Showing papers by "Wright-Patterson Air Force Base published in 2010"
TL;DR: In this article, two refractory high-entropy alloys with nearequiatomic concentrations, WNB-Mo-Ta and WBMCV, were produced by vacuum arc melting and the lattice parameters were determined with high-energy X-ray diffraction using a scattering vector length range from 0.7 to 20A−1.
1,655 citations
TL;DR: It is found that the ability of biguanides to inhibit mTORC1 activation and signaling is, instead, dependent on the Rag GTPases.
769 citations
TL;DR: There are many challenges to overcome before the authors can determine if the benefits outweigh the risks associated with NPs, and some metal-based NPs are showing increased toxicity, even if the same material is relatively inert in its bulk form.
Abstract: Nanoparticles (NPs) can potentially cause adverse effects on organ, tissue, cellular, subcellular, and protein levels due to their unusual physicochemical properties (e.g., small size, high surface area to volume ratio, chemical composition, crystallinity, electronic properties, surface structure reactivity and functional groups, inorganic or organic coatings, solubility, shape, and aggregation behavior). Metal NPs, in particular, have received increasing interest due to their widespread medical, consumer, industrial, and military applications. However, as particle size decreases, some metal-based NPs are showing increased toxicity, even if the same material is relatively inert in its bulk form (e.g., Ag, Au, and Cu). NPs also interact with proteins and enzymes within mammalian cells and they can interfere with the antioxidant defense mechanism leading to reactive oxygen species generation, the initiation of an inflammatory response and perturbation and destruction of the mitochondria causing apoptosis or necrosis. As a result, there are many challenges to overcome before we can determine if the benefits outweigh the risks associated with NPs. WIREs Nanomed Nanobiotechnol 2010 2 544–568
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The view presented in this manuscript does not necessarily reflect those of Food and Drug Administration.
610 citations
TL;DR: The results indicate that Ag NPs in D. melanogaster induce heat shock stress, oxidative stress, DNA damage and apoptosis, which suggests that the organism is stressed and thus warrants more careful assessment ofAg NPs using in vivo models to determine if chronic exposure presents developmental and reproductive toxicity.
439 citations
TL;DR: The covalent linkage and the strong electronic interaction between the P3HT and graphene moieties in G-P3HT were confirmed by spectroscopic analyses and electrochemical measurements.
Abstract: CH2OH-terminated regioregular poly(3-hexylthiophene) (P3HT) was chemically grafted onto carboxylic groups of graphene oxide (GO) via esterification reaction. The resultant P3HT-grafted GO sheets (G-P3HT) are soluble in common organic solvents, facilitating the structure/property characterization and the device fabrication by solution processing. The covalent linkage and the strong electronic interaction between the P3HT and graphene moieties in G-P3HT were confirmed by spectroscopic analyses and electrochemical measurements. A bilayer photovoltaic device based on the solution-cast G-P3HT/C60 heterostructures showed a 200% increase of the power conversion efficiency (η = 0.61%) with respect to the P3HT/C60 counterpart under AM 1.5 illumination (100 mW/cm2).
415 citations
TL;DR: It is suggested that Ag-NPs may interact with the cerebral microvasculature producing a proinflammatory cascade, if left unchecked; these events may further induce brain inflammation and neurotoxicity.
298 citations
TL;DR: This paper investigates the thermal transport in one such novel architecture-a pillared-graphene network nanostructure which combines graphene sheets and carbon nanotubes to create a three-dimensional network and foresee that such architecture could potentially be used as a template for designing future structurally stable microscale systems with tailorable in-plane and out-of-plane thermal transport.
Abstract: Carbon nanotubes (CNT) and graphene are considered as potential future candidates for many nano/microscale integrated devices due to their superior thermal properties. Both systems, however, exhibit significant anisotropy in their thermal conduction, limiting their performance as three-dimensional thermal transport materials. From thermal management perspective, one way to tailor this anisotropy is to consider designing alternative carbon-based architectures. This paper investigates the thermal transport in one such novel architecture—a pillared-graphene (PG) network nanostructure which combines graphene sheets and carbon nanotubes to create a three-dimensional network. Nonequilibrium molecular dynamics simulations have been carried out using the AIREBO potential to calculate the thermal conductivity of pillared-graphene structures along parallel (in-plane) as well as perpendicular (out-of-plane) directions with respect to the graphene plane. The resulting thermal conductivity values for PG systems are di...
