Showing papers by "Wright-Patterson Air Force Base published in 2008"
TL;DR: A size-dependent toxicity was produced by silver nanoparticles, and one predominant mechanism of toxicity was found to be largely mediated through oxidative stress.
Abstract: The rapid advancement of nanotechnology has created a vast array of engineered nanomaterials (ENMs) which have unique physical (size, shape, crystallinity, surface charge) and chemical (surface coating, elemental composition and solubility) attributes. These physicochemical properties of ENMs can produce chemical conditions to induce a pro-oxidant environment in the cells, causing an imbalanced cellular energy system dependent on redox potential and thereby leading to adverse biological consequences, ranging from the initiation of inflammatory pathways through to cell death. The present study was designed to evaluate size-dependent cellular interactions of known biologically active silver nanoparticles (NPs, Ag-15nm, Ag-30nm, and Ag-55nm). Alveolar macrophages provide the first defense and were studied for their potential role in initiating oxidative stress. Cell exposure produced morphologically abnormal sizes and adherence characteristics with significant NP uptake at high doses after 24 h. Toxicity eva...
1,640 citations
881 citations
TL;DR: In this article, the authors presented 12−6 and 9−6 LJ parameters for several face-centered cubic metals (Ag, Al, Au, Cu, Ni, Pb, Pd, Pt) which reproduce densities, surface tensions, interface properties with water and (bio)organic molecules, as well as mechanical properties in quantitative (<0.1%) to good qualitative (25%) agreement with experiment under ambient conditions.
Abstract: Molecular dynamics and Monte Carlo simulations often rely on Lennard-Jones (LJ) potentials for nonbond interactions. We present 12−6 and 9−6 LJ parameters for several face-centered cubic metals (Ag, Al, Au, Cu, Ni, Pb, Pd, Pt) which reproduce densities, surface tensions, interface properties with water and (bio)organic molecules, as well as mechanical properties in quantitative (<0.1%) to good qualitative (25%) agreement with experiment under ambient conditions. Deviations associated with earlier LJ models have been reduced by 1 order of magnitude due to the precise fit of the new models to densities and surface tensions under standard conditions, which also leads to significantly improved results for surface energy anisotropies, interface tensions, and mechanical properties. The performance is comparable to tight-binding and embedded atom models at up to a million times lower computational cost. The models extend classical simulation methods to metals and a variety of interfaces with biopolymers, surfact...
753 citations
TL;DR: This work has created gecko-foot–mimetic dry adhesives that show macroscopic adhesive forces of ∼100 newtons per square centimeter, almost 10 times that of a gecko foot, and a much stronger shear adhesion force than the normalAdhesion force, to ensure strong binding along the shear direction and easy lifting in the normal direction.
Abstract: The ability of gecko lizards to adhere to a vertical solid surface comes from their remarkable feet with aligned microscopic elastic hairs. By using carbon nanotube arrays that are dominated by a straight body segment but with curly entangled top, we have created gecko-foot-mimetic dry adhesives that show macroscopic adhesive forces of approximately 100 newtons per square centimeter, almost 10 times that of a gecko foot, and a much stronger shear adhesion force than the normal adhesion force, to ensure strong binding along the shear direction and easy lifting in the normal direction. This anisotropic force distribution is due to the shear-induced alignments of the curly segments of the nanotubes. The mimetic adhesives can be alternatively binding-on and lifting-off over various substrates for simulating the walking of a living gecko.
702 citations
TL;DR: The results suggest that polysaccharide coated particles are more individually distributed while agglomeration of the uncoated particles limits the surface area availability and access to membrane bound organelles.
649 citations
TL;DR: In this paper, the authors investigated whether deployment with combat exposures was associated with new-onset or continued alcohol consumption, binge drinking, and alcohol-related problems at follow-up.
