Detecting hydrogen-containing contaminants on metal surfaces

Spark emission spectroscopy analyzes surface contamination of metals. This technique controls the quality of surface preparations and is useful in fundamental investigations of surface properties of metals

Orientation and symmetries of Alexandrov spaces with applications in positive curvature

We develop two new tools for use in Alexandrov geometry: a theory of ramified orientable double covers and a particularly useful version of the Slice Theorem for actions of compact Lie groups. These tools are applied to the classification of compact, positively curved Alexandrov spaces with maximal symmetry rank.Comment: 34 pages. Simplified proofs throughout and a new proof of the Slice Theorem, correcting omissions in the previous versio

A Multiparameter Network Reveals Extensive Divergence Between \u3cem\u3eC. elegans\u3c/em\u3e bHLH Transcription Factors: A Dissertation

It has become increasingly clear that transcription factors (TFs) play crucial roles in the development and day-to-day homeostasis that all biological systems experience. TFs target particular genes in a genome, at the appropriate place and time, to regulate their expression so as to elicit the most appropriate biological response from a cell or multicellular organism. TFs can often be grouped into families based on the presence of similar DNA binding domains, and these families are believed to have expanded and diverged throughout evolution by several rounds of gene duplication and mutation. The extent to which TFs within a family have functionally diverged, however, has remained unclear. We propose that systematic analysis of multiple aspects, or parameters, of TF functionality for entire families of TFs could provide clues as to how divergent paralogous TFs really are. We present here a multiparameter integrated network of the activity of the basic helix-loop-helix (bHLH) TFs from the nematode Caenorhabditis elegans. Our data, and the resulting network, indicate that several parameters of bHLH function contribute to their divergence and that many bHLH TFs and their associated parameters exhibit a wide range of connectivity in the network, some being uniquely associated to one another, whereas others are highly connected to multiple parameter associations. We find that 34 bHLH proteins dimerize to form 30 bHLH dimers, which are expressed in a wide range of tissues and cell types, particularly during the development of the nematode. These dimers bind to E-Box DNA sequences and E-Box-like sequences with specificity for nucleotides central to and flanking those E-Boxes and related sequences. Our integrated network is the first such network for a multicellular organism, describing the dimerization specificity, spatiotemporal expression patterns, and DNA binding specificities of an entire family of TFs. The network elucidates the state of bHLH TF divergence in C. elegans with respect to multiple functional parameters and suggests that each bHLH TF, despite many molecular similarities, is distinct from its family members. This functional distinction may indeed explain how TFs from a single family can acquire different biological functions despite descending from common genetic ancestry

Modeling the Pulse Profiles of Millisecond Pulsars in the Second LAT Catalog of gamma-ray Pulsars

Significant gamma-ray pulsations have been detected from ~40 millisecond pulsars (MSPs) using 3 years of sky-survey data from the Fermi LAT and radio timing solutions from across the globe. We have fit the radio and gamma-ray pulse profiles of these MSPs using geometric versions of slot gap and outer gap gamma-ray emission models and radio cone and core models. For MSPs with radio and gamma-ray peaks aligned in phase we also explore low-altitude slot gap gamma-ray models and caustic radio models. The best-fit parameters provide constraints on the viewing geometries and emission sites. While the exact pulsar magnetospheric geometry is unknown, we can use the increased number of known gamma-ray MSPs to look for significant trends in the population which average over these uncertainties.Comment: 4 pages, 2 figures, to appear in the proceedings of the 5th International Symposium on High-Energy Astronom

Local Axon Guidance in Cerebral Cortex and Thalamus: Are We There Yet?

Normal brain function requires the development of precise connections between thalamus and cerebral cortex. In this issue of Neuron, Cang et al. and Tori and Levitt argue that EphA/ephrin-A signaling in the target tissue guides sensory thalamic axons to the correct cortical area, and sensory cortical axons to precise thalamic targets. Although EphA/ephrin-A signaling organizes sensory maps within areas, and thalamocortical axons in the internal capsule, both papers argue that each developmental event is dissociable from the others

Die betekenis van Totius vir ons tyd*

Dit is nie my voorneme om hier ’n soort huldigende lofrede oor die mens Totius te hou nie. Die Totius-beeld het dit nie nodig nie en hyself het, waar dit sy persoon raak, nie van die woord huldi- ging gehou nie. By geleentheid het ek hom hoor sê: „Dis vir my ’n kwaai woord, die woord ‘huldiging

Positive allosteric modulators of the a-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor

L-glutamate is the major excitatory neurotransmitter in the mammalian central nervous system (CNS) and plays a fundamental role in the control of motor function, cognition and mood. The physiological effects of glutamate are mediated through two functionally distinct receptor families. While activation of metabotropic (G-protein coupled) glutamate receptors results in modulation of neuronal excitability and transmission, the ionotropic glutamate receptors (ligand-gated ion channels) are responsible for mediating the fast synaptic response to extracellular glutamate