Air Force Research Laboratory Research Articles

(Invited) Solid Oxide Cell Design for High Power Density and Reliability: Applications in Power and Fuels Production

Solid oxide fuel cells (SOFC) offer a carbon-neutral solution to power generation, fuel flexibility, and robust design suitable for stationary and air transportation applications. OxEon Energy developed an air electrode supported (AES) cell design that demonstrated 63% increase in power density compared with its heritage cell design in short stack tests.OxEon Energy team has been advancing solid oxide technology for over three decades and the stacks operate fully reversibly in fuel cell and electrolysis cell modes. The SOEC/SOFC technology builds on the success of the SOEC stack installed on NASA’s Mars Perseverance Rover as part of the MOXIE (Mars Oxygen In-situ resource utilization Experiment) mission. The MOXIE stack produced propellant grade, high-purity O2 by electrolyzing Mars atmosphere CO2. MOXIE stack used an electrolyte supported design to meet the reliability requirements for a space mission.An infiltrated air electrode cell design was developed to increase fuel cell stack specific power (kW/kg). Electrolyte thickness, the most resistive element of the SOFC, was reduced from ~250 microns to 70 microns. The fabrication process results in a bi-layer of dense scandia stabilized zirconia (ScSZ) electrolyte and a porous yttria stabilized zirconia (YSZ) matrix for air electrode infiltration. Fuel electrodes are screen printed. The reduced thickness of the electrolyte offers a compromise between improved performance over electrolyte supported design, while meeting robustness required for aerospace applications.Producing infiltrated electrodes with well-adhered and homogeneous distribution of active material is a challenge that requires multiple infiltration-calcination cycles to deposit sufficient material. Key variables are precursor chemistry to reduce the number of infiltrations and prevent interaction between electrode layers; intermediate calcination temperatures; and process development using infiltration equipment that enables volume production. OxEon partnered with National Energy Technology Laboratory (NETL) for electrode infiltration process development and PNNL for button cell and short stack validation testing.SOFC fuel flexibility was demonstrated in button cells and stacks previously; performance was nearly identical among hydrogen, ammonia, and reformed natural gas. Durability testing shows similarly stable performance in each fuel.A 10-cell AES stack was tested in SOFC mode at 800 °C in H2 and NH3 fuel feeds at 0.7 V/cell, and the same stack was operated in steam electrolysis to produce H2. SOFC testing demonstrated powder density of 0.35 W/ cm2 at 0.7 V/cell in the AES stack in ammonia feed; an electrolyte supported stack with equivalent materials measured 0.20 W/cm2 at 0.7 V. Long term testing in steam electrolysis showed stable performance at 800 °C and 1.2 V/ cell.Button cell tests show the thin electrolyte cell structure is capable of an area specific resistance (ASR) of 0.25 Ω-cm2 in H2- and NH3 fuel feeds. OxEon’s continued AES cell development is focused on improving manufacturability, infiltrated electrode stability, and implementing degradation mitigation strategies developed for electrolyte supported cell structures. Improved performance with AES cell design has critical implications for future integration in OxEon’s technology suite: SOEC systems to generate H2 and syngas from renewable energy, and Fischer-Tropsch to produce synthetic fuels.This material is based on research sponsored by Air Force Research Laboratory under agreement number FA8649-22-P-0792. The views expressed are those of the authors and do not necessarily reflect the official policy or position of the Department of the Air Force, the Department of Defense, or the U.S. government. Approved for public release; distribution is unlimited. Figure 1

Transcutaneous cervical vagus nerve stimulation enhances second-language vocabulary acquisition while simultaneously mitigating fatigue and promoting focus

Transcutaneous vagus nerve stimulation (tVNS) is a promising technique for enhancing cognitive performance and skill acquisition. Yet, its efficacy for enhancing learning rate and long-term retention in an ecologically valid learning environment has not been demonstrated. We conducted two double-blind sham-controlled experiments examining the efficacy of auricular tVNS (taVNS: Experiment (1) and cervical tVNS (tcVNS: Experiment (2), on a 5 day second-language vocabulary acquisition protocol among highly selected career linguists at the US Department of Defense’s premier language school. tcVNS produced accelerated recall performance during training (Day 2–4), benefits of which were maintained across a 24 h retention interval with no stimulation at the final test. Consistent with prior work, tcVNS also produced fatigue-mitigating and focus-promoting effects as measured by the Air Force Research Laboratory Mood Questionnaire. Based on the current and the previous findings supporting tVNS’ efficacy on performance, training enhancement, and fatigue mitigation, we believe tcVNS to be an effective learning acceleration tool that can be utilized at language-teaching and other institutions focused on intensive training of cognitive skills.

