2,598 research outputs found
Collective oscillations of a Fermi gas in the unitarity limit: Temperature effects and the role of pair correlations
We present detailed measurements of the frequency and damping of three
different collective modes in an ultracold trapped Fermi gas of Li atoms
with resonantly tuned interactions. The measurements are carried out over a
wide range of temperatures. We focus on the unitarity limit, where the
scattering length is much greater than all other relevant length scales. The
results are compared to theoretical calculations that take into account Pauli
blocking and pair correlations in the normal state above the critical
temperature for superfluidity. We show that these two effects nearly compensate
each other and the behavior of the gas is close to the one of a classical gas.Comment: 8 pages, 5 figure
Communication Concept of DeConSim: a Decentralized Control Simulator for Production Systems
Abstract In recent years, the price pressure and demand for personalised products in manufacturing increased continuously. As a reaction, technologies from the Information and Communication Technology (ICT) sector are applied by the industry, this trend is also known as digitalisation or Industry 4.0. Digitalisation might be effectively supported by simulation of production lines and will become crucial for manufacturing companies who want to benefit from the advances in ICT technologies, thus improving efficiency and competitiveness. Many agent-based simulators exist, nevertheless, most of them were developed for biological and social sciences whose use and specifications differ significantly from industrial applications. The commercial ones are expensive in terms of licensing, support and require specific training. We propose a communication concept for the simulator that we are developing called DeConSim, which aims at decentralized systems and is composed of several modules (representing resources, each with its own task and intelligence) and a core. DeConSim is capable of operating in two different modes: simulation mode and realtime mode. The former is used to achieve pure simulation results as fast as possible. The latter operates in real-time enabling DeConSim, in contrast to other existing simulators, to become the operational core of the control communication infrastructure of a real production line
eBay users form stable groups of common interest
Market segmentation of an online auction site is studied by analyzing the
users' bidding behavior. The distribution of user activity is investigated and
a network of bidders connected by common interest in individual articles is
constructed. The network's cluster structure corresponds to the main user
groups according to common interest, exhibiting hierarchy and overlap. Key
feature of the analysis is its independence of any similarity measure between
the articles offered on eBay, as such a measure would only introduce bias in
the analysis. Results are compared to null models based on random networks and
clusters are validated and interpreted using the taxonomic classifications of
eBay categories. We find clear-cut and coherent interest profiles for the
bidders in each cluster. The interest profiles of bidder groups are compared to
the classification of articles actually bought by these users during the time
span 6-9 months after the initial grouping. The interest profiles discovered
remain stable, indicating typical interest profiles in society. Our results
show how network theory can be applied successfully to problems of market
segmentation and sociological milieu studies with sparse, high dimensional
data.Comment: Major revision of the manuscript. Methodological improvements and
inclusion of analysis of temporal development of user interests. 19 pages, 12
figures, 5 table
Hypergraph model of social tagging networks
The past few years have witnessed the great success of a new family of
paradigms, so-called folksonomy, which allows users to freely associate tags to
resources and efficiently manage them. In order to uncover the underlying
structures and user behaviors in folksonomy, in this paper, we propose an
evolutionary hypergrah model to explain the emerging statistical properties.
The present model introduces a novel mechanism that one can not only assign
tags to resources, but also retrieve resources via collaborative tags. We then
compare the model with a real-world dataset: \emph{Del.icio.us}. Indeed, the
present model shows considerable agreement with the empirical data in following
aspects: power-law hyperdegree distributions, negtive correlation between
clustering coefficients and hyperdegrees, and small average distances.
