Dynamic delayed detached eddy simulation of a multi‐inlet vortex reactor

The multi‐inlet vortex reactor (MIVR) is used for flash nanoprecipitation to manufacture functional nanoparticles. A validated computational fluid dynamics model is needed for the design, scale‐up, and optimization of the MIVR. Unfortunately, available Reynolds‐averaged Navier‐Stokes methods are unable to accurately model the highly swirling flow in the MIVR. Large‐eddy simulations (LES) are also problematic, as excessively fine grids are required to accurately model this flow. These dilemmas led to the application of the dynamic delayed detached eddy simulation (DDES) method to the MIVR. In the dynamic DDES model, the eddy viscosity has a form similar to the Smagorinsky sub‐grid viscosity in LES, which allows the implementation of a dynamic procedure to determine its model coefficient. Simulation results using the dynamic DDES model are found to match well with experimental data in terms of mean velocity and turbulence intensity, suggesting that the dynamic DDES model is a good option for modeling the turbulent swirling flow in the MIVR. © 2016 American Institute of Chemical Engineers AIChE J, 62: 2570–2578, 2016     

Long-term stability of PEG-based antifouling surfaces in seawater

Poly(ethylene glycol) (PEG) is a hydrophilic polymer that has been extensively used in the biomedical and marine environment due to its antifouling properties. In the biomedical field, PEG has been successfully used to functionalize surfaces due to its resistance to cell and nonspecific protein adsorption. However, the long-term stability of PEG has limited its use in some areas. In the shipping industry, there is a great need for long-term solutions to keep the hulls of the ships fouling-free. The long-term stability of PEG in polydimethylsiloxane (PDMS) fouling-release coatings is studied here, in both accelerated laboratory tests and real seawater conditions. This article shows how PEG-based copolymers, which have been exposed in fouling-release coatings to real-life seawater conditions, are isolated and compared to those exposed to accelerated laboratory testing with successful results. The influence of the chemistry of the PEG compounds, the chosen laboratory degrading agents, and the possible degradation pathways and products are discussed.     

Liquid Loss as Effected by Post mortem Ultrastructural Changes in Fish Muscle: Cod (Gadus morhuaL) and Salmon (Salmo salar)

This study was performed in order to assess the effect of early post mortem structural changes in the muscle upon the liquid-holding capacity of wild cod, net-pen-fed cod (fed cod) and farmed salmon. The liquid-holding capacity was measured by a low speed centrifugation test. Transmission electron microscopy was used to discover ultrastructural changes both in the connective tissue and in the myofibrils. Differential scanning calorimetric thermograms of the muscle proteins were recorded to elucidate whether fundamental differences did exist between the proteins of the raw material tested. Multivariate statistics were used to explicate the main tendencies of variations in the thermograms. The salmon muscle possessed much better liquid-holding properties than the cod muscle, and wild cod better than fed cod regardless of the storage time. Both fed cod and farmed salmon, underwent the most severe structural alterations, probably caused by the low muscle pH values. The higher liquid-holding capacity of the salmon muscle was related to species specific structural features and better stability of the muscle proteins. The myofibrils of the salmon muscle were denser and intra- and extracellular spaces were filled by fat and a granulated material. The differences in thermograms of muscle from wild and fed cod were largely explained by the variations in pH. The severe liquid loss of fed cod is due to a low pH induced denaturation and shrinkage of the myofibrils. Post mortem degradation of the endomysial layer and the sarcolemma may have further facilitated the release of liquid.     

Structure and properties of poly(p-xylylene) composites made by electrochemical and vapor deposition polymerization

Poly(para-xylylene)(PPX)/carbon fiber towpregs were produced by two different in-situ polymerization processes: Electrochemcal polymerization (ECP) and vapor deposition polymerization (VDP). The monomer used for the ECP process was α, α′ -dibromo-para-xylylene and di-para-xylylene was the starting material for the VDP process. A series of tests, including FTIR, WAXD, DSC, TG, and SEM were carried out to identify and compare these two composite towpregs. It has been confirmed that the PPX samples obtained by the two different polymerization processes were basically chemically identical. However, the polymer coating on the fiber surface produced by the VDP process was much smoother than that produced by the ECP process, which produced a porous coating.     

