Showing papers by "Wright-Patterson Air Force Base published in 2001"

Scramjet Engines: The First Forty Years

Abstract: Ageneralreviewoftheemergenceandmaturingofsupersoniccombustionramjet (scramjet)enginetechnologies overthelast 40 years is presented. The review isgiven in terms of theeffortscompleted or proceeding in theUnited States, Russia, France, Germany, Japan, Australia, and other countries. A brief account of the challenges of scramjet combustor development is given, and attention is directed toward other source references for more detailed accounts of technology evolution. Two emerging scramjet applications are identie ed, namely, hydrogenfueledhigh-speed engines foraccess to spaceand hydrocarbon-fueled enginesforhypersonicair-launched missiles.

Surrogate Mixtures to Represent Complex Aviation and Rocket Fuels

Abstract: Surrogate mixtures of one to 10 hydrocarbons that have similar properties to aviation fuels are desirable for experimental and computationaltractability and reproducibility. However, aviation fuels, such as Jet A, JP-8, and JP-5, contain hundreds of hydrocarbons. This paper describes appropriate “surrogate” mixtures to reproduce the behavior of multicomponent aviation fuels. Surrogate mixtures from the literature and their applicability to various situations are summarized.

Fundamental Studies of Cavity-Based Flameholder Concepts for Supersonic Combustors

Abstract: Experimentalandcomputationalinvestigationsofthee owe eldassociatedwithseveralcavity-basede ameholders in a nonreacting supersonic e ow are described. All cavity e ows were of the open type, that is, length-to-depth ratio L/D<10. Two values of L/D were studied with several offset ratios (OR) and aft ramp angles µ. Results indicate that the aft ramp angle plays an important role in determining the character of the shear layer that spans the cavity. For a rectangular cavity with OR=1 and µ=90 deg, a compression wave forms as the e ow separates from the cavity’ s upstream corner. A strong recompression occurs at the aft wall, and the e ow is visibly unsteady. The pressure on the cavity fore wall decreases steadily and the recompression process occurs more gradually with decreasing aftrampangle.Higherdrag coefe cientsandshorterresidencetimesarefoundin cavitieswithshallower ramp angles.

The standardization of terminology for researchers in female pelvic floor disorders.

Abstract: The lack of standardized terminology in pelvic floor disorders (pelvic organ prolapse, urinary incontinence, and fecal incontinence) is a major obstacle to performing and interpreting research. The National Institutes of Health convened the Terminology Workshop for Researchers in Female Pelvic Floor Disorders to: (1) agree on standard terms for defining conditions and outcomes; (2) make recommendations for minimum data collection for research; and (3) identify high priority issues for future research. Pelvic organ prolapse was defined by physical examination staging using the International Continence Society system. Stress urinary incontinence was defined by symptoms and testing; ‘cure’ was defined as no stress incontinence symptoms, negative testing, and no new problems due to intervention. Overactive bladder was defined as urinary frequency and urgency, with and without urge incontinence. Detrusor instability was defined by cystometry. For all urinary symptoms, defining ‘improvement’ after intervention was identified as a high priority. For fecal incontinence, more research is needed before recommendations can be made. A standard terminology for research on pelvic floor disorders is presented and areas of high priority for future research are identified.

The laser additive manufacture of Ti-6Al-4V

Abstract: Laser additive manufacturing (LAM) is a manufacturing technique with cost-reduction potential for titanium aerospace components. The mechanical properties of LAM Ti-6Al-4V have been investigated extensively, but little work on microstructure evolution has been performed to date. The results presented here provide a first look at the relationships between LAM processing parameters and microstructure in as-deposited Ti-6Al-4V.

Supersonic Combustion Experiments with a Cavity-Based Fuel Injector

Abstract: Recent results from combustion experimentsin a direct-connectsupersoniccombustorarepresented. Successful ignition and sustained combustion of gaseous ethylene have been achieved using an injector/e ameholder concept with low-angle, e ush-wall fuel injection upstream of a wall cavity. Two interchangeable facility nozzles (Mach 1.8 and 2.2) were used to obtain combustor inlet e ow properties that simulate e ight conditions between Mach 4 and 6 at a dynamic pressure of 47.9 kPa. Mainstream combustion was achieved at equivalence ratios between 0.25 and 0.75 using only a spark plug and no other external ignition aids. Delta-force levels between 667 and 1779 N were measured, with corresponding combustor pressure ratios between 3.1 and 4.0. Video records of the e ame zone show an intensely active combustion zone with rapid e ame spreading. One-dimensional performance analysis of the test data indicates a combustion efe ciency around 80% with an average combustor skin friction coefe cient of 0.0028.

