Association of Escherichia coli O157:H7 with preharvest leaf lettuce upon exposure to contaminated irrigation water.

Recent foodborne outbreaks have linked infection by enterohemorrhagic Escherichia coli (EHEC) serotype O157:H7 to the consumption of contaminated lettuce. Contamination via food handler error and on-the-farm contamination are thought to be responsible for several outbreaks. Though recent studies have examined the application of EHEC to store-bought lettuce, little is known about the attachment of EHEC to growing plants. We investigated the association of lettuce seedlings with EHEC O157:H7 strains implicated in lettuce or fruit outbreaks using hydroponic and soil model systems. EHEC strains that express the green fluorescent protein were observed by stereomicroscopy and confocal laser scanning microscopy to determine adherence patterns on growing lettuce seedlings. Bacteria adhered preferentially to plant roots in both model systems and to seed coats in the hydroponic system. Two of five nonpathogenic E. coli strains showed decreased adherence to seedling roots in the hydroponic system. EHEC was associated with plants in as few as 3 days in soil, and contamination levels were dose-dependent. EHEC levels associated with young plants inoculated with a low dose suggested that the bacteria had multiplied. These data suggest that preharvest crop contamination via contaminated irrigation water can occur through plant roots.     

Laser‐Induced Direct Lithography for Patterning of Carbon with sp3 and sp2 Hybridization

A new method of laser‐induced lithography for direct writing of carbon on a glass surface is described, in which deposition occurs from a transparent precursor solution. At the glass–solution interface where the laser spot is focused, a micro‐explosion process takes place, leading to the deposition of pure carbon on the glass surface. Transmission electron microscopy (TEM) analysis shows two distinct co‐existing phases. The dominant one shows a mottled morphology with diffraction typical of cubic (sp³) diamond. The other region shows an ordered array of graphene sheets with diffraction pattern typical of sp²‐bonded carbon. The sp³ crystallites range in size from 9 to 30 Å and are scattered randomly throughout the sample. A UV Raman spectrum shows a broad band at the location of the expected diamond peak, together with a peak corresponding to the graphite region. We conclude that the patterned carbon is composed of a mixture of nanocrystalline sp³ and sp² carbon forms.     

Structural Determinants of the Sign of the Pyroelectric Effect in Quasi‐Amorphous SrTiO3 Films

The magnitude and direction of the permanent electric polarization in the non‐crystalline, polar phase (termed quasi‐amorphous) of SrTiO₃ in SiSiO₂MeSrTiO₃Me, (Me = Cr or W), SiSrRuO₃SrTiO₃, and SiSrTiO₃ layered structures were investigated. Three potential sources of the polarization which appears after the material is pulled through a temperature gradient were considered: a) contact potential difference; b) a flexoelectric effect due to a strain gradient caused by substrate curvature; and c) a flexoelectric effect due to the thermally induced strain gradient that develops while pulling through the steep temperature gradient. Measurements show that options a) and b) can be eliminated from consideration. In most cases studied in this (SiSrTiO₃, SiSiO₂MeSrTiO₃Me, M = Cr or W) and previous works (SiBaTiO₃, SiBaZrO₃), the top surface of the quasi‐amorphous phase acquires a negative charge upon heating. However, in SiSrRuO₃SrTiO₃ structures the top surface acquires a positive charge upon heating. On the basis of the difference in the measured expansion of the upper and lower surfaces of the SrTiO₃ layer in the presence and absence of SrRuO₃, we contend that the magnitude and direction of the pyroelectric effect are determined by the out‐of‐plane gradient of the in‐plane strain in the SrTiO₃ layer while pulling through the temperature gradient.     

Large Nonclassical Electrostriction in (Y,Nb)‐Stabilized δ‐Bi2O3

Classical electrostriction, describing a second‐order electromechanical response of insulating solids, scales with elastic compliance, S, and inversely with dielectric susceptibility, ε. This behavior, first noted 20 years ago by Robert Newnham, is shown to apply to a wide range of electrostrictors including polymers, glasses, crystalline linear dielectrics, and relaxor ferroelectrics. Electrostriction in fluorite ceramics of (Y, Nb)‐stabilized δ‐Bi₂O₃ is examined with 16%–23% vacant oxygen sites. Given the values of compliance and dielectric susceptibility, the electrostriction coefficients are orders of magnitude larger than those expected from Newnham's scaling law. In ambient temperature nanoindentation measurements, (Y, Nb)‐stabilized δ‐Bi₂O₃ displays primary creep. These findings, which are strikingly similar to those reported for Gd‐doped ceria, support the suggestion that ion conducting ceramics with the fluorite structure, a large concentration of anion vacancies and anelastic behavior, may constitute a previously unknown class of electrostrictors.     

