Army Research Laboratory Research Articles

Numerical Device Modeling, Analysis, and Optimization of Extended-SWIR HgCdTe Infrared Detectors

Imaging in the extended short-wavelength infrared (eSWIR) spectral band (1.7–3.0 μm) for astronomy applications is an area of significant interest. However, these applications require infrared detectors with extremely low dark current (less than 0.01 electrons per pixel per second for certain applications). In these detectors, sources of dark current that may limit the overall system performance are fundamental and/or defect-related mechanisms. Non-optimized growth/device processing may present material point defects within the HgCdTe bandgap leading to Shockley–Read–Hall dominated dark current. While realizing contributions to the dark current from only fundamental mechanisms should be the goal for attaining optimal device performance, it may not be readily feasible with current technology and/or resources. In this regard, the U.S. Army Research Laboratory performed physics-based, two- and three-dimensional numerical modeling of HgCdTe photovoltaic infrared detectors designed for operation in the eSWIR spectral band. The underlying impetus for this capability and study originates with a desire to reach fundamental performance limits via intelligent device design.

Coat of arms: Dovetailing the needs of outdoor sculpture and military assets to develop more durable and adaptable paint systems

The requirements for paints used on outdoor sculpture and military vehicles are similar: overall protection for the underlying substrate, and the ability to withstand prolonged outdoor exposure and recurring physical contact. Aesthetic requirements are different but stringent for both categories of coatings and include maintaining appearance over time. Building on prior work undertaken by the United States Department of Defense (DoD) Army Research Laboratory (ARL) to modify military coating systems into a matte black paint suitable for outdoor sculpture, a long-term interdisciplinary collaboration is under way between the ARL, the Getty Conservation Institute, Mack Art Conservation, and NCP Coatings, that aims to develop and evaluate a wider range of robust paint systems with novel attributes for both the DoD and outdoor painted sculptures. For the latter, this includes coatings with a broader range of gloss, formulated with a much more varied palette. New low-gloss coatings used on military assets were used to paint sculptures by Alexander Calder, Tony Smith, and Louise Nevelson, designed to an aesthetic standard based on approved colour and gloss levels by the relevant artists’ foundations and estates, and formulated to enhance durability. These new coatings offer the ability to match or meet a range of artists’ aesthetic preferences, and to use a variety of polymeric flattening agents to control gloss levels, reduce marring, and eliminate volatile and hazardous pollutants. The use of low molecular weight (LMW) resins provides 4–8 hour pot life to assist in the application process. Compared to current resins, the LMW systems reduce organic solvent levels, are low viscosity, and permit far easier application. In addition, the replacement of typical pigments with low solar absorbing (LSA) pigmentation provides higher reflection which ‘shields’ the resin/binder system and reduces degradation. A particular advantage to conservators from this collaboration is that the coatings on DoD assets provide a convenient indicator of the paint's performance and durability. The outcome will be a unique coating system to provide enhanced durability and maintain the original coating properties for a period of 6–10 years.

Efficient and Robust RFI Extraction Via Sparse Recovery

This paper presents a simple adaptive framework for robust separation and extraction of multiple sources of radio-frequency interference (RFI) from raw ultra-wideband (UWB) radar signals in challenging bandwidth management environments. RFI sources pose critical challenges for UWB systems since 1) RFI often occupies a wide range of the radar’s operating frequency spectrum; 2) RFI might have significant power; and 3) RFI signals are difficult to predict and model due to the nonstationary nature as well as the complexity of various communication devices. Our proposed framework involves an initial RFI estimation step that operates directly on already contaminated radar signals to identify RFI-dominant frequency sub-bands. This vital prior information is then taken into account to construct an adaptive RFI dictionary with various sinusoidal patterns covering the aforementioned RFI-contaminated frequency spectrum. Finally, we employ a sparsity-driven optimization strategy to separate and then extract RFI from the received radar signals. Our method can be implemented as a denoising preprocessing stage for raw radar signals prior to image formation and other follow-up tasks such as target detection and classification. Recovery results from extensive simulated data sets as well as real-world signals collected by the U.S. Army Research Laboratory (ARL) UWB synthetic aperture radar (SAR) systems illustrate the robustness and effectiveness of our proposed framework.

