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Porous ionic electrospray emitters have received significant interest for space propulsion due to their performance and operational simplicity. We have developed a diffusion equation for describing the transient flow response in a porous electrospray emitter, which allows for the prediction of the settling time for flow in the porous emitter. This equation accounts for both the change in liquid storage at exposed pores on the emitter with pressure, and viscous diffusion through Darcy's law. Transient flow solutions are provided for the most common emitter topologies: pillar, cone, and wedge. Transient flow solutions describe the settling time and magnitude of current overshoot from porous electrosprays. Comparing diffusion of pressure to the onset delay model for electrospray emission shows that diffusion is most relevant at higher voltages and when a porous reservoir is used. Accounting for multiple emission sites on the wedge geometry shows that emission sites settle in proportion to emission site spacing to the power -1.74. Applying the diffusion equation to published results shows good agreement between analytical predictions and experimental data.

The increasing capabilities of the CubeSat platform have led to growing interest in performing more complex commercial and science missions with these miniature spacecraft. In particular, electric ...

Molecular dynamics (MD) simulations were performed for ion extraction from electrospray thrusters to investigate relevant extraction processes numerically. To approximate the electrospray jet tip, a simulation domain consisting of 4-5 nm-sized ionic liquid droplets was used. The extracted ion angles and kinetic energies from EMI–BF4 (1-ethyl-3-methylimidazolium tetrafluoroborate) and EMI–Im (1-ethyl-3-methylimidazolium bis((trifluoromethyl)sulfonyl)imide) droplets were quantified by applying uniform electric fields of 1.3–1.7 V nm−1. The MD simulations are in great agreement with simulations presented in the literature and consistently show a greater preference for monomer emission than reported experimentally. At field strengths above 1.5 V nm−1, apparent droplet fracturing and breakup lead to an increase in ion angular velocity distributions. Greater mobility of EMI–BF4 ions than EMI–Im was also observed, indicative of the crucial role of cation-anion hydrogen bond strengths in ion extraction and beam composition between different propellants.

High-resolution mass flux measurements of an electrospray plume are reported at high (>30$$^{\circ }$$ ∘ ) angles, which are relevant to direct impingement of downstream electrodes. Interrogation of the plume edge greatly reduces uncertainty in electrospray device lifetime estimation related to mass flux to electrode surfaces. An angularly-actuated Thermoelectric Quartz Crystal Microbalance (TQCM) provides resolution down to $$\sim$$ ∼ 2 pg cm$$^{-2}$$ - 2 s$$^{-1}$$ - 1 , allowing the highest resolution mass flux measurements of an electrospray plume to be reported herein. In-situ microscopy of the electrospray meniscus revealed changes to the electrode lines-of-sight of approximately 2°–3° due to the increasing meniscus tip height with beam current. Using the TQCM measurements and previous QCM results, a data-driven model is proposed for estimating electrode impingement as a function of beam current and aperture line-of-sight, which quantitatively captures the rapid increase in mass flux at higher beam currents or at low angles. The results show it is possible to guarantee negligible electrode impingement within a specified range of throttle levels.

The coronavirus disease 2019 (COVID-19) pandemic has greatly stressed the global community, exposing vulnerabilities in the supply chains for disinfection materials, personal protective equipment, and medical resources worldwide. Disinfection methods based on cold atmospheric plasma (CAP) technologies offer an intriguing solution to many of these challenges because they are easily deployable and do not require resource-constrained consumables or reagents needed for conventional decontamination practices. CAP technologies have shown great promise for a wide range of medical applications from wound healing and cancer treatment to sterilization methods to mitigate airborne and fomite transfer of viruses. This review engages the broader community of scientists and engineers that wish to help the medical community with the ongoing COVID-19 pandemic by establishing methods to utilize broadly applicable CAP technologies.

