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.     

Symmetric inertial-confinement-fusion-capsule implosions in a double-z-pinch-driven hohlraum

An inertial-confinement-fusion (ICF) concept using two 60-MA Z pinches to drive a cylindrical hohlraum to 220 eV has been recently proposed. The first capsule implosions relevant to this concept have been performed at the same physical scale with a lower 20-MA current, yielding a 70+/-5 eV capsule drive. The capsule shell shape implies a polar radiation symmetry, the first high-accuracy measurement of this type in a pulsed-power-driven ICF configuration, within a factor of 1.6-4 of that required for scaling to ignition. The convergence ratio of 14-21 is to date the highest in any pulsed-power ICF system.     

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.     

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.     

High-gain magnetized inertial fusion

Magnetized inertial fusion (MIF) could substantially ease the difficulty of reaching plasma conditions required for significant fusion yields, but it has been widely accepted that the gain is not sufficient for fusion energy. Numerical simulations are presented showing that high-gain MIF is possible in cylindrical liner implosions based on the MagLIF concept [S. A. Slutz et al Phys. Plasmas 17, 056303 (2010)] with the addition of a cryogenic layer of deuterium-tritium (DT). These simulations show that a burn wave propagates radially from the magnetized hot spot into the surrounding much denser cold DT given sufficient hot-spot areal density. For a drive current of 60 MA the simulated gain exceeds 100, which is more than adequate for fusion energy applications. The simulated gain exceeds 1000 for a drive current of 70 MA.     

Measurements of magneto-Rayleigh-Taylor instability growth during the implosion of initially solid Al tubes driven by the 20-MA, 100-ns Z facility

The first controlled experiments measuring the growth of the magneto-Rayleigh-Taylor instability in fast (～100 ns) Z-pinch plasmas are reported. Sinusoidal perturbations on the surface of an initially solid Al tube (liner) with wavelengths of 25-400 μm were used to seed the instability. Radiographs with 15 μm resolution captured the evolution of the outer liner surface. Comparisons with numerical radiation magnetohydrodynamic simulations show remarkably good agreement down to 50 μm wavelengths.     

Fill-tube-induced mass perturbations on x-ray-driven, ignition-scale, inertial-confinement-fusion capsule shells and the implications for ignition experiments

On the first inertial-confinement-fusion ignition facility, the target capsule will be DT filled through a long, narrow tube inserted into the shell. microg-scale shell perturbations Delta m' arising from multiple, 10-50 microm-diameter, hollow SiO2 tubes on x-ray-driven, ignition-scale, 1-mg capsules have been measured on a subignition device. Simulations compare well with observation, whence it is corroborated that Delta m' arises from early x-ray shadowing by the tube rather than tube mass coupling to the shell, and inferred that 10-20 microm tubes will negligibly affect fusion yield on a full-ignition facility.