Purification and some properties of a cysteine proteinase from sorghum malt variety SK5912

A cysteine proteinase from sorghum malt variety SK5912 was purified by a combination of 4 M sucrose fractionation, ion‐exchange chromatography on Q‐ and S‐Sepharose (fast flow), gel filtration chromatography on Sephadex G‐100 and hydrophobic interaction chromatography on Phenyl Sepharose CL‐4B. The enzyme was purified 8.4‐fold to give a 13.4% yield relative to the total activity in the crude extract and a final specific activity of 2057.1 U mg^?1 protein. SDS—PAGE revealed two migrating protein bands corresponding to apparent relative molecular masses of 55 and 62 kDa, respectively. The enzyme was optimally active at pH 6.0 and 50 °C, not influenced across a relatively broad pH range of 5.0–8.0 and retained over 60% activity at 70 °C after 30‐min incubation. It was highly significantly (P < 0.001) inhibited by Hg²⁺, appreciably (P < 0.01) inhibited by Ag⁺, Ba²⁺ and Pb²⁺ but highly significantly (P < 0.001) activated by Co²⁺, Mn²⁺ and Sr²⁺. The proteinase was equally highly significantly (P < 0.001) inhibited by both iodoacetate and p‐chloromercuribenzoate and hydrolysed casein to give the following kinetic constants: K_m = 0.33 mg ml^?1; V_max = 0.08 µmol ml^?1 min^?1. Copyright © 2004 Society of Chemical Industry     

Additive manufactured bipolar plate for high-efficiency hydrogen production in proton exchange membrane electrolyzer cells

Additive manufacturing (AM) technology is capable of fast and low-cost prototyping from complex 3D digital models. To take advantage of this technology, a stainless steel (SS) plate with parallel flow field served as a combination of a cathode bipolar plate and a current distributor; it was fabricated using selective laser melting (SLM) techniques and investigated in a proton exchange membrane electrolyzer cell (PEMEC) in-situ for the first time. The experimental results show that the PEMEC with an AM SS cathode bipolar plate can achieve an excellent performance for hydrogen production for a voltage of 1.779 V and a current density of 2.0 A/cm². The AM SS cathode bipolar plate was also characterized by SEM and EDS, and the results show a uniform elemental distribution across the plate with very limited oxidization. This research demonstrates that AM method could be a route to aid cost-effective and rapid development of PEMECs.     

A jet fuel surrogate formulated by real fuel properties

An implicit methodology based on chemical group theory to formulate a jet aviation fuel surrogate by the measurements of several combustion related fuel properties is tested. The empirical formula and derived cetane number of an actual aviation fuel, POSF 4658, have been determined. A three component surrogate fuel for POSF 4658 has been formulated by constraining a mixture of n-decane, iso-octane and toluene to reproduce the hydrogen/carbon ratio and derived cetane number of the target fuel. The validity of the proposed surrogate is evaluated by experimental measurement of select combustion properties of POSF 4658, and the POSF 4658 surrogate.

(1)

A variable pressure flow reactor has been used to chart the chemical reactivity of stoichiometric mixtures of POSF 4658/O₂/N₂ and POSF 4658 surrogate/O₂/N₂ at 12.5 atm and 500-1000 K, fixing the carbon content at 0.3% for both mixtures.

(2)

The high temperature chemical reactivity and chemical kinetic-molecular diffusion coupling of POSF 4658 and POSF 4658 surrogate have been evaluated by measurement of the strained extinction limit of diffusion flames.

(3)

The autoignition behavior of POSF 4658 and POSF 4658 surrogate has been measured with a shock tube at 674-1222 K and with a rapid compression machine at 645-714 K for stoichiometric mixtures of fuel in air at pressures close to 20 atm.

The flow reactor study shows that the character and extent of chemical reactivity of both fuels at low temperature (500-675 K) and high temperature (900 K+) are extremely similar. Slight differences in the transition from the end of the negative temperature coefficient regime to hot ignition are observed. The diffusion flame strained extinction limits of the fuels are observed to be indistinguishable when compared on a molar basis. Ignition delay measurements also show that POSF 4658 exhibits NTC behavior. Moreover, the ignition delays of both fuels are also extremely similar over the temperature range studied in both shock tube and rapid compression machine experiments. A chemical kinetic model is constructed and utilized to interpret the experimental observations and provides a rationale as to why the real fuel and surrogate fuel exhibit such similar reactivity.     

Indoxylsulfate in milk

Indoxylsulfate in 27 individual milk samples ranged from 25.4 to 111 g/l (average 52.3 g/l); pooled milk samples from 12 farms contained 81.1 g/l (46.4–146 g/l); the variation in indoxylsulfate concentration of dried skimmed milk over a period of one year amounted to 23%. This variability is likely attributable to regional and seasonal, and hence to feeding effects. The indoxylsulfate content of milk seems also to be dependent upon the degree of fermentation during processing of milk; yoghurt contained very low amounts of this component (6.4 g/kg). On the other hand, heat treatment of the milk (HTST, UHT, sterilization) apparently does not affect its indoxylsulfate content. Indoxylsulfate concentrations in milk correlated positively with blood-serum indoxylsulfate content (r=0.752,n=20) and with the urea content of milk (r=0.61,n=12 pooled milks). Further research is suggested on the use of indoxylsulfate determinations as an aid to determine sweet whey added to dried skimmed milk, also as an analytical tool to differentiate bovine and sheep milks.

