Construction of a Single PEP4 Allele Deletion in Saccharomyces carlsbergensis and a Preliminary Evaluation of Its Brewing Performance

The secretion of proteinase A (encoded by PEP4) from brewer's yeast is detrimental to the foam stability of unpasteurized beer. The aim of this study was to construct mutants of the allopolyploid Saccharomyces carlsbergensis strain TT, which were partially or completely deficient in proteinase A activity. Allelic PEP4 genes were consecutively disrupted by using the Cre‐loxP recombination system combined with PCR‐mediated gene disruption. A single PEP4 deletion mutant TT‐M was successfully constructed. However, no viable mutant could be obtained when the second allelic PEP4 gene was deleted. The brewing performances of the parent strain and the modified strain were compared on a 100 L pilot fermenter scale. Proteinase A activity in fermented wort brewed with mutant strain TT‐M was significantly lower (p<0.05) than that of the parent strain TT, whereas no significant difference on either maltose or maltotriose assimilation (p>0.05) was found. The mutant TT‐M remained genetically stable, as shown by diagnostic PCR, after re‐streaking for 20 generations. The flavor and taste of the final fermented wort, brewed with the mutant strain TT‐M, was evaluated by the Tsingtao expert sensory panel, and found to be comparable to that of the parent strain and exhibited no distinct defects. The flavor component profiles of these two finished products were also comparable. The study demonstrated allelic genes in polyploid industrial yeasts could be efficiently and consecutively deleted by the retractive primer disruption strategy, and the mutant of Saccharomyces carlsbergensis partially deficient in proteinase A contributed to an improvement in foam stability.     

Monoterpene and sesquiterpene emission estimates for the United States

Biogenic volatile organic compounds (BVOC) contribute significantly to the formation of ozone and secondary organic aerosol (SOA). The Model of Emissions of Gases and Aerosols from Nature (MEGANv2.02) is used to estimate emissions of isoprene, monoterpenes (MT), and sesquiterpenes (SQT) across the United States. Compared to the Biogenic Emission Inventory System (BEIS3.0), MEGANv2.02 estimates higher isoprene but lower MT emissions for July 2001 and January 2002. A sensitivity study of SQT and MT emission factors and algorithm parameters was conducted by assigning values to four plant functional types (PFTs) using both recent measurements and literature values. The standard deviations of the emissions factors within these PFTs were two to four times the averages because of the variation in experimental basal emissions rate data. More recently published SQT and MT basal emission rates are generally lower than those reported in the literature through 2004. With the new emissions factors, monthly average SQT emission rates for the contiguous United States are equal to 16% of the MT emissions during July and 9% of the emissions during January. The SQT emissions distribution is strongly influenced by the grass and crop PFT, for which SQT emissions data are quite limited.     

Simulation and experimental analysis of the clamping pressure distribution in a PEM fuel cell stack

High performance and efficiency are often reported in single-cell polymer electrolyte membrane (PEM) fuel cell (FC) experiments. This however, can reduce substantially when moving from single-cell experiments to multiple cells. Fuel cell performance is degraded for many reasons when adding cells, but; possibly the most important, is contact resistance between the bipolar plate and gas diffusion layer (GDL). Contact resistance is in direct relation to the clamping configuration and clamping pressure applied to a FC stack. Simulation of a single cell and 16-cell FC was performed at various clamping pressures resulting in detailed 3D plots of stress and deformation. The stress on the GDL, for any value of clamping pressure simulated in this study, is around 1.5 MPa for the 16-cell stack and around 4 MPa in single cell simulations. Experimental testing of clamping pressure effects was performed on a 16-cell stack by placing a thin pressure-sensitive film between GDL and bipolar plate. Clamping pressure was applied using various loads, durations, and two types of GDLs. The results from experimental testing show that pressure on the GDL is in the range of 0–2.5 MPa. When using rectangular cells, experimental results show nearly zero pressure in the center of each cell and the center cells of the stack, regardless of clamping method.     

Analysis of an Ultrathin Graphite-Based Compact Heat Exchanger

The emerging production of ultrathin graphite material is applied to thermal management in a numerical comparison of aluminum and graphite-based plate-fin heat exchangers. Considering anisotropic thermal conductivity in which out-of-plane transport is about two orders of magnitude lower than in-plane values, the ultrathin graphite-based solution outperforms aluminum by rejecting up to 20% more heat on a volumetric basis. Thermal and hydraulic performance is characterized for both solutions over a range of airflow rates in a notional water/air device. Laminar through fully turbulent regimes are considered. Steady and unsteady three-dimensional (3-D) conjugate simulations reveal a faster equilibration rate for the ultrathin graphite-based solution, minimizing thermal lag that must be accounted for in on-demand electronics cooling. Fin optimization studies predict equivalent conductance with graphite at one-tenth the thickness of aluminum. The combination of improved heat rejection, rapid response rate, and low material density make an ultrathin graphite-based solution uniquely suited to aerospace thermal management.     

