterization of Fe, Ni, Co nanoparticles dispersed in phyllosilicate type silicon oxide
International audienceWe present the magnetic properties of silica-supported metal (Fe,catalyst) nanoparticles synthesized by precipitation of metal nitrate in ammonia-based medium. Our goal is the study of possible metal-support interactions in the nanoporous catalyst. The temperature dependence of the magnetization for all samples display spin-glass like behavior below c.a. 11-12 K, with clear Curie-Weiss dependence in the high-temperature regime. Spin-glass-like behavior was inferred from dynamic AC susceptibility data after analyzing the frequency-dependence of the in-phase component χ'(f) by the expression W = ΔTf/[Tf Δlog(f)] = 3.0 × 10−3. We found that the magnetic behavior of the catalyst is drastically affected by the existence of interactions between the metal and the support
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