9,512 research outputs found
Spectrum of Galactic Cosmic Rays Accelerated in Supernova Remnants
The spectra of high-energy protons and nuclei accelerated by supernova
remnant shocks are calculated taking into account magnetic field amplification
and Alfvenic drift both upstream and downstream of the shock for different
types of supernova remnants during their evolution. The maximum energy of
accelerated particles may reach eV for Fe ions in Type IIb
SNRs. The calculated energy spectrum of cosmic rays after propagation through
the Galaxy is in good agreement with the spectrum measured at the Earth.Comment: 9 pages, 3 figures, accepted to Ap
New results on source and diffusion spectral features of Galactic cosmic rays: I- B/C ratio
In a previous study (Maurin et al., 2001), we explored the set of parameters
describing diffusive propagation of cosmic rays (galactic convection,
reacceleration, halo thickness, spectral index and normalization of the
diffusion coefficient), and we identified those giving a good fit to the
measured B/C ratio. This study is now extended to take into account a sixth
free parameter, namely the spectral index of sources. We use an updated version
of our code where the reacceleration term comes from standard minimal
reacceleration models. The goal of this paper is to present a general view of
the evolution of the goodness of fit to B/C data with the propagation
parameters. In particular, we find that, unlike the well accepted picture, and
in accordance with our previous study, a Kolmogorov-like power spectrum for
diffusion is strongly disfavored. Rather, the analysis points towards
along with source spectra index . Two
distinct energy dependences are used for the source spectra: the usual
power-law in rigidity and a law modified at low energy, the second choice being
only slightly preferred. We also show that the results are not much affected by
a different choice for the diffusion scheme. Finally, we compare our findings
to recent works, using other propagation models. This study will be further
refined in a companion paper, focusing on the fluxes of cosmic ray nuclei.Comment: 32 pages, 13 figures, accepted in A&
Historical trends and variability in heat waves in the United Kingdom
This is the final version of the article. Available from MDPI via the DOI in this record.Increases in numbers and lengths of heat waves have previously been identified in global temperature records, including locations within Europe. However, studies of changes in UK heat wave characteristics are limited. Historic daily maximum temperatures from 29 weather stations with records exceeding 85 years in length across the country were examined. Heat waves were defined as periods with unusually high temperatures for each station, even if the temperatures would not be considered warm in an absolute sense. Positive trends in numbers and lengths of heat waves were identified at some stations. However, for some stations in the south east of England, lengths of very long heat waves (over 10 days) had declined since the 1970s, whereas the lengths of shorter heat waves had increased slightly. Considerable multidecadal variability in heat wave numbers and lengths was apparent at all stations. Logistic regression, using a subset of eight stations with records beginning in the nineteenth century, suggested an association between the Atlantic Multidecadal Oscillation and the variability in heat wave numbers and lengths, with the summertime North Atlantic Oscillation playing a smaller role. The results were robust against different temperature thresholds.This work was funded under the National Institute for Health Research Health Protection Research Unit (NIHR HPRU) in environmental change and health, led by the London School of Hygiene and Tropical Medicine in partnership with Public Health England (PHE), the University of Exeter and the Met Office
The EPOCH Project: I. Periodic variable stars in the EROS-2 LMC database
The EPOCH (EROS-2 periodic variable star classification using machine
learning) project aims to detect periodic variable stars in the EROS-2 light
curve database. In this paper, we present the first result of the
classification of periodic variable stars in the EROS-2 LMC database. To
classify these variables, we first built a training set by compiling known
variables in the Large Magellanic Cloud area from the OGLE and MACHO surveys.
We crossmatched these variables with the EROS-2 sources and extracted 22
variability features from 28 392 light curves of the corresponding EROS-2
sources. We then used the random forest method to classify the EROS-2 sources
in the training set. We designed the model to separate not only Scuti
stars, RR Lyraes, Cepheids, eclipsing binaries, and long-period variables, the
superclasses, but also their subclasses, such as RRab, RRc, RRd, and RRe for RR
Lyraes, and similarly for the other variable types. The model trained using
only the superclasses shows 99% recall and precision, while the model trained
on all subclasses shows 87% recall and precision. We applied the trained model
to the entire EROS-2 LMC database, which contains about 29 million sources, and
found 117 234 periodic variable candidates. Out of these 117 234 periodic
variables, 55 285 have not been discovered by either OGLE or MACHO variability
studies. This set comprises 1 906 Scuti stars, 6 607 RR Lyraes, 638
Cepheids, 178 Type II Cepheids, 34 562 eclipsing binaries, and 11 394
long-period variables. A catalog of these EROS-2 LMC periodic variable stars
will be available online at http://stardb.yonsei.ac.kr and at the CDS website
(http://vizier.u-strasbg.fr/viz-bin/VizieR).Comment: 18 pages, 20 figures, suggseted language-editing by the A&A editorial
office is applie
The contribution of supernova remnants to the galactic cosmic ray spectrum
The supernova paradigm for the origin of galactic cosmic rays has been deeply
affected by the development of the non-linear theory of particle acceleration
at shock waves. Here we discuss the implications of applying such theory to the
calculation of the spectrum of cosmic rays at Earth as accelerated in supernova
remnants and propagating in the Galaxy. The spectrum is calculated taking into
account the dynamical reaction of the accelerated particles on the shock, the
generation of magnetic turbulence which enhances the scattering near the shock,
and the dynamical reaction of the amplified field on the plasma. Most
important, the spectrum of cosmic rays at Earth is calculated taking into
account the flux of particles escaping from upstream during the Sedov-Taylor
phase and the adiabatically decompressed particles confined in the expanding
shell and escaping at later times. We show how the spectrum obtained in this
way is well described by a power law in momentum with spectral index close to
-4, despite the concave shape of the instantaneous spectra of accelerated
particles. On the other hand we also show how the shape of the spectrum is
sensible to details of the acceleration process and environment which are and
will probably remain very poorly known.Comment: 19 pages, 8 figures, published version (references updated
Extensive Air Showers and Accelerator Data - The NEEDS Workshop
Very high energy cosmic rays are typically studied by measuring extensive air
showers formed by secondary particles produced in collisions with air nuclei.
