Genetic Carriers and Genomic Distribution of cadA6—A Novel Variant of a Cadmium Resistance Determinant Identified in Listeria spp.

Listeria monocytogenes is a pathogen responsible for severe cases of food poisoning. Listeria spp. strains occurring in soil and water environments may serve as a reservoir of resistance determinants for pathogenic L. monocytogenes strains. A large collection of Listeria spp. strains (155) isolated from natural, agricultural, and urban areas was screened for resistance to heavy metals and metalloids, and the presence of resistance determinants and extrachromosomal replicons. Of the tested strains, 35% were resistant to cadmium and 17% to arsenic. Sequence analysis of resistance plasmids isolated from strains of Listeria seeligeri and Listeria ivanovii, and the chromosome of L. seeligeri strain Sr73, identified a novel variant of the cadAC cadmium resistance efflux system, cadA6, that was functional in L. monocytogenes cells. The cadA6 cassette was detected in four Listeria species, including strains of L. monocytogenes, isolated from various countries and sources—environmental, food-associated, and clinical samples. This resistance cassette is harbored by four novel composite or non-composite transposons, which increases its potential for horizontal transmission. Since some cadAC cassettes may influence virulence and biofilm formation, it is important to monitor their presence in Listeria spp. strains inhabiting different environments.     

USING REINFORCEMENT LEARNING TO COORDINATE BETTER

This paper examines the potential and the impact of introducing learning capabilities into autonomous agents that make decisions at run-time about which mechanism to exploit to coordinate their activities. Specifically, our motivating hypothesis is that to deal with dynamic and unpredictable environments it is important to have agents that learn the right situations in which to attempt coordination , and the right coordination method to use in those situations . In particular, the efficacy of learning is evaluated when agents have varying types and amounts of information when those coordinating decisions are taken. This hypothesis is evaluated empirically, in a grid-world scenario in which (a) an agent's predictions about the other agents in the environment are approximately correct and (b) an agent cannot correctly predict the others' behavior. The results presented show when, where and why learning is effective when it comes to making a decision about selecting a coordination mechanism.     

Influence of thermal treatments on Ag Sn Cu powders in order to reduce mercury contents in dental amalgam

The mercury content of dental amalgams is a controversial subject with regard to the biological properties of these materials. The object of this study is to optimize the thermal treatments performed on an experimental powder in order to obtain a low mercury ratio (41% by weight) while preserving the desirable clinical qualities of the material. Using atomized powder, two types of thermal treatments are performed: A1, to obtain a partially annealed structure and A2, to obtain a complete homogenization. The kinetics of the amalgamation reaction is mainly evaluated by X-ray diffraction to identify the newly formed phases as a function of setting time. Mechanical properties are evaluated according to the ISO norms at 37 °C. Metallographical examination of the amalgams shows a «Ag-Hg» phase which acts as a matrix incorporating the «Cu-Sn» and «Ag-Sn» compounds. The setting kinetics of the A1 amalgams is linear and slightly more rapid than that of the A2 amalgam. The mechanical properties of the amalgams are significantly improved regarding the higher mercury content commercial amalgams. A specific thermal treatment permits us to slow down the diffusion of mercury between the different intermetallic compounds into the powder. The final amalgam composition, thus, most approaches the stoechiometric ratio calculated from a quaternary diagram.     

Electronic diary evidence on energy erosion in clinical burnout.

Burnout is generally defined as a state of severe exhaustion. So far, research has predominantly focused on relatively mild burnout in employees able to work despite their complaints. This study examines energy depletion in clinical burnout (e.g., the severest cases on extended sick leave) by comparing the diurnal patterns of fatigue and exhaustion with those of healthy individuals. Sixty clinically burned-out and 40 healthy participants kept an electronic diary for 14 days, 7 times a day, yielding a total of 8,116 diary entries. This study shows that burned-out individuals typically suffer continuously from a severe fatigue throughout the day. The resulting flattened diurnal cycles mark a stable exhaustion that is uncommon in healthy persons. The current results provide novel support for the existence of severe energy erosion in clinical burnout. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Investigations on the variation of corrosion and contact resistance characteristics of metallic bipolar plates manufactured under long-run conditions

Tribological variations, surface conditions (roughness, hardness, coating) and surface interactions between micro-stamping dies and bipolar plate blanks play a critical role in determining the surface quality, channel formation and precision of bipolar plates. This study is aimed to understand the cause, mechanism and consequences of interactions between micro-stamping process conditions and bipolar plate quality. A total of 2000 repeated micro-stamping of 51 μm-thick uncoated and 1 μm-thick ZrN coated SS316L sheet blanks into an array of 750 μm micro-channels were performed using 175-220 kN force levels with constant stamping speed of 1 mm/s. Microscopic examinations were conducted periodically on both die and coated & uncoated plate surfaces to observe topographic variations. In addition, corrosion and contact resistance tests were carried out in the same intervals. Analysis of variance (ANOVA) technique was used to determine the significance of the process parameters on channel height, roughness, corrosion and contact resistance differences. The results revealed similar roughness trends for die and plate surfaces during 2000 micro-stampings. ZrN coating with 1 μm thickness dramatically improved corrosion and contact resistance behavior of plates.     

