The groupoidal analogue Theta~ to Joyal's category Theta is a test category

We introduce the groupoidal analogue \tilde\Theta to Joyal's cell category \Theta and we prove that \tilde\Theta is a strict test category in the sense of Grothendieck. This implies that presheaves on \tilde\Theta model homotopy types in a canonical way. We also prove that the canonical functor from \Theta to \tilde\Theta is aspherical, again in the sense of Grothendieck. This allows us to compare weak equivalences of presheaves on \tilde\Theta to weak equivalences of presheaves on \Theta. Our proofs apply to other categories analogous to \Theta.Comment: 41 pages, v2: references added, Remark 7.3 added, v3: metadata update

THE INFLUENCE OF WATER QUALITY ON THE HOUSING PRICE AROUND LAKE ERIE

The primary objective of this paper is to estimate the influence of Lake Erie water quality on the housing price by taking spatial effects into account. The robust LM tests for spatial autocorrelation suggested that spatial error model specification is more likely model in our study. Fecal coliform counts and Secchi depth disk reading are used as water quality measures. In order to overcome the spatio-temporal aspects of Secchi depth disk reading data, Kriging was used for spatial prediction. We found the significant influences of both water quality measures on housing values. Gradient effects considering the distance from a beach and water quality variables are also observed.Public Economics,

Ken Jacobs, Alchemist

Optic Antics: The Cinema of Ken Jacobs edited by Michele Pierson, David E. James, and Paul Arthur. Oxford: Oxford University Press, 2011. Pp. 312; 48 photographs. $99.00 cloth,$39.95 paper, 26.99 E-book

Absorption enhancing proximity effects in aperiodic nanowire arrays

Aperiodic Nanowire (NW) arrays have higher absorption than equivalent periodic arrays, making them of interest for photovoltaic applications. An inevitable property of aperiodic arrays is the clustering of some NWs into closer proximity than in the equivalent periodic array. We focus on the modes of such clusters and show that the reduced symmetry associated with cluster formation allows external coupling into modes which are dark in periodic arrays, thus increasing absorption. To exploit such modes fully, arrays must include tightly clustered NWs that are unlikely to arise from fabrication variations but must be created intentionally.Comment: Accepted by Optics Expres

Boron bridging of rhamnogalacturonan-II in Rosa and arabidopsis cell cultures occurs mainly in the endo-membrane system and continues at a reduced rate after secretion

BACKGROUND AND AIMS: Rhamnogalacturonan-II (RG-II) is a domain of primary cell-wall pectin. Pairs of RG-II domains are covalently cross-linked via borate diester bridges, necessary for normal cell growth. Interpreting the precise mechanism and roles of boron bridging is difficult because there are conflicting hypotheses as to whether bridging occurs mainly within the Golgi system, concurrently with secretion or within the cell wall. We therefore explored the kinetics of RG-II bridging. METHODS: Cell-suspension cultures of Rosa and arabidopsis were pulse-radiolabelled with [(14)C]glucose, then the boron bridging status of newly synthesized [(14)C]RG-II domains was tracked by polyacrylamide gel electrophoresis of endo-polygalacturonase digests. KEY RESULTS: Optimal culture ages for (14)C-labelling were ~5 and ~1 d in Rosa and arabidopsis respectively. De-novo [(14)C]polysaccharide production occurred for the first ~90 min; thereafter the radiolabelled molecules were tracked as they ‘aged’ in the wall. Monomeric and (boron-bridged) dimeric [(14)C]RG-II domains appeared simultaneously, both being detectable within 4 min of [(14)C]glucose feeding, i.e. well before the secretion of newly synthesized [(14)C]polysaccharides into the apoplast at ~15–20 min. The [(14)C]dimer : [(14)C]monomer ratio of RG-II remained approximately constant from 4 to 120 min, indicating that boron bridging was occurring within the Golgi system during polysaccharide biosynthesis. However, [(14)C]dimers increased slightly over the following 15 h, indicating that limited boron bridging was continuing after secretion. CONCLUSIONS: The results show where in the cell (and thus when in the ‘career’ of an RG-II domain) boron bridging occurs, helping to define the possible biological roles of RG-II dimerization and the probable localization of boron-donating glycoproteins or glycolipids

Arabinogalactan-Proteins as Boron-Acting Enzymes, Cross-Linking the Rhamnogalacturonan-II Domains of Pectin

Most pectic rhamnogalacturonan-II (RG-II) domains in plant cell walls are borate-bridged dimers. However, the sub-cellular locations, pH dependence, reversibility and biocatalyst involvement in borate bridging remain uncertain. Experiments discussed here explored these questions, utilising suspension-cultured plant cells. In-vivo pulse radiolabelling showed that most RG-II domains dimerise extremely quickly (3 required the simultaneous presence of RG-II-binding ‘chaperones’: co-ordinately binding metals and/or ionically binding cationic peptides. Natural chaperones of the latter type include highly basic arabinogalactan protein fragments, e.g., KHKRKHKHKRHHH, which catalyse a reaction [2 RG-II + B(OH)3 → RG-II–B–RG-II], suggesting that plants can ‘enzymically’ metabolise boron