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Search Results: 1 - 10 of 459193 matches for " N-J. Nicholas "
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Ratios of Elastic Scattering of Pions from 3H and 3He
W. J. Briscoe,B. L. Berman,R. W. C. Carter,K. S. Dhuga,S. K. Matthews,N-J. Nicholas,S. J. Greene,B. M. K. Nefkens,J. W. Price,L. D. Isenhower,M. E. Sadler,I. Slaus,I. Supek
Physics , 2002, DOI: 10.1103/PhysRevC.66.054006
Abstract: We have measured the elastic-scattering ratios of normalized yields for charged pions from 3H and 3He in the backward hemisphere. At 180 MeV, we completed the angular distribution begun with our earlier measurements, adding six data points in the angular range of 119 deg to 169 deg in the pi-nucleus center of mass. We also measured an excitation function with data points at 142, 180, 220, and 256 MeV incident pion energy at the largest achievable angle for each energy between 160 deg and 170 deg in the pi-nucleus center of mass. This excitation function corresponds to the energies of our forward-hemisphere studies. The data, taken as a whole, show an apparent role reversal of the two charge-symmetric ratios r1 and r2 in the backward hemisphere. Also, for data > 100 deg we observe a strong dependence on the four-momentum transfer squared (-t) for all of the ratios regardless of pion energy or scattering angle, and we find that the superratio R data match very well with calculations based on the forward-hemisphere data that predicts the value of the difference between the even-nucleon radii of 3H and 3He. Comparisons are also made with recent calculations incorporating different wave functions and double scattering models.
Millán-J.,Carolina; Chacón,Patricia; Giraldo,Alan;
Boletín Científico. Centro de Museos. Museo de Historia Natural , 2009,
Abstract: two sampling activities (march 2007 and april 2008) were carried out in the municipal rural settlement of morales (caloto-cauca) in order to evaluate the day-butterfly diversity associated with four intervened biotopes: riparian forest, sugarcane plantations, coffee-plantain crop and natural fence. the 1594 individuals were collected using van someren-rydon traps, belonging to 90 species from six families; nymphalidae with 60 species from the subfamilies nymphalinae (14), charaxinae (6), morphinae (2), satyrinae (5), heliconiinae (8), ithomiinae (6), danainae (3), acraeinae (5), limenitidinae (2), biblidinae (5) and melitaeinae (4), pieridae (11) hesperiidae (6), papilionidae (7), lycaenidae (4) and riodinidae (2). additionally, 39% of the species were polyphagous and generalists, represented by the genera anartia (144 individuals), actinote (69), caligo (14), urbanus (72), anteos (44), phoebis (56) and eurema (223). all these have been recognized as genera associated to anthropogenic intervened areas. the presence of the satyrinae subfamily (108 individuals) and the morpho genus (9 individuals) in the study zone, suggest the presence of high quality forest relicts. the abundance of ithomiinae (199 individuals) in the shaded coffee-plantain crop indicates that this biotope offers a suitable habitat for this subfamily.
It's All in the Timing: Too Much E2F Is a Bad Thing
Brandon N. Nicolay,Nicholas J. Dyson
PLOS Genetics , 2012, DOI: 10.1371/journal.pgen.1002909
Magneto-photoluminescence of GaN/AlGaN quantum wells: valence band reordering and excitonic binding energies
P. A. Shields,R. J. Nicholas,N. Grandjean,J. Massies
Physics , 2001, DOI: 10.1103/PhysRevB.63.245319
Abstract: A re-ordered valence band in GaN/AlGaN quantum wells with respect to GaN epilayers has been found as a result of the observation of an enhanced g-factor in magneto-luminescence spectra in fields up to 55 T. This has been caused by a reversal of the states in the strained AlGaN barriers thus giving different barrier heights for the different quantum well hole states. From k.p calculations in the quasi-cubic approximation, a change in the valence-band ordering will account for the observed values for the g-factors. We have also observed the well-width dependence of the in-plane extent of the excitonic wavefunction from which we infer an increase in the exciton binding energy with the reduction of the well width in general agreement with theoretical calculations of Bigenwald et al (phys. stat. sol. (b) 216, 371 (1999)) that uses a variational approach in the envelope function formalism that includes the effect of the electric field in the wells.
Cellular Levels and Binding of c-di-GMP Control Subcellular Localization and Activity of the Vibrio cholerae Transcriptional Regulator VpsT
Nicholas J. Shikuma,Jiunn C. N. Fong,Fitnat H. Yildiz
PLOS Pathogens , 2012, DOI: 10.1371/journal.ppat.1002719
Abstract: The second messenger, cyclic diguanylate (c-di-GMP), regulates diverse cellular processes in bacteria. C-di-GMP is produced by diguanylate cyclases (DGCs), degraded by phosphodiesterases (PDEs), and receptors couple c-di-GMP production to cellular responses. In many bacteria, including Vibrio cholerae, multiple DGCs and PDEs contribute to c-di-GMP signaling, and it is currently unclear whether the compartmentalization of c-di-GMP signaling components is required to mediate c-di-GMP signal transduction. In this study we show that the transcriptional regulator, VpsT, requires c-di-GMP binding for subcellular localization and activity. Only the additive deletion of five DGCs markedly decreases the localization of VpsT, while single deletions of each DGC do not impact VpsT localization. Moreover, mutations in residues required for c-di-GMP binding, c-di-GMP-stabilized dimerization and DNA binding of VpsT abrogate wild type localization and activity. VpsT does not co-localize or interact with DGCs suggesting that c-di-GMP from these DGCs diffuses to VpsT, supporting a model in which c-di-GMP acts at a distance. Furthermore, VpsT localization in a heterologous host, Escherichia coli, requires a catalytically active DGC and is enhanced by the presence of VpsT-target sequences. Our data show that c-di-GMP signaling can be executed through an additive cellular c-di-GMP level from multiple DGCs affecting the localization and activity of a c-di-GMP receptor and furthers our understanding of the mechanisms of second messenger signaling.
