958 research outputs found
The two-dimensional two-component plasma plus background on a sphere : Exact results
An exact solution is given for a two-dimensional model of a Coulomb gas, more
general than the previously solved ones. The system is made of a uniformly
charged background, positive particles, and negative particles, on the surface
of a sphere. At the special value of the reduced inverse
temperature, the classical equilibrium statistical mechanics is worked out~:
the correlations and the grand potential are calculated. The thermodynamic
limit is taken, and as it is approached the grand potential exhibits a
finite-size correction of the expected universal form.Comment: 23 pages, Plain Te
Two-dimensional two-component plasma with adsorbing impurities
We study the behavior of the two-dimensional two-component plasma in the
presence of some adsorbing impurities. Using a solvable model, we find analytic
expressions for the thermodynamic properties of the plasma such as the -body
densities, the grand potential, and the pressure. We specialize in the case
where there are one or two adsorbing point impurities in the plasma, and in the
case where there are one or two parallel adsorbing lines. In the former case we
study the effective interaction between the impurities, due to the charge
redistribution around them. The latter case is a model for electrodes with
adsorbing sticky sites on their surface
Casimir force between two ideal-conductor walls revisited
The high-temperature aspects of the Casimir force between two neutral
conducting walls are studied. The mathematical model of "inert" ideal-conductor
walls, considered in the original formulations of the Casimir effect, is based
on the universal properties of the electromagnetic radiation in the vacuum
between the conductors, with zero boundary conditions for the tangential
components of the electric field on the walls. This formulation seems to be in
agreement with experiments on metallic conductors at room temperature. At high
temperatures or large distances, at least, fluctuations of the electric field
are present in the bulk and at the surface of a particle system forming the
walls, even in the high-density limit: "living" ideal conductors. This makes
the enforcement of the inert boundary conditions inadequate. Within a hierarchy
of length scales, the high-temperature Casimir force is shown to be entirely
determined by the thermal fluctuations in the conducting walls, modelled
microscopically by classical Coulomb fluids in the Debye-H\"{u}ckel regime. The
semi-classical regime, in the framework of quantum electrodynamics, is studied
in the companion letter by P.R.Buenzli and Ph.A.Martin, cond-mat/0506363,
Europhys.Lett.72, 42 (2005).Comment: 7 pages.One reference updated. Domain of validity of eq.(11)
correcte
Determination of force platform parameters during sit to stand movement in elderly: A preliminary study
The Ideal Conductor Limit
This paper compares two methods of statistical mechanics used to study a
classical Coulomb system S near an ideal conductor C. The first method consists
in neglecting the thermal fluctuations in the conductor C and constrains the
electric potential to be constant on it. In the second method the conductor C
is considered as a conducting Coulomb system the charge correlation length of
which goes to zero. It has been noticed in the past, in particular cases, that
the two methods yield the same results for the particle densities and
correlations in S. It is shown that this is true in general for the quantities
which depend only on the degrees of freedom of S, but that some other
quantities, especially the electric potential correlations and the stress
tensor, are different in the two approaches. In spite of this the two methods
give the same electric forces exerted on S.Comment: 19 pages, plain TeX. Submited to J. Phys. A: Math. Ge
Statistical properties of charged interfaces
We consider the equilibrium statistical properties of interfaces submitted to
competing interactions; a long-range repulsive Coulomb interaction inherent to
the charged interface and a short-range, anisotropic, attractive one due to
either elasticity or confinement. We focus on one-dimensional interfaces such
as strings. Model systems considered for applications are mainly aggregates of
solitons in polyacetylene and other charge density wave systems, domain lines
in uniaxial ferroelectrics and the stripe phase of oxides. At zero temperature,
we find a shape instability which lead, via phase transitions, to tilted
phases. Depending on the regime, elastic or confinement, the order of the
zero-temperature transition changes. Thermal fluctuations lead to a pure
Coulomb roughening of the string, in addition to the usual one, and to the
presence of angular kinks. We suggest that such instabilities might explain the
tilting of stripes in cuprate oxides. The 3D problem of the charged wall is
