A method to model realistic particle shape and inertia in DEM

A simple and fast original method to create irregular particle shapes for the discrete element method using overlapping spheres is described. The effects of its parameters on the resolution of the particle shape are discussed. Overlapping spheres induce a non-uniform density inside the particle leading to incorrect moments of inertia and therefore rotational behaviour. A simple method to reduce the error in the principal moments of inertia which acts on the individual densities of the spheres is also described. The pertinence of the density correction is illustrated by the case of free falling ballast particles forming a heap on a flat surface. In addition to improve behaviour, the correction reduces also computational time. The model is then used to analyse the interaction between ballast and geogrid by simulating pull-out tests. The pulling force results show that the model apprehends better the ballast geogrid interlocking than models with simple representation of the shape of the particles. It points out the importance of modelling accurately the shape of particles in discrete element simulations.     

Occurrence of α- and β-nortestosterone residues in the urine of injured male cattle

The administration of anabolic steroids, for the purposes of growth promotion, to food-producing animals is banned in the EU. Among the compounds covered by this prohibition is ß-nortestosterone (β-NT). This hormone is known to occur naturally in stallions and boars, and its main bovine metabolite, α-nortestosterone (α-NT), occurs naturally in pregnant cows and neonatal calves. However, neither compound is believed to occur naturally in male cattle. During 2006, the presence of α-NT and, on occasion, β-NT was confirmed in male cattle (bulls and steers) slaughtered in Northern Ireland on welfare grounds, as a result of acute injury. Subsequent investigations revealed no evidence of abuse at any of the farms involved and revealed that the phenomenon also occurred in three other regions of the EU, in similarly injured animals. A hypothetical link to release of the adrenal steroid, dehydroepiandrosterone (DHEA), in response to the stress of the injury was tested. Following the intravenous administration of DHEA to two normal steers, β-NT (but not α-NT) was confirmed in the urine of one steer. Thus, it may be concluded that both β-NT and, by implication, α-NT can occur naturally in male cattle (or a specific cohort thereof) in contrast to previously accepted scientific knowledge.     

On the sources of methane to the los angeles atmosphere

We use historical and new atmospheric trace gas observations to refine the estimated source of methane (CH(4)) emitted into California's South Coast Air Basin (the larger Los Angeles metropolitan region). Referenced to the California Air Resources Board (CARB) CO emissions inventory, total CH(4) emissions are 0.44 ± 0.15 Tg each year. To investigate the possible contribution of fossil fuel emissions, we use ambient air observations of methane (CH(4)), ethane (C(2)H(6)), and carbon monoxide (CO), together with measured C(2)H(6) to CH(4) enhancement ratios in the Los Angeles natural gas supply. The observed atmospheric C(2)H(6) to CH(4) ratio during the ARCTAS (2008) and CalNex (2010) aircraft campaigns is similar to the ratio of these gases in the natural gas supplied to the basin during both these campaigns. Thus, at the upper limit (assuming that the only major source of atmospheric C(2)H(6) is fugitive emissions from the natural gas infrastructure) these data are consistent with the attribution of most (0.39 ± 0.15 Tg yr(-1)) of the excess CH(4) in the basin to uncombusted losses from the natural gas system (approximately 2.5-6% of natural gas delivered to basin customers). However, there are other sources of C(2)H(6) in the region. In particular, emissions of C(2)H(6) (and CH(4)) from natural gas seeps as well as those associated with petroleum production, both of which are poorly known, will reduce the inferred contribution of the natural gas infrastructure to the total CH(4) emissions, potentially significantly. This study highlights both the value and challenges associated with the use of ethane as a tracer for fugitive emissions from the natural gas production and distribution system.     

Radiation sensitivity and postirradiation growth of foodborne pathogens on a ready-to-eat frankfurter on a roll product in the presence of modified atmosphere and antimicrobials

Intervention technologies including ionizing radiation, antimicrobials, and modified atmospheres (MA) can be used to inhibit the growth of or inactivate foodborne pathogens on complex ready-to-eat foods such as sandwiches. However, the effect of these technologies when used in combination (the hurdle concept) on the survival of foodborne pathogens is unknown. The ability of ionizing radiation to inactivate Escherichia coli O157:H7, Salmonella, Listeria monocytogenes, and Staphylococcus aureus inoculated onto a frankfurter on a roll product containing the antimicrobials sodium diacetate and potassium lactate in the presence of an MA (100% N2, 50% N2 plus 50% CO2, or 100% CO2) was investigated. The radiation resistances (D10-values) of the foodborne pathogens were 0.43 to 0.47 kGy for E. coli O157:H7, 0.61 to 0.71 kGy for Salmonella, 0.53 to 0.57 for L. monocytogenes, and 0.56 to 0.60 for S. aureus. The MA had no effect on the radiation resistance of the pathogens. During a 2-week storage period under mild temperature abuse (10 degrees C), none of the pathogens were able to proliferate on the frankfurter on a roll product, regardless of the MA used. However, application of sublethal doses of ionizing radiation resulted in increased mortality of the gram-positive pathogens L. monocytogenes and S. aureus during the storage period regardless of the MA. Although the pathogens were unable to proliferate on the frankfurter on a roll product during the storage period, application of a postpackaging intervention step was needed to actually inactivate the foodborne pathogens. Ionizing radiation used in combination with sodium diacetate and potassium lactate resulted in additional mortality of L. monocytogenes and S. aureus, independent of the MA, during the 2-week storage period.     

