Monday, March 07, 2016

Crystal structure, pulsar timing: new publications from faculty and alumni

Lai, Holden W. H. '15, Ren A. Wisconsin '15, Cassandra A. Zentner '13, M. Zeller, and Jesse L. C. Rowsell  2016. Supramolecular Assembly of Tris(4-carboxyphenyl)arenes: Relationship between Molecular Structure and Solid-State Catenation Motifs. Crystal Growth & Design 16:821-833.
abbreviated abstract:
The crystal structures of seven 1,3,5-tris(4-carboxyphenyl)arenes with functionalized central arene rings are reported... To better understand and appreciate these complicated crystal structures, they were categorized into four distinct stacking/catenation families: simple stacking, single-layer offset catenation, double-layer offset catenation, and rotated-layer catenation. The unique structure of the unfunctionalized parent compound 1,3,5-tris(4-carboxyphenyl)benzene is rationalized in light of the structural behavior of its derivatives.   deceased
subscriber access at American Chemical Society

Cordes, J. M., R. M. Shannon, and Daniel R. Stinebring. 2016. Frequency-Dependent Dispersion Measures and Implications for Pulsar Timing. Astrophysical Journal 817:16.
abbreviated abstract:
The dispersion measure (DM), the column density of free electrons to a pulsar, is shown to be frequency dependent because of multipath scattering from small-scale electron-density fluctuations. DMs vary between propagation paths whose transverse extent varies strongly with frequency, yielding arrival times that deviate from the highfrequency scaling ... We discuss implications for methodologies that use large frequency separations or wide bandwidth receivers for timing measurements. Chromatic DMs are partially mitigable by including an additional chromatic term in arrival time models. Without mitigation, an additional term in the noise model for pulsar timing is implied. In combination with measurement errors from radiometer noise, an arbitrarily large increase in total frequency range (or bandwidth) will yield diminishing benefits and may be detrimental to overall timing precision.
subscriber access at Institute of Physics IOPScience

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