Publications

The purpose of this report is to provide an overview of Micro-System technology as it applies to inertial sensing. Transduction methods are reviewed with capacitance and piezoresistive being the most often used in COTS Micro-electro-mechanical system (MEMS) inertial sensors. Optical transduction is the most recent transduction method having significant impact on improving sensor resolution. A few other methods are motioned which are in a R&D status to hopefully allow MEMS inertial sensors to become viable as a navigation grade sensor. The accelerometer, gyroscope and gravity gradiometer are the type of inertial sensors which are reviewed in this report. Their method of operation and a sampling of COTS sensors and grade are reviewed as well.

We previously demonstrated that the supramolecular self-assembly of cyanines could be useful for developing fluorescent enzymatic assays. We took that concept a step further by synthesizing a covalent adduct of the tetrapeptide Asp-Glu-Val-Asp (DEVD) and a cyanine (DEVD-cyanine). The DEVD-cyanine due to its canonical sequence was recognized and hydrolyzed by the proteases, Caspase-3 and -7 in 96- or 384-microwell plate reactions. The catalytically liberated cyanine self-assembled upon scaffolds of carboxymethylamylose (CMA), carboxymethylcellulose (CMC), or a mixture of CMA and CMC resulting in a J aggregate exhibiting bright fluorescence at a 470 nm emission wavelength (optimum signal/background using excitation wavelengths of 415-440 nm). The fluorescence intensity increased with enzyme and substrate concentrations or reaction time and exhibited classical saturation profiles of a rectangular hyperbola. Saturation of the reaction was at 30 U/mL (1 μg/mL) Caspase-3 and 250 μM DEVD-cyanine. The reaction kinetics was linear between 1 and 20 min and saturated at 60 min. The affinity constant (Km) for DEVD-cyanine was ∼23 μM, similar to those of previously reported values for other DEVD substrates of Caspase-3. Maximal fluorescence emission was observed by using a mixture of CMA and CMC scaffolds at 65 and 35 μM, respectively. The reaction kinetics of Caspase-7 executed in a 384-well plate was similar to the reaction kinetics of Caspase-3 conducted in a 96-well plate. We believe that this is the first demonstration of a cyanine liberated from a covalent adduct due to protease action, leading to supramolecular self-assembly and the detection of protease activity. © 2009 American Chemical Society.

The outline of this presentation is: (1) Applications of Kovar Alloy in metal/ceramic brazing; (2) Diffusion bonding of precision-photoetched Kovar parts; (3) Sample composition and annealing conditions; (4) Intermediate temperature creep properties (350-650 C); (5) Power law creep correlations--with and without modulus correction; (6) Compressive stress-strain properties (23-900 C); (7) Effect of creep deformation on grain growth; and (8) Application of the power law creep correlation to the diffusion bonding application. The summary and conclusions are: Elevated temperature creep properties of Kovar from 750-900 C obey a power law creep equation with a stress exponent equal to 4.9, modulus compensated activation energy of 47.96 kcal/mole. Grain growth in Kovar creep samples tested at 750 and 800 C is quite sluggish. Significant grain growth occurs at 850 C and above, this is consistent with isothermal grain growth studies performed on Kovar alloy wires. Finite element analysis of the diffusion bonding of Kovar predict that stresses of 30 MPa and higher are needed for good bonding at 850 C, we believe that 'sintering' effects must be accounted for to allow FEA to be predictive of actual processing conditions. Additional creep tests are planned at 250-650 C.

A study proposed that metal-organic frameworks (MOF) can potentially offer the desired level of structural control, leading to the formation of a new class of radiation detection materials. It was found that the rigid structure of MOFs can create permanent nonporosity. It was demonstrated permanent nonporosity has the potential for gas storage,separations, catalysis, and sensing. It was demonstrated that this feature of MOFs can be beneficial in scintillation materials, enabling MOFs to serve as hosts for wavelength shifters, or elements designed to improve the detection cross-section. It was observed that MOFs, along with scintillation materials, present significant opportunity to perform crystal engineering, creating the potential for rational design of new scintillation materials. Spectroscopic measurements of these MOFs, using single crystals demonstrated that they respond to ionizing radiation by emitting light, creating a new class of scintillation materials.