Humeral head intraosseous access: Filling the military training gap

Humeral head intraosseous (HHIO) infusion is the process of injecting fluids directly into the marrow of the humerus, or upper arm bone, to provide a non-collapsible entry point into the circulatory system. This technique provides fluids and medication quickly when intravenous (IV) access is not feasible in emergency situations. As of 2010, Tactical Combat Casualty Care guidelines recommend using intraosseous (IO) infusion in any resuscitation scenario where IV access is not feasible. The US Army Center for Pre-Hospital Medicine (CPHM) provides pre-deployment training to Roles I, II, and III medical providers. In addition, the CPHM provides training for deploying Forward Surgical Teams and en route care via the Critical Care Flight Paramedic Program. The Army’s Program of Instruction currently lacks an adequate simulation-based training model for the HHIO procedure and relies on live tissue training. The US Army Research Laboratory, Human Research and Engineering Directorate, Advanced Training and Simulation Division, developed a capability (i.e., Partial Task Trainer, or PTT) to train this procedure. This study assessed the usability of the PTT device for training on the IO procedure. Specifically, this paper seeks to identify statistically significant differences among the usability ratings of the PTT for paramedics and emergency medicine physicians.

Large Eddy Simulation of High Reynolds Number Nonreacting and Reacting JP-8 Sprays in a Constant Pressure Flow Vessel With a Detailed Chemistry Approach

In military propulsion applications, the characterization of internal combustion engines operating with jet fuel is vital to understand engine performance, combustion phasing, and emissions when JP-8 is fully substituted for diesel fuel. In this work, high-resolution large eddy simulation (LES) simulations have been performed in-order to provide a comprehensive analysis of the detailed mixture formation process in engine sprays for nozzle configurations of interest to the Army. The first phase examines the behavior of a nonreacting evaporating spray, and demonstrates the accuracy in predicting liquid and vapor transient penetration profiles using a multirealization statistical grid-converged approach. The study was conducted using a suite of single-orifice injectors ranging from 40 to 147 μm at a rail pressure of 1000 bar and chamber conditions at 900 K and 60 bar. The next phase models the nonpremixed combustion behavior of reacting sprays and investigates the submodel ability to predict auto-ignition and lift-off length (LOL) dynamics. The model is constructed using a Kelvin Helmholtz–Rayleigh Taylor (KH–RT) spray atomization framework coupled to an LES approach. The liquid physical properties are defined using a JP-8 mixture containing 80% n-decane and 20% trimethylbenzene (TMB), while the gas phase utilizes the Aachen kinetic mechanism (Hummer, et al., 2007, “Experimental and Kinetic Modeling Study of Combustion of JP-8, Its Surrogates, and Reference Components in Laminar Non Premixed Flows,” Proc. Combust. Inst., 31, pp. 393–400 and Honnet, et al., 2009, “A Surrogate Fuel for Kerosene,” Proc. Combust. Inst., 32, pp. 485–492) and a detailed chemistry combustion approach. The results are in good agreement with the spray combustion measurements from the Army Research Laboratory (ARL), constant pressure flow (CPF) facility, and provide a robust computational framework for further JP-8 studies of spray combustion.

Turn-on of High-Voltage SiC Thyristors for Fast-Switching Applications

This paper is focused on the characterization of the turn-ON transition of high-voltage SiC thyristors of different epi-layer thicknesses and active-area sizes to determine their suitability and limitations in high- $dI/dt$ , fast-switching applications. The unique aspects of this paper include the very high current density being switched through the thyristors over a short period of time at initial turn-ON, resulting in very high instantaneous dissipated power over the small device volume. The devices that were characterized were 6-kV, 0.5-cm2 thyristors; 10-kV, 1.05-cm2 thyristors; and 15-kV, 1.05-cm2 thyristors, all fabricated by Cree, Inc. (now Wolfspeed) for the U.S. Army Research Laboratory. The highest dI/dt and the current density were 13 kA/ms and 3.2 kA/cm2 for a parallel pair of 0.5-cm2 thyristors, with pulsed current peaking 250 ns from initial gate trigger. All devices evaluated were capable of switching a current pulse >2 kA/cm2 within a period of less than $2~\mu \text{s}$ . These evaluations have broad application in helping to inform SiC device design tradeoffs for increasing epi thickness, increasing device area, and the effects of lifetime enhancement processes. Results are also presented for initial exploration of fast-switching applications for these devices.

