29,050 research outputs found
A mass-transportation approach to a one dimensional fluid mechanics model with nonlocal velocity
We consider a one dimensional transport model with nonlocal velocity given by
the Hilbert transform and develop a global well-posedness theory of probability
measure solutions. Both the viscous and non-viscous cases are analyzed. Both in
original and in self-similar variables, we express the corresponding equations
as gradient flows with respect to a free energy functional including a singular
logarithmic interaction potential. Existence, uniqueness, self-similar
asymptotic behavior and inviscid limit of solutions are obtained in the space
of probability measures with finite second
moments, without any smallness condition. Our results are based on the abstract
gradient flow theory developed in \cite{Ambrosio}. An important byproduct of
our results is that there is a unique, up to invariance and translations,
global in time self-similar solution with initial data in
, which was already obtained in
\textrm{\cite{Deslippe,Biler-Karch}} by different methods. Moreover, this
self-similar solution attracts all the dynamics in self-similar variables. The
crucial monotonicity property of the transport between measures in one
dimension allows to show that the singular logarithmic potential energy is
displacement convex. We also extend the results to gradient flow equations with
negative power-law locally integrable interaction potentials
Mean-field analysis of the majority-vote model broken-ergodicity steady state
We study analytically a variant of the one-dimensional majority-vote model in
which the individual retains its opinion in case there is a tie among the
neighbors' opinions. The individuals are fixed in the sites of a ring of size
and can interact with their nearest neighbors only. The interesting feature
of this model is that it exhibits an infinity of spatially heterogeneous
absorbing configurations for whose statistical properties we
probe analytically using a mean-field framework based on the decomposition of
the -site joint probability distribution into the -contiguous-site joint
distributions, the so-called -site approximation. To describe the
broken-ergodicity steady state of the model we solve analytically the
mean-field dynamic equations for arbitrary time in the cases n=3 and 4. The
asymptotic limit reveals the mapping between the statistical
properties of the random initial configurations and those of the final
absorbing configurations. For the pair approximation () we derive that
mapping using a trick that avoids solving the full dynamics. Most remarkably,
we find that the predictions of the 4-site approximation reduce to those of the
3-site in the case of expectations involving three contiguous sites. In
addition, those expectations fit the Monte Carlo data perfectly and so we
conjecture that they are in fact the exact expectations for the one-dimensional
majority-vote model
Upper bound for the conductivity of nanotube networks
Films composed of nanotube networks have their conductivities regulated by
the junction resistances formed between tubes. Conductivity values are enhanced
by lower junction resistances but should reach a maximum that is limited by the
network morphology. By considering ideal ballistic-like contacts between
nanotubes we use the Kubo formalism to calculate the upper bound for the
conductivity of such films and show how it depends on the nanotube
concentration as well as on their aspect ratio. Highest measured conductivities
reported so far are approaching this limiting value, suggesting that further
progress lies with nanowires other than nanotubes.Comment: 3 pages, 1 figure. Minor changes. Accepted for publication in Applied
Physics Letter
Electrochemical and STM Study of α,ω-alkanedithiols Self-assembled Monolayers
Self-assembled monolayers (SAMs), prepared by the immersion method, from ethanolic solutions containing α,ω-alkanedithiol, n-alkanethiol or mixed thiol/dithiol solutions, with 6, 9 and 10 carbon atoms in the alkyl chain, have been investigated. The amount of adsorbate and the SAM stability in alkaline medium is evaluated by reductive desorption of the prepared monolayers by cyclic voltammetry. An upright orientation of the dithiol self-assembled molecules and disulfide bonding at the SAM/solution interface
are suggested by the higher reductive desorption charge of the dithiol monolayers (relative to thiol SAMs) for n = 6 and 9. The results show that an improvement on the stability of these dithiol SAMs is obtained by the presence of monothiols, resulting in mixed
monolayers. Mixed SAMs prepared from longer alkane chain thiols, n = 10, allow to overcome the increased possibility of loop formation and therefore lower surface coverage is obtained for the 1,10-decanedithiol monolayers. Morphological characterisation of
the modified electrodes is performed by scanning tunnelling microscopy (STM) ex situ, in air. Typical one atom deep thiol induced depressions are observed in the STM images of the dithiol and mixed SAMs
Resistivity study of the pseudogap phase for (Hg,Re) - 1223 superconductors
The pseudogap phase above the critical temperature of high
superconductors (HTSC) presents different energy scales and it is currently a
matter of intense study. The complexity of the HTSC normal state requires very
accurate measurements with the purpose of distinguishing different types of
phenomena. Here we have performed systematically studies through electrical
resistivity () measurements by several different current densities in
order to obtain an optimal current for each sample. This approach allows to
determine reliable values of the pseudogap temperature , the layer
coupling temperature between the superconductor layers , the
fluctuation temperature and the critical temperature as
function of the doping . The interpretation of these different temperature
scales allows to characterize possible scenarios for the (Hg,Re) - 1223 normal
state. This method, described in detail here, and used to derive the
(Hg,Re)-1223 phase diagram is general and can be applied to any HTSC.Comment: 31 pages, 12 figures, Latex; 25 pages, LaTeX; 11 figures; rewrited
section II and III; added 18 reference; rewrited title, added discussion
sectio
Teste de um modelo agrometeorológico para estudo da influência da variabilidade climática na cultura da soja.
Com o objetivo de verificar o efeito do clima sobre a produtividade da cultura da soja em Minas Gerais, foi desenvolvido um modelo de simulação dinâmico, mecanístico e deterrninístico. A principal característica do modelo foi a busca do equilíbrio entre a simplicidade no seu manuseio e o rigor científico necessário. Como variáveis de entrada, o modelo utiliza os elementos climáticos precipitação, temperatura e insolação. Os resultados mostraram que o modelo simulou satisfatoriamente a produtividade da soja para os anos agrícolas de 1995/96 e 1996/97, evídenciando as diferenças morfológicas e fisiológicas da cultura, em resposta às variações climáticas, o que evidencia o seu alto potencial de aplicação no entendimento das relações entre clima e cultura
Caracterização molecular de isolados de Fusarium oxysporum f. sp. cubense no Brasil.
Segundo a FAO o Brasil foi em 2010 o quinto produtor de banana do mundo e o maior do hemisfério sul. A produção brasileira em 2010 foi de 7,0 milhões de toneladas em 487 mil hectares
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