The effect of biotin on the production of succinic acid byAnaerobiospirillum succiniciproducens

Applied Biochemistry and Biotechnology - The effect of biotin at 50 mg/L on the production of succinic acid byA. succiniciproducens has been studied. Biotin improved glucose consumption, cell...     

The production and evolution of multiple converging radiative shock waves in gas-filled cylindrical liner z-pinch experiments

A cylindrical liner z-pinch configuration has been used to drive converging radiative shock waves into different gases. On application of a 1.4 MA, 240 ns rise-time current pulse, a series of cylindrical shocks moving at typical velocities of 20 km s^?1 are consecutively launched from the inside liner wall into an initially static gas-fill of density ～10^?5 g cm^?3. The drive current skin depth calculated prior to resistive heating was slightly less than the liner wall thickness and no bulk liner implosion occurred. Axial laser probing images show the shock fronts to be smooth and azimuthally symmetric, with instabilities developing downstream of each shock. Evidence for a radiative precursor ahead of the first shock was seen in laser interferometry imaging and time-gated, spatially resolved optical spectroscopy. The interferometry diagnostic was able to simultaneously resolve the radiative precursor and the density jumps at the shock fronts. Optical streak photography provided information on shock timing and shock trajectories and was used to gain insight into the shock launching mechanisms.     

Estimation of biologically damaging UV levels in marine surface waters with DNA and viral dosimeters

We have surveyed the biologically harmful radiation penetrating the water column along a transect in the western Gulf of Mexico using dosimeters consisting of intact viruses or naked calf-thymus DNA (ctDNA). The indigenous marine bacteriophage PWH3a-P1, which lytically infects the heterotrophic bacterium Vibrio natriegens (strain PWH3a), displayed decay rates for infectivity approaching 1.0 h(-1) in surface waters when deployed in a seawater-based dosimeter. The accumulation of pyrimidine dimers in ctDNA dosimeters provided a strong correlation to these results, with pyrimidine dimers representing more than 0.3% (up to ca 3800 dimers Mb(-1) DNA) of the total DNA in dosimeters exposed to sea surface levels of solar radiation. The results demonstrate a strong correlation between the dimer formation in the DNA dosimeters, the decay rates of viral infectivity and the penetration of UVB radiation into the water column. The decay of viral infectivity attenuated with depth in a manner similar to the decay of solar radiation and was still significant at 10 m in offshore oligotrophic water and at dimer frequencies less than 0.1% (ca 200-300 dimers Mb(-1) DNA).     

Optical Thomson scattering measurements of plasma parameters in the ablation stage of wire array Z pinches

A Thomson scattering diagnostic has been used to measure the parameters of cylindrical wire array Z pinch plasmas during the ablation phase. The scattering operates in the collective regime (α>1) allowing spatially localized measurements of the ion or electron plasma temperatures and of the plasma bulk velocity. The ablation flow is found to accelerate towards the axis reaching peak velocities of 1.2-1.3×10(7) cm/s in aluminium and ～1×10(7) cm/s in tungsten arrays. Precursor ion temperature measurements made shortly after formation are found to correspond to the kinetic energy of the converging ablation flow.     

Crystal lattice effects in the Sm(n, α)Nd reaction induced by thermal neutrons

The thermal neutron induced reaction, ¹⁴⁹Sm(n, α)¹⁴⁶Nd, is influenced by the chemical form and temperature of the target material. The detection of this dependence is due to the rather unique features of the thermal neutron capture of ¹⁴⁹Sm which make it particularly sensitive to the effective neutron energy spectrum.     

Changes in polyvinylpyrrolidone coil dimensions by complexation with organic anions: effect of chain length

Changes in polyvinylpyrrolidone (PVP) coil dimensions by complexation with small organic anions were studied by dilure solution viscometry Intrinsic viscosity provides a convenient measure of the dimensions assumed by a flexible polymer chain in solution as a result of interactions with all components in its environment. Molecular interactions between PVP and sodium benzoate and salicylate were investigated over a range of low concentrations of each anion, from 2.5 to 90 mM, and as a function of five molecular weight grades of PVP. This study showed that both contraction and expansion of polymer coils were sensitive to the concentration and chemical structure of the cosolute. In addition, at high anion concentrations changes in polymer conformation by complexation were dependent on both the chain length of PVP and charge density of bound anions through excluded volume effects. Experimental results demonstrating these observations are presented in a three-dimensional surface plot of intrinsic viscosity ratio, polymer size, and anion concentration. A distinct local minimum in the surface plane was exhibited for each cosolute.     

Interaction of radiatively cooled plasma jets with neutral gases for laboratory astrophysics studies

A supersonic (Mach～2–3), radiatively cooled plasma jet is produced by the ablation of aluminium plasma from a radial foil, a disc subjected to a ～1.4 MA, 250 ns current from the MAGPIE pulsed-power generator. The ablated plasma converges on axis, producing a steady and collimated jet with axial velocities reaching ～100 km/s. The study of jet-ambient interactions is achieved by introducing a neutral gas above the foil using a fast valve with a supersonic gas nozzle. The system has flexibility to study different interaction geometries in order to vary critical dimensionless parameters for astrophysical studies. In particular the effects of radiative cooling on the working surface of the jet are strongly affected by varying the gas composition. Experimental results are compared to numerical simulations using the 3-D MHD code GORGON.     

Production of succinic acid by anaerobiospirillum succiniciproducens

The effect of an external supply of carbon dioxide and pH on the production of succinic acid byAnaerobiospirillum succiniciproducens was studied. In a rich medium containing yeast extract and peptone, when the external carbon dioxide supply was provided by a 1.5M Na₂CO₃ solution that also was used to maintain the pH at 6.0, no additional carbon dioxide supply was needed. In fact, sparging CO₂ gas into the fermenter at 0.025 L/L-min or higher rates resulted in significant decreases in both production rate and yield of succinate. Under the same conditions, the production of the main by-product acetate was not affected by sparging CO₂ gas into the fermenter. The optimum pH (pH 6.0) for the production of succinic acid was found to be in agreement with results previously reported in the literature. Succinic acid production also was studied in an industrial-type inexpensive medium in which light steep water was the only source of organic nutrients. At pH 6.0 and with a CO₂ gas sparge rate of 0.08 L/L-min, succinate concentration reached a maximum of 32 g/L in 27 h with a yield of 0.99 g succinate/g glucose consumed.