Mechanisms of paramagnetic relaxation

An experimental study has been made of the paramagnetic spin-lattice relaxation properties of some transition metal ions. Three trivalent metal ions were studied, namely those of titanium, chromium and ruthenium, in the form of acetyl-acetonate compounds of the general formula M (C(_5)H(_7)Q(_2))(_3). By the use of the corresponding diamagnetic aluminium or cobalt compounds, mixed single crystals were grown with various paramagnetic concentrations. Measurements were made at low temperatures in the liquid helium range, at X band microwave frequencies (9.3 KMc/s). Some measurements were also made at higher microwave frequencies (35.5 KMc/s).In all cases the relaxation behaviour observed in magnetically dilute crystals is in good agreement with the well established theories relating to single ion relaxation. Particular attention has been given however to the study of the relaxation processes in more concentrated crystals, where concentration dependent relaxation is found. The results obtained have been compared with the two theoretical suggestions that have been proposed to account for these effects. Although neither proposal is entirely satisfactory, the one involving exchange interactions within paramagnetic ion clusters is shown to account in a qualitative way for the observed behaviour. A detailed study of the E.F.R. spectrum of chromium doped crystals has been made which shows that significant exchange interactions do exist in these materials

An Overview of Partnerships: An Alternative to Traditional Planning

Overview of Partnership

An Overview of Partnerships: An Alternative to Traditional Planning

Overview of Partnership

Predicting iron and folate deficiency anaemias from standard blood testing: the mechanism and implications for clinical medicine and public health in developing countries

BACKGROUND: Developing countries have high prevalence of diseases, but facilities to diagnose and treat them are limited. We must use available resources in ways not needed where there are sophisticated equipment and trained staff. Anaemia is common; iron deficiency affects health and productivity; folate deficiency in pregnant women causes foetal abnormalities. Few developing countries can measure serum folate or ferritin, but standard automated blood analyses are widely available and can help predict folate and iron deficiency. The RDW-CV% (coefficient of variation of the red cell width) measures the variability in the size of red blood cells (RBC) in routine automated analysis of blood cells, but is seldom reported. Levels of RDW-CV% and haemoglobin (Hb) can predict iron deficiency anaemia. METHOD AND RESULTS: I have written a computer model based on the standard mechanism for blood formation and destruction. This shows that before anaemia develops and during recovery, there are both normal and abnormal RBC (small in iron deficiency and large in folate deficiency) in the circulation. The model calculates the abnormality in the RDW-CV% in standard automated blood analyses. In early iron deficiency and during recovery the full blood count shows the Hb near the lower limit of normal, a low MCV and a high RDW-CV%. A similar pattern, but with a higher MCV, develops in folate deficiency. Folate deficiency is often brief and may not cause anaemia. The high RDW-CV% may persist for three months. CONCLUSION: This long footprint could be medically useful for detecting folate deficiency and so limiting foetal damage in individuals and communities. Few clinicians or public health workers know about RDW-CV%. Standard blood reports for clinical use should include the RDW-CV% and note the possible significance of abnormal values

Probing the Fermi surface by positron annihilation and Compton scattering

Positron annihilation and Compton scattering are important probes of the Fermi surface. Relying on conservation of energy and momentum, being bulk sensitive and not limited by short electronic mean-free-paths, they can provide unique information in circumstances when other methods fail. Using a variety of examples, their contribution to knowledge about the electronic structure of a wide range of materials is demonstrated

Fermi surface of the colossal magnetoresistance perovskite La_{0.7}Sr_{0.3}MnO_{3}

Materials that exhibit colossal magnetoresistance (CMR) are currently the focus of an intense research effort, driven by the technological applications that their sensitivity lends them to. Using the angular correlation of photons from electron-positron annihilation, we present a first glimpse of the Fermi surface of a material that exhibits CMR, supported by ``virtual crystal'' electronic structure calculations. The Fermi surface is shown to be sufficiently cubic in nature that it is likely to support nesting.Comment: 5 pages, 5 PS figure

Three-dimensional in situ observations of compressive damage mechanisms in syntactic foam using X-ray microcomputed tomography

Royal Society Grant number RG140680 Lloyd's Register Foundation (GB) Oil and Gas Academy of Scotland Open access via Springer Compact AgreementPeer reviewedPublisher PD

Critical examination of cohesive-zone models in the theory of dynamic fracture

We have examined a class of cohesive-zone models of dynamic mode-I fracture, looking both at steady-state crack propagation and its stability against out-of-plane perturbations. Our work is an extension of that of Ching, Langer, and Nakanishi (CLN) (Phys. Rev. E, vol. 53, no. 3, p. 2864 (1996)), who studied a non-dissipative version of this model and reported strong instability at all non-zero crack speeds. We have reformulated the CLN theory and have discovered, surprisingly, that their model is mathematically ill-posed. In an attempt to correct this difficulty and to construct models that might exhibit realistic behavior, we have extended the CLN analysis to include dissipative mechanisms within the cohesive zone. We have succeeded to some extent in finding mathematically well posed systems; and we even have found a class of models for which a transition from stability to instability may occur at a nonzero crack speed via a Hopf bifurcation at a finite wavelength of the applied perturbation. However, our general conclusion is that these cohesive-zone models are inherently unsatisfactory for use in dynamical studies. They are extremely difficult mathematically, and they seem to be highly sensitive to details that ought to be physically unimportant.Comment: 19 pages, REVTeX 3.1, epsf.sty, also available at http://itp.ucsb.edu/~lobkovs

Female teat size is a reliable indicator of annual breeding success in European badgers: Genetic validation

Assessing which females have bred successfully is a central requirement in many ecological field studies, providing an estimate of the effective female population size. Researchers have applied teat measurements previously to assess whether females, in a variety of mammalian species, have bred; however, this technique has not been validated genetically. Furthermore, several analytical techniques are available to classify individuals, but their misclassification rates have not been compared. We used 22 microsatellite loci to assign maternity, with 95% confidence, within a high-density population of European badgers Meles meles, as plural and subterranean breeding means that maternity cannot be inferred from behavioural observations. The teat lengths and diameters of 136 females, measured May–July 1994–2005, from social groups in which all offspring were assigned a mother, were reliable indicators of recent breeding success. A Generalised Linear Mixed Model (GLMM) classified both breeding and non-breeding females with lower error rates than discriminant analyses and crude teat-size criteria. The GLMM model logit probability = −20 + 1.8 month + 1.6 mean teat length + 1.0 mean teat diameter can be applied quickly in the field to assess the probability with which a female badger should be assigned maternity. This is a low-cost measure which, after validation, could be used in other badger or mammalian populations to assess the breeding success of females. This may be a particularly useful welfare tool for veterinary practitioners, especially during badger culls