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The noble gas argon has demonstrated biological activity that may prove useful as a medical intervention. Pharmacokinetics, the disposition of the drug molecule in the body through time, is fundamental necessary knowledge to drug discovery, development and even post-marketing. The fundamental measurement in pharmacokinetic studies is blood concentration of the molecule (and its metabolites) of interest. While a physiologically based model of argon pharmacokinetics has appeared in the literature, no experimental data have been published. Thus, argon pharmaceutical development requires measurement of argon solubility in blood. This paper reports on the development of a technique based on mass spectrometry for measuring argon solubility in liquids, including blood, to be further employed in pharmacokinetics testing of argon. Based on a prototype, results are reported from sensitivity experiments using ambient air, water and rabbit blood. The key takeaway is that the system was sensitive to argon during all of the testing. We believe the technique and prototype of the quadrupole mass spectrometer gas analyzer will be capable of inferring argon pharmacokinetics through the analysis of blood samples. [ABSTRACT FROM AUTHOR]

Background: Cancer diagnoses are associated with an increased risk for suicide. The aim of this study was to evaluate this association among Veterans receiving Veterans Health Administration (VHA) care, a population that has an especially high suicide risk. Methods: Among 4,926,373 Veterans with VHA use in 2011 and in 2012 or 2013, and without VHA cancer diagnoses in 2011, we assessed suicide risk following incident cancer diagnoses. Risk time was from initial VHA use in 2012–2013 to 12/31/2018 or death, whichever came first. Cox proportional hazards regression models evaluated associations between new cancer diagnoses and suicide risk, adjusting for age, sex, VHA regional network, and mental health comorbidities. Suicide rates were calculated among Veterans with new cancer diagnoses through 84 months following diagnosis. Results: A new cancer diagnosis corresponded to a 47% higher suicide risk (Adjusted Hazard Ratio [aHR] = 1.47, 95% CI: 1.33–1.63). The cancer subtype associated with the highest suicide risk was esophageal cancer (aHR = 6.01, 95% CI: 3.73–9.68), and other significant subtypes included head and neck (aHR = 3.55, 95% CI: 2.74–4.62) and lung cancer (aHR = 2.35, 95% CI: 1.85–3.00). Cancer stages 3 (aHR = 2.36, 95% CI: 1.80–3.11) and 4 (aHR = 3.53, 95% CI: 2.81–4.43) at diagnosis were positively associated with suicide risk. Suicide rates were highest within 3 months following diagnosis and remained elevated in the 3–6‐ and 6–12‐month periods following diagnosis. Conclusion: Among Veteran VHA users, suicide risk was elevated following new cancer diagnoses. Risk was particularly high in the first 3 months. Additional screening and suicide prevention efforts may be warranted for VHA Veterans newly diagnosed with cancer. [ABSTRACT FROM AUTHOR]

A well-known concern for polar orbiting spacecraft at the Earth is spacecraft charging due to the aurora. Studies of Jupiter reveal the presence of a variety of similar auroral phenomena. In particular, three regions have been identified--a narrow auroral zone at high latitudes, a complex and variable environment over the poles, and auroralike features associated with the main jovian moons and their magnetic flux tubes. These auroral structures are, like their earthly counterparts, expected to be sources of charging. This paper reviews the observational data and models of the jovian aurora zone and polar regions. In combination with models of the jovian plasma environment, the ambient charging currents are then computed with the intention of providing realistic estimates of spacecraft potentials at Jupiter. These are of particular importance to the Juno mission as it is a Jupiter polar orbiter and will pass through the jovian auroral zones near the planet. Of special concern, unlike previous missions to Jupiter, Juno will utilize large solar arrays. While previous missions (e.g., the Voyagers and Galileo) utilized RTGs and were carefully designed to avoid differential surface charging, the Juno mission's solar arrays may make it more sensitive to surface charging. Although the jovian aurora is a possibly serious threat to Juno and similar missions, as will be discussed, an understanding of the environment and proper mitigation techniques should limit their effects. Index Terms--Aurora, Jupiter, spacecraft charging, space plasma.

