6,744 research outputs found
The iron Kalpha Compton Shoulder in transmitted and reflected spectra
We calculate the Equivalent Widht of the Core and the centroid energy and
relative flux of the 1st order Compton Shoulder of the iron Kalpha emission
line from neutral matter. The calculations are performed with Monte Carlo
simulations. We explore a large range of column densities for both transmitted
and reflected spectra, and study the dependence on the iron abundance. The
Compton Shoulder is now becoming observable in many objects thanks to the
improved sensitivity and/or energy resolution of XMM-Newton and Chandra
satellites, and the present work aims to provide a tool to derive informations
on the geometry and element abundances of the line emitting matter from Compton
Shoulder measurements.Comment: 4 pages; accepted for publication in MNRA
Topological Optimization of the Evaluation of Finite Element Matrices
We present a topological framework for finding low-flop algorithms for
evaluating element stiffness matrices associated with multilinear forms for
finite element methods posed over straight-sided affine domains. This framework
relies on phrasing the computation on each element as the contraction of each
collection of reference element tensors with an element-specific geometric
tensor. We then present a new concept of complexity-reducing relations that
serve as distance relations between these reference element tensors. This
notion sets up a graph-theoretic context in which we may find an optimized
algorithm by computing a minimum spanning tree. We present experimental results
for some common multilinear forms showing significant reductions in operation
count and also discuss some efficient algorithms for building the graph we use
for the optimization
The C-peptide Signaling
For years an assumption was made that C-peptide, a
byproduct of insulin biosynthesis, possessed no appreciable
physiologic role. As other contributions in this volume
amply testify, the time has come to re-evaluate that notion.
C-peptide either directly through interaction with its specific
cell-surface receptor or indirectly through an interaction
with a related membrane entity, exerts a unique effect
on several intracellular processes.We review here results of
studies attempting to elucidate such molecular effects of
C-peptide in different cell systems and tissues. Lacking a
purified C-peptide receptor, we also demonstrate C-peptide
effects on distinct elements of the insulin signal transduction
pathways
Hybrid Method for Numerical Implementation of Segmented Power Cable Conductors in Finite-element Based Ampacity Calculation
This paper addresses challenges with modelling of segmented power cable conductors using finite element analysis (FEA) for ampacity calculation. Segmented conductors improve current distribution by minimizing skin and proximity effects, thus reducing conductor losses. 2D FEA simulation offers high flexibility and accuracy beyond IEC 60287 for complex laying geometries, but the modelling of losses in segmented constructions using FEA has proven difficult due to the big difference in wire size and twisting pitch, requiring great amounts of computational power. In this paper a hybrid method is proposed, in which the IEC 60287 empirical formulae for segmented conductors are included in a 2D FEA model. The proposed method shows a good correspondence to IEC standard calculations, with deviations in conductor AC resistance of less than 1 %.Hybrid Method for Numerical Implementation of Segmented Power Cable Conductors in Finite-element Based Ampacity CalculationpublishedVersio
Transition from single to multi-walled carbon nanotubes grown by inductively coupled plasma enhanced chemical vapor deposition
In this work a simple and up-scalable technique for creating arrays of high purity carbon nanotubes via plasma enhanced chemical vapor deposition is demonstrated. Inductively coupled plasma enhanced chemical vapor deposition was used with methane and argon mixtures to grow arrays in a repeatable and controllable way. Changing the growth conditions such as temperature and growth time led to a transition between single and multi-walled carbon nanotubes and was investigated. This transition from single to multi-walled carbon nanotubes is attributed to a decrease in catalytic activity with time due to amorphous carbon deposition combined with a higher susceptibility of single-walled nanotubes to plasma etching. Patterning of these arrays was achieved by physical masking during the iron catalyst deposition process. The low growth pressure of 100 mTorr and lack of reducing gas such as ammonia or hydrogen or alumina supporting layer further show this to be a simple yet versatile procedure. These arrays were then characterized using scanning electron microscopy, Raman spectroscopy and x-ray photoelectron spectroscopy. It was also observed that at high temperature (550â°C) single-walled nanotube growth was preferential while lower temperatures (450â°C) produced mainly multi-walled arrays
Quasi-Static Fractures in Disordered Media and Iterated Conformal Maps
We study the geometrical characteristic of quasi-static fractures in
disordered media, using iterated conformal maps to determine the evolution of
the fracture pattern. This method allows an efficient and accurate solution of
the Lam\'e equations without resorting to lattice models. Typical fracture
patterns exhibit increased ramification due to the increase of the stress at
the tips. We find the roughness exponent of the experimentally relevant
backbone of the fracture pattern; it crosses over from about 0.5 for small
scales to about 0.75 for large scales, in excellent agreement with experiments.
We propose that this cross-over reflects the increased ramification of the
fracture pattern.Comment: submitted to Physical Review Letter
Further evidence of Chelonid herpesvirus 5 (ChHV5) latency : High levels of ChHV5 DNA detected in clinically healthy marine turtles
The Chelonid herpesvirus 5 (ChHV5) has been consistently associated with fibropapillomatosis (FP), a transmissible neoplastic disease of marine turtles. Whether ChHV5 plays a causal role remains debated, partly because while FP tumours have been clearly documented to contain high concentrations of ChHV5 DNA, recent PCRbased studies have demonstrated that large proportions of asymptomatic marine turtles are also carriers of ChHV5. We used a real-time PCR assay to quantify the levels of ChHV5 Glycoprotein B (gB) DNA in both tumour and non-tumour skin tissues, from clinically affected and healthy turtles drawn from distant ocean basins across four species. In agreement with previous studies, higher ratios of viral to host DNA were consistently observed in tumour versus non-tumour tissues in turtles with FP. Unexpectedly however, the levels of ChHV5 gB DNA in clinically healthy turtles were significantly higher than in non-tumour tissues from FP positive turtles. Thus, a large proportion of clinically healthy sea turtle populations worldwide across species carry ChHV5 gB DNA presumably through persistent latent infections. ChHV5 appears to be ubiquitous regardless of the animals' clinical conditions. Hence, these results support the theory that ChHV5 is a near ubiquitous virus with latency characteristics requiring co-factors, possibly environmental or immune related, to induce FP
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