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Biomedical subjects

H H Robinson

Publications and source records attributed to H H Robinson.

8 recordsLinked to original sources
PubMed1986

Fracture toughness of Kevlar 29/poly(methyl methacrylate) composite materials for surgical implantations.

A study of the fracture behaviour of Kevlar 29 reinforced dental cement is undertaken using both linear elastic and nonlinear elastic fracture mechanics techniques. Results from both approaches--of which the nonlinear elastic is believed to be more appropriate--indicate that a reinforcing effect is obtained for the fracture toughness even at very low fibre content. The flexural strength and modulus are apparently not improved, however, by the incorporation of Kevlar 29 fibres in the PMMA cement, probably because of the presence of voids, the poor fibre/matrix interfacial bonding and unsatisfying cement mixing practice. When compared to other PMMA composite cements, the present system appears to be probably more effective than carbon/PMMA, for example, in terms of fracture toughness. More experimental and analytical work is needed so as to optimize the mechanical properties with respect to structural parameters and cement preparation technique.

Biomedical Engineering↗
PubMed1980

NMR relaxivity changes in chloroplast suspensions. Effects of NH2OH and of treatments altering the redox state of the photosynthetic electron transport chain.

Treatments (illumination, chemical oxidation or reduction) which are potentially capable of producing paramagnetic centers in chloroplast thylakoid membranes do not produce enhancements of the proton magnetic relaxivities of these preparations. However, exposure of thylakoid membranes to varying concentrations of hydroxylamine induces a time-dependent increase in relaxivity for which the steady-state magnitude is dependent on hydroxylamine concentration. The appearance of relaxivity is correlated kinetically with inactivation of oxygen-evolving centers; in addition both processes show a threshold effect with respect to hydroxylamine concentration. Kinetic analyses of these hydroxylamine-induced effects suggest that at low (less than or equal to 100 microM) and at intermediate (200--500 microM) concentrations, hydroxylamine extraction is partially counteracted by a reverse process that reactivates oxygen-evolving centers in the dark.

Chloroplasts↗
PubMed1980

Cyclic photophosphorylation reactions catalyzed by ferredoxin, methyl viologen and anthraquinone sulfonate. Use of photochemical reactions to optimize redox poising.

The flavin analogue 5-deazariboflavin is a convenient catalyst for the photoreduction of low-potential redox compounds. In an anaerobic medium with Tricine buffer as the electron donor, 5-deazariboflavin is capable of photo-reducing both ferredoxin and methyl viologen. We have used this method to conduct a comparative study of the Photosystem I photophosphorylation activities supported by the reduced forms of ferredoxin, methyl viologen and anthraquinone sulfonate. All of these catalysts are capable of generating high rates (200-500 mumol ATP/h per mg chlorophyll) of cyclic photophosphorylation, but only the activity dependent on ferredoxin exhibits sensitivity to antimycin A. This finding suggests that the size of the catalyst and its ability to approach the thylakoid membrane, rather than low-redox potential, governs antimycin A sensitivity. Ferredoxin-catalyzed activity is, however, less sensitive to inhibition by dibromothymoquinone than are the activities supported by methyl viologen and anthraquinone sulfonate. This discrepancy is due to binding of the inhibitor by ferredoxin.

Anthraquinones↗