Factors That Influence Health care-Seeking Behavior and Health Information Disclosure Among U.S. Air Force Pilots.

The reality of pilot health care avoidance behavior is often common knowledge to both pilots and aeromedical physicians, but the underlying factors leading to this behavior are less understood. In the current study, we conducted a qualitative assessment of a sample of U.S. Air Force (USAF) pilots to gather firsthand perceptions of the factors that encourage and discourage disclosure during aeromedical screening and use of mental and physical health care services, as well as recommendations to improve the USAF aeromedical health care system. We conducted interviews with 21 USAF pilots on their perceptions of seeking medical care to identify factors that uniquely discourage or encourage disclosure and health care utilization to understand factors that aid the aeromedical provider/aviator relationship and to elicit interventions that could be prospectively researched. This work was reviewed by the Air Force Research Laboratory Institutional Review Board at Wright-Patterson Air Force Base and designated as exempt research, FWR20220103E. The most reported factors that discourage military pilot health care disclosure and health care utilization overall were medical revocation, stigma, and lack of trust in providers. Unit-embedded services, ease of access, and severity of condition were the most reported factors encouraging disclosure and utilization. Factor descriptions and exemplary quotes from pilots and pilot recommendations to encourage health care utilization and disclosure are provided. Results from firsthand interviews with pilots provide valuable information for flight surgeons to focus on building trust with their pilots to reduce health care avoidance.

Optimizing Dynamic Airlift Operations: Winning Strategies in the AFRL Airlift Challenge

The Air Force Research Laboratory (AFRL) has sponsored the Airlift Challengeover the past two years, aimed at addressing the dynamic airlift problem. Thedynamic nature of the challenge included the random disappearance of graphedges to simulate adverse weather conditions and the spontaneous appearance ofcargo requiring delivery. This poster presents the systems that won both the 2023and 2024 challenges. The initial approach focused on intelligent solutions for subtasks, or 'build-smart'. It soon became clearthat the optimization of the scoring rate, points per second, was moreimportant than single instance metric performance. In the subsequentcompetition, a 'build-fast' strategy was adopted due to this observation. Thispaper discusses the impact of iteration on algorithm selection for optimizationproblems and suggests considerations for structuring scoring processes infuture competitions.

Information Extraction and Three-Dimensional Contour Reconstruction of Vehicle Target Based on Multiple Different Pitch-Angle Observation Circular Synthetic Aperture Radar Data

The circular synthetic aperture radar (CSAR) has the ability of all-round continuous observation and high-resolution imaging detection, and can obtain all-round scattering information and higher-resolution images of the observation scene, so as to realize the target information extraction and three-dimensional (3D) contour reconstruction of the observation targets. However, the existing methods are not accurate enough to extract the information of vehicle targets. Through the analysis of the vehicle target scattering model and CSAR image characteristics, this paper proposes a vehicle target information extraction and 3D contour reconstruction method based on multiple different pitch-angle observation CSAR data. The proposed method creatively utilizes the projection relationship of the vehicle in 2D CSAR imaging to reconstruct the 3D contour of the vehicle, without prior information. Firstly, the CSAR data obtained from multiple different pitch-angle observations are fully utilized, and the scattering points of odd-bounce reflection and even-bounce reflection echoes are extracted from the two-dimensional (2D) coherent CSAR images of the vehicle target. Secondly, the basic contour of the vehicle body is extracted from the scattering points of the even-bounce reflected echoes. Then, the geometric projection relationship of the “top–bottom shifting” effect of odd-bounce reflection is used to calculate the height and position information of the scattering points of odd-bounce reflection, so as to extract the multi-layer 3D contour of the vehicle target. Finally, the basic contour and the multi-layer 3D contour of the vehicle are fused to realize high-precision 3D contour reconstruction of the vehicle target. The correctness and effectiveness of the proposed method are verified by using the CVDomes simulation dataset of the American Air Force Research Laboratory (AFRL), and the experimental results show that the proposed method can achieve high-precision information extraction and realize distinct 3D contour reconstruction of the vehicle target.

