3,132 research outputs found
Computer simulations of electrorheological fluids in the dipole-induced dipole model
We have employed the multiple image method to compute the interparticle force
for a polydisperse electrorheological (ER) fluid in which the suspended
particles can have various sizes and different permittivites. The point-dipole
(PD) approximation being routinely adopted in computer simulation of ER fluids
is shown to err considerably when the particles approach and finally touch due
to multipolar interactions. The PD approximation becomes even worse when the
dielectric contrast between the particles and the host medium is large. From
the results, we show that the dipole-induced-dipole (DID) model yields very
good agreements with the multiple image results for a wide range of dielectric
contrasts and polydispersity. As an illustration, we have employed the DID
model to simulate the athermal aggregation of particles in ER fluids both in
uniaxial and rotating fields. We find that the aggregation time is
significantly reduced. The DID model accounts for multipolar interaction
partially and is simple to use in computer simulation of ER fluids.Comment: 22 pages, 7 figures, submitted to Phys. Rev.
Arc Phenomena and Gasdynamic Effects due to Interaction of Shock Waves with Magnetic Fields
Structures of electromagnetic type on vector bundles
10 pages.Structures of electromagnetic type on a vector bundle are introduced and studied. The metric case is also defined and studied. The sets of compatible connections are determined and a canonical connection is defined.MICINN-CSIC.Peer reviewe
Applications of the Gauss-Bonnet theorem to gravitational lensing
In this geometrical approach to gravitational lensing theory, we apply the
Gauss-Bonnet theorem to the optical metric of a lens, modelled as a static,
spherically symmetric, perfect non-relativistic fluid, in the weak deflection
limit. We find that the focusing of the light rays emerges here as a
topological effect, and we introduce a new method to calculate the deflection
angle from the Gaussian curvature of the optical metric. As examples, the
Schwarzschild lens, the Plummer sphere and the singular isothermal sphere are
discussed within this framework.Comment: 10 pages, 1 figure, IoP styl
Gaming with eutrophication: Contribution to integrating water quantity and quality management at catchment level
The Metropolitan Region of Sao Paulo (MRSP) hosts 18 million inhabitants. A complex system of 23 interconnected reservoirs was built to ensure its water supply. Half of the potable water produced for MRSP's population (35 m3/s) is imported from a neighbour catchment, the other half is produced within the Alto Tietê catchment, where 99% of the population lives. Perimeters of land use restriction were defined to contain uncontrolled urbanization, as domestic effluents were causing increasing eutrophication of some of these reservoirs. In the 90's catchment committees and sub committees were created to promote discussion between stakeholders and develop catchment plans. The committees are very well structured "on paper". However, they are not very well organised and face a lack of experience. The objective of this work was to design tools that would strengthen their discussion capacities. The specific objective of the AguAloca process was to integrate the quality issue and its relation to catchment management as a whole in these discussions. The work was developed in the Alto Tietê Cabeceiras sub-catchment, one of the 5 sub catchments of the Alto-Tietê. It contains 5 interconnected dams, and presents competitive uses such as water supply, industry, effluent dilution and irrigated agriculture. A RPG was designed following a companion modelling approach (Etienne et al., 2003). It contains a friendly game-board, a set of individual and collective rules and a computerized biophysical model. The biophysical model is used to simulate water allocation and quality processes at catchment level. It articulates 3 modules. A simplified nutrient discharge model permits the estimation of land use nutrient exportation. An arc-node model simulates water flows and associated nutrient charges from one point of the hydrographical network to another. The Vollenweider model is used for simulating specific reservoir dynamics. The RPG allows players to make individual and collective decisions related to water allocation and the management of its quality. Impacts of these decisions are then simulated using the biophysical model. Specific indicators of the game are then updated and may influence player's behaviour (actions) in following rounds. To introduce discussions on the management of water quality at a catchment level, an issue that is rarely explicitly dealt with, four game sessions were implemented involving representatives of basin committees and water and sanitation engineers. During the game session, the participants took advantage of the water quality output of the biophysical model to test management alternatives such as rural sewage collection or effluent dilution. The biophysical model accelerated calculations of flows and eutrophication rates that were then returned to the game board with explicit indicators of quantity and quality. Players could easily test decisions impacting on qualitative water processes and visualize the simulation results directly on the game board that was representing a friendly, virtual and simplified catchment. The Agualoca game proved its ability to turn complex water processes understandable for a non totally initiated public. This experience contributed to a better understanding of multiple-use water management and also of joint management of water quality and quantity. (Résumé d'auteur
