13,674 research outputs found
Loschmidt echoes in two-body random matrix ensembles
Fidelity decay is studied for quantum many-body systems with a dominant
independent particle Hamiltonian resulting e.g. from a mean field theory with a
weak two-body interaction. The diagonal terms of the interaction are included
in the unperturbed Hamiltonian, while the off-diagonal terms constitute the
perturbation that distorts the echo. We give the linear response solution for
this problem in a random matrix framework. While the ensemble average shows no
surprising behavior, we find that the typical ensemble member as represented by
the median displays a very slow fidelity decay known as ``freeze''. Numerical
calculations confirm this result and show, that the ground state even on
average displays the freeze. This may contribute to explanation of the
``unreasonable'' success of mean field theories.Comment: 9 pages, 5 figures (6 eps files), RevTex; v2: slight modifications
following referees' suggestion
Violation of the isotropic- approximation in overdoped La_{2-x}Sr_xCuO_4
Magnetotransport measurements on the overdoped cuprate La_{1.7}Sr_{0.3}CuO_4
are fitted using the Ong construction and band parameters inferred from
angle-resolved photoemission. Within a band picture, the low temperature Hall
data can only be fitted satisfactorily by invoking strong basal-plane
anisotropy in the mean-free-path . This violation of the isotropic-
approximation supports a picture of dominant small-angle elastic scattering in
cuprates due to out-of-plane substitutional disorder. We show that both band
anisotropy and anisotropy in the elastic scattering channel strongly
renormalize the Hall coefficient in overdoped La_{2-x}Sr_xCuO_4 over a wide
doping and temperature range.Comment: 4 pages, 4 figure
Experiences of people living with HIV and people living close to them of a comprehensive HIV stigma reduction community intervention in an urban and a rural setting
HIV stigma remains high globally. Although there is a selection of HIV stigma reduction interventions discussed in the literature, there is a paucity of research about the effectiveness of these interventions. This study aimed at gaining a deeper understanding of the experiences of people living with HIV (PLWH) and people living close to them from six designated groups during and after having undergone a comprehensive HIV stigma reduction community intervention in both an urban and a rural setting. Attention was focused on their expressedĀ experiences of the workshop and projects executed. A qualitative interpretive description approach was used. PLWH as participants were selected through purposive voluntary sampling and through snowball sampling for the people living close to them. Recruitment was from both urban and rural settings in the North West Province, South Africa. Data collection was via in-depth interviews with 23 PLWH and 60 people living close to them from specific designated groups. The data were thematically analysed through manual open coding. The results from the urban and rural settings were pooled, as there were no noteworthy differences in the themes between them. The results indicated that there was an increase in knowledge in all the groups, as well as experiences of enhanced relationships and of being equipped with leadership skills in order to go out into the community and being part of HIV stigma reduction actions. The intervention in its comprehensive nature was found to have been successful and promising for future use in reducing HIV stigma.Keywords: community, comprehensive, HIV, intervention, stigmaLa stigmatisation lieĀ“e au VIH est reĀ“pandue dans le monde. Bien que la documentation sur le sujet aborde un ensemble dāinterventions en faveur de sa reĀ“duction, les recherches sur lāefficaciteĀ“ de telles interventions restent limiteĀ“es. Cette eĀ“tude vise donc a` mieux comprendre lāexpeĀ“rience des personnes vivant avec le VIH (PVVIH) et de leur entourage dans six groupes seĀ“lectionneĀ“s pendant et apre`s une intervention communautaire globale de reĀ“duction de la stigmatisation lieĀ“e au VIH, en milieu urbain et rural. Lāon a accordeĀ“ une attentionĀ particulie`re aux expeĀ“riences partageĀ“es sur lāatelier et les projets entrepris. Une approche de description qualitative et interpreĀ“tative a eĀ“teĀ“ adopteĀ“e. Les PVVIH participantes ont eĀ“teĀ“ seĀ“lectionneĀ“es graĖce a` un eĀ“chantillonnage dirigeĀ“ et volontaire, et un eĀ“chantillon boule de neige pour lāentourage. Les personnes recruteĀ“es provenaient de milieux urbains et ruraux de la province du Nord-Ouest, Afrique du Sud. La collecte de donneĀ“es sāest faite par des entretiens approfondis avec 23 PVVIH et 60 personnes de leur entourage, toutes issues de groupes speĀ“cifiques deĀ“signeĀ“s. Les donneĀ“es ont eĀ“teĀ“ analyseĀ“es theĀ“matiquement par codageĀ ouvert et manuel. Les reĀ“sultats des milieux urbains et ruraux ont ensuite eĀ“teĀ“ regroupeĀ“s car il ne semblait pas y avoir de diffeĀ“rence remarquable entre les the`mes souleveĀ“s dans les deux milieux. Dans tous lesĀ groupes, les reĀ“sultats indiquaient un accroissement des connaissances, de lāameĀ“lioration des relations, et des compeĀ“tences de leadership pour prendre part a` la vie communautaire et participer aux activiteĀ“s de reĀ“duction de la stigmatisation. La reĀ“ussite de la nature globale de lāintervention est prometteuse pour les activiteĀ“sĀ futures de reĀ“duction de la stigmatisation du VIH.Mots-cleĀ“s: communauteĀ“, global(e), VIH, intervention, stigmatisatio
Some Remarks about Variable Mass Systems
We comment about the general argument given to obtain the rocket equation as
it is exposed in standard textbooks. In our opinion, it can induce students to
a wrong answer when solving variable mass problems.Comment: 2 page
Intelligent Sensing for Robotic Re-Manufacturing in Aerospace - An Industry 4.0 Design Based Prototype
Emerging through an industry-academia
collaboration between the University of Sheffield and VBC
Instrument Engineering Ltd, a proposed robotic solution for remanufacturing
of jet engine compressor blades is under ongoing
development, producing the first tangible results for evaluation.
