158,665 research outputs found
Band engineering in dilute nitride and bismide semiconductor lasers
Highly mismatched semiconductor alloys such as GaNAs and GaBiAs have several
novel electronic properties, including a rapid reduction in energy gap with
increasing x and also, for GaBiAs, a strong increase in spin orbit- splitting
energy with increasing Bi composition. We review here the electronic structure
of such alloys and their consequences for ideal lasers. We then describe the
substantial progress made in the demonstration of actual GaInNAs telecomm
lasers. These have characteristics comparable to conventional InP-based
devices. This includes a strong Auger contribution to the threshold current. We
show, however, that the large spin-orbit-splitting energy in GaBiAs and GaBiNAs
could lead to the suppression of the dominant Auger recombination loss
mechanism, finally opening the route to efficient temperature-stable telecomm
and longer wavelength lasers with significantly reduced power consumption.Comment: 27 pages, 11 figure
Evaluation of the ADVIA (R) Centaur (TM) TSH-3 assay
An analytical evaluation of the thyroid stimulating hormone (TSH-3) assay on the Sayer ADVIA(R) Centaur(TM) immunoassay system was performed. General analytical requirements (linearity, resistance to typical interferences, absence of a carry-over effect) were fulfilled and reproducibility was satisfactory. Inter-assay coefficient of variation (CV) of a human serum pool with a concentration of 0.014 mU/l was 22.3%; at concentrations between 0.26 and 83 mU/l CV was below 6%. Method comparison study demonstrated close agreement of TSH results compared to those obtained with the Roche Elecsys(R) 2010 TSH assay (ADVIA Centaur = 1.08 x Elecsys - 0.18 mU/l; r = 0.987; n = 324). Handling and practicability of the ADVIA Centaur system proved to be convenient with a very high sample throughput. We conclude that the ADVIA Centaur TSH-3 assay meets requirements for clinical use
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Incorporation of membrane proteins into large single bilayer vesicles. Application to rhodopsin.
A general procedure to incorporate membrane proteins in a native state into large single bilayer vesicles is described. The results obtained with rhodopsin from vertebrate and invertebrate retinas are presented. The technique involves: (a) the direct transfer of rhodopsin-lipid complexes from native membranes into ether or pentane, and (b) the sonication of the complex in apolar solvent with aqueous buffer followed by solvent evaporation under reduced pressure. The spectral properties of rhodopsin in the large vesicles are similar to those of rhodopsin in photoreceptors; furthermore, bleached bovine rhodopsin is chemically regenerable with 9-cis retinal. These results establish the presence of photochemically functional rhodopsin in the large vesicles. Freeze-fracture replicas of the vesicles reveal that both internal and external leaflets contain numerous particles approximately 80 A in diameter, indicating that rhodopsin is symmetrically distributed within the bilayer. More than 75% of the membrane area is incorporated into vesicles larger than 0.5 micron and approximately 40% into vesicles larger than 1 micron
Fault Models of Inverter-Interfaced Distributed Generators: Experimental Verification and Application to Fault Analysis
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A review of portfolio planning: Models and systems
In this chapter, we first provide an overview of a number of portfolio planning models
which have been proposed and investigated over the last forty years. We revisit the
mean-variance (M-V) model of Markowitz and the construction of the risk-return
efficient frontier. A piecewise linear approximation of the problem through a
reformulation involving diagonalisation of the quadratic form into a variable
separable function is also considered. A few other models, such as, the Mean
Absolute Deviation (MAD), the Weighted Goal Programming (WGP) and the
Minimax (MM) model which use alternative metrics for risk are also introduced,
compared and contrasted. Recently asymmetric measures of risk have gained in
importance; we consider a generic representation and a number of alternative
symmetric and asymmetric measures of risk which find use in the evaluation of
portfolios. There are a number of modelling and computational considerations which
have been introduced into practical portfolio planning problems. These include: (a)
buy-in thresholds for assets, (b) restriction on the number of assets (cardinality
constraints), (c) transaction roundlot restrictions. Practical portfolio models may also
include (d) dedication of cashflow streams, and, (e) immunization which involves
duration matching and convexity constraints. The modelling issues in respect of these
features are discussed. Many of these features lead to discrete restrictions involving
zero-one and general integer variables which make the resulting model a quadratic
mixed-integer programming model (QMIP). The QMIP is a NP-hard problem; the
algorithms and solution methods for this class of problems are also discussed. The
issues of preparing the analytic data (financial datamarts) for this family of portfolio
planning problems are examined. We finally present computational results which
provide some indication of the state-of-the-art in the solution of portfolio optimisation
problems
Physical properties of 6dF dwarf galaxies
Spectral synthesis is basically the decomposition of an observed spectrum in
terms of the superposition of a base of simple stellar populations of various
ages and metallicities, producing as output the star formation and chemical
histories of a galaxy, its extinction and velocity dispersion. The STARLIGHT
code provides one of the most powerful spectral synthesis tools presently
available. We have applied this code to the entire Six-Degree-Field Survey
(6dF) sample of nearby star-forming galaxies, selecting dwarf galaxy candidates
with the goal of: (1) deriving the age and metallicity of their stellar
populations and (2) creating a database with the physical properties of our
sample galaxies together with the FITS files of pure emission line spectra
(i.e. the observed spectra after subtraction of the best-fitting synthetic
stellar spectrum). Our results yield a good qualitative and quantitative
agreement with previous studies based on the Sloan Digital Sky Survey (SDSS).
