Computerized Searches on Articles Reporting Reading Research: A Closer Look

This article, which draws on examples supplied by previous studies involving fifty articles in the psycholinguistic literature [ 4], [5], [6], explores how the choice of terminology used in database records and in searches may actually impede retrieval, and it suggests compensatory measures

Entire solutions of hydrodynamical equations with exponential dissipation

We consider a modification of the three-dimensional Navier--Stokes equations and other hydrodynamical evolution equations with space-periodic initial conditions in which the usual Laplacian of the dissipation operator is replaced by an operator whose Fourier symbol grows exponentially as \ue ^{|k|/\kd} at high wavenumbers $|k|$. Using estimates in suitable classes of analytic functions, we show that the solutions with initially finite energy become immediately entire in the space variables and that the Fourier coefficients decay faster than \ue ^{-C(k/\kd) \ln (|k|/\kd)} for any $C<1/(2\ln 2)$. The same result holds for the one-dimensional Burgers equation with exponential dissipation but can be improved: heuristic arguments and very precise simulations, analyzed by the method of asymptotic extrapolation of van der Hoeven, indicate that the leading-order asymptotics is precisely of the above form with $C= C_\star =1/\ln2$. The same behavior with a universal constant $C_\star$ is conjectured for the Navier--Stokes equations with exponential dissipation in any space dimension. This universality prevents the strong growth of intermittency in the far dissipation range which is obtained for ordinary Navier--Stokes turbulence. Possible applications to improved spectral simulations are briefly discussed.Comment: 29 pages, 3 figures, Comm. Math. Phys., in pres

Evaluation of beneficial and inhibitory effects of nitrate on nodulation and nitrogen fixation in common bean (Phaseolus vulgaris)

AbstractThe effects of applied nitrate on symbiotic nitrogen fixation in legumes are complex. Both inhibition and promotion of nodulation by nitrate have been observed in a dose‐dependent manner. The objectives of this study were to determine the effects of nitrate at different concentrations on root nodulation in different genotypes in common bean (Phaseolus vulgaris). Six genotypes were inoculated with the same rhizobial strain and grown hydroponically in growth pouches in a growth chamber and exposed to six nitrate concentrations, including 0, 2.5, 5, 10, 15, and 20 mM for 4 weeks. The tested genotypes included three recombinant inbred lines (RILs, 25, 46, and 70) that differed in their responses to nitrogen (based on observations of one field growing season), their parents (Mist and Sanilac—registered varieties), which are different in N‐fixing abilities, and one nonnodulating mutant (R99). Our results showed that small amounts of nitrate (2.5 and 5 mM) promoted nodule formation and increased nodule biomass, compared with plants in the 0 nitrate control treatment. In contrast, nitrate concentrations over 10 mM inhibited nodulation, resulting in reductions in nodule number and nodule biomass. Nodulation was completely inhibited by 15‐mM nitrate in all the genotypes. Regression analyses indicated that 5‐mM nitrate is the optimum concentration for promoting nodulation as measured by the total number of nodules formed, the number of effective nodules formed, and the nodule biomass formed. In contrast, nitrogen fixation was inhibited by all levels of nitrate. No genotypic differences were observed in nodulation among the three RILs and their parental cultivars, but all were significantly different than R99, a nonnodulating mutant

Image reconstruction in optical interferometry: Benchmarking the regularization

With the advent of infrared long-baseline interferometers with more than two telescopes, both the size and the completeness of interferometric data sets have significantly increased, allowing images based on models with no a priori assumptions to be reconstructed. Our main objective is to analyze the multiple parameters of the image reconstruction process with particular attention to the regularization term and the study of their behavior in different situations. The secondary goal is to derive practical rules for the users. Using the Multi-aperture image Reconstruction Algorithm (MiRA), we performed multiple systematic tests, analyzing 11 regularization terms commonly used. The tests are made on different astrophysical objects, different (u,v) plane coverages and several signal-to-noise ratios to determine the minimal configuration needed to reconstruct an image. We establish a methodology and we introduce the mean-square errors (MSE) to discuss the results. From the ~24000 simulations performed for the benchmarking of image reconstruction with MiRA, we are able to classify the different regularizations in the context of the observations. We find typical values of the regularization weight. A minimal (u,v) coverage is required to reconstruct an acceptable image, whereas no limits are found for the studied values of the signal-to-noise ratio. We also show that super-resolution can be achieved with increasing performance with the (u,v) coverage filling. Using image reconstruction with a sufficient (u,v) coverage is shown to be reliable. The choice of the main parameters of the reconstruction is tightly constrained. We recommend that efforts to develop interferometric infrastructures should first concentrate on the number of telescopes to combine, and secondly on improving the accuracy and sensitivity of the arrays.Comment: 15 pages, 16 figures; accepted in A&