Energy decay for the damped wave equation under a pressure condition
We establish the presence of a spectral gap near the real axis for the damped
wave equation on a manifold with negative curvature. This results holds under a
dynamical condition expressed by the negativity of a topological pressure with
respect to the geodesic flow. As an application, we show an exponential decay
of the energy for all initial data sufficiently regular. This decay is governed
by the imaginary part of a finite number of eigenvalues close to the real axis.Comment: 32 page
Magnetized strangelets at finite temperature
The main properties of magnetized strangelets, namely, their energy per
baryon, radius and electric charge, are studied. Temperature effects are also
taken into account in order to study their stability compared to the 56Fe
isotope and non-magnetized strangelets using the liquid drop model. Massive
quarks are considered with the aim to have a more realistic description for
strangelets in the astrophysical context and the environment of heavy ion
colliders, playing also an important role in the thermodynamical quantities of
the quark gas. It is concluded that the presence of a magnetic field tends to
stabilize more the strangelets, even when temperature effects are taken into
account. Magnetized strangelets in a paired superconductor phase (magnetized
color flavor locked phase) are also discussed. It is shown that they are more
stable than ordinary magnetized strangelets for typical gap values of the order
of O(100) MeV.Comment: 10 pages, 10 figures, discussion extended, new references adde
A Hardy inequality in twisted waveguides
We show that twisting of an infinite straight three-dimensional tube with
non-circular cross-section gives rise to a Hardy-type inequality for the
associated Dirichlet Laplacian. As an application we prove certain stability of
the spectrum of the Dirichlet Laplacian in locally and mildly bent tubes.
Namely, it is known that any local bending, no matter how small, generates
eigenvalues below the essential spectrum of the Laplacian in the tubes with
arbitrary cross-sections rotated along a reference curve in an appropriate way.
In the present paper we show that for any other rotation some critical strength
of the bending is needed in order to induce a non-empty discrete spectrum.Comment: LaTeX, 20 page
Cell-Free Synthesis of the Mitochondrial ADP/ATP Carrier Protein of Neurospora crassa
ADP/ATP carrier protein was synthesized in heterologous cell-free systems programmed with Neurospora poly(A)-containing RNA and homologous cell-free systems from Neurospora. The apparent molecular weight of the product obtained in vitro was the same as that of the authentic mitochondrial protein. The primary translation product obtained in reticulocyte lysates starts with formylmethionine when formylated initiator methionyl-tRNA (fMet-tRNAfMet) was present. The product synthesized in vitro was released from the ribosomes into the postribosomal supernatant.
The evidence presented indicates that the ADP/ATP carrier is synthesized as a polypeptide with the same molecular weight as the mature monomeric protein and does not carry an additional sequence
Statistical-mechanical theory of the overall magnetic properties of mesocrystals
The mesocrystal showing both electrorheological and magnetorheological
effects is called electro-magnetorheological (EMR) solids. Prediction of the
overall magnetic properties of the EMR solids is a challenging task due to the
coexistence of the uniaxially anisotropic behavior and structural transition as
well as long-range interaction between the suspended particles. To consider the
uniaxial anisotropy effect, we present an anisotropic Kirkwood-Fr\"{o}hlich
equation for calculating the effective permeabilities by adopting an explicit
characteristic spheroid rather than a characteristic sphere used in the
derivation of the usual Kirkwood-Fr\"{o}hlich equation. Further, by applying an
Ewald-Kornfeld formulation we are able to investigate the effective
permeability by including the structural transition and long-range interaction
explicitly. Our theory can reduce to the usual Kirkwood-Fr\"{o}hlich equation
and Onsager equation naturally. To this end, the numerical simulation shows the
validity of monitoring the structure of EMR solids by detecting their effective
permeabilities.Comment: 14 pages, 1 figur
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