Two-color resonant four-wave-mixing spectroscopy (TC-RFWM) is used to investigate ground-state energy transfer of hydroxyl radical in atmospheric-pressure flames. Two amplified distributed-feedback dye lasers produce 50-ps, nearly transform-limited, infrared (IR) and ultraviolet pulses. The infrared pump laser is tuned to individual rovibrational transitions of OH X {sup 2}{pi}{sub 3/2} (v{prime}=1, N{prime}) {l_arrow} X {sup 2}{pi}{sub 3/2} (v{double_prime}=0, N{double_prime}), and the ultraviolet pulse probes either the directly pumped or collisionally populated intermediate levels via A{sup 2}{Sigma}{sup +} (v*=1, N*) {l_arrow} X{sup 2}{pi}{sub 3/2}(v{prime}=1, N{prime}). By time-delaying the probe pulse with respect to the pump pulse, and appropriately constraining the polarizations of each of the four fields taking part in the wave-mixing process, we are able to independently and unambiguously measure the moments of the rotational angular momentum distribution in single rotational levels of the ground state. We present measurements of population, alignment, and orientation decay in X {sup 2}{pi}{sub 3/2} for several flame conditions. These experiments provide data necessary for the development of accurate models for diagnostic techniques using saturating laser pulses.
An alternative theory of solid mechanics, known as the peridynamic theory, formulates problems in terms of integral equations rather than partial differential equations. This theory assumes that particles in a continuum interact with each other across a finite distance, as in molecular dynamics. Damage is incorporated in the theory at the level of these two-particle interactions, so localization and fracture occur as a natural outgrowth of the equation of motion and constitutive models. A numerical method for solving dynamic problems within the peridynamic theory is described. Accuracy and numerical stability are discussed. Examples illustrate the properties of the method for modeling brittle dynamic crack growth.
Three methods that were used to measure the chemical changes associated with oxidative degradation of polymeric materials are presented. The first method is based on the nuclear activation of {sup 18}O in an elastomer that was thermally aged in an {sup 18}O{sub 2} atmosphere. Second, the alcohol groups in a thermally aged elastomer were derivatized with trifluoroacetic anhydride and their concentration measured via {sup 19}F NMR spectroscopy. Finally, a respirometer was used to directly measure the oxidative rates of a polyurethane foam as a function of aging temperature. The measurement of the oxidation rates enabled acceleration factors for oxidative degradation of these materials to be calculated.
An environmentally friendly method and materials study for desalinating inland brackish waters (i.e., coal bed methane produced waters) using a set of ion-exchange materials is presented. This desalination process effectively removes anions and cations in separate steps with minimal caustic waste generation. The anion-exchange material, hydrotalcite (HTC), exhibits an ion-exchange capacity (IEC) of {approx} 3 mequiv g{sup -1}. The cation-exchange material, an amorphous aluminosilicate permutite-like material, (Na{sub x+2y}Al{sub x}Si{sub 1-x}O{sub 2+y}), has an IEC of {approx}2.5 mequiv g{sup -1}. These ion-exchange materials were studied and optimized because of their specific ion-exchange capacity for the ions of interest and their ability to function in the temperature and pH regions necessary for cost and energy effectiveness. Room temperature, minimum pressure column studies (once-pass through) on simulant brackish water (total dissolved solids (TDS) = 2222 ppm) resulted in water containing TDS = 25 ppm. A second once-pass through column study on actual produced water (TDS = {approx}11,000) with a high carbonate concentration used an additional lime softening step and resulted in a decreased TDS of 600 ppm.
