2,526 research outputs found
A Measurement of the UHECR Spectrum with the HiRes FADC Detector
We have measured the energy spectrum of ultra-high energy cosmic rays (UHECR)
with the HiRes FADC detector (HiRes-2) in monocular mode. A detailed Monte
Carlo simulation of the detector response to air showers has been used to
calculate the energy dependent acceptance of the air fluorescence detector. The
measured spectrum complements the measurement by the HiRes-1 detector down to
lower energies. Systematic effects of the assumed input spectrum and
composition on the aperture are presented, as well as systematics due to the
atmosphere.Comment: 6 pages, 8 figures, to be included in the CRIS '04 (Cosmic Ray
International Seminar) proceedings (Nucl. Phys. B
Imaging of Hepatocellular Carcinoma by Computed Tomography and Magnetic Resonance Imaging: State of the Art
Hepatocellular carcinoma (HCC) is a very frequent tumor worldwide. Its incidence is linked to the distribution of liver cirrhosis and viral hepatitis, which are the main risk factors for the development of HCC. For the evaluation of the cirrhotic liver and for the diagnosis of HCC, multidetector computed tomography (MDCT) proved to be a robust and reliable tool. In MDCT the diagnosis of HCC can be made based on neovascularization with increased arterial and decreased portal venous supply. With modern magnetic resonance imaging (MRI), spatial resolution and robustness increased dramatically. Beside the evaluation of neovascularization by means of gadolinium-enhanced early dynamic MRI, the main advantages of MRI are additional information on tissue composition and liver-specific function. With diffusion-weighted imaging or plain T(1)- and T(2)-weighted sequences, different tissue elements like fat, hemorrhage, glycogen, edema and cellular density can be evaluated. Liver-specific contrast agents give insight into the Kupffer cell density or the hepatocellular function. The integration of all these parts into the MR examination allows for a very high detection rate for overt HCC nowadays, although very small HCCs are still a challenge. Moreover, insight into the different stages of hepatocarcinogenesis can be possible with MRI. Despite its limited availability in some countries, it has to be rendered to be the modality of choice for the distinct evaluation of the cirrhotic liver. Copyright (C) 2009 S. Karger AG, Base
TeV gamma rays from blazars beyond z=1?
At TeV energies, the gamma-ray horizon of the universe is limited to
redshifts z<<1, and, therefore, any observation of TeV radiation from a source
located beyond z=1 would call for a revision of the standard paradigm. While
robust observational evidence for TeV sources at redshifts z>1 is lacking at
present, the growing number of TeV blazars with redshifts as large as z~0.5
suggests the possibility that the standard blazar models may have to be
reconsidered. We show that TeV gamma rays can be observed even from a source at
z>1, if the observed gamma rays are secondary photons produced in interactions
of high-energy protons originating from the blazar jet and propagating over
cosmological distances almost rectilinearly. This mechanism was initially
proposed as a possible explanation for the TeV gamma rays observed from blazars
with redshifts z~0.2, for which some other explanations were possible. For TeV
gamma-ray radiation detected from a blazar with z>1, this model would provide
the only viable interpretation consistent with conventional physics. It would
also have far-reaching astronomical and cosmological ramifications. In
particular, this interpretation would imply that extragalactic magnetic fields
along the line of sight are very weak, in the range 0.01 < fG < 10 fG, assuming
random fields with a correlation length of 1 Mpc, and that acceleration of E>
0.1 EeV protons in the jets of active galactic nuclei can be very effective.Comment: 8 pages, 4 figure
Shocks in relativistic transverse stratified jets, a new paradigm for radio-loud AGN
The transverse stratification of active galactic nuclei (AGN) jets is
suggested by observations and theoretical arguments, as a consequence of
intrinsic properties of the central engine (accretion disc + black hole) and
external medium. On the other hand, the one-component jet approaches are
heavily challenged by the various observed properties of plasmoids in radio
jets (knots), often associated with internal shocks. Given that such a
transverse stratification plays an important role on the jets acceleration,
stability, and interaction with the external medium, it should also induce
internal shocks with various strengths and configurations, able to describe the
observed knots behaviours. By establishing a relation between the transverse
stratification of the jets, the internal shock properties, and the multiple
observed AGN jet morphologies and behaviours, our aim is to provide a
consistent global scheme of the various AGN jet structures. Working on a large
sample of AGN radio jets monitored in very long baseline interferometry (VLBI)
by the MOJAVE collaboration, we determined the consistency of a systematic
association of the multiple knots with successive re-collimation shocks. We
then investigated the re-collimation shock formation and the influence of
different transverse stratified structures by parametrically exploring the two
relativistic outflow components with the specific relativistic hydrodynamic
(SRHD) code AMRVAC. We were able to link the different spectral classes of AGN
with specific stratified jet characteristics, in good accordance with their
VLBI radio properties and their accretion regimes.Comment: 16 pages, 12 figures, accepted for publication in A&
De Rham compatible Deep Neural Network FEM
On general regular simplicial partitions of bounded polytopal
domains , , we construct \emph{exact
neural network (NN) emulations} of all lowest order finite element spaces in
the discrete de Rham complex. These include the spaces of piecewise constant
functions, continuous piecewise linear (CPwL) functions, the classical
``Raviart-Thomas element'', and the ``N\'{e}d\'{e}lec edge element''. For all
but the CPwL case, our network architectures employ both ReLU (rectified linear
unit) and BiSU (binary step unit) activations to capture discontinuities. In
the important case of CPwL functions, we prove that it suffices to work with
pure ReLU nets. Our construction and DNN architecture generalizes previous
results in that no geometric restrictions on the regular simplicial partitions
of are required for DNN emulation. In addition, for CPwL
functions our DNN construction is valid in any dimension . Our
``FE-Nets'' are required in the variationally correct, structure-preserving
approximation of boundary value problems of electromagnetism in nonconvex
polyhedra . They are thus an essential ingredient
in the application of e.g., the methodology of ``physics-informed NNs'' or
``deep Ritz methods'' to electromagnetic field simulation via deep learning
techniques. We indicate generalizations of our constructions to higher-order
compatible spaces and other, non-compatible classes of discretizations, in
particular the ``Crouzeix-Raviart'' elements and Hybridized, Higher Order (HHO)
methods
Diaphragmatic hernia with strangulated loop of bowel presenting after colonoscopy: case report
<p>Abstract</p> <p>Background</p> <p>The incidence of diaphragmatic hernias caused or exacerbated by diagnostic colonoscopy is not well elucidated at this time, and is believed to be very rare.</p> <p>Case Presentation</p> <p>We present the case of a 57 year old man with remote history of traumatic injury who first presented with vague left shoulder pain for two weeks, mild anemia, and tested positive for fecal occult blood. Four days post colonoscopy the patient was found to have a strangulated loop of bowel herniated through the diaphragm into the left hemithorax.</p> <p>Conclusions</p> <p>In patients with previous history of serious traumatic injury and particularly those with previous splenectomy, a thorough history and physical examination before routine colonoscopy is important. A high level of suspicion for post-operative complications should also be maintained when assessing such patients.</p
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