A subscale experiment has been constructed using fins mounted on one wall of a transonic wind tunnel to investigate the influence of fin trailing vortices upon downstream control surfaces. Data were collected using a fin balance instrumenting the downstream fin to measure the aerodynamic forces of the interaction, combined with stereoscopic particle image velocimetry to determine vortex properties. The fin balance data show that the response of the downstream fin essentially is shifted from the baseline single-fin data dependent upon the angle of attack of the upstream fin. Freestream Mach number and the spacing between fins have secondary effects. The velocimetry shows the increase in vortex strength with upstream fin angle of attack, but no variation with Mach number can be discerned in the normalized velocity data. Correlations between the force data and the velocimetry indicate that the interaction is fundamentally a result of an angle of attack superposed upon the downstream fin by the vortex shed from the upstream fin tip. The Mach number influence arises from differing vortex lift on the leading edge of the downstream fin even when the impinging vortex is Mach invariant. Copyright Clearance Center, Inc.

Stratified flames are common in practical combustion systems. However, relatively little is known about the detailed structure of turbulent stratified flames. Multiscalar laser diagnostics, consisting of simultaneous line imaging of Raman scattering, Rayleigh scattering, and two-photon laser-induced fluorescence (LIF) of CO, combined with crossed planar imaging of OH LIF, are applied to turbulent premixed and stratified CH4/air flames stabilized above a slot burner. A new detection system for the line-imaged measurements allows a pixel resolution of 0.104 mm in the results for temperature, major species concentrations, and the local equivalence ratio. Results from premixed flames demonstrate that this diagnostic system is capable of resolving the internal structure of stratified flames at atmospheric pressure. In particular, the local equivalence ratio and the gradient in temperature are measured with good accuracy on a single-shot basis. Results from stratified flames reveal a broad range of instantaneous conditions, and show that significant gradients in equivalence ratio can occur within the instantaneous thermal thickness of turbulent stratified flames. © 2009 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

The kinetics of the CH3 + HO2 bimolecular reaction and the thermal decomposition of CH3OOH are studied theoretically. Direct variable reaction coordinate transition state theory (VRC-TST), coupled with high level multireference electronic structure calculations, is used to compute capture rates for the CH3 + HO2 reaction and to characterize the transition state of the barrierless CH3O + OH product channel. The CH2O + H2O product channel and the CH3 + HO2 → CH4 + O2 reaction are treated using variational transition state theory and the harmonic oscillator and rigid rotor approximations. Pressure dependence and product branching in the bimolecular and decomposition reactions are modeled using master equation simulations. The predicted rate coefficients for the major products channels of the bimolecular reaction, CH3O + OH and CH 4 + O2, are found to be in excellent agreement with values obtained in two recent modeling studies. The present calculations are also used to obtain rate coefficients for the CH3O + OH association/ decomposition reaction. © 2009 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

The combustion chemistry of morpholine (l-oxa-4-aza-cyclohexane) was investigated under laminar, premixed low-pressure conditions. Morpholine, as a heterocyclic secondary amine with numerous industrial applications, was studied as a model fuel which simultaneously contains oxygen and nitrogen heteroatoms. Stable and radical intermediates and products of the combustion process in a slightly fuel-rich φ = 1.3 (C/O = 0.41) flat premixed morpholine-oxygen- argon flame at 40 mbar (4kPa) were identified. A detailed fuel destruction scheme is proposed based on combined measurements using two different in situ molecular beam mass spectrometry (MBMS) techniques. The results are discussed with special attention to hydrocarbon, oxygenated and N-containing compounds important in pollutant emission. © 2009 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

