197 research outputs found
In search of the ideal periosteal flap for bone non-union: the chimeric fibula-periosteal flap
Vascularized periosteal flaps may increase union rates in recalcitrant long bone non-union. The fibula-periosteal chimeric flap utilizes periosteum raised on an independent periosteal vessel. This allows the periosteum to be inset freely around the osteotomy site, thereby facilitating bone consolidation.
Patients and Methods:
10 patients underwent fibula-periosteal chimeric flaps (2016 – 2022) at Canniesburn Plastic Surgery Unit, UK. Preceding non-union 18.6 months, with bone gap 7.5 cm. Patients underwent pre-operative CT angiography to identify periosteal branches. A case-control approach was used. Patients acted as their own controls with one osteotomy covered by the chimeric periosteal flap and one without, although in two patients both osteotomies were covered by a long periosteal flap.
Results:
A chimeric periosteal flap was used in 12 of 20 osteotomy sites. Periosteal flap osteotomies had a primary union rate of 100% (11/11) versus those without 28.6% (2/7) (p=0.0025). Union occurred in the chimeric periosteal flaps at 8.5 months versus 16.75 in the control group (p=0.023). 1 case excluded from primary analysis due to recurrent mycetoma. Number needed to treat = 2, indicating that 2 patients would require a chimeric periosteal flap to avoid one non-union. Survival curves with hazards ratio 4.1, equating to 4 times higher chance of union with periosteal flaps (log rank p=0.0016).
Conclusions:
The chimeric fibula-periosteal flap may increase consolidation rates in difficult cases of recalcitrant non-union. This elegant modification of the fibula flap uses periosteum that is normally discarded, and adds to accumulating data supporting the use of vascularised periosteal flaps in non-union
Radio relics in cosmological simulations
Radio relics have been discovered in many galaxy clusters. They are believed
to trace shock fronts induced by cluster mergers. Cosmological simulations
allow us to study merger shocks in detail since the intra-cluster medium is
heated by shock dissipation. Using high resolution cosmological simulations,
identifying shock fronts and applying a parametric model for the radio emission
allows us to simulate the formation of radio relics. We analyze a simulated
shock front in detail. We find a rather broad Mach number distribution. The
Mach number affects strongly the number density of relativistic electrons in
the downstream area, hence, the radio luminosity varies significantly across
the shock surface. The abundance of radio relics can be modeled with the help
of the radio power probability distribution which aims at predicting radio
relic number counts. Since the actual electron acceleration efficiency is not
known, predictions for the number counts need to be normalized by the observed
number of radio relics. For the characteristics of upcoming low frequency
surveys we find that about thousand relics are awaiting discovery.Comment: 10 pages, 4 figures, Invited talk at the conference "Diffuse
Relativistic Plasmas", Bangalore, 1-4 March 2011; in press in special issue
of Journal of Astrophysics and Astronom
High Energy Cosmic Rays From Supernovae
Cosmic rays are charged relativistic particles that reach the Earth with
extremely high energies, providing striking evidence of the existence of
effective accelerators in the Universe. Below an energy around
eV cosmic rays are believed to be produced in the Milky Way while above that
energy their origin is probably extragalactic. In the early '30s supernovae
were already identified as possible sources for the Galactic component of
cosmic rays. After the '70s this idea has gained more and more credibility
thanks to the the development of the diffusive shock acceleration theory, which
provides a robust theoretical framework for particle energization in
astrophysical environments. Afterwards, mostly in recent years, much
observational evidence has been gathered in support of this framework,
converting a speculative idea in a real paradigm. In this Chapter the basic
pillars of this paradigm will be illustrated. This includes the acceleration
mechanism, the non linear effects produced by accelerated particles onto the
shock dynamics needed to reach the highest energies, the escape process from
the sources and the transportation of cosmic rays through the Galaxy. The
theoretical picture will be corroborated by discussing several observations
which support the idea that supernova remnants are effective cosmic ray
