Defining and delineating the central areas of towns for statistical monitoring using continuous surface representations

The increasing availability of very high spatial resolution data using the unit postcode as its geo-reference is making possible new kinds of urban analysis andmodelling. However, at this resolution the granularity of the data used to representurban functions makes it difficult to apply traditional analytical and modellingmethods. An alternative suggested here is to use kernel density estimation totransform these data from point or area 'objects' into continuous surfaces of spatialdensities. The use of this transformation is illustrated by a study in which we attemptto develop a robust, generally applicable methodology for identifying the centralareas of UK towns for the purpose of statistical reporting and comparison.Continuous density transformations from unit post code data relating to a series ofindicators of town centredness created using ArcView are normalised and thensummed to give a composite ?Index of Town Centredness?. Selection of key contourson these index surfaces enables town centres to be delineated. The work results froma study on behalf of DETR

On a pterosaur jaw from the Upper Jurassic of Tendaguru (Tanzania)

A short section of a mandibular symphysis is the first cranial fossil of a pterosaur to be reported from the Upper Jurassic of Tendaguru, Tanzania. It is made the holotype of a new dsungaripteroid pterosaur, Tendaguripterus recki n. gen. n. sp. All previously named pterosaur taxa from Tendaguru are shown to be nomina dubia. The pterosaur assemblage from Tendaguru contains a "rhamphorhynchoid", as well as the dsungaripteroid, and is similar in its systematic composition to other Late Jurassic pterosaur assemblages from Laurasia. The diversity and broad distribution of dsungaripteroids in the Late Jurassic suggests that the group was already well established by this time. Der erste Schädelrest eines Flugsauriers aus dem Oberjura von Tendaguru in Tansania wird beschrieben. Bei dem Fundstück handelt es sich um ein bezahntes Unterkieferbruchstück aus der Symphysenregion. Der Fund gehört zu einem neuen Taxon, das als Tendaguripterus recki n. gen. n. sp. bezeichnet und zur Überfamilie Dsungaripteroidea gestellt wird. Alle zuvor aus den Tendaguru-Schichten beschriebenen Taxa werden als nomina dubia angesehen. In Tendaguru sind Verteter der „Rhamphorhynchoidea“ und Dsungaripteroidea nachgewiesen. Diese systematische Zusammensetzung ist derjenigen anderer Flugsaurier-Vergesellschaftungen der späten Jura-Zeit ähnlich. Die Vielfalt und die weite Verbreitung der Dsungaripteroidea in Laurasia läßt darauf schließen, daß sich diese Flugsauriergruppe bereits in der späten Jura-Zeit erfolgreich durchgesetzt hatte. doi:10.1002/mmng.1999.4860020109</a

A Hydrophobic Gate in an Ion Channel: The Closed State of the Nicotinic Acetylcholine Receptor

The nicotinic acetylcholine receptor (nAChR) is the prototypic member of the `Cys-loop' superfamily of ligand-gated ion channels which mediate synaptic neurotransmission, and whose other members include receptors for glycine, gamma-aminobutyric acid, and serotonin. Cryo-electron microscopy has yielded a three dimensional structure of the nAChR in its closed state. However, the exact nature and location of the channel gate remains uncertain. Although the transmembrane pore is constricted close to its center, it is not completely occluded. Rather, the pore has a central hydrophobic zone of radius about 3 A. Model calculations suggest that such a constriction may form a hydrophobic gate, preventing movement of ions through a channel. We present a detailed and quantitative simulation study of the hydrophobic gating model of the nicotinic receptor, in order to fully evaluate this hypothesis. We demonstrate that the hydrophobic constriction of the nAChR pore indeed forms a closed gate. Potential of mean force (PMF) calculations reveal that the constriction presents a barrier of height ca. 10 kT to the permeation of sodium ions, placing an upper bound on the closed channel conductance of 0.3 pS. Thus, a 3 A radius hydrophobic pore can form a functional barrier to the permeation of a 1 A radius Na+ ion. Using a united atom force field for the protein instead of an all atom one retains the qualitative features but results in differing conductances, showing that the PMF is sensitive to the detailed molecular interactions.Comment: Accepted by Physical Biology; includes a supplement and a supplementary mpeg movie can be found at http://sbcb.bioch.ox.ac.uk/oliver/download/Movies/watergate.mp

