812 research outputs found
Diffusive propagation of cosmic rays from supernova remnants in the Galaxy. I: spectrum and chemical composition
In this paper we investigate the effect of stochasticity in the spatial and
temporal distribution of supernova remnants on the spectrum and chemical
composition of cosmic rays observed at Earth. The calculations are carried out
for different choices of the diffusion coefficient D(E) experienced by cosmic
rays during propagation in the Galaxy. In particular, at high energies we
assume that D(E)\sim E^{\delta}, with and being the
reference scenarios. The large scale distribution of supernova remnants in the
Galaxy is modeled following the distribution of pulsars, with and without
accounting for the spiral structure of the Galaxy. We find that the stochastic
fluctuations induced by the spatial and temporal distribution of supernovae,
together with the effect of spallation of nuclei, lead to mild but sensible
violations of the simple, leaky-box-inspired rule that the spectrum observed at
Earth is with , where
is the slope of the cosmic ray injection spectrum at the sources. Spallation of
nuclei, even with the small rates appropriate for He, may account for slight
differences in spectral slopes between different nuclei, providing a possible
explanation for the recent CREAM observations. For we find that
the slope of the proton and helium spectra are and
respectively at energies above 1 TeV (to be compared with the measured values
of and ). For the hardening of the He
spectra is not observed. We also comment on the effect of time dependence of
the escape of cosmic rays from supernova remnants, and of a possible clustering
of the sources in superbubbles. In a second paper we will discuss the
implications of these different scenarios for the anisotropy of cosmic rays.Comment: 28 pages, To appear in JCA
Interventional radiology of the thyroid gland : critical review and state of the art
Thyroid nodules are a common incidental finding during a routinely ultrasound (US) exam unrelated to the thyroid gland in the healthy adult population with a prevalence of 20-76%. As treated before with surgery, in the last years new minimally invasive techniques have been developed as an alternative to surgery. The aim of this review, based on newly revised guidelines, is to provide some information regarding the basic principles, indications, materials, techniques, and results of mini-invasive procedures or treatments for thyroid nodules. We performed a narrative review including both newest and representative papers and guidelines based on the different procedures of ablation techniques developed in the last years for the diagnosis and the treatment of thyroid nodules. All examined papers referred very good results in term of volume nodule reduction, improvement in related symptoms and cosmetic problems, with a very low rate of complications and side effects for all the minimally invasive technique analyzed. Obviously, some differents between technique based on different kind of thyroid nodules and different indication were found. In conclusion, many thyroid nodules nowadays could be treated thanks to the advent of new mini-invasive technique that are less expensive and present a lower risk of major complications and side effects compared to surgery
Shifting a Quantum Wire through a Disordered Crystal: Observation of Conductance Fluctuations in Real Space
A quantum wire is spatially displaced by suitable electric fields with
respect to the scatterers inside a semiconductor crystal. As a function of the
wire position, the low-temperature resistance shows reproducible fluctuations.
Their characteristic temperature scale is a few hundred millikelvin, indicating
a phase-coherent effect. Each fluctuation corresponds to a single scatterer
entering or leaving the wire. This way, scattering centers can be counted one
by one.Comment: 4 pages, 3 figure
A first glance on the epigenome of Capra hircus
DNA methylation and microRNAs (miRNA) are two important forms of epigenetic modifications that play an important role in gene regulation in animals. Methylation at the carbon 5 position of cytosine residues is a fundamental layer of cellular differentiation through the control of transcriptional potential. MiRNA are small noncoding RNA molecules that regulate gene expression. Complete DNA methylomes for several organisms are now available; at the present, methylome of the domestic goat is unexplored. There is also still limited knowledge about miRNAs expression profiles in small ruminant species. Therefore, to contribute information on epigenetic modification in Capra hircus, we analysed the methylome and the miRNA population of three tissues (hypothalamus, pituitary and ovary) from 3 adult Saanen goats. We used Methylated DNA binding domain sequencing with enrichment of methylated DNA fragments and next generation sequencing. We produced least 23 million reads per sample, which were aligned to the goat reference genome. Further analyses were performed to identify peaks corresponding to hyper-methylated regions. We sequenced miRNAs expressed in the three tissues with Illumina high-throughput sequencing. Reads were mapped on the Capra hircus reference genome and both known and novel miRNAs, and miRNA target sites were identified using information collected in miRBase and using specific bioinformatic tools. This study produced a comprehensive miRNA profile related to the biology of goat. Furthermore, this is the first work dealing with methylome in Capra hircus: our preliminary results could provide new information for a deeper comprehension of epigenetic mechanisms of this species
Understanding hadronic gamma-ray emission from supernova remnants
We aim to test the plausibility of a theoretical framework in which the
gamma-ray emission detected from supernova remnants may be of hadronic origin,
i.e., due to the decay of neutral pions produced in nuclear collisions
involving relativistic nuclei. In particular, we investigate the effects
induced by magnetic field amplification on the expected particle spectra,
outlining a phenomenological scenario consistent with both the underlying
Physics and the larger and larger amount of observational data provided by the
present generation of gamma experiments, which seem to indicate rather steep
spectra for the accelerated particles. In addition, in order to study to study
how pre-supernova winds might affect the expected emission in this class of
sources, the time-dependent gamma-ray luminosity of a remnant with a massive
progenitor is worked out. Solid points and limitations of the proposed scenario
are finally discussed in a critical way.Comment: 30 pages, 5 figures; Several comments, references and a figure added.