An extensive 2-D computational model of the fundamental ionization and transport processes that occur inside electric propulsion hollow cathodes has been developed over the last few years. The computed charged-particle fluxes from the plasma to the internal cathode surfaces have been used as input to a rudimentary hollow-cathode thermal model also developed recently. It is shown that, in hollow cathodes with a very small diameter orifice, the plasma density peaks inside the orifice and that the cathode is heated primarily by the orifice plate which is, in turn, heated by the plasma inside the orifice and along the orifice plate. As the orifice diameter increases the peak plasma density moves upstream of the orifice with ions and electrons contributing to the heating of both the orifice plate and the insert. In hollow cathodes with a very large diameter orifice the plasma extends along much of the insert, the plasma density peaks well within the insert region, and the cathode is heated primarily by ion bombardment of the insert. By solving a 2-D axisymmetric boundary value problem, it is also shown that when a voltage is applied between the ends of a long cylindrical channel the potential in the absence of the plasma falls almost by one order of magnitude with each radius downstream of the entrance. The implication is that cathodes with orifices of large length-to-radius ratio will be harder to ignite. Index Terms--Electric propulsion life modeling, hollow cathode, numerical simulation of partially ionized gas.

Jet Propulsion Laboratory (JPL) is currently assessing the applicability of the 25-cm Xenon Ion Propulsion System (XIPS) as part of an effort to infuse low-cost technically mature commercial ion thruster systems into NASA deep space missions. Since these mission require extremely long thruster lifetimes to attain the required mission [DELTA]V, this paper is focused on understanding the dominate wear mechanisms that effect the life of the XIPS three-grid system. Analysis of the XIPS three-grid configuration with JPL's CEX3D grid erosion model shows that the third 'decel' grid effectively protects the accel grid from pits and grooves erosion that is commonly seen with two-grid ion thruster grid systems. For a three-grid system, many of the charge-exchange ions created downstream of the grid plane will impact the decel grid at relatively low energies (~25 V), instead of impacting the accel grid at high energies (~200 V), thus reducing overall erosion. JPL's CEX3D accurately predicts the erosion patterns for the accel grid, although it appears to overpredict the pits and grooves erosion rates due, mainly, to uncertainties in incident energies and angles for sputtering ions and since it does not account for local redeposition of sputtered material. Since the model accurately simulates the erosion pattern but tends to overpredict the erosion rates for both the two- and three-grid sets, this comparative analysis clearly shows how the decel grid significantly suppresses the erosion of the downstream surface of the accel grid as observed in experimental tests. The results also show that the decel grid has a relatively small effect on barrel erosion (erosion of the aperture wall) and erosion of the upstream surface of the accel grid. Decreasing the accel grid voltage of the XIPS can reduce barrel (and total) erosion of the accel grid and should be considered for high-[DELTA]V missions. Index Terms--Decel grid, grid erosion, ion thruster, Xenon Ion Propulsion System (XIPS).

To match the observed thrust and discharge current in Hall thrusters, computer simulations have typically assumed anomalous electron transport mechanisms, such as Bohm diffusion, to enhance electron mobility across magnetic field lines. Without enhanced electron transport, the simulations predict a much lower discharge current than observed, and too much of the potential drop is downstream of the channel exit. Rather than search for mechanisms to increase the electron scattering frequency, we seek to identify mechanisms that would increase the fraction of the current carried by ions, thus reducing the required electron current. We describe two mechanisms that enhance the current carried by ions. The first mechanism increases the ion current carried in the channel by simply including the effects of multiply charged ions on the plasma response. The importance of using accurate ionization cross sections and the need to include multiply charged ions even for discharge voltages of 300 V are discussed. The second mechanism is a process we term 'ion reflux.' In this process, current is carried by ions generated downstream of the channel exit. Portions of these ions impact the center of the thruster and are neutralized by cathode electrons. A large fraction of the resultant neutral atoms are reionized as they pass through the main exhaust beam. These newly born ions then carry additional current through the plume. Since neutrals freely move across magnetic field lines, ion reflux effectively enhances the cross-field electron transport. This second mechanism operates downstream of the exit plane and does not enhance electron transport in the acceleration region. Both of these mechanisms, i.e., multiply charged ions and ion reflux, reduce the need to invoke anomalous electron transport mechanisms in Hall thruster computer simulations. However, to date, no Hall thruster simulation has produced results in agreement with data without assuming some anomalous electron transport. Index Terms--Electron transport, Hall thrusters, particle simulations, plasma propulsion.

