564 research outputs found
Growth, microstructure, and failure of crazes in glassy polymers
We report on an extensive study of craze formation in glassy polymers.
Molecular dynamics simulations of a coarse-grained bead-spring model were
employed to investigate the molecular level processes during craze nucleation,
widening, and breakdown for a wide range of temperature, polymer chain length
, entanglement length and strength of adhesive interactions between
polymer chains. Craze widening proceeds via a fibril-drawing process at
constant drawing stress. The extension ratio is determined by the entanglement
length, and the characteristic length of stretched chain segments in the
polymer craze is . In the craze, tension is mostly carried by the
covalent backbone bonds, and the force distribution develops an exponential
tail at large tensile forces. The failure mode of crazes changes from
disentanglement to scission for , and breakdown through scission
is governed by large stress fluctuations. The simulations also reveal
inconsistencies with previous theoretical models of craze widening that were
based on continuum level hydrodynamics
K_S\rightarrow \gamma\gamma , K_L\rightarrow\pi^0\gamma\gamma$ and Unitarity
Agreement between the experimental value and the number predicted via a one-loop chiral perturbation
theory calculation has been cited as a success for the latter. On the other
hand the one-loop prediction for the closely related process has been found to be a factor three below the experimental
value. Using the inputs of unitarity and dispersion relations, we demonstrate
the importance of higher order loop effects to both of these processes.Comment: 20 pages (4 figures available on request), UMHEP-39
Non trivial generalizations of the Schwinger pair production result
We present new, non trivial generalizations of the recent Tomaras, Tsamis and
Woodard extension of the original Schwinger formula for charged pair production
in a constant field.Comment: 11 page
Rapid modification of the bone microenvironment following short-term treatment with Cabozantinib in vivo
Introduction: Bone metastasis remains incurable with treatment restricted to palliative care. Cabozantinib (CBZ) is
targeted against multiple receptor tyrosine kinases involved in tumour pathobiology, including hepatocyte growth
factor receptor (MET) and vascular endothelial growth factor receptor 2 (VEGFR-2). CBZ has demonstrated clinical
activity in advanced prostate cancer with resolution of lesions visible on bone scans, implicating a potential role of
the bone microenvironment as a mediator of CBZ effects. We characterised the effects of short-term administration
of CBZ on bone in a range of in vivo models to determine how CBZ affects bone in the absence of tumour.
Methods: Studies were performed in a variety of in vivo models including male and female BALB/c nude mice (age 6â
17-weeks). Animals received CBZ (30 mg/kg, 5Ă weekly) or sterile H2O control for 5 or 10 days. Effects on bone integrity
(ÎŒCT), bone cell activity (PINP, TRAP ELISA), osteoblast and osteoclast number/mm trabecular bone surface,
area of epiphyseal growth plate cartilage, megakaryocyte numbers and bone marrow composition were assessed.
Effects of longer-term treatment (15-day & 6-week administration) were assessed in male NOD/SCID and beige
SCID mice.
Results: CBZ treatment had significant effects on the bone microenvironment, including reduced osteoclast and increased
osteoblast numbers compared to control. Trabecular bone structure was altered after 8 administrations. A
significant elongation of the epiphyseal growth plate, in particular the hypertrophic chondrocyte zone, was observed
in all CBZ treated animals irrespective of administration schedule. Both male and female BALB/c nude mice had increased
megakaryocyte numbers/mm2 tissue after 10-day CBZ treatment, in addition to vascular ectasia, reduced
bone marrow cellularity and extravasation of red blood cells into the extra-vascular bone marrow. All CBZinduced
effects were transient and rapidly lost following cessation of treatment.
Conclusion: Short-term administration of CBZ induces rapid, reversible effects on the bone microenvironmentin vivo
highlighting a potential role in mediating treatment responses
Who on Earth Is âMr. Cypherâ: Automated Friend Injection Attacks on Social Networking Sites
Multiscale multiphysics model for hydrogen embrittlement in polycrystalline nickel
RĂ©fĂ©rence bibliographique : Rol, 102487Appartient Ă lâensemble documentaire : Pho20RolAppartient Ă lâensemble documentaire : PACA1Image de press
Self-consistent description of nuclear compressional modes
Isoscalar monopole and dipole compressional modes are computed for a variety
of closed-shell nuclei in a relativistic random-phase approximation to three
different parametrizations of the Walecka model with scalar self-interactions.
Particular emphasis is placed on the role of self-consistency which by itself,
and with little else, guarantees the decoupling of the spurious
isoscalar-dipole strength from the physical response and the conservation of
the vector current. A powerful new relation is introduced to quantify the
violation of the vector current in terms of various ground-state form-factors.
For the isoscalar-dipole mode two distinct regions are clearly identified: (i)
a high-energy component that is sensitive to the size of the nucleus and scales
with the compressibility of the model and (ii) a low-energy component that is
insensitivity to the nuclear compressibility. A fairly good description of both
compressional modes is obtained by using a ``soft'' parametrization having a
compression modulus of K=224 MeV.Comment: 28 pages and 10 figures; submitted to PR
Imaging Spectroscopy of a White-Light Solar Flare
We report observations of a white-light solar flare (SOL2010-06-12T00:57,
M2.0) observed by the Helioseismic Magnetic Imager (HMI) on the Solar Dynamics
Observatory (SDO) and the Reuven Ramaty High-Energy Solar Spectroscopic Imager
(RHESSI). The HMI data give us the first space-based high-resolution imaging
spectroscopy of a white-light flare, including continuum, Doppler, and magnetic
signatures for the photospheric FeI line at 6173.34{\AA} and its neighboring
continuum. In the impulsive phase of the flare, a bright white-light kernel
appears in each of the two magnetic footpoints. When the flare occurred, the
spectral coverage of the HMI filtergrams (six equidistant samples spanning
\pm172m{\AA} around nominal line center) encompassed the line core and the blue
continuum sufficiently far from the core to eliminate significant Doppler
crosstalk in the latter, which is otherwise a possibility for the extreme
conditions in a white-light flare. RHESSI obtained complete hard X-ray and
\Upsilon-ray spectra (this was the first \Upsilon-ray flare of Cycle 24). The
FeI line appears to be shifted to the blue during the flare but does not go
into emission; the contrast is nearly constant across the line profile. We did
not detect a seismic wave from this event. The HMI data suggest stepwise
changes of the line-of-sight magnetic field in the white-light footpoints.Comment: 14 pages, 7 figures, Accepted by Solar Physic
High-Energy Aspects of Solar Flares: Overview of the Volume
In this introductory chapter, we provide a brief summary of the successes and
remaining challenges in understanding the solar flare phenomenon and its
attendant implications for particle acceleration mechanisms in astrophysical
plasmas. We also provide a brief overview of the contents of the other chapters
in this volume, with particular reference to the well-observed flare of 2002
July 23Comment: This is the introductory article for a monograph on the physics of
solar flares, inspired by RHESSI observations. The individual articles are to
appear in Space Science Reviews (2011
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