Some typos correcte
Constraints on Dark Matter Annihilation in Clusters of Galaxies with the Fermi Large Area Telescope
Nearby clusters and groups of galaxies are potentially bright sources of
high-energy gamma-ray emission resulting from the pair-annihilation of dark
matter particles. However, no significant gamma-ray emission has been detected
so far from clusters in the first 11 months of observations with the Fermi
Large Area Telescope. We interpret this non-detection in terms of constraints
on dark matter particle properties. In particular for leptonic annihilation
final states and particle masses greater than ~200 GeV, gamma-ray emission from
inverse Compton scattering of CMB photons is expected to dominate the dark
matter annihilation signal from clusters, and our gamma-ray limits exclude
large regions of the parameter space that would give a good fit to the recent
anomalous Pamela and Fermi-LAT electron-positron measurements. We also present
constraints on the annihilation of more standard dark matter candidates, such
as the lightest neutralino of supersymmetric models. The constraints are
particularly strong when including the fact that clusters are known to contain
substructure at least on galaxy scales, increasing the expected gamma-ray flux
by a factor of ~5 over a smooth-halo assumption. We also explore the effect of
uncertainties in cluster dark matter density profiles, finding a systematic
uncertainty in the constraints of roughly a factor of two, but similar overall
conclusions. In this work, we focus on deriving limits on dark matter models; a
more general consideration of the Fermi-LAT data on clusters and clusters as
gamma-ray sources is forthcoming.Comment: accepted to JCAP, Corresponding authors: T.E. Jeltema and S. Profumo,
minor revisions to be consistent with accepted versio
Chronobiology, sleep-related risk factors and light therapy in perinatal depression : the "Life-ON" project
Perinatal depression (PND) has an overall estimated prevalence of roughly 12\ua0%. Untreated PND has significant negative consequences not only on the health of the mothers, but also on the physical, emotional and cognitive development of their children. No certain risk factors are known to predict PND and no completely safe drug treatments are available during pregnancy and breastfeeding. Sleep and depression are strongly related to each other because of a solid reciprocal causal relationship. Bright light therapy (BLT) is a well-tested and safe treatment, effective in both depression and circadian/sleep disorders
Azimuthal asymmetries of charged hadrons produced by high-energy muons scattered off longitudinally polarised deuterons
Azimuthal asymmetries in semi-inclusive production of positive (h^+) and
negative hadrons (h^-) have been measured by scattering 160 GeV muons off
longitudinally polarised deuterons at CERN. The asymmetries were decomposed in
several terms according to their expected modulation in the azimuthal angle phi
of the outgoing hadron. Each term receives contributions from one or several
spin and transverse-momentum-dependent parton distribution and fragmentation
functions. The amplitudes of all phi-modulation terms of the hadron asymmetries
integrated over the kinematic variables are found to be consistent with zero
within statistical errors, while the constant terms are nonzero and equal for
h^+ and h^- within the statistical errors. The dependencies of the
phi-modulated terms versus the Bjorken momentum fraction x, the hadron
fractional momentum z, and the hadron transverse momentum p_h^T were studied.
The x dependence of the constant terms for both positive and negative hadrons
is in agreement with the longitudinal double-spin hadron asymmetries, measured
in semi-inclusive deep-inelastic scattering. The x dependence of the sin
phi-modulation term is less pronounced than that in the corresponding HERMES
data. All other dependencies of the phi-modulation amplitudes are consistent
with zero within the statistical errors.Comment: 12 pages, 11 Figures; revision 1 signs in Eq 5 corrected, polishe
An Integrated TCGA Pan-Cancer Clinical Data Resource to Drive High-Quality Survival Outcome Analytics
For a decade, The Cancer Genome Atlas (TCGA) program collected clinicopathologic annotation data along with multi-platform molecular profiles of more than 11,000 human tumors across 33 different cancer types. TCGA clinical data contain key features representing the democratized nature of the data collection process. To ensure proper use of this large clinical dataset associated with genomic features, we developed a standardized dataset named the TCGA Pan-Cancer Clinical Data Resource (TCGA-CDR), which includes four major clinical outcome endpoints. In addition to detailing major challenges and statistical limitations encountered during the effort of integrating the acquired clinical data, we present a summary that includes endpoint usage recommendations for each cancer type. These TCGA-CDR findings appear to be consistent with cancer genomics studies independent of the TCGA effort and provide opportunities for investigating cancer biology using clinical correlates at an unprecedented scale. Analysis of clinicopathologic annotations for over 11,000 cancer patients in the TCGA program leads to the generation of TCGA Clinical Data Resource, which provides recommendations of clinical outcome endpoint usage for 33 cancer types
- …