Abstract: Context High rates of alcohol misuse after deployment have been reported among personnel returning from past conflicts, yet investigations of alcohol misuse after return from the current wars in Iraq and Afghanistan are lacking. Objectives To determine whether deployment with combat exposures was associated with new-onset or continued alcohol consumption, binge drinking, and alcohol-related problems. Design, Setting, and Participants Data were from Millennium Cohort Study participants who completed both a baseline (July 2001 to June 2003; n=77 047) and follow-up (June 2004 to February 2006; n=55 021) questionnaire (follow-up response rate = 71.4%). After we applied exclusion criteria, our analyses included 48 481 participants (active duty, n = 26 613; Reserve or National Guard, n = 21 868). Of these, 5510 deployed with combat exposures, 5661 deployed without combat exposures, and 37 310 did not deploy. Main Outcome Measures New-onset and continued heavy weekly drinking, binge drinking, and alcohol-related problems at follow-up. Results Baseline prevalence of heavy weekly drinking, binge drinking, and alcohol-related problems among Reserve or National Guard personnel who deployed with combat exposures was 9.0%, 53.6%, and 15.2%, respectively; follow-up prevalence was 12.5%, 53.0%, and 11.9%, respectively; and new-onset rates were 8.8%, 25.6%, and 7.1%, respectively. Among active-duty personnel, new-onset rates were 6.0%, 26.6%, and 4.8%, respectively. Reserve and National Guard personnel who deployed and reported combat exposures were significantly more likely to experience new-onset heavy weekly drinking (odds ratio [OR], 1.63; 95% confidence interval [CI], 1.36-1.96), binge drinking (OR, 1.46; 95% CI, 1.24-1.71), and alcohol-related problems (OR, 1.63; 95% CI, 1.33-2.01) compared with nondeployed personnel. The youngest members of the cohort were at highest risk for all alcohol-related outcomes. Conclusion Reserve and National Guard personnel and younger service members who deploy with reported combat exposures are at increased risk of new-onset heavy weekly drinking, binge drinking, and alcohol-related problems.
636 citations
TL;DR: In this article, high frequency and large amplitude oscillations are driven by laser exposure in cantilevers made from a photosensitive liquid crystal polymer, which is called photo-sensitive liquid crystal polymers (PLCP).
Abstract: High frequency and large amplitude oscillations are driven by laser exposure in cantilevers made from a photosensitive liquid crystal polymer.
381 citations
TL;DR: It is confirmed that acquisitions do not lead to higher performance on average, but it is found that complementary resource profiles in target and acquiring firms are associated with abnormal returns.
Abstract: We explore the role of resource interactions in explaining firm performance in the context of acquisitions. Although we confirm that acquisitions do not lead to higher performance on average, we do find that complementary resource profiles in target and acquiring firms are associated with abnormal returns. Specifically, we find that acquiring firm marketing resources and target firm technology resources positively reinforce (complement) each other; meanwhile, acquiring and target firm technology resources negatively reinforce (substitute) one another. Implications for management theory and practice are identified.
259 citations
TL;DR: The objective function of the triangulation technique is modified further to overcome the inherent difficulties associated with multiple singularities and to maximize the efficiency of the acoustic emission data for multiple receiving sensors.
199 citations
TL;DR: In this article, the authors provide an overview of the modes of detection, theory behind the transduction mechanisms, materials employed as active layers, and some of the important applications of microcantilevers.
Abstract: : Microcantilevers, one of the most common MEMS structures, have been introduced as a novel sensing paradigm nearly a decade ago. Ever since, the technology has emerged to find important applications in chemical, biological and physical sensing areas. Today the technology stands at the verge of providing the next generation of sophisticated sensors (such as artificial nose, artificial tongue) with extremely high sensitivity and miniature size. The article provides an overview of the modes of detection, theory behind the transduction mechanisms, materials employed as active layers, and some of the important applications. Emphasizing the material design aspects, the review underscores the most important findings, current trends, key challenges and future directions of the microcantilever based sensor technology.
169 citations
TL;DR: Favorable agreement of the predicted cores with limited experimental measurements demonstrates the need for quantum mechanical treatment of dislocation cores and eliminates uncertainties resulting from the wide range of previous results.
Abstract: The strain field of isolated screw and edge dislocation cores in aluminum are calculated using density-functional theory and a flexible boundary condition method. Nye tensor density contours and differential displacement fields are used to accurately bound Shockley partial separation distances. Our results of 5-7.5 A (screw) and 7.0-9.5 A (edge) eliminate uncertainties resulting from the wide range of previous results based on Peierls-Nabarro and atomistic methods. Favorable agreement of the predicted cores with limited experimental measurements demonstrates the need for quantum mechanical treatment of dislocation cores.
