No abstract

Purpose -The purpose of this paper is to develop and characterize a pulsed plasma thruster (PPT) that does not need a spark plug to initiate the plasma discharge. Design/methodology/approach -Two parallel rail thrusters were built and their performances were characterized inside a vacuum chamber to elucidate the effect of vacuum level and thruster geometry on the performance. The thruster electrical performance was quantified by measuring the voltage output from a Rogowski coil connected to the power supply. The thrust produced by the developed thruster was estimated by measuring the force exerted by the plume on a light weight pendulum, whose deflection was measured using a laser displacement sensor. Findings -The thruster can operate without a spark plug. In general, the performance parameters such as thrust, mass ablation, impulse bit, and specific impulse per discharge, would increase with increasing pressure levels up to an optimum level due to the increase in discharge energy as well as the decrease in the total impedance of the plasma discharge. The discharge frequency is function of the breakdown potential, the total resistance in the equivalent circuit, and the capacitance of the circuit. The total impedance of the circuit decreases with pressure level and hence the discharge energy increases. The thrust efficiency is found to be affected by the thruster geometry as well as the discharge energy.Research limitations/implications -The studies reported in this paper have been carried out at relatively higher pressure levels compared than prevail in space. However, it should be possible to extrapolate these results to the lower vacuum levels at which the performance is independent of the geometry. Practical implications -The results reported in this paper suggest a design guideline for auto-initiated PPT. Originality/value -If the spark plug is eliminated, the size of the thrusters can be reduced and arrays of such thrusters can be manufactured using micro electro mechanical systems techniques, which can provide tremendous control authority over the satellite positioning. Nomenclature¼ conversion factor for Isp between SI and imperial units (m/s 2 )¼ highest absolute Rogowski coil voltage peak (V) V2¼ second absolute Rogowski coil voltage peak (V) V, G(pd) ¼ discharge voltage, also the breakdown potential function (V) V o ¼ power supply output voltage (V) n ¼ velocity of pendulum during discharge (m/s) h ¼ thrust efficiency

Calcium signaling is required in bodily functions essential for survival, such as muscle contractions and neuronal communications. Of note, the voltage-gated calcium channels (VGCCs) expressed on muscle and neuronal cells, as well as some endocrine cells, are transmembrane protein complexes that allow for the selective entry of calcium ions into the cells. The α1 subunit constitutes the main pore-forming subunit that opens in response to membrane depolarization, and its biophysical functions are regulated by various auxiliary subunits–β, α2δ, and γ subunits. Within the cardiovascular system, the γ-subunit is not expressed and is therefore not discussed in this review. Because the α1 subunit is the pore-forming subunit, it is a prominent druggable target and the focus of many studies investigating potential therapeutic interventions for cardiovascular diseases. While this may be true, it should be noted that the direct inhibition of the α1 subunit may result in limited long-term cardiovascular benefits coupled with undesirable side effects, and that its expression and biophysical properties may depend largely on its auxiliary subunits. Indeed, the α2δ subunit has been reported to be essential for the membrane trafficking and expression of the α1 subunit. Furthermore, the β subunit not only prevents proteasomal degradation of the α1 subunit, but also directly modulates the biophysical properties of the α1 subunit, such as its voltage-dependent activities and open probabilities. More importantly, various isoforms of the β subunit have been found to differentially modulate the α1 subunit, and post-translational modifications of the β subunits further add to this complexity. These data suggest the possibility of the β subunit as a therapeutic target in cardiovascular diseases. However, emerging studies have reported the presence of cardiomyocyte membrane α1 subunit trafficking and expression in a β subunit-independent manner, which would undermine the efficacy of β subunit-targeting drugs. Nevertheless, a better understanding of the auxiliary β subunit would provide a more holistic approach when targeting the calcium channel complexes in treating cardiovascular diseases. Therefore, this review focuses on the post-translational modifications of the β subunit, as well as its role as an auxiliary subunit in modulating the calcium channel complexes.

Previous studies that have reported an association between obstructive sleep apnea and adverse cardiac events were confounded by a high prevalence of diabetes mellitus. We investigated the relationship between obstructive sleep apnea and the occurrence of major adverse cardiac events in non-diabetic patients who presented with ST-segment elevation myocardial infarction. A total of 41 patients who underwent overnight sleep screening within 5 days after admission for myocardial infarction from January 2007 to December 2008 were identified. Major adverse cardiac events-defined as a composite of cardiac death, non-fatal myocardial infarction, hospitalization for angina and congestive heart failure at 5-year follow-up-were determined. The patients were divided into two groups: those who experienced major adverse cardiac events and those who did not. In the overall cohort, the prevalence of obesity was 4.9 %. A total of 13 (31.7 %) patients had major adverse cardiac events. The mean apnea-hypopnea index was 25.4 ± 20.3. The group that experienced major adverse cardiac events had a higher apnea-hypopnea index than the group that did not (36.1 ± 21.0 vs 20.4 ± 18.2; P = 0.016). After adjusting for the resolution of ST-segment elevation and the use of a glycoprotein IIb/IIIa inhibitor, logistic regression analysis revealed that the apnea-hypopnea index remained an independent predictor of major adverse cardiac events (odds ratio 1.044; 95 % confidence interval 1.003-1.086; P = 0.033). In non-diabetic patients, the severity of obstructive sleep apnea was associated with the occurrence of major adverse cardiac events at 5-year follow-up after ST-segment elevation myocardial infarction.