We present a dual-pump coherent anti-Stokes Raman scattering (CARS) instrument, which has been constructed for the probing of temperature fluctuations in turbulent pool fires of meter-scale. The measurements were performed at the Fire Laboratory for Accreditation of Models and Experiments (FLAME) facility at Sandia National Laboratories, which provides a canonical fire plume in quiescent wind conditions, with well-characterized boundary conditions and access for modern laser-diagnostic probes. The details of the dual-pump CARS experimental facility for the fire-science application are presented, and single-laser-shot CARS spectra containing information from in-fire N2, O2, H2, and CO2 are provided. Single-shot temperatures are obtained from spectral fitting of the Raman Q-branch signature of N2, from which histograms that estimate the pdf of the enthalpy-averaged temperature fluctuations at the center of the fire plume are presented. Results from two different sooting fire experiments reveal excellent test-to-test repeatability of the fire plume provided by FLAME, as well as the CARS-measured temperatures. The accuracy and precision of the CARS temperatures is assessed from measurements in furnace-heated air, where the temperature can be accurately determined by a thermocouple. At temperatures in excess of 500 K, the furnace results show that the CARS measurements are accurate to within 2-3% and precise to within ±3-5% of the measured absolute temperature. © 2009 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

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An automated procedure has been previously developed to generate simplified skeletal reaction mechanisms for the combustion of n-heptane/air mixtures at equivalence ratios between 0.5 and 2.0 and different pressures. The algorithm is based on a Computational Singular Perturbation (CSP)-generated database of importance indices computed from homogeneous n-heptane/air ignition solutions. In this paper, we examine the accuracy of these simplified mechanisms when they are used for modeling laminar n-heptane/air premixed flames. The objective is to evaluate the accuracy of the simplified models when transport processes lead to local mixture compositions that are not necessarily part of the comprehensive homogeneous ignition databases. The detailed mechanism was developed by Curran et al. and involves 560 species and 2538 reactions. The smallest skeletal mechanism considered consists of 66 species and 326 reactions. We show that these skeletal mechanisms yield good agreement with the detailed model for premixed n-heptane flames, over a wide range of equivalence ratios and pressures, for global flame properties. They also exhibit good accuracy in predicting certain elements of internal flame structure, especially the profiles of temperature and major chemical species. On the other hand, we find larger errors in the concentrations of many minor/radical species, particularly in the region where low-temperature chemistry plays a significant role. We also observe that the low-temperature chemistry of n-heptane can play an important role at very lean or very rich mixtures, reaching these limits first at high pressure. This has implications to numerical simulations of non-premixed flames where these lean and rich regions occur naturally. © 2009 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

A subscale experiment has been constructed using fins mounted on one wall of a transonic wind tunnel to investigate the influence of fin trailing vortices upon downstream control surfaces. Data were collected using a fin balance instrumenting the downstream fin to measure the aerodynamic forces of the interaction, combined with stereoscopic particle image velocimetry to determine vortex properties. The fin balance data show that the response of the downstream fin essentially is shifted from the baseline single-fin data dependent upon the angle of attack of the upstream fin. Freestream Mach number and the spacing between fins have secondary effects. The velocimetry shows the increase in vortex strength with upstream fin angle of attack, but no variation with Mach number can be discerned in the normalized velocity data. Correlations between the force data and the velocimetry indicate that the interaction is fundamentally a result of an angle of attack superposed upon the downstream fin by the vortex shed from the upstream fin tip. The Mach number influence arises from differing vortex lift on the leading edge of the downstream fin even when the impinging vortex is Mach invariant. Copyright Clearance Center, Inc.

Although smolder combustion has been extensively studied both computationally and experimentally, relatively few theoretical studies have examined the two-dimensional structure of the smolder wave. In this paper, two-dimensional smolder in polyurethane foam is modeled with a two-dimensional numerical formulation that includes a seven-step kinetic model of the polyurethane smolder reaction mechanism. The two-dimensional model formulation includes the effects of heat, mass, species, and momentum transfer of the porous solid and gas phase. The seven-step decomposition reaction mechanism, which includes a secondary char oxidation and an additional char pyrolysis step, was developed using genetic algorithm optimization. The mechanism is capable of modeling both forward and opposed smolder. The model was used to study the two-dimensionality of a forward propagating smolder wave. The model results show a two-dimensional structure in the temperature, species, and reaction profiles that agrees qualitatively with experimental observations. Oxygen is consumed at the reaction front, as expected, which leads to different reaction pathways governing the final products (i.e. thermal char and oxidative char). It was found that the model response is sensitive to boundary conditions, thermal properties, and heats of reaction for the char oxidation reaction. The incorporation of the secondary oxidation reaction step in the model paves the way to further analysis of the transition to flaming process. © 2009 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

