2,731 research outputs found
The Use of Artificial Neural Networks in Prediction of Congenital CMV Outcome from Sequence Data
A large number of CMV strains has been reported to circulate in the human population, and the biological significance of these strains is currently an active area of research. The analysis of complex genetic information may be limited using conventional phylogenetic techniques
Optical properties of bialkali photocathodes
The optical properties of the `bialkali' KCsSb and RbCsSb photomultiplier
cathodes have been experimentally investigated in the visible range. The
measurements carried out include the absolute reflectance at near-normal
incidence, the polarization-dependent relative reflectance at various angles
and the change in polarization upon reflection from the photocathode. These
experimental inputs have been combined with a theoretical model to determine
the complex refractive index of the photocathodes in the wavelength range 380
to 680 nm and their thickness. As a result of this work, we derive a model
which predicts the fraction of light impinging on a photomultiplier tube that
is reflected, absorbed or transmitted, as a function of wavelength and angle,
and dependent on the medium to which the photomultiplier is coupled.Comment: 51 pages (double spacing), 16 figures, submitted for publication in
NIM
Benefits of a marketing cooperative in transition agriculture: MĂłrakert purchasing and service co-operative
The paper analyses the potential benefits of marketing cooperatives in Hungary, employing a transaction cost economics framework. We found that the purchased quantity, the existence of contracts, flexibility and trust are the most important factors farmers consider when selling their products via a cooperative. The most striking result is that diversification has positive influences on the share of cooperatives in farmersâ sale. Furthermore, farmers with larger bargaining power have less willingness to sell their product to the cooperative. Surprisingly, asset specificity has rather negative effects on the share of cooperatives in membersâ sales
The [4+2]âCycloaddition of αâNitrosoalkenes with Thiochalcones as a Prototype of Periselective HeteroâDielsâAlder ReactionsâExperimental and Computational Studies
The [4+2]âcycloadditions of αânitrosoalkenes with thiochalcones occur with high selectivity at the thioketone moiety of the dienophile providing styrylâsubstituted 4Hâ1,5,2âoxathiazines in moderate to good yields. Of the eight conceivable heteroâDielsâAlder adducts only this isomer was observed, thus a prototype of a highly periselective and regioselective cycloaddition has been identified. Analysis of crude product mixtures revealed that the αânitrosoalkene also adds competitively to the thioketone moiety of the thiochalcone dimer affording bisâheterocyclic [4+2]âcycloadducts. The experiments are supported by highâlevel DFT calculations that were also extended to related heteroâDielsâAlder reactions of other nitroso compounds and thioketones. These calculations reveal that the title cycloadditions are kinetically controlled processes confirming the role of thioketones as superdienophiles. The computational study was also applied to the experimentally studied thiochalcone dimerization, and showed that the 1,2âdithiin and 2Hâthiopyran isomers are in equilibrium with the monomer. Again, the DFT calculations indicate kinetic control of this process
The South Australian Heat Flow Anomaly in east Antarctica: hot rocks in a cool place.