Having successfully overcome concept adaptation, funding
mechanisms, design processes, with research and development
trials, the stage of concept optimization and end-user application
has commenced. A variety of new challenges is emerging, with
multiple parameters requiring control and intelligence. An
interlinked collaboration between operational controllers,
Quality Assurance (QA) and Quality Control (QC) systems,
databases, safety and monitoring systems, is creating a complex
network, transforming the traditional manual re-manufacturing
method to an advanced intelligent modern smart-factory.
Incorporating machine vision systems for characterization,
inspection and fault detection, alongside advanced real-time
sensor data acquisition for monitoring and evaluating the
welding process, a huge amount of valuable industrial data is
produced. Information regarding each individual blade is
combined with data acquired from the system, embedding data
analytics and the concept of ƬInternet of ThingsƮ (IoT) into the
aerospace re-manufacturing industry. The aim of this paper is to
give a first insight into the challenges of the development of an
Industry 4.0 prototype system and an evaluation of first results of
the operational prototype
Intruder States and their Local Effect on Spectral Statistics
The effect on spectral statistics and on the revival probability of intruder
states in a random background is analysed numerically and with perturbative
methods. For random coupling the intruder does not affect the GOE spectral
statistics of the background significantly, while a constant coupling causes
very strong correlations at short range with a fourth power dependence of the
spectral two-point function at the origin.The revival probability is
significantly depressed for constant coupling as compared to random coupling.Comment: 18 pages, 10 Postscript figure
1/f noise in the Two-Body Random Ensemble
We show that the spectral fluctuations of the Two-Body Random Ensemble (TBRE)
exhibit 1/f noise. This result supports a recent conjecture stating that
chaotic quantum systems are characterized by 1/f noise in their energy level
fluctuations. After suitable individual averaging, we also study the
distribution of the exponent \alpha in the 1/f^{\alpha} noise for the
individual members of the ensemble. Almost all the exponents lie inside a
narrow interval around \alpha=1 suggesting that also individual members exhibit
1/f noise, provided they are individually unfoldedComment: 4 pages, 3 figures, Accepted for publication in Phys. Rev.
Process monitoring and industrial informatics for on-line optimization of Welding Procedure Specifications (WPS) in Gas Tungsten Arc Welding (GTAW) ā Industry 4.0 for robotic additive re-manufacturing of aeroengine components
Industry 4.0, the scheme that drives the fourth industrial revolution, has been, since its conception, reshaping the manufacturing industry. To advance current industrial chains into the smart factories of the future, cyber-physical systems are monitored and communicate with each other to ensure transparent interoperability, giving birth to the emerging field of industrial informatics. To enable the repair and recycling of high value jet engine compressor blades, additive manufacturing is utilized. The complex geometries and asymmetrical wear of the blades require robotic welding systems to be trained by experienced human welding engineers in order to be able to adapt to differing components. Demonstrated in this paper, process monitoring and industrial informatics are introduced to the adaption of Welding Procedure Specifications (WPS) utilized by a developing robotic system for the additive re-manufacturing of aeroengine components. Using a novel variant of Gas Tungsten Arc Welding (GTAW), the robotic welding system under development is a product of an industry-academia collaboration between the Enabling Sciences for Intelligent Manufacturing Group (ESIM) of the University of Sheffield and VBC Instrument Engineering Ltd
A Trial of a 7-Valent Pneumococcal Conjugate Vaccine in HIV-Infected Adults.
BACKGROUND: Streptococcus pneumoniae is a leading and serious coinfection in adults with human immunodeficiency virus (HIV) infection, particularly in Africa. Prevention of this disease by vaccination with the current 23-valent polysaccharide vaccine is suboptimal. Protein conjugate vaccines offer a further option for protection, but data on their clinical efficacy in adults are needed. METHODS: In this double-blind, randomized, placebo-controlled clinical efficacy trial, we studied the efficacy of a 7-valent conjugate pneumococcal vaccine in predominantly HIV-infected Malawian adolescents and adults who had recovered from documented invasive pneumococcal disease. Two doses of vaccine were given 4 weeks apart. The primary end point was a further episode of pneumococcal infection caused by vaccine serotypes or serotype 6A. RESULTS: From February 2003 through October 2007, we followed 496 patients (of whom 44% were male and 88% were HIV-seropositive) for 798 person-years of observation. There were 67 episodes of pneumococcal disease in 52 patients, all in the HIV-infected subgroup. In 24 patients, there were 19 episodes that were caused by vaccine serotypes and 5 episodes that were caused by the 6A serotype. Of these episodes, 5 occurred in the vaccine group and 19 in the placebo group, for a vaccine efficacy of 74% (95% confidence interval [CI], 30 to 90). There were 73 deaths from any cause in the vaccine group and 63 in the placebo group (hazard ratio in the vaccine group, 1.18; 95% CI, 0.84 to 1.66). The number of serious adverse events within 14 days after vaccination was significantly lower in the vaccine group than in the placebo group (3 vs. 17, P=0.002), and the number of minor adverse events was significantly higher in the vaccine group (41 vs. 13, P=0.003). CONCLUSIONS: The 7-valent pneumococcal conjugate vaccine protected HIV-infected adults from recurrent pneumococcal infection caused by vaccine serotypes or serotype 6A. (Current Controlled Trials number, ISRCTN54494731.) Copyright 2010 Massachusetts Medical Society
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