Furthermore, the model indicates that most tagging behaviors are motivated by
labeling tags to resources, and tags play a significant role in effectively
retrieving interesting resources and making acquaintance with congenial
friends. The proposed model may shed some light on the in-depth understanding
of the structure and function of folksonomy.Comment: 7 pages,7 figures, 32 reference
Pairing-gap, pseudo-gap, and no-gap phases in the radio-frequency spectra of a trapped unitary 6Li gas
Radio frequency spectra of a trapped unitary 6Li gas are reported and
analyzed in terms of a theoretical approach that includes both final-state and
trap effects. Final-state effects play a crucial role in evidencing two main
peaks both above and below the critical temperature Tc as being associated with
two distinct phases that reside in different trap regions. These are the
pairing-gap and pseudo-gap phases below Tc, which evolve into the pseudo-gap
and no-gap phases above Tc. In this way, a long standing puzzle about the
interpretation of rf spectra for 6Li in a trap is solved.Comment: 5 pages, 6 figures (final version
Hydrodynamic Modes in a Trapped Strongly Interacting Fermi Gases of Atoms
The zero-temperature properties of a dilute two-component Fermi gas in the
BCS-BEC crossover are investigated. On the basis of a generalization of the
variational Schwinger method, we construct approximate semi-analytical formulae
for collective frequencies of the radial and the axial breathing modes of the
Fermi gas under harmonic confinement in the framework of the hydrodynamic
theory. It is shown that the method gives nearly exact solutions.Comment: 11 page
Atomic Hole Doping of Graphene
Graphene is an excellent candidate for the next generation of electronic
materials due to the strict two-dimensionality of its electronic structure as
well as the extremely high carrier mobility. A prerequisite for the development
of graphene based electronics is the reliable control of the type and density
of the charge carriers by external (gate) and internal (doping) means. While
gating has been successfully demonstrated for graphene flakes and epitaxial
graphene on silicon carbide, the development of reliable chemical doping
methods turns out to be a real challenge. In particular hole doping is an
unsolved issue. So far it has only been achieved with reactive molecular
adsorbates, which are largely incompatible with any device technology. Here we
show by angle-resolved photoemission spectroscopy that atomic doping of an
epitaxial graphene layer on a silicon carbide substrate with bismuth, antimony
or gold presents effective means of p-type doping. Not only is the atomic
doping the method of choice for the internal control of the carrier density. In
combination with the intrinsic n-type character of epitaxial graphene on SiC,
the charge carriers can be tuned from electrons to holes, without affecting the
conical band structure
Trust and Credibility in Web-Based Health Information: A Review and Agenda for Future Research
Background: Online sources are becoming increasingly important in health information seeking, such that they may have a significant effect on health care decisions and outcomes. Hence, given the wide range of different sources of online health information from different organisations and individuals, it is important to understand how information seekers evaluate and select the sources that they use, and, more specifically how they assess their credibility and trustworthiness.
Objectives: This article reviews empirical studies on trust and credibility in the use of online health information. The article seeks to present a profile of the research conducted on trust and credibility in online health information seeking, to identify the factors that impact judgements of trustworthiness and credibility, and to explore the role of demographic factors affecting trust formation. On this basis, it aims to identify the gaps in current knowledge and to propose an agenda for future research.
Methods: A systematic literature review was conducted. Searches were conducted using a variety of combinations of the terms: online health information, trust, credibility, and their variants, in four multi-disciplinary and four health-oriented databases. Articles selected were published in English from 2000 onwards; this process generated 3827 unique records. After the application of exclusion criteria, this was reduced to a final dataset of 73 articles, which was analysed in full.
Results: Interest in this topic has persisted over the last 15 years, with articles being published in medicine, social science and computer science, and focussing mostly on the USA and the UK. Documents in the dataset fell into three categories: those using trust or credibility as a dependent variable, those using trust or credibility as an independent variable, and studies of the demographic factors that influence the role of trust or credibility in online health information seeking. There is a consensus that in terms of website design, clear layout and design, interactive features and the authority of the owner have a positive effect on trust or credibility, whilst advertising has a negative effect. With regard to content features, authority of the author, ease of use and content have a positive effect on trust or credibility formation. Demographic factors influencing trust formation are age, gender and perceived health status.
Conclusions: There is considerable scope for further research. This includes: increased clarity of the interaction between the variables associated with health information seeking; increased consistency on the measurement of trust and credibility; a greater focus on specific online health information sources; and, enhanced understanding of the impact of demographic variables on trust and credibility judgement
Trim17, novel E3 ubiquitin-ligase, initiates neuronal apoptosis
Accumulating data indicate that the ubiquitin-proteasome system controls apoptosis by regulating the level and the function of key regulatory proteins. In this study, we identified Trim17, a member of the TRIM/RBCC protein family, as one of the critical E3 ubiquitin ligases involved in the control of neuronal apoptosis upstream of mitochondria. We show that expression of Trim17 is increased both at the mRNA and protein level in several in vitro models of transcription-dependent neuronal apoptosis. Expression of Trim17 is controlled by the PI3K/Akt/GSK3 pathway in cerebellar granule neurons (CGN). Moreover, the Trim17 protein is expressed in vivo, in apoptotic neurons that naturally die during post-natal cerebellar development. Overexpression of active Trim17 in primary CGN was sufficient to induce the intrinsic pathway of apoptosis in survival conditions. This pro-apoptotic effect was abolished in Bax(-/-) neurons and depended on the E3 activity of Trim17 conferred by its RING domain. Furthermore, knock-down of endogenous Trim17 and overexpression of dominant-negative mutants of Trim17 blocked trophic factor withdrawal-induced apoptosis both in CGN and in sympathetic neurons. Collectively, our data are the first to assign a cellular function to Trim17 by showing that its E3 activity is both necessary and sufficient for the initiation of neuronal apoptosis. Cell Death and Differentiation (2010) 17, 1928-1941; doi: 10.1038/cdd.2010.73; published online 18 June 201
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