The oxygen uptake of suspensions and cultures of a free-living bacterium

RESP-206

The isolation of Nitrosomonas europaea in pure culture

RESP-288

Iron and the nitrifying bacteria

RESP-317

Soil microbiology

RESP-385

Skeleton Cave, Leigh Woods, Bristol

An account is given of the discovery and excavation of this small cave in the 1960s. It is recorded that archaeological finds were made, but of these, only a single human mandible can now be traced. Radiocarbon dating shows the specimen to be early Neolithic in age; a metrical analysis was less conclusive.http://www.ubss.org.uk/resources/proceedings/vol27/UBSS_Proc_27_2_197-209.pd

Simple mechanism for a positive exchange bias

We argue that the interface coupling, responsible for the positive exchange bias (HE) observed in ferromagnetic/compensated antiferromagnetic (FM/AF) bilayers, favors an antiferromagnetic alignment. At low cooling field this coupling polarizes the AF spins close to the interface, which spin configuration persists after the sample is cooled below the Neel temperature. This pins the FM spins as in Bean's model and gives rise to a negative HE. When the cooling field increases, it eventually dominates and polarizes the AF spins in an opposite direction to the low field one. This results in a positive HE. The size of HE and the crossover cooling field are estimated. We explain why HE is mostly positive for an AF single crystal, and discuss the role of interface roughness on the magnitude of HE, and the quantum aspect of the interface coupling.Comment: 10 pages, 2 figures, to be published on May 1 issue of PR

Observations on the Oxygen Uptake of Isolated Plant Tissue: I. The Effect of Phosphate and of Added Carbohydrate

RESP-210

Observations on the Oxygen Uptake of Isolated Plant Tissue: II. The Effect of Inhibitors

RESP-210

Genetic polymorphisms, platelet activation and plasma homocysteine concentrations in atherothrombotic stroke

Atherothrombotic stroke arises following rupture of an atheromatous plaque, and occlusion occurs directly due to thrombosis in small arteries, or indirectly by embolisation if a large vessel plaque ruptures. Three risk factors that are claimed to influence these process were investigated. The influence of platelet activation and genetic polymorphisms of platelet membrane glycoproteins on the risk of thrombotic stroke was assessed. Following plaque rupture, platelets have a pivotal role in arterial thrombus formation, and platelet membrane glycoproteins (GP) IIIa (the fibrinogen receptor) and Ib (which binds von Willebrand factor) are crucial in this process. The lb allele of the HPA 1a/1b GPIIIa polymorphism and the 2b allele of the HPA 2a/2b GPIb polymorphism are claimed to be risk factors for stroke and myocardial infarction (MI), but reports are conflicting and consistent functional evidence of enhanced thrombogenicity is lacking. Increased factor VII activity (VIIc) has been claimed to be a risk factor for MI and stroke, but the data are conflicting. VIIc is dependent on both environmental and genetic influences, and recently two polymorphisms of the factor VII gene associated with lower VIIc have been claimed to be protective against MI. A raised plasma homocysteine concentration has been proposed as a cause for atherosclerosis. However the role of homocysteine in stroke aetiology remains controversial, since prospective studies have reported a weaker association than those conducted retrospectively. Furthermore there are few reports of plasma homocysteine concentrations both before and after the event. The following studies were conducted to address these issues: An investigation of the effect of HPA la/lb genotype on platelet fibrinogen binding by whole blood flow cytometry in healthy subjects. The effect of the lb allele on platelet fibrinogen binding was investigated in healthy subjects by whole blood flow cytometry. 35 platelet or plasma donors (34 HPA 1a/1b and one HPA 1b/1b) possessing the lb allele were compared with 35 donors homozygous for the la allele. There was no allele dependent difference in the percentage of platelets binding fibrinogen at baseline (p=0.14, Mann Whitney U test) or following stimulation with ADP (p=0.72, Student's t-test). An paradoxical increase in the density of fibrinogen binding sites was observed in la platelets after ADP stimulation (p=0.05, Mann Whitney U test), 1b platelets tended to exhibit greater activation as assessed by the percentage of platelets expressing P-Selectin, but this did not reach statistical significance (p=0.08, Mann-Whitney U test). These data do not identify a functional mechanism by which the 1b allele might mediate an increased risk of arterial thrombosis. (Abstract shortened by ProQuest.)

Metastable Random Field Ising model with exchange enhancement: a simple model for Exchange Bias

We present a simple model that allows hysteresis loops with exchange bias to be reproduced. The model is a modification of the T=0 random field Ising model driven by an external field and with synchronous local relaxation dynamics. The main novelty of the model is that a certain fraction f of the exchange constants between neighbouring spins is enhanced to a very large value J_E. The model allows the dependence of the exchange bias and other properties of the hysteresis loops to be analyzed as a function of the parameters of the model: the fraction f of enhanced bonds, the amount of the enhancement J_E and the amount of disorder which is controlled by the width sigma of the Gaussian distribution of the random fields.Comment: 8 pages, 11 figure