TL;DR: In this article, an adaptive Mo2N/MoS2/Ag nanocomposite coatings were deposited from three individual Mo, MoS2, and Ag targets in a nitrogen environment onto Si (111), 440C grade stainless steel, and inconel 600 substrates.
Abstract: Reactively sputtered Mo2N/MoS2/Ag nanocomposite coatings were deposited from three individual Mo, MoS2, and Ag targets in a nitrogen environment onto Si (111), 440C grade stainless steel, and inconel 600 substrates. The power to the Mo target was kept constant, while power to the MoS2 and Ag targets was varied to obtain different coating compositions. The coatings consisted of Mo2N, with silver and/or sulfur additions of up to approximately 24 at%. Coating chemistry and crystal structure were evaluated using X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD), which showed the presence of tetragonal Mo2N and cubic Ag phases. The MoS2 phase was detected from XPS analysis and was likely present as an amorphous inclusion based on the absence of characteristic XRD peaks. The tribological properties of the coatings were investigated in dry sliding at room temperature against Si3N4, 440C stainless steel, and Al2O3. Tribological testing was also conducted at 350 and 600 °C against Si3N4. The coatings and respective wear tracks were examined using scanning electron microscopy (SEM), optical microscopy, profilometry, energy dispersive X-ray spectroscopy (EDX), and micro-Raman spectroscopy. During room temperature tests, the coefficients of friction (CoF) were relatively high (0.5–1.0) for all coating compositions, and particularly high against Si3N4 counterfaces. During high-temperature tests, the CoF of single-phase Mo2N coatings remained high, but much lower CoFs were observed for composite coatings with both Ag and S additions. CoF values were maintained as low as 0.1 over 10,000 cycles for samples with Ag content in excess of 16 at% and with sulfur content in the 5–14 at% range. The chemistry and phase analysis of coating contact surfaces showed temperature-adaptive behavior with the formation of metallic silver at 350 °C and silver molybdate compounds at 600 °C tests. These adaptive Mo2N/MoS2/Ag coatings exhibited wear rates that were two orders of magnitude lower compared to Mo2N and Mo2N/Ag coatings, hence providing a high potential for lubrication and wear prevention of high-temperature sliding contacts.
TL;DR: In this article, the authors examined the voltage requirements for the plasma actuators to reattach the flow at the leading edge of airfoils at poststall angles of attack for a range of flow parameters in order to establish scaling between laboratory and full flight conditions.
Abstract: We present experimental results to yield insight into the scalability and control effectiveness of single-dielectricbarrier-discharge plasma actuators for leading-edge separation control on airfoils. The parameters investigated are chord Reynolds number, Mach number, leading-edge radius, actuator amplitude, and unsteady frequency. This includes chord Reynolds numbers up to 1:0 � 106 and a maximum freestream speed of 60 m=s corresponding to a Mach number of 0.176. The main objective of this work is to examine the voltage requirements for the plasma actuators to reattach the flow at the leading edge of airfoils at poststall angles of attack for a range of flow parameters in order to establish scaling between laboratory and full-flight conditions. For the full range of conditions, an optimum unsteady actuator frequency f is found to minimize the actuator voltage needed to reattach the flow, such that F� � fLsep=U1 � 1. At the optimum frequencies, the minimum voltage required to reattach the flow is weakly dependent on chord Reynolds number and strongly dependent on the poststall angle of attack and leading-edge radius. The results indicate that the voltage required to reattach the flow scales as the square of the leading-edge radius.
TL;DR: In this article, the authors examined the mechanisms of fatigue-crack formation by quantifying critical microstructural features observed in the fatiguecrack initiation region, and found that the fracture surface near the fatigue crack-initiation site was crystallographic in nature.