Air breathing electric propulsion (atmosphere-breathing electric propulsion) (ABEP) has attracted significant interest as an enabling technology for long duration space missions in very low Earth orbit (VLEO) altitudes below about 300 km. The ABEP spacecraft and mission analysis model developed allows parametric characterization of key spacecraft geometry and thruster performance parameters such as spacecraft length-to-diameter, the ratio of solar array span to spacecraft diameter, thrust-to-power, effective exhaust velocity, and inlet efficiency. For the missions analyzed ABEP generally outperforms conventional electric propulsion (EP) below 250 km altitude. Using a 6U spacecraft architecture the model shows that below 220 km ABEP is the only viable propulsion option for desirable mission lifetimes. Parametric evaluations of key spacecraft and ABEP characteristics show that the most significant technological improvements to ABEP spacecraft performance and range of applicability for VLEO missions will come from advancements in inlet efficiency, low drag materials, solar array efficiency, and thrust-to-power.

Complex material surfaces can reduce secondary electron emission (SEE) and sputtering via geometric trapping. In this work, the SEE yields for a range of open-cell reticulated carbon foam geometries are characterized using scanning electron microscopy. The total reduction in the SEE yield from carbon foams with a 3% volume fill density and 10–100 pores per inch (PPI) is shown to be between 23.5% and 35.0%. Contributions of a foam backplate are assessed by experimentally and analytically defining the critical parameter, transparency. The transparency of a foam is quantified and is shown to affect the primary electron angular dependence on the SEE yield. For the same thickness of 6 mm, it is found that higher PPI decreases foam transparency from 32% to 0% and reduces the SEE yield. The SEE yield from carbon foams is also shown to have weaker dependence on the morphology of the surface compared with fuzzes and velvets and less variation across individual sample surfaces due to the rigidity of their ligament structures and isotropic geometries.

Biplane wind turbine blades have been shown to have improved structural performance, aerodynamic performance, and reduced aerodynamic loads compared to conventional blade designs. Here, the impact of these factors on blade mass is quantified for the first time. The objectives of this work are to quantify the mass of biplane wind turbine blades which have been designed for realistic loads, and to understand the mass-driving constraints for such blades. A numerical optimization approach is used to design the internal structure of biplane wind turbine blades, minimizing blade mass subject to a number of design requirements which are imposed as constraints. The mass reductions are significant, showing that the optimal biplane blades are more than 45% lighter than a similarly-optimized monoplane blade. This is primarily due to the improved resistance to flapwise deflection when compared to the monoplane blades, which allows for considerably less spar cap material to be used in the biplanes. Biplane blades are also shown to have improved resistance to edgewise fatigue damage, requiring less trailing edge reinforcement. Given such large mass reductions, some criticality is required, and the limitations of the present approach are discussed. The results of the optimization present strong evidence that biplane wind turbine blades may be an enabling concept for the next generation of lighter, larger, and more cost-effective wind turbine blades.

Elemental sulfur is a promising medium for moderate to high-temperature thermal energy storage (TES) systems due to its low cost and excellent chemical stability up to very high temperatures (1200 °C). Previous studies show that vertically-oriented tubes of isochorically contained thermal storage media (i.e., supercritical CO2) can exhibit higher heat transfer rates than horizontal tubes. Storing thermal storage media in vertical tubes in a TES system also has some potential system-level advantages related to exergy capacity, operation and maintenance, and cost. This paper investigates the heat transfer behavior and performance of sulfur contained in vertically-oriented tubes between room temperature (25 °C) and 600 °C. Experimental and computational analyses show that the natural convection heat transfer behavior for sulfur in a vertically-oriented tube is strongly dependent on the sulfur viscosity, which varies greatly over the range of temperatures used in this study. Validated Nusselt number correlations for vertical tubes of lengths between 0.5 and 3 m and diameters between 5.5 and 21.2 cm are developed for use in parametric studies and designs. In comparison to the horizontally-oriented tube, the vertical tube can have better heat transfer performance with some ranges of tube length and diameter. Therefore, the selection of the tube orientation strongly depends on the tube dimensions and application needs. The results from the current study provide important quantitative and qualitative design bases for sulfur-based TES (SulfurTES) systems.