Abstract Background Inhalation of helium-oxygen (He/O2) mixtures has been explored as a means to lower the work of breathing of patients with obstructive lung disease. Non-invasive ventilation (NIV) with positive pressure support is also used for this purpose. The bench experiments presented herein were conducted in order to compare simulated patient inspiratory effort breathing He/O2 with that breathing medical air, with or without pressure support, across a range of adult, obstructive disease patterns. Methods Patient breathing was simulated using a dual-chamber mechanical test lung, with the breathing compartment connected to an ICU ventilator operated in NIV mode with medical air or He/O2 (78/22 or 65/35%). Parabolic or linear resistances were inserted at the inlet to the breathing chamber. Breathing chamber compliance was also varied. The inspiratory effort was assessed for the different gas mixtures, for three breathing patterns, with zero pressure support (simulating unassisted spontaneous breathing), and with varying levels of pressure support. Results Inspiratory effort increased with increasing resistance and decreasing compliance. At a fixed resistance and compliance, inspiratory effort increased with increasing minute ventilation, and decreased with increasing pressure support. For parabolic resistors, inspiratory effort was lower for He/O2 mixtures than for air, whereas little difference was measured for nominally linear resistance. Relatively small differences in inspiratory effort were measured between the two He/O2 mixtures. Used in combination, reductions in inspiratory effort provided by He/O2 and pressure support were additive. Conclusions The reduction in inspiratory effort afforded by breathing He/O2 is strongly dependent on the severity and type of airway obstruction. Varying helium concentration between 78% and 65% has small impact on inspiratory effort, while combining He/O2 with pressure support provides an additive reduction in inspiratory effort. In addition, breathing He/O2 alone may provide an alternative to pressure support in circumstances where NIV is not available or poorly tolerated.

Abstract Background Expiratory time constants are used to quantify emptying of the lung as a whole, and emptying of individual lung compartments. Breathing low-density helium/oxygen mixtures may modify regional time constants so as to redistribute ventilation, potentially reducing gas trapping and hyperinflation for patients with obstructive lung disease. In the present work, bench and mathematical models of the lung were used to study the influence of heterogeneous patterns of obstruction on compartmental and whole-lung time constants. Methods A two-compartment mechanical test lung was used with the resistance in one compartment held constant, and a series of increasing resistances placed in the opposite compartment. Measurements were made over a range of lung compliances during ventilation with air or with a 78/22% mixture of helium/oxygen. The resistance imposed by the breathing circuit was assessed for both gases. Experimental results were compared with predictions of a mathematical model applied to the test lung and breathing circuit. In addition, compartmental and whole-lung time constants were compared with those reported by the ventilator. Results Time constants were greater for larger minute ventilation, and were reduced by substituting helium/oxygen in place of air. Notably, where time constants were long due to high lung compliance (i.e. low elasticity), helium/oxygen improved expiratory flow even for a low level of resistance representative of healthy, adult airways. In such circumstances, the resistance imposed by the external breathing circuit was significant. Mathematical predictions were in agreement with experimental results. Time constants reported by the ventilator were well-correlated with those determined for the whole-lung and for the low-resistance compartment, but poorly correlated with time constants determined for the high-resistance compartment. Conclusions It was concluded that breathing a low-density gas mixture, such as helium/oxygen, can improve expiratory flow from an obstructed lung compartment, but that such improvements will not necessarily affect time constants measured by the ventilator. Further research is required to determine if alternative measurements made at the ventilator level are predictive of regional changes in ventilation. It is anticipated that such efforts will be aided by continued development of mathematical models to include pertinent physiological and pathophysiological phenomena that are difficult to reproduce in mechanical test systems.