Abstract: The fatigue behavior of an alpha + beta titanium alloy, Ti-6Al-2Sn-4Zr-6Mo, has been characterized in the very-high-cycle fatigue (VHCF) regime using ultrasonic-fatigue (20 kHz) techniques Stress levels (σ
max) of 40 to 60 pct of the yield strength of this alloy have been examined Fatigue lifetimes in the range of 106 to 109 cycles are observed, and fatigue cracks initiate from both surface and subsurface sites This study examines the mechanisms of fatigue-crack formation by quantifying critical microstructural features observed in the fatigue-crack initiation region The fracture surface near the fatigue-crack-initiation site was crystallographic in nature Facets, which result from the fracture of primary alpha (α
p
) grains, are associated with the crack-initiation process The α
p
grains that form facets are typically larger in size than average The spatial distribution of α
p
grains relative to each other observed near the initiation site did not correlate with fatigue life Furthermore, the spatial distribution of α
p
grains did not provide a suitable means for discerning crack-initiation sites from randomly selected nominal areas Stereofractography measurements have shown that the facets observed at or near the initiation sites are oriented for high shear stress; ie, they are oriented close to 45 deg with respect to the loading axis Furthermore, a large majority of the grains and laths near the site of crack initiation are preferentially oriented for either basal or prism slip, suggesting that regions where α
p
grains and α laths have similar crystallographic orientations favor crack initiation Microtextured regions with favorable and similar orientations of α
p
grains and the lath α are believed to promote cyclic-strain accumulation by basal and prism slip Orientation imaging microscopy (OIM) indicates that these facets form on the basal plane of α
p
grains The absence of a significant role of spatial clustering of α
p
grains, coupled with the observation of regions of microtexture on the order of 300 to 500 μm supports the idea that variability in fatigue life in the very-high-cycle fatigue regime results from the variability in the nature (intensity, coherence, and size) of these microtextured regions
TL;DR: In this article, the authors present a computational approach for large-eddy simulation of flows with active control, where the numerical scheme is predicated upon an implicit time-marching algorithm and utilizes a high-order compact finite-difference approximation to represent spatial derivatives.
07 Jan 2008
TL;DR: AlGaN/GaN high electron mobility transistor (HEMT) device operation was modeled from the sub-micrometer scale to the substrate using a combination of an electro-thermal device model for the active device with realistic power dissipation within the device and a coupled three dimensional thermal model to account for the substrate.
TL;DR: A class of new conjugated copolymers containing a donor (thiophene)-acceptor (2-pyran-4-ylidene-malononitrile) was synthesized via Stille coupling polymerization, providing a novel concept for developing high Voc photovoltaic cells based on donor-pi-acceptor conjugations by adjusting the donor/acceptor ratio.
Abstract: A class of new conjugated copolymers containing a donor (thiophene)−acceptor (2-pyran-4-ylidene-malononitrile) was synthesized via Stille coupling polymerization. The resulting copolymers were characterized by 1H NMR, elemental analysis, GPC, TGA, and DSC. UV−vis spectra indicated that the increase in the content of the thiophene units increased the interaction between the polymer main chains to cause a red-shift in the optical absorbance. Cyclic voltammetry was used to estimate the energy levels of the lowest unoccupied molecular orbital (LUMO) and the highest occupied molecular orbital (HOMO) and the band gap (Eg) of the copolymers. The basic electronic structures of the copolymers were also studied by DFT calculations with the GGA/B3LYP function. Both the experimental and the calculated results indicated an increase in the HOMO energy level with increasing the content of thiophene units, whereas the corresponding change in the LUMO energy level was much smaller. Polymer photovoltaic cells of a bulk het...
TL;DR: In this article, atomic simulations are used to investigate how grain boundary structure influences dislocation nucleation under uniaxial tension and compression for a specific class of symmetric tilt grain boundaries that contain the E structural unit.
TL;DR: Data from this meta-analysis suggest a modest role for probiotics in pediatric AD, seen in moderately severe rather than mild disease, and in children with moderately severe disease were more likely to benefit.
Abstract: Background Several articles describing the efficacy of probiotics in atopic dermatitis (AD) have been published. However, not all studies support a similar outcome. Objective To determine whether probiotics are efficacious in treating AD and to explore whether type of probiotic used, duration of therapy, patient age, severity of disease, and IgE sensitization are factors in determining efficacy. Methods For this meta-analysis of randomized controlled trials describing the efficacy of probiotics in AD, a comprehensive search was performed of databases through January 2008. Three reviewers independently evaluated the studies for methodological qualities. All the data were analyzed, and forest plots were evaluated for the overall efficacy of probiotics in AD and the therapeutic benefit to subgroups of selected patient populations. Results Eleven studies were identified, and data from 10 studies (n = 678) were available to analyze. There was an overall statistically significant difference favoring probiotics compared with placebo in reducing the Scoring of Atopic Dermatitis Severity Index score (mean change from baseline, −3.01; 95% confidence interval, −5.36 to −0.66; P = .01). Children with moderately severe disease were more likely to benefit. Duration of probiotic administration, age, and type of probiotic used did not affect outcome. Conclusion Data from this meta-analysis suggest a modest role for probiotics in pediatric AD. The effect is seen in moderately severe rather than mild disease.