The Arsenic Water Technology Partnership program is a multi-year program funded by a congressional appropriation through the Department of Energy. The program is designed to move technologies from benchscale tests to field demonstrations. It will enable water utilities, particularly those serving small, rural communities and Indian tribes, to implement the most cost-effective solutions to their arsenic treatment needs. As part of the Arsenic Water Technology Partnership program, Sandia National Laboratories is carrying out field demonstration testing of innovative technologies that have the potential to substantially reduce the costs associated with arsenic removal from drinking water. The scope for this work includes: (1) Selection of sites and identification of technologies for pilot demonstrations; (2) Laboratory studies to develop rapid small-scale test methods; and (3) Pilot-scale studies at community sites involving side-by-side tests of innovative technologies. The goal of site selection is to identify sites that allow examination of treatment processes and systems under conditions that are relevant to different geochemical settings throughout the country. A number of candidate sites have been identified through reviews of groundwater quality databases, conference proceedings and discussions with state and local officials. These include sites in New Mexico, Arizona, Colorado, Oklahoma, Michigan, and California. Candidate technologies for the pilot tests are being reviewed through vendor forums, proof-of-principle benchscale studies managed by the American Water Works Association Research Foundation (AwwaRF) and the WERC design contest. The review considers as many potential technologies as possible and screens out unsuitable ones by considering data from past performance testing, expected costs, complexity of operation and maturity of the technology. The pilot test configurations will depend on the site-specific conditions such as access, power availability, waste disposal options and availability of permanent structures to house the test. Conducting pilot tests for media comparison at all sites in need of arsenic treatment would be extremely time consuming and costly. Laboratory studies are being conducted using rapid small-scale column tests (RSSCTs) to predict the performance of pilot-scale adsorption columns. RSSCTs are a rapid and inexpensive method of investigating innovative technologies while varying water quality and/or system design. RSSCTs are scaled down columns packed with smaller diameter adsorption media that receive higher hydraulic loading rates to significantly reduce the duration of experiments. Results for RSSCTs can be obtained in a matter of days to a few weeks, whereas pilot tests can take a number of months to over a year. In the pilot tests, the innovative technologies will be evaluated in terms of adsorptive capacity for arsenic; robustness of performance with respect to water quality parameters including pH, TDS, foulants such as Fe, Mn, silica, and organics, and other metals and radionuclides; and potentially deleterious effects on the water system such as pipe corrosion from low pH levels, fluoride removal, and generation of disinfection by-products. The new arsenic MCL will result in modification of many rural water systems that otherwise would not require treatment. Simultaneous improvement of water quality in systems that will require treatment for other contaminants such as uranium, radon and radium would be an added benefit of this program.
The use of rotational echo adiabatic passage double resonance (REAPDOR) solid-state nuclear magnetic resonance (NMR) to determine the site location of an adsorbed polar molecule in a zeolite cage is presented. Nitrogen-15 labeled ammonia is used as a probe molecule to characterize the initial adsorption site in 3A zeolite molecular sieves. The relative position of the ammonia adsorption site in the cage is determined by measuring the internuclear distance between the N on ammonia and both a Na cation site and an Al framework environment using {sup 15}N/{sup 23}Na and {sup 15}N/{sup 27}Al REAPDOR NMR experiments, respectively. The measured internuclear distances are similar to a specific ammonia adsorption site for the zeolite 4A ammonia sorption complex located using X-ray diffraction. Additional details regarding the ammonia hydrogen-bonding environment can be extracted from {sup 1}H/{sup 23}Na and {sup 1}H/{sup 27}Al REAPDOR NMR measurements.
Sandia National Laboratories has previously tested a capability to impose a 7.5 g-rms (30 g peak) radial vibration load up to 2 kHz on a 25 lb object with superimposed 50 g acceleration at its centrifuge facility. This was accomplished by attaching a 3,000 lb Unholtz-Dickie mechanical shaker at the end of the centrifuge arm to create a 'Vibrafuge'. However, the combination of non-radial vibration directions, and linear accelerations higher than 50g's are currently not possible because of the load capabilities of the shaker and the stresses on the internal shaker components due to the combined centrifuge acceleration. Therefore, a new technique using amplified piezo-electric actuators has been developed to surpass the limitations of the mechanical shaker system. They are lightweight, modular and would overcome several limitations presented by the current shaker. They are 'scalable', that is, adding more piezo-electric units in parallel or in series can support larger-weight test articles or displacement/frequency regimes. In addition, the units could be mounted on the centrifuge arm in various configurations to provide a variety of input directions. The design along with test results will be presented to demonstrate the capabilities and limitations of the new piezo-electric Vibrafuge.
