17,523 research outputs found
An exploratory study on the social and genotypic clustering of HIV infection in men having sex with men
OBJECTIVE: To explore the clustering of HIV infected men having sex with men (MSM) using social network approach in conjunction with the phylogenetic relationship of the virus strains. DESIGN: An exploratory study incorporating social network and phylogenetic analysis. METHODS: Recently diagnosed HIV-infected MSM attending one major HIV specialist clinic in Hong Kong were recruited in the study involving the administration of a self-administered questionnaire on behaviours and partnership patterns using a Likert Scale, the results of which were assessed using social network analysis and in context of the phylogenetic analysis from sequencing the HIV-1 pol gene, as part of the clinical investigation for genotypic resistance. Clusters were defined using social and molecular methods. RESULTS: An 'Internet-centred' cluster and 'Sauna-centred' cluster could be delineated using correspondence analysis and network diagrams. The main distinguishing features of MSM in the 'Internet-centred' social cluster were: younger age, higher education level, and multiple partner types. Three genetic clusters could be identified in the phylogenetic tree, two of which associated with Internet use and one with sauna for sex partnership. There were partial overlaps between social and genetic clusters. Characteristically, the virus strains in sauna users were more disperse compared with the closely knit configuration of those using Internet. CONCLUSION: The principle of the duality of place and person can be strategically applied in epidemiologic investigation. The characterization of MSM cluster using anonymized network data provides a potentially powerful tool for informing public health intervention. © 2009 Lippincott Williams & Wilkins, Inc.postprin
Holographic DC conductivities from the open string metric
We study the DC conductivities of various holographic models using the open
string metric (OSM), which is an effective metric geometrizing density and
electromagnetic field effect. We propose a new way to compute the nonlinear
conductivity using OSM. As far as the final conductivity formula is concerned,
it is equivalent to the Karch-O'Bannon's real-action method. However, it yields
a geometrical insight and technical simplifications. Especially, a real-action
condition is interpreted as a regular geometry condition of OSM. As
applications of the OSM method, we study several holographic models on the
quantum Hall effect and strange metal. By comparing a Lifshitz background and
the Light-Cone AdS, we show how an extra parameter can change the temperature
scaling behavior of conductivity. Finally we discuss how OSM can be used to
study other transport coefficients, such as diffusion constant, and effective
temperature induced by the effective world volume horizon.Comment: 33 page
Two-dimensional superconductivity at a Mott-Insulator/Band-Insulator interface: LaTiO3/SrTiO3
Transition metal oxides display a great variety of quantum electronic
behaviours where correlations often play an important role. The achievement of
high quality epitaxial interfaces involving such materials gives a unique
opportunity to engineer artificial structures where new electronic orders take
place. One of the most striking result in this area is the recent observation
of a two-dimensional electron gas at the interface between a strongly
correlated Mott insulator LaTiO3 and a band insulator SrTiO3. The mechanism
responsible for such a behaviour is still under debate. In particular, the
influence of the nature of the insulator has to be clarified. Here we show that
despite the expected electronic correlations, LaTiO3/SrTiO3 heterostructures
undergo a superconducting transition at a critical temperature Tc=300 mK. We
have found that the superconducting electron gas is confined over a typical
thickness of 12 nm. We discuss the electronic properties of this system and
review the possible scenarios
Zero Sound in Effective Holographic Theories
We investigate zero sound in -dimensional effective holographic theories,
whose action is given by Einstein-Maxwell-Dilaton terms. The bulk spacetimes
include both zero temperature backgrounds with anisotropic scaling symmetry and
their near-extremal counterparts obtained in 1006.2124 [hep-th], while the
massless charge carriers are described by probe D-branes. We discuss
thermodynamics of the probe D-branes analytically. In particular, we clarify
the conditions under which the specific heat is linear in the temperature,
which is a characteristic feature of Fermi liquids. We also compute the
retarded Green's functions in the limit of low frequency and low momentum and
find quasi-particle excitations in certain regime of the parameters. The
retarded Green's functions are plotted at specific values of parameters in
, where the specific heat is linear in the temperature and the
quasi-particle excitation exists. We also calculate the AC conductivity in
-dimensions as a by-product.Comment: 29 pages, 1 figur
