2,289 research outputs found
Detection of Anomalous Microwave Emission in the Pleiades Reflection Nebula with WMAP and the COSMOSOMAS Experiment
We present evidence for anomalous microwave emission (AME) in the Pleiades
reflection nebula, using data from the seven-year release of the Wilkinson
Microwave Anisotropy Probe (WMAP) and from the COSMOSOMAS experiment. The flux
integrated in a 1-degree radius around R.A.=56.24^{\circ}, Dec.=23.78^{\circ}
(J2000) is 2.15 +/- 0.12 Jy at 22.8 GHz, where AME is dominant. COSMOSOMAS data
show no significant emission, but allow to set upper limits of 0.94 and 1.58 Jy
(99.7% C.L.) respectively at 10.9 and 14.7 GHz, which are crucial to pin down
the AME spectrum at these frequencies, and to discard any other emission
mechanisms which could have an important contribution to the signal detected at
22.8 GHz. We estimate the expected level of free-free emission from an
extinction-corrected H-alpha template, while the thermal dust emission is
characterized from infrared DIRBE data and extrapolated to microwave
frequencies. When we deduct the contribution from these two components at 22.8
GHz the residual flux, associated with AME, is 2.12 +/- 0.12 Jy (17.7-sigma).
The spectral energy distribution from 10 to 60 GHz can be accurately fitted
with a model of electric dipole emission from small spinning dust grains
distributed in two separated phases of molecular and atomic gas, respectively.
The dust emissivity, calculated by correlating the 22.8 GHz data with
100-micron data, is found to be 4.36+/-0.17 muK/MJy/sr, a value that is rather
low compared with typical values in dust clouds. The physical properties of the
Pleiades nebula indicate that this is indeed a much less opaque object than
others were AME has usually been detected. This fact, together with the broad
knowledge of the stellar content of this region, provides an excellent testbed
for AME characterization in physical conditions different from those generally
explored up to now.Comment: Accepted for publication in ApJ. 12 pages, 8 figure
Host adapted serotypes of <i>Salmonella enterica</i>
Salmonella constitutes a genus of zoonotic bacteria of worldwide economic and health importance. The current view of salmonella taxonomy assigns the members of this genus to two species: S. enterica and S. bongori. S. enterica itself is divided into six subspecies, enterica, salamae, arizonae, diarizonae, indica, and houtenae, also known as subspecies I, II, IIIa, IIIb, IV, and VI, respectively. Members of Salmonella enterica subspecies enterica are mainly associated with warm-blooded vertebrates and are usually transmitted by ingestion of food or water contaminated by infected faeces. The pathogenicity of most of the distinct serotypes remains undefined, and even within the most common serotypes, many questions remain to be answered regarding the interactions between the organism and the infected host.
Salmonellosis manifests itself in three major forms: enteritis, septicaemia, and abortion, each of which may be present singly or in combination, depending on both the serotype and the host involved. Although currently over 2300 serovars of Salmonella are recognized, only about 50 serotypes are isolated in any significant numbers as human or animal pathogens and they all belong to subspecies enterica. Of these, most cause acute gastroenteritis characterized by a short incubation period and a severe systemic disease in man or animals, characterized by septicaemia, fever and/or abortion, and such serotypes are often associated with one or few host species.
It is the intention of this review to present a summary of current knowledge of these host-adapted serotypes of S. enterica. The taxonomic relationships between the serotypes will be discussed together with a comparison of the pathology and pathogenesis of the disease that they cause in their natural host(s). Since much of our knowledge on salmonellosis is based on the results of work on Typhimurium, this serotype will often be used as the baseline in discussion. It is hoped that an appreciation of the differences that exist in the way these serotypes interact with the host will lead to a greater understanding of the complex host–parasite relationship that characterizes salmonella infections
Detailed study of the microwave emission of the supernova remnant 3C 396
We have observed the supernova remnant 3C~396 in the microwave region using
the Parkes 64-m telescope. Observations have been made at 8.4 GHz, 13.5 GHz,
and 18.6 GHz and in polarisation at 21.5 GHz. We have used data from several
other observatories, including previously unpublished observations performed by
the Green Bank Telescope at 31.2 GHz, to investigate the nature of the
microwave emission of 3C 396. Results show a spectral energy distribution
dominated by a single component power law emission with . Data do not favour the presence of anomalous microwave emission coming
from the source. Polarised emission at 21.5 GHz is consistent with
synchrotron-dominated emission. We present microwave maps and correlate them
with infrared (IR) maps in order to characterise the interplay between thermal
dust and microwave emission. IR vs. microwave TT plots reveal poor correlation
between mid-infrared and microwave emission from the core of the source. On the
other hand, a correlation is detected in the tail emission of the outer shell
of 3C 396, which could be ascribed to Galactic contamination.Comment: published in MNRA
CMB power spectrum parameter degeneracies in the era of precision cosmology
Cosmological parameter constraints from the CMB power spectra alone suffer
several well-known degeneracies. These degeneracies can be broken by numerical
artefacts and also a variety of physical effects that become quantitatively
important with high-accuracy data e.g. from the Planck satellite. We study
degeneracies in models with flat and non-flat spatial sections, non-trivial
dark energy and massive neutrinos, and investigate the importance of various
physical degeneracy-breaking effects. We test the CAMB power spectrum code for
numerical accuracy, and demonstrate that the numerical calculations are
accurate enough for degeneracies to be broken mainly by true physical effects
(the integrated Sachs-Wolfe effect, CMB lensing and geometrical and other
effects through recombination) rather than numerical artefacts. We quantify the
impact of CMB lensing on the power spectra, which inevitably provides
degeneracy-breaking information even without using information in the
non-Gaussianity. Finally we check the numerical accuracy of sample-based
parameter constraints using CAMB and CosmoMC. In an appendix we document recent
changes to CAMB's numerical treatment of massive neutrino perturbations, which
are tested along with other recent improvements by our degeneracy exploration
results.Comment: 27 pages, 28 figures. Latest CAMB version available from
http://camb.info/. Reduced number of figures, plot legend corrected and minor
edits to match published versio
First principles theory of chiral dichroism in electron microscopy applied to 3d ferromagnets
Recently it was demonstrated (Schattschneider et al., Nature 441 (2006),
486), that an analogue of the X-ray magnetic circular dichroism (XMCD)
experiment can be performed with the transmission electron microscope (TEM).