Experimental design on high-speed sliding wear

This paper recounts research that develops, conducts, and analyzes an experimental design characterizing wear rates of various materials sliding at high speeds along an AISI 4340 steel rail. The work supports Holloman Air Force Base’s engineering of a more wear-resistant rocket slipper for their high-speed test track. A design of experiments approach is used to systematically identify and evaluate potential slipper attributes that mitigate wear based on a heat transfer model. Results include recommendations of slipper materials that theoretically perform similar to or better than the baseline Vascomax®C300 maraging steel as well as statistical evaluation of the finite element analysis heat transfer model of the Air Force Research Laboratory’s pin-on-disk rig.

Integrating Battlefield Documentation into Virtual Reality Medical Simulation Training: Virtual Battlefield Assisted Trauma Distributed Observation Kit (BATDOK).

Clinical documentation is an essential component of the provision of medical care, enabling continuity of information across provider and site handoffs. This is particularly important in the combat casualty care setting when a single casualty may be treated by four or more or five completely disparate teams across the roles of care. The Battlefield Assisted Trauma Distributed Observation Kit (BATDOK) is a digital battlefield clinical documentation system developed by the Air Force Research Laboratory to address this need. To support the deployment of this tool, we integrated BATDOK into a commercially available virtual reality (VR) medical simulation platform used by the U.S. Air Force and Defense Health Agency personnel in order to provide an immersive simulation training experience which included battlefield documentation. A multidisciplinary team consisting of medical educators, VR simulation engineers, emergency physicians and pararescuemen, and BATDOK developers first developed a specification for a virtual BATDOK capability, including a detailed listing of learning objectives, critical interfaces and task plans, and sensor integrations. These specifications were then implemented into the commercially available Virtual Advancement of Learning for Operational Readiness VR Medical Simulation System and underwent developmental testing and evaluation during pararescueman training exercises at the Air Force Special Operations Command Special Operations Center for Medical Integration and Development. The BATDOK capability was successfully implemented within the VR Medical Simulation System. The capability consisted of a virtual tablet with replicated interfaces and capabilities based on the developed specifications. These capabilities included integrated point-of-care ultrasound capability, multi-patient management, vitals sign monitoring with sensor pairing and continuous monitoring, mechanism of injury documentation (including injury pattern documentation), intervention logging (including tourniquets, dressing, airways, lines, tubes and drains, splints, fluids, and medications), and event logging. The capability was found to be operational and in alignment with learning objectives and user acceptance goals.

Mineral Composition Effects on Dust Deposition at Realistic Engine Conditions

Abstract In this article, the role of mineral composition was assessed for Air Force Research Laboratory Test Dust (AFRL), for deposition in a realistic gas turbine engine environment. Experiments were performed on an effusion cooling test article with a coolant flow temperature of 894 K and surface temperature of 1144 K. Aerosolized dust with a 0–10 µm particle size distribution was delivered to the test article. The mineral recipe of AFRL was altered such that the presence of each of the five components ranged from 0% to 100%, and capture efficiency, hole capture efficiency, blockage per gram, and normalized deposit height were reported. Results are compared to a previous study of the intermineral synergies in an impingement cooling jet at the same temperature conditions. Despite differences in experimental facility flow geometry, overall agreement was found between the trends in the deposition behavior of the dust blends. The strong deposition effects that were observed were shown to be related to adhesion forces of particles, mechanical properties, and chemical properties of the dust minerals. Supplemental testing was performed in a high-temperature (1425–1650 K) impinging jet (200–260 m/s) to evaluate mineral effects at hot gas path conditions. Capture efficiency and morphology of dust deposits are reported. The capture efficiency in this regime was shown to correlate well with temperature, with chemical effects being secondary. An attempt was made to predict capture efficiency using chemical assessments such as a ratio of bases to acids, Ca:Si ratio, and optical basicity with only modest success.

