Observations of metal concentrations in tilapia (Oreochromis mossambicus)in reservoirs of South Sri Lanka

Samples of the muscle and liver of tilapia (Oreochromis mossambicus) obtained from the five reservoirs in four catchments in southern Sri Lanka in 1998 were analyzed for 16 elements: As, Ca, Cd, Co, Cr, Cu, Fe, K, Mg, Mn, Na, Ni, Pb, Sr, and Zn by inductively coupled plasma emission spectrophotometry, and Hg by atomic absorption spectrophotometry. The concentrations of Cr, Ni, and Pb were below the detection limits of the instrumental techniques employed in all samples. The elements As, Ca, Co, Cu, Fe, Hg, K, Mg, Mn, Na, Sr, and Zn were detected in the muscle and liver tissue, with Cd detected in some liver samples. There were no statistically significant differences between the individual concentrations of any of the metals and the site from which the tilapia were collected (P>0.05). Furthermore, no statistically significant correlations were found between total length of fish and metal concentration. No elements were found at concentrations of toxicological concern. However, a principal component analysis suggests that the populations of tilapia in the reservoirs may be exposed to different regimes of metals, possibly associated with different catchment land-use patterns.

Perinatal ω-3 polyunsaturated fatty acid supply modifies brain zinc homeostasis during adulthood

Dietary ω-3 polyunsaturated fatty acid (PUFA) influences the expression of a number of genes in the brain. Zinc transporter (ZnT) 3 has been identified as a putative transporter of zinc into synaptic vesicles of neurons and is found in brain areas such as hippocampus and cortex. Neuronal zinc is involved in the formation of amyloid plaques, a major characteristic of Alzheimer's disease. The present study evaluated the influence of dietary ω-3 PUFA on the expression of the ZnT3 gene in the brains of adult male Sprague-Dawley rats. The rats were raised and/or maintained on a control (CON) diet that contained ω-3 PUFA or a diet deficient (DEF) in ω-3 PUFA. ZnT3 gene expression was analyzed by using real-time PCR, free zinc in brain tissue was determined by zinquin staining, and total zinc concentrations in plasma and cerebrospinal fluid were determined by atomic absorption spectrophotometry. Compared with CON-raised animals, DEF-raised animals had increased expression of ZnT3 in the brain that was associated with an increased level of free zinc in the hippocampus. In addition, compared with CON-raised animals, DEF-raised animals had decreased plasma zinc level. No difference in cerebrospinal fluid zinc level was observed. The results suggest that overexpression of ZnT3 due to a perinatal ω-3 PUFA deficiency caused abnormal zinc metabolism in the brain. Conceivably, the influence of dietary ω-3 PUFA on brain zinc metabolism could explain the observation made in population studies that the consumption of fish is associated with a reduced risk of dementia and Alzheimer's disease.

Egg colour matching in an African cuckoo, as revealed by ultraviolet-visible reflectance spectrophotometry

Despite major differences between human and avian colour vision, previous studies of cuckoo egg mimicry have used human colour vision (or standards based thereon) to assess colour matching. Using ultraviolet-visible reflectance spectrophotometry (300-700 nm), we measured museum collections of eggs of the red-chested cuckoo and its hosts. The first three principal components explained more than 99% of the variance in spectra, and measures of cuckoo-host egg similarity derived from these transformations were compared with measures of cuckoo-host egg similarity estimated by human observers unaware of the hypotheses we were testing. Monte Carlo methods were used to simulate laying of cuckoo eggs at random in nests. Results showed that host and cuckoo eggs were very highly matched for an ultraviolet versus greenness component, which was not detected by humans. Furthermore, whereas cuckoo and host were dissimilar in achromatic brightness, humans did not detect this difference. Our study thus reveals aspects of cuckoo-host egg colour matching which have hitherto not been described. These results suggest subtleties and complexities in the evolution of host-cuckoo egg mimicry that were not previously suspected. Our results also have the potential to explain the longstanding paradox that some host species accept cuckoo eggs that are non-mimetic to the human eye.

