3,223 research outputs found
Nano granular metallic Fe - oxygen deficient TiO composite films: A room temperature, highly carrier polarized magnetic semiconductor
Nano granular metallic iron (Fe) and titanium dioxide (TiO) were
co-deposited on (100) lanthanum aluminate (LaAlO) substrates in a low
oxygen chamber pressure using a pulsed laser ablation deposition (PLD)
technique. The co-deposition of Fe and TiO resulted in 10 nm
metallic Fe spherical grains suspended within a TiO matrix. The
films show ferromagnetic behavior with a saturation magnetization of 3100 Gauss
at room temperature. Our estimate of the saturation magnetization based on the
size and distribution of the Fe spheres agreed well with the measured value.
The film composite structure was characterized as p-type magnetic semiconductor
at 300 K with a carrier density of the order of . The
hole carriers were excited at the interface between the nano granular Fe and
TiO matrix similar to holes excited in the metal/n-type
semiconductor interface commonly observed in Metal-Oxide-Semiconductor (MOS)
devices. From the large anomalous Hall effect directly observed in these films
it follows that the holes at the interface were strongly spin polarized.
Structure and magneto transport properties suggested that these PLD films have
potential nano spintronics applications.Comment: 6 pages in Latex including 8 figure
Mathematical modelling long-term effects of replacing Prevnar7 with Prevnar13 on invasive pneumococcal diseases in England and Wales
England and Wales recently replaced the 7-valent pneumococcal conjugate vaccine (PCV7) with its 13-valent equivalent (PCV13), partly based on projections from mathematical models of the long-term impact of such a switch compared to ceasing pneumococcal conjugate vaccination altogether. A compartmental deterministic model was used to estimate parameters governing transmission of infection and competition between different groups of pneumococcal serotypes prior to the introduction of PCV13. The best-fitting parameters were used in an individual based model to describe pneumococcal transmission dynamics and effects of various options for the vaccination programme change in England and Wales. A number of scenarios were conducted using (i) different assumptions about the number of invasive pneumococcal disease cases adjusted for the increasing trend in disease incidence prior to PCV7 introduction in England and Wales, and (ii) a range of values representing serotype replacement induced by vaccination of the additional six serotypes in PCV13. Most of the scenarios considered suggest that ceasing pneumococcal conjugate vaccine use would cause an increase in invasive pneumococcal disease incidence, while replacing PCV7 with PCV13 would cause an overall decrease. However, the size of this reduction largely depends on the level of competition induced by the additional serotypes in PCV13. The model estimates that over 20 years of PCV13 vaccination, around 5000â62000 IPD cases could be prevented compared to stopping pneumococcal conjugate vaccination altogether. Despite inevitable uncertainty around serotype replacement effects following introduction of PCV13, the model suggests a reduction in overall invasive pneumococcal disease incidence in all cases. Our results provide useful evidence on the benefits of PCV13 to countries replacing or considering replacing PCV7 with PCV13, as well as data that can be used to evaluate the cost-effectiveness of such a switch
CMB Temperature Polarization Correlation and Primordial Gravitational Waves
We examine the use of the CMB's TE cross correlation power spectrum as a
complementary test to detect primordial gravitational waves (PGWs). The first
method used is based on the determination of the lowest multipole, ,
where the TE power spectrum, , first changes sign. The second
method uses Wiener filtering on the CMB TE data to remove the density
perturbations contribution to the TE power spectrum. In principle this leaves
only the contribution of PGWs. We examine two toy experiments (one ideal and
another more realistic) to see their ability to constrain PGWs using the TE
power spectrum alone. We found that an ideal experiment, one limited only by
cosmic variance, can detect PGWs with a ratio of tensor to scalar metric
perturbation power spectra at 99.9% confidence level using only the TE
correlation. This value is comparable with current constraints obtained by WMAP
based on the upper limits to the B-mode amplitude. We demonstrate
that to measure PGWs by their contribution to the TE cross correlation power
spectrum in a realistic ground based experiment when real instrumental noise is
taken into account, the tensor-to-scalar ratio, , should be approximately
three times larger.Comment: 13 pages, 13 figures, version matches published version. Combined
with 0710.365
Resistivity of Mixed-Phase Manganites
The resistivity of manganites is studied using a
random-resistor-network, based on phase-separation between metallic and
insulating domains. When percolation occurs, both as chemical composition and
temperature vary, results in good agreement with experiments are obtained.