A Set-Covering Approach to Customized Coverage Instrumentation

Program coverage customization selectively adds instrumentation to a compiled computer program so that a limited amount of directly observed data can be used to infer other program coverage information after a run. A good instrumentation plan can reduce run-time overheads while still giving software developers the information they need. Unfortunately, optimal coverage planning is NP-hard, limiting either the quality of heuristic plans or the sizes of programs that can be instrumented optimally. We exploit the monotonicity property of feasible instrumentations to formulate this problem as an intraprocedural set covering problem. Our formulation has an exponential number of constraints, and we design a polynomial-time separation algorithm to incrementally add the necessary subset of these inequalities. Our approach reduces expected run-time probing costs compared with existing methods, offers a guarantee of the optimality of the instrumentation, and has compilation-time overhead suitable for wide practical use. History: Accepted by Pascal Van Hentenryck, Area Editor for Computational Modeling: Methods & Analysis. Funding: This work was supported by the National Science Foundation [Grants CCF-1318489, CCF-1420866, and CCF-1423237] and the Air Force Research Laboratory [Grant FA8750-14-2-0270]. Supplemental Material: The software that supports the findings of this study is available within the paper and its Supplemental Information ( https://pubsonline.informs.org/doi/suppl/10.1287/ijoc.2021.0349 ) as well as from the IJOC GitHub software repository ( https://github.com/INFORMSJoC/2021.0349 ). The complete IJOC Software and Data Repository is available at https://informsjoc.github.io/ .

Frequency-dependent directivity and sound power measurements of two launched United Launch Alliance Atlas V rockets

The noise generated during rocket launches is both intense and directional. Historically, rocket noise directivity has been studied using static firing data. Although such tests result in greater averaging times at all angles, it is also possible to estimate directivity curves and sound power for a launched rocket so long as the trajectory data and microphone locations are known. Acoustical measurements were made during two United Launch Alliance Atlas V launches out of Vandenberg Space Force Base, CA. Multiple microphones were placed around the base ranging from 300–7000 m from the launch pad at different azimuthal angles around the pad. Frequency-dependent directivity curve estimates and sound power spectra are calculated and compared between measurement sites and launches. Directivity indices are compared with those found in the literature. The overall sound power levels agree well between the two launches, though a general trend persists where the sound power estimate decreases as a function of measurement distance. The sound power spectra are also nondimensionalized using Strouhal number scaling and compared with historical literature. [Work supported in part by the Oak Ridge Institute for Science and Education and the Air Force Research Laboratory.]

Validation of an image source method room acoustics software in a highly reverberant room with a directional impulsive noise source

Exposure to impulsive noise sources is common during routine operations military contexts. This type of noise exposure is prevalent in training procedures carried out with small caliber firearms in both indoor and outdoor settings. Typically, hearing protection is required to mitigate hearing damage risk to military personnel. Consequently, proper prescription of hearing protection required bioenvironmental engineers and industrial hygienists to travel and collect data in situ which can be time consuming and expensive. As such, the researchers at the 711th Human Performance Wing of the United States Air Force Research Lab have developed a software named the Shooting Range Impulse Noise Calculator (ShRINC). The ShRINC software provides the capability to simulate high fidelity acoustic levels within indoor and outdoor shooting ranges with directional impulsive noise sources. This is accomplished by leveraging principles from Image Source Room (ISM) based room acoustics and combining them with weapon source models with complicated directivity patterns. In this work, validation will be completed by comparing results collected in a highly reverberant facility with the M4A1 firearm operating blank rounds. An investigation into the proper order for the ISM solver will be analyzed and sound exposure levels between the simulation and measured data will be compared.

LES MODELING OF HIGH-LIFT HIGH-WORK LPT BLADES: PART II—VALIDATION AND APPLICATION

Abstract Over the years, computational fluids dynamics (CFD) has matured to such a state so as to be indispensable in turbine design. In the past two decades, significant advances in turbine design have been made through the use of CFD—in particular, through the use of Reynolds-Averaged Navier-Stokes (RANS) simulations. Currently, turbine design is RANS-driven; however, significant gains in performance and efficiency are becoming more difficult to achieve using RANS. For this reason, the turbomachinery CFD community is moving toward Large-Eddy Simulations (LES). In the design of low-pressure turbine (LPT) blades, LES is particularly beneficial owing to its ability to capture accurately both transition and separation. In this paper, LES is used to characterize a new family of high-lift high-work LPT blades—designated the LXFHW-LS family—designed at the U.S. Air Force Research Laboratory (AFRL). LES simulations are conducted in accordance with the methodology outlined in Part I of this paper. The purpose of this paper is twofold: 1) to use LES to predict the performance of the LXFHW-LS family and compare to measurements in a low-speed linear cascade and, in doing so, 2) to illustrate how LES may be used in LPT design as it evolves from RANS-driven to LES-driven. For each blade in the family, the loading distribution and loss coefficient are computed for sixteen separate Reynolds numbers. Computational results are validated using detailed experimental measurements from a low-speed linear cascade wind tunnel.

