821 research outputs found
Frozen Fronts Selection in flow against self-sustained chemical waves
Autocatalytic reaction fronts between two reacting species in the absence of
fluid flow, propagate as solitary waves. The coupling between autocatalytic
reaction front and forced hydrodynamic flow may lead to stationary front whose
velocity and shape depend on the underlying flow field. We focus on the issue
of the chemo-hydrodynamic coupling between forced advection opposed to
self-sustained chemical waves which can lead to static stationary fronts, i.e
Frozen Fronts, . Towards that purpose, we perform experiments, analytical
computations and numerical simulations with the autocatalytic Iodate Arsenious
Acid reaction () over a wide range of flow velocities around a solid disk.
For the same set of control parameters, we observe two types of frozen fronts:
an upstream which avoid the solid disk and a downstream with two
symmetric branches emerging from the solid disk surface. We delineate the range
over which we do observe these Frozen Fronts. We also address the relevance of
the so-called eikonal, thin front limit to describe the observed fronts and
select the frozen front shapes.Comment: draf
Logistic Barriers to U.S.–Mexico Grain and Soybean Trade
Fourteen years after the implementation of the North American Free Trade Agreement (NAFTA), border-crossing restrictions still remain with Mexico. Although studies have analyzed the impact of NAFTA trade liberalization, there has only been limited research on effects of informal trade barriers on U.S.–Mexico grain and soybean flows. This paper quantitatively measures the impact of logistic barriers impeding U.S.–Mexico grain and soybean trade. A conditional model testing for the presence of asymmetries in grain trade suggests that logistic barriers and transshipments are correlated. Econometric analysis rejects the null hypoInternational Relations/Trade,
Machinery-Sharing Contractual Issues and Impacts on Cash Flows of Agribusinesses
Contractual arrangements for joint machinery ownership between independent agribusinesses are explored. A two-farm economic simulation model of locations in Texas, Colorado, and Montana is developed to provide insight associated with sharing combines. Important variables include combine size (efficiency), yield losses resulting from untimely access to equipment, the penalty structure for untimely delivery, and cost-sharing and depreciation deductions claimed between producers. Combine sharing is risk-reducing in most cases. The gains to both parties are lowest when harvesting periods overlap. While the value of sharing is positive under many scenarios, benefits from sharing are small relative to total farm revenue.combines, machinery sharing, risk, simulation, Agribusiness, Agricultural Finance,
Socio-Economic support for good health in rural Malawi
Objective: To study the socio-economic support for good health among subsistence farmers in rural Malawi.Design: A cross-sectional survey.Setting: Lungwena, a rural area with 17000 inhabitants in southern Malawi.Participants: Seven hundred and ninety five pregnant women who attended the antenatal clinic at Lungwena Health Centre between June 1995 and September 1996. Interventions: Interviews about socio-economic conditions. Measurements of cultivated land areas and distances between home and the local health centre. Main outcome measures: Proportion of households lacking literate adults, adequate water source and sanitation, easy access to modern health care or food security.Results: Only 14% of the interviewed women could read and write and half of the households had no literate members. Every fifth household was lacking both an access to safe drinking water and a proper sanitary facility. The distance to the health centre was more than 5 kmamong half of the households and only 37% had enough land to grow food for all family members. When other potential means of obtaining food were taken into account, 27% of the households had no food security. Numerous households were lacking more than one socioeconomic prerequisites of good health: three or more were missing from a quarter of the families.Conclusions: Socio-economic prerequisites of health were commonly missing in Lungwena. Subsequent health interventions should strengthen the investments into general poverty alleviation
MEMPHYS:A large scale water Cerenkov detector at Fr\'ejus
A water \v{C}erenkov detector project, of megaton scale, to be installed in
the Fr\'ejus underground site and dedicated to nucleon decay, neutrinos from
supernovae, solar and atmospheric neutrinos, as well as neutrinos from a
super-beam and/or a beta-beam coming from CERN, is presented and compared with
competitor projects in Japan and in the USA. The performances of the European
project are discussed, including the possibility to measure the mixing angle
and the CP-violating phase .Comment: 1+33 pages, 14 figures, Expression of Interest of MEMPHYS projec
Yukawa potentials in systems with partial periodic boundary conditions I : Ewald sums for quasi-two dimensional systems
Yukawa potentials are often used as effective potentials for systems as
colloids, plasmas, etc. When the Debye screening length is large, the Yukawa
potential tends to the non-screened Coulomb potential ; in this small screening
limit, or Coulomb limit, the potential is long ranged. As it is well known in
computer simulation, a simple truncation of the long ranged potential and the
minimum image convention are insufficient to obtain accurate numerical data on
systems. The Ewald method for bulk systems, i.e. with periodic boundary
conditions in all three directions of the space, has already been derived for
Yukawa potential [cf. Y., Rosenfeld, {\it Mol. Phys.}, \bm{88}, 1357, (1996)
and G., Salin and J.-M., Caillol, {\it J. Chem. Phys.}, \bm{113}, 10459,
(2000)], but for systems with partial periodic boundary conditions, the Ewald
sums have only recently been obtained [M., Mazars, {\it J. Chem. Phys.}, {\bf
126}, 056101 (2007)]. In this paper, we provide a closed derivation of the
Ewald sums for Yukawa potentials in systems with periodic boundary conditions
in only two directions and for any value of the Debye length. A special
attention is paid to the Coulomb limit and its relation with the
electroneutrality of systems.Comment: 40 pages, 5 figures and 4 table
Inter-areal coordination of columnar architectures during visual cortical development
The occurrence of a critical period of plasticity in the visual cortex has
long been established, yet its function in normal development is not fully
understood. Here we show that as the late phase of the critical period unfolds,
different areas of cat visual cortex develop in a coordinated manner.
Orientation columns in areas V1 and V2 become matched in size in regions that
are mutually connected. The same age trend is found for such regions in the
left and right brain hemisphere. Our results indicate that a function of
critical period plasticity is to progressively coordinate the functional
architectures of different cortical areas - even across hemispheres.Comment: 30 pages, 1 table, 6 figure
Nonlinear interaction of charged particles with a free electron gas beyond the random-phase approximation
A nonlinear description of the interaction of charged particles penetrating a
solid has become of basic importance in the interpretation of a variety of
physical phenomena. Here we develop a many-body theoretical approach to the
quadratic decay rate, energy loss, and wake potential of charged particles
moving in an interacting free electron gas. Explicit expressions for these
quantities are obtained either within the random-phase approximation (RPA) or
with full inclusion of short-range exchange and correlation effects. The Z^3
correction to the energy loss of ions is evaluated beyond RPA, in the limit of
low velocities.Comment: 5 pages, 2 figures To appear in Phys. Rev.
Resonance production by neutrinos: I. J=3/2 Resonances
The article contains general formulas for the production of J=3/2 resonances
by neutrinos and antineutrinos. It specializes to the P_{33}(1232) resonance
whose form factors are determined by theory and experiment and then are
compared with experimental results at low and high energies. It is shown that
the minimum in the low Q^2 region is a consequence of a combined effect from
the vanishing of the vector form factors, the muon mass and Pauli blocking.
Several improvements for the future investigations are suggested.Comment: 10 pages, LaTeX, misprints corrected, 1 reference adde
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