On the Nature of Andromeda IV

Lying at a projected distance of 40' or 9 kpc from the centre of M31, Andromeda IV is an enigmatic object first discovered during van den Bergh's search for dwarf spheroidal companions to M31. Being bluer, more compact and higher surface brightness than other known dwarf spheroidals, it has been suggested that And IV is either a relatively old `star cloud' in the outer disk of M31 or a background dwarf galaxy. We present deep HST WFPC2 observations of And IV and the surrounding field which, along with ground-based long-slit spectroscopy and Halpha imagery, are used to decipher the true nature of this puzzling object. We find compelling evidence that And IV is a background galaxy seen through the disk of M31. The moderate surface brightness (SB(V)~24), very blue colour (V-I<~0.6), low current star formation rate (~0.001 solar mass/yr) and low metallicity (~10% solar) reported here are consistent with And IV being a small dwarf irregular galaxy, perhaps similar to Local Group dwarfs such as IC 1613 and Sextans A. Although the distance to And IV is not tightly constrained with the current dataset, various arguments suggest it lies in the range 5<~D<~8 Mpc, placing it well outside the confines of the Local Group. It may be associated with a loose group of galaxies, containing major members UGC 64, IC 1727 and NGC 784. We report an updated position and radial velocity for And IV.Comment: 26 pages, LaTex with 9 figures (including 6 jpg plates). Accepted for publication in A

Zero modes, entropy bounds and partition functions

Some recent finite temperature calculations arising in the investigation of the Verlinde-Cardy relation are re-analysed. Some remarks are also made about temperature inversion symmetry.Comment: 12 pages, JyTe

The Application of a Hypothesis-driven Strategy to the Sensitive Detection and Location of Acetylated Lysine Residues

The application of a hypothesis-driven method for the sensitive determination of lysine acetylation sites on enzymatically digested proteins is described. Comparative sensitivity tests were carried out using serial dilution of an acetylated bovine serum albumin (AcBSA) digest to assess the performance of a multiple reaction monitoring (MRM)–based approach as compared to a more conventional precursor scanning (PS) method. Both methods were capable of selectively detecting an acetylated peptide at the low femtomole level when spiked into a background of 500 fmol six-protein tryptic digest. The MRM approach was roughly tenfold more sensitive than precursor scanning with one acetylated peptide detected and sequenced at the level of 2 fmol on-column. The technique was subsequently applied to a gel-derived sample of cytokeratin-8 (CK8) shown to contain acetylated lysine residues by Western blot analysis. The strategy applied herein, termed MRM-initiated detection and sequencing (MIDAS), resulted in the facile identification of novel sites of acetylation on this protein

Simultaneous topography and reaction flux mapping at and around electrocatalytic nanoparticles

The characterization of electrocatalytic reactions at individual nanoparticles (NPs) is presently of considerable interest but very challenging. Herein, we demonstrate how simple-to-fabricate nanopipette probes with diameters of approximately 30 nm can be deployed in a scanning ion conductance microscopy (SICM) platform to simultaneously visualize electrochemical reactivity and topography with high spatial resolution at electrochemical interfaces. By employing a self-referencing hopping mode protocol, whereby the probe is brought from bulk solution to the near-surface at each pixel, and with potential-time control applied at the substrate, current measurements at the nanopipette can be made with high precision and resolution (30 nm resolution, 2600 pixels μm–2, <0.3 s pixel−1) to reveal a wealth of information on the substrate physicochemical properties. This methodology has been applied to image the electrocatalytic oxidation of borohydride at ensembles of AuNPs on a carbon fiber support in alkaline media, whereby the depletion of hydroxide ions and release of water during the reaction results in a detectable change in the ionic composition around the NPs. Through the use of finite element method simulations, these observations are validated and analyzed to reveal important information on heterogeneities in ion flux between the top of a NP and the gap at the NP-support contact, diffusional overlap and competition for reactant between neighboring NPs, and differences in NP activity. These studies highlight key issues that influence the behavior of NP assemblies at the single NP level and provide a platform for the use of SICM as an important tool for electrocatalysis studies

The Speed and Orientation of the Parsec-Scale Jet in 3C 279

We have calculated inverse-Compton Doppler factors for 3C 279 using the collection of VLBI data recently published by us, and the collection of multiwavelength spectra recently published by Hartman et al. From the Doppler factor and superluminal apparent speed, we then calculate the Lorentz factor and angle to the line-of-sight of the parsec-scale relativistic jet. We model the jet components as homogeneous spheres and the VLBI core as an unresolved inhomogeneous conical jet. The conical-jet model can be made to match both the observed X-ray emission and the VLBI properties of the core with a suitable choice of Doppler factor, implying the core makes a significant contribution to the X-ray emission. The parameters of the conical models indicate the jet is particle dominated at the radii that produce significant emission, and is not in equipartition. At the inner radius of the conical jet the magnetic field is of order 0.1 G and the relativistic-particle number density is of order 10 cm^{-3}. When all components are included in the calculation, then on average the core produces about half of the X-rays, with the other half being split between the long-lived component C4 and the brightest inner-jet component. We calculate an average speed and angle to the line-of-sight for the region of the jet interior to 1 mas of v=0.992c (gamma=8) and 4 degrees, and an average speed and angle to the line-of-sight for C4 (at a distance from the core of 3 mas) of v=0.997c (gamma=13) and 2 degrees. These values imply average Doppler factors of delta=12 for the inner jet, and delta=21 for C4