The leaky-dielectric model is incorporated in the Finite Volume Method (FVM) code, OpenFOAM, to investigate the electrospray emission behavior of low to moderate conductivity liquids. This work extends FVM modeling to moderate conductivities by employing a new interface interpolation scheme that is devised in the volume of fluid method to ensure charge conservation for accurate reproduction of charge accumulation and resulting meniscus shape in the cone-to-jet region and jet breakup. The model results agree well with experiments and scaling laws for droplet diameter and total current for low and moderate conductivity fluids, i.e., heptane and tributyl phosphate, respectively. The droplet diameter is shown to increase as the dimensionless flow rate increases or the electric Reynolds number decreases. The results are also consistent with a parametric investigation of the meniscus shape and the maximum charge density for key operating conditions (flow rate and extraction potential) and liquid properties (conductivity, surface tension, viscosity, and relative permittivity). These results show that the new interface interpolation scheme provides accurate results for a wide range of conductivities, fluid properties, and operating conditions. The results also provide valuable physical insight for varying liquid conductivity in the electrospray emission process. In particular, low dimensionless flow rate or high electric Reynolds number leads to the emergence of convex-outward menisci associated with a high charge density in the cone-to-jet region, resulting in high jetting velocity and high specific charge droplets.

Surgery represents the major option for treating most solid tumors. Despite continuous improvements in surgical techniques, cancer recurrence after surgical resection remains the most common cause of treatment failure. Here, we report cold atmospheric plasma (CAP)–mediated postsurgical cancer treatment, using a portable air-fed CAP (aCAP) device. The aCAP device we developed uses the local ambient air as the source gas to generate cold plasma discharge with only joule energy level electrical input, thus providing a device that is simple and highly tunable for a wide range of biomedical applications. We demonstrate that local aCAP treatment on residual tumor cells at the surgical cavities effectively induces cancer immunogenic cell death in situ and evokes strong T cell–mediated immune responses to combat the residual tumor cells. In both 4T1 breast tumor and B16F10 melanoma models, aCAP treatment after incomplete tumor resection contributes to inhibiting tumor growth and prolonging survival.

In near-Earth space, the magnetosphere, energetic electrons (tens to thousands of kiloelectron volts) orbit around Earth, forming the radiation belts. When scattered by magnetospheric processes, these electrons precipitate to the upper atmosphere, where they deplete ozone, a radiatively active gas, modifying global atmospheric circulation. Relativistic electrons (those above a few hundred kiloelectron volts), can reach the lowest altitudes and have the strongest effects on the upper atmosphere; their loss from the magnetosphere is also important for space weather. Previous models have only considered magnetospheric scattering and precipitation of energetic electrons; atmospheric scattering of such electrons has not been adequately considered, principally due to lack of observations. Here we report the first observations of this process. We find that atmospherically-scattered energetic (relativistic) electrons form a low-intensity, persistent “drizzle”, whose integrated energy flux is comparable to (greater than) that of the more intense but ephemeral precipitation by magnetospheric scattering. Thus, atmospheric scattering of energetic electrons is important for global atmospheric circulation, radiation belt flux evolution, and the repopulation of the magnetosphere with lower-energy, secondary electrons.

Aluminum microfoams are found to exhibit persistent sputtering yield reductions of 40%--80% compared to a flat aluminum surface under 100 to 300 eV argon plasma bombardment. An analytical model reveals a strong dependency of the yield on the foam geometry and plasma sheath. For foam pore sizes near or larger than the sheath thickness, the plasma infuses the foam and transitions the plasma-surface interactions from superficial to volumetric phenomena. By defining a plasma infusion parameter, the sputtering behavior of foams is shown to be separated into the plasma-facing and plasma-infused regimes. While plasma infusion leads to a larger effective sputtering area, geometric recapture of ejected particles facilitates an overall reduction in yield. For a given level of plasma infusion, the reductions in normalized yield are more pronounced at lower ion energies since angular sputtering effects enable more effective geometric recapture of sputterants.