A measure of centrality based on the spectrum of the Laplacian

We introduce a family of new centralities, the k-spectral centralities. k-Spectral centrality is a measurement of importance with respect to the deformation of the graph Laplacian associated with the graph. Due to this connection, k-spectral centralities have various interpretations in terms of spectrally determined information. We explore this centrality in the context of several examples. While for sparse unweighted networks 1-spectral centrality behaves similarly to other standard centralities, for dense weighted networks they show different properties. In summary, the k-spectral centralities provide a novel and useful measurement of relevance (for single network elements as well as whole subnetworks) distinct from other known measures.Comment: 12 pages, 6 figures, 2 table

Constraining Disk Parameters of Be Stars using Narrowband H-alpha Interferometry with the NPOI

Interferometric observations of two well-known Be stars, gamma Cas and phi Per, were collected and analyzed to determine the spatial characteristics of their circumstellar regions. The observations were obtained using the Navy Prototype Optical Interferometer equipped with custom-made narrowband filters. The filters isolate the H-alpha emission line from the nearby continuum radiation, which results in an increased contrast between the interferometric signature due to the H-alpha-emitting circumstellar region and the central star. Because the narrowband filters do not significantly attenuate the continuum radiation at wavelengths 50 nm or more away from the line, the interferometric signal in the H-alpha channel is calibrated with respect to the continuum channels. The observations used in this study represent the highest spatial resolution measurements of the H-alpha-emitting regions of Be stars obtained to date. These observations allow us to demonstrate for the first time that the intensity distribution in the circumstellar region of a Be star cannot be represented by uniform disk or ring-like structures, whereas a Gaussian intensity distribution appears to be fully consistent with our observations.Comment: 23 pages, 14 figures, accepted for publication in A

Nonattacking Queens in a Rectangular Strip

The function that counts the number of ways to place nonattacking identical chess or fairy chess pieces in a rectangular strip of fixed height and variable width, as a function of the width, is a piecewise polynomial which is eventually a polynomial and whose behavior can be described in some detail. We deduce this by converting the problem to one of counting lattice points outside an affinographic hyperplane arrangement, which Forge and Zaslavsky solved by means of weighted integral gain graphs. We extend their work by developing both generating functions and a detailed analysis of deletion and contraction for weighted integral gain graphs. For chess pieces we find the asymptotic probability that a random configuration is nonattacking, and we obtain exact counts of nonattacking configurations of small numbers of queens, bishops, knights, and nightriders.Comment: 21 pages, 3 figures, preprint of published version copyright Springer Basel AG 2011, Published online February 15, 2011, submitted March 15, 200

The Nature of the Molecular Environment within 5 pc of the Galactic Center

We present a detailed study of molecular gas in the central 10pc of the Galaxy through spectral line observations of four rotation inversion transitions of NH3 made with the VLA. Updated line widths and NH3(1,1) opacities are presented, and temperatures, column densities, and masses are derived. We examine the impact of Sgr A East on molecular material at the Galactic center and find that there is no evidence that the expansion of this shell has moved a significant amount of the 50 km/s GMC. The western streamer, however, shows strong indications that it is composed of material swept-up by the expansion of Sgr A East. Using the mass and kinematics of the western streamer, we calculate an energy of E=(2-9)x10^{51} ergs for the progenitor explosion and conclude that Sgr A East was most likely produced by a single supernova. The temperature structure of molecular gas in the central ~20pc is also analyzed in detail. We find that molecular gas has a ``two-temperature'' structure similar to that measured by Huttemeister et al. (2003a) on larger scales. The largest observed line ratios, however, cannot be understood in terms of a two-temperature model, and most likely result from absorption of NH3(3,3) emission by cool surface layers of clouds. By comparing the observed NH3 (6,6)-to-(3,3) line ratios, we disentangle three distinct molecular features within a projected distance of 2pc from Sgr A*. Gas associated with the highest line ratios shows kinematic signatures of both rotation and expansion. The southern streamer shows no significant velocity gradients and does not appear to be directly associated with either the circumnuclear disk or the nucleus. The paper concludes with a discussion of the line-of-sight arrangement of the main features in the central 10pc.Comment: 51 pages, 16 figures, accepted for publication in ApJ. Due to size limitations, some of the images have been cut from this version. A complete, color PS or PDF version can be downloaded from http://www.astro.columbia.edu/~herrnstein/NH3/paper