5,818 research outputs found
Study of the average vertical distribution of temperature in the martian atmosphere final report
Convective-radiative equilibrium model for computing temperature profile - vertical temperature distribution in Martian atmospher
Burley tobacco clubs in Malawi : nonmarket institutions for exports
This paper studies nonmarket institutions that facilitate exports. In Malawi, as in many other developing countries, farmers face numerous constraints that disconnect them from export markets. The paper explores the role of a local institution, the burley tobacco clubs, in bridging smallholders to exports. Burley clubs potentially enable farmers to increase their tobacco farming productivity by providing services related to institutional access, collective action, economies of scale, and supporting network. Using matching methods and instrumental variable techniques, the authors find that tobacco club membership causes an increase of between 40-74 percent in output per acre and an increase of between 45-89 percent in tobacco sales per acre. Instead, neither the land share allocated to tobacco nor the unit value obtained by the producers is affected by club membership.Tobacco Use and Control,Alcohol and Substance Abuse,Crops&Crop Management Systems,Adolescent Health,Access to Finance
One pion production in neutrino-nucleon scattering and the different parametrizations of the weak vertex
The weak vertex provides an important contribution to the one
pion production in neutrino-nucleon and neutrino-nucleus scattering for
invariant masses below 1.4 GeV. Beyond its interest as a tool in neutrino
detection and their background analyses, one pion production in
neutrino-nucleon scattering is useful to test predictions based on the quark
model and other internal symmetries of strong interactions. Here we try to
establish a connection between two commonly used parametrizations of the weak
vertex and form factors (FF) and we study their effects on the
determination of the axial coupling , the common normalization of the
axial FF, which is predicted to hold 1.2 by using the PCAC hypothesis.
Predictions for the total cross sections within
the two approaches, which include the resonant and other
background contributions in a coherent way, are compared to experimental data.Comment: Submitted to Physics Letters
Multiplicative Lidskii's inequalities and optimal perturbations of frames
In this paper we study two design problems in frame theory: on the one hand,
given a fixed finite frame \cF for \hil\cong\C^d we compute those dual
frames \cG of \cF that are optimal perturbations of the canonical dual
frame for \cF under certain restrictions on the norms of the elements of
\cG. On the other hand, for a fixed finite frame \cF=\{f_j\}_{j\in\In} for
\hil we compute those invertible operators such that is a
perturbation of the identity and such that the frame V\cdot
\cF=\{V\,f_j\}_{j\in\In} - which is equivalent to \cF - is optimal among
such perturbations of \cF. In both cases, optimality is measured with respect
to submajorization of the eigenvalues of the frame operators. Hence, our
optimal designs are minimizers of a family of convex potentials that include
the frame potential and the mean squared error. The key tool for these results
is a multiplicative analogue of Lidskii's inequality in terms of
log-majorization and a characterization of the case of equality.Comment: 22 page
Optimal dual frames and frame completions for majorization
In this paper we consider two problems in frame theory. On the one hand,
given a set of vectors we describe the spectral and geometrical
structure of optimal completions of by a finite family of vectors
with prescribed norms, where optimality is measured with respect to
majorization. In particular, these optimal completions are the minimizers of a
family of convex functionals that include the mean square error and the
Bendetto-Fickus' frame potential. On the other hand, given a fixed frame
we describe explicitly the spectral and geometrical structure of
optimal frames that are in duality with and such that
the Frobenius norms of their analysis operators is bounded from below by a
fixed constant. In this case, optimality is measured with respect to
submajorization of the frames operators. Our approach relies on the description
of the spectral and geometrical structure of matrices that minimize
submajorization on sets that are naturally associated with the problems above.Comment: 29 pages, with modifications related with the exposition of the
materia
Relic density calculations beyond tree-level, exact calculations versus effective couplings: the ZZ final state
The inferred value of the relic density from cosmological observations has
reached a precision that is akin to that of the LEP precision measurements.
This level of precision calls for the evaluation of the annihilation cross
sections of dark matter that goes beyond tree-level calculations as currently
implemented in all codes for the computation of the relic density. In
supersymmetry radiative corrections are known to be large and thus must be
implemented. Full one-loop radiative corrections for many annihilation
processes have been performed. It is important to investigate whether the bulk
of these corrections can be parameterised through an improved Born
approximation that can be implemented as a selection of form factors to a
tree-level code. This paper is a second in a series that addresses this issue.
After having provided these form factors for the annihilation of the
neutralinos into fermions, which cover the case of a bino-like LSP (Lightest
Supersymmetric Particle), we turn our attention here to a higgsino-like dark
matter candidate through its annihilation into . We also investigate the
cases of a mixed LSP. In all cases we compare the performance of the form
factor approach with the result of a full one-loop correction. We also study
the issue of the renormalisation scheme dependence. An illustration of the
phenomenon of non decoupling of the heavy sfermions that takes place for the
annihilation of the lightest neutralino into is also presented.Comment: 20
Planetary meteorology Final report
Temperature profile, wind measurement, radiative heat transfer, and diurnal variations in Martian atmospher
Black brane solutions and their solitonic extremal limit in Einstein-scalar gravity
We investigate static, planar, solutions of Einstein-scalar gravity admitting
an anti-de Sitter (AdS) vacuum. When the squared mass of the scalar field is
positive and the scalar potential can be derived from a superpotential, minimum
energy theorems indicate the existence of a scalar soliton. On the other hand,
for these models, no-hair theorems forbid the existence of hairy black brane
solutions with AdS asymptotics. By considering a specific example (an exact
integrable model which has the form of a Toda molecule) and by deriving
explicit exact solution, we show that these models allow for hairy black brane
solutions with non-AdS domain wall asymptotics, whose extremal limit is a
scalar soliton. The soliton smoothly interpolates between a non-AdS domain wall
solution at and an AdS solution near .Comment: 5 pages, no figure
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