Occurrence, virulence genes and antibiotic resistance of Escherichia coli O157 isolated from raw bovine, caprine and ovine milk in Greece

The examination of 2005 raw bovine (n = 950), caprine (n = 460) and ovine (n = 595) bulk milk samples collected throughout several regions in Greece for the presence of Escherichia coli serogroup O157 resulted in the isolation of 29 strains (1.4%) of which 21 were isolated from bovine (2.2%), 3 from caprine (0.7%) and 5 from ovine (0.8%) milk. Out of the 29 E. coli O157 isolates, only 12 (41.4%) could be classified as Shiga-toxigenic based on immunoassay and PCR results. All 12 Shiga-toxigenic E. coli serogroup O157 isolates belonged to the E. coli O157:H7 serotype. All except one of the 12 Shiga-toxin positive isolates were stx₂-positive, five of which were also stx₁-positive. The remaining isolate was positive only for the stx₁ gene. All stx-positive isolates (whether positive for stx₁, stx₂ or stx₁ and stx₂) were also PCR-positive for the eae and ehxA genes. The remaining 17 E. coli O157 isolates (58.6%) were negative for the presence of the H7 flagellar gene by PCR, tested negative for Shiga-toxin production both by immunoassay and PCR, and among these, only four and three strains were PCR-positive for the eae and ehxA genes, respectively. All 29 E. coli O157 isolates displayed resistance to a wide range of antimicrobials, with the stx-positive isolates being, on average, resistant to a higher number of antibiotics than those which were stx-negative.     

Optimal Node Visitation in Acyclic Stochastic Digraphs with Multi-threaded Traversals and Internal Visitation Requirements

The original definition of the problem of optimal node visitation (ONV) in acyclic stochastic digraphs concerns the identification of a routing policy that will enable the visitation of each leaf node a requested number of times, while minimizing the expected number of the graph traversals. The original work of Bountourelis and Reveliotis (2006) formulated this problem as a Stochastic Shortest Path (SSP) problem, and since the state space of this SSP formulation is exponentially sized with respect to the number of the target nodes, it also proposed a suboptimal policy that is computationally tractable and asymptotically optimal. This paper extends the results of Bountourelis and Reveliotis (2006) to the cases where (i) the tokens traversing the graph can “split” during certain transitions to a number of (sub-)tokens, allowing, thus, the satisfaction of many visitation requirements during a single graph traversal, and (ii) there are additional visitation requirements attached to the internal graph nodes, which, however, can be served only when the visitation requirements of their successors have been fully met. In addition, the presented set of results establishes stronger convergence properties for the proposed suboptimal policies, and it provides a formal complexity analysis of the considered ONV formulations. From a practical standpoint, the extension of the original results performed in this paper enables their effective usage in the application domains that motivated the ONV problem, in the first place.

FIB-SEM Sectioning Study of Decarburization Products in the Microstructure of HVOF-Sprayed WC-Co Coatings

The thermal dissolution and decarburization of WC-based powders that occur in various spray processes are a widely studied phenomenon, and mechanisms that describe its development have been proposed. However, the exact formation mechanism of decarburization products such as metallic W is not yet established. A WC-17Co coating is sprayed intentionally at an exceedingly long spray distance to exaggerate the decarburization effects. Progressive xenon plasma ion milling of the examined surface has revealed microstructural features that would have been smeared away by conventional polishing. Serial sectioning provided insights on the three-dimensional structure of the decarburization products. Metallic W has been found to form a shell around small splats that did not deform significantly upon impact, suggesting that its crystallization occurs during the in-flight stage of the particles. W₂C crystals are more prominent on WC faces that are in close proximity with splat boundaries indicating an accelerated decarburization in such sites. Porosity can be clearly categorized in imperfect intersplat contact and oxidation-generated gases via its shape.     

Stability and release properties of curcumin encapsulated in Saccharomyces cerevisiae, β-cyclodextrin and modified starch

Curcumin, a polyphenol with pharmacological function and colouring power, was encapsulated in baker’s yeast (Saccharomyces cerevisiae) cells, β-cyclodextrin (β-CD) and modified starch (MS) by various methods. The encapsulation forms were evaluated for their efficiency in overcoming curcumin’s heat, light and oxygen sensitivity (storage stability). The release (dissolution) profile of curcumin in simulated gastric (SGF) and pancreatic fluid (SPF) was, also, obtained. All the encapsulation forms drastically increased curcumin’s solubility in SGF. A rapid dissolution of curcumin was observed for β-CD and MS microcapsules in SGF while, in yeast microcapsules, a slow and prolonged release occurred, along with low degradation rate in SPF. All the microcapsules tested protected curcumin against oxidation in environments of elevated relative humidity (%RH) and yeast microcapsules stabilized curcumin at RH above 75.5%, where oxidation was significantly increased. Yeast cells offered better protection to curcumin than did β-CD or MS against deleterious photochemical reactions and against heat degradation following isothermal (inert or oxidative) heating at 200 °C. Heating at lower temperatures (isothermal and non-isothermal) revealed that β-CD and MS can also enhance curcumin’s heat resistance.     

