The application of scalable distributed memory computers to the finite element modeling of electromagnetic scattering

Large-scale parallel computation can be an enabling resource in many areas of engineering and science if the parallel simulation algorithm attains an appreciable fraction of the machine peak performance, and if undue cost in porting the code or in developing the code for the parallel machine is not incurred. The issue of code parallelization is especially significant when considering unstructured mesh simulations. The unstructured mesh models considered in this paper result from a finite element simulation of electromagnetic fields scattered from geometrically complex objects (either penetrable or impenetrable.) The unstructured mesh must be distributed among the processors, as must the resultant sparse system of linear equations. Since a distributed memory architecture does not allow direct access to the irregularly distributed unstructured mesh and sparse matrix data, partitioning algorithms not needed in the sequential software have traditionally been used to efficiently spread the data among the processors. This paper presents a new method for simulating electromagnetic fields scattered from complex objects; namely, an unstructured finite element code that does not use traditional mesh partitioning algorithms. © 1998 This paper was produced under the auspices of the U.S. Government and it is therfore not subject to copyright in the U.S.     

Cr (VI) adsorption from aqueous solutions on grafted chitosan

Chitosan was grafted on the surface of a cotton gauze (20, 50, and 100 mg chitosan g⁻¹ cotton) to improve its stability in aqueous solutions. The adsorption of hexavalent chromium ions from water on the grafted chitosan was evaluated to determine, by means of linear and nonlinear models, the kinetic and isotherm adsorption of the process. The kinetics of pseudo second-order, pseudo first-order, and adsorption isotherms type II were obtained, that is, a monolayer adsorption on nonporous adsorbents with physical adsorption was present. The most probable energy of adsorption corresponded to a physisorption with hydrogen bond interactions between chromium ions and ammonium groups. Moreover, three different cross-sectional areas of hexavalent chromium ions were calculated and used to estimate the specific surface area employed by active sites to adsorb metal ions in terms of chitosan or cotton mass. Finally, the percentage of the area occupied by chromium ions on the surface was estimated by dividing the resulting specific surface area in terms of cotton mass by the specific surface area of cotton reported in literature. As a result, it was determined that the occupied area is between 6% (for 20 mg chitosan g⁻¹ cotton)-24% (for 100 mg chitosan g⁻¹ cotton) from the total area of cotton.     

Controlled synthesis of carbon nanostructures using aligned ZnO nanorods as templates

By combining in situ X-ray photoemission spectroscopy, ex situ high resolution transmission electron microscopy, scanning electron microscopy, and Raman spectroscopy, we show that chemical vapor deposition (CVD) on vertically aligned ZnO nanorods can synthesize different carbon nanostructures (CNs), whose morphology is driven by the ZnO nanorods and whose dimensions and structures change as a function of the process temperature. The CNs range from amorphous carbon cups, completely covering the nanorods, to high density one-dimensional carbon nano-dendrites (CNDs), which start to appear like short hairs on the ZnO nanorods. The nanorods are partially etched when the process is done at 630–800 °C, while they are completely etched at temperatures higher than 800 °C. In the latter case, CNDs emerge from a porous carbon sponge formed at the substrate interface but they are preferentially aligned along the location of the pristine ZnO nanorods. When used as a chemiresisitor the CND–ZnO structures have a higher sensitivity to ammonia compared to chemiresistors made by bare ZnO nanorods, to other one-dimensional CNs, like carbon nanotubes or other metal/metal-oxides hybrid CNs.     

LC/ESI–MS/MS method for the identification and quantification of spinosad residues in olive oils

This paper reports the use of liquid chromatography/electrospray ionisation tandem mass spectrometry (LC/ESI-MS/MS) method for the identification and quantification of residues of the natural insect control agent Spinosad in olive oils. The method determines the active ingredients Spinosyns A and D and two minor metabolites Spinosyns B and K without laborious sample treatment. All four analytes are determined simultaneously in a single injection using positive electrospray ionisation LC–MS with multiple reaction monitoring (MRM). For the quantitative analysis of samples an external calibration curve was built. The calibration curves for each analyte were linear in the concentration range 20–500 ng/mL with a correlation coefficient ranging between 0.995 and 0.999. Results from spike and recovery experiments at levels of 100 and 200 ng/mL gave mean recoveries ranging from 87–116% with satisfactory precision (relative standard deviation (RSD) from 1–8%). The excellent selectivity and sensitivity allows quantification and identification of low levels of Spinosad in olive oils (limits of quantification (LOQs) 0.004–0.073).     