An experimental study was performed to determine the fraction of the heat flux that is due to radiation (sometimes referred to as radiation partitioning of the total heat flux measurement) to a calorimeter engulfed in a large methanol pool fire to improve understanding and develop high-quality data for the validation of fire models. Diagnostics employed include Coherent Anti-Stokes Raman Spectroscopy (CARS), Particle Image Velocimetry (PIV), total and radiative thermometry, and thermocouples. Data are presented not only for the physics measurements but also for all initial and boundary conditions required as necessary inputs to computational models. The large physical scale, the experimental design (enhanced convection relative to radiation heat transfer), the use of independent measurement techniques, and the attention to data quality, provide a unique dataset that emphasizes the convective component to support numerical fire model validation for convective and radiative heat transfer in fires. © 2009 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

This paper develops deformational response power descriptions of multiple degree-of-freedom systems due to stationary random vibration excitation. Two new concepts are developed. The deformational response power density (DRPD) can be computed when a structure's natural frequencies and modal masses are available. The DRPD shows the spectral content of the deformational power delivered to a specific structure by the stationary, random excitation. This function can be found through a weighted windowing of the power spectrum of the input acceleration excitation. Deformational response input power spectra (DRIPS), similar to the input energy spectrum and shock response spectrum, give the power delivered to single-degree-of-freedom systems as a function of natural frequency. It is shown that the DRIPS is simply a smoothed version of the power spectrum of the input acceleration excitation. The DRIPS gives rise to a useful power-based data smoothing operation. © 2009 - IOS Press.

Advanced compression-ignition (CI) engines can deliver both high efficiencies and very low NOx and particulate (PM) emissions. Efficiencies are comparable to conventional diesel engines, but unlike conventional diesel engines, the charge is highly dilute and premixed (or partially premixed) to achieve low emissions. Dilution is accomplished by operating either lean or with large amounts of EGR. The development of these advanced CI engines has evolved mainly along two lines. First, for fuels other than diesel, a combustion process commonly known as homogeneous charge compression-ignition (HCCI) is generally used, in which the charge is premixed before being compression ignited. Although termed "homogeneous," there are always some thermal or mixture inhomogeneities in real HCCI engines, and it is sometimes desirable to introduce additional stratification. Second, for diesel fuel (which autoignites easily but has low volatility) an alternative low-temperature combustion (LTC) approach is used, in which the autoignition is closely coupled to the fuel-injection event to provide control over ignition timing. To obtain dilute LTC, this approach relies on high levels of EGR, and injection timing is typically shifted 10-15° CA earlier or later than for conventional diesel combustion so temperatures are lower, which delays ignition and provides more time for premixing. Although these advanced CI combustion modes have important advantages, there are difficulties to implementing them in practical engines. In this article, the principles of HCCI and diesel LTC engines are reviewed along with the results of research on the in-cylinder processes. This research has resulted in substantial progress toward overcoming the main challenges facing these engines, including: improving low-load combustion efficiency, increasing the high-load limit, understanding fuel effects, and maintaining low NOx and PM emissions over the operating range. © 2009 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

The development of a manufactured solution for enclosure radiation in an infinitely long circular cylinder with a nonparticipating medium is presented. This solution is then used to verify the correct implementation of the commonly used discrete enclosure equations. The circular cross section is approximated by a faceted geometry; the numbers of facets used are 4, 8, 16, 32, 64, and 128. The crossed-string method, which is exact in this application, is used to compute the view factors. Computational results using six levels of grid refinement suggest that the error norm between the integral equation solution and the discrete equation solution behaves as h2 where h is a characteristic mesh size.