Conventional plasma jets for biomedical applications tend to have several drawbacks, such as high voltages, high gas delivery, large plasma probe volume, and the formation of discharge within the organ. Therefore, it is challenging to employ these jets inside a living organism&rsquo, s body. Thus, we developed a single-electrode tiny plasma jet and evaluated its use for clinical biomedical applications. We investigated the effect of voltage input and flow rate on the jet length and studied the physical parameters of the plasma jet, including discharge voltage, average gas and subject temperature, and optical emissions via spectroscopy (OES). The interactions between the tiny plasma jet and five subjects (de-ionized (DI) water, metal, cardboard, pork belly, and pork muscle) were studied at distances of 10 mm and 15 mm from the jet nozzle. The results showed that the tiny plasma jet caused no damage or burning of tissues, and the ROS/RNS (reactive oxygen/nitrogen species) intensity increased when the distance was lowered from 15 mm to 10 mm. These initial observations establish the tiny plasma jet device as a potentially useful tool in clinical biomedical applications.

Syndrome coronavirus 2 (SARS-CoV-2) infectious virions are viable on various surfaces (e.g., plastic, metals, and cardboard) for several hours. This presents a transmission cycle for human infection that can be broken by developing new inactivation approaches. We employed an efficient cold atmospheric plasma (CAP) with argon feed gas to inactivate SARS-CoV-2 on various surfaces including plastic, metal, cardboard, basketball composite leather, football leather, and baseball leather. These results demonstrate the great potential of CAP as a safe and effective means to prevent virus transmission and infections for a wide range of surfaces that experience frequent human contact. Since this is the first-ever demonstration of cold plasma inactivation of SARS-CoV-2, it is a significant milestone in the prevention and treatment of coronavirus disease 2019 (COVID-19) and presents a new opportunity for the scientific, engineering, and medical communities.

Electrospray thruster life and mission performance are strongly influenced by grid impingement, the extent of which can be correlated with emission modes that occur at steady-state extraction voltages, and thruster command transients. Most notably, we experimentally observed skewed cone-jet emission during steady-state electrospray thruster operation, which leads to the definition of an additional grid impingement mechanism that we termed &ldquo, tilted emission&rdquo, Long distance microscopy was used in conjunction with high speed videography to observe the emission site of an electrospray thruster operating with an ionic liquid propellant (EMI-Im). During steady-state thruster operation, no unsteady electrohydrodynamic emission modes were observed, though the conical meniscus exhibited steady off-axis tilt of up to 15&deg, Cone tilt angle was independent over a wide range of flow rates but proved strongly dependent on extraction voltage. For the geometry and propellant used, the optimal extraction voltage was near 1.6 kV. A second experiment characterized transient emission behavior by observing startup and shutdown of the thruster via flow or voltage. Three of the four possible startup and shutdown procedures transition to quiescence within &sim, 475 &mu, s, with no observed unsteady modes. However, during voltage-induced thruster startup, unsteady electrohydrodynamic modes were observed.

Correction to: Space Sci. Rev. (2020) 216: 103 Affiliation 2 in this article is the wrong affiliation that instead should read: “Institute of Geophysics and Planetary Physics, University of California, Los Angeles, CA, USA” which should be regarded as the final version by the reader.