The adiabatic correction factor for deformation heating during the uniaxial compression test

Abstract: The isothermal uniaxial compression test is a common method to determine the flow stress of metals. For accurate flow stress data at strain rates >10−3 s−1, the data must be corrected for flow softening due to deformation heating. The first step in the correction is to determine the increase in temperature. An adiabatic correction factor, η, is used to determine the temperature between strain rates of 10−3 to 101 s−1. The adiabatic correction factor is the fraction of adiabatic heat retained in the workpiece after heat loss to the dies, η=(ΔT ACTUAL)/(ΔT ADIABATIC), where ΔT ADIABATIC=(0.95 f σdɛ)/(ρC p ). The term η is typically taken to be constant with strain and to vary linearly (0 to 1) with log ( $$\dot \varepsilon $$ ) between 10−3) and 101 s−1. However, using the finite element method (FEM) and a one-dimensional, lumped parameter method, η has been found to vary with strain, die and workpiece thermal conductivities, and the interface heat-transfer coefficient (HTC). Using the lumped parameter method, an analytical expression for η was derived. In this expression, η is a function of the die and workpiece thermal conductivities, the interface heat-transfer coefficient, workpiece heat capacity, strain, and strain rate. The results show that an increase in the HTC or thermal conductivity decreases η.

Ultrafast holographic nanopatterning of biocatalytically formed silica

Abstract: Diatoms are of interest to the materials research community because of their ability to create highly complex and intricate silica structures under physiological conditions: what these single-cell organisms accomplish so elegantly in nature requires extreme laboratory conditions to duplicate1,2—this is true for even the simplest of structures. Following the identification of polycationic peptides from the diatom Cylindrotheca fusiformis, simple silica nanospheres can now be synthesized in vitro from silanes at nearly neutral pH and at ambient temperatures and pressures3,4. Here we describe a method for creating a hybrid organic/inorganic ordered nanostructure of silica spheres through the incorporation of a polycationic peptide (derived from the C. fusiformis silaffin-1 protein) into a polymer hologram created by two-photon-induced photopolymerization. When these peptide nanopatterned holographic structures are exposed to a silicic acid, an ordered array of silica nanospheres is deposited onto the clear polymer substrate. These structures exhibit a nearly fifty-fold increase in diffraction efficiency over a comparable polymer hologram without silica. This approach, combining the ease of processability of an organic polymer with the improved mechanical and optical properties of an inorganic material, could be of practical use for the fabrication of photonic devices.

Heterogeneity of crystallographic texture in friction stir welds of aluminum

Abstract: Over the past decade, friction stir welding (FSW) has rapidly become an important industrial joining process, particularly in the aluminum industry Included among the advantages of FSW are such important attributes as improved weld strength and the elimination of cracking and porosity During the friction stir process, the metal undergoes a tortuous deformation path that is not yet fully understood The crystallographic texture that evolves during FSW contains sharp spatial gradients that undoubtedly influence the integrity of the weld and surrounding region in subsequent performance The locally measured textures are discussed in the context of the material flow required to produce such textures, ultimately resulting in an estimate of the flow field present during FSW

Penetration Failure Mechanisms of Armor-Grade Fiber Composites under Impact:

Abstract: The penetration failure mechanisms of“armor-grade” fiber-reinforced composites with very low resin content were assessed under transverse impact loading in comparison with those of dry reinforcing fabrics. Failure of dry fabrics consisted of the successive fracture of individual yarns along the periphery of the penetrating head as well as the movement of yarns slipping off from the penetrator. In contrast, the principal yarns in the composites, which faced the penetrating head, failed to carry the load mostly through fracture due to the constraint of the resin matrix and the reduced yarn mobility. As a result, the composites absorbed more energy than the fabrics. The ratio of the number of broken yarns in the fabrics to that of the composites correlated quite well with the corresponding ratio of energy absorbed, confirming that fiber straining is responsible for most of the energy absorption in penetration failure. Numerical modeling was utilized to show that yarn slippage in the fabrics results in a smal...