Phononic crystals are the acoustic wave analogue of photonic crystals. Here a periodic array of scattering inclusions located in a homogeneous host material forbids certain ranges of acoustic frequencies from existence within the crystal, thus creating what are known as acoustic bandgaps. The majority of previously reported phononic crystal devices have been constructed by hand, assembling scattering inclusions in a viscoelastic medium, predominantly air, water or epoxy, resulting in large structures limited to frequencies below 1 MHz. Recently, phononic crystals and devices have been scaled to VHF (30-300 MHz) frequencies and beyond by utilizing microfabrication and micromachining technologies. This paper reviews recent developments in the area of micro-phononic crystals including design techniques, material considerations, microfabrication processes, characterization methods and reported device structures. Micro-phononic crystal devices realized in low-loss solid materials are emphasized along with their potential application in radio frequency communications and acoustic imaging for medical ultrasound and nondestructive testing. The reported advances in batch micro-phononic crystal fabrication and simplified testing promise not only the deployment of phononic crystals in a number of commercial applications but also greater experimentation on a wide variety of phononic crystal structures. © 2009 IOP Publishing Ltd.

This paper presents a derivation of an expression to estimate the accommodation coefficient for gas collisions with a graphite surface, which is meant for use in models of laser-induced incandescence (LII) of soot. Energy transfer between gas molecules and solid surfaces has been studied extensively, and a considerable amount is known about the physical mechanisms important in thermal accommodation. Values of accommodation coefficients currently used in LII models are temperature independent and are based on a small subset of information available in the literature. The expression derived in this study is based on published data from state-to-state gas-surface scattering experiments. The present study compiles data on the temperature dependence of translational, rotational, and vibrational energy transfer for diatomic molecules (predominantly NO) colliding with graphite surfaces. The data were used to infer partial accommodation coefficients for translational, rotational, and vibrational degrees of freedom, which were consolidated to derive an overall accommodation coefficient that accounts for accommodation of all degrees of freedom of the scattered gas distributions. This accommodation coefficient can be used to calculate conductive cooling rates following laser heating of soot particles.

The combination of Proximity-field nanoPatterning (PnP) and graded temperature ALD has enabled the synthesis of robust three dimensional nanostructures. The PnP process uses a simple elastomeric optical phase mask to generate a complex three dimensional interference pattern in photopolymer 1. Once the photopolymer structure has been obtained, it is subsequently used as a template for graded temperature ALD. The graded temperature ALD chemistry is used to coat and lock-in the designed nanostructure without melting the template. This process generates a thermally robust nanostructure for further, higher temperature, ALD surface treatments. The ALD chemistry is performed at various (increasing) temperatures to secure the nanostructure and to reduce the macroscopic stress of the structure as higher temperature depositions are performed. Three methods for nanostructure characterization have been useful in interrogating these structures: quartz crystal microbalance (QCM), optical interference, and focused ion beam scanning electron microscopy (FIB-SEM). This paper will cover the fabrication process for generating PnP nanostructures. Details of the graded temperature ALD chemical process for AI2O3 will be covered. Also, structural characterizations using SEM and optical interference will be used to quantify the degree of deposition and the thermal stability of these interesting structures. © The Electrochemical Society.

During this study, flow visualization through the use of imaging provided visual data of the events that occurred as the flame oscillated. Imaging was performed in two different ways: 1) the first method was phase-locked imaging to capture a detailed history by simply advancing the phase angle during each image capture, 2) the second method involved high-speed imaging to gather visual image data of a natural or forced oscillating flame. For visualization, two items were considered. The first one was the shape of the flame envelope as it evolved during one oscillation cycle. From the data gathered, it was confirmed that the flame stretched in the vertical direction before quenching in the region near its center. The second consideration was imaging of the oxidizer (air) in the region immediately outside the flame. This was done by imaging the laser light reflected from particles seeded into the flow, which revealed formation of vortical structures in those regions where quenching had occurred. It was noted that quenching took place primarily by the entrainment of fresh non-reacting air into the flame. The quenching process was in turn responsible for the oscillatory behavior. © 2009 The Visualization Society of Japan.