Performance and Selection of Pour Point Depressants

1 IntroductionParaffinic mineral oil base stocks contain waxy hydro-carbons that come out of solution when temperature de-creases.The lower the molecular weight of the paraffinand the higher its level of branching,thelower the precipi-tation temperature.Initially,tiny crystals are for medwhich diffract light making the solution hazy to the nakedeye.The temperature at which this occurs is called thecloud point.When temperature is further lowered,addi-tional wax precipitates,the crystals grow i…     

CHARACTERIZATION AND POTENTIAL UTILIZATION OF WHITEROCKS (UTAH) TAR SAND BITUMEN

ABSTRACT

The native Whiterocks (Utah) tar sand bitumen was separated into several boiling range fractions for detailed analysis and characterization. The lighter fraction (477-617 K) was evaluated for use as a transportation fuel and the residues (>617 K and >728 K) were evaluated for use as road asphalts. The 617 K plus residue from the Whiterocks bitumen can be classified as a viscosity grade AC-10 asphalt whereas the 728 K plus residue failed to meet asphalt specifications. Apart from the asphalt specification tests, several sophisticated techniques were used to characterize these fractions. The detailed structure of the low molecular weight portions of Whiterocks bitumen (477-617 K and 617-728 K) was determined by combined GC-MS. Several physical properties were also measured to evaluate the potential of the 477-617 K fraction as a high density/energy aviation turbine fuel. This lower molecular weight fraction of the bitumen contained predominantly naphthenic hydrocarbons and lesser concentrations of aromatic hydrocarbons. This was confirmed by the FTIR spectra and by the GC-MS analyses. As a result, the 477-617 K fraction appeared to be an excellent candidate as a feedstock for the production of high density, aviation turbine fuels following mild hydro treating. The heat of combustion, 135,500 BTU/gal., exceeded the specification for the high density/energy JP -11 aviation turbine fuel. The naphthenic hydrocarbons included alkylcyclohexanes, alkyldecalins, tricyclic terpanes, steranes, tetracyclic terpanes, and pentacyclic terpanes. The aromatic constituents were determined to be alkylbenzenes, benzomono-cycloparaffins, phenyl(cyclohexyl) alkanes, alkylnaphthalenes, benzodicycloparaffins, benzotricycloparaffins. alkylacenaphthenes, and naphthalene monocycloparaffins. These compounds were similar in nature to those found in the Green River shale oil.     

Predicting the response of Hamilton Harbour to the nutrient loading reductions: A modeling analysis of the “ecological unknowns”

We examine the likelihood of delisting the Hamilton Harbour as an Area of Concern, if the nutrient loading reductions proposed by the Remedial Action Plan are actually implemented. Our analysis suggests that the chl a criterion of 10 μg L^{− 1} is achievable, but the water quality setting process should explicitly accommodate the natural variability by allowing for a realistic percentage of violations, e.g., exceedences of less than 10–15% of the weekly samples during the stratified period should still be considered as compliance of the system. The current epilimnetic total phosphorus criterion of 17 μg L^{− 1} is probably stringent and therefore a somewhat higher value (e.g., 20 μg L^{− 1}) may provide a more realistic goal. Phosphorus dynamics in the sediment–water column interface need to be revisited, as the internal nutrient loading can conceivably be a regulatory factor of the duration of the transient phase and the recovery resilience of the Harbour. We also pinpoint two critical aspects of the system dynamics that invite further investigation and will likely determine our predictive capacity to assess compliance with the chlorophyll a criterion of 10 μg L^{− 1}, i.e., the nutrient recycling mediated by the microbial food web and the structural shifts towards a zooplankton community dominated by large-sized and fast-growing herbivores. The latter prospect highlights the notion that the bottom-up (i.e., nutrient loading reduction) approach historically followed in the Harbour was sufficient to bring the system in its present state, but any further improvements should be viewed in the context of a combined bottom-up and top-down (i.e., alleviation of the zooplanktivorous pressure) control.     

Effects of water on starch-g-polystyrene and starch-g-poly(methyl acrylate) extrudates

Polystyrene and poly(methyl acrylate) were grafted onto wheat starch by gamma radiation and chemical initiation, respectively. The respective percent add-on values were 46 and 45;68% of the polystyrene formed was grafted to starch, and the corresponding proportion of poly(methyl acrylate) was 41%. The molecular weight distributions of the homopolymer and graft portions were characterized, and extrusion conditions were established for production of ribbon samples of starch-g-PS and starch-g-PMA. Both copolymer types were considerably weakened by soaking in water, and this effect was more immediate and drastic for starch-g-poly(methyl acrylate). Both graft copolymers regained their original tensile strengths on drying, but the poly(methyl acrylate) specimens did not recover their original unswollen dimensions and retained high breaking elongations characteristic of soaked specimens. Tensile and dynamic mechanical properties of extruded and molded samples of both graft polymers are reported, and the plasticizing effects of water are summarized.     

Simultaneous bio-hydrogen and reducing sugar formation by the aqueous phase biomass reforming

A hydrothermal–chemical process for the simultaneous biomass hydrolysis and bio-hydrogen formation was proposed in this study. Current results revealed that a maximum reducing sugar concentration of 26.01 g/L and the yield of bio-hydrogen of 0.9098 mmol/g-cellulose were attained with the designated experimental parameters. Consequently, this study provided a potential route to produce bio-hydrogen and reducing sugar simultaneously in a one-step reaction process by using the energy crops or the agriculture wastes as the substrate.