U.S. Army Combat Capabilities Development Command Aviation & Missile Center

ADVERTISEMENT RETURN TO ISSUEPREVCommunicationIonic Liquids as Hypergolic FuelsStefan Schneider, *†, Tommy Hawkins, †, Michael Rosander, †, Ghanshyam Vaghjiani, †, Steven Chambreau, †, and Gregory Drake, ‡View Author Information Air Force Research Laboratory, 10 East Saturn Boulevard, Building 8451, Edwards Air Force Base, California 93524, and Propulsion and Structures Directorate, United States Army Aviation and Missile Research, Development, and Engineering Center, AMSRD-AMR-PS-PT, Building 7120, Redstone Road Redstone Arsenal, Alabama 35898* To whom correspondence should be addressed. Fax: (+1) 661-275-5471. E-mail: [email protected]†Air Force Research Laboratory.‡U.S. Army Aviation and Missile RD&E Center.Cite this: Energy Fuels 2008, 22, 4, 2871–2872Publication Date (Web):June 17, 2008Publication History Received24 April 2008Revised2 June 2008Published online17 June 2008Published inissue 1 July 2008https://pubs.acs.org/doi/10.1021/ef800286bhttps://doi.org/10.1021/ef800286brapid-communicationACS PublicationsCopyright © 2008 American Chemical SocietyRequest reuse permissionsArticle Views3320Altmetric-Citations298LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-AlertscloseSupporting Info (2)»Supporting Information Supporting Information SUBJECTS:Alcohols,Anions,Fuels,Liquids,Salts Get e-Alerts

We have developed a paradigm methodology that can isothermally crystallize halide perovskites at room temperature.

We show that N-doped ZnO films grown on sapphire can exhibit significant (∼1018 cm−3) room-temperature p-type behavior when sufficient nitrogen (N) is incorporated and the material is annealed appropriately. Substitutional N on the oxygen (O) sublattice is a deep acceptor; however, shallow acceptor complexes involve N, H, and zinc vacancies (VZn). Combining secondary ion mass spectrometry, Raman-scattering, photoluminescence, and Hall-effect data, we establish the evolution of N from its initial incorporation on a Zn site to a final shallow acceptor complex VZn_NO_H+ with an ionization energy of ca. 130 meV. This complex is responsible for the observed p-type behavior.

By implementing a built-in sensor network on a composite structure, crucial information regarding the condition, damage state, and service environment of the structure can be obtained. In this study, methods for integrating piezoelectric sensor networks into a composite structure during different fabrication processes, including the resin transfer molding (RTM) and filament winding processes, are examined. To integrate sensor networks with different contours of structures, the method to fabricate a three-dimensional (3-D) diagnostic layer is developed. It is demonstrated that a large number of sensors supported on a thin flexible dielectric film, called a SMART Layer, offers a simple and efficient way to integrate a large sensor network onto a complex 3-D structure. The sensor network permanently embedded inside the composite structures can be used with either active sensing or passive sensing to monitor the health condition of a structure throughout its lifetime.

Sulfur-doped zinc oxide (ZnO) nanowires grown on gold-coated silicon substrates inside a horizontal tube furnace exhibit remarkably strong visible wavelength emission with a quantum efficiency of 30%, an integrated intensity 1600 times stronger than band edge ultraviolet emission, and a spectral distribution that closely matches the dark-adapted human eye response. By comparatively studying sulfur-doped and undoped ZnO micropowders, we clarify how sulfur doping and nanostructuring affect the visible luminescence and the underlying energy transfer mechanisms.