Combined experimental and numerical studies of the transient response of ignition to strained flows require a well-characterized ignition trigger. Laser deposition of a small radical pool provides a reliable method for initiating ignition of mixtures that are near the ignition limit. Two-dimensional direct numerical simulations are used to quantify the sensitivity of ignition kernel formation and subsequent edge-flame propagation to the oxidizer temperature and the initial width and amplitude of O-atom deposition used to trigger ignition in an axisymmetric counterflow of heated air versus ambient hydrogen/nitrogen. The ignition delay and super-equilibrium OH concentration in the nascent ignition kernel are highly sensitive to variations in these initial conditions. The ignition delay decreases as the amplitude of the initial O-atom deposition increases. The spatial distribution and the magnitude of the OH overshoot are governed by multi-dimensional effects. The degree of OH overshoot near the burner centerline increases as the diameter of the initial O-atom deposition region decreases. This result is attributed to preferential diffusion of hydrogen in the highly curved leading portion of the edge flame that is established following thermal runaway. The edge-flame speed and OH overshoot at the leading edge of the edge flame are relatively insensitive to variations in the initial conditions of the ignition. The steady edge-flame speed is approximately twice the corresponding laminar flame speed. The rate at which the edge flame approaches its steady state is insensitive to the initial conditions and depends solely on the diffusion time scale at the edge flame. The edge flame is curved toward the heated oxidizer stream as a result of differences in the chemical kinetics between the leading edge and the trailing diffusion flame. The structure of the highly diluted diffusion flame considered in this study corresponds to Liñán's 'premixed flame regime' in which only the oxidizer leaks through the reaction zone such that the flame is located at fuel lean rather than stoichiometric mixture fraction conditions.

Under extreme loading conditions most often the extent of material and structural fracture is pervasive in the sense that a multitude of cracks are nucleating, propagating in arbitrary directions, coalescing, and branching. Pervasive fracture is a highly nonlinear process involving complex material constitutive behavior, material softening, localization, surface generation, and ubiquitous contact. A pure Lagrangian computational method based on randomly close packed Voronoi tessellations is proposed as a rational and robust approach for simulating the pervasive fracture of materials and structures. Each Voronoi cell is formulated as a finite element using the Reproducing Kernel Method. Fracture surfaces are allowed to nucleate only at the intercell faces, and cohesive tractions are dynamically inserted. The randomly seeded Voronoi cells provide a regularized random network for representing fracture surfaces. Example problems are used to demonstrate the proposed numerical method. The primary numerical challenge for this class of problems is the demonstration of model objectivity and, in particular, the identification and demonstration of a measure of convergence for engineering quantities of interest. © 2009 Springer-Verlag.

The Design for Tractable Analysis (DTA) framework was developed to address the analysis of complex systems and so-called “wicked problems.” DTA is distinctive because it treats analytic processes as key artifacts that can be created and improved through formal design processes. Systems (or enterprises) are analyzed as a whole, in conjunction with decomposing them into constituent elements for domain-specific analyses that are informed by the whole. After using the Systems Modeling Language (SysML) to frame the problem in the context of stakeholder needs, DTA harnesses the Design Structure Matrix (DSM) to structure the analysis of the system and address questions about the emergent properties of the system. The novel use of DSM to “design the analysis” makes DTA particularly suitable for addressing the interdependent nature of complex systems. The use of DTA is demonstrated by a case study of sensor grid placement decisions to secure assets at a fixed site. © 2009, IGI Global. All rights reserved.

Diesel injection parameters effect on liquid-phase diesel spray penetration after the end-of-injection (EOI) is investigated in a constant-volume chamber over a range of ambient and injector conditions typical of a diesel engine. Our past work showed that the maximum liquid penetration length of a diesel spray may recede towards the injector after EOI at some conditions. Analysis employing a transient jet entrainment model showed that increased fuel-ambient mixing occurs during the fuel-injection-rate ramp-down as increased ambient-entrainment rates progress downstream (i.e. the entrainment wave), permitting complete fuel vaporization at distances closer to the injector than the quasi-steady liquid length. To clarify the liquid-length recession process, in this study we report Mie-scatter imaging results near EOI over a range of injection pressure, nozzle size, fuel type, and rate-of-injection shape. We then use a transient jet entrainment model for detailed analysis. Results show that an increased injection pressure correlates well with increasing liquid length recession due to an increased entrainment wave speed. Likewise, an increased nozzle size, with higher jet momentum and faster entrainment wave, enhances the liquid length recession. A low-density, high-volatility fuel does not decrease the strength of the entrainment wave; however, it decreases the steady liquid length causing the entrainment wave to reach the liquid spray tip earlier, which ultimately results in faster liquid length recession. A slow ramp down in injection rate causes a weaker entrainment wave so that the liquid length recession occurs even prior to injector close.