However, an advantage of 6dF spectra is that they are taken within a twice as
large fiber aperture, much reducing aperture effects in studies of nearby dwarf
galaxies.Comment: To appear in JENAM Symposium "Dwarf Galaxies: Keys to Galaxy
Formation and Evolution", P. Papaderos, S. Recchi, G. Hensler (eds.). Lisbon,
September 2010, Springer Verlag, in pres
Experimental Analysis of Algorithms for Coflow Scheduling
Modern data centers face new scheduling challenges in optimizing job-level
performance objectives, where a significant challenge is the scheduling of
highly parallel data flows with a common performance goal (e.g., the shuffle
operations in MapReduce applications). Chowdhury and Stoica introduced the
coflow abstraction to capture these parallel communication patterns, and
Chowdhury et al. proposed effective heuristics to schedule coflows efficiently.
In our previous paper, we considered the strongly NP-hard problem of minimizing
the total weighted completion time of coflows with release dates, and developed
the first polynomial-time scheduling algorithms with O(1)-approximation ratios.
In this paper, we carry out a comprehensive experimental analysis on a
Facebook trace and extensive simulated instances to evaluate the practical
performance of several algorithms for coflow scheduling, including the
approximation algorithms developed in our previous paper. Our experiments
suggest that simple algorithms provide effective approximations of the optimal,
and that the performance of our approximation algorithms is relatively robust,
near optimal, and always among the best compared with the other algorithms, in
both the offline and online settings.Comment: 29 pages, 8 figures, 11 table
Chiral corrections to the Gell-Mann-Oakes-Renner relation
The next to leading order chiral corrections to the
Gell-Mann-Oakes-Renner (GMOR) relation are obtained using the pseudoscalar
correlator to five-loop order in perturbative QCD, together with new finite
energy sum rules (FESR) incorporating polynomial, Legendre type, integration
kernels. The purpose of these kernels is to suppress hadronic contributions in
the region where they are least known. This reduces considerably the systematic
uncertainties arising from the lack of direct experimental information on the
hadronic resonance spectral function. Three different methods are used to
compute the FESR contour integral in the complex energy (squared) s-plane, i.e.
Fixed Order Perturbation Theory, Contour Improved Perturbation Theory, and a
fixed renormalization scale scheme. We obtain for the corrections to the GMOR
relation, , the value . This result
is substantially more accurate than previous determinations based on QCD sum
rules; it is also more reliable as it is basically free of systematic
uncertainties. It implies a light quark condensate . As a byproduct, the chiral perturbation theory (unphysical) low energy
constant is predicted to be , or .Comment: A comment about the value of the strong coupling has been added at
the end of Section 4. No change in results or conslusion
The game transfer phenomena scale: an instrument for investigating the nonvolitional effects of video game playing
A variety of instruments have been developed to assess different dimensions of playing videogames and its effects on cognitions, affect, and behaviors. The present study examined the psychometric properties of the Game Transfer Phenomena Scale (GTPS) that assesses non-volitional phenomena experienced after playing videogames (i.e., altered perceptions, automatic mental processes, and involuntary behaviors). A total of 1,736 gamers participated in an online survey used as the basis for the analysis. Confirmatory factor analysis (CFA) was performed to confirm the factorial structure of the GTPS. The five-factor structure using the 20 indicators based on the analysis of gamersâ self-reports fitted the data well. Population cross-validity was also achieved and the positive associations between the session length and overall scores indicate the GTPS warranted criterion-related validity. Although the understanding of GTP is still in its infancy, the GTPS appears to be a valid and reliable instrument for assessing non-volitional gaming-related phenomena. The GTPS can be used for understanding the phenomenology of post-effects of playing videogames
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