17,357 research outputs found
Next-to-leading order predictions for WW+jet production
In this work we report on a next-to-leading order calculation of WW + jet
production at hadron colliders, with subsequent leptonic decays of the W-bosons
included. The calculation of the one-loop contributions is performed using
generalized unitarity methods in order to derive analytic expressions for the
relevant amplitudes. These amplitudes have been implemented in the parton-level
Monte Carlo generator MCFM, which we use to provide a complete next-to-leading
order calculation. Predictions for total cross-sections, as well as
differential distributions for several key observables, are computed both for
the LHC operating at 14 TeV as well as for a possible future 100 TeV
proton-proton collider.Comment: 14 pages, 7 figures; v2: several references added, 2 typos corrected.
Corresponds to published journal versio
Investigation of structural behavior of candidate Space Station structure
Quantitative evaluations of the structural loads, stiffness and deflections of an example Space Station truss due to a variety of influences, including manufacturing tolerances, assembly operations, and operational loading are reported. The example truss is a dual-keel design composed of 5-meter-cube modules. The truss is 21 modules high and 9 modules wide, with a transverse beam 15 modules long. One problem of concern is the amount of mismatch which will be expected when the truss is being erected on orbit. Worst-case thermal loading results in less than 0.5 inch of mismatch. The stiffness of the interface is shown to be less than 100 pounds per inch. Thus, only moderate loads will be required to overcome the mismatch. The problem of manufacturing imperfections is analyzed by the Monte Carlo approach. Deformations and internal loads are obtained for ensembles of 100 example trusses. All analyses are performed on a personal computer. The necessary routines required to supplement commercially available programs are described
Homogeneous CO Hydrogenation: Ligand Effects on the Lewis Acid-Assisted Reductive Coupling of Carbon Monoxide
Structure-function studies on the role of pendent Lewis acids in the reductive coupling of CO are reported. Cationic rhenium carbonyl complexes containing zero, one, or two phosphinoborane ligands (Ph_2P(CH_2)_nB(C_8H_(14)), n=1-3) react with the nucleophilic hydride [HPt(dmpe)_2]^+
to reduce [M-CO]^+ to M-CHO; this step is relatively insensitive to the Lewis acid, as both pendent
(internal) and external boranes of appropriate acid strength can be used. In contrast, whether a
second hydride transfer and C-C bond forming steps occur depends strongly on the number of carbon atoms between P and B in the phosphinoborane ligands, as well as the number of pendent acids in the complex: shorter linker chain lengths favor such reductive coupling, whereas longer
chains and external boranes are ineffective. A number of different species containing partially reduced CO groups, whose exact structures vary considerably with the nature and
number of phosphinoborane ligands, have been crystallographically characterized. The reaction of [(Ph -2P(CH_2)_2B(C_8H_(14)))_2Re(CO)4]^+ with [HPt(dmpe)_2]^+
takes place via a âhydride shuttleâ mechanism, in which hydride is transferred from Pt to a pendent borane and thence to CO, rather than by direct hydride attack at CO. Addition of a second hydride in C_6D_5Cl at -40 ÂșC affords an unusual anionic bis(carbene) complex, which converts to a C-C bonded product on warming. These results support a working model for Lewis acid-assisted reductive coupling of CO, in which B (pendent or external) shuttles hydride from Pt to coordinated CO, followed by formation of an
intramolecular B-O bond, which facilitates reductive coupling
A De-biased Direct Question Approach to Measuring Consumers' Willingness to Pay
Knowledge of consumers' willingness to pay (WTP) is a prerequisite to
profitable price-setting. To gauge consumers' WTP, practitioners often rely on
a direct single question approach in which consumers are asked to explicitly
state their WTP for a product. Despite its popularity among practitioners, this
approach has been found to suffer from hypothetical bias. In this paper, we
propose a rigorous method that improves the accuracy of the direct single
question approach. Specifically, we systematically assess the hypothetical
biases associated with the direct single question approach and explore ways to
de-bias it. Our results show that by using the de-biasing procedures we
propose, we can generate a de-biased direct single question approach that is
accu-rate enough to be useful for managerial decision-making. We validate this
approach with two studies in this paper.Comment: Market Research, Pricing, Demand Estimation, Direct Estimation,
