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Full-Text Articles in Physical Sciences and Mathematics
Effect Of High Temperature Heat Treatments On The Quality Factor Of A Large-Grain Superconducting Radio-Frequency Niobium Cavity, P. Dhakal, G. Ciovati, G. R. Myneni, K. E. Gray, Et Al., Robert D. Pike
Effect Of High Temperature Heat Treatments On The Quality Factor Of A Large-Grain Superconducting Radio-Frequency Niobium Cavity, P. Dhakal, G. Ciovati, G. R. Myneni, K. E. Gray, Et Al., Robert D. Pike
Arts & Sciences Articles
Large-grain Nb has become a viable alternative to fine-grain Nb for the fabrication of superconducting radio-frequency cavities. In this contribution we report the results from a heat treatment study of a large-grain 1.5 GHz single-cell cavity made of “medium purity” Nb. The baseline surface preparation prior to heat treatment consisted of standard buffered chemical polishing. The heat treatment in the range 800–1400°C was done in a newly designed vacuum induction furnace. Q0 values of the order of 2×1010 at 2.0 K and peak surface magnetic field (Bp) of 90 mT were achieved reproducibly. A Q0 value of (5±1)×1010 at 2.0 …
Local Solvent Acidities In Beta-Cyclodextrin Complexes With Prodan Derivatives, Christopher J. Abelt
Local Solvent Acidities In Beta-Cyclodextrin Complexes With Prodan Derivatives, Christopher J. Abelt
Arts & Sciences Articles
The local solvent acidities (SA scale) of six 6-carbonyl-2-aminonaphthalene derivatives as beta-cyclodextrin complexes in water are determined through fluorescence quenching. The local polarities (E-T(N) scale) are determined through the shift of the emission center-of-mass. The apparent SA values reflect the solvent structure surrounding the guest's carbonyl group, whereas the apparent E-T(N) values reveal the net polarity of the entire guest molecule. Comparison of these values affords greater insight into the structures of the host-guest complexes. Derivatives 1 and 5 show unusually large acidities, indicative of highly exposed carbonyl groups. The remaining compounds give emission intensities pointing to shielded carbonyl groups. …
Carbonate-Templated Self-Assembly Of An Alkylthiolate-Bridged Cadmium Macrocycle, Wei La, Steven M. Berry, William P. Kaplan, Et Al., John C. Poutsma, Robert D. Pike, Deborah C. Bebout
Carbonate-Templated Self-Assembly Of An Alkylthiolate-Bridged Cadmium Macrocycle, Wei La, Steven M. Berry, William P. Kaplan, Et Al., John C. Poutsma, Robert D. Pike, Deborah C. Bebout
Arts & Sciences Articles
In the presence of Cd(ClO4)2 and a base, a new mixed N,S-donor alkylthiolate ligand supported both carbonate formation from atmospheric CO2 and the self-assembly of a novel bicapped puckered (CdS)6 molecular wheel. The remarkable stability of the complex was demonstrated by slow intermolecular ligand exchange on the 2J(HH) and J(111/113Cd1H) time scales at elevated temperature. Both CO2 and the base were required to convert amorphous “CdLClO4” precipitated in the absence of air to the carbonate complex. The complex shares structural features with the ζ-carbonic anhydrase class associating cadmium(II) with the biogeochemical cycling of carbon and is the …
Atom Economical, One-Pot, Three-Reaction Cascade To Novel Tricyclic 2,4-Dihydro-1h-Benzo[F]Isochromenes, Robert J. Hinkle, Shane E. Lewis
Atom Economical, One-Pot, Three-Reaction Cascade To Novel Tricyclic 2,4-Dihydro-1h-Benzo[F]Isochromenes, Robert J. Hinkle, Shane E. Lewis
Arts & Sciences Articles
A three-step domino reaction between 1-aryl-3-hexyne-2,6-diol derivatives and aldehydes is used to construct tricyclic 1,4-dihydro-2H-benzo[f]isochromenes. The cascade is initiated by BF3·OEt2 and involves alkynyl-Prins cyclization, Friedel–Crafts alkenylation, and dehydration/aromatization to create a new, central aromatic ring and eliminate 2 equiv. of water. Electron-donating substituents on the aryl ring of the 1-aryl-3-hexyne-2,6-diols significantly increase overall yields as do electron-rich aldehyde reaction partners. For 2,4-disubstituted 2H-benzo[f]isochromene products, diastereoselectivities in the alkynyl-Prins reaction are ∼1.4 : 1 in favor of the cis-diastereomer. The stereochemistry of one cis-product was verified by …