863 research outputs found
Saturation of Magnetorotational Instability through Magnetic Field Generation
The saturation mechanism of Magneto-Rotational Instability (MRI) is examined
through analytical quasilinear theory and through nonlinear computation of a
single mode in a rotating disk. We find that large-scale magnetic field is
generated through the alpha effect (the correlated product of velocity and
magnetic field fluctuations) and causes the MRI mode to saturate. If the
large-scale plasma flow is allowed to evolve, the mode can also saturate
through its flow relaxation. In astrophysical plasmas, for which the flow
cannot relax because of gravitational constraints, the mode saturates through
field generation only.Comment: 9 pages, 10 figures to appear in ApJ, Jun 2009, 10 v69
Methods of olfactory ensheathing cell harvesting from the olfactory mucosa in dogs
Olfactory ensheathing cells are thought to support regeneration and remyelination of damaged axons when transplanted into spinal cord injuries. Following transplantation, improved locomotion has been detected in many laboratory models and in dogs with naturally-occurring spinal cord injury; safety trials in humans have also been completed. For widespread clinical implementation, it will be necessary to derive large numbers of these cells from an accessible and, preferably, autologous, source making olfactory mucosa a good candidate. Here, we compared the yield of olfactory ensheathing cells from the olfactory mucosa using 3 different techniques: rhinotomy, frontal sinus keyhole approach and rhinoscopy. From canine clinical cases with spinal cord injury, 27 biopsies were obtained by rhinotomy, 7 by a keyhole approach and 1 with rhinoscopy. Biopsy via rhinoscopy was also tested in 13 cadavers and 7 living normal dogs. After 21 days of cell culture, the proportions and populations of p75-positive (presumed to be olfactory ensheathing) cells obtained by the keyhole approach and rhinoscopy were similar (~4.5 x 106 p75-positive cells; ~70% of the total cell population), but fewer were obtained by frontal sinus rhinotomy. Cerebrospinal fluid rhinorrhea was observed in one dog and emphysema in 3 dogs following rhinotomy. Blepharitis occurred in one dog after the keyhole approach. All three biopsy methods appear to be safe for harvesting a suitable number of olfactory ensheathing cells from the olfactory mucosa for transplantation within the spinal cord but each technique has specific advantages and drawbacks
p 167symptoms reported at initial diagnosis of metastatic pancreatic adenocarcinoma m pac in routine clinical practice and variation in frequencies across europe
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pd 004baseline characteristics and second line treatment for metastatic pancreatic adenocarcinoma mpac patients receiving first line folfirinox gemcitabine nab paclitaxel or gemcitabine monotherapy in routine clinical practice across europe
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o 002geographic variation in systemic treatment of metastatic pancreatic adenocarcinoma mpac patients in real world across europe
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Interfacial layering in a three-component polymer system
We study theoretically the temporal evolution and the spatial structure of
the interface between two polymer melts involving three different species (A,
A* and B). The first melt is composed of two different polymer species A and A*
which are fairly indifferent to one another (Flory parameter chi_AA* ~ 0). The
second melt is made of a pure polymer B which is strongly attracted to species
A (chi_AB 0). We then show
that, due to these contradictory tendencies, interesting properties arise
during the evolution of the interface after the melts are put into contact: as
diffusion proceeds, the interface structures into several adjacent
"compartments", or layers, of differing chemical compositions, and in addition,
the central mixing layer grows in a very asymmetric fashion. Such unusual
behaviour might lead to interesting mechanical properties, and demonstrates on
a specific case the potential richness of multi-component polymer interfaces
(as compared to conventional two-component interfaces) for various
applications.Comment: Revised version, to appear in Macromolecule
Locked modes and magnetic field errors in the Madison Symmetric Torus
In the Madison Symmetric Torus (MST) reversed-field pinch [Fusion Technol. 19, 13 1 ( 1991)] magnetic oscillations become stationary (locked) in the lab frame as a result of a process involving interactions between the modes, sawteeth, and field errors. Several helical modes become phase locked to each other to form a rotating localized disturbance, the disturbance locks to an impulsive field error generated at a sawtooth crash, the error fields grow monotonically after locking (perhaps due to an unstable interaction between the modes and field error), and over tens of milliseconds of growth confinement degrades and the discharge event.ually terminates. Field error control has been partially su&essful in eliminating locking
Tensile Fracture of Welded Polymer Interfaces: Miscibility, Entanglements and Crazing
Large-scale molecular simulations are performed to investigate tensile
failure of polymer interfaces as a function of welding time . Changes in the
tensile stress, mode of failure and interfacial fracture energy are
correlated to changes in the interfacial entanglements as determined from
Primitive Path Analysis. Bulk polymers fail through craze formation, followed
by craze breakdown through chain scission. At small welded interfaces are
not strong enough to support craze formation and fail at small strains through
chain pullout at the interface. Once chains have formed an average of about one
entanglement across the interface, a stable craze is formed throughout the
sample. The failure stress of the craze rises with welding time and the mode of
craze breakdown changes from chain pullout to chain scission as the interface
approaches bulk strength. The interfacial fracture energy is calculated
by coupling the simulation results to a continuum fracture mechanics model. As
in experiment, increases as before saturating at the average
bulk fracture energy . As in previous simulations of shear strength,
saturation coincides with the recovery of the bulk entanglement density. Before
saturation, is proportional to the areal density of interfacial
entanglements. Immiscibiltiy limits interdiffusion and thus suppresses
entanglements at the interface. Even small degrees of immisciblity reduce
interfacial entanglements enough that failure occurs by chain pullout and
Explicit formulae in probability and in statistical physics
We consider two aspects of Marc Yor's work that have had an impact in
statistical physics: firstly, his results on the windings of planar Brownian
motion and their implications for the study of polymers; secondly, his theory
of exponential functionals of Levy processes and its connections with
disordered systems. Particular emphasis is placed on techniques leading to
explicit calculations.Comment: 14 pages, 2 figures. To appear in Seminaire de Probabilites, Special
Issue Marc Yo
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