15,016 research outputs found
On the Statistical Foundations of Kaluza's Magnetohydrodynamics
The introduction of electromagnetic fields into the Boltzmann equation
following a 5D general relativistic approach is considered in order to
establish the transport equations for dilute charged fluids in the presence of
a weak electromagnetic field. The conserved 5D stress-energy tensor is
evaluated using the J\"uttner function for non-degenerate relativistic gases in
local equilibrium, and the evolution equations for the local thermodynamic
variables are established by means of relativistic kinetic theory. An outline
of the possibilities offered by the Kaluza-type approach to MHD is also
included.Comment: 10 page
Light Cone analysis of relativistic first-order in the gradients hydrodynamics
This work applies a Rayleigh-Brillouin light spectrum analysis in order to
establish a causality test by means of a frequency cone. This technique allows
to identify forbidden and unforbidden regions in light scattering experiments
and establishes if a set of linearized transport equations admits causal
solutions. It is shown that, when studying a relativistic fluid with its
acoustic modes interacting with light, Eckart's formalism yields a non causal
behavior. In this case the solutions describing temperature, density and
pressure fluctuations are located outside the frequency cone. In contrast, the
set of equations that arises from modified Eckart's theory (based on
relativistic kinetic theory) yields solutions that lie within the cone, so that
they are causal.Comment: 6 pages, no figure
CNS Control of Glucose Metabolism: Response to Environmental Challenges
Over the last 15 years, considerable work has accumulated to support the role of the CNS in regulating postprandial glucose levels. As discussed in the first section of this review, the CNS receives and integrates information from afferent neurons, circulating hormones, and postprandially generated nutrients to subsequently direct changes in glucose output by the liver and glucose uptake by peripheral tissues. The second major component of this review focuses on the effects of external pressures, including high fat diet and changes to the light:dark cycle on CNS-regulating glucose homeostasis. We also discuss the interaction between these different pressures and how they contribute to the multifaceted mechanisms that we hypothesize contribute to the dysregulation of glucose in type 2 diabetes mellitus (T2DM). We argue that while current peripheral therapies serve to delay the progression of T2DM, generating combined obesity and T2DM therapies targeted at the CNS, the primary site of dysfunction for both diseases, would lead to a more profound impact on the progression of both diseases
Formation of Nanotwin Networks during High-Temperature Crystallization of Amorphous Germanium
Germanium is an extremely important material used for numerous functional
applications in many fields of nanotechnology. In this paper, we study the
crystallization of amorphous Ge using atomistic simulations of critical
nano-metric nuclei at high temperatures. We find that crystallization occurs by
the recurrent transfer of atoms via a diffusive process from the amorphous
phase into suitably-oriented crystalline layers. We accompany our simulations
with a comprehensive thermodynamic and kinetic analysis of the growth process,
which explains the energy balance and the interfacial growth velocities
governing grain growth. For the crystallographic
orientation, we find a degenerate atomic rearrangement process, with two
zero-energy modes corresponding to a perfect crystalline structure and the
formation of a twin boundary. Continued growth in this direction
results in the development a twin network, in contrast with all other growth
orientations, where the crystal grows defect-free. This particular mechanism of
crystallization from amorphous phases is also observed during solid-phase
epitaxial growth of semiconductor crystals, where growth is
restrained to one dimension. We calculate the equivalent X-ray diffraction
pattern of the obtained nanotwin networks, providing grounds for experimental
validation
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