293 citations
TL;DR: In this paper, the authors describe a totally solid-state, rechargeable, long cycle life lithium-oxygen battery cell, which is comprised of a Li metal anode, a highly Li-ion conductive solid electrolyte membrane laminate fabricated from glass-ceramic (GC) and polymerceramic materials.
Abstract: This paper describes a totally solid-state, rechargeable, long cycle life lithium-oxygen battery cell. The cell is comprised of a Li metal anode, a highly Li-ion conductive solid electrolyte membrane laminate fabricated from glass-ceramic (GC) and polymer-ceramic materials, and' a solid-state composite air cathode prepared from high surface area carbon and ionically conducting GC powder. The cell exhibited excellent thermal stability and rechargeability in the 30-105°C temperature range. It was subjected to 40 charge-discharge cycles at current densities ranging from 0.05 to 0.25 mA/cm 2 . The reversible charge/discharge voltage profiles of the Li―O 2 cell with low polarizations between the discharge and charge are remarkable for a displacement-type electrochemical cell reaction involving the reduction of oxygen to form lithium peroxide. The results represent a major contribution in the quest of an ultrahigh energy density electrochemical power source. We believe that the Li―O 2 cell, when fully developed, could exceed specific energies of 1000 Wh/kg in practical configurations.
281 citations
TL;DR: In this paper, a laser and sunlight driven, fast and large oscillation of cantilevers composed of photoresponsive liquid crystal polymer materials was reported. But the experimental frequency response is accurately described by the calculated natural resonant frequency for a non-damped cantilever.
Abstract: We report on the laser and sunlight driven, fast and large oscillation of cantilevers composed of photoresponsive liquid crystal polymer materials. The oscillation frequency, driven with a focused 100 mW laser of multiple wavelengths (457, 488, 514 nm), is as high as 270 Hz and is shown to be strongly correlated to the physical dimensions of the cantilever. The experimental frequency response is accurately described by the calculated natural resonant frequency for a non-damped cantilever. To further understand the conversion efficiency of light energy to mechanical work in the system, the oscillatory behavior of a 2.7 mm × 0.7 mm × 0.04 mm cantilever was examined at pressures ranging from 1 atm to 0.03 atm. A large increase in amplitude from 110° at STP to 250° at low pressure was observed. A first approximation of the system efficiency was calculated at 0.1%. The large increase in amplitude at low pressure indicates strong hydrodynamic loss and thus, the material efficiency is potentially much greater. Using a simple optical setup, oscillatory behavior was also demonstrated using sunlight. This work indicates the potential for remotely triggered photoactuation of photoresponsive polymer cantilevers from long distances with lasers or focused sunlight.
278 citations
TL;DR: A review of the state of the art in the use of cholesteric liquid crystals (CLCs) as color changing optical materials can be found in this article, with a brief summary of thermal and electrically induced color changes.
Abstract: ROY G. BIV is the acronym used around the English-speaking world to aid children in the memorization of the traditional colors of the rainbow (red, orange, yellow, green, blue, indigo, and violet). Color surrounds us and the ability to change color by external stimuli (heat, force, light exposure, magnetic or electric field) continues to be leveraged for many present day applications. This review focuses on the state of the art in the use of cholesteric liquid crystals (CLCs) as color changing optical materials. After a brief summary of thermal and electrically induced color changes, the bulk of the article describes recent efforts in photoresponsive CLCs, materials in which light is used to control the color output.
250 citations
TL;DR: The data revealed that already at a concentration of 10 microg/ml, silver nanoparticles specifically interact with Fyn kinase downstream of Ret and impair SSC proliferation in vitro, and it was demonstrated that the particle coating was degraded upon interaction with the intracellular microenvironment, reducing biocompatibility.
TL;DR: The results reveal that SWNT carpet growth is maximized by very low Ostwald ripening rates, mild subsurface diffusion rates, and high porosity, which is best achieved in the sputtered/Fe catalyst.