The new phenomenon has been named energy-loss magnetic chiral dichroism (EMCD).
In this work we present a detailed ab initio study of the chiral dichroism in
the Fe, Co and Ni transition elements. We discuss the methods used for the
simulations together with the validity and accuracy of the treatment, which
can, in principle, apply to any given crystalline specimen. The dependence of
the dichroic signal on the sample thickness, accuracy of the detector position
and the size of convergence and collection angles is calculated.Comment: 9 pages, 6 figures, submitted to Physical Review
Detection of anomalous microwave emission in the Perseus molecular cloud with the COSMOSOMAS experiment
We present direct evidence for anomalous microwave emission in the Perseus
molecular cloud, which shows a clear rising spectrum from 11 to 17 GHz in the
data of the COSMOSOMAS experiment. By extending the frequency coverage using
WMAP maps convolved with the COSMOSOMAS scanning pattern we reveal a peak flux
density of 42 (+/-) 4 Jy at 22 GHz integrated over an extended area of 1.65 x
1.0 deg centered on RA = 55.4 (+/-) 0.1 deg and Dec = 31.8 (+/-) 0.1 deg
(J2000). The flux density that we measure at this frequency is nearly an order
of magnitude higher than can be explained in terms of normal galactic emission
processes (synchrotron, free-free and thermal dust). An extended IRAS dust
feature G159.6-18.5 is found near this position and no bright unresolved source
which could be an ultracompact HII region or gigahertz peaked source could be
found. An adequate fit for the spectral density distribution can be achieved
from 10 to 50 GHz by including a very significant contribution from electric
dipole emission from small spinning dust grains.Comment: 5 pages, 2 postscript figures, accepted ApJ Let
Prospects for high-z cluster detections with Planck, based on a follow-up of 28 candidates using MegaCam@CFHT
The Planck catalogue of SZ sources limits itself to a significance threshold
of 4.5 to ensure a low contamination rate by false cluster candidates. This
means that only the most massive clusters at redshift z>0.5, and in particular
z>0.7, are expected to enter into the catalogue, with a large number of systems
in that redshift regime being expected around and just below that threshold. In
this paper, we follow-up a sample of SZ sources from the Planck SZ catalogues
from 2013 and 2015. In the latter maps, we consider detections around and at
lower significance than the threshold adopted by the Planck Collaboration. To
keep the contamination rate low, our 28 candidates are chosen to have
significant WISE detections, in combination with non-detections in SDSS/DSS,
which effectively selects galaxy cluster candidates at redshifts .
By taking r- and z-band imaging with MegaCam@CFHT, we bridge the 4000A
rest-frame break over a significant redshift range, thus allowing accurate
redshift estimates of red-sequence cluster galaxies up to z~0.8. After
discussing the possibility that an overdensity of galaxies coincides -by
chance- with a Planck SZ detection, we confirm that 16 of the candidates have
likely optical counterparts to their SZ signals, 13 (6) of which have an
estimated redshift z>0.5 (z>0.7). The richnesses of these systems are generally
lower than expected given the halo masses estimated from the Planck maps.
However, when we follow a simplistic model to correct for Eddington bias in the
SZ halo mass proxy, the richnesses are consistent with a reference
mass-richness relation established for clusters detected at higher
significance. This illustrates the benefit of an optical follow-up, not only to
obtain redshift estimates, but also to provide an independent mass proxy that
is not based on the same data the clusters are detected with, and thus not
subject to Eddington bias.Comment: 13 pages, 7 figures. Accepted for publication in A&
Simulation of magnetic circular dichroism in the electron microscope
International audienceAs Electron Energy-Loss Spectroscopy (EELS) and X-ray Absorption Spectroscopy (XAS) probe the same transitions from core-shell states to unoccupied states above the Fermi energy, it should be always possible to apply the two techniques to the same physical phenomena, such as magnetic dichroism, and obtain the same information. Indeed, the similarity in the expression of the electron and x-ray crosssections had been already exploited to prove the equivalence of X-ray Magnetic Linear Dichroism (XMLD) and anisotropy in EELS, by noting that the polarization vector of a photon plays the same role as the momentum transfer in electron scattering. Recently, the same was proven true for X-ray Magnetic Circular Dichroism (XMCD) by establishing a new TEM technique called EMCD (Electron energy-loss Magnetic Chiral Dichroism) [ ? ], which makes use of special electron scattering conditions to force the absorption of a circularly polarized virtual photon. The intrinsic advantage of EMCD over XMCD is the high spatial resolution of electron microscopes, which are readily available. Among the particular obstacles in EMCD that do not exist for synchrotron radiation is the notoriously low signal and the very particular scattering conditions necessary to observe a chiral dichroic signal. In spite of that, impressive progress was made in the last years. The signal strength could be considerably increased, and some innovations such as using a convergent beam have been introduced. EMCD has evolved into several techniques, which make full use of the versatility of the TEM and energy filtering, spectroscopy or STEM conditions [ ? ]
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