Effects of Image Scale and System Time Delay on Simulator Sickness within Head-Coupled Virtual Environments

Abstract: Novel patterns of visual-vestibular intersensory stimulation often result in symptoms of simulator sickness, raising health and safety concerns regarding virtual environment exposure. Two experiments investigated the effect of conflicting visual-vestibular cues on subjective reports of simulator sickness during and after a 50-min exposure to a head-coupled virtual interface. Virtual image scale factors (0.5. 1.0, 2.0 magnification, generated by varying geometric field of view angle) were investigated in Experiment 1, and additional system time delays (125, 250 ms) were investigated in Experiment 2. Simulator sickness metrics included spoken self-reports during exposure and simulator sickness questionnaires (pre-exposure, immediate postexposure, and 20 min postexposure). Head yaw angular position data were also recorded. Reports of simulator sickness symptoms were significantly greater in the minification (0.5) and magnification (2.0) image scale factor conditions than in the neutral condition (1.0). Simulator sickness did not vary with changes in time delay, however. Furthermore, a comparison across experiments suggests no appreciable increase in simulator sickness with increasing time delays above the nominal value (48 ms). Head angular position data exhibited certain systematic variations across conditions. Actual or potential applications of this research include virtual environment training, simulation, and entertainment systems.

An XPS study of cerium dopants in sol–gel coatings for aluminum 2024-T3

Abstract: Corrosion protection is a key requirement for coatings on aircraft as the US Air Force extends the lifetime of its fleet. Coating systems for aluminum have long incorporated chromates in conversion coatings to protect against corrosion, but environmental restrictions require that alternative coating systems be developed. Cerium has been proposed as an alternative to chromate inhibitors, as have several other rare earth elements, because the rare earths behave as cathodic inhibitors in aluminum. Epoxy silicate sol–gels, containing a few wt.% of cerium salts, were investigated as coatings on aluminum alloy 2024-T3. The salts used were cerium(III) chloride, cerium(III) nitrate hexahydrate, and ammonium cerium(IV) nitrate. X-Ray photoelectron spectroscopy (XPS/ESCA) was used to study both the doped sol–gels and reference cerium compounds in order to determine the oxidation state of the cerium at the surface of the sol–gel coatings. No change in the oxidation state of the cerium in the sol–gels was found. Coupled with electrical impedance spectroscopy measurements, the incorporation of cerium into sol–gels seems promising for future corrosion protection of aluminum 2024-T3.

Potentiodynamic evaluation of sol–gel coatings with inorganic inhibitors

Abstract: Sol–gel coatings were investigated as potential replacements for chromate-based surface treatments on aircraft aluminum alloys. Unlike chromate based treatments current sol–gel coatings do not have the ability to leach corrosion inhibitors upon coating damage and minimize corrosion of the unprotected area. As an alternative, environmentally compliant non-chromate inhibitors of Ce(NO3)3, NaVO3 and Na2MoO4 were incorporated into a Zr-epoxy sol–gel. Results are reported on the coatings chemical analysis and their corrosion protection performance based on electrochemical studies. Aluminum alloy 2024-T3 test coupons coated with protective sol–gel films were found to provide considerable corrosion protection. The improved performance characteristics were derived from the sol–gel ability to form a uniform, low defect, barrier coating. Coatings doped with Ce(NO3)3 had barrier properties at least as good as the standard sol–gel coatings. Coatings with Na2MoO4 and NaVO3 did not provide adequate corrosion protection. The use of corrosion inhibitors within organically modified sol–gel coatings is discussed.

Large-Eddy Simulation of Supersonic Compression-Ramp Flow by High-Order Method

Abstract: A high-order method is used to perform large-eddy simulations of a supersonic compression-ramp flowfield. The procedure employs an implicit approximately factored finite difference algorithm, which is used in conjunction with a 10th-order nondispersive filter. Spatial derivatives are approximated by a sixth-order compact scheme, and Newton-like subiterations are applied to achieve second-order temporal accuracy. In the region of strong shock waves, the compact differencing of convective fluxes is replaced locally by an upwind-biased scheme. Both the Smagorinsky and dynamic subgrid-scale stress models are incorporated in the simulations. Details of the method are summarized, and a number of computations are carried out. Comparisons are made between the respective solutions as well as with available experimental data and with previous numerical results

A review of the neurotoxicity risk of selected hydrocarbon fuels.