factories.Comment: Final draft of a chapter in "Handbook of Supernovae" edited by Athem
W. Alsabti and Paul Murdi
Rayleigh-Taylor Instabilities in Type Ia Supernova Remnants undergoing Cosmic-Ray Particle Acceleration - Low Adiabatic Index Solutions
This study investigates the evolution of Rayleigh-Taylor (R-T) instabilities
in Type Ia supernova remnants that are associated with a low adiabatic index
gamma, where gamma < 5/3, which reflects the expected change in the supernova
shock structure as a result of cosmic-ray particle acceleration. Extreme cases,
such as the case with the maximum compression ratio that corresponds to
gamma=1.1, are examined. As gamma decreases, the shock compression ratio rises,
and an increasingly narrow inter shock region with a more pronounced initial
mixture of R-T unstable gas is produced. Consequently, the remnant outline may
be perturbed by small-amplitude, small-wavelength bumps. However, as the
instability decays over time, the extent of convective mixing in terms of the
ratio of the radius of the R-T fingers to the blast wave does not strongly
depend on the value of gamma for gamma >= 1.2. As a result of the age of the
remnant, the unstable gas cannot extend sufficiently far to form metal-enriched
filaments of ejecta material close to the periphery of Tycho's supernova
remnant. The consistency of the dynamic properties of Tycho's remnant with the
adiabatic model gamma=5/3 reveals that the injection of cosmic rays is too weak
to alter the shock structure. Even with very efficient acceleration of cosmic
rays at the shock, significantly enhanced mixing is not expected in Type Ia
supernova remnants.Comment: 11 pages, 10 figures, MNRAS, accepte
Restrictions and extensions of semibounded operators
We study restriction and extension theory for semibounded Hermitian operators
in the Hardy space of analytic functions on the disk D. Starting with the
operator zd/dz, we show that, for every choice of a closed subset F in T=bd(D)
of measure zero, there is a densely defined Hermitian restriction of zd/dz
corresponding to boundary functions vanishing on F. For every such restriction
operator, we classify all its selfadjoint extension, and for each we present a
complete spectral picture.
We prove that different sets F with the same cardinality can lead to quite
different boundary-value problems, inequivalent selfadjoint extension
operators, and quite different spectral configurations. As a tool in our
analysis, we prove that the von Neumann deficiency spaces, for a fixed set F,
have a natural presentation as reproducing kernel Hilbert spaces, with a
Hurwitz zeta-function, restricted to FxF, as reproducing kernel.Comment: 63 pages, 11 figure
Fast responsive and morphologically robust thermo-responsive hydrogel nanofibres from poly(N-isopropylacrylamide) and POSS crosslinker
Stable thermo-responsive hydrogel nanofibres have been prepared by electrospinning of commercial poly(N-isopropylacrylamide) (PNIPAM) in the presence of a polyhedral oligomeric silsesquioxane (POSS) possessing eight epoxide groups and of an organic-base catalyst, followed by a heat curing treatment. The nanofibres showed excellent hydrogel characteristics with fast swelling and de-swelling responses triggered by temperature changes. They were also morphologically robust as their physical integrity was preserved upon repeated hydration/dehydration cycles and exposure to solvents.<br /
Relics as probes of galaxy cluster mergers
Galaxy clusters grow by mergers with other clusters and galaxy groups. These
mergers create shocks within the intracluster medium (ICM). It is proposed that
within the shocks particles can be accelerated to extreme energies. In the
presence of a magnetic field these particles should then form large regions
emitting synchrotron radiation, creating so-called radio relics. An example of
a cluster with relics is CIZA J2242.8+5301. Here we present hydrodynamical
simulations of idealized binary cluster collisions with the aim of constraining
the merger scenario for this cluster. We conclude that by using the location,
size and width of double radio relics we can set constraints on the mass
ratios, impact parameters, timescales, and viewing geometries of binary cluster
merger events.Comment: Accepted for publication in special issue of Journal of Astrophysics
and Astronomy: conference proceedings of "Diffuse Relativistic Plasmas"
conference, Bangalore, 1-4 March 2011, 4 pages, 2 figure
Using performance-based regulation to reduce childhood obesity
