374 research outputs found
An infinite family of tight, not semi-fillable contact three-manifolds
We prove that an infinite family of virtually overtwisted tight contact
structures discovered by Honda on certain circle bundles over surfaces admit no
symplectic semi-fillings. The argument uses results of Mrowka, Ozsvath and Yu
on the translation-invariant solutions to the Seiberg-Witten equations on
cylinders and the non-triviality of the Kronheimer-Mrowka monopole invariants
of symplectic fillings.Comment: Published by Geometry and Topology at
http://www.maths.warwick.ac.uk/gt/GTVol7/paper30.abs.htm
Nonequilibrium Approach to Bloch-Peierls-Berry Dynamics
We examine the Bloch-Peierls-Berry dynamics under a classical nonequilibrium
dynamical formulation. In this formulation all coordinates in phase space
formed by the position and crystal momentum space are treated on equal footing.
Explicitly demonstrations of the no (naive) Liouville theorem and of the
validity of Darboux theorem are given. The explicit equilibrium distribution
function is obtained. The similarities and differences to previous approaches
are discussed. Our results confirm the richness of the Bloch-Peierls-Berry
dynamics
Fetal Spinal Cord Tissue in Mini-Guidance Channels Promotes Longitudinal Axonal Growth after Grafting into Hemisected Adult Rat Spinal Cords
Solid fetal spinal cord (FSC) tissue, seeded into semipermeable mini-guidance channels, was tested for the ability to promote axonal
growth across the gap created by a midthoracic (T8) hemisection in adult rats. Fetal thoracic spinal cords, at embryonic days 13 to
15, were harvested and gently aspirated into mini-guidance channels (1.25 mm in diameter and 3.0 mm in length). Care was taken to
maintain the rostro-caudal orientation of the FSC. In control rats, the FSC-channel congraft struct was exposed to 5 freeze/thaw cycles to
produce non-viable grafts before implantation into the hemisected cord. All cases revealed intact tissue cables of various diameters spanning the rostro-caudal extent of the lesion cavity, with integration of host-graft tissues at both interfaces. Immunofluorescence results
indicated that numerous neurofilament-positive axons were present within the FSC tissue cable. Double-labeling of a subpopulation of these axons with calcitonin generelated peptide indicated their peripheral nervous system (PNS) origin. Descending serotonergic and noradrenergic axons were found in the proximity of the rostral host-graft interface, but were not observed to grow into the FSC-graft. Anterograde tracing of propriospinal axons with Phaseolus vulgaris-leucoagglutinin demonstrated that axons had regenerated into the FSC-graft and had traveled longitudinally to the distal end of the channel. Few axons were observed to cross the distal host-graft interface to enter the host spinal cord. Cross-sectional analysis at the midpoint of the tissue cable stained with toluidine blue demonstrated a significant increase (P<0.01) in myelinated axons in viable FSC grafts (1455±663, mean±S.E.M.; n=6) versus freeze-thaw control grafts (155±50; n=5). In addition to the myelinated axons, many unmyelinated axons were observed in the tissue cable at the electron microscopic level. Areas resembling the PNS with typical Schwann cells, as well as those resembling the central nervous system with neurons and central neuropil, were also seen. In freeze-thaw control grafts, neither viable neurons nor central neuropil were observed. Retrograde tracing with Fast Blue and Diamidino Yellow demonstrated that neurons within the FSC graft extended axons into the host spinal cord at least for 2 mm from both the rostral and caudal host-graft interfaces. We conclude that viable FSC grafts within semipermeable guidance channels may serve both as a permissive bridge for longitudinally directed axonal growth and a potential relay for conveying information across a lesion site in
the adult rat spinal cord
Breakdown of the Luttinger sum-rule at the Mott-Hubbard transition in the one-dimensional t1-t2 Hubbard model
We investigate the momentum distribution function near the Mott-Hubbard
transition in the one-dimensional t1-t2 Hubbard model (the zig-zag Hubbard
chain), with the density-matrix renormalization-group technique. We show that
for strong interactions the Mott-Hubbard transition occurs between the