Highly Conductive Graphene/Ag Hybrid Fibers for Flexible Fiber-Type Transistors
Mechanically robust, flexible, and electrically conductive textiles are highly suitable for use in wearable electronic applications. In this study, highly conductive and flexible graphene/Ag hybrid fibers were prepared and used as electrodes for planar and fiber-type transistors. The graphene/Ag hybrid fibers were fabricated by the wet-spinning/drawing of giant graphene oxide and subsequent functionalization with Ag nanoparticles. The graphene/Ag hybrid fibers exhibited record-high electrical conductivity of up to 15,800 S cm(-1). As the graphene/Ag hybrid fibers can be easily cut and placed onto flexible substrates by simply gluing or stitching, ion gel-gated planar transistors were fabricated by using the hybrid fibers as source, drain, and gate electrodes. Finally, fibertype transistors were constructed by embedding the graphene/Ag hybrid fiber electrodes onto conventional polyurethane monofilaments, which exhibited excellent flexibility (highly bendable and rollable properties), high electrical performance (mu(h) = 15.6 cm(2) V-1 s(-1), I-on/I-off > 10(4)), and outstanding device performance stability (stable after 1,000 cycles of bending tests and being exposed for 30 days to ambient conditions). We believe that our simple methods for the fabrication of graphene/Ag hybrid fiber electrodes for use in fiber-type transistors can potentially be applied to the development all-organic wearable devices.111912Ysciescopu
Improved cascaded h‐bridge multilevel inverters with voltage‐boosting capability
This paper proposes two improved cascaded H‐bridge (ICHB) multilevel inverters that feature voltage‐boosting capability. The conventional H‐bridge with a front‐end dc–dc boost converter was restructured for single‐stage operation. The developed three‐level topology not only saves one power switch but also exhibits lower voltage stress across its capacitor. Extension to five-level generation was also introduced by merely adding two power switches and one capacitor. The final five‐level topology outperforms the classical cascaded H‐bridge (CHB) multilevel inverter with a significant reduction in the power switch count, with a 42% and 50% reduction in both the isolated dc source and inductor counts. The power efficiency was also improved without compromising the modularity feature of the classical CHB multilevel inverter. The operation and theoretical analysis of the proposed topologies were validated via simulations and experimental tests
Modeling Resolution of Resources Contention in Synchronous Data Flow Graphs
Synchronous Data Flow graphs are widely adopted in the designing of streaming applications, but were originally formulated to describe only how an application is partitioned and which data are exchanged among different tasks. Since Synchronous Data Flow graphs are often used to describe and evaluate complete design solutions, missing information (e.g., mapping, scheduling, etc.) has to be included in them by means of further actors and channels to obtain accurate evaluations. To address this issue preserving the simplicity of the representation, techniques that model data transfer delays by means of ad-hoc actors have been proposed, but they model independently each communication ignoring contentions. Moreover, they do not usually consider at all delays due to buffer contentions, potentially overestimating the throughput of a design solution. In this paper a technique to extend Synchronous Data Flow graphs by adding ad-hoc actors and channels to model resolution of resources contentions is proposed. The results show that the number of added actors and channels is limited but that they can significantly increase the Synchronous Data Flow graph accuracy
Implementing guidelines for the prescribing of vancomycin and teicoplanin
published_or_final_versio
Holographic Superconductors
A holographic model of superconductors based on the action proposed by
Benini, Herzog, and Yarom [arXiv:1006.0731] is studied. This model has a
charged spin two field in an AdS black hole spacetime. Working in the probe
limit, the normalizable solution of the spin two field in the bulk gives rise
to a superconducting order parameter at the boundary of the AdS. We
calculate the fermion spectral function in this\ superconducting background and
confirm the existence of fermi arcs for non-vanishing Majorana couplings. By
changing the relative strength of the and condensations, the
position and the size of the fermi arcs are changed. When , the
spectrum becomes isotropic and the spectral function is s-wave like. By
changing the fermion mass, the fermi momentum is changed. We also calculate the
conductivity for these holographic superconductors where time reversal
symmetry has been broken spontaneously. A non-vanishing Hall conductivity is
obtained even without an external magnetic field.Comment: 24 pages,17 figures, Add more discussions on hall conductivity, two
new figures, Matched with published versio
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