Lightweight Solid Oxide Cell Design for Ammonia-Fed SOFC Systems

OxEon Energy team has been advancing solid oxide fuel cell (SOFC) technology for over three decades and solid oxide electrolysis cell (SOEC) technology using identical stacks for 15 years.OxEon’s SOEC/SOFC technology builds on the success of the SOEC stack installed on NASA’s Mars Perseverance Rover that produces high-purity O2 by electrolyzing Mars atmosphere CO2. The OxEon team worked with Jet Propulsion Laboratory (JPL) and Massachusetts Institute of Technology (MIT) to validate the MOXIE (Mars Oxygen In-situ resource utilization Experiment) stack.MOXIE stack demonstrated that the operational performance on Mars matched results from pre-launch earth testing. MOXIE stack design forms the basis for developing lightweight fuel cell design suitable for an electric Vertical Take-off and Landing (eVTOL). Demonstration of SOFC performance using carbon-free fuels such as ammonia is another critical objective.A lightweight cell design was developed to increase specific power (kW/kg) of the fuel cell stack. The electrolyte thickness, the most resistive element of the SOFC, was reduced from ~250 microns to 70 microns (72% decrease). The fabrication process results in a dense scandia stabilized zirconia ScSZ electrolyte and a porous yttria stabilized zirconia (YSZ) matrix for cathode (air electrode) infiltration. For the fuel electrode, both an infiltrated and screen printed options are evaluated.Producing an infiltrated electrode with a well-adhered and homogeneous distribution of active material is a challenge that requires multiple infiltration-calcination cycles to deposit sufficient material. Key variables are precursor chemistry to reduce the number of infiltrations and to prevent interaction between electrode layers; intermediate calcination temperatures, and process development using an infiltration equipment that enables volume production. OxEon partnered with National Energy Technology Laboratory (NETL) for electrode infiltration process development and PNNL for validation testing of cells. Full size cells are in production for stack testing.Fuel flexibility was demonstrated in button cells and stacks previously. Button cell and stack performance was nearly identical among hydrogen, ammonia, and reformed natural gas. Durability testing shows similarly stable performance in each fuel.A button cell test in ammonia at 800 °C using the thin electrolyte cell structure measured a button cell area specific resistance (ASR) of 0.25 Ω-cm2 in H2/N2 and NH3 fuel feeds and showed a peak power density of 0.98 W/ cm2 in NH3 fuel feed. Short term hold at 0.7 V showed stable performance.Analysis of additional button cell tests and stack tests using thin electrolyte cell structure will inform test stand design modifications that address balance of plant size requirements.This material is based on research sponsored by Air Force Research Laboratory under agreement number FA8649-22-P-0792. The views expressed are those of the authors and do not necessarily reflect the official policy or position of the Department of the Air Force, the Department of Defense, or the U.S. government. Approved for public release; distribution is unlimited. Public Affairs release approval #_______________. Figure 1

Bipropellant Enabled Solid Oxide Fuel Cell Stack Power Supply: Energy Agility for Space Vehicles

Spacecraft often have instances where they are required to operate for long periods of time with significant power requirements and no access to solar power. While a battery system could be designed to meet these occasional, and possibly unexpected requirements, creating a power supply to meet these infrequent demands results in having a battery system that is excessively large, massive, and inefficient. A Solid Oxide Fuel Cell (SOFC) system capable of running on the same fuel and oxidizer as the onboard thruster of a bipropellant thruster equipped spacecraft can eliminate much of the added mass and volume needed to enable batteries to meet extreme power demands and create more operational flexibility on how the chemical energy in stowed bipropellants are used. If the spacecraft needs thrust, the bipropellant can be ignited to provide thrust. If the spacecraft needs electric power, the spacecraft can consume bipropellant to generate auxiliary power. In this work, the proven bipropellant pair ammonia (NH3) and nitrous oxide (N2O) are shown to be a viable fuel and oxidant for hydrogen (H2) consuming air breathing SOFCs, as spontaneous NH3 decomposition will generate H2 and spontaneous N2O decomposition will generate O2. A scale up to a 5-cell SOFC stack fed NH3 and N2O produced power up to ~89W. Higher power can be achieved by scaling up the number of cells in a stack to achieve required power demands. The results of this study demonstrate the potential and feasibility of integrating SOFCs with a bipropellant thruster to creating a dual functioning spacecraft system that can satisfy operational power requirements and on-orbit maneuverability.This material is based on research sponsored by Air Force Research Laboratory under agreement number FA9453-21-C-0060. The views expressed are those of the authors and do not reflect the official guidance or position of the United States Government, the Department of Defense or of the United States Air Force. Approved for public release; distribution is unlimited. Public Affairs release approval #AFRL20230023. Figure 1

Ion-molecule studies of energetic oxygen allotropes in flow tubes: .