Nonparametric Sparsification of Complex Multiscale Networks
Nicholas J. Foti,James M. Hughes,Daniel N. Rockmore
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0016431
Abstract: Many real-world networks tend to be very dense. Particular examples of interest arise in the construction of networks that represent pairwise similarities between objects. In these cases, the networks under consideration are weighted, generally with positive weights between any two nodes. Visualization and analysis of such networks, especially when the number of nodes is large, can pose significant challenges which are often met by reducing the edge set. Any effective “sparsification” must retain and reflect the important structure in the network. A common method is to simply apply a hard threshold, keeping only those edges whose weight exceeds some predetermined value. A more principled approach is to extract the multiscale “backbone” of a network by retaining statistically significant edges through hypothesis testing on a specific null model, or by appropriately transforming the original weight matrix before applying some sort of threshold. Unfortunately, approaches such as these can fail to capture multiscale structure in which there can be small but locally statistically significant similarity between nodes. In this paper, we introduce a new method for backbone extraction that does not rely on any particular null model, but instead uses the empirical distribution of similarity weight to determine and then retain statistically significant edges. We show that our method adapts to the heterogeneity of local edge weight distributions in several paradigmatic real world networks, and in doing so retains their multiscale structure with relatively insignificant additional computational costs. We anticipate that this simple approach will be of great use in the analysis of massive, highly connected weighted networks.
Preparation of many-body states for quantum simulation
Nicholas J. Ward,Ivan Kassal,Alán Aspuru-Guzik
Physics , 2008, DOI: 10.1063/1.3115177
Abstract: While quantum computers are capable of simulating many quantum systems efficiently, the simulation algorithms must begin with the preparation of an appropriate initial state. We present a method for generating physically relevant quantum states on a lattice in real space. In particular, the present algorithm is able to prepare general pure and mixed many-particle states of any number of particles. It relies on a procedure for converting from a second-quantized state to its first-quantized counterpart. The algorithm is efficient in that it operates in time that is polynomial in all the essential descriptors of the system, such the number of particles, the resolution of the lattice, and the inverse of the maximum final error. This scaling holds under the assumption that the wavefunction to be prepared is bounded or its indefinite integral known and that the Fock operator of the system is efficiently simulatable.
The Re-Emergence of Critical Pedagogy: A Three-Dimensional Framework for Teacher Education in the Age of Teacher Effectiveness  [PDF]
Nicholas J. Shudak
Creative Education (CE) , 2014, DOI: 10.4236/ce.2014.511113
Abstract: In light of the extensive treatment given over its thirty year existence, this article develops a framework for helping teachers understand the applicability and relevance of critical pedagogy in the classroom during this age of effectiveness and standardization. To do this, critical pedagogy is theoretically framed three-dimensionally. The purpose is to help teachers think through critical pedagogy in a way that might encourage them to analyze their own practices and thus create and enact critical pedagogies that are uniquely their own. The first dimension pertains to its contested terrain. An understanding of critical pedagogy must begin with a disclaimer. This disclaimer suggests that though there are common objectives, there are key points of contestation. The second dimension, then, seeks to find the common ground. This dimension focuses on the commitments of critical pedagogy, and thus, the commitments of those who might try. Lastly, critical pedagogy impels teachers to use their classrooms to make life more humane. To aid in this task, teachers engaging in critical pedagogics take certainphilosophical positions, the third dimension of critical pedagogy.
The anaemia of Plasmodium vivax malaria
Nicholas M Douglas, Nicholas M Anstey, Pierre A Buffet, Jeanne R Poespoprodjo, Tsin W Yeo, Nicholas J White, Ric N Price
Malaria Journal , 2012, DOI: 10.1186/1475-2875-11-135
Analysis of Nitrate Concentrations Using Nonlinear Time Series Models
Peter Valent, Nicholas J. K. Howden, Ján Szolgay, Magda Komorníková
Journal of Hydrology and Hydromechanics , 2011, DOI: 10.2478/v10098-011-0013-9
Abstract: This study examines two long-term time series of nitrate-nitrogen concentrations from the River Ouse and Stour situated in the Eastern England. The time series of monthly averages were decomposed into trend, seasonal and cyclical components and residuals to create a simple additive model. Residuals were then modelled by linear time series models represented by models of the ARMA (autoregressive moving average) class and nonlinear time series models with multiple regimes represented by SETAR (self-exciting threshold autoregressive) and MSW (Markov switching) models. The analysis showed that, based on the minimal value of residual sum of squares (RSS) of one-step ahead forecast in both datasets, SETAR and MSW models described the time series better than models ARMA. However, the relative improvement of SETAR models against ARMA models was low ranging between 1% and 4% with the exception of the three-regime model for the River Stour where the improvement was 48.9%. In comparison, the relative improvement of MSW models was between 44.6% and 52.5 for two-regime and from 60.4% to 75% for three-regime models. However, the visual assessment of models plotted against original datasets showed that despite a high value of RSS, some ARMA models could describe the analyzed time series better than AR (autoregressive), MA (moving average) and SETAR models with lower values of RSS. In both datasets MSW models provided a very good visual fit describing most of the extreme values. The results of this work could be used as a base for construction of other time series models used to describe or predict nitrate-nitrogen concentrations.
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