Use of an improved internal-standard method in the quantitative sterol analyses of phytoplankton and oysters

Most work reporting the sterol composition of living organisms has not been done quantitatively, although good quantitative data are available for fatty acids and many other cellular components using an internal-standard method that compensates for errors during gas chromatographic analysis. In this paper, we report on the use of 7-stigmastenyl acetate as an internal standard for sterol analysis in two species of phytoplankton and oysters produced with two different diets. This internal-standard method provides an internal standard for this entire process of analysis, not just the gas chromatographic analysis. When analyzing 50-μg samples of cholesterol acetate after hydrolysis and acetylation, about 30% of the sample was lost, resulting in a 30% error using the older external-standard method. Using the internal-standard method, the analysis error was less than 2%. Losses of sterol during analysis apparently are greater with plant and animal samples than with pure sterol standards. This internal-standard method was shown to be extremely useful, especially for samples with less than 500 μg of sterol. Finally, the standard error in sterol analysis is much lower when the internal-standard, method is used, allowing statistical distinctions that are not possible otherwise. Use of 7-stigmastenyl acetate as an internal standard offers several advantages over the use of cholestane.     

In situ production of nickel/graphitic carbon nanofiber composites and application in catalytic hydrodechlorination

The action of Ni/SiO₂ in the gas phase hydrodechlorination (at 573 K) of chlorobenzene, 1,3-dichlorobenzene and 1,3,5-trichlorobenzene is compared with that of a Ni/SiO₂ + C composite. The latter was prepared in situ by the decomposition of chlorobenzene at 873 K to generate graphitic carbon nanofibers bearing Ni particles at the fiber tips. The Ni/SiO₂ and Ni/SiO₂ + C (with varying C content) catalysts have been characterized by TEM, SEM, XRD and H₂ chemisorption. While the Ni/SiO₂ + C system delivered a lower initial fractional dechlorination, the composite outperformed the starting Ni/SiO₂ in terms of long-term activity, an effect that is linked to the structural characteristics.     

Study of an air-lift system. Part I: Hydrodynamics of the atara piston bubble cannon mixer

Hydrodynamic studies of the two-phase flow of air-water mixtures were carried out in an innovative air-lift system called the “Atara Piston Bubble Cannon Mixer”. Slug and churn flows were observed in the discharge tube. The bubble velocity in the slug flow regime and the pressure drop were measured. Bubble entrance effects, found to affect the pressure drop particular to this configuration, are explained The air-lift pump performance is analysed and a hydrodynamic model is developed to predict the pumping capacity as a function of the gas flow rate.     

Morphological characterization of simulated polymer blends by light scattering

The morphology and the properties of polymer blends are closely related to processing conditions. A skin/core morphology, with a minor phase undergoing variations in orientation and aspect ratio from the surface to the core of the material is observed in processes such as the injection molding of blends. The use of optical inspection to control the stability and the quality of the product on-line is an interesting tool. In this paper, polymer composites made from glass fibers and glass microspheres embedded in a matrix of PS are used to simulate two-phase polymer blend morphology with a skin/core configuration. The relationships between the morphology of two-phase systems and the diffuse pattern scattered from an incident light beam are investigated through an analysis of the iso-intensity plots. Information can be obtained from the ratio of the axes of the ellipsoidal iso-intensity domains for depth-invariant blend morphology, and from the variation of this ratio as a function of the distance from the center of the pattern for depth-varying morphology samples. It is shown that one can differentiate the skin morphology and thickness effects.     

Frequency of Pore Location in Sintered Al2O3

The relative frequencies of pore location on grain corners, edges, and surfaces in final stage sintering have been measured in both pure and MgO-doped Al₂O₃. Both materials showed identical location frequencies, with an average of 58% of the pores on grain corners, 29% on grain edges, and 13% on grain surfaces, over a density range from 92% to > 99% of full density.     