Abstract: Over 1.3 million civilian and military personnel are occupationally exposed to hydrocarbon fuels, emphasizing gasoline, jet fuel, diesel fuel, or kerosene. These exposures may occur acutely or chronically to raw fuel, vapor, aerosol, or fuel combustion exhaust by dermal, respiratory inhalation, or oral ingestion routes, and commonly occur concurrently with exposure to other chemicals and stressors. Hydrocarbon fuels are complex mixtures of 150-260+ aliphatic and aromatic hydrocarbon compounds containing varying concentrations of potential neurotoxicants including benzene, n-hexane, toluene, xylenes, naphthalene, and certain n-C9-C12 fractions (n-propylbenzene, trimethylbenzene isomers). Due to their natural petroleum base, the chemical composition of different hydrocarbon fuels is not defined, and the fuels are classified according to broad performance criteria such as flash and boiling points, complicating toxicological comparisons. While hydrocarbon fuel exposures occur typically at concentrations below...

Effect of texture and slip mode on the anisotropy of plastic flow and flow softening during hot working of Ti-6Al-4V

Abstract: The effect of crystallographic texture and slip mode on the plastic flow of Ti-6Al-4V with either a colony- or globular-alpha microstructure was determined by conducting isothermal, constant-strainrate, hot-compression tests on specimens cut at various orientations (rolling direction (RD), transverse direction (TD), 45 deg, and normal) from hot-rolled plate. Testing was performed using a fixed strain rate (0.1 s−1) and various temperatures below the beta transus. The flow curves from all of the experiments exhibited a peak flow stress followed by a large and a small amount of flow softening for the colony and globular microstructures, respectively. Although the flow softening response did not depend noticeably on test direction for a given microstructure and test temperature, the peak flow stress and development of sample ovality did. This orientation dependence was interpreted using both lower-bound (isostress-type) and upper-bound (isostrain, Taylor/Bishop-Hill) models to deduce the operative slip systems in the alpha phase. These analyses suggested that prism 〈a〉 and basal 〈a〉 slip are considerably easier than pyramidal 〈c+a〉 or 〈a〉 slip at hot-working temperatures. A comparison of the flow curves for the colony and globular alpha microstructures suggested that slip transfer across alpha/beta interfaces and loss of Hall-Petch boundary strengthening can account for a substantial portion of the flow softening observed during hot working.

Development of Hydrocarbon-Fueled Scramjet Engines: The Hypersonic Technology (HyTech) Program

Abstract: The Hypersonic Technology (HyTech) program was initiated in 1995 to maintain a core competency in hypersonictechnologiesafterthecancellation of theNationalAerospacePlaneprogram.HyTech isfocusedon expanding the technology base for liquid-hydrocarbon-fueled scramjet propulsion systems and is complementary in many ways to similar hydrogen-fueled hypersonic programs, such as Hyper-X. The overall effort consists of government sponsored industry efforts and an in-house technology base program. The technical challenges of these efforts associated with successful scramjet operation are addressed, which include activity in inlet/isolator operation, combustor operation and stability, nozzle operation, material advancement, fuel system development and integration and operability. The program has positively demonstrated the technologies that are critical to successful scramjet operation. The current status of work in each of these areas is discussed, followed by a discussion of upcoming activities for the program.

Decentralized nonlinear output-feedback stabilization with disturbance attenuation

Abstract: As a continuation of our recent work (1999), this paper addresses the problem of decentralized robust output-feedback stabilization with disturbance attenuation for large-scale systems with strong nonlinear interconnections. We focuses on a constructive solution to this decentralized control problem without requiring common matching and growth conditions appearing in the past literature. The decentralized output-feedback laws proposed achieve internal global asymptotic stability in the sense of Lyapunov and external stability in the sense of Sontag (1995, 1998).

Lingual thyroid carcinoma: a case report and review of the literature.

Abstract: Ectopic thyroid tissue may reside anywhere along its embryologic path of descent. Most ectopias manifest as simple thyroglossal duct cysts in conjunction with a normally developed thyroid gland in its usual thyroid cervical bed. Lingual thyroid is a rare developmental abnormality characterized by the failure of the thyroid gland, or remnants, to descend from its embryologic site of origin at the foramen cecum to its usual pretracheal position. Carcinoma arising in a lingual thyroid is even more unusual with fewer than 30 cases reported in the literature. We report the second case of lingual papillary thyroid carcinoma and review the clinical features, natural history, diagnosis, and treatment of lingual thyroid carcinoma.

A review of the effects of uranium and depleted uranium exposure on reproduction and fetal development.

