581 research outputs found
Two-phase behavior in strained thin films of hole-doped manganites
We present a study of the effect of biaxial strain on the electrical and
magnetic properties of thin films of manganites. We observe that manganite
films grown under biaxial compressive strain exhibit island growth morphology
which leads to a non-uniform distribution of the strain. Transport and magnetic
properties of these films suggest the coexistence of two different phases, a
metallic ferromagnet and an insulating antiferromagnet. We suggest that the
high strain regions are insulating while the low strain regions are metallic.
In such non-uniformly strained samples, we observe a large magnetoresistance
and a field-induced insulator to metal transition.Comment: 5 pages ReVTeX, 5 figures included, Figures 3, 4 and 5 low
resolution, high resolution figures available on request from authors,
submitted to Phys. Rev.
Supermassive Black Holes in the Hierarchical Universe: A General Framework and Observational Tests
(Abridged) We present a simple framework for the growth and evolution of
supermassive black holes (SMBHs) in the hierarchical structure formation
paradigm. In our model, black hole accretion is triggered during major mergers
(mass ratio>~0.3) between host dark matter halos. The successive evolution of
quasar luminosities follows a universal light curve form: an initial
exponential growth at constant Eddington ratio of order unity until it reaches
the peak luminosity, followed by a power-law decay. Assuming that the peak
luminosity correlates with the post-merger halo mass, we convolve the light
curve with the triggering rate of quasar activity to predict the quasar
luminosity function (LF). Our model reproduces the observed LF at 0.5<z<4.5 for
the full luminosity ranges probed by current optical and X-ray surveys. Our
model reproduces both the observed redshift evolution and luminosity dependence
of the linear bias of quasar/AGN clustering. Due to the scatter between
instantaneous luminosity and halo mass, quasar/AGN clustering weakly depends on
luminosity at low to intermediate luminosities; but the linear bias rises
rapidly with luminosity at the high luminosity end and at high redshift. In our
model, the Eddington ratio distribution is roughly log-normal, which broadens
and shifts to lower mean values from high luminosity quasars (L_bol>~10^46 erg
s^-1) to low luminosity AGNs (L_bol<~ 10^45 erg s^-1), in good agreement with
observations.Comment: Matched to the accepted version; ApJ in pres
Analysis of Technological Innovation and Environmental Performance Improvement in Aviation Sector
The past oil crises have caused dramatic improvements in fuel efficiency in all industrial sectors. The aviation sector—aircraft manufacturers and airlines—has also made significant efforts to improve the fuel efficiency through more advanced jet engines, high-lift wing designs, and lighter airframe materials. However, the innovations in energy-saving aircraft technologies do not coincide with the oil crisis periods. The largest improvement in aircraft fuel efficiency took place in the 1960s while the high oil prices in the 1970s and on did not induce manufacturers or airlines to achieve a faster rate of innovation. In this paper, we employ a historical analysis to examine the socio-economic reasons behind the relatively slow technological innovation in aircraft fuel efficiency over the last 40 years. Based on the industry and passenger behaviors studied and prospects for alternative fuel options, this paper offers insights for the aviation sector to shift toward more sustainable technological options in the medium term. Second-generation biofuels could be the feasible option with a meaningful reduction in aviation’s lifecycle environmental impact if they can achieve sufficient economies of scale
On the radiative efficiencies, Eddington ratios, and duty cycles of luminous high-redshift quasars
We investigate the characteristic radiative efficiency \epsilon, Eddington
ratio \lambda, and duty cycle P_0 of high-redshift active galactic nuclei
(AGN), drawing on measurements of the AGN luminosity function at z=3-6 and,
especially, on recent measurements of quasar clustering at z=3-4.5 from the
Sloan Digital Sky Survey. The free parameters of our models are \epsilon,
\lambda, and the normalization, scatter, and redshift evolution of the relation
between black hole mass \mbh and halo virial velocity V_vir. We compute the
luminosity function from the implied growth of the black hole mass function and
the quasar correlation length from the bias of the host halos. We test our
adopted formulae for the halo mass function and halo bias against measurements
from the large N-body simulation developed by the MICE collaboration. The
strong clustering of AGNs observed at z=3 and, especially, at z=4 implies that
massive black holes reside in rare, massive dark matter halos. Reproducing the