Correction: Corrigendum: Origins of power-law degree distribution in the heterogeneity of human activity in social networks

Scientific Reports 3: Article number: 178310.1038/srep01783; published online: May072013; updated: November042015. The Acknowledgements section in this Article is incomplete. “We thank G. Khazankin, Research Institute of Physiology SB RAMS for kindly providing access to invaluable data on news2.ru user activity. The research is supported by NSF Emerging Frontiers, ARL, FP7 project SOCIONICAL and MULTIPLEX, CNPq, CAPES, FUNCAP and NSFC (11290141, 11201018).” should read: “We thank G. Khazankin, Research Institute of Physiology SB RAMS for kindly providing access to invaluable data on news2.ru user activity. The research is supported by NSF Emerging Frontiers, Army Research Laboratory Cooperative Agreement Number W911NF-09-2-0053 (the ARL Network Science CTA), FP7 project SOCIONICAL and MULTIPLEX, CNPq, CAPES, FUNCAP and NSFC (11290141, 11201018).”

Atmospheric compensation of acoustic signatures of aircraft

The U.S. Army Research Laboratory is investigating using low size, weight, power, and cost (SWaP-C) acoustic sensors to classify unmanned aircraft systems (UAS). One issue complicating UAS classification using acoustics is that the atmosphere attenuates the signature of the targets in a complex manner. To address this issue, we developed and tested a technique to mitigate the effect of atmospheric attenuation. We used Bass's model with inputs from temperature, relative humidity and range to estimate atmospheric attenuation, then we used techniques based upon a Wiener filter implemented in the frequency domain to adjust the amplitude of the measured signal. The Wiener filter reduced the amplification of the noise while improving the reproducibility of the signature at different ranges, particularly at higher frequencies. The results suggest that preprocessing the data using this technique should improve the performance of acoustic classifier algorithms.

Acoustic particle velocity sensor: Application to infrasonic detection

Infrasonics is the study of low-frequency acoustics that is below the normal limit of human hearing. Infrasound has the ability to propagate extremely long ranges and is often utilized to monitor naturally occurring phenomena and explosives. Acoustic particle velocity sensors have shown promise in detection and localization of transient signals in the audio range such as small arms fire, mortars, and rocket propelled grenades. Ideally, this sensor can be used to detect various targets spanning a broad range of frequencies to include that of infrasound. The primary objective of this research is to characterize the acoustic vector sensor’s localization performance for infrasonic sources given varying atmospheric conditions using algorithms developed at the Army Research Laboratory (ARL).

Standoff photoacoustic spectroscopy for hazard detection

Photoacoustic spectroscopy (PAS) is a versatile and sensitive chemical sensing method. This versatility allows for the construction of a variety of sensors that are optimized for specific sensing tasks. Current research at the U.S. Army Research Laboratory (ARL) is focused on the development of a standoff hazardous materials detection technique based on an interferometric sensor. The standoff detection paradigm increases operator safety and reduces sample preparation requirements as compared to traditional photoacoustic cell-based sensors. We demonstrate the collection of photoacoustic spectra of layered solid samples at a standoff distance of one meter. The layered samples are constructed via deposition of a thin layer of energetic or other hazardous substance upon a thick substrate. We will also discuss excitation source selection as it relates to the operating mode of the source (i.e., pulsed or continuous wave (CW) modulated).

Modeling of Advanced Combat Helmet Under Ballistic Impact

The use of combat helmets has greatly reduced penetrating injuries and saved lives of many soldiers. However, behind helmet blunt trauma (BHBT) has emerged as a serious injury type experienced by soldiers in battlefields. BHBT results from nonpenetrating ballistic impacts and is often associated with helmet back face deformation (BFD). In the current study, a finite element-based computational model is developed for simulating the ballistic performance of the Advanced Combat Helmet (ACH), which is validated against the experimental data obtained at the Army Research Laboratory. Both the maximum value and time history of the BFD are considered, unlike existing studies focusing on the maximum BFD only. The simulation results show that the maximum BFD, the time history of the BFD, and the shape and size of the effective area of the helmet shell agree fairly well with the experimental findings. In addition, it is found that ballistic impacts on the helmet at different locations and in different directions result in different BFD values. The largest BFD value is obtained for a frontal impact, which is followed by that for a crown impact and then by that for a lateral impact. Also, the BFD value is seen to decrease as the oblique impact angle decreases. Furthermore, helmets of four different sizes—extra large, large, medium, and small—are simulated and compared. It is shown that at the same bullet impact velocity the small-size helmet has the largest BFD, which is followed by the medium-size helmet, then by the large-size helmet, and finally by the extra large-size helmet. Moreover, ballistic impact simulations are performed for an ACH placed on a ballistic dummy head form embedded with clay as specified in the current ACH testing standard by using the validated helmet model. It is observed that the BFD values as recorded by the clay in the head form are in good agreement with the experimental data.

