Acrylonitrile-based copolymers: Synthesis,characterization, and formation of ultrafiltration membranes utilized for the immobilization of proteins

Various high molecular weight copolymers of acrylonitrile and a vinyl comonomer containing an aryl amine, a pyridine, or an aliphatic hydroxyl group were synthesized via slurry polymerization techniques so as to contain from 1 to 15 mol % functional comonomer. The comonomer content was quantitated by ultraviolet absorbance, base titration of acid polymer salts, and/or relative chemical reactivity with trichloro-s-triazine. Thin films were cast from copolymer solutions, coagulated into unsupported ultrafiltration membrances, and characterized with respect to both water permeability and pore size distribution. Analysis by size exclusion chromatography of the membrane permeate of a pool of dextran fractions yielded a continuous distribution curve for membrane pore size over the range 1.5 to 70 nm. The ultrafiltration membranes were used for protein immobilization after appropriate chemical activation. The three distinct types of functional copolymers gave comparable results for α-chymotrypsin, with protein weight loadings of 6–12% and 40–65% retention of enzymatic specific activity.     

How social comparison mediates the relation between ability-grouping practices and students' achievement expectancies in mathematics.

This investigation tested the hypothesis that social comparison processes mediate the relation between ability-grouping practices in mathematics and students' achievement expectancies in a district-wide sample of 6th graders (N?=?452). Compared with between-classroom ability grouping, within-classroom grouping raises high achievers' achievement expectancies, math grades, and tendency to make downward comparisons (i.e., with a classmate who is worse at math). Within-classroom grouping lowers low achievers' expectancies and math grades and increases their tendency to make upward comparisons. When controls for the direction of students' social comparison choices and for their mathematics grades are introduced, the independent effect of ability grouping on achievement expectancies is consistently and substantially reduced. It is argued that ability-grouping practices constrain the choices available to students and teachers for social comparison of abilities and thereby influence the frame of reference students use for self-assessment and teachers use for assigning grades. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effect of Contact Residual Stress Relaxation on Fracture Strength of Indented Soda-Lime Glass

The strength of Vickers-indented soda-lime glass measured in air at room temperature steadily increases with time after indentation, whereas optical retardation steadily decreases in the same interval. Annealing after indentation causes further strength increase and retardation decrease. The results are consistent with Marshall and Lawn's treatment of the slow crack growth of indentation flaws driven by the combined influence of residual contact stress and applied stress. Post-indentation strengthening of indentation flaws can be explained without recourse to flaw blunting.     

Synthesis of Si3N4 with Emphasis on Si-S-N Chemistry

Industrial production of Si₃N₄ from SiCI₄, is increasing. An element rivaling CI in abundance and cheapness with potentially suitable chemistry for this application is sulfur. Thus, Si–S–N chemistry was investigated to determine its usefulness in producing Si₃N₄. Bifunctionality in S, as opposed to mono-functionality in CI, may allow special routes via polymers to become important.     

Segregation of Isovalent Impurity Cations at the Surfaces of MgO and CaO

Enthalpies of segregation for isovalent impurities in magnesium and calcium oxide as a function of surface concentration were calculated by using an atomistic computer simulation method. We have considered Be²⁺, Mg²⁺, Ca²⁺, Ba²⁺, and Ni²⁺, segregating to both (001) and (110) faces. The results obtained can be extrapolated to predict the behavior of other impurities including Mn²⁺, Fe²⁺, and Co²⁺, We find, for example, that Fe²⁺, Mn²⁺, Ca²⁺, Sr²⁺, and Ba²⁺ will concentrate at the (001) surface of MgO, while Ni²⁺ will be depleted. The enthalpy of segregation is found to vary substantially with coverage particularly for the larger impurities. The enthalpy becomes less negative with increasing impurity concentration due to the increasing lattice strain until the surface is nearly saturated. Then additional stabilization is obtained by restructuring of the surface layer. We predict reconstructed surfaces for both the (001) and (110) faces, which contain a high concentration of a larger impurity ion. The enthalpy of segregation shows a maximum at around 50% surface coverage implying a bimodal surface distribution of segregant. The influence of segregation on surface energy suggests two unusual effects. The (001) surface energy of the impure crystal becomes negative for surface concentrations of impurity greater than 10% Ba²⁺ or 75% Sr²⁺ in MgO. This implies a thermodynamic barrier to sintering. At high coverages of Ba²⁺ in MgO the (110) surface becomes more stable than the (001) face suggesting that facetting may occur.     

Experimental Study of Porous Gel Sintering

Formation and disappearance of closed pores in silica gel during sintering were experimentally detected using a light-scattering technique. The disappearance of closed pores is strongly influenced by the atmosphere in which the gel is sintered.     

Factors affecting cloud point analysis of palm oleins

Some of the factors affecting cloud point determination of palm oleins are described. These are the type of container used, method of stirring, rate of stirring and bath temperature. The repeatability and reproducibility standard deviations of the method are determined from collaborative trials. Recommendations for the test are made to reduce the large variations among laboratories.