4,767 research outputs found
Non conventional screening of the Coulomb interaction in low dimensional and finite size system
We study the screening of the Coulomb interaction in non polar systems by
polarizable atoms. We show that in low dimensions and small finite size systems
this screening deviates strongly from that conventionally assumed. In fact in
one dimension the short range interaction is strongly screened and the long
range interaction is anti-screened thereby strongly reducing the gradient of
the Coulomb interaction and therefore the correlation effects. We argue that
this effect explains the success of mean field single particle theories for
large molecules.Comment: 4 pages, 5 figure
New directions for magnetic memory : alternative switching mechanisms for magnetic random-access memory
Electronic Correlations in Oligo-acene and -thiophene Organic Molecular Crystals
From first principles calculations we determine the Coulomb interaction
between two holes on oligo-acene and -thiophene molecules in a crystal, as a
function of the oligomer length. The relaxation of the molecular geometry in
the presence of holes is found to be small. In contrast, the electronic
polarization of the molecules that surround the charged oligomer, reduces the
bare Coulomb repulsion between the holes by approximately a factor of two. In
all cases the effective hole-hole repulsion is much larger than the calculated
valence bandwidth, which implies that at high doping levels the properties of
these organic semiconductors are determined by electron-electron correlations.Comment: 5 pages, 3 figure
Cooperative Games on Antimatroids
AMS classification: 90D12;game theory;cooperative games;antimatroids
Principal response curves technique for the analysis of multivariate biomonitoring time series
Although chemical and biological monitoring is often used to evaluate the quality of surface waters for regulatory purposes and/or to evaluate environmental status and trends, the resulting biological and chemical data sets are large and difficult to evaluate. Multivariate techniques have long been used to analyse complex data sets. This paper discusses the methods currently in use and introduces the principal response curves method, which overcomes the problem of cluttered graphical results representation that is a great drawback of most conventional methods. To illustrate this, two example data sets are analysed using two ordination techniques, principal component analysis and principal response curves. Whereas PCA results in a difficult-to-interpret diagram, principal response curves related methods are able to show changes in community composition in a diagram that is easy to read. The principal response curves method is used to show trends over time with an internal reference (overall mean or reference year) or external reference (e.g. preferred water quality or reference site). Advantages and disadvantages of both methods are discussed and illustrate
Grondbeleid in de Montpellier agglomeratie, Frankrijk
Van 2007 tot 2010 co-financierde het Ministerie van Landbouw, Natuur en Voedselkwaliteit het Europese PLUREL onderzoek naar ontwikkelingen en sturing daarop in de stadsranden van stedelijke regio‟s. In dit project trokken het Ruimtelijk structuurplan van Montpellier Agglomeratie en de daaromheen gehanteerde beleidsprocedures, wetgeving en grondbeleid-instrumenten de aandacht van het Ministerie. Doel van dit project was het verkrijgen van nader inzicht in de tools die de regio Montpellier inzet om een duurzaam groen peri-urbaan gebied te behouden, respectievelijk te ontwikkelen, waarbij de landbouw een voorname plaats inneemt. Het gaat in het bijzonder om tools inzake het grondbeleid
A Potts model for the distortion transition in LaMnO
The Jahn-Teller distortive transition of \lmo is described by a modified
3-state Potts model. The interactions between the three possible orbits depends
both on the orbits and their relative orientation on the lattice. Values of the
two exchange parameters which are chosen to give the correct low temperature
phase and the correct value for the transition temperature are shown to be
consistent with microscopy theory. The model predicts a first order transitions
and also a value for the entropy above the transition in good agreement with
experiment. The theory with the same parameters also predicts the temperature
dependence of the order parameter of orbital ordering agreeing well with
published experimental results. Finally, the type of the transition is shown to
be close to one of the most disordered phases of the generalised Potts model.
The short range order found experimentally above the transition is investigated
by this model.Comment: 16 pages, 7 figures and no tables. Re-submitted to Phys. Rev.
Visual localization of the horizontal as a function of body tilt up to plus or minus 90 deg from gravitational vertical
Visual localization of horizontal as function of body tilt utilizing several positions with respect to gravit
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