A Multiscale Approach Toward the Design and Understanding of Stable and Conductive Anion Exchange Membrane Materials

Improved anion exchange membrane (AEM) materials are needed to develop next generation electrochemical devices including fuel cells. In recent years, largely spurred by some developments with radiation grafted AEM materials out of the laboratories of Robert Slade and John Varcoe, there has been significant attention from within the energy conversion/storage communities [1-3]. In additional to the interest in the use of AEM materials for fuel cells [1-3], the community has given additional consideration to their use for areas including chemical processing and energy storage [3-6], electrolysis and solar-to-fuel production [3,6], desalination and dialysis [3], and purification and separation processes [3]. Many of the interest in these materials is a result of the opportunities that may be presented by a stable, anion-conducting polymer electrolyte materials. In this talk we will highlight our collaborative, simulation-focused efforts to develop and understand high performance AEM materials for electrochemical applications. Among other things, we will discuss our efforts to develop, validate, and apply simulation methodologies that can provide new and fundamental insights into the nature of the membrane(s) cationic stability, anionic conductivity, and the uncertainty in our respective models that range from atomistic to continuum scales. These multiscale modeling approaches include everything from atomistic MD simulations using reactive (ReaxFF) and polarizable force fields, to coarse-grained molecular dynamics simulations with developed using uncertainty quantification (UQ) based methodologies and continuum level modeling approaches. For our initial efforts that we will discuss in this talk, we utilize relatively simple backbone materials such as Poly(2,6-dimethyl-1,4-phenylene oxide) (PPO). These backbone materials are effectively used as a model material system. This enables us to develop and validate simulation methods that can predict and resolve the proper structure-property relationships; a key step before moving to more complex materials. Further, the simpler PPO-type backbone materials provide a key advantage at this stage in that they can concurrently be (i) processed, synthesized, and characterized in our labs, and (ii) subjected to unique processing methods/conditions that includes both casting and electro-spinning processes. This last capability is salient because the focus of the model and simulation development efforts are on the application to multi-scale systems. The ability to concurrently process the materials using different methods (i.e., cast, electro-spun, and co-spun with an inert matrix material) and under different conditions can drastically influence the material’s morphologies, structures, ordering, and properties. Acknowledgments: KNG, JPM, and DC gratefully acknowledge the support of the U.S. Department of the Army, Army Materiel Command, and U.S. Army Research Development and Engineering Command. This work was completed, in part, through the U.S. Army Research Laboratory’s Enterprise for the Multiscale Research of Materials (EMRM). This work was completed in conjunction with an Army Research Laboratory EMRM’s Multiscale Modeling of Electronic Materials (MSME) Collaborative Research Alliance (CRA). VM, LCJ, JL, DB, JBH, ZL, AvD, WZ, and RMK gratefully acknowledge the financial support of the MSME CRA.

