Biomedical subjects

S N Bland

Publications and source records attributed to S N Bland.

6 recordsLinked to original sources

PubMed2006

Dynamics of cylindrically converging precursor plasma flow in wire-array Z -pinch experiments.

This paper summarizes the present understanding of the processes leading to precursor column formation in cylindrical wire arrays on the 1 MA MAGPIE generator at Imperial College London. Direct experimental measurements of the diameter variation during the collapse and formation phase of the precursor column are presented, along with soft x-ray emission, and quantitative radiography. In addition, data from twisted cylindrical arrays are presented which give additional information on the behavior of coronal plasma generated in wire array z pinches. Three stages in precursor column formation are identifiable from the data: broad initial density profile, rapid contraction to small diameter, and slow expansion after formation. The correlation of emission to column diameter variation indicates the contraction phase is a nonlinear collapse resulting from the increasing on-axis density and radiative cooling rate. The variation in the minimum diameter is measured for several array materials, and data show good agreement with a pressure balance model. Comparison of column expansion rates to analytical models allows an estimate of column temperature variation, and estimates of the current in the column are also made. Formation data are in good agreement with both fluid and kinetic modeling, but highlight the need to include collisionless flow in the early time behavior.

Journal Article↗

PubMed2006

Dynamics of mass transport and magnetic fields in low-wire-number-array Z pinches.

The dynamics of mass transport were observed in a wire array implosion with multiframe laser probing. Plasma bubbles arise at breaks in the wires. Interferometry shows that the leading edge of the bubbles brings material to the axis of the array. The speed of this material was measured to be > or =3 x 10(7) cm/s during the wire array implosion. A shock was observed during the collision of the bubbles with the precursor. The Faraday effect indicates current flowing in breaks on the wires. The current switches from the imploding mass to the on-axis plasma column at the beginning of the x-ray pulse.

Journal Article↗

PubMed2005

Study of three-dimensional structure in wire-array z pinches by controlled seeding of axial modulations in wire radius.

Three-dimensional perturbations have been seeded in wire-array z pinches by etching 15 microm diameter aluminum wires to introduce 20% modulations in radius with a controlled axial wavelength. These perturbations seed additional three-dimensional imploding structures that are studied experimentally and with magnetohydrodynamics calculations, highlighting the role of current path nonuniformity in perturbation-induced magnetic bubble formation.

Journal Article↗

PubMed2005

Effect of radial-electric-field polarity on wire-array Z-pinch dynamics.

The formation of plasma in wire-array Z-pinch experiments was found to depend upon the polarity of the radial-electric field near the wires. Reversing the radial-electric field midway along the length of an array resulted in the ablation rate of one-half of the array being reduced by 50%, significantly delaying the start of its implosion and altering its acceleration towards the axis. The observed phenomena cannot be explained by the standard magnetohydrodynamic models of array behavior, suggesting that effects such as electron emission may be important, especially during wire initiation.

Journal Article↗

PubMed2002

Indirect-drive inertial confinement fusion using highly supersonic, radiatively cooled, plasma slugs.

We present a new approach to indirect-drive inertial confinement fusion which makes use of highly supersonic, radiatively cooled, slugs of plasma to energize a hohlraum. 2D resistive magnetohydrodynamic simulations of slug formation in shaped liner Z-pinch implosions are presented along with 2D-radiation-hydrodynamic simulations of the slug impacting a converter foil and 3D-view-factor simulations of a double-ended hohlraum. Results for the Z facility at Sandia National Laboratory indicate that two synchronous slugs of 250 kJ kinetic energy could be produced, resulting in a capsule surface temperature of approximately 225 eV.

Journal Article↗

PubMed2001

Bacterial and fungal biomass responses to feeding by larval Aedes triseriatus (Diptera: Culicidae).

We investigated the effect of different densities (0, 20, or 40) of developing larval Aedes triseriatus (Say) on bacterial abundance, bacterial productivity, and leaf fungal biomass in a microcosm experiment. Larvae in the low-density treatment developed normally, but larvae at the high density were significantly slower to develop. Both bacterial abundance (direct microscopic counts) and bacterial productivity (3H-leucine incorporation rates) on leaf material were significantly lower in the presence of larvae. Bacterial abundance in the water column did not change significantly with treatment, but bacterial productivity varied with time and declined significantly at both larval densities. Bacteria on the walls and bottom of the containers also were less abundant and significantly less productive in the presence of larvae. Aside from presence/absence effects, there was no clear evidence that larval impacts were density-dependent. Leaf-associated fungal biomass, as measured by ergosterol levels, varied with time but was not significantly affected by any treatment, suggesting most fungal tissue was incorporated in the leaf matrix and unavailable to larvae. Based upon estimated biomass accrual and respiration of larvae, it appears that bacterial biomass and production were insufficient to account for carbon demands of growing larvae. Because fungal biomass and leaf mass likely contributed little to gross larval demands, other carbon sources (e.g., protozoa and extracellular microbial components) were probably used by larvae. Although apparently insufficient for all larval carbon demands, bacterial and leaf fungal biomass may be adequate for other larval nutritional needs (i.e., nitrogen and essential lipids).

Aedes↗