10,415 research outputs found
A Force-Balanced Control Volume Finite Element Method for Multi-Phase Porous Media Flow Modelling
Dr D. Pavlidis would like to acknowledge the support from the following research grants: Innovate UK ‘Octopus’, EPSRC ‘Reactor Core-Structure Re-location Modelling for Severe Nuclear Accidents’) and Horizon 2020 ‘In-Vessel Melt Retention’. Funding for Dr P. Salinas from ExxonMobil is gratefully acknowledged. Dr Z. Xie is supported by EPSRC ‘Multi-Scale Exploration of Multi-phase Physics in Flows’. Part funding for Prof Jackson under the TOTAL Chairs programme at Imperial College is also acknowledged. The authors would also like to acknowledge Mr Y. Debbabi for supplying analytic solutions.Peer reviewedPublisher PD
Nonrelativistic Limit of the Scalar Chern-Simons Theory and the Aharonov-Bohm Scattering
We study the nonrelativistic limit of the quantum theory of a Chern-Simons
field minimally coupled to a scalar field with quartic self-interaction. The
renormalization of the relativistic model, in the Coulomb gauge, is discussed.
We employ a procedure to calculate scattering amplitudes for low momenta that
generates their expansion and separates the contributions coming from
high and low energy intermediary states. The two body scattering amplitude is
calculated up to order . It is shown that the existence of a critical
value of the self-interaction parameter for which the 2-particle scattering
amplitude reduces to the Aharonov-Bohm one is a strictly nonrelativistic
feature. The subdominant terms correspond to relativistic corrections to the
Aharonov-Bohm scattering. A nonrelativistic reduction scheme and an effective
nonrelativistic Lagrangian to account for the relativistic corrections are
proposed.Comment: 22 pages, 8 figures, revtex, to be published in Int. J. Mod. Phys.
Quantum Rod Emission Coupled to Plasmonic Lattice Resonances: A Collective Directional Source of Polarized Light
We demonstrate that an array of optical antennas may render a thin layer of
randomly oriented semiconductor nanocrystals into an enhanced and highly
directional source of polarized light. The array sustains collective plasmonic
lattice resonances which are in spectral overlap with the emission of the
nanocrystals over narrow angular regions. Consequently, different photon
energies of visible light are enhanced and beamed into definite directions.Comment: 4 pages, 3 figure
Ferromagnetism without flat bands in thin armchair nanoribbons
Describing by a Hubbard type of model a thin armchair graphene ribbon in the
armchair hexagon chain limit, one shows in exact terms, that even if the system
does not have flat bands at all, at low concentration a mesoscopic sample can
have ferromagnetic ground state, being metallic in the same time. The mechanism
is connected to a common effect of correlations and confinement.Comment: 37 pages, 12 figures, in press at Eur. Phys. Jour.
Chiral symmetry breaking in in presence of irrelevant interactions: a renormalization group study
Motivated by recent theoretical approaches to high temperature
superconductivity, we study dynamical mass generation in three dimensional
quantum electrodynamics ) in presence of irrelevant four-fermion
quartic terms. The problem is reformulated in terms of the renormalization
group flows of certain four-fermion couplings and charge, and then studied in
the limit of large number of fermion flavors . We find that the critical
number of fermions below which the mass becomes dynamically generated
depends continuously on a weak chiral-symmetry-breaking interaction. One-loop
calculation in our gauge-invariant approach yields in pure . We also find that chiral-symmetry-preserving mass cannot become
dynamically generated in pure .Comment: 7 pages, 7 figure
Topological mass mechanism and exact fields mapping
We present a class of mappings between models with topological mass mechanism
and purely topological models in arbitrary dimensions. These mappings are
established by directly mapping the fields of one model in terms of the fields
of the other model in closed expressions. These expressions provide the
mappings of their actions as well as the mappings of their propagators. For a
general class of models in which the topological model becomes the BF model the
mappings present arbitrary functions which otherwise are absent for
Chern-Simons like actions. This work generalizes the results of [1] for
arbitrary dimensions.Comment: 11 page
Neonatal pyruvate dehydrogenase deficiency due to a R302H mutation in the PDHA1 gene: MRI findings
Pyruvate dehydrogenase (PDH) deficiency is one of the most common causes of congenital lactic acidosis. Correlations between the genetic defect and neuroimaging findings are lacking. We present conventional and diffusion-weighted MRI findings in a 7-day-old male neonate with PDH deficiency due to a mosaicism for the R302H mutation in the PDHA1 gene. Corpus callosum dysgenesis, widespread increased diffusion in the white matter, and bilateral subependymal cysts were the main features. Although confirmation of PDH deficiency depends on specialized biochemical analyses, neonatal MRI plays a role in evaluating the pattern and extent of brain damage, and potentially in early diagnosis and clinical decision making
Excitons in quasi-one dimensional organics: Strong correlation approximation
An exciton theory for quasi-one dimensional organic materials is developed in
the framework of the Su-Schrieffer-Heeger Hamiltonian augmented by short range
extended Hubbard interactions. Within a strong electron-electron correlation
approximation, the exciton properties are extensively studied. Using scattering
theory, we analytically obtain the exciton energy and wavefunction and derive a
criterion for the existence of a exciton. We also systematically
investigate the effect of impurities on the coherent motion of an exciton. The
coherence is measured by a suitably defined electron-hole correlation function.
