Characterization of Listeria monocytogenes isolated from retail foods

Listeria monocytogenes isolates recovered from retail ready-to-eat (RTE) meats, raw chickens and fresh produce were characterized by serogroup identification using PCR, genotyping using pulsed-field gel electrophoresis (PFGE) and antimicrobial susceptibility testing. Five L. monocytogenes serogroups were identified. Of the 167 isolates 68 (41%) belonged to serogroup 1/2b, 3b; 53 (32%) belonged to serogroup 4b, 4d, 4e; 43 (26%) belonged to serogroup 1/2a, 3a; 2 (1.2%) belonged to serogroup 1/2c, 3c; and 1 (0.6%) belonged to serogroup 4a, 4c. PFGE generated 120 patterns which correlated well with PCR serogrouping. Most L. monocytogenes isolates were resistant to sulfonamide (73%) and some were resistant to tetracycline (8.4%) and ciprofloxacin (1.8%). Tetracycline resistance was conjugatively transferable and the tet(M) gene was identified in 14 tetracycline-resistant isolates as well as their transconjugants. These findings indicate that L. monocytogenes present in food were diverse, and that resistance to one or more antibiotics among these isolates was common. In addition, the presence of potential serotype 4b in all food categories is of public health concern, as serotype 4b has been the serotype most frequently associated with human listeriosis.     

A Computational Study of the Effects of Strain Hardening in Micro-asperity Friction Models

In this paper, we study the effects of plastic strain hardening and damage on the friction response of a surface at the microscopic and macroscopic scales. At the microscale, the role played by hardening and damage in the response of a single asperity is determined using three-dimensional finite element analysis. The sample materials for the asperity are Al 2024-T3 and Ti6Al4V, which are modeled as isotropic bilinear plastic and include Johnson–Cook damage. The friction responses for two different damage models (Johnson–Cook and Bao–Wierzbicki) are also compared for the perfectly plastic case. In the simulations the asperity is initially compressed in order to induce a normal preload and then sheared to study the friction response. Then a statistical homogenization approach is used to propagate these effects to the macroscale. Toward this end, the surface is modeled as an isotropic Gaussian random process. The computed microscale responses are parameterized, and the overall macroscopic response of the surface is determined. Results of this study show that, at the microscale, strain hardening increases the coefficient of friction, particularly at low interference values. Similarly, material response plays a significant role at the macroscale over a wide range of normal force values.     

Flow and heat transfer in serpentine channels

Serpentine channels are often used in microchannel reactors and heat exchangers. These channels offer better mixing, higher heat and mass‐transfer coefficients than straight channels. In the present work, flow and heat transfer experiments were carried out with a serpentine channel plate comprising of 10 units (single unit dimensions: 1 × 1.5 mm² in cross section, length 46.28 mm, D_h 1.2 mm) in series. Pressure drop and heat‐transfer coefficients were experimentally measured. Flow and heat transfer in the experimental set‐up were simulated using computational fluid dynamics (CFD) models to understand the mechanisms responsible for performance enhancement. The CFD methodology, thus, developed was applied to understand the effect of various geometrical parameters on heat transfer enhancement. A criterion was defined for evaluation of heat transfer performance (heat transfer per unit pumping power), thus, ensuring due considerations to required pumping power. The effect of geometrical parameters and the corresponding mechanisms contributing for enhancement are discussed briefly. Based on the results, a design map comprising different serpentine channels showing heat transfer enhancement with pumping power was developed for Reynolds number of 200 which will be useful for further work on flow and heat transfer in serpentine channels. © 2012 American Institute of Chemical Engineers AIChE J, 59: 1814–1827, 2013     

Distributed topology construction of Bluetooth wireless personal area networks

Bluetooth, a wireless technology based on a frequency-hopping physical layer, enables portable devices to form short-range wireless ad hoc networks. Bluetooth hosts are not able to communicate unless they have previously discovered each other through synchronization of their timing and frequency-hopping patterns. Thus, even if all nodes are within proximity of each other, only those nodes which are synchronized with the transmitter can hear the transmission. To support any-to-any communication, nodes must be synchronized so that the pairs of nodes, which can communicate with each other, form a connected graph. Using Bluetooth as an example, we first provide deeper insights into the issue of link establishment in frequency-hopping wireless systems. We then introduce an asynchronous distributed protocol that begins with nodes having no knowledge of their surroundings and terminates with the formation of a connected network topology satisfying all constraints posed by Bluetooth. An attractive protocol feature is its ease in implementation using the communication primitives offered by the Bluetooth Specification.     