also analyzed. The latter experiences instabilities towards various tilted
phases separated by a tricritical point in the elastic regime. In the
confinement regime, the increase of dimensionality favors either the melting of
the wall into a Wigner crystal of its constituent charges or a strongly
inclined wall which might have been observed in nickelate oxides.Comment: 17 pages, 11 figure
Both Grass Development Stage and Grazing Management Influence Milk Terpene Content
Terpenes are a wide group of molecules originating from plants’ secondary metabolism. Forage terpenes vary according to the botanical composition and in particular to the proportion of plants such as Apiaceae, Lamiaceae or Asteraceae. These molecules are considered effective milk markers for the presence of diversified forages in dairy cow diets. The variation in terpene content in the milk of grazing cows would depend on the period of development of terpene-rich plants and on the grazing management, whereby cows do or do not have the opportunity to choose and to modify the botanical composition of the ingested grass. The aim of this trial was to quantify the respective effects of grass development stage and grazing management on milk terpene content
A revised age, structural model and origin for the North Pennine Orefield in the Alston Block, northern England: intrusion (Whin Sill)-related base metal (Cu–Pb–Zn–F) mineralization
Mineralization and associated fluid migration events in the c. 1500 km2 North Pennine Orefield (NPO) are known to be associated with tectonic activity, but the age of these tectonic events and origins of the base metal sulfide mineralization remain unresolved. New fieldwork in the Alston Block shows that mineralization post-dates a weakly developed phase of north–south shortening consistent with far-field Variscan basin inversion during the late Carboniferous. New observations of field relationships, coupled with microstructural observations and stress inversion analyses, together with Re–Os sulfide geochronology show that the vein-hosted mineralization (apart from barium minerals) was synchronous with a phase of north–south extension and east–west shortening coeval with emplacement of the Whin Sill (c. 297–294 Ma). Thus the development of the NPO was related to an early Permian regional phase of transtensional deformation, mantle-sourced hydrothermal mineralization and magmatism in northern Britain. Previously proposed Mississippi Valley Type models, or alternatives relating mineralization to the influx of Mesozoic brines, can no longer be applied to the development of the NPO in the Alston Block. Our findings also mean that existing models for equivalent base metal sulfide fields worldwide (e.g. Zn–Pb districts of Silesia, Poland and Tennessee, USA) may need to be reassessed
Social drivers forewarn of marine regime shifts
Some ecosystems can undergo regime shifts to alternative compositions of species. Although ecological indicators can identify approaching regime shifts, we propose that rapid changes in the social drivers underlying ecosystem change may provide additional and potentially earlier indicators of impending shifts. We demonstrate this by reconstructing the underlying social drivers of four iconic marine regime shifts: Pacific kelp forests, Northwest Atlantic continental shelf, Jamaican coral reefs, and the Chesapeake Bay estuary. In all cases, a range of social drivers – including opening of lucrative markets, technological innovations, and policies that enhanced the driver – ultimately prompted these ecosystem shifts. Drawing on examples emerging from environmental management practice, we present three practical recommendations for using social drivers as early indicators: monitor social change, determine social trigger points, and identify policy responses. We argue that accounting for the underlying social drivers of ecosystem change could improve decision making
Equilibrium correlations in charged fluids coupled to the radiation field
We provide an exact microscopic statistical treatment of particle and field
correlations in a system of quantum charges in equilibrium with a classical
radiation field. Using the Feynman-Kac-Ito representation of the Gibbs weight,
the system of particles is mapped onto a collection of random charged wires.
The field degrees of freedom can be integrated out, providing an effective
pairwise magnetic potential. We then calculate the contribution of the
transverse field coupling to the large-distance particle correlations. The
asymptotics of the field correlations in the plasma are also exactly
determined.Comment: 31 pages, 0 figures. PACS 05.30.-d, 05.40.-a, 11.10.Wx. Changes:
Improved comparison with existing literature on field correlations. Added
Concluding Remarks. References update
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