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Search Results: 1 - 10 of 11780 matches for " Laura Churcher "
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Resolved Imaging of the HD191089 Debris Disc
Laura J. Churcher,Mark C. Wyatt,Rachel Smith
Physics , 2010, DOI: 10.1111/j.1365-2966.2010.17422.x
Abstract: Two thirds of the F star members of the 12 Myr old Beta Pictoris Moving Group (BPMG) show significant excess emission in the mid-infrared, several million years after the expected dispersal of the protoplanetary disc. Theoretical models of planet formation suggest that this peak in the mid-infrared emission could be due to the formation of Pluto-sized bodies in the disc, which ignite the collisional cascade and enhance the production of small dust. Here we present resolved mid-infrared imaging of the disc of HD191089 (F5V in the BPMG) and consider its implications for the state of planet formation in this system. HD191089 was observed at 18.3 microns using T-ReCS on Gemini South and the images were compared to models of the disc to constrain the radial distribution of the dust. The emission observed at 18.3 microns is shown to be significantly extended beyond the PSF at a position angle of 80 degrees. This is the first time dust emission has been resolved around HD191089. Modelling indicates that the emission arises from a dust belt from 28-90 AU, inclined at 35 degrees from edge on with very little emission from the inner 28AU of the disc, indicating the presence of an inner cavity. The steep slope of the inner edge is more consistent with truncation by a planet than with ongoing stirring. A tentative brightness asymmetry F(W)/F(E)=0.80+/-0.12 (1.8 sigma) between the two sides of the disc could be evidence for perturbations from a massive body on an eccentric orbit in the system.
Asymmetric Heating of the HR 4796A Dust Ring Due to Pericenter Glow
Margaret Moerchen,Laura Churcher,Charles Telesco,Mark Wyatt,R. Scott Fisher,Christopher Packham
Physics , 2010, DOI: 10.1051/0004-6361/201014881
Abstract: We have obtained new resolved images of the well-studied HR 4796A dust ring at 18 and 25 microns with the 8-meter Gemini telescopes. These images confirm the previously observed spatial extent seen in mid-IR, near-IR, and optical images of the source. We detect brightness and temperature asymmetries such that dust on the NE side is both brighter and warmer than dust in the SW. We show that models of so-called pericenter glow account for these asymmetries, thus both confirming and extending our previous analyses. In this scenario, the center of the dust ring is offset from the star due to gravitational perturbations of a body with an eccentric orbit that has induced a forced eccentricity on the dust particle orbits. Models with 2-micron silicate dust particles and a forced eccentricity of 0.06 simultaneously fit the observations at both wavelengths. We also show that parameters used to characterize the thermal-emission properties of the disk can also account for the disk asymmetry observed in shorter-wavelength scattered-light images.
Amphioxus (Branchiostoma floridae) has orthologs of vertebrate odorant receptors
Allison M Churcher, John S Taylor
BMC Evolutionary Biology , 2009, DOI: 10.1186/1471-2148-9-242
Abstract: We have identified 50 full-length and 11 partial ORs in Branchiostoma floridae. No ORs were identified in Ciona intestinalis. Phylogenetic analysis places the B. floridae OR genes in a monophyletic clade with the vertebrate ORs. The majority of OR genes in amphioxus are intronless and many are also tandemly arrayed in the genome. By exposing conserved amino acid motifs and testing the ability of those motifs to discriminate between ORs and non-OR GPCRs, we identified three OR-specific amino acid motifs common in cephalochordate, fish and mammalian and ORs.Here, we show that amphioxus has orthologs of vertebrate ORs. This conclusion demonstrates that the receptors, and perhaps other components of vertebrate