Abstract Thermoelectric (TE) generators enable the direct and reversible conversion between heat and electricity, providing applications in both refrigeration and power generation. In the last decade, several TE materials with relatively high figures of merit ( zT ) have been reported in the low‐ and high‐temperature regimes. However, there is an urgent demand for high‐performance TE materials working in the mid‐temperature range (400–700 K). Herein, p‐type AgSbTe 2 materials stabilized with S and Se co‐doping are demonstrated to exhibit an outstanding maximum figure of merit ( zT max ) of 2.3 at 673 K and an average figure of merit ( zT ave ) of 1.59 over the wide temperature range of 300–673 K. This exceptional performance arises from an enhanced carrier density resulting from a higher concentration of silver vacancies, a vastly improved Seebeck coefficient enabled by the flattening of the valence band maximum and the inhibited formation of n‐type Ag 2 Te, and ahighly improved stability beyond 673 K. The optimized material is used to fabricate a single‐leg device with efficiencies up to 13.3% and a unicouple TE device reaching energy conversion efficiencies up to 12.3% at a temperature difference of 370 K. These results highlight an effective strategy to engineer high‐performance TE material in the mid‐temperature range.

The terahertz region of the electromagnetic spectrum has been the least utilized owing to inadequacies of available sources. We introduce a compact, widely frequency-tunable, extremely bright source of terahertz radiation: a gas-phase molecular laser based on rotational population inversions optically pumped by a quantum cascade laser. By identifying the essential parameters that determine the suitability of a molecule for a terahertz laser, almost any rotational transition of almost any molecular gas can be made to lase. Nitrous oxide is used to illustrate the broad tunability over 37 lines spanning 0.251 to 0.955 terahertz, each with kilohertz linewidths. Our analysis shows that laser lines spanning more than 1 terahertz with powers greater than 1 milliwatt are possible from many molecular gases pumped by quantum cascade lasers.

This tutorial describes the application of digital holography to the terahertz spectral region and demonstrates how to reconstruct images of complex dielectric targets. Using highly coherent terahertz sources, high-fidelity amplitude and phase reconstructions are achieved, but because the millimeter-scale wavelengths approach the decimeter-sized targets and optical components, undesirable aperture diffraction degrades the quality of the reconstructions. Consequently, off-axis terahertz digital holography differs significantly from its visible light counterpart. This tutorial addresses these challenges within the angular spectrum method and the Fresnel approximation for digital hologram reconstruction, from which the longitudinal and transverse resolution limits may be specified. We observed longitudinal resolution ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="m1"> <mml:mrow> <mml:mi>λ</mml:mi> <mml:mo>/</mml:mo> <mml:mn>284</mml:mn> </mml:mrow> </mml:math> ) almost two times better than has been achieved with visible light digital holographic microscopy and demonstrate that submicrometer longitudinal resolution is possible using millimeter wavelengths for an imager limited ultimately by the phase stability of the terahertz source and/or receiver. Minimizing the number of optical components, using only large reflective optics, maximizing the angle of the off-axis reference beam, and judicious selection of spatial frequency filters all contribute to improve the quality of the reconstructed image. As in visible wavelength analog holography, the observed transverse resolution in terahertz digital holography is comparable to the wavelength but improves for features near the edge of the imaged object compared with features near the center, a behavior characterized by a modified description of the holographic transfer function introduced here. Holograms were recorded by raster scanning a sensitive superheterodyne receiver, and several visibly transparent and opaque dielectric structures were quantitatively examined to demonstrate the compelling application of terahertz digital holography for nondestructive test, evaluation, and analysis.

Deoxyribonucleic acid (DNA) has been recently recognized as hole transport material apart from its well-known generic role. The promising long-range hole transport capability in DNA make it potential “molecular wire” in optoelectronics. Here, we demonstrate a core–shell heterostructure of perovskite wrapped by cetyltrimethylammonium chloride modified DNA (DNA-CTMA) through a self-assembly process. Such a design results in enhanced extraction and transport of holes in the bio-photovoltaic device and boosts the efficiency to 20.63%. The hydrophobicity of the DNA-CTMA shell surrounding the perovskite grain boundary is also found to enhance the device stability, as the corresponding cell retained over 90% of initial efficiency after long-term ambient exposure. Building upon the hole transport characteristics of DNA-CTMA, a hole-free device is fabricated that exhibits high power conversion efficiency but has 50 000% reduced cost. These results not only demonstrate breakthrough in designing cheap, efficient, and stable bio-photovoltaics but also open the pathway towards the exciting possibility of controlled interaction between living and artificial semiconductors.