The mass-sensitive smart preconcentrator (SPC) consists of a Lorentz-Force-actuated MEMS resonator with an integral heater and surface coating for the collection of chemical analytes. Control circuitry is used to drive the SPC to resonance and measure its oscillation frequency. The frequency shift produced by adsorption of analyte on the SPC surface is inversely proportional to the mass of analyte collected. Thus, the SPC can measure when it has collected sufficient analyte for a downstream detection system. The limit of detection (LOD) of the SPC is less than 50 ppb for DMMP (dimethyl-methyl- phosphonate). At 1 ppm, less than 1 second collection of DMMP is sufficient to trigger analysis. An analytical model of operation of the SPC is used to predict the motion of the paddle and the shear modulus of silicon. © The Electrochemical Society.

The low-frequency meander of a trailing vortex shed from a tapered fin installed on a wind tunnel wall has been studied using stereoscopic particle image velocimetry in the near-wake at Mach 0.8. Distributions of the instantaneous vortex position reveal that the meander amplitude increases with downstream distance and decreases with vortex strength, indicating meander is induced external to the vortex. Trends with downstream distance suggest meander begins on the fin surface, prior to vortex shedding. Mean vortex properties are unaltered when considered in the meandering reference frame, apparently because turbulent fluctuations in the vortex shape and strength dominate positional variations. Conversely, a large peak of artificial turbulent kinetic energy is found centered in the vortex core, which almost entirely disappears when corrected for meander, though some turbulence remains near the core radius. Turbulence originating at the wind tunnel wall was shown to contribute to vortex meander by energizing the incoming boundary layer using low-profile vortex generators and observing a substantial increase in the meander amplitude while greater turbulent kinetic energy penetrates the vortex core. An explanatory mechanism has been hypothesized, in which the vortex initially forms at the apex of the swept leading edge of the fin where it is exposed to turbulent fluctuations within the wind tunnel wall boundary layer, introducing an instability into the incipient vortex core.

Effects of gas-phase collisions on active optical sensing and use of picosecond laser spectroscopy for their characterization are reviewed. Additionally, novel time-resolved approaches to reduce collisional sensitivity and to exploit species-dependent collision rates are discussed. © 2009 Optical Society of America.

The catalytic effect of nitric oxide (NO) on the dynamics of extinction and re-ignition of a vortex-perturbed non-premixed hydrogen-air flame is studied in a counterflow burner. A diffusion flame is established with counterflowing streams of nitrogen-diluted hydrogen at ambient temperature and air heated to a range of temperatures that brackets the auto-ignition temperature. Localized extinction is induced by impulsively driving a fuel-side toroidal vortex into the steady flame, and the recovery of the extinguished region is monitored by planar laser-induced fluorescence (PLIF) of the hydroxyl radical (OH). The dynamics of flame recovery depend on the air temperature and fuel concentration, and four different recovery modes are identified. These modes involve combinations of edge-flame propagation and the expansion of an auto-ignition kernel that forms within the extinguished region. The addition of a small amount of NO significantly alters the re-ignition process by shifting the balance between chain-termination and chain-propagation reactions to enhance auto-ignition. The ignition enhancement by this catalytic effect causes a shift in the conditions that govern the recovery modes. In addition, the effects of NO concentration and vortex strength on the flame recovery are examined. Direct numerical simulations of the flame-vortex interaction with and without NO doping show how the small amount of OH produced by NO-catalyzed reactions has a significant impact on the development of an auto-ignition kernel. This joint experimental and numerical study provides detailed insight into the interaction between transient flows and ignition processes.

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The authors establish a fundamental relationship between the phase and amplitude responses of an optomechanically variable photonic circuit and the forces and potentials produced by light. These results are illustrated through resonant and nonresonant multi-port systems.

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Using low-energy electron microscopy, we measure the diffusion of Pd into bulk Cu at the Cu(100) surface. Interdiffusion is tracked by measuring the dissolution of the Cu(100)-c(2 x 2)-Pd surface alloy during annealing (T > 240 C). The activation barrier for Pd diffusion from the surface alloy into the bulk is determined to be (1.8 {+-} 0.6) eV. During annealing, we observe the growth of a new layer of Cu near step edges. Under this new Cu layer, dilute Pd remaining near the surface develops a layered structure similar to the Cu{sub 3}Pd L 1{sub 2} bulk alloy phase.