olfaction, evolved at least 550 million years ago. We have also identified highly conserved amino acid motifs that may be important for maintaining receptor conformation or regulating receptor activity. We anticipate that the identification of vertebrate OR orthologs in amphioxus will lead to an improved understanding of OR gene family evolution, OR gene function, and the mechanisms that control cell-specific expression, axonal guidance, signal transduction and signal integration.Genes encoding odorant receptors (ORs) were first identified by Linda Buck and Richard Axel in 1991 [1]. Prior to 1991, experiments from several other labs suggested that odorant receptors were seven transmembrane (TM) domain G protein-coupled receptors (GPCRs), so Buck and Axel used PCR with degenerate primers designed from available GPCR sequences to query cDNA isolated from rat olfactory epithelium tissue. The new genes they discovered were then used as probes to search rat cDNA and genomic DNA for additional paralogs [1]. This similarity-based approach, in which query sequences are used to identify orthologs and then paralogs, is a staple of both molecular and bioinformatics research. These and subsequent studies have now uncovered over a thousand rat and mouse odorant receptors [2-5]
Resolving debris discs in the far-infrared: early highlights from the DEBRIS survey
DEBRIS Collaboration,Brenda Matthews,Bruce Sibthorpe,Grant Kennedy,Neil Phillips,Laura Churcher,Gaspard Duchêne,Jane Greaves,Jean-Francois Lestrade,Amaya Moro-Martin,Mark Wyatt,Pierre Bastien,Andy Biggs,Jerome Bouvier,Harold Butner,Bill Dent,James Di Francesco,Jochen Eisl?ffel,James Graham,Paul Harvey,Peter Hauschildt,Wayne Holland,Jonti Horner,Eduardo Ibar,Rob Ivison,Doug Johnstone,Paul Kalas,JJ Kavelaars,David Rodriguez,Stephane Udry,Paul van der Werf,David Wilner,Ben Zuckerman
Physics , 2010,
Abstract: We present results from the earliest observations of DEBRIS, a Herschel Key Programme to conduct a volume- and flux-limited survey for debris discs in A-type through M-type stars. PACS images (from chop/nod or scan-mode observations) at 100 and 160 micron are presented toward two A-type stars and one F-type star: beta Leo, beta UMa and eta Corvi. All three stars are known disc hosts. Herschel spatially resolves the dust emission around all three stars (marginally, in the case of beta UMa), providing new information about discs as close as 11 pc with sizes comparable to that of the Solar System. We have combined these data with existing flux density measurements of the discs to refine the SEDs and derive estimates of the fractional luminosities, temperatures and radii of the discs.
Combining Public Key Encryption with Schnorr Digital Signature  [PDF]
Laura Savu
Journal of Software Engineering and Applications (JSEA) , 2012, DOI: 10.4236/jsea.2012.52016
Abstract: This article presents a new signcryption scheme which is based on the Schnorr digital signature algorithm. The new scheme represents my personal contribution to signcryption area. I have implemented the algorithm in a program and here are provided the steps of the algorithm, the results and some examples. The paper also contains the presentation of the original Signcryption scheme, based on ElGamal digital signature and discusses the practical applications of Signcryption in real life. The purpose of the study is to combine the public key encryption with Schnorr digital signature in order to obtain less computational and communicational costs. Signcryption primitive is a better approach then Encrypt-then-Sign or Sign-then-Encrypt methods regarding the costs. All these algorithms offer the possibility to transmit a message over an insecure channel providing both authenticity and confidentiality.
Practical Stabilization for Uncertain Pseudo-Linear and Pseudo-Quadratic MIMO Systems  [PDF]
Laura Celentano
International Journal of Modern Nonlinear Theory and Application (IJMNTA) , 2013, DOI: 10.4236/ijmnta.2013.21004
Abstract:

In this paper the problem of practical stabilization for a significant class of MIMO uncertain pseudo-linear and pseudo-quadratic systems, with additional bounded nonlinearities and/or bounded disturbances, is considered. By using the concept of majorant system, via Lyapunov approach, new fundamental theorems, from which derive explicit formulas to design state feedback control laws, with a possible imperfect compensation of nonlinearities and disturbances, are stated. These results guarantee a specified convergence velocity of the linearized system of the majorant system and a desired steady-state output for generic uncertainties and/or generic bounded nonlinearities and/or bounded disturbances.

Book Announcement of L. Celentano, Robust Tracking Controllers Design with Generic References for Continuous and Discrete Uncertain Linear SISO Systems, LAP LAMBERT Academic Publishing, 2012  [PDF]
Laura Celentano
International Journal of Modern Nonlinear Theory and Application (IJMNTA) , 2014,
Abstract:

In this book new results on controller design techniques for the tracking of generic reference inputs are presented. They allow the design of a controller for an uncertain process, either continuous or discrete-time, without zeros, and with measurable state. The controller guarantees that the control system is Type 1 and has the desired constant gain and poles or that the control system tracks, with a specified maximum error and with a specified maximum time constant, a generic reference with bounded derivative (variation in the discrete-time case), also in the presence of a generic disturbance with bounded derivative (variation). In addition, it is considered the case in which the reference is known a priori.

The utility and the efficiency of the proposed methods are illustrated with attractive and significant examples of motion control and temperature control.

This book is useful for the design of control systems, especially for manufacturing systems, that are versatile, fast, precise and robust.

Gender in the American Anthology Apparatus: A Linguistic Analysis  [PDF]
Laura Aull
Advances in Literary Study (ALS) , 2014, DOI: 10.4236/als.2014.21008
Abstract:

Most American anthology and canon revision has focused on author and text selections but little on the anthology editorial apparatus. The following study responds to this gap by analyzing gender representation across prefaces and overviews of the Norton and Heath American anthologies (1979-2010). Through a combined rhetorical and corpus linguistic analysis, the study reveals disparate gender representation in these materials: women are increasingly mentioned over time, but men continue to emerge as individuals of importance while women are discussed primarily as a group. This examination suggests that the revisionist, feminist scrutiny of Norton and Heath inventory has not been brought to bear on the anthologies’ apparatus—and that discursive patterns therein remain largely invisible despite that they contradict efforts to revise gender bias in anthologies. In so doing, the study offers an exploratory analysis of new methods (combined linguistic and rhetorical analysis) and new sites (apparatus texts) for examining gender in canonical and pedagogical materials.

Does the Month of Birth Influence the Timing of Life Course Decisions? Evidence from a Natural Experiment in Italy  [PDF]
Laura Cavalli
Open Journal of Social Sciences (JSS) , 2014, DOI: 10.4236/jss.2014.21011
Abstract: Social scientists have observed for a long time a negative relationship between the time spent on education and the timing of family formation. Using data from the I.D.E.A. survey (2003), a birth-month experiment on a sample of 3000 young Italian adults is employed in order to explore whether a different month of birth leads to regular differences in life course decisions of young Italians. The results suggest that the “social” age, as determined by the school cohort, rather than the biological age, is an important determinant of the timing of demographic events during the transition to adulthood.
An Analysis of Genetic Diversity and Inbreeding in Wuchereria bancrofti: Implications for the Spread and Detection of Drug Resistance
Thomas S. Churcher ,Anne E. Schwab,Roger K. Prichard,María-Gloria Basá?ez
PLOS Neglected Tropical Diseases , 2008, DOI: 10.1371/journal.pntd.0000211
Abstract: Estimates of genetic diversity in helminth infections of humans often have to rely on genotyping (immature) parasite transmission stages instead of adult worms. Here we analyse the results of one such study investigating a single polymorphic locus (a change at position 200 of the β-tubulin gene) in microfilariae of the lymphatic filarial parasite Wuchereria bancrofti. The presence of this genetic change has been implicated in benzimidazole resistance in parasitic nematodes of farmed ruminants. Microfilariae were obtained from patients of three West African villages, two of which were sampled prior to the introduction of mass drug administration. An individual-based stochastic model was developed showing that a wide range of allele frequencies in the adult worm populations could have generated the observed microfilarial genetic diversity. This suggests that appropriate theoretical null models are required in order to interpret studies that genotype transmission stages. Wright's hierarchical F-statistic was used to investigate the population structure in W. bancrofti microfilariae and showed significant deficiency of heterozygotes compared to the Hardy-Weinberg equilibrium; this may be partially caused by a high degree of parasite genetic differentiation between hosts. Studies seeking to quantify accurately the genetic diversity of helminth populations by analysing transmission stages should increase their sample size to account for the variability in allele frequency between different parasite life-stages. Helminth genetic differentiation between hosts and non-random mating will also increase the number of hosts (and the number of samples per host) that need to be genotyped, and could enhance the rate of spread of anthelmintic resistance.
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