Multi-linear model-based fault detection during process transitions

Process transitions due to startup, shutdown, product slate changes, and feedstock changes are frequent in the process industry. Experienced operators usually execute transitions in the manual mode as transitions may involve unusual conditions and nonlinear process behavior. Processes are therefore more prone to faults as well as inadvertent operator errors during transitions. Fault detection during transition is critical as faults can lead to abnormal situations and even cause accidents. This paper proposes a model-based fault detection scheme that involves decomposition of nonlinear transient systems into multiple linear modeling regimes. Kalman filters and open-loop observers are used for state estimation and residual generation based on the resulting linear models. Analysis of residuals using thresholds, faults tags, and logic charts enables on-line detection and isolation of faults. The multi-linear model-based fault detection technique has been implemented using Matlab and successfully tested to detect process faults and operator errors during the startup transition of highly nonlinear pH neutralization reactor in the laboratory.     

Experimental analysis of the aqueous chemical environment following a loss-of-coolant accident

Five different 30-day tests were conducted to simulate the chemical environment in a pressurized water reactor containment water pool after a loss-of-coolant accident (LOCA). All chemical environments within the test apparatus included boric acid, lithium hydroxide, and hydrochloric acid. In addition, trisodium phosphate, sodium hydroxide, and sodium tetraborate were used to control pH in separate tests. Materials tested within this environment included representative amounts of submerged and unsubmerged metal coupons, concrete, insulation debris samples, concrete particulate, and latent debris. Visible changes were seen on the both submerged and unsubmerged metal coupons in each test because of corrosion. The tests with calcium silicate (cal-sil) insulation had considerably more sediment than the other tests with fiberglass insulation. Particulate deposits were found only on the exterior surfaces of the fiberglass bundles. The most particulate deposits were found on the fiberglass exterior from the test that involved cal-sil insulation and trisodium phosphate (TSP). In addition, snow-like white precipitates were found on top of the sediment in that test, that were rich in calcium and phosphorus. Precipitates were also present in the solutions of two tests when the solution was cooled to room temperature. These precipitates have high contents of aluminum and boron with small amounts of sodium and calcium. The presence of insulation debris, precipitates, and sediments is significant because of the impact they may have on the ECCS recirculation process.     

On the measurement of critical micelle concentrations of pure and technical-grade nonionic surfactants

The critical micelle concentrations (CMC) of nine commercial nonionic surfactants (Tween 20, 22, 40, 60, and 80; Triton X-100; Brij 35, 58, and 78) and two pure nonionics [C₁₂(EO)₅ and C₁₂(EO)₈] were determined by surface tension and dye micellization methods. Commercially available nonionic surfactants (technical grade) usually contain impurities and have a broad molecular weight distribution owing to the degree of ethoxylation. It was shown that the surface tension method (Wilhelmy plate) is very sensitive to the presence of impurities. Much lower CMC values were obtained with the surface tension method than with the dye micellization method (up to 6.5 times for Tween 22). In the presence of highly surfaceactive impurities, the air/liquid interface is already saturated at concentrations well below the true CMC, leading to a wrong interpretation of the break in the curve of surface tension (γ) vs. concentration of nonionic surfactant (log C). The actual onset of micellization happens at higher concentrations, as measured by the dye micellization method. Furthermore, it was shown that when a commercial surfactant sample (Tween 20) is subjected to foam fractionation, thereby removing species with higher surface activity, the sample yields almost the same CMC values as measured by surface tension and dye micellization methods. It was found that for monodisperse pure nonionic surfactants, both CMC determination methods yield the same results. Therefore, this study indicates that precaution should be taken when determining the CMC of commercial nonionic surfactants by the surface tension method, as it indicates the surface concentration of all surface-active species at the surface only, whereas the dye method indicates the presence of micelles in the bulk solution.     

Synthesis and characterization of novel copper/polyaniline nanocomposite and application as a catalyst in the Wacker oxidation reaction

Copper nanoclusters were synthesized by a chemical reduction of an aqueous copper salt solution by sodium borohydride. A polyaniline nanocomposite containing copper nanoclusters was prepared by polymerizing a monomer aniline hydrochloride solution containing the copper nanoclusters using ammonium persulfate as an oxidizing agent. The synthesized nanocomposite was characterized using various techniques such as UV‐visible spectroscopy, FTIR spectroscopy, X‐ray diffraction (XRD), and transmission electron microscopy (TEM). The presence of copper was confirmed by XRD and the size of the copper clusters was found to be ～53 nm, which is in good agreement with that obtained from the TEM. The synthesized nanocomposite was used to serve as a catalyst in a Wacker oxidation reaction for the conversion of 1‐decene to 2‐decanone in the presence of molecular oxygen. The formation of 2‐decanone was confirmed using GC‐MS. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2412–2417, 2003