The evolution of electron overdensities in magnetic fields

When a neutral gas impinges on a stationary magnetized plasma an enhancement in the ionization rate occurs when the neutrals exceed a threshold velocity. This is commonly known as the critical ionization velocity effect. This process has two distinct timescales: an ion–neutral collision time and electron acceleration time. We investigate the energization of an ensemble of electrons by their self-electric field in an applied magnetic field. The evolution of the electrons is simulated under different magnetic field and density conditions. It is found that electrons can be accelerated to speeds capable of electron impact ionization for certain conditions. In the magnetically dominated case the energy distribution of the excited electrons shows that typically 1% of the electron population can exceed the initial electrostatic potential associated with the unbalanced ensemble of electrons

Simulation of transient energy distributions in sub-ns streamer formation

Breakdown and streamer formation is simulated in atmospheric pressure nitrogen for a 2D planar electrode system. A PIC code with multigrid potential solver is used to simulate the evolution of the non-equilibrium ionization front on sub-nanosecond timescales. The ion and electron energy distributions are computed, accounting for the inclusion of inelastic scattering of electrons, and collisionally excited metastable production and ionization. Of particular interest is the increased production of metastable and low-energy ions and electrons when the applied field is reversed during the progress of the ionization front, giving insight into the improved species yields in nanosecond pulsed systems

Genetic information: important but not "exceptional"

Much legislation dealing with the uses of genetic information could be criticised for exceptionalising genetic information over other types of information personal to the individual. This paper contends that genetic exceptionalism clouds the issues, and precludes any real debate about the appropriate uses of genetic information. An alternative to “genetically exceptionalist” legislation is to “legislate for fairness”. This paper explores the “legislating for fairness” approach, and concludes that it demonstrates a fundamental misunderstanding of both how legislation is drafted, and how it is interpreted. The uncomfortable conclusion is this: policy-makers and legislators must tackle head-on the difficult policy questions concerning what should and should not be done with genetic information. Only by confronting this crucial issue will they achieve a workable legislative solution to the problems caused by genetic information

Environmental and Economically Conscious Magnesium Production: Solar Thermal Electrolytic Production of Mg from MgO

One method to improve the fuel efficiency of American made vehicles is to reduce vehicle weight by substituting steel components with lighter magnesium (Mg) components. Unfortunately, U.S. produced Mg currently costs approximately $3.31 per kg, over seven times the price of steel. Furthermore, Mg production has a staggering energy and environmental impact, consuming up to 102 kW-hr/kg-Mg of energy and producing 36 kg of CO2/kg-Mg. To reduce the overwhelming economic and environmental impact of Mg, a new solar thermal electrolytic process has been developed for the production of Mg from MgO. Through this process, liquid Mg is produced in a solar reactor utilizing both thermal and electrical energy. At elevated temperatures, the thermal energy from concentrated sunlight reduces the required electrical work below that of current processes. The reactor absorbs the concentrated solar energy, heating a molten salt-MgO mixture in an electrolytic cell. Electricity is then supplied to the cell, producing liquid Mg and CO. It is estimated that this new process will produce Mg at$2.50 per kg, with costs decreasing as the technology is further developed. This process requires approximately 8.3 kW-hr/kg-Mg of energy and produces only 3.44 kg of CO2/kg-Mg, large reductions compared to current processes

Balloon dilation of mitral stenosis in adult patients: Postmortem and percutaneous mitral valvuloplasty studies

Preliminary reports have documented the utility of percutaneous balloon valvuloplasty of the mitral valve in adult patients with mitral stenosis, but the mechanism of successful valve dilation and the effect of mitral valvuloplasty on cardiac performance have not been studied in detail. Accordingly, mitral valvuloplasty was performed in five postmortem specimens and in 18 adult patients with rheumatic mitral stenosis, using either one (25 mm) or two (18 and 20 mm) dilation balloons. Postmortem balloon dilation resulted in increased valve orifice area in all five postmortem specimens, secondary to separation of fused commissures and fracture of nodular calcium within the mitral leaflets. In no case did balloon dilation result in tearing of valve leaflets, disruption of the mitral ring or liberation of potentially embolic debris.Percutaneous mitral valvuloplasty in 18 patients with severe mitral stenosis (including 9 with a heavily calcified valve) resulted in an increase in cardiac output (4.3 ± 1.1 to 5.1 ± 1.5 liters/min, p < 0.01) and mitral valve area (0.9 ± 0.2 to 1.6 ± 0.4 cm2, p < 0.0001), and a decrease in mean mitral pressure gradient (15 ± 5 to 9 ± 4 mm Hg, p < 0.0001), pulmonary capillary wedge pressure (23 ± 7 to 18 ± 7 mm Hg, p < 0.0001) and mean pulmonary artery pressure (36 ± 12 to 33 ± 12 mm Hg, p < 0.01). Left ventriculography before and after valvuloplasty in 14 of the 18 patients showed a mild (≤1 +) increase in mitral regurgitation in five patients and no change in the remainder. Embolic phenomena were not observed in any patient.Serial radionuclide ventriculography showed an increase in left ventricular peak filling rate (2.20 ± 1.20 to 2.50 ± 1.20 end-diastolic volumes per second [EDV/s], p < 0.05). Serial echocardiography/phonocardiography showed improvement in mitral valve excursion (11 ± 6 to 14 ± 6 mm, p < 0.001), mitral EF slope (7 ± 4 to 13 ± 5, p < 0.001), left atrial diameter (5.7 ± 0.9 to 5.3 ± 0.8 cm, p < 0.001), S2-opening snap interval (0.07 ± 0.03 to 0.08 ± 0.02 second, p < 0.02) and mitral valve area (0.9 ± 0.2 to 1.5 ± 0.4 cm2, p < 0.0001). All patients were discharged from the hospital with de- creased symptoms after valvuloplasty.It is concluded that percutaneous mitral valvuloplasty can be performed in adult patients with mitral stenosis, including patients with calcific disease, and can result in significant improvement in valvular function. The mechanisms of successful dilation include commissural separation and fracture of nodular calcium

Electronic detection of charged particle effects in a Penning trap

We present a thorough analysis of the electronic detection of charged particles, confined in a Penning trap, via image charges induced in the trap electrodes. Trapping of charged particles in an electrode structure leads to frequency shifts, which are due to image charge and space charge effects. These effects are of importance for Penning trap experiments which involve high charge densities or require high precision in the motional frequencies. Our analysis of image charges shows that only (higher order) odd powers of the particle displacement lead to induced charge differences, giving rise to a signal. This implies that, besides the centre-of-mass frequency of a trapped particle cloud, also higher order individual particle frequencies induce a signal, which can be picked up by an electronic detection circuit attached to the trap electrodes. We also derive analytic expressions for the image charge and space charge induced frequency shifts and perform simulations of space charge effects. In relation to this, we discuss the consequences of the shifted particle frequencies for resistive cooling of the particle motion.Comment: 16 pages, 4 figure