Influence of punctures, cuts, and surface morphologies of golden delicious apples on penetration and growth of Escherichia coli O157:H7

The ability of Escherichia coli O157:H7 to penetrate and grow within punctures, fresh-cut surfaces, and calyces of Golden Delicious apples was investigated. A three-strain cocktail of E. coli O157:H7 resistant to ampicillin was used to inoculate fresh and 48-h-old punctures, fresh-cut surfaces, and open or closed calyces. A concentric cutting procedure was used to evaluate depth of penetration within punctures and prevent cross contamination during sampling. Within 2 h, E. coli O157:H7 penetrated vertically through the fresh punctures and 3.4 mm within the underlying parenchyma. After 48 h, E. coli O157: H7 cells penetrated up to 5.5 mm within the punctures and >2.6 mm horizontally away from fresh punctures. However, 48-h-old punctures did not permit penetration beyond their boundaries. Fresh-cut surfaces permitted up to 2.8 mm penetration after 24 h. Onset of growth of E. coli O157:H7 occurred 4 to 8 h postinoculation on fresh punctures and fresh-cut surfaces with populations increasing by 3 logs after 48 h. E. coli O157:H7 penetrated within calyces regardless of the extent of opening or method of inoculation. However, E. coli O157:H7 was never recovered from the inner core of apples. Computed tomography scan imaging revealed that closed calyces effectively prevented penetration of sodium iodide solutions within the calyx cavity. Lack of solution penetration may explain why sanitizing treatments are ineffective in inactivating microbial cells within the calyx. Understanding the role of morphological differences in permitting or restricting bacterial penetration may lead to development of more effective strategies to enhance the safety of fresh horticultural products.     

Rapid biological synthesis of silver nanoparticles using Kalopanax pictus plant extract and their antimicrobial activity

Silver nanoparticles (AgNPs) have promising potential in biomedicine, energy science, optics, and health care applications. We synthesized AgNPs using plant, Kalopanax pictus leaf extract. UV-visible spectrophotometric study showed the characteristic peak for AgNPs at wavelength 430 nm. The optical density at 430 nm increased after addition of plant leaf extract, indicating increase in formation of nanoparticles. Comparative time course analyses for AgNP synthesis carried out at different reaction temperatures (20, 60, and 90 °C) revealed higher reaction rate for K. pictus than Magnolia kobus plant leaf extract, which showed highest AgNP synthesis rate in the previous report. Electron microscopy analyses confirmed the presence of well dispersed AgNPs, predominantly with spherical shapes. In transmission electron microscopy, the particle size decreased with increase in temperature. Electron dispersive X-ray spectroscopy analyses indicated that Ag content increased with increase in reaction temperature. Fourier transform-infrared spectroscopy studies revealed capping of bioorganics from plant to the synthesized AgNPs. The antimicrobial activity of the synthesized AgNPs against Escherichia coli increased with increase in reaction temperature. The observations in this study will prove beneficial in approaching rapid synthesis of AgNPs and their antimicrobial application.     

电子系统级(ESL)设计:越早开始越好

功能更繁杂的设计需求,更短的上市时间,国际市场竞争的加剧,不断增加的成本压力使高质量的电子系统设计变得越来越复杂和困难,而这种趋势看起来还在加速.从应用概念到硅片实现的过程已经不能仅仅靠工程师聪明的大脑来完成,而更需要依赖于严格完善的设计方法学.电子系统级(ESL,Electronic System Level)设计正在从学术研究的课题变成业界广为接受的建模手段,它完成从理想应用优化到目标体系结构建立.而后依据预期产量规模的不同,用SoC芯片或可编程平台实现.近来,电子系统级设计建模手段和它在设计过程中的典型作用已经逐步被系统设计行业机构统一为SystemC的抽象描述.     

Clustering in WSN with Latency and Energy Consumption Constraints

  Sensor networks have emerged as a revolutionary technology for querying the physical world and hold promise in a wide variety of applications. However, the extremely energy constrained nature of these networks necessitate that their architecture be designed in an energy-aware manner. Clustering is the architecture of choice as it keeps the traffic local; sensor nodes would send only to nearby cluster-head within a fixed radius, independent of the network size.In this paper we address the problem of clustering in WSNs, subject to upper bounds on the maximum latency, the energy consumed by intermediate nodes, and clusters size. Those constraints are necessary for the reliability of the system and for extending its lifetime. We propose a polynomial time algorithm consisting of recursively computing minimum weighted dominating sets, while respecting latency and energy consumption constraints. We compare our algorithm to other alternatives and show that it consistently outperforms them.