Single Question Approach, Choice Experiments, Willingness to Pay,
Hypothetical Bia
Trialkylborane-Assisted CO_2 Reduction by Late Transition Metal Hydrides
Trialkylborane additives promote reduction of CO_2 to formate by bis(diphosphine) Ni(II) and Rh(III) hydride complexes. The late transition metal hydrides, which can be formed from dihydrogen, transfer hydride to CO_2 to give a formateborane adduct. The borane must be of appropriate Lewis acidity: weaker acids do not show significant hydride transfer enhancement, while stronger acids abstract hydride without CO_2 reduction. The mechanism likely involves a pre-equilibrium hydride transfer followed by formation of a stabilizing formateborane adduct
Homogeneous CO Hydrogenation: Dihydrogen Activation Involves a Frustrated Lewis Pair Instead of a Platinum Complex
During a search for conditions appropriate for Pt-catalyzed CO reduction using dihydrogen directly, metal-free conditions were discovered instead. A bulky, strong phosphazene base forms a âfrustratedâ Lewis pair (FLP) with a trialkylborane in the secondary coordination sphere of a rhenium carbonyl. Treatment of the FLP with dihydrogen cleanly affords multiple hydride transfers and CâC bond formation
The Impact of Collusion on Price Behavior: Empirical Results from Two Recent Cases
We used extensions of traditional ARCH and GARCH models to examine the difference in the behavior of the first two moments of the price distribution during collusion and the absence of it using prices from two recently discovered conspiracies, citric acid and lysine. According to our results, the citric acid conspiracy increased prices by 9 cents per pound relative to pre-cartel and post-cartel periods. The lysine conspiracy managed to raise prices by 25 cents per pound. In addition, the variance of prices during the lysine conspiracy was lower than the variance of prices during pre-cartel and post-cartel periods as we expected. In contrast, the variance of prices during the citric acid conspiracy was higher relative to more competitive periods.Demand and Price Analysis,
Mark E Josephson: Clinical Investigator
Mark E Josephson entered the world of clinical cardiac electrophysiology (EP) almost at its inception (1972); with so much to learn and so many directions one could take, he dived into the field with unbridled enthusiasm and an uncommon - perhaps almost unique - aptitude for asking questions and finding ways to answer them. Few aspects of EP escaped his indelible influence. In this short paper, I will attempt to touch on some of the high points of his astounding career as a clinical investigator
Test and Checkout Concept for Space Transportation Systems
Current space vehicles and missions are characterized by almost complete dependence upon ground support equipment and facilities for determination of vehicle status. For the manned missions of the post Apollo era, this dependence will degrade the probability of mission success. Achievement of autonomous space vehicles is necessary for the successful accomplishment of advanced manned missions.
The development of an on-board test and checkout concept and the design, fabrication and test of a major hardware element of the concept is described.
The integration of functions into an overall data management system for future vehicles, with the flight crew assuming the role of ultimate decision maker for resolution of nonnominal occurences is a logical and obvious extrapolation of-current technological developments, and will yield the autonomy required for tomorrows manned missions
Concepts and analysis for precision segmented reflector and feed support structures
Several issues surrounding the design of a large (20-meter diameter) Precision Segmented Reflector are investigated. The concerns include development of a reflector support truss geometry that will permit deployment into the required doubly-curved shape without significant member strains. For deployable and erectable reflector support trusses, the reduction of structural redundancy was analyzed to achieve reduced weight and complexity for the designs. The stiffness and accuracy of such reduced member trusses, however, were found to be affected to a degree that is unexpected. The Precision Segmented Reflector designs were developed with performance requirements that represent the Reflector application. A novel deployable sunshade concept was developed, and a detailed parametric study of various feed support structural concepts was performed. The results of the detailed study reveal what may be the most desirable feed support structure geometry for Precision Segmented Reflector/Large Deployable Reflector applications
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