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Displaying 1551 - 1575 of 2122

Control of Molecular Mass Distributions in Enzymatic Lactone Polymerizations

February 2, 2012
Author(s)
Santanu S. Kundu, Peter M. Johnson, Kathryn L. Beers
Using a model developed for the enzyme catalyzed polymerization and degradation of poly(caprolactone), we illustrate methods and the kinetic mechanisms necessary to improve molecular mass distributions by manipulating equilibrium reactions in the kinetic

Polymer Dynamics in Constrained Geometries

February 1, 2012
Author(s)
Christopher Soles, Ryan Nieuwendaal, Huagen H. Peng
The wide-spread interest in the dynamical property of organic materials under strong states of confinement largely began with differential scanning calorimeter (DSC) measurements in the early 90's of the glass transition and heat capacity of glass forming

Theoretical optical and x-ray spectra of liquid and solid H2O

January 3, 2012
Author(s)
Eric L. Shirley, Joshua J. Kas, J. T. Vinson, Fernando D. Vila, John J. Rehr
Theoretical optical and x-ray spectra of model structures of water and ice are calculated using a many-body perturbation theory, Bethe-Salpeter equation (BSE) approach implemented in the valence- and core-excitation codes AI2NBSE and OCEAN. These codes use

PROBING MATERIAL PROPERTIES WITH SHARP INDENTERS: A REVIEW

January 2, 2012
Author(s)
Brian R. Lawn, Robert F. Cook
A review on the use of sharp, fixed-profile indenters as materials probes is presented. Indentation is proposed as a simple but powerful methodology for evaluating basic mechanical properties—elastic modulus, hardness, toughness, etc.—in all classes of

Contributions to anelasticity in langasite and langatate

December 30, 2011
Author(s)
Ward L. Johnson, Sudook A. Kim, Christine F. Rivenbark, Satoshi Uda
Maximization of the quality factors Q of langasite (LGS) and langatate (LGT) is necessary for optimal performance of acoustic resonators of these materials in frequency-control and high-temperature sensing applications. In this report, measurements and

Reversible effect of strain on transport critical current in Bi 2 Sr 2 CaCu 2 O 8+x superconducting wires: A modified descriptive strain model

December 5, 2011
Author(s)
Najib Cheggour, Xifeng Lu, T G. Holesinger, Theodore C. Stauffer, J Jiang, Loren F. Goodrich
A reversible strain effect on transport critical current I c was found in Bi 2Sr 2CaCu 2O 8+x (Bi-2212) high-temperature superconducting round wires. I c showed unambiguous reversibility at 4 K and 16 T up to an irreversible strain limit of about 0.3 % in

Automated Data Processing and Quantification in Polymer Mass Spectrometry

December 1, 2011
Author(s)
Till Gruendling, Christopher Barner-Kowollik, William E. Wallace, Charles M. Guttman, Anthony J. Kearsley
An overview is given of some new techniques in quantitative composition and molecular mass distribution measurement of synthetic polymers by mass spectrometry. New concepts in data analysis, including peak picking and integration, are also described.

Mechanical Properties of Polymer Nano-Films

November 28, 2011
Author(s)
Junghyun Lee, Jun Y. Chung, Christopher Stafford
Three fundamental mechanical properties of supported glassy polystyrene films with thickness ranging from 250 nm to 9 nm were quantitatively determined by a recently developed wrinkling-cracking method. Films below about 40 nm showed a decrease in both

Minimizing damage during FIB-TEM sample preparation of soft materials

November 17, 2011
Author(s)
Nabil Bassim, Bradley De Gregorio, A. D. Kilcoyne, Keana Scott, Tsngming Chou, S. Wirick, George Cody, Rhonda Stroud
Although focused ion beam (FIB) microscopy has been used successfully for milling patterns and creating ultra-thin transmission electron microscopy (TEM) sections of polymers and other soft materials, little has been documented regarding FIB-induced damage

Self-Repairing Complex Helical Columns Generated via Kinetically Controlled Self-Assembly of Dendronized Perylene Bisimides

November 16, 2011
Author(s)
Virgil Percec, Steven Hudson, Mihai Peterca, Pawaret Leowanawat, Emad Aqad, Robert Graf, Hans -. Spiess, Xiangbing Zeng, Goran Ungar, Paul A. Heiney
The dendronized perylene 3,4:9,10-tetracarboxylic acid bisimide (PBI) (3,4,5)12G1-3-PBI was recently shown to self-assemble in a complex helical column containing tetramers of PBI as the basic repeat unit. The tetramers contain a pair of two molecules
Displaying 1551 - 1575 of 2122