TL;DR: A coal-based jet fuel that would serve the dual purpose of providing propulsion energy and excellent heat-sink capabilities was produced at pilot-plant scale by hydrotreating a 1:1 mixture of coal-derived refined chemical oil and petroleum-derived light cycle oil as discussed by the authors.
TL;DR: A synthesis based on the use of low pressures of the molecular precursor borazine in conjunction with a floating nickelocene catalyst resulted in the formation of double-walled boron nitride nanotubes.
Abstract: One-dimensional nanostructures exhibit quantum confinement which leads to unique electronic properties, making them attractive as the active elements for nanoscale electronic devices. Boron nitride nanotubes are of particular interest since, unlike carbon nanotubes, all chiralities are semiconducting. Here, we report a synthesis based on the use of low pressures of the molecular precursor borazine in conjunction with a floating nickelocene catalyst that resulted in the formation of double-walled boron nitride nanotubes. As has been shown for carbon nanotube production, the floating catalyst chemical vapor deposition method has the potential for creating high quality boron nitride nanostructures with high production volumes.
TL;DR: In this paper, the fabrication of micrometer-sized dimple patterns of different sizes on TiAlCN hard coatings produced by cathodic arc vacuum evaporation was reported.
Abstract: The production of surface micro-patterns in steel substrates for solid lubricant (SL) reservoirs was previously shown to provide improved wear and frictional properties in sliding contact. We report on the fabrication of micrometer-sized dimple patterns of different sizes on TiAlCN hard coatings produced by cathodic arc vacuum evaporation. These dimples were produced by reactive ion etching in a mixed Ar/CF 4 plasma. An overlayer of MoS 2 or Mo/MoS 2 /Ag SLs was deposited on the micro-textured surfaces using unbalanced magnetron sputtering. The tribological properties of the coatings were investigated against Si 3 N 4 in dry sliding at 25 °C and in air at 570 °C. The coatings and respective wear tracks were examined using scanning electron microscopy (SEM), optical microscopy (OM), optical profilometry (OP), energy dispersive x-ray spectroscopy (EDX), and micro-Raman spectroscopy. The frictional and wear properties of textured and flat surfaces were compared. A significant decrease in friction and wear coefficients was achieved at 25 °C and 570 °C for the textured films because the dimples acted as reservoirs that provided a new supply of SLs to the contact surfaces. The chemistry and phase analysis of the coating wear tracks showed temperature adaptive behavior with the lubrication being provided primarily by MoS 2 at 25 °C and by silver and silver molybdate compounds at high temperature.
TL;DR: In this paper, a large eddy simulation was used to explore plasma-based control strategies for the flow past a circular cylinder in crossflow at a Reynolds number of 10,000 solutions were obtained to the Navier-Stokes equations, using a simple phenomenological model to represent plasma-induced body forces imparted by actuators on the surrounding fluid.
Abstract: Large eddy simulation was used to explore plasma-based control strategies for the flow past a circular cylinder in crossflow at a Reynolds number of 10,000 Solutions were obtained to the Navier-Stokes equations, using a simple phenomenological model to represent plasma-induced body forces imparted by actuators on the surrounding fluid The numerical method used a high-fidelity time-implicit scheme, and an overset grid approach Two fundamentally different control strategies were investigated, consisting of larger actuators that produced a wall-jet-like flow, and smaller actuators that perturbed the unstable shear layers near the separation location The larger actuators achieved control via a "Coanda" effect, and were operated both continuously and in a pulsed manner For pulsed cases, two different bistable states with nonzero time-mean lift were identified All control cases resulted in at least a 50% decrease in drag, as well as elimination of oscillatory lift Comparison is made with available experimental data for the baseline case where no control was enforced Features of the control flowfields are described, and resultant solutions are compared with each other
26 Mar 2008
TL;DR: This work reviews applications of ultrafast lasers for optical measurements in combusting flows and sprays, emphasizing recent achievements and future opportunities.
