17,161 research outputs found
Variability of the chemical index of alteration (CIA) in the Paraná River suspended load
Variability of the chemical index of alteration (CIA) in the Paraná River suspended loa
Transit Lightcurve Signatures of Artificial Objects
The forthcoming space missions, able to detect Earth-like planets by the
transit method, will a fortiori also be able to detect the transit of
artificial planet-size objects. Multiple artificial objects would produce
lightcurves easily distinguishable from natural transits. If only one
artificial object transits, detecting its artificial nature becomes more
difficult. We discuss the case of three different objects (triangle, 2-screen,
louver-like 6-screen) and show that they have a transit lightcurve
distinguishable from the transit of natural planets, either spherical or
oblate, although an ambiguity with the transit of a ringed planet exists in
some cases. We show that transits, especially in the case of multiple
artificial objects, could be used for the emission of attention-getting
signals, with a sky coverage comparable to the laser pulse method. The large
number of expected planets (several hundreds) to be discovered by the transit
method by next space missions will allow to test these ideas.Comment: Accepted for publication in ApJ. Manuscript: 17 pages, 8 figure
Dynamical Selection of the Primordial Density Fluctuation Amplitude
In inflationary models, the predicted amplitude of primordial density
perturbations Q is much larger than the observed value (~10^{-5}) for natural
choices of parameters. To explain the requisite exponential fine-tuning,
anthropic selection is often invoked, especially in cases where microphysics is
expected to produce a complex energy landscape. By contrast, we find examples
of ekpyrotic models based on heterotic M-theory for which dynamical selection
naturally favors the observed value of Q.Comment: 4 pages; v2: version to be published in PR
Slices, slabs, and sections of the unit hypercube
Using combinatorial methods, we derive several formulas for the volume of
convex bodies obtained by intersecting a unit hypercube with a halfspace, or
with a hyperplane of codimension 1, or with a flat defined by two parallel
hyperplanes. We also describe some of the history of these problems, dating to
Polya's Ph.D. thesis, and we discuss several applications of these formulas.Comment: 11 pages; minor corrections to reference
Diversity in the Phoenix Universe
It has recently been argued by Copeland et al. that in eleven dimensions two
orbifold planes can collide and bounce in a regular way, even when the bulk
metric is perturbed away from Milne spacetime to a Kasner solution. In this
paper, we point out that as a consequence the global "phoenix" structure of the
cyclic universe is significantly enriched. Spatially separated regions, with
different density fluctuation amplitudes as well as different non-gaussian
characteristics, are all physically realized. Those regions containing by far
the most structure are specified by a fluctuation amplitude of Q ~ 10^{-4.5}
and local non-gaussianity parameters f_{NL} ~ O(+/- 10) and g_{NL} ~ O(-10^3),
in agreement with current observations.Comment: 20 pages, 3 figure
Deterministic-statistical model coupling in a DSS for river-basin management
This paper presents a method for appropriate coupling of deterministic and statistical models. In the decision-support system for the Elbe river, a conceptual rainfall-runoff model is used to obtain the discharge statistics and corresponding average number of flood days, which is a key input variable for a rule-based model for floodplain vegetation. The required quality of the discharge time series cannot be determined by a sensitivity analysis because a deterministic model is linked to a statistical model. To solve the problem, artificial discharge time series are generated that mimic the hypothetical output of rainfall-runoff models of different accuracy. The results indicate that a feasible calibration of the rainfall-runoff model is sufficient to obtain consistency with the vegetation model in view of its sensitivity to changes in the number of flood days in the floodplains
Multidimensional entropic uncertainty relation based on a commutator matrix in position and momentum spaces
The uncertainty relation for continuous variables due to Byalinicki-Birula
and Mycielski expresses the complementarity between two -uples of
canonically conjugate variables and in terms of Shannon differential entropy. Here, we consider the
generalization to variables that are not canonically conjugate and derive an
entropic uncertainty relation expressing the balance between any two
-variable Gaussian projective measurements. The bound on entropies is
expressed in terms of the determinant of a matrix of commutators between the
measured variables. This uncertainty relation also captures the complementarity
between any two incompatible linear canonical transforms, the bound being
written in terms of the corresponding symplectic matrices in phase space.
Finally, we extend this uncertainty relation to R\'enyi entropies and also
prove a covariance-based uncertainty relation which generalizes Robertson
relation.Comment: 8 pages, 1 figur
Toward an understanding of household vulnerability in rural Kenya
Considerations of risk and vulnerability are key to understanding the dynamics of poverty. This study conceives vulnerability as expected poverty and illustrates a methodology to empirically assess household vulnerability using pseudo panel data derived from repeated cross sections augmented with historical information on shocks. Application of the methodology to data from rural Kenya shows that in 1994 rural households faced on average a 40 percent chance of becoming poor in the future. Households in arid areas that experience large rainfall volatility appear more vulnerable than those in non-arid areas, where malaria emerges as a key risk factor. Idiosyncratic shocks also cause non-negligible consumption volatility. Possession of cattle and sheep/goats appears ineffective in protecting consumption against covariant shocks, though sheep/goat help reduce the effect of idiosyncratic shocks, especially in arid zones. Of the policy instruments simulated, interventions directed at reducing the incidence of malaria, promoting adult literacy, and improving market accessibility hold most promise to reduce vulnerability.Financial Intermediation,Environmental Economics&Policies,Economic Theory&Research,Health Economics&Finance,Housing&Human Habitats,Environmental Economics&Policies,Health Economics&Finance,Inequality,Financial Intermediation,Economic Theory&Research
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