UHECR acceleration at GRB internal shocks Globus, N; Allard, D; Mochkovitch, R ...
Monthly notices of the Royal Astronomical Society,
07/2015, Letnik:
451, Številka:
1
Journal Article
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Recent results from the Pierre Auger Observatory suggest that nuclei heavier than protons might be present in significant amounts among ultrahigh-energy cosmic rays (UHECRs). It is therefore ...interesting to investigate the acceleration both protons and nuclei in relativistic jets. We calculate the acceleration of a mixed composition of cosmic rays at Gamma-ray burst (GRB) internal shocks, taking into account the relevant energy loss processes. 3D trajectories during the relativistic Fermi cycles are simulated following previous works by Niemiec & Ostrowski. We use the internal shock model of Daigne & Mochkovitch to derive the evolution of the relevant physical quantities (magnetic fields, baryon and photon densities, shock velocity). We consider different phenomenological hypotheses about the sharing of the dissipated energy between accelerated cosmic rays, electrons and the magnetic field. For various choices of the parameters, we calculate the spectrum of cosmic rays escaping from the GRB environment as well as secondary particles produced either during the acceleration or extragalactic propagation of UHECRs. Only models where (i) the prompt emission represents only a small fraction of the energy dissipated at internal shocks and (ii) most of this dissipated energy is communicated to cosmic rays, are able to reproduce the magnitude of the UHECR flux observed on Earth. For these models, however, the observed shape of the UHECR spectrum can be well reproduced above the ankle, with an evolution of the composition compatible with the trend suggested by Auger, and associated diffuse fluxes of secondary particles which do not violate current observational limits.
While propagating from their source to the observer, ultrahigh energy cosmic rays interact with cosmological photon backgrounds and generate to the so-called ``cosmogenic neutrinos''. Here we study ...the parameter space of the cosmogenic neutrino flux given recent cosmic ray data and updates on plausible source evolution models. The shape and normalization of the cosmogenic neutrino flux are very sensitive to some of the current unknowns of ultrahigh energy cosmic ray sources and composition. We investigate various chemical compositions and maximum proton acceleration energies Ep,max which are allowed by current observations. We consider different models of source evolution in redshift and three possible scenarios for the Galactic to extragalactic transition. We summarize the parameter space for cosmogenic neutrinos into three regions: an optimistic scenario that is currently being constrained by observations, a plausible range of models in which we base many of our rate estimates, and a pessimistic scenario that will postpone detection for decades to come. We present the implications of these three scenarios for the detection of cosmogenic neutrinos from PeV to ZeV (1014-21 eV) with the existing and upcoming instruments. In the plausible range of parameters, the narrow flux variability in the EeV energy region assures low but detectable rates for IceCube (0.06-0.2 neutrino per year) and the Pierre Auger Observatory (0.03-0.06 neutrino per year), and detection should happen in the next decade. If EeV neutrinos are detected, PeV information can help select between competing models of cosmic ray composition at the highest energy and the Galactic to extragalactic transition at ankle energies. With improved sensitivity, ZeV neutrino observatories, such as ANITA and JEM-EUSO could explore and place limits on the maximum acceleration energy.
We study the production of cosmogenic neutrinos and photons during the extragalactic propagation of ultra-high-energy cosmic rays (UHECRs). For a wide range of models in cosmological evolution of ...source luminosity, composition and maximum energy we calculate the expected flux of cosmogenic secondaries by normalizing our cosmic ray output to experimental spectra and comparing the diffuse flux of GeV − TeV gamma-rays to the experimental one measured by the Fermi satellite. Most of these models yield significant neutrino fluxes for current experiments like IceCube or Pierre Auger. Furthermore, we discuss the possibilities of signing the presence of UHE proton sources either within or outside the cosmic ray horizon using neutrinos or photons observations even if the cosmic ray composition becomes heavier at the highest energies. We discuss the possible constraints that could be brought on the UHECR origin from the different messengers and energy ranges.
Abstract
Recent EACVI recommendations described the importance of limiting cardiovascular imaging during the COVID-19 pandemic in order to reduce virus transmission, protect healthcare professionals ...from contamination, and reduce consumption of personal protective equipment. However, an elevated troponin remains a frequent request for cardiac imaging in COVID-19 patients, partly because it signifies cardiac injury due to a variety of causes and partly because it is known to convey a worse prognosis. The present paper aims to provide guidance to clinicians regarding the appropriateness of cardiac imaging in the context of troponin elevation and myocardial injury, how best to decipher the mechanism of myocardial injury, and how to guide patient management.
Congenital ptosis SooHoo, Jeffrey R., MD; Davies, Brett W., MD; Allard, Felicia D., MD ...
