260,152 research outputs found
Transplantation of olfactory ensheathing cells into spinal cord lesions restores breathing and climbing
One of the most devastating effects of damage to the upper spinal cord is the loss of the ability to breathe; patients suffering these injuries can be kept alive only with assisted ventilation. No known method for repairing these injuries exists. We report here the return of supraspinal control of breathing and major improvements in climbing after the application of a novel endogenous matrix transfer method. This method permits efficient transfer and retention of cultured adult rat olfactory ensheathing cells when transplanted into large lesions that destroy all tracts on one side at the upper cervical level of the adult rat spinal cord. This demonstrates that transplantation can produce simultaneous repair of two independent spinal functions
Controlling diffusive transport in confined geometries
We analyze the diffusive transport of Brownian particles in narrow channels
with periodically varying cross-section. The geometrical confinements lead to
entropic barriers, the particle has to overcome in order to proceed in
transport direction. The transport characteristics exhibit peculiar behaviors
which are in contrast to what is observed for the transport in potentials with
purely energetic barriers. By adjusting the geometric parameters of the channel
one can effectively tune the transport and diffusion properties. A prominent
example is the maximized enhancement of diffusion for particular channel
parameters. The understanding of the role of channel-shape provides the
possibility for a design of stylized channels wherein the quality of the
transport can be efficiently optimized.Comment: accepted for publication in Acta Physica Polonica
The zero-energy state in graphene in a high magnetic field
The fate of the charge-neutral Dirac point in graphene in a high magnetic
field has been investigated at low temperatures ( 0.3 K). In samples
with small (the gate voltage needed to access the Dirac point), the
resistance at the Dirac point diverges steeply with , signalling a
crossover to an insulating state in intense field. The approach to the
insulating state is highly unusual. Despite the steep divergence in , the
profile of vs. in fixed saturates to a -independent value
below 2 K, consistent with charge carrying gapless excitations.Comment: 4 pages, 4 figures. Four new sub-figures have been added. Text
expanded to discuss data from more sample
The Topological Structure of the Space-Time Disclination
The space-time disclination is studied by making use of the decomposition
theory of gauge potential in terms of antisymmetric tensor field and
-mapping method. It is shown that the self-dual and anti-self-dual parts
of the curvature compose the space-time disclinations which are classified in
terms of topological invariants--winding number. The projection of space-time
disclination density along an antisymmetric tensor field is quantized
topologically and characterized by Brouwer degree and Hopf index.Comment: 18 pages, Revte
Interaction induced mergence of Dirac points in Non-Abelian optical lattices
We study the properties of an ultracold Fermi gas loaded in a square optical
lattice and subjected to an external and classical non-Abelian gauge field. We
calculate the energy spectrum of the system and show that the Dirac points in
the energy spectrum will remain quite stable under onsite interaction of
certain strength. Once the on-site interaction grows stronger than a critical
value, the Dirac points will no longer be stable and merge into a single hybrid
point. This mergence implies a quantum phase transition from a semimetallic
phase to a band insulator. The on-site interaction between ultracold fermions
could be conveniently controlled by Feshbach resonances in current experiments.
We proposed that this remarkable interaction induced mergence of Dirac points
may be observed in the ultracold fermi gas experiments
Cusp Summations and Cusp Relations of Simple Quad Lenses
We review five often used quad lens models, each of which has analytical
solutions and can produce four images at most. Each lens model has two
parameters, including one that describes the intensity of non-dimensional mass
density, and the other one that describes the deviation from the circular lens.
In our recent work, we have found that the cusp and the fold summations are not
equal to 0, when a point source infinitely approaches a cusp or a fold from
inner side of the caustic. Based on the magnification invariant theory, which
states that the sum of signed magnifications of the total images of a given
source is a constant, we calculate the cusp summations for the five lens
models. We find that the cusp summations are always larger than 0 for source on
the major cusps, while can be larger or smaller than 0 for source on the minor
cusps. We also find that if these lenses tend to the circular lens, the major
and minor cusp summations will have infinite values, and with positive and
negative signs respectively. The cusp summations do not change significantly if
the sources are slightly deviated from the cusps. In addition, through the
magnification invariants, we also derive the analytical signed cusp relations
on the axes for three lens models. We find that both on the major and the minor
axes the larger the lenses deviated from the circular lens, the larger the
signed cusp relations. The major cusp relations are usually larger than the
absolute minor cusp relations, but for some lens models with very large
deviation from circular lens, the minor cusp relations can be larger than the
major cusp relations.Comment: 8 pages, 4 figures, accepted for publication in MNRA
Energy-dependent Lorentz covariant parameterization of the NN interaction between 50 and 200 MeV
For laboratory kinetic energies between 50 and 200 MeV, we focus on
generating an energy-dependent Lorentz covariant parameterization of the
on-shell nucleon-nucleon (NN) scattering amplitudes in terms of a number of
Yukawa-type meson exchanges in first-order Born approximation. This
parameterization provides a good description of NN scattering observables in
the energy range of interest, and can also be extrapolated to energies between
40 and 300 MeV.Comment: 18 pages, 7 figures, Final version accepted by Physics Review
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