AY-9944 inhibition of sterol biosynthesis inChlorella emersonii

WhenChlorella emersonii, a green alga, was cultured in the presence of 20 ppm AY-9944, a number of sterols accumulated which appear to be intermediates of sterol biosynthesis in this organism. The sterols isolated include 14α-methyl-ergost-8-en-3β-ol, 14α-methyl 24S-stigmast-8-en-3β-ol, 14α-methyl ergosta-8,24(28)-dien-3β-ol and 4α, 14α-dimethyl 24S-stigmast-8-en-3β-ol. Smaller quantities of several other sterols were found in addition to the normally occurring Δ⁷, chondrillasterol and Δ⁷. Control cultures were found to contain, in addition to the normally occurring sterols, smaller quantities of most of the sterols isolated from AY-9944 inhibited cultures. AY-9944 is a specific inhibitor of Δ⁷ in cholesterol biosynthesis in animals. However, sinceC. emersonii terminates sterol biosynthesis one step prior to the Δ⁷ step, AY-9944 apparently inhibits sterol biosynthesis prior to this step in this organism. The accumulation of 14α-methyl sterols in treated cultures suggests that AY-9944 is an effective inhibitor of the 14α-methyl removal inC. emersonii. Scientific Article No. A1865, Contribution No. 4775 of the Maryland Agricultural Experiment Station.     

Quantification of Grain Boundary-Pore Contact During Sintering

A stereological method has been used to determine the degree of grain boundary-pore contact during sintering of Al₂O₃. Al₂O₃ doped with 200 ppm MgO exhibits a degree of contact of 5.7 times that expected from random intersections with pores, while pure Al₂O₃ shows a pore contact factor of 4.8. These data are larger than the values of 2.8 for sintered or hot-pressed UO₂, computed from published data, and values of 1.7 and 1.8 for sintered W and Cu powders, respectively. The degree of grain boundary-pore contact for each material remains constant throughout densification from pressed powder to near full density.     

Physicochemical Properties of Calcium Caseinate Films Cross-Linked by Gamma-Irradiation

Gamma-irradiation was used to produce freestanding, sterilized, cross-linked caseinate films and gels. Mechanical properties of gels and films and water vapor permeability of dried films were determined. Irradiated films were significantly ( p ≤0.05) more resistant to puncture and moisture. Also, gels were formed when protein solutions received radiation doses ≥16 kGy. The addition of CaCl 2 in the solution containing proteins, glycerol, and carboxymethylcellulose (base formulation) increased significantly the puncture strength for the films atirradiation doses ≥16 kGy. Sorbitol had the greatest plasticizing effect andsignificantly ( p ≤0.05) increased distance to puncture, while mannitoldecreased distance to puncture. Size-exclusion chromatography performed on the irradiated solutions of the base formulation showed that gamma-irradiation increased the molecular weight of calcium caseinate by 100 times; the molecular weight was ≥2×10 3 kDa. Films produced with base formulation were alsoimmersed in flasks containing 100mL of boiling water during 30 min forinsolubility measurements. Results showed that the proportion of the insolublefraction increased with the irradiationdose. Seventy percent of the irradiated films (32 kGy) remained insoluble after immersion in water at 100°C, 30 min and 20°C, 24 h. Water vapor permeability (WVP) of the base formulation films was reduced from 3.99±0.23 to 2.57±0.63 g.mm/m 2 .d.mmHg after irradiationtreatment. Microbial resistance of cross-linked films (base formulation)showed that 36% of N from calcium caseinate films was converted to soluble N after 60 d in presence of Pseudomonas aeruginosa .     

Gas and particle flow patterns in cyclones at room and elevated temperatures

Experimental results are presented for a study of gas and particle flows in a 102 mm diameter conventional cyclone operated at temperatures between 300 and 2000 K. Inlet gas velocities ranged from 3 to 42 m/s. Particle deposition patterns and the measurements of local pressures were used to determine the flow patterns and velocity profiles within the cyclone. A “Reynolds Number” has been defined based on the mean inlet velocity and the hydraulic diameter of the annulus between the cyclone wall and the gas outlet duct. An empirical equation was derived to correlate the ratio of the wall tangential velocity to the mean inlet velocity with this Reynolds Number.     

A simple model for non-linear stress relaxation

A simple model for the prediction of non-linear stress relaxation following the cessation of steady shear flow is proposed. The model allows the calculation of the shear and first normal stress difference components of the stress. The mathematical flexibility of the model is reduced to a minimum with the result that no adjustable parameters are employed and only linear dynamic deformation data are required to calculate the non-linear behaviour. Verification of the model was carried out with data available for two viscoelastic fluids and good agreement between the predictions and the experimental results was obtained for the range of shear rates examined (0.167 ? γ ? 16.7 sec^?1).