The Role of Pectobacterium atrosepticum Exopolysaccharides in Plant–Pathogen Interactions

The phytopathogenic bacterium Pectobacterium atrosepticum (Pba), one of the members of the soft rot Pectobacteriaceae, forms biofilm-like structures known as bacterial emboli when colonizing the primary xylem vessels of the host plants. The initial extracellular matrix of the bacterial emboli is composed of the host plant’s pectic polysaccharides, which are gradually substituted by the Pba-produced exopolysaccharides (Pba EPS) as the bacterial emboli “mature”. No information about the properties of Pba EPS and their possible roles in Pba-plant interactions has so far been obtained. We have shown that Pba EPS possess physical properties that can promote the maintenance of the structural integrity of bacterial emboli. These polymers increase the viscosity of liquids and form large supramolecular aggregates. The formation of Pba EPS aggregates is provided (at least partly) by the acetyl groups of the Pba EPS molecules. Besides, Pba EPS scavenge reactive oxygen species (ROS), the accumulation of which is known to be associated with the formation of bacterial emboli. In addition, Pba EPS act as suppressors of the quantitative immunity of plants, repressing PAMP-induced reactions; this property is partly lost in the deacetylated form of Pba EPS. Overall, our study shows that Pba EPS play structural, protective, and immunosuppressive roles during Pba–plant interactions and thus should be considered as virulence factors of these bacteria.     

Polarization and phase of light transmitted through polymer‐dispersed liquid‐crystal film

Abstract— A method for calculating the transmission coefficient, phase shift, and characteristics of the polarization state of light, transmitted through a PDLC film with nanosized nematic droplets, is considered. Functional dependences of these values on the morphological characteristics of a film are obtained and graphically illustrated. Good agreement between the theoretical and available experimental data is established.     

Visualization techniques for modelling carbon allotropes

Carbon takes many different forms, each with its own electronic structure and has a fantastic range of properties. As well as graphite/diamond, a hexagonal diamond called londsdaleite, and amorphous carbons of sp², sp³ and mixed natures there are all the fullerenes, graphene, nanotubes, etc. Fortunately, their different electronic structures take distinct geometrical forms, so that deducing the geometry of a sample that has been simulated is a crucial step towards understanding its properties. Visualization is essential for understanding sample geometries. AViz [J. Adler, Computers in Science and Engineering 5 (2003) 61] is an Atomistic Visualization package developed at the Technion that can be freely downloaded and installed. Both still and animated AViz implementations for viewing data from our atomistic simulations of carbon allotropes enable understanding of the simulation results and when compared with laboratory experiments and theoretical models provide insight into nanodiamond growth, gas flow in nanotubes, nanotube vibrations and other topics of current research interest.     

Editorial: Neural-Fuzzy Applications in Computer Vision

Editorial Introduction

Editorial: Neural-Fuzzy Applications in Computer Vision     

System for Precise Control of Volumetric Flow Rate during Sampling with a Cascade Impactor

Calculations were made with efficiency curves developed for the micro-orifice impactor (MOI) to estimate errors in mass collected on individual stages due to fluctuations in the flow rate during sampling of submicrometer particles. The sizes of these errors depend on the size distribution of the sampled aerosol and the level of flow rate fluctuation. For a log-normally distributed particle population, mass errors due to flow rate fluctuations were bimodally distributed about stages with cutpoints near the aerosol Mass Median Aerodynamic Diameter (MMAD). The largest errors occurred uniformly on the stage with the smallest cutpoint (here, 0.059 w m). These errors were asymmetric with respect to sign, which leads to a net error for a randomly fluctuating flow rate. In general, mass errors increased with decreasing geometric standard deviation ( σ g ) and were substantially greater for populations with 0.5 w m MMADs than for those with 0.2 w m MMADs. The largest net errors for the former were 4, 110, and 560% for σ g of 1.2 and flow rate fluctuations of - 1, - 5, and - 10%, respectively, but decreased to 0.03, 0.9, and 4%, respectively, for a σ g of 1.9. Flow rate fluctuations, therefore, lead to a positive bias in the geometric standard deviation inferred from the measured masses and reduce the user's ability to interpret differences in size distributions. To minimize these effects, we developed and tested a system for controlling the volumetric sampling rate through a MOI at 30 LPM with a precision of 0.06% (600 ms averaging; 0.67% for 5 ms averaging), a level of precision that allows for accurate relative calibration between flow systems and for which errors from flow rate fluctuations are reduced to <1%, even for a very narrow aerosol ( σ g 1.2). Mass errors for an uncontrolled field test were as large as -60%, but these were reduced to <0.22% in a comparable controlled field test. In two replicate tests of the system, agreements between stage masses collected on MOI stage 7 ( D 50 = 0.173 w m) of two simultaneously operated flow-controlled impactors sampling 0.2 w m diameter monodisperse test particles were 0.997 and 0.996, although differences as large as 4% were observed for some stages. The system is suitable for use with standard "Federal Reference Method" samplers.     