Minimizing cycle time and group scheduling, using Petri nets a study of heuristic methods

The objective of this paper is a study of minimizing the maximum completion time min F _max, or cycle time of the last job of a given family of jobs using flow shop heuristic scheduling techniques. Three methods are presented: minimize idle time (MIT); Campbell, Dudek and Smith (CDS); and Palmer. An example problem with ten jobs and five machines is used to compare results of these methods. A deterministic t-timed colored Petri net model has been developed for scheduling problem. An execution of the deterministic timed Petri net allows to compute performance measures by applying graph traversing algorithms starting from initial global state and going into a desirable final state(s) of the production system. The objective of the job scheduling policy is minimizing the cycle time of the last job scheduled in the pipeline of a given family of jobs. Three heuristic scheduling methods have been implemented. First, a sub-optimal sequence of jobs to be scheduled is generated. Second, a Petri net-based simulator with graphical user interface to monitor execution of the sequence of tasks on machines is dynamically designed. A deterministic t-timed colored Petri net model has been developed and implemented for flexible manufacturing systems (FMS). An execution of the deterministic timed Petri net into a reachability graph allows to compute performance measures by applying graph traversing algorithms starting from initial global state to a desirable final state(s) of the production system.     

群桩有限里兹单元法

介绍了群桩循环法、有限里兹单元法的循环法以及群桩模型的沉降、荷载传递和侧摩阻力计算,提出了群桩有限里兹单元法、对桩的刚度因子也作了研究,群桩有限里兹单元法是一种适合于计算实际群桩基础沉降的方法。本文就其正确性与前人工作作了比较分析。     

Biofilm formation, cellulose production, and curli biosynthesis by Salmonella originating from produce, animal, and clinical sources

The ability of 71 strains of Salmonella enterica originating from produce, meat, or clinical sources to form biofilms was investigated. A crystal violet binding assay demonstrated no significant differences in biofilm formation by isolates from any source when tested in any of the following three media: Luria-Bertani broth supplemented with 2% glucose, tryptic soy broth (TSB), or 1/20th-strength TSB. Incubation was overnight at 30 degrees C under static conditions. Curli production and cellulose production were monitored by assessing morphotypes on Luria-Bertani agar without salt containing Congo red and by assessing fluorescence on Luria-Bertani agar containing calcofluor, respectively. One hundred percent of the clinical isolates exhibited curli biosynthesis, and 73% demonstrated cellulose production. All meat-related isolates formed curli, and 84% produced cellulose. A total of 80% of produce-related isolates produced curli, but only 52% produced cellulose. Crystal violet binding was not statistically different between isolates representing the three morphotypes when grown in TSB; however, significant differences were observed when strains were cultured in the two other media tested. These data demonstrate that the ability to form biofilms is not dependent on the source of the test isolate and suggest a relationship between crystal violet binding and morphotype, with curli- and cellulose-deficient isolates being least effective in biofilm formation.     

Improved Recovery Procedure for Evaluation of Sanitizer Efficacy in Disinfecting Contaminated Cantaloupes

ABSTRACT: Improved methodology for recovering microbial contaminants from cantaloupe surface is needed. Recovery of bacteria from the entire rind of cantaloupes, obtained with a mechanical peeler, and use of a new method for calculating melon surface area were investigated using melons inoculated with Salmonella Poona or Escherichia coli NRRL B-766. Growth of Salmonella but not E. coli was found during post-inoculation storage at 20°C. The new sampling methodology was equivalent to use of replicate rind plugs, taken at multiple sites on the melon surface, in recovery of both organisms. Recovery was the same by both procedures for dip- and spot-inoculated samples, sanitized or not sanitized, and for post-inoculation holding times up to 72 h. Survival of Salmonella on dip- and spot-inoculated cantaloupe surfaces following sanitizer wash treatments was similar. Keywords: cantaloupe, dip-inoculation, spot-inoculation, recovery, disinfection, microbiological safety     

Fourier‐based schemes with modified Green operator for computing the electrical response of heterogeneous media with accurate local fields

A modified Green operator is proposed as an improvement of Fourier‐based numerical schemes commonly used for computing the electrical or thermal response of heterogeneous media. Contrary to other methods, the number of iterations necessary to achieve convergence tends to a finite value when the contrast of properties between the phases becomes infinite. Furthermore, it is shown that the method produces much more accurate local fields inside highly conducting and quasi‐insulating phases, as well as in the vicinity of phase boundaries. These good properties stem from the discretization of Green's function, which is consistent with the pixel grid while retaining the local nature of the operator that acts on the polarization field. Finally, a fast implementation of the ‘direct scheme’ of Moulinec et al. (1994) that allows for parsimonious memory use is proposed. Copyright © 2014 John Wiley & Sons, Ltd.