metallic-phase and an insulating dimerized phase with incommensurate spin
excitations, suggesting a decoupling of magnetic and charge excitations not
present in weak coupling. We illustrate the signatures for the Mott-Hubbard
transition and the commensurate-incommensurate transition in the insulating
spin-gapped state in their respective ground-state momentum distribution
functions
AAV-mediated expression of wild-type and ALS-linked mutant VAPB selectively triggers death of motoneurons through a Ca2+-dependent ER-associated pathway
A dominant mutation in the gene coding for the vesicle-associated membrane protein-associated protein B (VAPB) was associated with amyotrophic lateral sclerosis, a fatal paralytic disorder characterized by the selective loss of motoneurons in the brain and spinal cord. Adeno-associated viral vectors that we show to transduce up to 90% of motoneurons in vitro were used to model VAPB-associated neurodegenerative process. We observed that Adeno-associated viral-mediated over-expression of both wild-type and mutated form of human VAPB selectively induces death of primary motoneurons, albeit with different kinetics. We provide evidence that ER stress and impaired homeostatic regulation of calcium (Ca2+) are implicated in the death process. Finally, we found that completion of the motoneuron death program triggered by the over-expression of wild-type and mutant VAPB implicates calpains, caspase 12 and 3. Our viral-based in vitro model, which recapitulates the selective vulnerability of motoneurons to the presence of mutant VAPB and also to VAPB gene dosage effect, identifies aberrant Ca2+ signals and ER-derived death pathways as important events in the motoneuron degenerative process
Neutrophil-Derived CCL3 Is Essential for the Rapid Recruitment of Dendritic Cells to the Site of Leishmania major Inoculation in Resistant Mice
Neutrophils are rapidly and massively recruited to sites of microbial infection, where they can influence the recruitment of dendritic cells. Here, we have analyzed the role of neutrophil released chemokines in the early recruitment of dendritic cells (DCs) in an experimental model of Leishmania major infection. We show in vitro, as well as during infection, that the parasite induced the expression of CCL3 selectively in neutrophils from L. major resistant mice. Neutrophil-secreted CCL3 was critical in chemotaxis of immature DCs, an effect lost upon CCL3 neutralisation. Depletion of neutrophils prior to infection, as well as pharmacological or genetic inhibition of CCL3, resulted in a significant decrease in DC recruitment at the site of parasite inoculation. Decreased DC recruitment in CCL3−/− mice was corrected by the transfer of wild type neutrophils at the time of infection. The early release of CCL3 by neutrophils was further shown to have a transient impact on the development of a protective immune response. Altogether, we identified a novel role for neutrophil-secreted CCL3 in the first wave of DC recruitment to the site of infection with L. major, suggesting that the selective release of neutrophil-secreted chemokines may regulate the development of immune response to pathogens
Materials with Colossal Dielectric Constant: Do They Exist?
Experimental evidence is provided that colossal dielectric constants, epsilon
>= 1000, sometimes reported to exist in a broad temperature range, can often be
explained by Maxwell-Wagner type contributions of depletion layers at the
interface between sample and contacts, or at grain boundaries. We demonstrate
this on a variety of different materials. We speculate that the largest
intrinsic dielectric constant observed so far in non-ferroelectric materials is
of order 100.Comment: 3 figure
The parabola theorem on continued fractions
Using geometric methods borrowed from the theory of Kleinian groups, we interpret the parabola theorem on continued fractions in terms of sequences of Möbius transformations. This geometric approach allows us to relate the Stern–Stolz series, which features in the parabola theorem, to the dynamics of certain sequences of Möbius transformations acting on three-dimensional hyperbolic space. We also obtain a version of the parabola theorem in several dimensions
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