Cortical surface shape analysis based on spherical wavelets

In vivo quantification of neuroanatomical shape variations is possible due to recent advances in medical imaging and has proven useful in the study of neuropathology and neurodevelopment. In this paper, we apply a spherical wavelet transformation to extract shape features of cortical surfaces reconstructed from magnetic resonance images (MRIs) of a set of subjects. The spherical wavelet transformation can characterize the underlying functions in a local fashion in both space and frequency, in contrast to spherical harmonics that have a global basis set. We perform principal component analysis (PCA) on these wavelet shape features to study patterns of shape variation within normal population from coarse to fine resolution. In addition, we study the development of cortical folding in newborns using the Gompertz model in the wavelet domain, which allows us to characterize the order of development of large-scale and finer folding patterns independently. Given a limited amount of training data, we use a regularization framework to estimate the parameters of the Gompertz model to improve the prediction performance on new data. We develop an efficient method to estimate this regularized Gompertz model based on the Broyden-Fletcher-Goldfarb-Shannon (BFGS) approximation. Promising results are presented using both PCA and the folding development model in the wavelet domain. The cortical folding development model provides quantitative anatomic information regarding macroscopic cortical folding development and may be of potential use as a biomarker for early diagnosis of neurologic deficits in newborns.     

Electroluminescence from a mixed red-green-blue colloidal quantum dot monolayer

We demonstrate light emitting devices (LEDs) with a broad spectral emission generated by electroluminescence from a mixed-monolayer of red, green, and blue emitting colloidal quantum dots (QDs) in a hybrid organic/inorganic structure. The colloidal QDs are reproducibly synthesized and yield high luminescence efficiency materials suitable for LED applications. Independent processing of the organic charge transport layers and the QD luminescent layer allows for precise tuning of the emission spectrum without changing the device structure, simply by changing the ratio of different color QDs in the active layer. Spectral tuning is demonstrated through fabrication of white QD-LEDs that exhibit external quantum efficiencies of 0.36% (Commission Internationale de l'Eclairage) coordinates of (0.35, 0.41) at video brightness, and color rendering index of 86 as compared to a 5500 K blackbody reference.     

The adaptive character of the attentional system: Statistical sensitivity in a target localization task.

A localization task required participants to indicate which of 4 locations contained a briefly displayed target. Most displays also contained a distractor that was not equally probable in these locations, affecting performance dramatically. Responses were faster when a display had no distractor and almost as fast when the distractor was in its frequent location. Conversely, responses were slower when targets appeared in frequent-distractor locations, even though targets were equally likely in each location. Negative-priming effects were reliably smaller when targets followed distractors in the frequent-distractor location compared to the rare-distractor location, challenging the episodic-retrieval account. Experiment 2 added a 5th location that rarely displayed distractors and never targets, yet responses slowed most when distractors appeared there. The results confirmed that the attentional system is sensitive to first- and higher-order statistical patterns and can make short- and long-term adjustments in preferences based on prior history of inspecting unsuccessful locations. (PsycINFO Database Record (c) 2010 APA, all rights reserved)