Abstract: We have studied the lifetime, activity, and evolution of Fe catalysts supported on different types of alumina: (a) sputter deposited alumina films (sputtered/Fe), (b) electron-beam deposited alumina films (e-beam/Fe), (c) annealed e-beam deposited alumina films (annealed e-beam/Fe), (d) alumina films deposited by atomic layer deposition (ALD/Fe), and (e) c-cut sapphire (sapphire/Fe). We show that the catalytic behavior, Ostwald ripening, and subsurface diffusion rates of Fe catalyst supported on alumina during water-assisted growth or "supergrowth" of single-walled carbon nanotube (SWNT) carpets are strongly influenced by the porosity of the alumina support. The catalytic activity increases in the following order: sapphire/Fe < annealed e-beam/Fe < ALD/Fe < e-beam/Fe < sputtered/Fe. With a combination of microscopic and spectroscopic characterization, we further show that the Ostwald ripening rates of the catalysts and the porosity of the alumina support correlate with the lifetime and activity of the catalysts. Specifically, our results reveal that SWNT carpet growth is maximized by very low Ostwald ripening rates, mild subsurface diffusion rates, and high porosity, which is best achieved in the sputtered/Fe catalyst. These results not only emphasize the connection between catalytic activity and particle stability during growth, but guide current efforts aimed at rational design of catalysts for enhanced and controlled SWNT carpet growth.
TL;DR: In this article, the authors developed a specialty paper made of carbon nanofibers and nickel nanostrands as a surface layer on the composite panels and explored potential replacement for existing lightning strike protection materials.
Abstract: Carbon fiber reinforced polymer matrix composites have been increasingly used for aircraft structures. Such relatively low-conductivity composite materials need to be engineered with lightning strike protection to achieve lightning tolerance comparable to metallic components. This study developed a specialty paper made of carbon nanofibers and nickel nanostrands as a surface layer on the composite panels and explored potential replacement for existing lightning strike protection materials. The porous, flexible, non-woven papers of nanofibers and nanostrands were first prepared by the papermaking process. They were then incorporated onto the surface of carbon fiber reinforced polymer composites through resin transfer molding process. A method of applying a temporary surface barrier on the paper was developed to prevent the infused resin from breaching the paper’s surface. This minimized the resin on the composite panel’s surface and allowed its surface conductivity to remain high. The lightning strike tests conducted on these composite panels showed that lightning strike tolerance correlated to the surface conductivities of composite panels.
TL;DR: The results show that graphene can be selectively recognized even in nanometer-defined strips and modification of graphene with bifunctional peptides reveals both the ability to impart selective recognition of gold nanoparticles and the development of an ultrasensitive graphene-based TNT sensor.
Abstract: The development of a general approach for the nondestructive chemical and biological functionalization of graphene could expand opportunities for graphene in both fundamental studies and a variety of device platforms. Graphene is a delicate single-layer, two-dimensional network of carbon atoms whose properties can be affected by covalent modification. One method for functionalizing materials without fundamentally changing their inherent structure is using biorecognition moieties. In particular, oligopeptides are molecules containing a broad chemical diversity that can be achieved within a relatively compact size. Phage display is a dominant method for identifying peptides that possess enhanced selectivity toward a particular target. Here, we demonstrate a powerful yet benign approach for chemical functionalization of graphene via comprehensively screened phage displayed peptides. Our results show that graphene can be selectively recognized even in nanometer-defined strips. Further, modification of graphen...
TL;DR: In this article, the authors measured spatiotemporal structures of excited species by laser spectroscopic methods in a plasma jet, which was driven by a bipolar impulse voltage pulse train of the order of kilohertz repetition rate applied across a pair of electrodes wrapped around a glass tube with a helium gas flow.