Abstract: Depleted uranium (DU) is used in armor-penetrating munitions, military vehicle armor, and aircraft, ship and missile counterweighting/ballasting, as well as in a number of other military and commercial applications. Recent combat applications of DU alloy [i.e., Persian Gulf War (PGW) and Kosovo peacekeeping objective] resulted in human acute exposure to DU dust, vapor or aerosol, as well as chronic exposure from tissue embedding of DU shrapnel fragments. DU alloy is 99.8% 238Uranium, and emits approximately 60% of the alpha, beta, and gamma radiation found in natural uranium (4.05×10-7 Ci/g DU alloy). DU is a heavy metal that is 160% more dense than lead and can remain within the body for many years and slowly solubilize. High levels of urinary uranium have been measured in PGW veterans 10 years after exposure to DU fragments and vapors. In rats, there is strong evidence of DU accumulation in tissues including testes, bone, kidneys, and brain. In vitro tests indicate that DU alloy may be both genotoxic an...

Tribological properties of adaptive nanocomposite coatings made of yttria stabilized zirconia and gold

Abstract: Composite coating architectures where hard nanocrystalline grains are embedded in an amorphous matrix provide considerable improvement in hardness, toughness, wear resistance, and environmental adaptation. Using this concept, nanocrystalline yttria stabilized zirconia (YSZ) was embedded in an amorphous YSZ/Au matrix to address problems with YSZ ceramics in sliding wear. The coatings were produced by a hybrid of laser ablation of YSZ and magnetron sputtering of Au. Coating composition and microstructure were investigated using a number of analytical techniques, and correlated with results of sliding friction tests at 25 and 500°C. In situ transmission electron microscope imaging of microstructure evolution during a temperature cycling from 25 to 500°C was performed to explain changes in tribological properties. In comparison to YSZ ceramic, YSZ/Au coatings were tougher, formed less wear debris, and reduced friction coefficients from 1.0 to 0.3–0.4 at 25°C and to 0.2 at heating to 500°C. Improvements in tribological properties were related to the microstructure adaptive changes at elevated temperatures and formation of lubricating Au transfer films.

Vibration-Dissociation Coupling Using Master Equations in Nonequilibrium Hypersonic Blunt-Body Flow

Abstract: Numerical simulations are presented of a steady-state hypersonic flow past a hemisphere cylinder. Two types of models, one a lumped Landau-Teller vibrational relaxation model (Landau, L., and Teller, E.) and the other a discrete state kinetic relaxation model (DSKR), were used to study effects of vibration-dissociation coupling on the flow physics. The widely used Park's dissociation model was used as baseline for coupling vibration and dissociation processes (Park, C.). For a Mach 8.6 flow, both relaxation models matched experimental data. At Mach 11.18, however, the underprediction of shock-standoff distance by both relaxation models using Park's model for dissociation coupling provided the motivation to implement a new master equation-based (DSKR) depletion model. The new model was used to study the effect of dissociation on population depletion in the vibrational states of the nitrogen molecule. The new model helps explain the restricted success of Park's dissociation model in certain temperature ranges of hypersonic flow past a blunt body. In the range of 5000-15,000 K, the new model yielded a substantial rate reduction relative to Park's equilibrium rate at lower temperatures and a consistent value at the high end

Effect of conductivity and dielectric constant on the modulation voltage for nonlinear optic polymer based opto-electronic devices

Abstract: Presented is the effect of using various cladding materials with different conductivities and dielectric constants on the applied voltage for optoelectronic (OE) devices based on nonlinear optical (NLO) polymers. Using a conductive polymer, we have demonstrated a 3 to 13 times increase in the effective electro-optic (EO) coefficient of electrode- poled NLO polymers, compared to using passive polymer claddings. We have achieved the lowest poling voltage to date for maximum EO coefficient, 300 V, for a two-layer waveguide structure consisting of a 2-?m- thick NLO polymer layer and a 2-?m-thick conductive cladding layer. The dielectric constants of both the NLO polymer core and passive polymer cladding materials used for conventional polymer-based integrated optic devices are typically very similar in magnitude. This suggests that only a small fraction of the applied modulation voltage is reaching the NLO polymer core layer, requiring 4 to 5 times higher modulation voltage than the desired V?. We have demonstrated a factor-of-2 decrease in the modulation voltage using the same conductive polymer, due to its possessing a much higher dielectric constant than the core material at the modulation frequency tested. The results show promise for shorter, lower-operating-voltage devices.

Clostridium difficile Small Bowel Enteritis Occurring after Total Colectomy

Abstract: Clostridium difficile infection is usually associated with antibiotic therapy and is almost always limited to the colonic mucosa. Small bowel enteritis is rare: only 9 cases have been previously cited in the literature. This report describes a case of C. difficile small bowel enteritis that occurred in a patient after total colectomy and reviews the 9 previously reported cases of C. difficile enteritis.