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Indoxylsulfat in Milch

Zusammenfassung In 27 individuellen Milchproben wurde ein mittlerer Gehalt an Indoxylsulfat von 52,3 g/l mit einem Bereich von 25,4 bis 111 g/l gefunden, bei Sammelmilchproben von 12 Höfen waren die Werte 81,1 g/l bzw. 46,4 bis 146 g/l. In Magermilchpulver variierte der Indoxylsulfatgehalt im Verlaufe eines Jahres um 23%. Die Variation ist auf regionale und saisonale fütterungsabhängige Effekte zurückzuführen. Der Gehalt an Indoxylsulfat wird auch durch Mikroorganismen beeinflußt. Joghurt enthielt nur 6,4 g/kg an Indoxylsulfat. Dagegen beeinflussen Erhitzungsprozesse den Gehalt nicht. Der Indoxylsulfat-Gehalt der Milch korreliert positiv mit dem des Blutserums (r=0,752,n=20) und dem Harnstoffgehalt der Milch (r=0,61,n=12). Es scheint möglich zu sein, den Indoxylsulfat-Gehalt der Milch zum Nachweis von Molke in Milchpulver zu nutzen Bowie zwischen Kuh- und Schafmilch zu unterscheiden.

     

Statistical studies of mortality and air pollution: Multiple regression analyses stratified by age group

Multiple regression analyses are presented relating age-specific mortality rates for up to 158 U.S. cities for 1969–1971 to community air pollution and socioeconomic variables, including an index of cigarette smoking. The results showed that excess mortality was associated with concentrations of airborne manganese and, to a lesser extent, total suspended particulates (TSP). The associations tended to be stronger for the older age groups (>65).In exploring these associations further, it was shown that the regression results were not inconsistent with a lag effect, i.e., that pollution from a 10 year or more earlier time period was implicated. Analysis for pollutant thresholds indicated none for manganese, but the suggestion of a no-effect threshold for TSP at 85–130 μg/m³.In contrast to some previous studies by other authors, no consistent (positive) associations were found between excess mortality and suspended sulfates.     

Statistical studies of mortality and air pollution multiple regression analyses by cause of death

Multiple regression analyses are presented relating community air quality, socio-economic variables, and mortality rates for all cancers, respiratory system cancer, respiratory disease, and external causes, for U.S. cities for 1969–1971. Socioeconomic variables included an index of cigarette smoking (by state), which was usually highly significant. Most air pollution variables were not significant, however, with the exception of the trace metal manganese, which was associated with cancers and respiratory disease. Because of the low ambient concentrations in this study, it is likely that manganese is serving as a surrogate for some other effect, such as occupational influences for example.     

Tethered methanol droplet combustion in carbon-dioxide enriched environment under microgravity conditions

Tethered methanol droplet combustion in carbon dioxide enriched environment is simulated using a transient one-dimensional spherosymmetric droplet combustion model that includes the effects of tethering. A priori numerical predictions are compared against recent experimental data. The numerical predictions compare favorably with the experimental results and show significant effects of tethering on the experimental observations. The presence of a relatively large quartz fiber tether increases the burning rate significantly and hence decreases the extinction diameter. The simulations further show that the extinction diameter depends on both the initial droplet diameter and the ambient concentration of carbon dioxide. Increasing the droplet diameter and ambient carbon dioxide concentration both of them lead to a decrease in the burning rate and increase in the extinction diameter. The influence of ambient carbon dioxide concentration on extinction shows a sharp transition in extinction for larger size droplets (d_o > 1.5 mm) due to a change in the mode of extinction from diffusive to radiative control. In addition predictions from the numerical model is compared against a recently developed simplified theoretical model for predicting extinction diameter for methanol droplets, where the presence and heat transfer contribution of the tether is not taken into account implicitly. The numerical results suggest some limitation in the theoretical modeling assumptions for favorable comparisons with the experimental data.     

A radical index for the determination of the chemical kinetic contribution to diffusion flame extinction of large hydrocarbon fuels

The extinction limits of diffusion flames have been measured experimentally and computed numerically for fuels of three different molecular structures pertinent to surrogate fuel formulation: n-alkanes, alkyl benzenes, and iso-octane. The focus of this study is to isolate the thermal and mass transport effects from chemical kinetic contributions to diffusion flame extinction, allowing for a universal correlation of extinction limit to molecular structure. A scaling analysis has been performed and reveals that the thermal and mass transport effects on the extinction limit can be normalized by consideration of the enthalpy flux to the flame via the diffusion process. The transport-weighted enthalpy is defined as the product of the enthalpy of combustion per unit mole of fuel and the inverse of the square root of fuel molecular weight. The chemical kinetic contribution provided by the specific fuel chemistry has thus been elucidated for tested individual component and multi-component surrogate fuels. A chemical kinetic flux analysis for n-decane flames shows that the production/consumption rates of the hydroxyl (OH) radical govern the heat release rate in these flames and therefore play significant roles in defining the extinction limit. The rate of OH formation has been defined by considering the OH concentration, flame thickness, and flow strain rate. A fuel-specific radical index has been introduced as a concept to represent and quantify the kinetic contribution to the extinction limit owing to the fuel-specific chemistry. A relative radical index scale, centered on the radical index of a series of n-alkanes which are observed and fundamentally explained to be common, is established. A universal correlation of the observed extinction limits of all tested fuels has been obtained through a combined metric of radical index and transport-weighted enthalpy. Finally, evidence as to the validity of the fundamental arguments presented is provided by the success of the universal correlation in predicting the extinction limits of the multi-component mixtures typical of surrogate fuels.