Pyridoxal 5'-phosphate and the regulation of ornithine decarboxylase activity and stability

There are two forms of ornithine decarboxylase with respect to pyridoxal 5'-phosphate (pyridoxal-P) affinity in exponentially-growing Swiss 3T3 mouse fibroblasts: form I (Km approximately 10 muM) accounts for 30% of the total activity, and form II (Km approximately 0.4 muM) the remainder. Each form of the enzyme is in rapid equilibrium with ornithine and pyridoxal-P; neither form recognizes the Schiff base between ornithine and pyridoxal-P as a substrate. Total pyridoxal-P concentrations indicate that both forms may normally be at least partially active in vivo. Upon stimulation of 3T3 cells by pituitary growth factors, form I becomes undetectable within 4 h. As total activity increases over 10-fold during this time and continues to increase thereafter, a possible conversion of form I to form II could account for this increase only if the Km change reflects other changes in preexisting enzyme. The rates of cofactor dissociation are apparently the same for each form and neither rate changes with the growth state. Since rapid equilibrium kinetics apply, the forms apparently differ in their rate of cofactor association. The half-lives of the two forms in vivo are the same in unstimulated cells when measured concurrently. Also, the half-life of total activity decreases markedly upon stimulation as form II becomes dominant. These and other observations are not consistent with pyridoxal-P serving a major protective function for the enzyme in vivo.     

Atmospheric outflow of anthropogenic semivolatile organic compounds from East Asia in spring 2004

To estimate the emissions of anthropogenic semivolatile organic compounds (SOCs) from East Asia and to identify unique SOC molecular markers in Asian air masses, high-volume air samples were collected on the island of Okinawa, Japan between 22 March and 2 May 2004. Contributions from different source regions (China, Japan, the Koreas, Russia, and ocean/local) were estimated by use of source region impact factors (SRIFs). Elevated concentrations of hexachlorobenzene (HCB), hexachlorcyclohexanes (HCHs), dichlorodiphenyltrichloroethanes (DDTs), and particulate-phase polycyclic aromatic hydrocarbons (PAHs) were attributed to air masses from China. A large proportion of the variation in the current-use pesticides, gas-phase PAHs, and polychlorinated biphenyl (PCB) concentrations was explained by meteorology. Chlordanes showed a technical mixture profile and similar concentrations regardless of source region. alpha/gamma HCH and trans/cis chlordane ratios did not vary significantly with different source regions and had regional averages of 2.5 +/- 1.0 and 1.2 +/- 0.3, respectively. Particulate-phase PAH concentrations were significantly correlated (p value < 0.05) with other incomplete combustion byproduct concentrations, including elemental mercury (Hg0), CO, NOx, black carbon, submicrometer aerosols, and SO2. By use of measured PAH, CO, and black carbon concentrations and estimated CO and black carbon emission inventories, the emission of six carcinogenic particulate-phase PAHs was estimated to be 1518-4179 metric tons/year for Asia and 778-1728 metric tons/year for China, respectively. These results confirm that East Asian outflow contains significant emissions of carcinogenic particulate-phase PAHs.     

Relative dominance of physical versus chemical effects on the transport of adhesion-deficient bacteria in intact cores from South Oyster, Virginia

Bacterial transport experiments were conducted using intact sediment cores collected from sites on the Delmarva Peninsula near South Oyster, VA, to delineate the relative importance of physical and chemical heterogeneity in controlling transport of an adhesion-deficient bacterial strain. Electron microscopy revealed that the sediments consisted of quartz and feldspar with a variable amount of clay and iron and aluminum hydroxide coatings on the grains. A nonmotile, gram-negative indigenous groundwater strain, designated as Comamonas sp. DA001, was injected into the cores along with a conservative tracer bromide (Br). DA001 cells were 1.2 x 0.6 microm in size with a hydrophilic surface and a slightly negative surface charge. Bacterial breakthrough preceded that of Br. This differential advection phenomenon can be accounted for by reduction of the effective porosity for the bacteria relative to Br. The distribution of cells remaining in the core as determined by scintillation counting and phosphor imaging techniques was variable, ranging from nearly uniform concentrations throughout the core to exponentially decreasing concentrations with distance from the point of injection. The fraction of bacterial retention in the core was positively correlated with the abundance of the metal hydroxides and negatively correlated with grain size. Because grain size was inversely correlated with the abundance of the metal hydroxide coatings, it was necessary to separate the effects of grain size and mineralogy. The fraction of the bacterial retention accounting for the effect of grain size, the collision efficiency, exhibited no correlation with the abundance of the metal hydroxides, indicating that the bacterial retention was primarily controlled by grain size. Reasons for the lack of influence of mineralogy on bacterial transport include (i) the slightly negatively charged bacterial surfaces; (ii) an insufficient heterogeneity of sediment surface properties; and (iii) the masking of the positive charge of the metal hydroxide surfaces by adsorbed organic carbon (up to 1180 ppm). This study demonstrates that the laboratory-based bacterial transport experiments are effective in delineating physical versus chemical controlling factors and provide an important link to field-based bacterial transport studies.     

Chemical characterization of the mutagenic neutral aromatic polar fractions of petroleum substitutes

The constituents of the neutral aromatic polar subfractions of two coal-derived oils, a shale-derived oil and a petroleum oil were analysed and compared. Chemical ionization mass spectra, using methanol and ammonia as reagent gases, were used to characterize the oxygen-and nitrogen-containing constituents, respectively. The compositions of the petroleum substitutes were found to differ from those of petroleum in containing primary polycyclic aromatic amines, azaarenes, polycyclic hydroxyaromatics and, in one case, aromatic ketones.