observed luminosity function then requires high efficiency \epsilon and/or low
Eddington ratio \lambda, with a lower limit (based on 2\sigma agreement with
the measured z=4 correlation length) \epsilon> 0.7\lambda/(1+0.7\lambda),
implying \epsilon > 0.17 for \lambda > 0.25. Successful models predict high
duty cycles, P_0~0.2, 0.5, and 0.9 at z=3.1, 4.5 and 6, respectively, and they
require that the fraction of halo baryons locked in the central black hole is
much larger than the locally observed value. The rapid drop in the abundance of
the massive and rare host halos at z>7 implies a proportionally rapid decline
in the number density of luminous quasars, much stronger than simple
extrapolations of the z=3-6 luminosity function would predict. (abridged)Comment: Replaced with version accepted by ApJ. More detailed analysis
including black hole mergers. Results unchange
The evolution of massive black hole seeds
We investigate the evolution of high redshift seed black hole masses at late
times and their observational signatures. The massive black hole seeds studied
here form at extremely high redshifts from the direct collapse of pre-galactic
gas discs. Populating dark matter halos with seeds formed in this way, we
follow the mass assembly of these black holes to the present time using a
Monte-Carlo merger tree. Using this machinery we predict the black hole mass
function at high redshifts and at the present time; the integrated mass density
of black holes and the luminosity function of accreting black holes as a
function of redshift. These predictions are made for a set of three seed models
with varying black hole formation efficiency. Given the accuracy of current
observational constraints, all 3 models can be adequately fit. Discrimination
between the models appears predominantly at the low mass end of the present day
black hole mass function which is not observationally well constrained.
However, all our models predict that low surface brightness, bulgeless galaxies
with large discs are least likely to be sites for the formation of massive seed
black holes at high redshifts. The efficiency of seed formation at high
redshifts has a direct influence on the black hole occupation fraction in
galaxies at z=0. This effect is more pronounced for low mass galaxies. This is
the key discriminant between the models studied here and the Population III
remnant seed model. We find that there exists a population of low mass galaxies
that do not host nuclear black holes. Our prediction of the shape of the black
hole mass - velocity dispersion relation at the low mass end is in agreement
with the recent observational determination from the census of low mass
galaxies in the Virgo cluster.Comment: MNRAS in pres
Successful treatment of fusarium solani ecthyma gangrenosum in a patient affected by leukocyte adhesion deficiency type 1 with granulocytes transfusions
<p>Abstract</p> <p>Background</p> <p>Ecthyma gangrenosum (EG) manifests as a skin lesion affecting patients suffering extreme neutropenia and is commonly associated with <it>Pseudomonas aeruginosa </it>in immunocompromised patients. Leukocyte adhesion deficiency I (LAD I) which count among primary immunodeficiency syndromes of the innate immunity, is an autosomal recessive disorder characterized in its severe phenotype by a complete defect in CD18 expression on neutrophils, delayed cord separation, chronic skin ulcers mainly due to recurrent bacterial and fungal infections, leucocytosis with high numbers of circulating neutrophils and an accumulation of abnormally low number of neutrophils at sites of infection.</p> <p>Case Presentation</p> <p>We report at our knowledge the first case of a child affected by LAD-1, who experienced during her disease course a multi-bacterial and fungal EG lesion caused by <it>fusarium solani</it>. Despite targeted antibiotics and anti-fungi therapy, the lesion extended for as long as 18 months and only massive granulocytes pockets transfusions in association with G-CSF had the capacity to cure this lesion.</p> <p>Conclusion</p> <p>We propose that granulocytes pockets transfusions will be beneficial to heal EG especially in severely immunocompromised patients.</p
Transplantation of Neural Stem Cells in Anosmic Mice