The influence of thermal stratification on auto-ignition at constant volume and high pressure is studied by Direct Numerical Simulation (DNS) with complex H{sub 2}/air chemistry with a view to providing better understanding of combustion processes in homogeneous charge compression ignition engines. In particular the dependence of overall ignition progress on initial mixture conditions is determined. The propagation speed of ignition fronts that emanate from 'hot spots' given by a temperature spectrum is monitored by using the displacement velocity of a scalar that tracks the location of maximum heat release. The evolution of the front velocity is compared for different initial temperature distributions and the role of scalar dissipation of heat and mass is identified. It is observed that both deagrative as well as spontaneous ignition front propagation occur depending upon the local temperature gradient. It is found that the ratio of the instantaneous front speed to the deflagrative speed is a good measure of the local mode of propagation. This is verified by examining the energy and species balances. A parametric study in the amplitudes of the initial temperature fluctuation is performed and shows that this parameter has a significant influence on the observed combustion mode. Higher levels of stratification lead to more front-like structures. Predictions of the multi-zone model are presented and explained using the diagnostics developed.
The impacts of small niobium additions to processing, microstructure, and electrical properties in the Zr-rich lead zirconate titanate ceramics (PZT 95/5) were investigated. The influence of niobium content on dielectric responses and the characteristics of ferroelectric behaviors, as well as the relative phase stability and the hydrostatic pressure induced ferroelectric-to- antiferroelectric phase transformation are reported. Results indicate that increasing the niobium concentration in the solid solutions enhances densification, refines the microstructure, decreases dielectric constant and spontaneous polarization, and stabilizes the ferroelectric phase. The stabilization of ferroelectric phase with respect to the antiferroelectric phase near PZT 95/5 composition dramatically increases the pressure required for the ferroelectric-to-antiferroelectric phase transformation. These observations were correlated to the creation of A-site vacancies and a slight modification of the crystal structure. The importance of these composition-property relationships on device application will be presented.
Optical actuation of microelectromechanical systems (MEMS) is advantageous for applications for which electrical isolation is desired. Thirty-two polycrystalline silicon opto-thermal actuators, optically-powered MEMS thermal actuators, were designed, fabricated, and tested. The design of the opto-thermal actuators consists of a target for laser illumination suspended between angled legs that expand when heated, providing the displacement and force output. While the amount of displacement observed for the opto-thermal actuators was fairly uniform for the actuators, the amount of damage resulting from the laser heating ranged from essentially no damage to significant amounts of damage on the target. The likelihood of damage depended on the target design with two of the four target designs being more susceptible to damage. Failure analysis of damaged targets revealed the extent and depth of the damage.
A three-dimensional tungsten photonic crystal is thermally excited and shown to emit light at a narrow band, {lambda} = 3.3-4.25 {micro}m. The emission is experimentally observed to exceed that of the free-space Planck radiation over a wide temperature range, T = 475-850 K. it is proposed that an enhanced density of state associated with the propagating electromagnetic Bloch waves in the photonic crystal is responsible for this experimental finding.
This paper provides a brief overview of the fields of biological micro-electromechanical systems (bioMEMs) and associated nanobiotechnologies, collectively denoted as BioMicroNano. Although they are developing at a very rapid pace and still redefining themselves, several stabilized areas of research and development can be identified. Six major areas are delineated, and specific examples are discussed and illustrated. Various applications of the technologies are noted, and potential market sizes are compared.