Starting in the 1960s, flow tube apparatuses have played a central role in the study of ion-molecule kinetics, allowing for immense chemical diversity of cationic, anionic, and neutral reactants. Here, we review studies of oxygen allotropes, excluding ground state O2 ( ), and focusing instead on reactions of cations, anions, and metal chemi-ionization reactions with ground state atomic oxygen (O 3 P), vibrationally excited molecular oxygen (O2 (v)), electronically excited molecular oxygen (O2 ( )), and ozone (O3 ). Historical outlines of work over several decades are given along with a focus on more recent work by our group at the Air Force Research Laboratory.

Validated and Deployable AI/ML for NDT Data Diagnostics

While artificial intelligence/machine learning (AI/ML) methods have shown promise for the analysis of image and signal data, applications using nondestructive testing (NDT) for managing the safety of systems must meet a high level of quantified capability. Engineering decisions require technique validation with statistical bounds on performance to enable integration into critical analyses, such as life management and risk analysis. The Air Force Research Laboratory (AFRL) has pursued several projects to apply a hybrid approach that integrates AI/ML methods with heuristic and model-based algorithms to assist inspectors in accomplishing complex NDT evaluations. Three such examples are described in this article, including a method that was validated through a probability of detection (POD) study and deployed by the Department of the Air Force (DAF) in 2004 (Lindgren et al. 2005). Key lessons learned include the importance of considering the wide variability present in NDT applications upfront and maintaining a critical role for human inspectors to ensure NDT data quality and address outlier indications.

Characteristics of Boomerang Whistler‐Mode Waves Emitted From the DSX Spacecraft

AbstractThe Air Force Research Laboratory's Demonstration and Science Experiments (DSX) spacecraft carried a high‐voltage very low frequency transmitter and a sensitive broadband receiver to medium Earth orbit in 2019. During many pulsed transmission experiments, DSX detected apparent “boomerang” echoes when its emitted waves refracted in the magnetosphere and returned to the spacecraft. We simulated a series of these detected pulses using cold plasma ray tracing to characterize their likely wavelengths, indices of refraction, and initial wave normal angles. The waves were shown to remain relatively local to DSX, to be lightly damped, and to have a wide variety of wavelengths and indices of refraction, but they were all emitted with very oblique wave normal angles tightly clustered about half a degree from the Gendrin angle, which theoretical antenna models predict is preferentially excited. Our results are remarkably consistent with this prediction but are statistically biased closer to the resonance cone, possibly because of limitations in the ray tracing technique. The result is robust to perturbations of the simulation and confirms a very narrow beam of oblique radiation quite unlike the behavior of a dipole in vacuo.

Linear and Nonlinear Disturbance Evolution on the Frustum of Hypersonic Ogive Cylinders

Aspects of transition mechanisms on a 14° sharp-nosed ogive cylinder at Mach 6 are elucidated by considering linear and nonlinear disturbance evolution of freestream stochastic and wave packet forcing at different locations downstream of the ogive-cylinder junction. The spectral response of the stochastic forcing displays favorable agreement with experimental observations from Air Force Research Laboratory on which the configuration is based. Intermittent wave packets are generated from small-amplitude continuous freestream pressure forcing. Linear wave packet evolution reveals that Mack modes are the dominant primary instabilities, followed by relatively weaker first-mode waves. The nonlinear wavepacket displays a three-legged wall pressure perturbation signature, which is traced to spanwise curvature effects, and fundamental resonance is the dominant secondary instability mechanism. At higher amplitudes of excitation, weak signatures of subharmonic and oblique resonance phenomena are identified. Downstream placement of the small-amplitude disturbance diminishes amplification of first-mode waves; however, with high-amplitude forcing, the location of actuation does not significantly vary the disturbance evolution signature or the secondary instability mechanisms.

