DYNGA: a general purpose QM-MM-MD program. I. Application to water

We present a general purpose QM-MM-MD engine (DYNGA) designed to test alternative hybrid Hamiltonians geared towards the treatment of problems of interest in structural biology including the use of experimental data constraints. In this first presentation we use DYNGA to explore the behaviour of a traditional QM-MM approach in the treatment of the water—water interaction. We find the potential energy hypersurface for the water dimer computed with the HF 4–31G*/TIP3P hybrid Hamiltonian tends to be too flat. We also explore the effect of using traditional QM-MM techniques on proton wires and conclude there is a need for improvement, possibly addressed by using polarizable force fields.     

PAST AND FUTURE MANAGEMENT OF A COLLAPSED FISHERY: THE BAY OF BISCAY ANCHOVY

Abstract We analyze the efficiency of the international management of the Bay of Biscay anchovy. While a sharing agreement between France and Spain has been in place since 1992, the fish stock collapsed in 2005 and the fishery closed from 2005 to spring 2010. We consider differences in production technologies between both countries and calibrate our model using data from 1987 to 2009. Our results suggest two sources of rent dissipation under the existing sharing agreement: inefficient quota allocation and production inefficiencies due to inflexible national regulations. We discuss several alternatives to improve management.     

ConFlo III - an interface for high precision delta(13)C and delta(15)N analysis with an extended dynamic range

A newly developed interface coupling a CHN combustion device (elemental analyser 'EA') to an isotope ratio mass spectrometer is described and evaluated. The purpose of the device is to extend the dynamic range of delta(13)C and delta(15)N analysis from less than 2 orders of magnitude to more than 3 orders of magnitude. Carbon isotope ratio measurements of atropine as a model compound have been performed analysing between 1 μg to 5 mg C with acceptable to excellent precision (0.6 to 0.06 per thousand, delta-notation). The correction due to the blank signal is critical for sample amounts smaller than 4 μg C. The maximum sample weight is determined by the combustion capacity of the EA. Larger sample amounts are measured using dilution of a small part of the EA effluent with helium. The dilution mechanism works virtually free of isotope fractionation. Copyright 1999 John Wiley & Sons, Ltd.     

Geochemical association of plutonium in sediments of the Trombay coastal environment

Geochemical association of plutonium in the coastal environment of Trombay has been studied. A sequential leaching method was employed for chemical partitioning of plutonium in sediments. The results show that 95±15% of plutonium was extracted by different leaching reagents out of which 85±14% was associated with organic matter and hydrous oxide and 9±4% with residual fraction.The presence of significant fraction of Pu bound with organic matter of the sediment is an important factor in determining the extent to which an element becomes available to bottom feeding biota and so enters the aquatic food chain.     

Determination of plutonium and americium in environmental samples and assessment of thorium in bone samples from normal and high background areas

The procedures developed and standardised for estimation of ultra trace quantities of Pu and Am in environmental samples involve matrix dependent sample preparation, preconcentration of the nuclides by coprecipitation on iron hydroxide and or bismuth phosphate, ion exchange, electrodeposition and counting by alpha spectrometry. Isotopic analysis of Th in chicken bone using oxalate precipitation, ion exchange, electrodeposition and alpha spectrometry has indicated higher build up of²²⁸Th in chicken bone from monazite areas possibly from metabolized²²⁸Ra.     

Distribution of Pu and Am in different parts of mango trees

Study of plutonium and americium in the mango leaves and the distribution of their concentration in different parts of the mango fruit were performed. The generally observed trend is leaves > cotyledon > shell > fresh. These results suggest that the contamination of mango fruits by Pu and Am will not pose any radiation risk because the edible portion of the mango has the lowest activity.