Simplified models that are based on macroscopic force balances and droplet-geometry approximations are presented for predicting the onset of instability leading to removal of water droplets at the gas diffusion layer (GDL)/gas flow channel (GFC) interface. Visualization experiments are carried out to observe the formation, growth, and removal or instability of the water droplets at the GDL/GFC interface of a simulated polymer electrolyte fuel cell cathode. Droplet-instability diagrams or windows computed by the simplified models are compared with those measured experimentally, and good agreement is obtained. Two-dimensional flow simulations employing the finite element method coupled with an arbitrary Lagrangian-Eulerian formulation for determining the liquid/gas interface position are also performed to assess the simplified cylindrical-droplet model. Necessary conditions for preventing fully grown droplets from lodging in the flow channel are derived using the simplified models. It is found that droplet removal can be enhanced by increasing flow channel length or mean gas flow velocity, decreasing channel height or contact angle hysteresis, or making the GDL/GFC interface more hydrophobic.
Concerns over the illicit trafficking of radiological and nuclear materials were focused originally on the lack of security and accountability of such material throughout the former Soviet states. This is primarily attributed to the frequency of events that have occurred involving the theft and trafficking of critical material components that could be used to construct a Radiological Dispersal Device (RDD) or even a rudimentary nuclear device. However, with the continued expansion of nuclear technology and the deployment of a global nuclear fuel cycle these materials have become increasingly prevalent, affording a more diverse inventory of dangerous materials and dual-use items. To further complicate the matter, the list of nuclear consumers has grown to include: (1) Nation-states that have gone beyond the IAEA agreed framework and additional protocols concerning multiple nuclear fuel cycles and processes that reuse the fuel through reprocessing to exploit technologies previously confined to the more industrialized world; (2) Terrorist organizations seeking to acquire nuclear and radiological material due to the potential devastation and psychological effect of their use; (3) Organized crime, which has discovered a lucrative market in trafficking of illicit material to international actors and/or countries; and (4) Amateur smugglers trying to feed their families in a post-Soviet era. An initial look at trafficking trends of this type seems scattered and erratic, localized primarily to a select group of countries. This is not necessarily the case. The success with which other contraband has been smuggled throughout the world suggests that nuclear trafficking may be carried out with relative ease along the same routes by the same criminals or criminal organizations. Because of the inordinately high threat posed by terrorist or extremist groups acquiring the ingredients for unconventional weapons, it is necessary that illicit trafficking of these materials be better understood as to prepare for the sustained global development of the nuclear fuel cycle. Conversely, modeling and analyses of this activity must not be limited in their scope to loosely organized criminal smuggling, but address the problem as a commercial, industrial project for the covert development of nuclear technologies and unconventional weapon development.
The nation's electric power sector is highly interdependent with the economic sectors it serves; electric power needs are driven by economic activity while the economy itself depends on reliable and sustainable electric power. To advance higher level understandings of the vulnerabilities that result from these interdependencies and to identify the loss prevention and loss mitigation policies that best serve the nation, the National Infrastructure Simulation and Analysis Center is developing and using N-ABLE{trademark}, an agent-based microeconomic framework and simulation tool that models these interdependencies at the level of collections of individual economic firms. Current projects that capture components of these electric power and economic sector interdependencies illustrate some of the public policy issues that should be addressed for combined power sector reliability and national economic security.
The thermal interdiffusion of AlSb/GaSb multiquantum wells was measured and the intrinsic diffusivities of Al and Ga determined over a temperature range of 823-948 K for 30-9000 s. The 77-K photoluminescence (PL) was used to monitor the extent of interdiffusion through the shifts in the superlattice luminescence peaks. The chemical diffusion coefficient was quantitatively determined by fitting the observed PL peak shifts to the solution of the Schroedinger equation, using a potential derived from the solution of the diffusion equation. The value of the interdiffusion coefficient ranged from 5.2 x 10{sup -4} to 0.06 nm{sup 2}/s over the conditions studied and was characterized by an activation energy of 3.0 {+-} 0.1 eV. The intrinsic diffusion coefficients for Al and Ga were also determined with higher values for Al than for Ga, described by activation energies of 2.8 {+-} 0.4 and 1.1 {+-} 0.1 eV, respectively.