Experimental Development of Acid-Alkaline Bipolar Membrane Electrolytes

Anion-exchange membranes (AEMs) have received attention for use in alkaline fuel cells and bipolar membrane applications [1] The bipolar membrane concept was recently demonstrated by Unlu et al. as a way to reduce fuel cell costs (i.e., Pt loading) and the overall balance of plant (BOP).[2-3] Bipolar membranes are typically comprised of an H+-conducting membrane adjacent to an OH--conducting membrane with at least one internal acid-alkaline junction. However, most AEMs studied to-date are organic and exhibit low chemical stabilities and low ionic conductivities after prolonged exposure to high pH media and temperatures greater than 60°C.[4] A number of advancements have been made to increase the ion-exchange group stability by using phenyl guanidinium-[5], imidazolium-[6] and other metal-cation exchange groups[7], among others; all of which provide potential routes to circumvent stability issues. In this study, we prepared AEM and PEM precursors which are further developed into bipolar membranes. The combination of our precursors and our electrospinning process proves useful for preparing H+- and OH--conducting membranes. In addition to the aforementioned AEM stability issues, bipolar membranes can suffer from material compatibility issues at the AEM/PEM junction. We demonstrate an approach to create bipolar membranes by, for example, co-electrospinning that allows for short- and long-range fabrication with desirable AEM/PEM interfacial binding. For example, Park et al. recently demonstrated a novel approach for creating AEM membranes by electrospinning, which we extend specifically to develop bipolar membranes.[8] As a proof of concept, we chose PEM and AEM components made primarily of Nafion and modified polysulfone or modified poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) derivatives, respectively. We present 3 different approaches for conjoining the AEM and PEM layers to create the bipolar membranes. Ex-situ ion-transport measurements are presented for bulk in-plane ionic conductivities (σ) of the isolated membranes in OH--, H+- and CO3 2—forms and are compared to the through-plane σ for the bipolar membranes. Physical characterizations such as SEM, BET, and gravimetric swelling measurements are presented for each isolated and combined membranes. For select membranes, we show polarization (i-V) curves for a single MEA operating under H2/O2. Figure 1 shows a schematic of the electrospinning process whereby a rotating roll configuration is utilized for fabricating a co-electrospun bipolar membrane with a typical SEM image shown for an AEM fiber mat. Acknowledgments: We gratefully acknowledge the fuel cell team at the U.S. Army Research Laboratory. We acknowledge the U.S. Department of the Army, AMC and RDECOM for funding and support.

Understanding the Acid-Alkaline Bipolar Membrane Electrolyte for Fuel Cell Applications

One of the challenges confronting fuel cell technologies is their integration into a practical, robust system. The Balance of Plant (BoP) components needed to manage the fuel and oxidant, humidification and/or water removal, and thermal loads are often cumbersome to integrate. These issues can present unique requirements and are persistent across most types of fuel cell applications (e.g., wearable and portable, transportation, backup and primary power, etc.) and fuel cell types (e.g., polymer electrolyte, direct methanol, reformed methanol, solid oxide, and so forth). The research and development efforts presented in this work are specifically geared toward wearable and portable power applications. In this configuration, a compact, lightweight, and cost effective system with a high specific energy (density) is desired. Polymer electrolyte fuel cells with energy dense liquid fuels such as methanol are often used in attempt to fill this need. Direct methanol fuel cell (DMFC) systems have shown that they can reliably provide large energy density values over a wide range of environmental and operational conditions; however, DMFCs size/footprint and cost continue to be a drawback. The size and complexity of present DMFC systems are largely dictated by the fuel/water and thermal management components. Costs are often attributed to those associated with the membrane electrode assembly (MEA) and specifically platinum-based electrocatalysts, but other factors such as packaging and BoP also play a role. In this talk, we will present our efforts to develop bipolar membrane fuel cell (BMFC) technologies to address some of these shortcomings. The BMFC uses a hybrid of proton exchange membrane (PEM) and anion exchange membrane (PEM) materials such that there is at least one internal acid-alkaline membrane junction, or interface. Depending on the respective configuration, water generation or consumption will occur at the junction. Paul Kohl’s group has demonstrated how this junction can be (i) used to improving hydrogen/oxygen MEA performance at low relative humidity such that the need for external humidification in reduced, and (ii) integrated into low temperature DMFC MEAs [1-3]. Bipolar membrane configurations may additionally be used to adjust the respective anode and cathode chemistries (i.e., acid or alkaline) such that the electrochemical kinetics may be improved and/or the amount of platinum-based electrocatalysts may be reduced. The focus of this talk will be the modeling of the bipolar membrane electrolyte materials and the BMFC system that complement our ongoing experimental materials and systems development efforts. A specific focus will be placed on understanding the nature of the bipolar membrane junction and its influence on transport phenomena within the BMFC. The insights from this modeling effort on the utilization of this technology for the development of a BMFC based DMFC with improved water/fuel and thermal management will be discussed. Acknowledgments: KNG, JPM, and DC gratefully acknowledge support from the U.S. Department of the Army, U.S. Army Materiel Command, Research Development and Engineering Command, and U.S. Army Research Laboratory. JMA, LL, and PAK gratefully acknowledge support from the U.S. Department of the Army, Deputy Assistant Secretary of the Army (DASA) International Collaboration Program through contract no. W911NF-14-2-0008.