Significant improvement of structural and optical qualities of GaN thin films on sapphire substrates was achieved by metal organic chemical vapor deposition with in situ SiNx nanonetwork. Transmission electron microscope (TEM) studies revealed that screw- and edge-type dislocations were reduced to 4.4×107 and 1.7×107cm−2, respectively, for a ∼5.5-μm-thick layer. Furthermore, room temperature carrier lifetimes of 2.22 and 2.49ns were measured by time-resolved photoluminescence (TRPL) for samples containing single and double SiNx network layers, respectively, representing a significant improvement over the previous studies. The consistent trends among the TEM, x-ray diffraction, and TRPL measurements suggest that in situ SiNx network reduces line defects effectively as well as the point-defect-related nonradiative centers.

In this study, the as-deposited microstructure and mechanical properties are examined for both the wrought strain hardened Al-Mg-Mn alloy (AA5083-H131) feedstock and the AA5083 machine chip waste feedstock processed with Additive Friction Stir Deposition (AFSD). Monotonic tensile and uniaxial fatigue experiments compared three specimen types: AA5083-H131 Wrought control, AA5083 AFSD-Recycled, and AA5083 AFSD-Solid bar. Tensile and fatigue results demonstrated comparable performance between the recycled material and wrought control. Experimental results indicate the thermo-mechanical processing of AFSD resulted in an exchange of strengthening mechanisms – replacing the strength of wrought material from strain-hardening to grain boundary strengthening from a refined as-deposited microstructure. Although strengthening mechanisms evolved in AA5083, the mechanical performance of the AFSD-Recycled material including improved fatigue performance over the wrought control samples illustrates the potential use of the AFSD process to reclaim waste machine chips into components or repairs while maintaining high mechanical performance requirements.

This paper presents the design and development of a passive wireless sensor for the detection of bio-hazard materials and vapors using chemiresistive thin films. Composite polymer thin film with functionalized carbon nanotubes (f-CNT) and polymethylmethacrylate (PMMA) is employed as a sensing material. It is investigated that resistance change is determined with the concentration of dichloromethane vapors diffused into composite thin film, due to electrical transition from direct contact to tunneling in carbon nanotube nanojunctions. The chemiresistive film is integrated into a passive wireless system which works based on the change in phase of the reflected RF signal. Measurement results of sensors in a wireless sensing system show a large differential phase shift, which can be utilized for remote monitoring of bio-hazard vapors in real time.

An overview of new capabilities recently included in the HPCMP CREATE TM -AV Helios high-delity rotorcraft simulation code is presented. These include a new implicit obody Cartesian solver to support both steady solutions and time-accurate RANS/DES in the wake, a new body hierarchy formulation to support coupled wing/rotor aeroelastics and maneuvering ight, a new strand-based near-body solver intended to support enhanced automation and accuracy, the inclusion of two new unstructured near-body solvers { FUN3D from NASA and kCFD from CREATE-AV Kestrel. New unsteady particle tracing and moving contour plane capability have been added to runtime-based in situ visualization. Example application of these capabilities are presented.

An experiment involving a Mach-scaled, 11:08 f t: diameter rotor was performed in hover during the summer of 2016 at NASA Langley Research Center. The experiment investigated the hover performance as a function of the laminar to turbulent transition state of the boundary layer, including both natural and fixed transition cases. The boundary layer transition locations were measured on both the upper and lower aerodynamic surfaces simultaneously. The measurements were enabled by recent advances in infrared sensor sensitivity and stability. The infrared thermography measurement technique was enhanced by a paintable blade surface heater, as well as a new high-sensitivity long wave infrared camera. The measured transition locations showed extensive amounts, x=c&gt;0:90, of laminar flow on the lower surface at moderate to high thrust (CT=s &gt; 0:068) for the full blade radius. The upper surface showed large amounts, x=c &gt; 0:50, of laminar flow at the blade tip for low thrust (CT=s &lt; 0:045). The objective of this paper is to provide an experimental data set for comparisons to newly developed and implemented rotor boundary layer transition models in CFD and rotor design tools. The data is expected to be used as part of the AIAA Rotorcraft SimulationWorking Group

