840 research outputs found
Conductivity of Coulomb interacting massless Dirac particles in graphene: Regularization-dependent parameters and symmetry constraints
We compute the Coulomb correction to the a. c. conductivity of
interacting massless Dirac particles in graphene in the collisionless limit
using the polarization tensor approach in a regularization independent
framework. Arbitrary parameters stemming from differences between
logarithmically divergent integrals are fixed on physical grounds exploiting
only spatial rotational invariance of the model which amounts to
transversality of the polarization tensor. Consequently is
unequivocally determined to be within this effective model. We
compare our result with explicit regularizations and discuss the origin of
others results for found in the literature
Educação corporativa na Embrapa Trigo: uma breve explanação.
Editores técnicos: Joseani Mesquita Antunes, Ana Lídia Variani Bonato, Márcia Barrocas Moreira Pimentel
Evolução da produção e do mercado mundial do feijão.
Realizou-se uma avaliação do mercado internacional de feijão, considerando produção, exportação e importação, mostrando o comportamento e oscilações dos principais países
Non-planar snake gaits: from Stigmatic-starts to Sidewinding
Of the vast variety of animal gaits, one of the most striking is the
non-planar undulating helical motion of a sidewinder. But non-planar helical
gaits are not limited to sidewinders. Here we report a new non-planar gait used
as an escape strategy in juvenile anacondas (Eunectes notaeus). In the
S(tigmatic)-start, named for its eponymous shape, transient locomotion arises
when the snake writhes and bends out of the plane while rolling forward about
its midsection without slippage. We present a mathematical model for an active
non-planar filament that interacts anisotropically with a frictional substrate
to quantify our observations and show that locomotion is due to a propagating
localized pulse of a topological quantity, the link density. A phase diagram as
a function of scaled body size and muscular torques shows that relatively light
juveniles are capable of S-starts but heavy adults are not, consistent with our
experimental observations. We further show theoretically that a periodic
sequence of S-starts naturally leads to sidewinding. All together, our
characterization of a novel escape strategy in snakes using non-planar gaits
highlights the role of topology in locomotion, provides a phase diagram for
gait feasibility as a function of body size, and shows that the S-start forms
the fundamental kernel underlying sidewinding
Giant congenital melanocytic naevi: review of literature
giant congenital pigmented naevi is a great reconstructive challenge for the pediatric and plastic surgeons. due to the increased risk of malignant transformation in such lesions, many procedures have been used to remove giant congenital naevi like dermoabrasion, laser treatment or surgical excision combined with reconstruction through skin expansion or skin grafting; among these, only a complete excision can offer an efficacious treatment. in our centre we use the "tissue expansion" technique in order to achieve a sufficient quantity of normal skin to perform a both staged and radical excision of these giant lesions
Nature versus Nurture: The curved spine of the galaxy cluster X-ray luminosity -- temperature relation
The physical processes that define the spine of the galaxy cluster X-ray
luminosity -- temperature (L-T) relation are investigated using a large
hydrodynamical simulation of the Universe. This simulation models the same
volume and phases as the Millennium Simulation and has a linear extent of 500
h^{-1} Mpc. We demonstrate that mergers typically boost a cluster along but
also slightly below the L-T relation. Due to this boost we expect that all of
the very brightest clusters will be near the peak of a merger. Objects from
near the top of the L-T relation tend to have assembled much of their mass
earlier than an average halo of similar final mass. Conversely, objects from
the bottom of the relation are often experiencing an ongoing or recent merger.Comment: 8 pages, 7 figures, submitted to MNRA
Weighted Sobolev spaces of radially symmetric functions
We prove dilation invariant inequalities involving radial functions,
poliharmonic operators and weights that are powers of the distance from the
origin. Then we discuss the existence of extremals and in some cases we compute
the best constants.Comment: 38 page
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