Richard P. Wool, PhD, Professor, FRSC In memoriam

It is with great sadness to communicate to you the news of Professor Richard P. Wool's unexpected passing on Tuesday, March 24, 2015. Richard was a Professor of Chemical and Biomolecular Engineering at the University of Delaware, U.S.A., a member of the University's Center for Composite Materials, and a Fellow of both the Royal Society of Chemistry and the American Physical Society, Division of High Polymer Physics. Richard was born in Cork, Ireland in 1947. He met his wife, Deborah Fitzgerald Wool, in 1969 at University College Cork, Ireland, where he completed his BSc Honors Degree in Chemistry in 1970. He received both his MS (1972) and Doctorate (1974) in Materials Science and Engineering from the University of Utah, U.S.A. Richard remained in the U.S.A. and after teaching at the University of New York and the University of Colorado, he became a member of the Materials Science and Engineering Department at the University of Illinois at Urbana-Champaign. He and Deb lived near the university for 18 years and started a family: three daughters Sorcha, Meghan, and Breeda. In Illinois, he developed underlying physics behind polymers under stress, polymer fracture, polymer adhesion, and polymer welds. In 1995 the Wool family moved to Delaware, and Richard joined the faculty of the Chemical and Biomolecular Engineering Department of the University of Delaware. At Delaware, he developed and taught popular classes on polymers, bio-based materials and green engineering, and established the Affordable Composites from Renewable Sources (ACRES) laboratory. From here he led the world towards refocusing on sustainable thermosets and composites, developing triglyceride-based crosslinkers, fatty acid-based pressure sensitive adhesives, polyurethane foams, lignin-derived reactive diluents, chicken feather-based composites and eco leather, and lignin-derived replacements for bisphenol A. Some of Richard's professional awards include the 2013 United States Environmental Protection Agency Presidential Green Chemistry Challenge Award, the 2011 American Chemical Society's Affordable Green Chemistry Award, the 2012 Lifetime Achievement Award from the Bio-Environmental Polymer Society, and the 2014 Faculty Research Innovation Award from the International Textiles and Apparel Association. He holds four patents, wrote two books and published over 200 papers, of which 22 were published in the Journal of Applied Polymer Science. He was a guest Professor in the Physics Department, Trinity College Dublin, Ireland, 2002; Condensed Matter Physics, Ecole Polytechnique, Paris, France, 1991; and Natta Laboratory, Politecnico Di Milano, Milan, Italy, 1984. Many of Richard's countless accomplishments throughout his personal and professional life were noteworthy. He brought joy to everyone with his unconditional generosity and kindness, his humor and laughter, his music, his wisdom and intellect, and, most especially, with his love of life. He was a lifelong sailor and musician who loved to share both with everyone he met. All, especially those in the Polymer Science, Polymer Engineering, and Green Chemistry and Engineering communities, will truly miss his leadership, good wit, strong support, and love. John La Scala Chief, Coatings, Corrosion, and Engineered Polymers Branch Army Pollution Prevention Chairman U.S. Army Research Laboratory Aberdeen Proving Ground, U.S.A. Joseph F. Stanzione, III Assistant Professor of Chemical Engineering Director, Sustainable Materials Research Laboratories Rowan University Glassboro, U.S.A.

Data processing and temperature-emissivity separation for tower-based imaging Fourier transform spectrometer data

In this article we describe the end-to-end processing of image Fourier transform spectrometry data taken at Picatinny Arsenal in New Jersey with the long-wave hyperspectral camera manufactured by the Telops company. The first part of the article discusses the processing from raw data to calibrated radiance and emissivity data. Data were taken during several months under different weather conditions every 6 min from a 213 ft-high tower of surrogate tank targets for a project sponsored by the Army Research Laboratory in Adelphi, Maryland. The second part discusses environmental effects such as diurnal and seasonal atmospheric and temperature changes and the effect of cloud cover on the data. To test the effect of environmental conditions, a range-invariant anomaly detection approach is applied to calibrate radiance, brightness temperature, and emissivity data. The data set presented in this article is due to be released publicly so that more detailed studies can be performed not only on the man-made targets but also on the changes of natural background of vegetation and gravel with time of day and seasons.

