8,254 research outputs found
Evaluation of Audio Compression Artifacts
This paper deals with subjective evaluation of audio-coding systems. From this evaluation, it is found that, depending on the type of signal and the algorithm of the audio-coding system, different types of audible errors arise. These errors are called coding artifacts. Although three kinds of artifacts are perceivable in the auditory domain, the author proposes that in the coding domain there is only one common cause for the appearance of the artifact, inefficient tracking of transient-stochastic signals. For this purpose, state-of-the art audio coding systems use a wide range of signal processing techniques, including application of the wavelet transform, which is described here.
Design of the EURISOL multi-MW target assembly: radiation and safety issues
The multi-MW target proposed for the EURISOL facility will be based on
fission of uranium (or thorium) compounds to produce rare isotopes far from
stability. A two-step process is used for the isotope production. First,
neutrons are generated in a liquid mercury target, irradiated by the 1 GeV
proton or deuteron beam, provided by the EURISOL linac driver. Then, the
neutrons induce fission in a surrounding assembly of uranium carbide. R&D
projects on several aspects of the target assembly are ongoing. Key criteria
for the target design are a maximum beam power capability of 4 MW, a remote
handling system with minimum downtime and maximum reliability, as well as
radiation safety, minimization of hazards and the classification of the
facility. In the framework of the ongoing radiation characterization and safety
studies, radiation transport simulations have been performed to calculate the
prompt radiation dose in the target and surrounding materials, as well as to
determine shielding material and angle-dependent parameters. In this paper, we
report the results of these studies and the proposed radiation shield design
for the multi-MW target area. Furthermore, accurate estimates have been
performed of the amount of fissile elements being produced in the uranium
target assembly, for typical running conditions, in order to understand the
implications for the classification of the facility. The results are reported
and briefly discussed.Comment: 11 pages,5 figures, Invited talk at the SATIF-8 Workshop, May
22-24,2006, Pohang Accelerator Laboratory, Rep. Of Kore
A causal model of radiating stellar collapse
We find a simple exact model of radiating stellar collapse, with a shear-free
and non-accelerating interior matched to a Vaidya exterior. The heat flux is
subject to causal thermodynamics, leading to self-consistent determination of
the temperature . We solve for exactly when the mean collision time
is constant, and perturbatively in a more realistic case of variable
. Causal thermodynamics predicts temperature behaviour that can
differ significantly from the predictions of non-causal theory. In particular,
the causal theory gives a higher central temperature and greater temperature
gradient.Comment: Latex [ioplppt style] 9 pages; to appear Class. Quantum Gra
Space-time inhomogeneity, anisotropy and gravitational collapse
We investigate the evolution of non-adiabatic collapse of a shear-free
spherically symmetric stellar configuration with anisotropic stresses
accompanied with radial heat flux. The collapse begins from a curvature
singularity with infinite mass and size on an inhomogeneous space-time
background. The collapse is found to proceed without formation of an even
horizon to singularity when the collapsing configuration radiates all its mass
energy. The impact of inhomogeneity on various parameters of the collapsing
stellar configuration is examined in some specific space-time backgrounds.Comment: To appear in Gen. Relativ. Gra
Study of scintillation in natural and synthetic quartz and methacrylate
Samples from different materials typically used as optical windows or light
guides in scintillation detectors were studied in a very low background
environment, at the Canfranc Underground Laboratory, searching for
scintillation. A positive result can be confirmed for natural quartz: two
distinct scintillation components have been identified, not being excited by an
external gamma source. Although similar effect has not been observed neither
for synthetic quartz nor for methacrylate, a fast light emission excited by
intense gamma flux is evidenced for all the samples in our measurements. These
results could affect the use of these materials in low energy applications of
scintillation detectors requiring low radioactive background conditions, as
they entail a source of background.Comment: Accepted for publication in Optical Material
The nature of domain walls in ultrathin ferromagnets revealed by scanning nanomagnetometry
The recent observation of current-induced domain wall (DW) motion with large
velocity in ultrathin magnetic wires has opened new opportunities for
spintronic devices. However, there is still no consensus on the underlying
mechanisms of DW motion. Key to this debate is the DW structure, which can be
of Bloch or N\'eel type, and dramatically affects the efficiency of the
different proposed mechanisms. To date, most experiments aiming to address this
question have relied on deducing the DW structure and chirality from its motion
under additional in-plane applied fields, which is indirect and involves strong
assumptions on its dynamics. Here we introduce a general method enabling
direct, in situ, determination of the DW structure in ultrathin ferromagnets.