It is shown that, for impurities with an on-site potential, a crossover
behavior will occur if the impurity strength is comparable to the bandwidth of
the exciton, corresponding to exciton localization. For a charged impurity with
a spatially extended potential, in addition to localization the exciton will
dissociate into an uncorrelated electron-hole pair when the impurity is
sufficiently strong to overcome the Coulomb interaction which binds the
electron-hole pair. Interchain coupling effects are also discussed by
considering two polymer chains coupled through nearest-neighbor interchain
hopping and interchain Coulomb interaction . Within the
matrix scattering formalism, for every center-of-mass momentum, we find two
poles determined only by , which correspond to the interchain
excitons. Finally, the exciton state is used to study the charge transfer from
a polymer chain to an adjacent dopant molecule.Comment: 24 pages, 23 eps figures, pdf file of the paper availabl
Maximal height statistics for 1/f^alpha signals
Numerical and analytical results are presented for the maximal relative
height distribution of stationary periodic Gaussian signals (one dimensional
interfaces) displaying a 1/f^alpha power spectrum. For 0<alpha<1 (regime of
decaying correlations), we observe that the mathematically established limiting
distribution (Fisher-Tippett-Gumbel distribution) is approached extremely
slowly as the sample size increases. The convergence is rapid for alpha>1
(regime of strong correlations) and a highly accurate picture gallery of
distribution functions can be constructed numerically. Analytical results can
be obtained in the limit alpha -> infinity and, for large alpha, by
perturbation expansion. Furthermore, using path integral techniques we derive a
trace formula for the distribution function, valid for alpha=2n even integer.
From the latter we extract the small argument asymptote of the distribution
function whose analytic continuation to arbitrary alpha > 1 is found to be in
agreement with simulations. Comparison of the extreme and roughness statistics
of the interfaces reveals similarities in both the small and large argument
asymptotes of the distribution functions.Comment: 17 pages, 8 figures, RevTex
Sanidade de sementes de girassol provenientes de três municípios do estado do Maranhão.
RESUMO: A crescente importância do girassol leva à necessidade da realização de estudos sobre detecção de patógenos, a fim de garantir a sanidade da cultura e a identificação de patógenos em novas áreas. Com o objetivo de avaliar a qualidade sanitária de sementes de girassol, foram analisadas sementes de vários de genótipos produzidas em ensaios na Embrapa Soja, Londrina, PR. Os ensaios foram conduzidos em três municípios do estado do Maranhão: Balsas, São Luís e Timon. A análise sanitária das sementes foi feita pelo método de papel de filtro e a identificação dos diferentes patógenos foi realizada com base nas características morfológicas. Verificou-se a ocorrência de Fusarium sp., Alternaria spp., Curvularia sp., Dreschelera sp., Aspergillus sp., Penicillium sp., Phoma sp., Trichoderma sp., Botrytis sp., Rhizoctonia sp., Rhizopus sp., Colletotrichum sp., Chaetomium sp., Cladosporium sp. e Sclerotinia sclerotiorum foi observada nas sementes de girassol, com índices de incidência variáveis. ABSTRACT: The increasing importance of sunflower leads to studies on seed pathogen, to guarantee crop sanity and to provide identification of pathogens in new areas. Genotypes seeds lots produced in Embrapa Soja assays carried out in tree cities of the State of Maranhão, Brazil (Balsas, São Luís and Timon) were analyzed, with the objective of evaluating sanitary quality of sunflower seeds. Sanitary analysis was performed by blotter test method and identification of fungi genera was based on morphological features. The occurrence of Fusarium sp., Alternaria spp., Curvularia sp., Dreschelera sp., Aspergillus sp., Penicillium sp., Phoma sp., Trichoderma sp., Botrytis sp., Rhizoctonia sp., Rhizopus sp., Colletotrichum sp., Chaetomium sp., Cladosporium sp. and Sclerotinia sclerotiorum was observed in seeds of sunflower, with variable incidences.Título em inglês: Sanity quality of sunflower seeds from three regions the state of Maranhão
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