384 research outputs found
Onset of entanglement
We have developed a theory of polymer entanglement using an extended
Cahn-Hilliard functional, with two extra terms. One is a nonlocal attractive
term, operating over mesoscales, which is interpreted as giving rise to
entanglement, and the other a local repulsive term indicative of excluded
volume interactions. We show how such a functional can be derived using notions
from gauge theory. We go beyond the Gaussian approximation, to the one-loop
level, to show that the system exhibits a crossover to a state of entanglement
as the average chain length between points of entanglement decreases. This
crossover is marked by critical slowing down, as the effective diffusion
constant goes to zero. We have also computed the tensile modulus of the system,
and we find a corresponding crossover to a regime of high modulus.Comment: 18 pages, with 4 figure
Orthopedic surgery increases atherosclerotic lesions and necrotic core area in ApoE-/- mice
Background and aims Observational studies show a peak incidence of cardiovascular events after major surgery. For example, the risk of myocardial infarction increases 25-fold early after hip replacement. The acuteness of this increased risk suggests abrupt enhancement in plaque vulnerability, which may be related to intra-plaque inflammation, thinner fibrous cap and/or necrotic core expansion. We hypothesized that acute systemic inflammation following major orthopedic surgery induces such changes. Methods ApoE−/− mice were fed a western diet for 10 weeks. Thereafter, half the mice underwent mid-shaft femur osteotomy followed by realignment with an intramedullary K-wire, to mimic major orthopedic surgery. Mice were sacrificed 5 or 15 days post-surgery (n = 22) or post-saline injection (n = 13). Serum amyloid A (SAA) was measured as a marker of systemic inflammation. Paraffin embedded slides of the aortic root were stained to measure total plaque area and to quantify fibrosis, calcification, necrotic core, and inflammatory cells. Results Surgery mice showed a pronounced elevation of serum amyloid A (SAA) and developed increased plaque and necrotic core area already at 5 days, which reached significance at 15 days (p = 0.019; p = 0.004 for plaque and necrotic core, respectively). Macrophage and lymphocyte density significantly decreased in the surgery group compared to the control group at 15 days (p = 0.037; p = 0.024, respectively). The density of neutrophils and mast cells remained unchanged. Conclusions Major orthopedic surgery in ApoE−/− mice triggers a systemic inflammatory response. Atherosclerotic plaque area is enlarged after surgery mainly due to an increase of the necrotic core. The role of intra-plaque inflammation in this response to surgical injury remains to be fully elucidated. © 2016 Elsevier Ireland Lt
Mean-atom-trajectory model for the velocity autocorrelation function of monatomic liquids
We present a model for the motion of an average atom in a liquid or
supercooled liquid state and apply it to calculations of the velocity
autocorrelation function and diffusion coefficient . The model
trajectory consists of oscillations at a distribution of frequencies
characteristic of the normal modes of a single potential valley, interspersed
with position- and velocity-conserving transits to similar adjacent valleys.
The resulting predictions for and agree remarkably well with MD
simulations of Na at up to almost three times its melting temperature. Two
independent processes in the model relax velocity autocorrelations: (a)
dephasing due to the presence of many frequency components, which operates at
all temperatures but which produces no diffusion, and (b) the transit process,
which increases with increasing temperature and which produces diffusion.
Because the model provides a single-atom trajectory in real space and time,
including transits, it may be used to calculate all single-atom correlation
functions.Comment: LaTeX, 8 figs. This is an updated version of cond-mat/0002057 and
cond-mat/0002058 combined Minor changes made to coincide with published
versio
HI in the Outskirts of Nearby Galaxies
The HI in disk galaxies frequently extends beyond the optical image, and can
trace the dark matter there. I briefly highlight the history of high spatial
resolution HI imaging, the contribution it made to the dark matter problem, and
the current tension between several dynamical methods to break the disk-halo
degeneracy. I then turn to the flaring problem, which could in principle probe
the shape of the dark halo. Instead, however, a lot of attention is now devoted
to understanding the role of gas accretion via galactic fountains. The current
cold dark matter theory has problems on galactic scales, such as
the core-cusp problem, which can be addressed with HI observations of dwarf
galaxies. For a similar range in rotation velocities, galaxies of type Sd have
thin disks, while those of type Im are much thicker. After a few comments on
modified Newtonian dynamics and on irregular galaxies, I close with statistics
on the HI extent of galaxies.Comment: 38 pages, 17 figures, invited review, book chapter in "Outskirts of
Galaxies", Eds. J. H. Knapen, J. C. Lee and A. Gil de Paz, Astrophysics and
Space Science Library, Springer, in pres
Lesions of the suprachiasmatic nucleus do not disturb sexual orientation of the adult male rat
First-principles characterization of a heteroceramic interface: ZrO2(001) deposited on an alpha-Al2O3(1(1)over-bar02) substrate
Complex geoarcheological investigation at the Székelyudvarhely-Kadicsfalva/Cãdiseni site (Romania)
History of clinical transplantation
How transplantation came to be a clinical discipline can be pieced together by perusing two volumes of reminiscences collected by Paul I. Terasaki in 1991-1992 from many of the persons who were directly involved. One volume was devoted to the discovery of the major histocompatibility complex (MHC), with particular reference to the human leukocyte antigens (HLAs) that are widely used today for tissue matching.1 The other focused on milestones in the development of clinical transplantation.2 All the contributions described in both volumes can be traced back in one way or other to the demonstration in the mid-1940s by Peter Brian Medawar that the rejection of allografts is an immunological phenomenon.3,4 © 2008 Springer New York
Tides in colliding galaxies
Long tails and streams of stars are the most noticeable upshots of galaxy
collisions. Their origin as gravitational, tidal, disturbances has however been
recognized only less than fifty years ago and more than ten years after their
first observations. This Review describes how the idea of galactic tides
emerged, in particular thanks to the advances in numerical simulations, from
the first ones that included tens of particles to the most sophisticated ones
with tens of millions of them and state-of-the-art hydrodynamical
prescriptions. Theoretical aspects pertaining to the formation of tidal tails
are then presented. The third part of the review turns to observations and
underlines the need for collecting deep multi-wavelength data to tackle the
variety of physical processes exhibited by collisional debris. Tidal tails are
not just stellar structures, but turn out to contain all the components usually
found in galactic disks, in particular atomic / molecular gas and dust. They
host star-forming complexes and are able to form star-clusters or even
second-generation dwarf galaxies. The final part of the review discusses what
tidal tails can tell us (or not) about the structure and content of present-day
galaxies, including their dark components, and explains how tidal tails may be
used to probe the past evolution of galaxies and their mass assembly history.
On-going deep wide-field surveys disclose many new low-surface brightness
structures in the nearby Universe, offering great opportunities for attempting
galactic archeology with tidal tails.Comment: 46 pages, 13 figures, Review to be published in "Tidal effects in
Astronomy and Astrophysics", Lecture Notes in Physics. Comments are most
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