It relies on local measurements of the stray field distribution above the DW
using a scanning nanomagnetometer based on the Nitrogen-Vacancy defect in
diamond. We first apply the method to a Ta/Co40Fe40B20(1 nm)/MgO magnetic wire
and find clear signature of pure Bloch DWs. In contrast, we observe left-handed
N\'eel DWs in a Pt/Co(0.6 nm)/AlOx wire, providing direct evidence for the
presence of a sizable Dzyaloshinskii-Moriya interaction (DMI) at the Pt/Co
interface. This method offers a new path for exploring interfacial DMI in
ultrathin ferromagnets and elucidating the physics of DW motion under current.Comment: Main text and Supplementary Information, 33 pages and 12 figure
Leishmaniose en Equateur : 1. Incidence de la leishmaniose tégumentaire sur la façade pacifique
Une enquête porte à porte sur 961 personnes dans deux stations de la côte Pacifique de l'Equateur a permis d'évaluer l'incidence et la prévalence de la leishmaniose tégumentaire à #Leishmania panamensis$, et de noter ses manifestations cliniques. Dans les collines subandines, à Paraiso Escondido, la prévalence de cas actifs était de 4,8 %; dans les collines de la cordillère littorale, elle était de 3,6 %, et dans les deux cas il n'y avait pas de différence significative entre les sexes. L'incidence de nouveaux cas en 1991 était forte, 147 °/oo à Paraiso Escondido, et 106 °/oo à La Tablada. La prévalence cumulée atteignait 66 % à Paraiso Escondido, et 47 % à La Tablada. 62 % des patients des deux stations présentaient une seule lésion ou cicatrice. Autochtones et migrants se contaminent dans leurs cinq premières années d'existence en zone d'endémie. Néammoins, l'incidence reste élevée dans toutes les classes d'âge en raison du grand nombre de migrants (50 %). Les questionnaires ont révélé une contamination en saison sèche, de juillet jusqu'à la fin d'année. La moustiquaire était utilisée comme protection contre les phlébotomes. Ces caractéristiques clinico-épidémiologiques étaient corroborées par celles, obtenues en détection passive, à l'Hôpital A. Egas de Santo Domingo. La contamination de jeunes enfants et d'adultes des deux sexes, les lésions à la face, suggèrent une transmission domiciliaire. (Résumé d'auteur
Rational Design of Resveratrol O-methyltransferase for the Production of Pinostilbene
Pinostilbene is a monomethyl ether analog of the well-known nutraceutical resveratrol. Both compounds have health-promoting properties, but the latter undergoes rapid metabolization and has low bioavailability. O-methylation improves the stability and bioavailability of resveratrol. In plants, these reactions are performed by O-methyltransferases (OMTs). Few efficient OMTs that monomethylate resveratrol to yield pinostilbene have been described so far. Here, we report the engineering of a resveratrol OMT from Vitis vinifera (VvROMT), which has the highest catalytic efficiency in di-methylating resveratrol to yield pterostilbene. In the absence of a crystal structure, we constructed a three-dimensional protein model of VvROMT and identified four critical binding site residues by applying different in silico approaches. We performed point mutations in these positions generating W20A, F24A, F311A, and F318A variants, which greatly reduced resveratrol’s enzymatic conversion. Then, we rationally designed eight variants through comparison of the binding site residues with other stilbene OMTs. We successfully modified the native substrate selectivity of VvROMT. Variant L117F/F311W showed the highest conversion to pinostilbene, and variant L117F presented an overall increase in enzymatic activity. Our results suggest that VvROMT has potential for the tailor-made production of stilbenes.This research was funded by PROYECTO INTERDISCIPLINA-VRI-UC-II160020, number 3514-913, Pontificia Universidad Católica de Chile (to L.P.P. and A.S.) and BECA DE DOCTORADO NACIONAL 2016, number 21161084, National Agency for Research and Development (ANID), Chile (to D.P.H.), for which we are grateful. The APC was funded by Pontificia Universidad Católica de Chile
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