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Rubbers and elastomers will change their material properties due to environmental influences such as temperature, oxygen, radiation and similar conditions. The reason for this material change is the modification of the polymer network. In the case of sulphur cured natural rubber it can result in hardening of the material and pronounced surface hardening for thick walled products. This is known as the diffusion limited oxidation effect when oxidation is the key environmental influence. This paper describes a model which is designed to calculate the change in network density caused by thermo-oxidative aging and the required measurements for the parameterisation. The model is validated by simulating the intermediate stress relaxation experiments and showed good correlation with the experimental data.

The membrane lipid fluidity of normal human erythrocytes was modified by enrichment and depletion in cholesterol, and the expression of I and SP1 antigens was assayed by quantitative hemagglutination from 4 degrees to 24 degrees C by use of a continuous flow system. Below 16 degrees--18 degrees C, cholesterol enrichment increased and cholesterol depletion decreased percent agglutination. As temperatures approached approximately 18 degrees--20 degrees C, differences in agglutination between modified and unmodified erythrocytes became insignificant despite marked differences in lipid fluidity at that temperature. Thus, fluidity changes alone cannot be responsible for the effect of membrane cholesterol on cold agglutination. In an additional study, the temperature dependence of a relative equilibrium association constant, estimated by probit analysis of percent agglutination at various antisera concentrations, was biphasic with a sharp break at 16 degrees C. Our studies are consistent with the hypothesis that I and Sp1 antigens preferentially partition into a lipid domain that forms during lateral phase separation of membrane lipid developing at low temperature. A resulting increase in antigen density would then become responsible for augmented agglutination by specific antibody.

Sulfhydryl substituents of the hexose transport mechanism of human erythrocyte membranes were studied with membrane-impermeant and -permeant maleimide derivatives. Three sulfhydryl classes have been identified on the basis of their reactivity toward the reagents and their effects on the transport mechanism. Type I sulfhydryl is located at the outer (exofacial) surface of the membrane and bound covalently on treatment of intact cells with the membrane-impermeant glutathione-maleimide. This sulfhydryl is required for the transport, and it is protected from alkylation, i.e., its reactivity toward maleimides is decreased by the presence of D-glucose or cytochalasin B. Type II sulfhydryl is also required for the transport, but it differs from type I in that D-glucose (but not cytochalasin B) increases the reactivity toward maleimides. Further, it is located at the endofacial surface of the membrane, since reaction with glutathione-maleimide occurs only in leaky ghosts and not in intact cells. Alkylation by glutathione-maleimide of type I and type II sulfhydryls increases the half-saturation for the binding of D-glucose to erythrocyte membranes. In contrast, inactivation of type III sulfhydryls by N-ethylmaleimide or dipyridyl disulfide decreases the half-saturation concentration for the binding of D-glucose and other transported hexoses to the membranes; nontransported sugars are not affected similarly. Type III sulfhydryl is not inactivated by the polar reagent glutathione-maleimide and is probably located in a nonpolar domain of the transport mechanism. Inactivation of either type I or II sulfhydryls decreases or eliminates the flux asymmetry of the hexose transport mechanism.

To date, DNA-binding factors with a developmental pattern of expression have not been described in human erythroid cells to explain the switch from fetal (gamma-) to adult (delta- and beta-) globin gene expression. Here we describe a factor present in nuclear extracts from adult mouse and human hematopoietic cells that binds to an oligopyrimidine repeat approximately 960 base pairs upstream from the human delta-globin gene. The binding site for the factor is within an unusual 250-base-pair domain that is greater than 95% pyrimidines on one strand. This domain is preferentially sensitive to S1 nuclease in supercoiled plasmids, indicating that it can adopt an alternative non-B-DNA conformation. A number of S1-sensitive sites within the domain, including the factor-binding site, have sequence characteristics associated with the formation of a triple helix (H-DNA). The position of the binding site between the fetal and adult beta-globin-like genes, its potential for adopting an unusual secondary structure, and the restricted activity of the binding factor to adult hematopoietic tissues suggest possible roles in hematopoietic cell development and hemoglobin switching.

Previews the summer 1992 crop of movies from Hollywood. `Lethal Weapon 3,' starring Mel Gibson and Danny Glover; `Encino Man,' starring MTV's Pauly Shore; `Far and Away,' starring Tom Cruise and Nicole Kidman; More; Comments on the diversity of the season's offerings. INSET: Lori Petty (profile), by A. Berger; Sarah Jessica Parker....

Discusses this summer's action films. `RoboCop 2'; `Air America'; `Flatliners'; Actors Peter Weller, Robert Downey Jr., Kiefer Sutherland and Danny Glover; More.

The article presents information about the book "Philip Larkin: Collected Poems," edited by Antony Thwaite. The graceful but forgettable early work that has been tucked in at the back of the Collected Poems reveals an unearthly soul prematurely despairing of love and life. The book, with the works dated on the bottom and arranged chronologically, has none of the dramatic tension or thematic arguments the scholar Philip Larkin's own arrangements convey, making it useful mainly for those readers already familiar with him.

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Profiles Ben Cheever, 44, the son of the much-decorated novelist and short-story master John Cheever, who has joined the family business by writing a charming first novel, `The Plagiarist.' Struggle to write fiction all his life; Comments on father.