18,347 research outputs found
Linking genebanks and farmers to urban high-value markets - The case of chili peppers in Peru and Bolivia [Poster]
Poster presented at Tropentag Conference. Stuttgart-Hohenheim (Germany), 17-19 Sep 201
FRW in cosmological self-creation theory: Hamiltonian approach
We use the Brans-Dicke theory from the framework of General Relativity
(Einstein frame), but now the total energy momentum tensor fulfills the
following condition . We take as a first model the flat FRW metric in the
Hamilton-Jacobi scheme and we present the Lagrange-Charpit approach in order to
find classical solutions. In the quantum scheme, once we determine the
characteristic surfaces, the quantum solution is obtained. These two classes of
solutions are found for all values of the barotropic parameter .Comment: 9 pages, latex2e. arXiv admin note: substantial text overlap with
arXiv:1206.541
Antisymmetric tensor Z_p gauge symmetries in field theory and string theory
We consider discrete gauge symmetries in D dimensions arising as remnants of
broken continuous gauge symmetries carried by general antisymmetric tensor
fields, rather than by standard 1-forms. The lagrangian for such a general
gauge theory can be described in terms of a -form gauge field
made massive by a -form, or other dual realizations, that we also
discuss. The theory contains charged topological defects of different
dimensionalities, generalizing the familiar charged particles and strings in
D=4. We describe realizations in string theory compactifications with torsion
cycles, or with background field strength fluxes. We also provide examples of
non-abelian discrete groups, for which the group elements are associated with
charged objects of different dimensionality.Comment: 16 pages; v2: references added and typos fixe
Non-integrability of the Armbruster-Guckenheimer-Kim quartic Hamiltonian through Morales-Ramis theory
We show the non-integrability of the three-parameter
Armburster-Guckenheimer-Kim quartic Hamiltonian using Morales-Ramis theory,
with the exception of the three already known integrable cases. We use
Poincar\'e sections to illustrate the breakdown of regular motion for some
parameter values.Comment: Accepted for publication in SIAM Journal on Applied Dynamical
Systems. Adapted version for arxiv with 19 pages and 11 figure
Simulation of quantum zero-point effects in water using a frequency-dependent thermostat
Molecules like water have vibrational modes with a zero-point energy well
above room temperature. As a consequence, classical molecular dynamics
simulations of their liquids largely underestimate the energy of modes with a
higher zero-point temperature, which translates into an underestimation of
covalent interatomic distances due to anharmonic effects. Zero-point effects
can be recovered using path integral molecular dynamics simulations, but these
are computationally expensive, making their combination with ab initio
molecular dynamics simulations a challenge. As an alternative to path integral
methods, from a computationally simple perspective, one would envision the
design of a thermostat capable of equilibrating and maintaining the different
vibrational modes at their corresponding zero-point temperatures. Recently,
Ceriotti et al. (Phys. Rev. Lett. 102 020601 (2009)) introduced a framework to
use a custom-tailored Langevin equation with correlated noise that can be used
to include quantum fluctuations in classical molecular dynamics simulations.
Here we show that it is possible to use the generalized Langevin equation with
suppressed noise in combination with Nose-Hoover thermostats to efficiently
impose a zero-point temperature on independent modes in liquid water. Using our
simple and inexpensive method, we achieve excellent agreement for all atomic
pair correlation functions compared to the path integral molecular dynamics
simulation.Comment: 27 pages, 12 figs, Published versio
- DO WIVES EARNINGS CONTRIBUTE TO REDUCE INCOME INEQUALITY?: EVIDENCE FROM SPAIN
In this paper we analyze the effect of female labor force participation on income inequality. We present evidence from Spain by using data from the Family Expenditure Survey for 1980 and 1990. The case of Spain is particulary interesting because inequality decreased over the eighties, while the labor force participation rate of married women increased substantially over the same period. Our results show that although female labor force participation has contributed to decrease income inequality in Spain, it is far from being one of the main factors behind the observed decrease in inequality over the eighties.Income Ínequality; Female Earnings; Female Participation.
Faster ASV decomposition for orthogonal polyhedra using the Extreme Vertices Model (EVM)
The alternating sum of volumes (ASV) decomposition is a widely used
technique for converting a B-Rep into a CSG model. The obtained CSG
tree has convex primitives at its leaf nodes, while the contents of
its internal nodes alternate between the set union and difference
operators.
This work first shows that the obtained CSG tree T can also be
expressed as the regularized Exclusive-OR operation among all the
convex primitives at the leaf nodes of T, regardless the structure and
internal nodes of T. This is an important result in the case in which
EVM represented orthogonal polyhedra are used because in this model
the Exclusive-OR operation runs much faster than set union and
difference operations. Therefore this work applies this result to EVM
represented orthogonal polyhedra. It also presents experimental
results that corroborate the theoretical results and includes some
practical uses for the ASV decomposition of orthogonal polyhedra.Postprint (published version
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