59 research outputs found
Geometry of W-algebras from the affine Lie algebra point of view
To classify the classical field theories with W-symmetry one has to classify
the symplectic leaves of the corresponding W-algebra, which are the
intersection of the defining constraint and the coadjoint orbit of the affine
Lie algebra if the W-algebra in question is obtained by reducing a WZNW model.
The fields that survive the reduction will obey non-linear Poisson bracket (or
commutator) relations in general. For example the Toda models are well-known
theories which possess such a non-linear W-symmetry and many features of these
models can only be understood if one investigates the reduction procedure. In
this paper we analyze the SL(n,R) case from which the so-called W_n-algebras
can be obtained. One advantage of the reduction viewpoint is that it gives a
constructive way to classify the symplectic leaves of the W-algebra which we
had done in the n=2 case which will correspond to the coadjoint orbits of the
Virasoro algebra and for n=3 which case gives rise to the Zamolodchikov
algebra. Our method in principle is capable of constructing explicit
representatives on each leaf. Another attractive feature of this approach is
the fact that the global nature of the W-transformations can be explicitly
described. The reduction method also enables one to determine the ``classical
highest weight (h. w.) states'' which are the stable minima of the energy on a
W-leaf. These are important as only to those leaves can a highest weight
representation space of the W-algebra be associated which contains a
``classical h. w. state''.Comment: 17 pages, LaTeX, revised 1. and 7. chapter
An Observational Study on the Pharmacokinetics of Oseltamivir in Lactating Influenza Patients
Influenza infection may lead to serious complications in the postpartum period, therefore, oseltamivir treatment in these patients and their breastfed infants is of great importance. However, the pharmacokinetics of oseltamivir in postpartum lactating women with acute influenza infection, and the consequent infant exposure to oseltamivir are still unknown, and these data would help in assessing risk and the need for dose adjustment in breastfed infants
Chiral properties of SU(3) sextet fermions
SU(3) gauge theory with overlap fermions in the 2-index symmetric (sextet)
and fundamental representations is considered. A priori it is not known what
the pattern of chiral symmetry breaking is in a higher dimensional
representation although the general expectation is that if two representations
are both complex, the breaking pattern will be the same. This expectation is
verified for the sextet at N_f = 0 in several exact zero mode sectors. It is
shown that if the volume is large enough the same random matrix ensemble
describes both the sextet and fundamental Dirac eigenvalues. The number of zero
modes for the sextet increases approximately 5-fold relative to the fundamental
in accordance with the index theorem for small lattice spacing but zero modes
which do not correspond to integer topological charge do exist at larger
lattice spacings. The zero mode number dependence of the random matrix model
predictions correctly match the simulations in each sector and each
representation.Comment: 38 pages (12 pages text and gazillion tables/figures), minor
modification, references adde
An ideal toy model for confining, walking and conformal gauge theories: the O(3) sigma model with theta-term
A toy model is proposed for four dimensional non-abelian gauge theories
coupled to a large number of fermionic degrees of freedom. As the number of
flavors is varied the gauge theory may be confining, walking or conformal. The
toy model mimicking this feature is the two dimensional O(3) sigma model with a
theta-term. For all theta the model is asymptotically free. For small theta the
model is confining in the infra red, for theta = pi the model has a non-trivial
infra red fixed point and consequently for theta slightly below pi the coupling
walks. The first step in investigating the notoriously difficult systematic
effects of the gauge theory in the toy model is to establish non-perturbatively
that the theta parameter is actually a relevant coupling. This is done by
showing that there exist quantities that are entirely given by the total
topological charge and are well defined in the continuum limit and are
non-zero, despite the fact that the topological susceptibility is divergent.