ObjectivesTreating olfactory dysfunction is a challenge for physicians. One of the therapeutic options could be transplantation of stem cells. In this study, neural stem cells were transplanted into anosmic mice.MethodsNeural stem cells were generated from the olfactory bulb of green fluorescent protein (GFP)-transgenic C57BL6 mice. Anosmia were induced by injection of intraperitoneal 3-methylindole. The neural stem cells were transplanted transnasally on the next day. The olfactory function was evaluated by a food-finding test once a week. The olfactory neuroepithelium was harvested for histologic examination and protein analysis at 4 weeks.ResultsTwenty-five percent (6/24) of the control mice that were not transplanted with neural stem cells survived at 4 weeks while 67% (8/12) of the transplanted mice survived (P=0.029). The food finding test showed that the transplanted mice resumed finding food at 3 weeks while the control mice resumed finding food at 4 weeks. GFP-positive cells were observed in the olfactory neuroepithelium of the transplanted mice. Western blotting revealed that the olfactory marker protein expression was significantly lower in the control mice than that in the transplanted mice.ConclusionThis study demonstrated that improvement of mouse survival was achieved and recovery of olfactory function was promoted by transnasal transplantation of neural stem cells in the anosmic mouse model. These results indicate that stem cells might be one of the future modalities for treating olfactory impairment
An Analytic Model of Angular Momentum Transport by Gravitational Torques: From Galaxies to Massive Black Holes
We present analytic calculations of angular momentum transport and gas inflow
in galaxies, from scales of ~kpc to deep in the potential of a central black
hole (BH). We compare these analytic calculations to numerical simulations and
use them to develop a sub-grid model of BH growth that can be incorporated into
semi-analytic models or cosmological simulations. Both analytic calculations
and simulations argue that the strongest torque on gas arises when
non-axisymmetric perturbations to the stellar gravitational potential produces
orbit crossings and shocks in the gas. This is true both at large radii ~0.01-1
kpc, where bar-like modes dominate the non-axisymmetric potential, and at
smaller radii <10 pc, where a lopsided/eccentric disk dominates. The
traditional orbit crossing criterion is not always adequate to predict the
locations of, and inflow due to, shocks in gas+stellar disks with finite sound
speeds. We derive a modified criterion that predicts the presence of shocks in
stellar dominated systems even absent formal orbit crossing. We then derive
analytic expressions for the loss of angular momentum and the resulting gas
inflow rates in the presence of such shocks. We test our analytic predictions
using hydrodynamic simulations at a range of galactic scales, and show that
they successfully predict the mass inflow rates and quasi-steady gas surface
densities with small scatter (0.3 dex). We use our analytic results to
construct a new estimate of the BH accretion rate given galaxy properties at
larger radii. This captures the key scalings in the numerical simulations.
Alternate estimates such as the local viscous accretion rate or the spherical
Bondi rate fail systematically to reproduce the simulations.Comment: 23 pages, 10 figures, minor revisions to match version accepted to
MNRA
Capture the fracture: a best practice framework and global campaign to break the fragility fracture cycle
Summary
The International Osteoporosis Foundation (IOF) Capture the Fracture Campaign aims to support implementation of Fracture Liaison Services (FLS) throughout the world.
Introduction
FLS have been shown to close the ubiquitous secondary fracture prevention care gap, ensuring that fragility fracture sufferers receive appropriate assessment and intervention to reduce future fracture risk.
Methods
Capture the Fracture has developed internationally endorsed standards for best practice, will facilitate change at the national level to drive adoption of FLS and increase awareness of the challenges and opportunities presented by secondary fracture prevention to key stakeholders. The Best Practice Framework (BPF) sets an international benchmark for FLS, which defines essential and aspirational elements of service delivery.
Results
The BPF has been reviewed by leading experts from many countries and subject to beta-testing to ensure that it is internationally relevant and fit-for-purpose. The BPF will also serve as a measurement tool for IOF to award ‘Capture the Fracture Best Practice Recognition’ to celebrate successful FLS worldwide and drive service development in areas of unmet need. The Capture the Fracture website will provide a suite of resources related to FLS and secondary fracture prevention, which will be updated as new materials become available. A mentoring programme will enable those in the early stages of development of FLS to learn from colleagues elsewhere that have achieved Best Practice Recognition. A grant programme is in development to aid clinical systems which require financial assistance to establish FLS in their localities.
Conclusion
Nearly half a billion people will reach retirement age during the next 20 years. IOF has developed Capture the Fracture because this is the single most important thing that can be done to directly improve patient care, of both women and men, and reduce the spiralling fracture-related care costs worldwide.</p
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