Large-scale 3D modeling of projectile impact damage in brittle plates

The damage and failure of brittle plates subjected to projectile impact is investigated through large-scale three-dimensional simulation using the DG/CZM approach introduced by Radovitzky et al. [Comput. Methods Appl. Mech. Eng. 2011; 200(1–4), 326–344]. Two standard experimental setups are considered: first, we simulate edge-on impact experiments on Al2O3 tiles by Strassburger and Senf [Technical Report ARL-CR-214, Army Research Laboratory, 1995]. Qualitative and quantitative validation of the simulation results is pursued by direct comparison of simulations with experiments at different loading rates and good agreement is obtained. In the second example considered, we investigate the fracture patterns in normal impact of spheres on thin, unconfined ceramic plates over a wide range of loading rates. For both the edge-on and normal impact configurations, the full field description provided by the simulations is used to interpret the mechanisms underlying the crack propagation patterns and their strong dependence on loading rate.

Comparisons of semi-porous fabric domes and cylindrical wind fence enclosures for infrasonic wind noise reduction

This investigation compares the measured wind noise of two types of infrasonic wind noise reduction barriers. The first type is a set of 2.0 m diameter semi-porous fabric domes constructed and tested by the Army Research Laboratory [J. Acoust. Soc. Am. 136, 2139 (2014)]. The type second is a set of single and multi-layer cylindrically shaped variable-porous wind fence enclosures measuring 5.0 m and 10.0 m, constructed and tested by the National Center for Physical Acoustics [J. Acoust. Soc. Am. 134, 4161 (2013)]. Preliminary investigations showed that for wind speeds between 3—6 m/s the measured power spectra densities of the fabric domes were comparable to the measured power spectra densities of the single layer, 5.0 m diameter wind fence enclosures at mid-range porosities. The measured power spectra densities of the fabric domes were higher than the measured power spectra densities for the 10.0 m diameter and multi-layer wind fences enclosures. For wind speeds greater than 6 m/s, the measured wind noise for the fabric domes was comparable to or lower than the measured wind noise for the wind fence enclosures.

Giant and Tunable Mechanical Impulse of Energetic Nanocrystalline Porous Silicon

In this paper, a nanocrystalline porous silicon-based propulsion system is designed, and its explosion impulse is tuned by varying the propulsion design parameters and etching duration. The porous silicon is ignited by an electrical current passed through 100-nm-thick aluminum film deposited on the unpolished side of the wafer and the ignited porous silicon caused strong explosion, which destroys the chip into tiny fragments. The explosion impulse in the system can reach about at optimal conditions, which is two orders stronger than the impulse produced by conventional propellants (ZakarE., “Technology Challenges in Solid Energetic Materials for Micro Propulsion Applications” U.S. Army Research Lab. Rept. ARL-TR-5035, Nov. 2009). It is also shown that, by varying the etching time, which is an important factor that determines the porous layer thickness and the volume of nanocrystallite, the strength of the impulse can be tuned. Furthermore, a linear increasing trend of the explosion impulse with etching time is observed, which can be explained as the results of heat trapping, materials confinement, and the increasing number of reaction centers.

Measuring Human Workload in a Collaborative Human-Robot Team

Successful human-robot (H-R) teams working with direct interaction and close coupling will have relationships that vary, depending on whether or not collaboration is prioritized and how collaboration changes the human mental workload and the team’s task performance. Modeling of representative functions can provide predictions of changes in mental workload and the potential impact on team performance. The presented research focuses on modeling and quantifying mental workload for H-R teams in which team members have some individually assigned responsibilities but must also make joint decisions with a teammate. IMPRINT Pro, a discrete event simulation modeling tool created by the U.S. Army Research Laboratory, was used to model human-human (H-H) and H-R teams completing a reconnaissance task in a building. This research evaluated H-H and H-R teams completing the same reconnaissance tasks. Predictions of mental-workload levels from the model and the evaluation results showed that mental workload was lower for the H-R teams. The results for the closely coupled teams were compared to results from a prior evaluation with a master-slave relationship; similar results were found for both evaluations. Mental workload was lower in H-R teams than in H-H teams, but task performance did not differ between the two.