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2000

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Articles 2911 - 2919 of 2919

Full-Text Articles in Physical Sciences and Mathematics

Bismuth(Iii) Oxide Perchlorate Promoted Rearrangement Of Epoxides To Aldehydes And Ketones, Ram S. Mohan, Andrew M. Anderson, Jesse M. Blazek, Parie Garg, Brian J. Payne Dec 1999

Bismuth(Iii) Oxide Perchlorate Promoted Rearrangement Of Epoxides To Aldehydes And Ketones, Ram S. Mohan, Andrew M. Anderson, Jesse M. Blazek, Parie Garg, Brian J. Payne

Ram S. Mohan

Aryl-substituted epoxides and aliphatic epoxides with a tertiary epoxide carbon undergo smooth rearrangement in the presence of 10–50 mol% bismuth(III) oxide perchlorate, BiOClO4•xH2O, to give carbonyl compounds. The rearrangement is regioselective with aryl substituted epoxides and a single carbonyl compound arising from cleavage of benzylic C―O bond is formed. BiOClO4•xH2O is relatively non-toxic, insensitive to air and inexpensive, making this catalyst an attractive alternative to more corrosive and toxic Lewis acids such as BF3•Et2O or InCl3 currently used to effect epoxide rearrangements.

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Trajectory Mapping: A Tool For Validation Of Trace Gas Observations, Gary A. Morris, James F. Gleason, Jerald Ziemke, Mark R. Schoeberl Dec 1999

Trajectory Mapping: A Tool For Validation Of Trace Gas Observations, Gary A. Morris, James F. Gleason, Jerald Ziemke, Mark R. Schoeberl

Gary A. Morris

We investigate the effectiveness of trajectory mapping(TM) as a data validation tool. TM combines a dynamical model of the atmosphere with trace gas observations to provide more statistically robust estimates of instrument performance over much broader geographic areas than traditional techniques are able to provide. We present four detailed case studies selected so that the traditional techniques are expected to work well. In each case the TM results are equivalent to or improve upon the measurement comparisons performed with traditional approaches. The TM results are statistically more robust than those achieved using traditional approaches since the TM comparisons occur over …

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Configurational Entropy And Diffusivity Of Supercooled Water, Francis W. Starr, A. Scala, E. La Nave, F. Sciortino, H. E. Stanley Dec 1999

Configurational Entropy And Diffusivity Of Supercooled Water, Francis W. Starr, A. Scala, E. La Nave, F. Sciortino, H. E. Stanley

Francis Starr

No abstract provided.

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Semiparametric Regression: An Exposition And Application To Print Advertising Data, Michael S. Smith, Robert Kohn, Sharat K. Mathur Dec 1999

Semiparametric Regression: An Exposition And Application To Print Advertising Data, Michael S. Smith, Robert Kohn, Sharat K. Mathur

Michael Stanley Smith

A new regression based approach is proposed for modeling marketing databases. The approach is Bayesian and provides a number of significant improvements over current methods. Independent variables can enter into the model in either a parametric or nonparametric manner, significant variables can be identified from a large number of potential regressors and an appropriate transformation of the dependent variable can be automatically selected from a discrete set of pre-specified candidate transformations. All these features are estimated simultaneously and automatically using a Bayesian hierarchical model coupled with a Gibbs sampling scheme. Being Bayesian, it is straightforward to introduce subjective information about …

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Working Memory And Executive Function: Evidence From Neuroimaging, Patricia A. Carpenter, Marcel Adam Just, Erik D. Reichle Dec 1999

Working Memory And Executive Function: Evidence From Neuroimaging, Patricia A. Carpenter, Marcel Adam Just, Erik D. Reichle

Marcel Adam Just

No abstract provided.

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Reflexive Autopoietic Systems Theory, Kent D. Palmer Dec 1999

Reflexive Autopoietic Systems Theory, Kent D. Palmer

Kent D. Palmer

Exploring the Meta-systems of Emergent Worlds

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Wolf-Rayet Wind Structure And Optical Variability., Q. Li, J. C. Brown, R. Ignace, J. P. Cassinelli, L. M. Oskinova Dec 1999

Wolf-Rayet Wind Structure And Optical Variability., Q. Li, J. C. Brown, R. Ignace, J. P. Cassinelli, L. M. Oskinova

Richard Ignace

Results are presented on the expected variability of Wolf-Rayet (WR) stars in broad-band optical polarimetry and photometry, and in emission line profiles, due to an inhomogeneous random distribution of blobs in spherical geometry. Time dependent 3-D simulations are carried out with blob ejection random in time and direction, and the radiation properties are evaluated in the optically thin limit. In contrast with previous purely statistical analyses, inclusion in the present treatment of a beta velocity law and stellar occultation effects can yield results consistent with observations of the mean polarisation bar p and the ratio R=sigma_p /sigma_phot of polarimetric to …

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Adaptive Testing In Arch Models, Douglas G. Steigerwald, Oliver Linton Dec 1999

Adaptive Testing In Arch Models, Douglas G. Steigerwald, Oliver Linton

Douglas G. Steigerwald

Specification tests for conditional heteroskedasticity that are derived under the assumption that the density of the innovation is Gaussian may not be powerful in light of the recent empirical results that the density is not Gaussian. We obtain specification tests for conditional heteroskedasticity under the assumption that the innovation density is a member of a general family of densities. Our test statistics maximize asymptotic local power and weighted average power criteria for the general family of densities. We establish both first-order and second-order theory for our procedures. Simulations indicate that asymptotic power gains are achievable in finite samples.

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An Elliptic Equation With Spike Solutions Concentrating At Local Minima Of The Laplacian Of The Potential, Gregory S. Spradlin Dec 1999

An Elliptic Equation With Spike Solutions Concentrating At Local Minima Of The Laplacian Of The Potential, Gregory S. Spradlin

Gregory S. Spradlin

We consider a singularly perturbed elliptic PDE that arises in the study of nonlinear Schrodinger equations. We seek solutions that are positive on the entirety of Euclidean space and that vanish at infinity. Under the assumption that the nonlinear term of the PDE satisfies super-linear and sub-critical growth conditions, we show that for small values of the epsilon parameter in the PDE, there solutions that concentrate near local minima of V (a coefficient function in the PDE) . The local minima may occur in unbounded components, as long as the Laplacian of V achieves a strict local minimum along such …

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