BackgroundWorldwide, the public health community has recognized the growing problem of childhood obesity. But, unlike tobacco control policy, there is little evidence about what public policies would work to substantially reduce childhood obesity. Public health leaders currently tend to support traditional "command and control" schemes that order private enterprises and governments to stop or start doing specific things that, is it hoped, will yield lower childhood obesity rates. These include measures such as 1) taking sweetened beverages out of schools, 2) posting calorie counts on fast-food menu boards, 3) labeling foods with a "red light" if they contain high levels of fat or sugar, 4) limiting the density of fast food restaurants in any neighborhood, 5) requiring chain restaurants to offer "healthy" alternatives, and 6) eliminating junk food ads on television shows aimed at children. Some advocates propose other regulatory interventions such as 1) influencing the relative prices of healthy and unhealthy foods through taxes and/or subsidies and 2) suing private industry for money damages as a way of blaming childhood obesity on certain practices of the food industry (such as its marketing, product composition, or portion size decisions). The food industry generally seeks to deflect blame for childhood obesity onto others, such as parents and schools
A Jet-ADAF model for Sgr A*
The recent {\em Chandra} observation of the radio source at the center of our
Galaxy, Sgr A, puts new constraints on its theoretical models. The spectrum
is very soft, and the source is rapidly variable. We consider different models
to explain the observations. We find that the features of the x-ray spectrum
can be marginally explained with an advection-dominated accretion flow (ADAF)
model while it does not well fit the radio spectrum. An ADAF with strong winds
(ADIOS) model is not favored if we assume that the wind does not radiate.
Alternatively, we propose a coupled jet plus accretion disk model to explain
the observations for Sgr A. The accretion flow is described as an ADAF fed
by Bondi-Hoyle accretion of hot plasma in the Galactic Center region. A small
fraction of the accretion flow is ejected near the black hole, forming a jet
after passing through a shock. As a result, the electron temperature increases
to , which is about 10 times higher than the
highest temperature attained in the ADAF. The model is self-consistent since
the main jet parameters are determined by the underlying accretion disk at the
inner edge. The emergent spectrum of Sgr A is the sum of the emission from
jet and underlying ADAF. The very strong Comptonization of synchrotron emission
from the jet dominates the bremsstrahlung from the ADAF, therefore, a very
short variability timescale is expected and the predicted X-ray slope and the
radio spectrum is in very good agreement with the observations.Comment: 10 pages, 3 figures, accepted by Astronomy & Astrophysic
Surprisingly Simple Mechanical Behavior of a Complex Embryonic Tissue
Background: Previous studies suggest that mechanical feedback could coordinate morphogenetic events in embryos. Furthermore, embryonic tissues have complex structure and composition and undergo large deformations during morphogenesis. Hence we expect highly non-linear and loading-rate dependent tissue mechanical properties in embryos. Methodology/Principal Findings: We used micro-aspiration to test whether a simple linear viscoelastic model was sufficient to describe the mechanical behavior of gastrula stage Xenopus laevis embryonic tissue in vivo. We tested whether these embryonic tissues change their mechanical properties in response to mechanical stimuli but found no evidence of changes in the viscoelastic properties of the tissue in response to stress or stress application rate. We used this model to test hypotheses about the pattern of force generation during electrically induced tissue contractions. The dependence of contractions on suction pressure was most consistent with apical tension, and was inconsistent with isotropic contraction. Finally, stiffer clutches generated stronger contractions, suggesting that force generation and stiffness may be coupled in the embryo. Conclusions/Significance: The mechanical behavior of a complex, active embryonic tissue can be surprisingly well described by a simple linear viscoelastic model with power law creep compliance, even at high deformations. We found no evidence of mechanical feedback in this system. Together these results show that very simple mechanical models can be useful in describing embryo mechanics. © 2010 von Dassow et al
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