Similar conclusions are reached using quantum calculations and microscopic
considerations. Above the Curie temperature, it is argued that ferromagnetic
clusters should exist in Mn-oxides. Small magnetic fields induce large
changes and a bad-metal state with (disconnected) insulating
domains.Comment: 4 pages, 4 eps figure
Constraints on the Progenitor System of the Type Ia Supernova SN 2011fe/PTF11kly
Type Ia supernovae (SNe) serve as a fundamental pillar of modern cosmology,
owing to their large luminosity and a well-defined relationship between
light-curve shape and peak brightness. The precision distance measurements
enabled by SNe Ia first revealed the accelerating expansion of the universe,
now widely believed (though hardly understood) to require the presence of a
mysterious "dark" energy. General consensus holds that Type Ia SNe result from
thermonuclear explosions of a white dwarf (WD) in a binary system; however,
little is known of the precise nature of the companion star and the physical
properties of the progenitor system. Here we make use of extensive historical
imaging obtained at the location of SN 2011fe/PTF11kly, the closest SN Ia
discovered in the digital imaging era, to constrain the visible-light
luminosity of the progenitor to be 10-100 times fainter than previous limits on
other SN Ia progenitors. This directly rules out luminous red giants and the
vast majority of helium stars as the mass-donating companion to the exploding
white dwarf. Any evolved red companion must have been born with mass less than
3.5 times the mass of the Sun. These observations favour a scenario where the
exploding WD of SN 2011fe/PTF11kly, accreted matter either from another WD, or
by Roche-lobe overflow from a subgiant or main-sequence companion star.Comment: 22 pages, 6 figures, submitte
A Millimeter-Wave Galactic Plane Survey With The BICEP Polarimeter
In addition to its potential to probe the Inflationary cosmological paradigm,
millimeter-wave polarimetry is a powerful tool for studying the Milky Way
galaxy's composition and magnetic field structure. Towards this end, presented
here are Stokes I, Q, and U maps of the Galactic plane from the millimeter-wave
polarimeter BICEP covering the Galactic longitude range 260 - 340 degrees in
three atmospheric transmission windows centered on 100, 150, and 220 GHz. The
maps sample an optical depth 1 < AV < 30, and are consistent with previous
characterizations of the Galactic millimeter-wave frequency spectrum and the
large-scale magnetic field structure permeating the interstellar medium.
Polarized emission is detected over the entire region within two degrees of the
Galactic plane and indicates that the large-scale magnetic field is oriented
parallel to the plane of the Galaxy. An observed trend of decreasing
polarization fraction with increasing total intensity rules out the simplest
model of a constant Galactic magnetic field throughout the Galaxy. Including
WMAP data in the analysis, the degree-scale frequency spectrum of Galactic
polarization fraction is plotted between 23 and 220 GHz for the first time. A
generally increasing trend of polarization fraction with electromagnetic
frequency is found, which varies from 0.5%-1.5%at frequencies below 50 GHz to
2.5%-3.5%above 90 GHz. The BICEP and WMAP data are fit to a two-component
(synchrotron and dust) model showing that the higher frequency BICEP data are
necessary to tightly constrain the amplitude and spectral index of Galactic
dust. Furthermore, the dust amplitude predicted by this two-component fit is
consistent with model predictions of dust emission in the BICEP bands
Accreting Black Holes
This chapter provides a general overview of the theory and observations of
black holes in the Universe and on their interpretation. We briefly review the
black hole classes, accretion disk models, spectral state classification, the
AGN classification, and the leading techniques for measuring black hole spins.
We also introduce quasi-periodic oscillations, the shadow of black holes, and
the observations and the theoretical models of jets.Comment: 41 pages, 18 figures. To appear in "Tutorial Guide to X-ray and
Gamma-ray Astronomy: Data Reduction and Analysis" (Ed. C. Bambi, Springer
Singapore, 2020). v3: fixed some typos and updated some parts. arXiv admin
note: substantial text overlap with arXiv:1711.1025
Diets containing sea cucumber (Isostichopus badionotus) meals are hypocholesterolemic in young rats
Peer reviewedPublisher PD
Interacting Supernovae: Types IIn and Ibn
Supernovae (SNe) that show evidence of strong shock interaction between their
ejecta and pre-existing, slower circumstellar material (CSM) constitute an
interesting, diverse, and still poorly understood category of explosive
transients. The chief reason that they are extremely interesting is because
they tell us that in a subset of stellar deaths, the progenitor star may become
wildly unstable in the years, decades, or centuries before explosion. This is
something that has not been included in standard stellar evolution models, but
may significantly change the end product and yield of that evolution, and
complicates our attempts to map SNe to their progenitors. Another reason they
are interesting is because CSM interaction is an efficient engine for making
bright transients, allowing super-luminous transients to arise from normal SN
explosion energies, and allowing transients of normal SN luminosities to arise
from sub-energetic explosions or low radioactivity yield. CSM interaction
shrouds the fast ejecta in bright shock emission, obscuring our normal view of
the underlying explosion, and the radiation hydrodynamics of the interaction is
challenging to model. The CSM interaction may also be highly non-spherical,
perhaps linked to binary interaction in the progenitor system. In some cases,
these complications make it difficult to definitively tell the difference
between a core-collapse or thermonuclear explosion, or to discern between a
non-terminal eruption, failed SN, or weak SN. Efforts to uncover the physical
parameters of individual events and connections to possible progenitor stars
make this a rapidly evolving topic that continues to challenge paradigms of
stellar evolution.Comment: Final draft of a chapter in the "SN Handbook". Accepted. 25 pages, 3
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