The indirect character of the measurement makes the physics interpretation of
cosmic ray data strongly dependent on simulations of multiparticle production
in showers. In April 2002 about 50 physicists met in Karlsruhe to discuss
various aspects of hadronic multiparticle production with the aim of
intensifying the interaction between high energy physics and cosmic ray groups.
Current and upcoming possibilities at accelerators for measuring features of
hadronic interactions of relevance to air showers were the focus of the
workshop. This article is a review of the discussions and conclusions.Comment: 10 pages, 11 figures, talk given at 12th ISVHECRI, Geneva, July
15-20, 200
Initial experience of dedicated breast PET imaging of ER+ breast cancers using [F-18]fluoroestradiol.
Dedicated breast positron emission tomography (dbPET) is an emerging technology with high sensitivity and spatial resolution that enables detection of sub-centimeter lesions and depiction of intratumoral heterogeneity. In this study, we report our initial experience with dbPET using [F-18]fluoroestradiol (FES) in assessing ER+ primary breast cancers. Six patients with >90% ER+ and HER2- breast cancers were imaged with dbPET and breast MRI. Two patients had ILC, three had IDC, and one had an unknown primary tumor. One ILC patient was treated with letrozole, and another patient with IDC was treated with neoadjuvant chemotherapy without endocrine treatment. In this small cohort, we observed FES uptake in ER+ primary breast tumors with specificity to ER demonstrated in a case with tamoxifen blockade. FES uptake in ILC had a diffused pattern compared to the distinct circumscribed pattern in IDC. In evaluating treatment response, the reduction of SUVmax was observed with residual disease in an ILC patient treated with letrozole, and an IDC patient treated with chemotherapy. Future study is critical to understand the change in FES SUVmax after endocrine therapy and to consider other tracer uptake metrics with SUVmax to describe ER-rich breast cancer. Limitations include variations of FES uptake in different ER+ breast cancer diseases and exclusion of posterior tissues and axillary regions. However, FES-dbPET has a high potential for clinical utility, especially in measuring response to neoadjuvant endocrine treatment. Further development to improve the field of view and studies with a larger cohort of ER+ breast cancer patients are warranted
A measurement of parity-violating gamma-ray asymmetries in polarized cold neutron capture on 35Cl, 113Cd, and 139La
An apparatus for measuring parity-violating asymmetries in gamma-ray emission
following polarized cold neutron capture was constructed as a 1/10th scale test
of the design for the forthcoming n+p->d+gamma experiment at LANSCE. The
elements of the polarized neutron beam, including a polarized 3He neutron spin
filter and a radio frequency neutron spin rotator, are described. Using CsI(Tl)
detectors and photodiode current mode readout, measurements were made of
asymmetries in gamma-ray emission following neutron capture on 35Cl, 113Cd, and
139La targets. Upper limits on the parity-allowed asymmetry were set at the level of 7 x 10^-6 for all three
targets. Parity-violating asymmetries were observed in
35Cl, A_gamma = (-29.1 +- 6.7) x 10^-6, and 139La, A_gamma = (-15.5 +- 7.1) x
10^-6, values consistent with previous measurements.Comment: 19 pages, 4 figures, submitted to Nucl. Instr. and Meth.
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Exploration of PET and MRI radiomic features for decoding breast cancer phenotypes and prognosis.
Radiomics is an emerging technology for imaging biomarker discovery and disease-specific personalized treatment management. This paper aims to determine the benefit of using multi-modality radiomics data from PET and MR images in the characterization breast cancer phenotype and prognosis. Eighty-four features were extracted from PET and MR images of 113 breast cancer patients. Unsupervised clustering based on PET and MRI radiomic features created three subgroups. These derived subgroups were statistically significantly associated with tumor grade (p = 2.0 × 10-6), tumor overall stage (p = 0.037), breast cancer subtypes (p = 0.0085), and disease recurrence status (p = 0.0053). The PET-derived first-order statistics and gray level co-occurrence matrix (GLCM) textural features were discriminative of breast cancer tumor grade, which was confirmed by the results of L2-regularization logistic regression (with repeated nested cross-validation) with an estimated area under the receiver operating characteristic curve (AUC) of 0.76 (95% confidence interval (CI) = [0.62, 0.83]). The results of ElasticNet logistic regression indicated that PET and MR radiomics distinguished recurrence-free survival, with a mean AUC of 0.75 (95% CI = [0.62, 0.88]) and 0.68 (95% CI = [0.58, 0.81]) for 1 and 2 years, respectively. The MRI-derived GLCM inverse difference moment normalized (IDMN) and the PET-derived GLCM cluster prominence were among the key features in the predictive models for recurrence-free survival. In conclusion, radiomic features from PET and MR images could be helpful in deciphering breast cancer phenotypes and may have potential as imaging biomarkers for prediction of breast cancer recurrence-free survival
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