Geometrical characterization of stall cells on rectangular wings

The onset of stall cells (SCs) is experimentally investigated on a flattop loaded 18% thick airfoil optimized for use on wind turbine blades, exhibiting trailing edge separation. SCs are dynamic coherent vortical structures that appear on wings under separated flow conditions. Although SCs have been known for long, neither are their characteristics completely documented nor their generating mechanisms fully understood. The present investigation aims at providing additional information on the geometric characteristics in terms of width, length and occupied area. The relevant data are presented as functions of Reynolds (Re) number, angle of attack and aspect ratio (AR) of the model. In the tests reported, the dynamic character of SCs is suppressed by imposing a localized flow disturbance. For the specific airfoil and for the Re and AR range tested, it is found that: the angle of attack at which SCs are initially formed decreases linearly with Re number and independently of the AR; unlike two‐dimensional separation, their chordwise length increases with Re; the SC area relative to the wing planform area (defined as the relative SC area) grows asymptotically with angle of attack and Re number reaching an upper bound, which is independent of the AR; at intermediate angles of attack, the SC relative area is higher for the lower AR wing; for a fixed increment in Re number, the growth of the SC relative area is independent of the initial Re number; at lower angles of attack, the actual SC area is independent of the wing span. Copyright © 2013 John Wiley & Sons, Ltd.     

A multimedia application for watermarking digital images based on a content based image retrieval technique

The current work is focused on the implementation of a robust multimedia application for watermarking digital images, which is based on an innovative spread spectrum analysis algorithm for watermark embedding and on a content-based image retrieval technique for watermark detection. The existing highly robust watermark algorithms are applying “detectable watermarks” for which a detection mechanism checks if the watermark exists or not (a Boolean decision) based on a watermarking key. The problem is that the detection of a watermark in a digital image library containing thousands of images means that the watermark detection algorithm is necessary to apply all the keys to the digital images. This application is non-efficient for very large image databases. On the other hand “readable” watermarks may prove weaker but easier to detect as only the detection mechanism is required. The proposed watermarking algorithm combine’s the advantages of both “detectable” and “readable” watermarks. The result is a fast and robust multimedia application which has the ability to cast readable multibit watermarks into digital images. The watermarking application is capable of hiding 2¹⁴ different keys into digital images and casting multiple zero-bit watermarks onto the same coefficient area while maintaining a sufficient level of robustness.     

Computational Intelligence Techniques for Short-Term Electric Load Forecasting

Electric load forecasting has received an increasing attention over the years by academic and industrial researchers and practitioners due to its major role for the effective and economic operation of power utilities. The aim of this paper is to provide a collective unified survey study on the application of computational intelligence (CI) model-free techniques to the short-term load forecasting of electric power plants. All four classes of CI methodologies, namely neural networks (NNs), fuzzy logic (FL), genetic algorithms (GAs) and chaos are addressed. The paper starts with some background material on model-based and knowledge-based forecasting methodologies revealing a number of key issues. Then, the pure NN-based and FL-based forecasting methodologies are presented in some detail. Next, the hybrid neurofuzzy forecasting methodology (ANFIS, GARIC and Fuzzy ART variations), and three other hybrid CI methodologies (KB-NN, Chaos-FL, Neurofuzzy-GA) are reviewed. The paper ends with eight representative case studies, which show the relative merits and performance that can be achieved by the various forecasting methodologies under a large repertory of geographic, weather and other peculiar conditions. An overall evaluation of the state-of-art of the field is provided in the conclusions.     

Econometric and Statistical Computing Using Ox

This paper reviews the matrix programminglanguage Ox from the viewpoint of an econometrician/statistician.We focus on scientific programming using Ox and discussexamples of possible interest to econometricians and statisticians, such as random number generation, maximum likelihood estimation, andMonte Carlo simulation. Ox is a remarkable matrix programming language which is well suited to research and teaching in econometrics and statistics.