Prevalence, distribution, and diversity of Listeria monocytogenes in retail environments, focusing on small establishments and establishments with a history of failed inspections

Despite growing concerns about cross-contamination of ready-to-eat foods with Listeria monocytogenes, our knowledge about the ecology and transmission of L. monocytogenes in retail establishments has remained limited. We conducted a cross-sectional study to characterize the prevalence, distribution, and subtype diversity of L. monocytogenes in 120 New York State retail deli establishments that were hypothesized to present an increased risk for environmental L. monocytogenes contamination (i.e., small establishments and establishments with a history of failed New York State Agriculture and Markets inspections). Analysis of these data along with previously reported data for 121 predominantly larger retail establishments in New York State identified establishment size, geographic location, and inspection history as significant predictors of L. monocytogenes presence and prevalence. The odds of an establishment being L. monocytogenes positive were approximately twice as high for large establishments, establishments located in New York City, or establishments with poor inspection history (as compared with establishments without these attributes), even though correlation between location and inspection history complicated interpretation of results. Within an establishment, L. monocytogenes was significantly more prevalent on nonfood contact surfaces than on food contact surfaces; prevalence was particularly high for floors and in floor drains, sinks, the dairy case, and milk crates. L. monocytogenes subtype diversity differed between sites, with lineage I isolates significantly associated with nonfood contact surfaces and lineage II isolates significantly associated with food contact surfaces. Isolates belonging to the same ribotype were often found dispersed across multiple sites within an operation.     

Prechamber NOx formation in low BMEP 2-stroke cycle natural gas engines

Precombustion chambers (PCCs) are an ignition technology for large bore, natural gas engines enabling increased combustion stability while extending the lean limit of operation. A PCC is a small chamber, typically 1–2% of the clearance volume, in which a near-stoichiometric mixture of fuel and air is ignited by a standard spark plug. After the mixture in the PCC is ignited, its pressure rises and expels a flame jet of hot gas mixture into the main chamber. The amount of energy a typical PCC produces is roughly one million times that of a conventional spark plug. In this work the role that the PCC plays in the formation of oxides of nitrogen (NO_x) is investigated. Previous research indicates that the PCC is responsible for a significant part of engine-out NO_x, especially near the lean limit of engine operation. Experimental results are presented from a large bore lean-burn 2-stroke cycle engine. The data shows that the PCC is responsible for a significant part of engine-out NO_x emissions. However, the PCC NO_x does not form in the PCC. Rather it forms within the gas jet after it penetrates into the main chamber combustion gases.     

Homonuclear Decoupling of 1H Dipolar Interactions in Solids by means of Heteronuclear Recoupling

Line narrowing has been traditionally achieved in solid-state ¹H NMR spectroscopy by applying pulse sequences that combine multiple-pulse operations with magic-angle spinning (MAS), to effectively average out the dipole dipole homonuclear Hamiltonian. The present study explores a new alternative that departs from the usual concept of directly acting on the strongly coupled spins with radiofrequency pulses; instead, we seek to achieve a net homonuclear dipolar decoupling in solids by exploring the reintroduction of MAS-averaged heteronuclear dipolar couplings between the ¹H nuclei and directly bonded ¹³C or ¹⁵N nuclei. This recoupling anti-recoupling (RaR) scheme thus relies on the recoupling of the dipolar interaction with heteronuclear spins, which, under fast MAS, will exceed the strength and will not commute with the homonuclear ¹H ¹H coupling one is intending to average out. Subsequent removal (“antiRecoupling”) of these heteronuclear interactions can lead to narrowed ¹H resonances, without ever pulsing on the aforementioned channel. The line-narrowing properties of RaR are illustrated with numerical simulations and with experiments on model organic solids.