Survey of ophthalmology,
09/2014, Letnik:
59, Številka:
5
Journal Article
Recenzirano
Abstract Congenital blepharoptosis presents within the first year of life either in isolation or as a part of many different ocular or systemic disorders. Surgical repair is challenging, and ...recurrence necessitating more than one operation is not uncommon. Not all patients with congenital ptosis require surgery, but children with amblyopia due to astigmatic anisometropia or deprivation may benefit from early surgical correction. A variety of surgical procedures to correct congenital ptosis have been described. The choice of procedure depends on a number of patient-specific factors, such as degree of ptosis and levator function, as well as surgeon preference and resource availability. We review the genetics, associated syndromes, and surgical treatments of congenital ptosis.
The monitoring of earth surface dynamic processes requires global observations of the structure and the functioning of vegetation. Moderate resolution sensors (with pixel size ranging from 250 m to ...7 km) provide frequent estimates of biophysical variables to characterize vegetation such as the leaf area index (LAI). However, the computation of LAI from moderate resolution remote sensing data induces a scaling bias on the LAI estimate if the moderate resolution pixel is heterogeneous and if the transfer function that relates remote sensing data to LAI is non-linear.
This study provides a model to evaluate and correct the scaling bias. The model is built first for a univariate semi-empirical transfer function relating LAI directly to NDVI. The scaling bias is a function of (i) the degree of non-linearity of the transfer function quantified by its second derivative and (ii) the spatial heterogeneity of the moderate resolution pixel quantified by the variogram of the high spatial resolution (20 m) NDVI image. Then, the model is extended to a bivariate transfer function where LAI is related to red and near infrared reflectances. The scaling bias depends on (i) the Hessian matrix of the transfer function and (ii) the variograms and cross variogram of the red and near infrared reflectances.
The scaling bias is investigated on several distinct landscapes from the VALERI database. Adjusting for scaling bias is critical on crop sites which are the most heterogeneous sites at the landscape level. Regarding the univariate transfer function, the magnitude of the scaling bias increases rapidly with pixel size until this size is larger than the typical spatial scale of the data. For the bivariate transfer function, it results from the addition of several components that may add up or cancel each other out. It is thus more difficult to analyze.
The accuracy of the model to estimate the scaling bias is discussed. It depends mainly on the ability of the variograms and cross variogram to represent the local dispersion variances and covariance within the moderate resolution pixel. The model is generally highly accurate at 1000 m spatial resolution for the univariate transfer function and less accurate for the bivariate transfer function.
We extend previous studies of mixed-composition extragalactic cosmic-ray source models, investigating the influence of a non-negligible extragalactic magnetic field on the propagated cosmic-ray ...spectrum and composition. We study the transport of charged particles in turbulent fields and the transition from a ballistic to a diffusive propagation regime. We introduce a method allowing a fast integration of the particle trajectories, which allows us to calculate extragalactic cosmic-ray spectra in the general case, without using either the diffusive or the rectilinear approximation. We find that the main features of the mixed-composition models – regarding the interpretation of the ankle and the non-monotonous evolution of the average cosmic-ray mass – remain essentially unchanged as long as the magnetic field intensity does not exceed a few nG.
ZIP4 is overexpressed in human pancreatic cancer and promotes tumor growth. However, little is known about the role of ZIP4 in advanced stages of this dismal neoplasm. Our goal is to study the ...underlying mechanism and define a novel signaling pathway controlled by ZIP4-modulating pancreatic tumor metastasis.
The expression of ZIP4, ZO-1, claudin-1, and ZEB1 in human pancreatic cancer tissues, genetically engineered mouse model, xenograft tumor model, and pancreatic cancer cell lines were examined, and the correlations between ZIP4 and those markers were also analyzed. Functional analysis of ZO-1, claudin-1, and ZEB1 was investigated in pancreatic cancer cell lines and orthotopic xenografts.
Genetic inactivation of ZIP4 inhibited migration and invasion in pancreatic cancer and increased the expression of ZO-1 and claudin-1. Conversely, overexpression of ZIP4 promoted migration and invasion and increased the expression of ZEB1 and downregulation of the aforementioned epithelial genes. ZIP4 downregulation of ZO-1 and claudin-1 requires the transcriptional repressor ZEB1. Further analysis demonstrated that ZIP4-mediated repression of ZO-1 and claudin-1 leads to upregulation of their targets FAK and Paxillin. Silencing of ZIP4 caused reduced phosphorylation of FAK and Paxillin, which was rescued by simultaneous blocking of ZO-1 or claudin-1. Clinically, we demonstrated that ZIP4 positively correlates with the levels of ZEB1 and inversely associates with the expression of ZO-1 and claudin-1.
These findings suggest a novel pathway activated by ZIP4-controlling pancreatic cancer invasiveness and metastasis, which could serve as a new therapeutic target for this devastating disease.
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