The Electron Loss and Fields Investigation with a Spatio-Temporal Ambiguity-Resolving option (ELFIN-STAR, or simply: ELFIN) mission comprises two identical 3-Unit (3U) CubeSats on a polar (~93deg inclination), nearly circular, low-Earth (~450 km altitude) orbit. Launched on September 15, 2018, ELFIN is expected to have a >2.5 year lifetime. Its primary science objective is to resolve the mechanism of storm-time relativistic electron precipitation, for which electromagnetic ion cyclotron (EMIC) waves are a prime candidate. From its ionospheric vantage point, ELFIN uses its unique pitch-angle-resolving capability to determine whether measured relativistic electron pitch-angle and energy spectra within the loss cone bear the characteristic signatures of scattering by EMIC waves or whether such scattering may be due to other processes. Pairing identical ELFIN satellites with slowly-variable along-track separation allows disambiguation of spatial and temporal evolution of the precipitation over minutes-to-tens-of-minutes timescales, faster than the orbit period of a single low-altitude satellite (~90min). Each satellite carries an energetic particle detector for electrons (EPDE) that measures 50keV to 5MeV electrons with deltaE/E, Submitted to Space Science Reviews April 2020. 51 pages, 7 tables, 21 figures

The recent pandemic has greatly stressed supply chains, treatment modalities, and medical resources. Cold atmospheric plasma (CAP) has been used for a wide range of applications in biomedical engineering due to its many components including electrons, charged particles, reactive oxygen species (ROS), reactive nitrogen species (RNS), free radicals, ultraviolet (UV) photons, molecules, electromagnetic fields, physical forces, and electric fields. In this manuscript, we develop CAP devices for COVID-19. Our manuscript indicates the advantages of highlydeployable CAP devices for both sanitation and treatment, without the need for supply chains of special consumables such as hand sanitizers and the like. We hope that this timely research will help engage the broader community of engineers that wish to help the medical community with this pandemic and to prevent and treat future outbreaks.

Elemental sulfur provides a low-cost, high-performance thermal storage option for a wide range of applications and over an exceptionally wide range of temperatures (50 °C to over 600 °C). In previous efforts we have shown impressive performance for 200–600 °C, while in this study we examine the low-temperature (50–200 °C) thermal charge and discharge behavior of isochoric sulfur-based storage using a detailed computational model solving for the conjugate heat transfer and solid-liquid phase change dynamics. The model provides excellent agreement with experimental results. We show that sulfur exhibits lower viscosity because of reduction in the chain-length of polymeric sulfur caused by trace amounts of organic substances resulting in attractive charge and discharge performance. The results from the parametric analysis of pipe diameter on the charge and discharge heat transfer characteristics are used to develop a simple, generalized correlation that relates the transient sulfur temperature and liquid fraction evolution as a function of dynamically evolving buoyancy-Fourier number due to the solid-liquid phase change. This solid-liquid buoyancy-Fourier, BFs-l, correlation can be used for effectively designing sulfur-based thermal energy storage systems for transient operation in low temperature applications.

An experimental investigation into the correlation between ion acoustic turbulence (IAT) and anomalous ion heating in the plume of a 100 A-class LaB6 hollow cathode is presented. Laser-induced fluo...

Elemental sulfur is a low-cost energy storage media suitable for many medium to high temperature applications, including trough and tower concentrated solar power (CSP) and combined heat and power (CHP) systems. In this study, we have demonstrated the viability of an elemental sulfur thermal energy storage (SulfurTES) system using a laboratory-scale thermal battery. The SulfurTES battery design uses a shell-and-tube thermal battery configuration, wherein stationary elemental sulfur is isochorically stored in multiple stainless steel tubes and a heat transfer fluid (air) is passed over them through the surrounding shell. The safe and reliable operation was demonstrated for twelve thermal charge–discharge cycles in the temperature range of 200–600 °C, during which the SulfurTES battery stored up to 7.6 kW h of thermal energy with volumetric energy density range up to 255 kW h/m3. Furthermore, the SulfurTES battery is operated in a hybrid thermal charging mode to demonstrate its ability to store surplus electrical energy. The present study establishes the feasibility of SulfurTES as a concept that could provide attractive system cost and volumetric energy density for a wide range of thermal energy storage applications.