Abstract: We have measured spatiotemporal structures of excited species by laser spectroscopic methods in a plasma jet, which was driven by a bipolar impulse voltage pulse train of the order of kilohertz repetition rate applied across a pair of electrodes wrapped around a glass tube with a helium gas flow. We noticed the differences between the positive and the negative phases of the voltage applied to the front-side electrode placed closer to the tube exit while the back-side electrode was grounded. The experimental results showed that the radial distribution of the excited species had a hollow shape at the centre in the positive voltage phase, while it had a more uniform shape in the negative phase. The peak density of the helium metastable atom in the positive phase was almost constant irrespective of the peak applied voltage. However, it increased with the increase in the peak applied voltage in the negative phase. The mechanism causing these differences was argued from the respects of positive and negative corona discharges. We have also investigated the property of the plasma plume under conditions similar to material processing with a conductive substrate placed in front of the plasma jet. In this case, the plasma production by electron impact ionization became dominant near the substrate as was revealed from the spatiotemporal distributions of helium metastable atom and nitrogen ion densities.
TL;DR: In this article, a mechanism by which catalyst deactivation occurs during vertically aligned single-walled carbon nanotube (SWNT) growth is demonstrated, and it is shown that a combination of both Ostwald ripening and subsequent subsurface diffusion leads to loss of the Fe catalyst.
Abstract: A mechanism by which catalyst deactivation occurs during vertically aligned single-walled carbon nanotube (SWNT) growth is demonstrated. We have used both quantitative measurements of nanotube growth rates and ex situ and in situ transmission electron microscopy observations to show that termination of carbon nanotube (CNT) array growth can be intrinsically linked to evolution of the catalyst morphology. Specifically, we find that a combination of both Ostwald ripening and subsequent subsurface diffusion leads to loss of the Fe catalyst, and through direct observations, we correlate this with nanotube growth termination. These observations indicate that careful design of the catalyst and its support − as well as the interaction between the two − is required to maximize nanotube yields.
TL;DR: In this article, a split-cycle constant-period frequency modulation (CDFM) was used to control a flapping-wing micro air vehicle by varying the velocity profiles of the wing strokes.
Abstract: A new method of controlling a flapping-wing micro air vehicle by varying the velocity profiles of the wing strokes is presented in this manuscript. An exhaustive theoretical analysis along with simulation results show that this new method, called split-cycle constant-period frequency modulation, is capable of providing independent control over vertical and horizontal body forces as well as rolling and yawing moments using only two physical actuators, whose oscillatory motion is defined by four parameters. An actuated bob-weight is introduced to enable independent control of pitching moment. A general method for deriving sensitivities of cycle-averaged forces and moments to changes in wingbeat kinematic parameters is provided, followed by an analytical treatment for a case where the angle of attack of each wing is passively regulated and the motion of the wing spar in the stroke plane is driven by a split-cycle waveform. These sensitivities are used in the formulation of a cycle-averaged control law that successfully stabilizes and controls two different simulation models of the aircraft. One simulation model is driven by instantaneous aerodynamic forces derived from blade-element theory, while the other is driven by an empirical representation of an unsteady aerodynamic model that was derived from experiments.
TL;DR: In this paper, a microstructure-sensitive extreme value statistical framework was proposed to quantify the effects of interactions between various micro-structure attributes on fatigue life in the HCF regime.
TL;DR: These observations are the first to suggest that nanoparticles can induce brain edema formation by influencing BBB breakdown in vivo.
Abstract: Nanoparticles are small sized (1–100 nm) particles derived from transition metals, silver, copper, aluminum, silicon, carbon and metal oxides that can easily cross the blood–brain barrier (BBB) and/or produce damage to the barrier integrity by altering endothelial cell membrane permeability. However, the influence of nanoparticles on BBB integrity is still not well-known. In this investigation, effect of nanoparticles derived from Ag, Al and Cu (50–60 nm) on BBB permeability in relation to brain edema formation was examined in a rat model. Intravenous (30 mg/kg), intraperitoneal (50 mg/kg) or intracerebral (20 µg in 10 µL) administration of Ag, Cu or Al nanoparticles disrupted the BBB function to Evans blue albumin (EBA) and radioiodine in rats 24 h after administration and induced brain edema formation. The leakage of Evans blue dye was observed largely in the ventral surface of brain and in the proximal frontal cortex. The dorsal surfaces of cerebellum showed mild to moderate EBA staining. These effects were most pronounced in animals that received Ag or Cu nanoparticles compared to Al nanoparticles through intravenous routes. These observations are the first to suggest that nanoparticles can induce brain edema formation by influencing BBB breakdown in vivo.