Saturated Fats: A Perspective from Lactation and Milk Composition

For recommendations of specific targets for the absolute amount of saturated fat intake, we need to know what dietary intake is most appropriate? Changing agricultural production and processing to lower the relative quantities of macronutrients requires years to accomplish. Changes can have unintended consequences on diets and the health of subsets of the population. Hence, what are the appropriate absolute amounts of saturated fat in our diets? Is the scientific evidence consistent with an optimal intake of zero? If not, is it also possible that a finite intake of saturated fats is beneficial to overall health, at least to a subset of the population? Conclusive evidence from prospective human trials is not available, hence other sources of information must be considered. One approach is to examine the evolution of lactation, and the composition of milks that developed through millennia of natural selective pressure and natural selection processes. Mammalian milks, including human milk, contain 50% of their total fatty acids as saturated fatty acids. The biochemical formation of a single double bond converting a saturated to a monounsaturated fatty acid is a pathway that exists in all eukaryotic organisms and is active within the mammary gland. In the face of selective pressure, mammary lipid synthesis in all mammals continues to release a significant content of saturated fatty acids into milk. Is it possible that evolution of the mammary gland reveals benefits to saturated fatty acids that current recommendations do not consider?     

Effect of manufacturing processes on formability and surface topography of proton exchange membrane fuel cell metallic bipolar plates

Metallic bipolar plates in PEM fuel cells offer low-volume, low-mass and low-cost stack fabrication in addition to superior durability when compared to composite bipolar plates, which suffer due to their much higher thickness and less durability. This study aims to address the formability and surface topography issues of metallic bipolar plates fabricated by stamping and hydroforming technologies. Particular emphasis was given to process repeatability, surface topology, and dimensional quality of bipolar plates that would greatly affect the corrosion and contact resistance characteristics. Thin metal sheets of several alloys (i.e., SS304, SS316L, SS430, Ni270, Ti grades 1 and 2) were used in the fabrication experiments. SS304 and SS316L were shown to possess better formability when compared to other alloys that were used in this study, while SS430 and Ti grade 2 demonstrated the worst among all. Channel formability was observed to be greatly affected by the hydroforming pressure, while it does not differ much above certain level of stamping force. The confocal microscopy analyses showed that surface roughness values of the formed samples were altered significantly when compared to the initial flat blanks. In general, increasing hydroforming pressure and stamping force yielded higher surface roughness values at channel peaks. In addition, the surface topography was shown to be influenced mainly by the pressure level rather than the pressure rate in hydroforming process.     

Perfluorinated acids in Arctic snow: new evidence for atmospheric formation

Perfluorinated acids (PFAs) are ubiquitously found in water and biota, including remote regions such as the High Arctic. Under environmental conditions, PFAs exist mainly as anions and are not expected to be subject to long-range atmospheric transport in the gas phase. Fluorinated telomer alcohols (FTOHs) are volatile and can be atmospherically oxidized to form perfluorocarboxylic acids. Analogously, fluorosulfamido alcohols can be oxidized to form perfluorooctane sulfonate (PFOS). High Arctic ice caps experience contamination solely from atmospheric sources. By examining concentrations of PFAs in ice cap samples, it is possible to determine atmospheric fluxes to the Arctic. Ice samples were collected from high Arctic ice caps in the spring of 2005 and 2006. Samples were concentrated using solid-phase extraction and analyzed by LC-MS-MS. PFAs were observed in all samples, dating from 1996 to 2005. Concentrations were in the low-mid pg L(-1) range and exhibited seasonality, with maximum concentrations in the spring-summer. The presence of perfluorodecanoic acid (PFDA) and perfluoroundecanoic acid (PFUnA) on the ice cap was indicative of atmospheric oxidation as a source. Ratios of PFAs to sodium concentrations were highly variable, signifying PFA concentrations on the ice cap were unrelated to marine chemistry. Fluxes of the PFAs were estimated to the area north of 65 degrees N for the 2005 season, which ranged from 114 to 587 kg year(-1) for perfluorooctanoic acid (PFOA), 73 to 860 kg year(-1) for perfluorononanoic acid (PFNA), 16 to 84 kg year(-1) for PFDA, 26 to 62 kg year(-1) for PFUnA, and 18 to 48 kg year(-1) for PFOS. The PFOA and PFNA fluxes agreed with FTOH modeling estimations. A decrease in PFOS concentrations through time was observed, suggesting a fast response to changes in production. These data suggest that atmospheric oxidation of volatile precursors is a primary source of PFAs to the Arctic.     

Microstructure,mechanical properties,and corrosion resistance of Ti-20Zr alloy in undoped and NaF doped artificial saliva

The corrosion behavior of a new, advanced Ti-20Zr alloy with α+β microstructure (determined by optical microscopy, XRD, and SEM) and very good mechanical properties (obtained from the stress-strain curve) is studied in this paper. The composition of the alloy native passive film was determined from a XPS analysis and the long-term corrosion resistance in undoped and doped states with 0.05M NaF artificial Carter-Brugirard saliva of different pH values, simulating the severe functional conditions of a dental implant, was analyzed by electrochemical methods. This alloy possesses an advantageous balance between good mechanical resistance and plasticity and Young’s modulus and exhibits more favorable electrochemical parameters and corrosion resistance than CP Ti due to its more resistant passive layer containing Ti₂O₃, TiO₂, and ZrO₂ protective oxides. After 1000 h of immersion in saliva, the protective properties of the alloy were enhanced due to the deposited surface layer that incorporated protective phosphates (shown by SEM and XPS).