More precisely it is established that the differences of connected correlation
functions of the topological charge (the cumulants) are finite and non-zero and
consequently there is only a single divergent parameter in Z(theta) but
otherwise it is finite. This divergent constant can be removed by an
appropriate counter term rendering the theory completely finite even at theta >
0.Comment: 9 pages, 2 figures, minor modification, references adde
Spatiotemporal Differences in Gene Expression Between Motor and Sensory Autografts and Their Effect on Femoral Nerve Regeneration in the Rat
To improve the outcome after autologous nerve grafting in the clinic, it is important to understand the limiting variables such as distinct phenotypes of motor and sensory Schwann cells. This study investigated the properties of phenotypically different autografts in a 6 mm femoral nerve defect model in the rat, where the respective femoral branches distally of the inguinal bifurcation served as homotopic, or heterotopic autografts. Axonal regeneration and target reinnervation was analyzed by gait analysis, electrophysiology, and wet muscle mass analysis. We evaluated regeneration-associated gene expression between 5 days and 10 weeks after repair, in the autografts as well as the proximal, and distal segments of the femoral nerve using qRT-PCR. Furthermore we investigated expression patterns of phenotypically pure ventral and dorsal roots. We identified highly significant differences in gene expression of a variety of regeneration-associated genes along the central – peripheral axis in healthy femoral nerves. Phenotypically mismatched grafting resulted in altered spatiotemporal expression of neurotrophic factor BDNF, GDNF receptor GFRα1, cell adhesion molecules Cadm3, Cadm4, L1CAM, and proliferation associated Ki67. Although significantly higher quadriceps muscle mass following homotopic nerve grafting was measured, we did not observe differences in gait analysis, and electrophysiological parameters between treatment paradigms. Our study provides evidence for phenotypic commitment of autologous nerve grafts after injury and gives a conclusive overview of temporal expression of several important regeneration-associated genes after repair with sensory or motor graft
Topology and higher dimensional representations
SU(3) gauge theory in the 2-index symmetric (sextet) and fundamental
representations is considered in symmetric and periodic boxes. Using the
overlap formulation in the quenched approximation it is shown that the
topological charge obtained from the sextet index theorem always leads to an
integer value and agrees with the charge obtained from the fundamental index
theorem in the continuum. At larger lattice spacing configurations exist with
fractional topological charge if the sextet index is used but these are lattice
artifacts and the probability of finding such a configuration rapidly
approaches zero. By considering the decomposition of the sextet representation
with respect to an SU(2) subgroup it is shown that the SU(2) adjoint index
theorem leads to integer charge as well. We conclude that the non-zero value of
the bilinear gaugino condensate in N=1 super-Yang-Mills theory cannot be
attributed to configurations with fractional topological charge once periodic
boundary conditions are imposed.Comment: 14 pages, 7 figures; discussion and references adde
A horse’s locomotor signature: COP path determined by the individual limb
Introduction
Ground reaction forces in sound horses with asymmetric hooves show systematic differences in the horizontal braking force and relative timing of break-over. The Center Of Pressure (COP) path quantifies the dynamic load distribution under the hoof in a moving horse. The objective was to test whether anatomical asymmetry, quantified by the difference in dorsal wall angle between the left and right forelimbs, correlates with asymmetry in the COP path between these limbs. In addition, repeatability of the COP path was investigated.
Methods
A larger group (n = 31) visually sound horses with various degree of dorsal hoof wall asymmetry trotted three times over a pressure mat. COP path was determined in a hoof-bound coordinate system. A relationship between correlations between left and right COP paths and degree of asymmetry was investigated.
Results
Using a hoof-bound coordinate system made the COP path highly repeatable and unique for each limb. The craniocaudal patterns are usually highly correlated between left and right, but the mediolateral patterns are not. Some patterns were found between COP path and dorsal wall angle but asymmetry in dorsal wall angle did not necessarily result in asymmetry in COP path and the same could be stated for symmetry.
Conclusion
This method is a highly sensitive method to quantify the net result of the interaction between all of the forces and torques that occur in the limb and its inertial properties. We argue that changes in motor control, muscle force, inertial properties, kinematics and kinetics can potentially be picked up at an early stage using this method and could therefore be used as an early detection method for changes in the musculoskeletal apparatus
Cytokine signaling by grafted neuroectodermal stem cells rescues motoneurons destined to die
Following an injury to their axons close to the cell body, adult motoneurons generally die. This type of injury, typically caused by avulsion of the spinal ventral root, initiates the activation of astrocytes and microglial cells and the extracellular space becomes loaded with excessive amounts of excitotoxic glutamate. We have provided evidence that, following ventral root avulsion and reimplantation, murine embryonic neuroectodermal stem cells (NE-GFP-4C) grafted into the rat spinal cord rescue the vast majority of the motoneurons that would otherwise die, and enable them to reinnervate peripheral targets. Stem cell grafts produced the modulatory cytokines IL-1-alpha, IL-6, IL-10, TNF-alpha and MIP-1-alpha, but not neurotrophic factors. The neurons and astrocytes in the ventral horn of grafted animals also produced IL-6 and MIP-1-alpha, indicating a strong interaction between the graft and the host tissue. The infusion of function-blocking antibodies against all cytokines into the grafted cords completely abolished their motoneuron-rescuing effect, while neutralization of only IL-10 suggested its strong effectivity as concerns motoneuron survival and a milder effect on reinnervation. It is suggested that, apart from the anti-inflammatory function of IL-10, the pro-inflammatory cytokines produced exert a strong modulatory function in the CNS, promoting the prevention of neuronal cell death
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