The double life of electrons in magnetic iron pnictides, as revealed by NMR

We present a phenomenological, two-fluid approach to understanding the magnetic excitations in Fe pnictides, in which a paramagnetic fluid with gapless, incoherent particle-hole excitations coexists with an antiferromagnetic fluid with gapped, coherent spin wave excitations. We show that this two-fluid phenomenology provides an excellent quantitative description of NMR data for magnetic "122" pnictides, and argue that it finds a natural justification in LSDA and spin density wave calculations. We further use this phenomenology to estimate the maximum renormalisation of the ordered moment that can follow from low-energy spin fluctuations in Fe pnictides. We find that this is too small to account for the discrepancy between ab intio calculations and neutron scattering measurements.Comment: Accepted for publication in Europhys. Lett. 6 pages, 4 figure

Divergence and Shannon information in genomes

Shannon information (SI) and its special case, divergence, are defined for a DNA sequence in terms of probabilities of chemical words in the sequence and are computed for a set of complete genomes highly diverse in length and composition. We find the following: SI (but not divergence) is inversely proportional to sequence length for a random sequence but is length-independent for genomes; the genomic SI is always greater and, for shorter words and longer sequences, hundreds to thousands times greater than the SI in a random sequence whose length and composition match those of the genome; genomic SIs appear to have word-length dependent universal values. The universality is inferred to be an evolution footprint of a universal mode for genome growth.Comment: 4 pages, 3 tables, 2 figure

Long-Lived Engineering of Glycans to Direct Stem Cell Fate

Glycans mediate many critical, long-term biological processes, such as stem cell differentiation. However, few methods are available for the sustained remodeling of cells with specific glycan structures. A new strategy that enables the long-lived presentation of defined glycosaminoglycans on cell surfaces using HaloTag proteins (HTPs) as anchors is reported. By controlling the sulfation patterns of heparan sulfate (HS) on pluripotent embryonic stem cell (ESC) membranes, it is demonstrated that specific glycans cause ESCs to undergo accelerated exit from self-renewal and differentiation into neuronal cell types. Thus, the stable display of glycans on HTP scaffolds provides a powerful, versatile means to direct key signaling events and biological outcomes such as stem cell fate

Three approaches to qualitative content analysis.

Content analysis is a widely used qualitative Researchers regard content analysis as a flexible method for analyzing text data The differentiation of content analysis is usually limited to classifying it as primarily a qualitative versus quantitative research method. A more thorough analysis of the ways in which qualitative content analysis can be used would potentially illuminate key issues for researchers to consider in the design of studies purporting to 1277 AUTHORS' NOTE: We wish to express our gratitude to Drs. Pamela L. Jordan, Carol J. Leppa, and J. Randall Curtis for their feedback and support in writing this article. QUALITATIVE HEALTH RESEARCH, Vol. 15 No. 9, November 2005 1277-1288 DOI: 10.1177/1049732305276687 © 2005 use content analysis and the analytic procedures employed in such studies, thus avoiding a muddling of methods Our purpose in this article is to present the breadth of approaches categorized as qualitative content analysis. We have identified three distinct approaches: conventional, directed, and summative. All three approaches are used to interpret text data from a predominately naturalistic paradigm. We begin with a brief review of the history and definitions of content analysis. We then illustrate the three different approaches to qualitative content analysis with hypothetical studies to explicate the issues of study design and analytical procedures for each approach

The Active Asteroids

Some asteroids eject dust, unexpectedly producing transient, comet-like comae and tails. First ascribed to the sublimation of near-surface water ice, mass losing asteroids (also called "main-belt comets") can in fact be driven by a surprising diversity of mechanisms. In this paper, we consider eleven dynamical asteroids losing mass, in nine of which the ejected material is spatially resolved. We address mechanisms for producing mass loss including rotational instability, impact ejection, electrostatic repulsion, radiation pressure sweeping, dehydration stresses and thermal fracture, in addition to the sublimation of ice. In two objects (133P and 238P) the repetitive nature of the observed activity leaves ice sublimation as the only reasonable explanation while, in a third ((596) Scheila), a recent impact is the cause. Another impact may account for activity in P/2010 A2 but this tiny object can also be explained as having shed mass after reaching rotational instability. Mass loss from (3200) Phaethon is probably due to cracking or dehydration at extreme (~1000 K) perihelion temperatures, perhaps aided by radiation pressure sweeping. For the other bodies, the mass loss mechanisms remain unidentified, pending the acquisition of more and better data. While the active asteroid sample size remains small, the evidence for an astonishing diversity of mass loss processes in these bodies is clear.Comment: 42, pages, 9 figures, The Astronomical Journal, in pres

Directing Neuronal Signaling through Cell-Surface Glycan Engineering

The ability to tailor plasma membranes with specific glycans may enable the control of signaling events that are critical for proper development and function. We report a method to modify cell surfaces with specific sulfated chondroitin sulfate (CS) glycosaminoglycans using chemically modified liposomes. Neurons engineered to display CS-E-enriched polysaccharides exhibited increased activation of neurotrophin-mediated signaling pathways and enhanced axonal growth. This approach provides a facile, general route to tailor cell membranes with biologically active glycans and demonstrates the potential to direct important cellular events through cell-surface glycan engineering

Comprehensive mapping of O-GlcNAc modification sites using a chemically cleavable tag

The post-translational modification of serine or threonine residues of proteins with a single N-acetylglucosamine monosaccharide (O-GlcNAcylation) is essential for cell survival and function. However, relatively few O-GlcNAc modification sites have been mapped due to the difficulty of enriching and detecting O-GlcNAcylated peptides from complex samples. Here we describe an improved approach to quantitatively label and enrich O-GlcNAcylated proteins for site identification. Chemoenzymatic labelling followed by copper(I)-catalysed azide–alkyne cycloaddition (CuAAC) installs a new mass spectrometry (MS)-compatible linker designed for facile purification of O-GlcNAcylated proteins from cell lysates. The linker also allows subsequent quantitative release of O-GlcNAcylated proteins for downstream MS analysis. We validate the approach by unambiguously identifying several established O-GlcNAc sites on the proteins α-crystallin and O-GlcNAc transferase (OGT), as well as discovering new, previously unreported sites on OGT. Notably, these novel sites on OGT lie in key functional domains of the protein, underscoring how this site identification method may reveal important biological insights into protein activity and regulation

Public and private communication with a quantum channel and a secret key

We consider using a secret key and a noisy quantum channel to generate noiseless public communication and noiseless private communication. The optimal protocol for this setting is the publicly-enhanced private father protocol. This protocol exploits random coding techniques and "piggybacking" of public information along with secret-key-assisted private codes. The publicly-enhanced private father protocol is a generalization of the secret-key-assisted protocol of Hsieh, Luo, and Brun and a generelization of a protocol for simultaneous communication of public and private information suggested by Devetak and Shor.Comment: 15 pages, 2 figure

Gut Helicobacter presentation by multiple dendritic cell subsets enables context-specific regulatory T cell generation

Generation of tolerogenic peripheral regulatory T (pTreg) cells is commonly thought to involve CD10