Hollow Cathode and Low-Thrust Extraction Grid Analysis for a Miniature Ion Thruster

Miniature ion thrusters are well suited for future space missions that require high efficiency, precision thrust, and low contamination in the mN to sub-mN range. JPL’s miniature xenon Ion (MiXI) thruster has demonstrated an efficient discharge and ion extraction grid assembly using filament cathodes and the internal conduction (IC) cathode. JPL is currently preparing to incorporate a miniature hollow cathode for the MiXI discharge. Computational analyses anticipate that an axially upstream hollow cathode location provides the most favorable performance and beam profile; however, the hot surfaces of the hollow cathode must be sufficiently downstream to avoid demagnetization of the cathode magnet at the back of the chamber, which can significantly reduce discharge performance. MiXI’s ion extraction grids are designed to provide >3mN of thrust; however, previous to this effort, the low-thrust characteristics had not been investigated. Experimental results obtained with the MiXI-II thruster (a near replica or the original MiXI thruster) show that sparse average discharge plasma densities of ∼5×10^15–5×10^16 m^−3 allow the use of very low beamlet focusing extraction voltages of only ∼250–500 V, thus providing thrust levels as low as 0.03 mN for focused beamlet conditions. Consequently, the thrust range thus far demonstrated by MiXI in this and other tests is 0.03–1.54 mN

Comparing supplementary oxygen benefits from a portable oxygen concentrator and a liquid oxygen portable device during a walk test in COPD patients on long-term oxygen therapy

SummaryBackgroundDifferences in oxygen delivery between portable oxygen concentrators (POC) and liquid oxygen (LO) portable units, pose a question if POCs are equally effective as LOs in reducing exercise-induced hypoxaemia.DesignRandomized, single-blind clinical trial.PatientsThirteen COPD patients (means: age 66±11 year, FEV1 35.2±13.7% predicted) and respiratory failure (means: PaO2 52±5mmHg, PaCO2 51.3±7.5mmHg).MethodsAll patients underwent a series of 6-min walk tests (6MWT) carried out in random order among one of the three devices: POC, LO cylinder and cylinder with compressed air (CA). Oxygen supplementation was 3lpm for LO and an equivalent to 3lpm in a pulse flow system for POC.ResultsThe mean SpO2 was equally improved at rest: 92.9±2.8% with POC and 91.7±2.0% with LO compared to CA—87.8±2.7% (POC and LO vs. CA p<0.05). POC and LO significantly improved oxygenation during 6MWT (mean SpO2 was 84.3±5% and 83.8±4.2%, respectively) compared to breathing CA—77.6±7.4%, p<0.05. Mean 6MWT distance increased with LO (350±83m) and POC (342±96m) when compared to CA (317±84m), however, these differences were not statistically significant. Dyspnoea score assessed at the end of the exercise (Borg scale) was significantly lower when breathing oxygen (4.2±1.2 with POC and 4.1±1.7 with LO vs. 5.4±1.9 with CA, p<0.05).ConclusionsEffectiveness of oxygen supplementation from a POC did not differ from the LO source during 6MWT in COPD patients with respiratory failure. Oxygen at 3lpm flow was not sufficient to prevent hypoxaemia during strenuous exercise

Evidence for ion acceleration by oscillations in the discharge plasma of ion engines

The hollow cathode discharge plasma in ion engines is highly non-uniform, geometrically complex, and confined by a magnetic field; elucidating the mechanisms responsible for producing ions with anomalously high energies observed in the downstream regions of hollow cathodes will contribute to understanding the behavior of complex plasmas. Ions with energies in excess of ten times greater than the energy associated with electrostatic acceleration from the largest steady-state potential difference in the plasma discharge of ion engines have been detected

Variants of significance: medical genetics and surgical outcomes in congenital heart disease

Purpose of review: This article reviews the current understanding and limitations in knowledge of the effect genetics and genetic diagnoses have on perioperative and postoperative surgical outcomes in patients with congenital heart disease (CHD). Recent findings: Presence of a known genetic diagnosis seems to effect multiple significant outcome metrics in CHD surgery including length of stay, need for extracorporeal membrane oxygenation, mortality, bleeding, and heart failure. Data regarding the effects of genetics in CHD is complicated by lack of standard genetic assessment resulting in inaccurate risk stratification of patients when analyzing data. Only 30% of variation in CHD surgical outcomes are explained by currently measured variables, with 2.5% being attributed to diagnosed genetic disorders, it is thought a significant amount of the remaining outcome variation is because of unmeasured genetic factors. Summary: Genetic diagnoses clearly have a significant effect on surgical outcomes in patients with CHD. Our current understanding is limited by lack of consistent genetic evaluation and assessment as well as evolving knowledge and discovery regarding the genetics of CHD. Standardizing genetic assessment of patients with CHD will allow for the best risk stratification and ultimate understanding of these effects