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Competition in defense acquisition: Myths and facts
The article of record as published may be found at https://doi.org/10.1080/0743017890840540
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General pole number model for the brushless doubly-fed machine
The Brush less Doubly-Fed Machine (BDFM) has the potential to be a more cost effective replacement for conventional induction or synchronous machine drives. The BDFM has two stator windings: a power winding and a control winding. An electronic power converter of variable voltage and frequency is connected to the control winding and allows the speed of the machine to be adjusted synchronously. The power winding, by design, carries the majority of the current needed for operation, the control winding only a fraction of the current, thus enabling the converter rating to be as low as 25% of the rating of the machine depending on the speed range of operation. To date, only one specific stator pole-pair combination has been investigated, namely the 3/1 combination, where 3 and 1 refer to the power winding pole-pairs and the control winding pole-pair, respectively. Since the speed of the machine is dependent on the sum of the pole-pairs of the stator windings, a general pole numbered model is needed to evaluate the performance of such general machines with other pole-pair number machines. The BDFM describing system equations are transformed to the two axis (dq) rotor reference frame using a power invariant transformation. The analysis shows an additional term involving the common bar impedance which was not present in earlier analyses. The dynamic model is simplified to yield a steady state synchronous model. The synchronous frequency of analysis is investigated which results in two equivalent steady state models. The models developed can easily handle excitation of any frequency or sequence on the control winding without the use of an auxiliary model as used in previous analyses. The voltage forced model predictions match data taken for a 5 hp BDFM laboratory prototype, establishing the validity of the analysis. The model is used in illustrating the torque producing capabilities and unity power factor operation of the machine under a variety of inputs. Using the model, predictions are made on a different pole-pair combination machine (4/2 BDFM) for use as a 60 hp pump drive as an alternative to a 3/1 BDFM for the same application
A Unified Monte Carlo Treatment of Gas-Grain Chemistry for Large Reaction Networks. I. Testing Validity of Rate Equations in Molecular Clouds
In this study we demonstrate for the first time that the unified Monte Carlo
approach can be applied to model gas-grain chemistry in large reaction
networks. Specifically, we build a time-dependent gas-grain chemical model of
the interstellar medium, involving about 6000 gas-phase and 200 grain surface
reactions. This model is used to test the validity of the standard and modified
rate equation methods in models of dense and translucent molecular clouds and
to specify under which conditions the use of the stochastic approach is
desirable.
We found that at temperatures 25--30 K gas-phase abundances of HO,
NH, CO and many other gas-phase and surface species in the stochastic model
differ from those in the deterministic models by more than an order of
magnitude, at least, when tunneling is accounted for and/or diffusion energies
are 3x lower than the binding energies. In this case, surface reactions,
involving light species, proceed faster than accretion of the same species. In
contrast, in the model without tunneling and with high binding energies, when
the typical timescale of a surface recombination is greater than the timescale
of accretion onto the grain, we obtain almost perfect agreement between results
of Monte Carlo and deterministic calculations in the same temperature range. At
lower temperatures ( K) gaseous and, in particular, surface abundances
of most important molecules are not much affected by stochastic processes.Comment: 33 pages, 9 figures, 1 table. Accepted for publication in Ap
Urinary eicosanoid metabolites in HIV-infected women with central obesity switching to raltegravir: an analysis from the women, integrase, and fat accumulation trial.
Chronic inflammation is a hallmark of HIV infection. Eicosanoids reflect inflammation, oxidant stress, and vascular health and vary by sex and metabolic parameters. Raltegravir (RAL) is an HIV-1 integrase inhibitor that may have limited metabolic effects. We assessed urinary F2-isoprostanes (F2-IsoPs), prostaglandin E2 (PGE-M), prostacyclin (PGI-M), and thromboxane B2 (TxB2) in HIV-infected women switching to RAL-containing antiretroviral therapy (ART). Thirty-seven women (RAL = 17; PI/NNRTI = 20) with a median age of 43 years and BMI 32 kg/m(2) completed week 24. TxB2 increased in the RAL versus PI/NNRTI arm (+0.09 versus -0.02; P = 0.06). Baseline PGI-M was lower in the RAL arm (P = 0.005); no other between-arm cross-sectional differences were observed. In the PI/NNRTI arm, 24-week visceral adipose tissue change correlated with PGI-M (rho = 0.45; P = 0.04) and TxB2 (rho = 0.44; P = 0.005) changes, with a trend seen for PGE-M (rho = 0.41; P = 0.07). In an adjusted model, age â„ 50 years (N = 8) was associated with increased PGE-M (P = 0.04). In this randomized trial, a switch to RAL did not significantly affect urinary eicosanoids over 24 weeks. In women continuing PI/NNRTI, increased visceral adipose tissue correlated with increased PGI-M and PGE-M. Older age (â„ 50) was associated with increased PGE-M. Relationships between aging, adiposity, ART, and eicosanoids during HIV-infection require further study
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