We present a bottom-up synthesis, spectroscopic characterization, and ab initio simulations of star-shaped hexagonal zinc oxide (ZnO) nanowires. The ZnO nanostructures were synthesized by a low-temperature hydrothermal growth method. The cross-section of the ZnO nanowires transformed from a hexagon to a hexagram when sulfur dopants from thiourea [SC(NH2)2] were added into the growth solution, but no transformation occurred when urea (OC(NH2)2) was added. Comparison of the X-ray photoemission and photoluminescence spectra of undoped and sulfur-doped ZnO confirmed that sulfur is responsible for the novel morphology. Large-scale theoretical calculations were conducted to understand the role of sulfur doping in the growth process. The ab initio simulations demonstrated that the addition of sulfur causes a local change in charge distribution that is stronger at the vertices than at the edges, leading to the observed transformation from hexagon to hexagram nanostructures.

, self-healing and self-cleaning). In this review, we discuss the bio-inspired/-mimetic structures, experimental models, and working principles, with the goal of revealing physics and bio-microstructures relevant for PV-MPS. Here the emphasis is on identifying the strategies and material designs towards improvement of the performance of emerging halide perovskite PVs and strategizing their bridge to future MPS.

This article summarizes the capabilities and development of the Helios version 2.0, or Shasta, software for rotary wing simulations. Specific capabilities enabled by Shasta include off-body adaptive mesh refinement and the ability to handle multiple interacting rotorcraft components such as the fuselage, rotors, flaps and stores. In addition, a new run-mode to handle maneuvering flight has been added. Fundamental changes of the Helios interfaces have been introduced to streamline the integration of these capabilities. Various modifications have also been carried out in the underlying modules for near-body solution, off-body solution, domain connectivity, rotor fluid structure interface and comprehensive analysis to accommodate these interfaces and to enhance operational robustness and efficiency. Results are presented to demonstrate the mesh adaptation features of the software for the NACA0015 wing, TRAM rotor in hover and the UH-60A in forward flight.

While lithium-sulfur (Li-S) batteries promise very high gravimetric energy densities, they typically suffer from short cycle life and low power densities, particularly at high electrode loadings. Highly concentrated electrolytes (2M-5M) may demonstrate improved capacity retention, but at the expense of added weight and cost of electrolyte salts and reduced rate performance. Here we report our counter-intuitive findings on very promising performance of electrolyte compositions with salt concentrations below 0.3M. Such a low concentration enables effective use of unconventional salts and electrolyte additives which do not dissolve in the ether-based solvents at higher concentrations typically used in experimental and commercial batteries, thus substantially increasing cell design freedom. The significantly lower viscosity of the low concentration electrolytes also allows for faster electrolyte permeation. This report opens a new and promising field of studying low concentration electrolytes for Li-S and likely other chemistries.

Ultrafast time-resolved photoluminescence spectroscopy following one- and two-photon excitations of ZnO powder is used to gain unprecedented insight into the surprisingly high external quantum efficiency of its ``green'' defect emission band. The role of exciton diffusion, the effects of reabsorption, and the spatial distributions of radiative and nonradiative traps are comparatively elucidated for the ultraviolet excitonic and ``green'' defect emission bands in both unannealed nanometer-sized ZnO powders and annealed micrometer-sized ZnO:Zn powders. We find that the primary mechanism limiting quantum efficiency is surface recombination because of the high density of nonradiative surface traps in these powders. It is found that unannealed ZnO has a high density of bulk nonradiative traps as well, but the annealing process reduces the density of these bulk traps while simultaneously creating a high density of green-emitting defects near the particle surface. The data are discussed in the context of a simple rate equation model that accounts for the quantum efficiencies of both emission bands. The results indicate how defect engineering could improve the efficiency of ultraviolet-excited ZnO:Zn-based white light phosphors.

High power and high energy density are important requirements for advanced energy storage systems in mobile electronic devices, electric vehicles, and military-grade high-rate energy storage systems.