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Research into the use of multiframe superresolution has led to the development of algorithms for providing images with enhanced resolution using several lower resolution copies. An integral component of these algorithms is the determination of the registration of each of the low resolution images to a reference image. Without this information, no resolution enhancement can be attained. We have endeavored to find a suitable method for registering severely undersampled images by comparing several approaches. To test the algorithms, an ideal image is input to a simulated image formation program, creating several undersampled images with known geometric transformations. The registration algorithms are then applied to the set of low resolution images and the estimated registration parameters compared to the actual values. This investigation is limited to monochromatic images (extension to color images is not difficult) and only considers global geometric transformations. Each registration approach will be reviewed and evaluated with respect to the accuracy of the estimated registration parameters as well as the computational complexity required. In addition, the effects of image content, specifically spatial frequency content, as well as the immunity of the registration algorithms to noise will be discussed.

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Pb-based ferroelectrics are useful because of their large dielectric constants, high polarization values, and strong piezoelectric coefficients, but typically require sintering temperatures >1200 C, which leads to loss of the volatile Pb cation and necessitates the use of Pt electrodes for cofired parts. Reduced sintering temperatures can minimize lead loss and enable the use of cheaper electrodes, but must not sacrifice electrical performance. A systematic study of dopants to lower the sintering temperature of PNSZT (Pb0.992 (Zr0.815 Ti0.05 Sn0.135)0.9845 Nb0.155 O3) led to densities greater than 98.5% of theoretical at temperatures as low as 1100 C with as little as 0.2 wt% of a Pb glass additive or as high as 98% at 900 C with Cu2O additions with equivalent electrical properties to undoped materials.

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A standard and widespread approach to part-of-speech tagging is based on Hidden Markov Models (HMMs). An alternative approach, pioneered by Schütze (1993), induces parts of speech from scratch using singular value decomposition (SVD). We introduce DEDICOM as an alternative to SVD for part-of-speech induction. DEDICOM retains the advantages of SVD in that it is completely unsupervised: no prior knowledge is required to induce either the tagset or the associations of types with tags. However, unlike SVD, it is also fully compatible with the HMM framework, in that it can be used to estimate emission- and transition-probability matrices which can then be used as the input for an HMM. We apply the DEDICOM method to the CONLL corpus (CONLL 2000) and compare the output of DEDICOM to the part-of-speech tags given in the corpus, and find that the correlation (almost 0.5) is quite high. Using DEDICOM, we also estimate part-of-speech ambiguity for each type, and find that these estimates correlate highly with part-of-speech ambiguity as measured in the original corpus (around 0.88). Finally, we show how the output of DEDICOM can be evaluated and compared against the more familiar output of supervised HMM-based tagging.

Dispersion and attenuation relations are derived for both the continuous and discrete velocity-memory-stress systems governing 3D anelastic wave propagation in a standard linear solid. Phase speed and attenuation factor curves extracted from these relations enable optimal selection of spatial and temporal gridding intervals to achieve finite-difference algorithm efficiency, while simultaneously minimizing numerical inaccuracy.

Cationic polymer membranes that conduct free anions comprise an enabling research area for alkaline membrane fuel cells and other solid-state electrochemical devices that operate at high pH. The synthesis of anion exchange membranes based on a poly(phenylene) backbone prepared by a Diels-Alder reaction is demonstrated as a potential material for alkaline fuel cells. The poly(phenylene)s have benzylic methyl groups that are converted to bromomethyl groups by a radical reaction. Cationic polymers result from conversion of the bromomethyl groups to ionic moieties by quaternization with trimethylamine in the solid state. The conversion to benzyltrimethyl ammonium groups is incomplete as evidenced by the differences between the IEC values measured by titration and the theoretical IECs based on 1H NMR measurements. The anion exchange membranes formed from these polymers have hydroxide ion conductivities as high as 50 mS/cm in liquid water and they are stable under highly basic conditions at elevated temperatures. ©The Electrochemical Society.