Abstract: Optical measurement techniques are powerful tools for the detailed study of combustion chemistry and physics. Although traditional combustion diagnostics based on continuous-wave and nanosecond-pulsed lasers continue to dominate fundamental combustion studies and applications in reacting flows, revolutionary advances in the science and engineering of ultrafast (picosecond- and femtosecond-pulsed) lasers are driving the enhancement of existing diagnostic techniques and enabling the development of new measurement approaches. The ultrashort pulses afforded by these new laser systems provide unprecedented temporal resolution for studies of chemical kinetics and dynamics, freedom from collisional-quenching effects, and tremendous peak powers for broad spectral coverage and nonlinear signal generation. The high pulse-repetition rates of ultrafast oscillators and amplifiers allow previously unachievable data-acquisition bandwidths for the study of turbulence and combustion instabilities. We review applications o...
TL;DR: In this article, a high speed camera was used to detect the ignition initiated by transient plasma at approximately 1 ms, leading to the formation of a wrinkled, cylindrically-shaped flame.
TL;DR: It is reported that in situ polymerization of a highly conductive self-doped conducting polymer "skin" around and along single stranded DNA dispersed and functionalized single wall carbon nanotubes can greatly decrease the contact resistance.
Abstract: The overall conductivity of SWNT networks is dominated by the existence of high resistance and tunneling/Schottky barriers at the intertube junctions in the network. Here we report that in situ polymerization of a highly conductive self-doped conducting polymer “skin” around and along single stranded DNA dispersed and functionalized single wall carbon nanotubes can greatly decrease the contact resistance. The polymer skin also acts as “conductive glue” effectively assembling the SWNTs into a conductive network, which decreases the amount of SWNTs needed to reach the high conductive regime of the network. The conductance of the composite network after the percolation threshold can be 2 orders of magnitude higher than the network formed from SWNTs alone.
Book•
27 Feb 2008TL;DR: In this paper, the Second Law is used to measure the expected irreversibilities of Incompressible Flows in a case study of automotive fuel cell design, and the second law is applied to the design of a magnetic Stirring Tank.
Abstract: Introduction Introduction Governing Equations of Fluid Flow and Heat Transfer Mathematical Properties of Entropy and Exergy Governing Equations of Entropy and the Second Law Formulation of Entropy Production and Exergy Destruction Statistical and Numerical Formulations of the Second Law Introduction Conservation Laws as Moments of the Boltzmann Equation Extended Probability Distributions Selected Multivariate Probability Distribution Functions Concave Entropy Functions Statistical Formulation of the Second Law Numerical Formulation of the Second Law Predicted Irreversibilities of Incompressible Flows Introduction Entropy Transport Equation for Incompressible Flows Formulation of Loss Coefficients with Entropy Production Upper Entropy Bounds in Closed Systems Case Study of Automotive Fuel Cell Design Case Study of Fluid Machinery Design Measured Irreversibilities of Incompressible Flows Introduction Experimental Techniques of Irreversibility Measurement Case Study of Magnetic Stirring Tank Design Case Study of Natural Convection in Cavities Measurement Uncertainties Entropy Production in Microfluidic Systems Introduction Pressure-Driven Flow in Microchannels Applied Electric Field in Microchannels Micropatterned Surfaces with Open Microchannels Numerical Error Indicators and the Second Law Introduction Discretization Errors of Numerical Convection Schemes Physical Plausibility of Numerical Results Entropy Difference in Residual Error Indicators Numerical Stability and the Second Law Introduction Stability Norms Entropy Stability of Finite Difference Schemes Stability of Shock Capturing Methods Entropy Transport with Phase Change Heat Transfer Introduction Entropy Transport Equations for Solidification and Melting Heat and Entropy Analogies in Phase Change Processes Numerical Stability of Phase Change Computations Thermal Control of Phase Change with Inverse Methods Entropy Production with Film Condensation Entropy Production in Turbulent Flows Introduction Reynolds Averaged Entropy Transport Equations Eddy Viscosity Models of Mean Entropy Production Turbulence Modeling with the Second Law