Resonant mechanisms for negative ionization of secondary emitted atoms from sputtered metals

A model is presented to describe negative ionization of low energy, secondary atomic particles ejected from sputtered metal surfaces. Focus is made on the diatomic systems formed, in the collision cascade generated by the primary ion beam, between secondary emitted atoms and their nearest-neighbor substrate atoms that provide the initial impulse for ejection. Two different resonant ionization mechanisms are investigated such that a conduction electron may tunnel into the affinity orbital of the ejected atom either by direct hopping or after an intermediate transition via the affinity orbital of the substrate atom. A numerical method is outlined to calculate the negative ionization probability of secondary emitted atoms. A good agreement is found with van Der Heide’s measurements of the Cu⁻ population sputtered from a clean Cu-surface, at emission energies below 100 eV.     

Broadening effects in Auger neutralization of 130–430 eV Ar ions at Al surfaces

We present a model for electron emission from Al surfaces by Auger neutralization of 130–430 eV Ar⁺ ions, that includes the singular response of the metal conduction band to the abrupt change of the surface potential caused by electron capture by the incident ion. This effect, previously identified in X-ray studies, produces a broadening that plays a significant role in reproducing the higher energy part of the experimental electron kinetic energy distributions.     

Penalized factor mixture analysis for variable selection in clustered data

A model-based clustering approach which contextually performs dimension reduction and variable selection is presented. Dimension reduction is achieved by assuming that the data have been generated by a linear factor model with latent variables modeled as Gaussian mixtures. Variable selection is performed by shrinking the factor loadings though a penalized likelihood method with an L1 penalty. A maximum likelihood estimation procedure via the EM algorithm is developed and a modified BIC criterion to select the penalization parameter is illustrated. The effectiveness of the proposed model is explored in a Monte Carlo simulation study and in a real example.     

Absolute method for the assay of oleuropein in olive oils by atmospheric pressure chemical ionization tandem mass spectrometry

Oleuropein (OLP, 1), the active ingredient present (i) in food integrators extracted from olive leaves, (ii) in table olives, and (iii) in extra virgin olive oils is a nutraceutical whose health benefits have been widely documented. A new analytical method for its assay, which is based on the utilization of atmospheric pressure chemical ionization tandem mass spectrometry and on the use of a synthetic labeled analogue, the 4-trideuteriocarboxyoleuropein (2), as an internal standard, is presented. The results obtained with extra virgin olive oils from different cultivars and different Italian regions are discussed.     

LaCoO3 nanosystems by a hybrid CVD/sol-gel approach

LaCoO3 nanosystems are receiving increasing attention for the development of innovative fuel cells and heterogeneous catalysts. In this report, we describe the synthesis of nanophasic LaCoO3 thin films by a hybrid chemical vapor deposition (CVD)/sol-gel (SG) approach. The adopted strategy consists in the CVD of La-O-based systems on SG cobalt oxide xerogels CoOx(OH)y at temperatures as low as 200 degrees C and in the subsequent thermal treatment in air (400-800 degrees C, 2-8 h). In this context, particular attention is devoted to achieving an intimate La/Co intermixing already in the as-prepared systems, in order to favor reactions yielding a single La-Co-O phase with uniform composition. The obtained results point out to the formation of pure and structurally homogeneous LaCoO3 nanosystems after annealing at 700 degrees C, 2 h, with a typical grain-like morphology. More severe thermal treatment resulted in the thermal decomposition of LaCoO3 nanocrystallites.     

Pseudoneglect and embryonic light stimulation in the avian brain.

A bias to allocate attention to the left hemispace, similar to the well-known pseudoneglect phenomenon shown by humans, has been recently reported in domestic chicks and other species of birds. Asymmetrical light exposure of the embryo of the domestic chick in a critical period before hatching is known to be responsible for a structural asymmetry in the visual ascending projections of the thalamofugal pathway and for lateralization of some visual behaviors. Thus the animal model provided by the chick makes possible investigation of the prenatal factors that may influence asymmetry in spatial attention. Here chicks coming from eggs exposed to light (light incubated, Li-chicks) and chicks incubated in darkness (dark incubated, Di-chicks) were tested in a task in which they were required to explore an area in front of them and to sample grains of food. The results showed that Li-chicks attended more to target stimuli located in the left hemispace, whereas no asymmetry was shown by Di-chicks. When grains of food were presented with small novel pebbles as distractors, both Li- and Di-chicks tended to allocate attention toward the left hemispace. When, however, chicks were tested after familiarization with pebbles, no bias was shown by either Li- and Di-chicks. Hence it seems that cerebral lateralization associated with right hemispheric involvement in response to novelty, interacts with the modulatory effect of asymmetric embryonic light stimulation on preferential allocation of spatial attention in the left hemispace (right hemisphere) and right eye (left hemisphere) control of visual discrimination during feeding. (PsycINFO Database Record (c) 2011 APA, all rights reserved)