New Dissociative Recombination Product Branching Fractions and Their Effect on Calculated Interstellar Molecular Abundances

Recent storage ring measurements of the complete product distributions for the dissociative recombination of assorted polyatomic ions (H_3^+, H_2O^+, H_3O^+, CH_3^+) show that there is significantly more fragmentation than previously believed. Generalizing these results, we consider the effect on gas-phase chemical models of dense interstellar clouds when a greater degree of fragmentation is assumed for the products of dissociative recombination reactions. In general, we find salient model results to be surprisingly insensitive to the change. We also generalize some conflicting experimental results for the branching fractions of H_3O^+ + e obtained in a flowing afterglow experiment. With this set of generalized branching fractions in our chemical model, there is a stronger change from previous results, especially for more saturated molecules, which are now difficult to produce in the gas phase

Thermodynamic and Tunneling Density of States of the Integer Quantum Hall Critical State

We examine the long wave length limit of the self-consistent Hartree-Fock approximation irreducible static density-density response function by evaluating the charge induced by an external charge. Our results are consistent with the compressibility sum rule and inconsistent with earlier work that did not account for consistency between the exchange-local-field and the disorder potential. We conclude that the thermodynamic density of states is finite, in spite of the vanishing tunneling density of states at the critical energy of the integer quantum Hall transition.Comment: 5 pages, 4 figures, minor revisions, published versio

EST analysis of gene expression in early cleavage-stage sea urchin embryos

A set of 956 expressed sequence tags derived from 7-hour (mid-cleavage) sea urchin embryos was analyzed to assess biosynthetic functions and to illuminate the structure of the message population at this stage. About a quarter of the expressed sequence tags represented repetitive sequence transcripts typical of early embryos, or ribosomal and mitochondrial RNAs, while a majority of the remainder contained significant open reading frames. A total of 232 sequences, including 153 different proteins, produced significant matches when compared against GenBank. The majority of these identified sequences represented ‘housekeeping’ proteins, i.e., cytoskeletal proteins, metabolic enzymes, transporters and proteins involved in cell division. The most interesting finds were components of signaling systems and transcription factors not previously reported in early sea urchin embryos, including components of Notch and TGF signal transduction pathways. As expected from earlier kinetic analyses of the embryo mRNA populations, no very prevalent protein-coding species were encountered; the most highly represented such sequences were cDNAs encoding cyclins A and B. The frequency of occurrence of all sequences within the database was used to construct a sequence prevalence distribution. The result, confirming earlier mRNA population analyses, indicated that the poly(A) RNA of the early embryo consists mainly of a very complex set of low-copy-number transcripts

Autocatalytic Activation of Influenza Hemagglutinin

Enveloped viruses contain surface proteins that mediate fusion between the viral and target cell membranes following an activating stimulus. Acidic pH induces the influenza virus fusion protein hemagglutinin (HA) via irreversible refolding of a trimeric conformational state leading to exposure of hydrophobic fusion peptides on each trimer subunit. Herein, we show that cells expressing fowl plague virus HA demonstrate discrete switching behavior with respect to the HA conformational change. Partially activated states do not exist at the scale of the cell, activation of HA leads to aggregation of cell surface trimers, and newly synthesized HA refold spontaneously in the presence of previously activated HA. These observations imply a feedback mechanism involving self-catalyzed refolding of HA and thus suggest a mechanism similar to the autocatalytic refolding and aggregation of prions

X-ray edge problem of graphene

The X-ray edge problem of graphene with the Dirac fermion spectrum is studied. At half-filling the linear density of states suppresses the singular response of the Fermi liquid, while away from half-filling the singular features of the Fermi liquid reappear. The crossover behavior as a function of the Fermi energy is examined in detail. The exponent of the power-law absorption rate depends both on the intra- and inter-valley scattering, and it changes as a function of the Fermi energy, which may be tested experimentally.Comment: 7 pages, 1 figur