TL;DR: This letter experimentally investigated the plasmonic focusing properties of the spiral lens using a collection mode near-field scanning optical microscope using a single Archimedes' spiral slot with a single turn.
Abstract: A spiral plasmonic lens can focus circular polarization of a given handedness while simultaneously defocus the circular polarization of the opposite chirality, which may be used as a miniature circular polarization analyzer. In this letter, we experimentally investigated the plasmonic focusing properties of the spiral lens using a collection mode near-field scanning optical microscope. A single Archimedes' spiral slot with a single turn was etched through gold thin film as a spiral plasmonic lens. The plasmonic field at the focus of a spiral lens strongly depends on the spin of the incident photon. Circular polarization extinction ratio better than 50 is obtainable with a device size as small as only 4 times of surface plasmon wavelength.
TL;DR: In this paper, a two-phase nanocomposite coating that consists of inclusions of silver in a vanadium nitride matrix (VN/Ag) was investigated as a potential adaptive coating with a reduced friction coefficient from 25 to 1000°C.
TL;DR: In this article, the authors investigated the anisotropic nature of thermal transport in molybdenum disulphide using molecular dynamics simulations, and they showed that the predicted values of thermal conductivity are about an order of magnitude higher with respect to experiments.
TL;DR: It is concluded that measures of resources, conceptualized as multiple energization processes, are potentially useful for diagnostic monitoring in applied settings.
Abstract: Loss of vigilance may lead to impaired performance in various applied settings including military operations, transportation, and industrial inspection. Individuals differ considerably in sustained attention, but individual differences in vigilance have proven to be hard to predict. The dependence of vigilance on workload factors is consistent with a resource model of sustained attention. Thus, measures of attentional resource availability may predict the operator's subsequent vigilance performance. In this study, we investigated whether a diagnostic battery of measures of response to a cognitive challenge would predict subsequent sustained attention. Measures that may relate to the mobilization of resources in response to task demands include subjective task engagement and coping, and a novel psychophysiological index, cerebral bloodflow velocity (CBFV). A two-phase design was used. First, participants were exposed to a challenging battery of short tasks that elevated CBFV. Second, participants performed a 36-min vigilance task. Two subgroups of participants performed either a sensory vigilance (N = 187) or a cognitive vigilance (N = 107) task. Measures of task engagement, coping, and CBFV response to the short task battery were compared as predictors of subsequent vigilance. Both subjective and CBFV indices of energization predicted sensory and cognitive vigilance, consistent with resource theory. Structural equation modeling was used to develop a latent factor model of influences on sustained attention. It is concluded that measures of resources, conceptualized as multiple energization processes, are potentially useful for diagnostic monitoring in applied settings. Use of a diagnostic task battery in military and transportation settings is discussed, along with some potential limitations on validity of the diagnostic test.
TL;DR: Transmission electron microscopy can be used to elucidate the intracellular fate of NPs, facilitating the development of biosensors and therapeutics, and provide a critical component for understanding NP toxicity.
Abstract: We describe the use of transmission electron microscopy (TEM) for cellular ultrastructural examination of nanoparticle (NP)-exposed biomaterials. Preparation and imaging of electron-transparent thin cell sections with TEM provides excellent spatial resolution (∼1 nm), which is required to track these elusive materials. This protocol provides a step-by-step method for the mass-basis dosing of cultured cells with NPs, and the process of fixing, dehydrating, staining, resin embedding, ultramicrotome sectioning and subsequently visualizing NP uptake and translocation to specific intracellular locations with TEM. In order to avoid potential artifacts, some technical challenges are addressed. Based on our results, this procedure can be used to elucidate the intracellular fate of NPs, facilitating the development of biosensors and therapeutics, and provide a critical component for understanding NP toxicity. This protocol takes ∼1 week.
TL;DR: In this paper, the design optimization of a flapping wing in forward flight with active shape morphing, aimed at maximizing propulsive efficiency under lift and thrust constraints, was performed with an inviscid three-dimensional unsteady vortex lattice method, whose lack of fidelity is offset by a relatively inexpensive computational cost.