The role of ultraviolet-A reflectance and ultraviolet-A induced fluorescence in the appearance of budgerigar plumage: insights from spectrofluorometry and reflectance spectrophotometry

Fluorescence has so far been found in 52 parrot species when illuminated with ultraviolet-A (UVA) 'black' lamps, and two attempts have been made to determine whether such fluorescence plays any role in sexual signalling. However, the contribution of the reflectance versus fluorescence to the total radiance from feathers, even in the most studied species to date (budgerigars), is unclear. Nor has the plumage of this study species been systematically assessed to determine the distribution of fluorescent patches. We therefore used spectrofluorometry to determine which areas of budgerigars fluoresce and the excitation and emission spectra involved; this is the first time that such a technique has been applied to avian plumage. We found that both the yellow crown and (normally hidden) white downy chest feathers exhibit strong UVA-induced fluorescence, with peak emissions at 527 nm and 436 nm, respectively. Conversely, the bright-green chest and dark-blue tail feathers do not fluoresce. When comparing reflectance spectra (400700 nm) from the yellow crown using illuminants with a proportion of UVA comparable to daylight, and illuminants with all UVA removed, no measurable difference resulting from fluorescence was found. This suggests that under normal daylight the contribution of fluorescence to radiance is probably trivial. Furthermore, these spectra revealed that males had fluorescent crowns with substantially higher reflectance than those of females, in both the UV waveband and at longer wavelengths. Reflectance spectrophotometry was also performed on a number of live wild-type male budgerigars to investigate the chromatic contrast between the different plumage areas. This showed that many plumage regions are highly UV-reflective. Overall our results suggest that rapid surveys using UVA black lamps may overestimate the contribution of fluorescence to plumage coloration, and that any signalling role of fluorescence emissions, at least from the yellow crown of budgerigars, may not be as important as previously thought.

Atomic scale simulation of deformation in magnesium single crystals

The deformation behaviour of magnesium single crystals under plane strain conditions has been examined using molecular dynamics modelling. The simulations were based on an existing atomic potential for magnesium taken from the literature. A strain of 10% was applied at rates of 3x10⁹s^-1 and 3x10⁷s^-1. The simulations predicted the formation of mechanical twins that accommodated extension in the c-axis direction of the hexagonal unit cell. However, the predicted twin is not of the same kind found in magnesium, but is that commonly observed in titanium. It is believed that further analysis of the physical properties predicted by this interatomic potential will shed more light on the atomic processes controlling twinning in Magnesium alloys. It also highlights the need for improvements to the interatomic potential such that more accurate deformation behaviour can be attained.

Double layer structure of ionic liquids at the Au(111) electrode interface : an atomic force microscopy investigation

The double layer structure of two ionic liquids (ILs), 1-butyl-1- methylpyrrolidinium tris(pentafluoroethyl)trifluorophosphate ([Py ₁,₄]FAP) and 1-ethyl-3-methylimidazolium tris(pentafluoroethyl) trifluorophosphate ([EMIm]FAP) at the polarized Au(111) electrode interface is probed using Atomic Force Microscopy force measurements. The force-separation profiles suggest a multilayered morphology is present at the electrified Au(111)-IL interface, with more near surface layers detected at higher potentials. At the (slightly negative) open circuit potential, multiple ion layers are present, and the innermost layer, in contact with the Au(111) surface, is enriched in the cation due to electrostatic adsorption. Upon applying negative electrode potentials (-1.0 V, -2.0 V), stronger IL near surface structure is detected: both the number of ion layers and the force required to rupture these layers increases. Positive electrode potentials (+1.0 V, +2.0 V) also enhance IL near surface structure, but not as much as negative potentials, because surface-adsorbed anions are less effective at templating structure in subsequent layers than cations. This interfacial structure is not consistent with a double layer in the Stern-Gouy-Chapman sense, as there is no diffuse layer. The structure is consistent with a capicitative double-layer model, with a very small separation distance between the planes of charge.

Mark Oliphant’s adventures in atomic wonderland

Australian physicist Mark Oliphant came to hold two oppositional views, both pro and anti nuclear weapons research. This, together with the dimensions of his ‘larger than life’ personality, impacted on his scientific reputation in the fall-out of Australia’s ‘McCarthyism’. Despite his bullying the Americans into funding the A-Bomb project, the atomic juggernaut unleashed on the world caused Oliphant to rethink his role as a scientist. Oliphant clashed with American hegemony and the Menzies Government’s duplication of the ‘Reds under the Bed’ paranoia in Australia in the 1950s. His outspokenness on the danger of nuclear proliferation found him out of step with the changed political climate of the Cold War. Drawing on neglected archival material and using a Brechtian theatrical mode, my play Ion Man’s Adventures in Atomic Wonderland investigates the tragic dimensions of a man who never fully understood, as Thomas Kuhn explained (The Structure of Scientific Revolutions), that scientific research is determined as much by politics and ideology as by the desire to understand the world.