Prevalence of Escherichia coli associated with a cabbage crop inadvertently irrigated with partially treated sewage wastewater

Preharvest contamination of field crops may have many sources, including feces, soil, and irrigation water. In March 2000, a sewage spill released unchlorinated tertiary-treated effluent into a creek used to irrigate commercial produce. A field of young cabbage transplants was irrigated with creek water as the contaminated water flowed past this land. Cabbage samples were taken from plots within this field, and Escherichia coli was isolated from the roots of these plants but not from the edible portion of the cabbage. No E. coli was isolated from water samples or from control samples taken from a nearby cabbage field watered with chlorinated municipal water. The cabbage field under study had not been fertilized with manure for at least 2 years prior to the contamination incident. Six different E. coli serotypes were identified, although none of them proved to be pathogenic. These serotypes were separated into five groups by a RiboPrinter; the resulting groups correlated well with the serotypes and the locations in the field from which these strains were isolated. We previously found that certain nonpathogenic E. coli strains displayed lower levels of adherence to lettuce seedling roots in a hydroponic adherence assay. The E. coli field strains displayed variable patterns of adherence to lettuce seedlings: strain MW421 showed significantly lower root and shoot adherence levels than did the other field strains, while strains MW423 and MW425 showed significantly higher root and shoot adherence levels. These data suggest that water quality is of paramount importance for the food safety of growing crops.     

Interaction of Carbohydrates with Phosphatidylcholine Inverse Micelles

Small angle X-ray scattering experiments indicate that egg phosphatidylcholine dissolved in benzene at a concentration of 12–50 mM organizes into approximately isometric inverse micelles with a size that depends upon the amount of water present. These inverse micelles can serve as self-assembled hosts for monosaccharide derivatives. For a given amount of water, addition of carbohydrates causes an increase in the micelle size. In contrast, cyclohexane solutions of egg phosphatidylcholine contain highly anisotropic structures, possibly elongated rods. Monosaccharide derivatives can be extracted into these structures and are bound, at low water content, to the polar head groups. Upon addition of water the sugar is probably displaced from the polar head groups and gains some motional freedom in the water pool which is formed. This fact indicates that the polar head group of phosphatidylcholine interacts, probably by means of hydrogen bond formation, with monosaccharides and brings about their solubilization in nonpolar solvents.     

How do we know psychology's limits?

Discusses T. R. Barnes's (1981) elaboration of P. L. Wachtel's (see record 1980-10864-001) discussion of why psychology is both a particularly easy and difficult field in which to conduct research. (2 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Psychodynamics, behavior therapy, and the implacable experimenter: An inquiry into the consistency of personality.

Considers that possible integrations of dynamic and behavioral approaches to theory and therapy have been obscured by polemics. One area of confusion concerns the degree of generality or specificity in personality. Variability in behavior from situation to situation has been misleadingly construed by some behavioral critics as casting doubt upon psychodynamic theories. This view is refuted, and a number of factors that account for the differing viewpoints of psychodynamic and behaviorally oriented approaches are considered. Among these are differences in Ss from which original ideas were generated, differences in phenomena of central interest (with special focus on the implications of psychodynamic concern with ambiguous affective phenomena), and the consequences of an experimental strategy (the "implacable experimenter") which limits the ways in which S may structure the environment in which he behaves. (58 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A new undergraduate computer arithmetic software laboratory

An undergraduate computer engineering laboratory that supports a one-quarter computer arithmetic course is described. This course is required for the computer engineering degree and is taken as a technical option by many students in electrical engineering and computer science. The features of this state-of-the-art laboratory include a local area network of computers, remote access via the campus network, electronic mail, online documentation, and automatic program submittal, grading, and plagiarism detection     

Stabilised finite element methods for a bending moment formulation of the Reissner-Mindlin plate model

This work presents new stabilised finite element methods for a bending moments formulation of the Reissner-Mindlin plate model. The introduction of the bending moment as an extra unknown leads to a new weak formulation, where the symmetry of this variable is imposed strongly in the space. This weak problem is proved to be well-posed, and stabilised Galerkin schemes for its discretisation are presented and analysed. The finite element methods are such that the bending moment tensor is sought in a finite element space constituted of piecewise linear continuos and symmetric tensors. Optimal error estimates are proved, and these findings are illustrated by representative numerical experiments.