Transcutaneous Cervical Vagus Nerve Stimulation Enhances Second-Language Vocabulary Acquisition While Simultaneously Mitigating Fatigue and Promoting Focus (P2-12.002)

<h3>Objective:</h3> To examine whether transcutaneous cervical and auricular vagus nerve stimulation (tcVNS &amp; taVNS) could enhance second language vocabulary acquisition among career linguists in a realistic multi-day learning protocol. <h3>Background:</h3> Cognitive performance and skill proficiency are important in a wide variety of careers. Recently, transcutaneous vagus nerve stimulation (tVNS) has emerged as a promising technique to enhance learning and skill acquisition. tVNS efficacy in a realistic, multi-day learning protocol has not been demonstrated. <h3>Design/Methods:</h3> We conducted two double-blind controlled experiments examining the efficacy of tcVNS and taVNS on a 5-day second-language vocabulary acquisition protocol in career linguists at the US Defense Language Institute Foreign Language Center. <h3>Results:</h3> tcVNS produced statistically significant benefit during training (Day 2–4; model estimated mean performance: sham-37.5% vs ctVNS-46%, <i>p</i> = .025), and the training benefit was sustained on the final test conducted at a 24-hour delay where no stimulation was administered. Additionally, using pre- and post-training day mood rating as measured by Air Force Research Laboratory Mood Questionnaire, tcVNS promoted focus (<i>p</i> = .001) and mitigated fatigue (<i>p</i> = .036). <h3>Conclusions:</h3> Our findings suggest that tcVNS promotes learning by inducing neuroplasticity as well as enhancing focus and mitigating fatigue. tcVNS training benefits are sustained for at least 24 hours after stimulation. Based on current and related demonstration of training enhancement, we believe tcVNS could be beneficial in language learning as well as acquisition of skills in intensive learning environments. This research was developed with funding from the Defense Advanced Research Projects Agency (DARPA). The views, opinions and/or findings expressed are those of the author and should not be interpreted as representing the official views or policies of the Department of Defense or the U.S. Government. <b>Disclosure:</b> Dr. Miyatsu has nothing to disclose. Miss Oviedo has nothing to disclose. Miss Reynaga has nothing to disclose. Ms. Karuzis has nothing to disclose. Dr. Martinez has nothing to disclose. Dr. Key has received personal compensation for serving as an employee of Infoscitex. Mrs. McIntire has nothing to disclose. Dr. Aue has received personal compensation for serving as an employee of United States Department of Defense. An immediate family member of Dr. Aue has received personal compensation for serving as an employee of Anthem. Dr. Pirolli has nothing to disclose. Dr. O’Rourke has nothing to disclose. The institution of Dr. McKinley has received research support from AFRL. The institution of Dr. McKinley has received research support from DARPA. Dr. McKinley has received personal compensation in the range of $100,000-$499,999 for serving as a Employee with Air Force Research Laboratory. Dr. Broderick has received personal compensation for serving as an employee of IHMC. Dr. Broderick has received personal compensation for serving as an employee of Wright State Boonshoft School of Medicine. The institution of Dr. Broderick has received research support from United States Department of Defense.

Whistler‐Mode Transmission Experiments in the Radiation Belts: DSX TNT Circuit Simulation and Data Analysis

AbstractHigh‐power transmission experiments in the very low frequency (VLF) mode have been conducted by the US Air Force Research Laboratory’s Demonstration and Science Experiments (DSX) satellite in the radiation belts using a novel transmitter that automatically tunes to find the resonance frequency of the transmitter circuit including the antenna. The resulting voltage–frequency curves are used to derive antenna impedance at the resonance. The analysis shows that the antenna reactance is far less than that of a dipole antenna in free space. The derived radiation resistance is up to several tens of kilo Ohms. Most interestingly, it is found that the radiation resistance is inversely proportional to the square of transmission wave frequency. The transmitted power can be up to 80 W for the DSX transmitter with an 82‐m long tip‐to‐tip antenna, showing that the high‐power VLF transmission is feasible. Whistler wave transmission inside the higher‐density plasmasphere is more efficient. Data analysis indicates that the antenna impedance does not vary systematically with the antenna orientation angle relative to the ambient magnetic field. The previous dominant theoretical studies yield not only incorrect values of the impedance but a completely different frequency dependence than that derived from DSX experiments. Instead, the recent theories correctly capture both the antenna impedance magnitude and the frequency dependence.