52 research outputs found
Alternative explanation for the relaxor ferroelectric behavior in FeTiNbO6 rutile ceramics: The influence of electrode contacts
The radio-frequency permittivity-temperature profiles of acceptor-donor codoped TiO2-based rutiles commonly produce higher than expected values (>103 at 300 K) often with conflicting interpretations. A combination of dielectric spectroscopy (DS) and impedance spectroscopy (IS) with different electrode materials is used to reinvestigate the electrical properties of Fe3+-Nb5+-doped rutile in the form of FeTiNbO6 ceramics that show permittivity-temperature characteristics that are consistent with relaxor ferroelectrics (RFE). IS results reveal semiconducting grains with an activation energy of ∼0.16eV, and relative permittivity of similar magnitude and temperature dependence to undoped TiO2(<250). Reducing the work function of the electrode material by replacing Au with InGa has a dramatic effect on the IS and DS data. We propose the apparent RFE behavior observed by DS and previously attributed to the formation of nanoclustering of the cations is an extrinsic effect primarily associated with the development of Schottky barriers between the semiconducting ceramics and Au contacts
Constraints on Decaying Dark Matter from Fermi Observations of Nearby Galaxies and Clusters
We analyze the impact of Fermi gamma-ray observations (primarily
non-detections) of selected nearby galaxies, including dwarf spheroidals, and
of clusters of galaxies on decaying dark matter models. We show that the fact
that galaxy clusters do not shine in gamma rays puts the most stringent limits
available to-date on the lifetime of dark matter particles for a wide range of
particle masses and decay final states. In particular, our results put strong
constraints on the possibility of ascribing to decaying dark matter both the
increasing positron fraction reported by PAMELA and the high-energy feature in
the electron-positron spectrum measured by Fermi. Observations of nearby dwarf
galaxies and of the Andromeda Galaxy (M31) do not provide as strong limits as
those from galaxy clusters, while still improving on previous constraints in
some cases.Comment: 27 pages, 5 figures, submitted to JCAP, revised version with some
additions and correction
Determining the WIMP mass using the complementarity between direct and indirect searches and the ILC
We study the possibility of identifying dark matter properties from
XENON-like 100 kg experiments and the GLAST satellite mission. We show that
whereas direct detection experiments will probe efficiently light WIMPs, given
a positive detection (at the 10% level for GeV), GLAST
will be able to confirm and even increase the precision in the case of a NFW
profile, for a WIMP-nucleon cross-section
pb. We also predict the rate of production of a WIMP in the next generation of
colliders (ILC), and compare their sensitivity to the WIMP mass with the XENON
and GLAST projects.Comment: 32 pages, new figures and a more detailed statistical analysis. Final
version to appear in JCA
On possible interpretations of the high energy electron-positron spectrum measured by the Fermi Large Area Telescope
The Fermi-LAT experiment recently reported high precision measurements of the
spectrum of cosmic-ray electrons-plus-positrons (CRE) between 20 GeV and 1 TeV.
The spectrum shows no prominent spectral features, and is significantly harder
than that inferred from several previous experiments. Here we discuss several
interpretations of the Fermi results based either on a single large scale
Galactic CRE component or by invoking additional electron-positron primary
sources, e.g. nearby pulsars or particle Dark Matter annihilation. We show that
while the reported Fermi-LAT data alone can be interpreted in terms of a single
component scenario, when combined with other complementary experimental
results, specifically the CRE spectrum measured by H.E.S.S. and especially the
positron fraction reported by PAMELA between 1 and 100 GeV, that class of
models fails to provide a consistent interpretation. Rather, we find that
several combinations of parameters, involving both the pulsar and dark matter
scenarios, allow a consistent description of those results. We also briefly
discuss the possibility of discriminating between the pulsar and dark matter
interpretations by looking for a possible anisotropy in the CRE flux.Comment: 29 pages, 12 figures. Final version accepted for publication in
Astroparticle Physic
Corrigendum to “Structure and dielectric properties of yttrium-doped Ca0.28Ba0.72Nb2O6 ceramics” [J. Alloys Compd. 950 (2023) 169891]
The authors regret the oversight resulting in an incomplete list of contributing authors. The following text provides the missing authorial recognition for Dr. Thomas E. Hooperc. c Department of Materials Science and Engineering, University of Sheffield, Sheffield S1 3JD, UK. The authors would like to apologise for any inconvenience caused
Extragalactic Inverse Compton Light from Dark Matter Annihilation and the Pamela Positron Excess
We calculate the extragalactic diffuse emission originating from the
up-scattering of cosmic microwave photons by energetic electrons and positrons
produced in particle dark matter annihilation events at all redshifts and in
all halos. We outline the observational constraints on this emission and we
study its dependence on both the particle dark matter model (including the
particle mass and its dominant annihilation final state) and on assumptions on
structure formation and on the density profile of halos. We find that for
low-mass dark matter models, data in the X-ray band provide the most stringent
constraints, while the gamma-ray energy range probes models featuring large
masses and pair-annihilation rates, and a hard spectrum for the injected
electrons and positrons. Specifically, we point out that the all-redshift,
all-halo inverse Compton emission from many dark matter models that might
provide an explanation to the anomalous positron fraction measured by the
Pamela payload severely overproduces the observed extragalactic gamma-ray
background.Comment: Version accepted for publication in JCAP, one new figure and text
added; 19 pages, 5 figure
The microbiome of the human lower airways : a next generation sequencing perspective
Abstract
For a long time, the human lower airways were considered a sterile environment where the presence of microorganisms, typically revealed by culturing, was interpreted as an abnormal health state. More recently, high-throughput sequencing-based studies have led to a shift in this perception towards the notion that even in healthy conditions the lower airways show either transient presence or even permanent colonization by microorganisms. However, challenges related to low biomass and contamination in samples still remain, and the composition, structure and dynamics of such putative microbial communities are unclear. Here, we review the evidence for the presence of microbial communities in the human lower airways, in healthy subjects and within the context of medical conditions of interest. We also provide an overview of the methodology pertinent to high-throughput sequencing studies, specifically those based on amplicon sequencing, including a discussion of good practices and common pitfalls
Developing and validating the Japanese version of professional attitude scale for nurses
Subcellular fractionation studies indicate an intracellular localization for human monocyte specific esterase (MSE)
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