Two-dimensional modelling of some CFC replacement compounds

The Cambridge 2-D Eulerian model has been used to study the potential atmospheric distributions and lifetimes of a number of CFC replacement compounds and their degradation products. The study has focused on HFC 134a and HCFCs 123, 141b and 142b and the major products formed by their atmospheric degradation. The loss of these compounds and their products by hydroxyl radical attack, photolysis and in-cloud hydrolysis have been investigated. The study has shown that HCFCs 141b and 142b have sufficiently long lifetimes to enter the stratosphere in significant quantities, where degradation leads to an increase in the total stratospheric chlorine concentration. The study has also highlighted areas where further experimental work would be valuable, in particular characterisation of the product channels for the degradation reactions and determination of the removal rates of the products in the aqueous phase.     

Holocene Environmental Change and River-Mouth Sedimentation in the Baie des Anges, French Riviera

River mouths on the steep, high-relief coast of the French Riviera exhibit thick sequences of Holocene marine, estuarine, deltaic, and river channel-floodplain sediments that overlie basal fluvial Pleistocene gravel. Gravel is uncommon in most of the early to middle Holocene aggradational-progradational marine, estuarine, deltaic sediments, despite an ample supply from rock units in the steep adjoining uplands. River-mouth gravel is common only in late Holocene river channels and in barrier beaches perched on finer-grained nearshore sediments. Neither downslope grain-size fining on alluvial fans nor sediment stacking patterns during sea-level (base-level) rise readily account for the lack of early to middle Holocene gravel in the river-mouth sediment wedges. Holocene sea-level rise led to the storage of fine-grained sediments in shallow marine, estuarine, and deltaic environments in the present coastal zone. We infer that humid temperate conditions, a dense forest cover, landscape stabilization, and a regular quiescent river flow regime associated with the Atlantic climatic optimum limited gravel supply in the adjoining catchments and gravel entrainment downstream during the early Holocene. Sea-level stabilization in the middle and late Holocene coincided with a marked change in bioclimatic conditions toward the present Mediterranean-type regime, which is characterized by a less dense forest cover, soil erosion, and episodic catastrophic floods. The late Holocene was thus a time of downstream bedload channel aggradation, fine-grained floodplain and paludal sedimentation, and seaward flushing of clasts leading to the formation and consolidation of the gravel barrier beaches that bound the rivermouths and embayments.     

The relationship between geothermal gradient and the composition of granitic magmas in orogenic belts

A comparison has been made between the average compositions of the granites in the Variscan, Caledonian, and Alpine orogenic belts of western Europe. Their respective compositions lie near the isobaric minima in the system Q-Or-Ab-H₂O for successively higher water pressures, whereas metamorphic facies series indicate that the three orogenic belts developed under successively lower geothermal gradients. These relationships are consistent with an origin of the granitic magmas by partial melting in the crust.     

Average chemical composition of the lunar surface

The available data on the chemical composition of the lunar surface at eleven sites (3 Surveyor, 5 Apollo and 3 Luna) are used to estimate the amounts of principal chemical elements (those present in more than about 0.5% by atom) in average lunar surface material. The terrae of the Moon differ from the maria in having much less iron and titanium and appreciably more aluminum and calcium.Paper dedicated to Prof. Harold C. Urey on the occasion of his 80th birthday on 29 April 1973.     

Finite element models for rock fracture mechanics

A finite element model for the prediction of discrete fracture propagation in rock structures loaded in compression is presented. The model integrates any one of three theories for mixed-mode fracture initiation; it contains an energy balance algorithm for predicting crack increment length, and incorporates recent developments in finite element stress-intensity factor computation. The predictions of the model are compared with the observed fracture response of a real rock structure. Results show that the model accurately predicts both stable and unstable fracture progagations observed experimentally.     

An evaluation of hemolymph cholinesterase activities in the tropical scallop,Euvola (Pecten) ziczac,for the rapid assessment of pesticide exposure

The use of sequential measurements of hemolymph cholinesterase activities as a non-invasive biomarker of seasonal organophosphate/carbamate exposure was investigated for the tropical scallop, Euvola (Pecten) ziczac. Overall activities of both acetylcholinesterase and butyrylcholinesterase were relatively high compared to studies with bivalve tissues. Acute in vivo experiments showed inhibition of hemolymph acetylcholinesterase activity at concentrations of the organophosphate insecticide chlorpyrifos of 0.1, 1 and 10 ng l(-1). Monthly sampling of hemolymph from scallops at two sites in Bermuda over a 15 month period showed seasonal acetylcholinesterase and butyrylcholinesterase inhibition. Direct and indirect evidence suggests that this inhibition did not relate to biochemical or physiological changes associated with gonad maturation and spawning, but rather reflected diffuse contamination of the marine environment by cholinesterase inhibitors or increased bioavailability of such inhibitors at these times. Repetitive sampling of scallop hemolymph for cholinesterase activities represents a rapid, sensitive and non-invasive method for assessing seasonal, sublethal pesticide exposure in these commercially important bivalves and suggests a wider use in marine pollution monitoring.     

Ferrihydrite dissolution by pyridine-2,6-bis(monothiocarboxylic acid) and hydrolysis products

Pyridine-2,6-bis(monothiocarboxylate) (pdtc), a metabolic product of microorganisms, including Pseudomonas putida and Pseudomonas stutzeri was investigated for its ability of dissolve Fe(III)(hydr)oxides at pH 7.5. Concentration dependent dissolution of ferrihydrite under anaerobic environment showed saturation of the dissolution rate at the higher concentration of pdtc. The surface controlled ferrihydrite dissolution rate was determined to be 1.2 × 10⁻⁶ mol m⁻² h⁻¹. Anaerobic dissolution of ferrihydrite by pyridine-2,6-dicarboxylic acid or dipicolinic acid (dpa), a hydrolysis product of pdtc, was investigated to study the mechanism(s) involved in the pdtc facilitated ferrihydrite dissolution. These studies suggest that pdtc dissolved ferrihydrite using a reduction step, where dpa chelates the Fe reduced by a second hydrolysis product, H₂S. Dpa facilitated dissolution of ferrihydrite showed very small increase in the Fe dissolution when the concentration of external reductant, ascorbate, was doubled, suggesting the surface dynamics being dominated by the interactions between dpa and ferrihydrite. Greater than stoichiometric amounts of Fe were mobilized during dpa dissolution of ferrihydrite assisted by ascorbate and cysteine. This is attributed to the catalytic dissolution of Fe(III)(hydr)oxides by the in situ generated Fe(II) in the presence of a complex former, dpa.