Abstract: This work considers the design optimization of a flapping wing in forward flight with active shape morphing, aimed at maximizing propulsive efficiency under lift and thrust constraints. This is done with an inviscid three-dimensional unsteady vortex lattice method, whose lack of fidelity is offset by a relatively inexpensive computational cost. The design is performed with a gradient-based optimization, where gradients are computed with an analytical sensitivity analysis. Wake terms provide the only connection between the forces generated at disparate time steps, and must be included to compute the derivative of the aerodynamic state at a time step with respect to the wing shape at all previous steps. The cyclic wing morphing, superimposed upon the flapping motions, is defined by a series of spatial and temporal approximations. The generalized coordinates of a finite number of twisting and bending modes are approximated by cubic splines. The amplitudes at the control points provide design variables; increasing the number of variables (providing the wing morphing with a greater degree of spatial and temporal freedom) is seen to provide increasingly superior designs, with little increase in computational cost. I. Introduction HE design and optimization of artificial flapping wing flyers presents considerable difficulties in terms of computational cost: the complex physical phenomena associated with the flight (unsteady low Reynolds number vortical flows in conjunction with a nonlinear elastic wing surface undergoing large prescribed rotations and translations) may require a high-fidelity computational tool. Furthermore, the search optimization process typically requires many function evaluations to converge to a relevant optimum. Lower fidelity numerical tools may help alleviate the burden, either used during the search process in conjunction with a higher-fidelity model 1
TL;DR: In this paper, the layered atomic structure of silver molybdate facilitates sliding, resulting in a low coefficient of friction (<0.2) from 300 to 500 C. And they showed that the sliding test can be used to evaluate the sliding properties of metal powders from 25 to 600 C.
TL;DR: In this article, a philosophy of employing computational simulation to establish relations between remote loading conditions and microstructure-scale slip behavior in terms of Fatigue Indicator Parameters (FIPs) as a function of stress amplitude, stress state and micro-structure, featuring calibration of mean experimental responses for known microstructures.
TL;DR: Functional near infrared spectroscopy measures of cerebral oxygenation levels were collected from participants performing difficult and easy versions of a 12 min vigilance task and for controls who merely watched the displays without a work imperative.
TL;DR: In this paper, the influence of cross-link density of azobenzene-containing liquid crystal polymer networks (azo-LCNs) on the thermomechanical properties and the laser-directed bending of cantilevers consisting of these materials was investigated.
Abstract: We report on the influence of cross-link density of azobenzene-containing liquid crystal polymer networks (azo-LCNs) on the thermomechanical properties and the laser-directed bending of cantilevers consisting of these materials. Cross-link density of azo-LCN was increased by adjusting the length of photocuring from 1 to 120 min. The storage modulus (E′), loss modulus (E′′), and glass transition temperature (Tg) of the azo-LCNs increase with cross-link density. Increasing the cross-link density of the polydomain azo-LCN reduces the magnitude of the bending angle of the cantilevers. The relationship between the thermomechanical and photomechanical properties of the polydomain azo-LCN reported here is further elucidated in the examination of laser-directed bending over a wide range of temperature. The temperature dependence of the equilibrium photodriven bending angle is shown to be strongly related to the temperature dependence of the storage modulus for a given azo-LCN sample. Normalizing the temperature d...
TL;DR: In this paper, a combination of Monte Carlo search, local optimization, and density functional theory (DFT) was used to identify the magic size (MS, ΔEn > 0) quantum dots.
Abstract: Structure and properties of small quantum dots are of fundamental and practical interest due to a broad range of applications that exploit their optical tunability. Although previous experimental and theoretical investigation of very small semiconductor quantum dots have shown relative stability for clusters that deviate from the bulk, these materials have not been systematically characterized. In this work, structures of (CdSe)n (n = 1−37) clusters were studied using a combination of structure enumeration, Monte Carlo search, and local optimization. Binding energy (En and relative binding energy, ΔEn = n(En+1 − En), per CdSe unit) calculations using density functional theory (DFT) were carried out to identify the so-called magic size (MS, ΔEn > 0) quantum dots. (CdSe)n with n = 9, 12, 16, 18, 21, 24, 28, 32, 33, 35, and 36 were found to have high relative stability. MS structural motifs were investigated further for clusters up to (CdSe)54. In addition, time-dependent DFT calculations of one-photon absor...