A number of industrial combustion systems are adopting oxygen-enhanced firing to improve heat transfer characteristics and reduce emissions. The exhaust gas from these systems is dominated by H2O and CO2 and therefore has substantially different gas properties from traditional combustion exhaust. In the past, laser-induced breakdown spectroscopy (LIBS) has been successfully used for the evaluation of alkali aerosol concentrations in air-based combustion systems. This paper presents results of LIBS measurements of alkali concentrations in a laboratory calibration setup and in an oxygen/natural gas container glass furnace. It shows how both gas conditions (composition and temperature) and the molecular form of the alkali species affect the LIBS signals. The paper proposes strategies for mitigating these effects in future applications of LIBS in oxygen-enhanced combustion systems.
The dimensionless extinction coefficient (K{sub e}) of soot must be known to quantify laser extinction measurements of soot concentration and to predict optical attenuation through smoke clouds. Previous investigations have measured K{sub e} for post-flame soot emitted from laminar and turbulent diffusion flames and smoking laminar premixed flames. This paper presents the first measurements of soot K{sub e} from within laminar diffusion flames, using a small extractive probe to withdraw the soot from the flame. To measure K{sub e}, two laser sources (635 nm and 1310 nm) were coupled to a transmission cell, followed by gravimetric sampling. Coannular diffusion flames of methane, ethylene and nitrogen-diluted kerosene burning in air were studied, together with slot flames of methane and ethylene. K{sub e} was measured at the radial location of maximum soot volume fraction at several heights for each flame. Results for K{sub e} at both 635 nm and 1310 nm for ethylene and kerosene coannular flames were in the range of 9-10, consistent with the results from previous studies of post-flame soot. The ethylene slot flame and the methane flames have lower K{sub e} values, in some cases as low as 2.0. These lower values of K{sub e} are found to result from the contributions of (a) the condensation of PAH species during the sampling of soot, (b) the wavelength-dependent absorptivity of soot precursor particles, and, in the case of methane, (c) the negligible contribution of soot scattering to the extinction coefficient. RDG calculations of soot scattering, in combination with the measured K{sub e} values, imply that the soot refractive index is in the vicinity of 1.75-1.03i at 635 nm.
A severe fire and explosion occurred at a propane storage yard in Truth or Consequences, N.M., when a truck ran into the pumping and plumbing system beneath a large propane tank. The storage tank emptied when the liquid-phase excess flow valve tore out of the tank. The ensuing fire engulfed several propane delivery trucks, causing one of them to explode. A series of elevated-temperature stress-rupture tears developed along the top of a 9800 L (2600 gal) truck-mounted tank as it was heated by the fire. Unstable fracture then occurred suddenly along the length of the tank and around both end caps, along the girth welds connecting the end caps to the center portion of the tank. The remaining contents of the tank were suddenly released, aerosolized, and combusted, creating a powerful boiling liquid expanding vapor explosion (BLEVE). Based on metallography of the tank pieces, the approximate tank temperature at the onset of the BLEVE was determined. Metallurgical analysis of the ruptured tank also permitted several hypotheses regarding BLEVE mechanisms to be evaluated. Suggestions are made for additional work that could provide improved predictive capabilities regarding BLEVEs and for methods to decrease the susceptibility of propane tanks to BLEVEs.
43rd AIAA Aerospace Sciences Meeting and Exhibit - Meeting Papers
Chen, Guoquan; Collis, S.S.
A new multidomain/multiphysics computational framework for optimal control of aeroacoustic noise has been developed based on a near-field compressible Navier-Stokes solver coupled with a far-field linearized Euler solver both based on a discontinuous Galerkin formulation. In this approach, the coupling of near- and far-field domains is achieved by weakly enforcing continuity of normal fluxes across a coupling surface that encloses all nonlinearities and noise sources. For optimal control, gradient information is obtained by the solution of an appropriate adjoint problem that involves the propagation of adjoint information from the far-field to the near-field. This computational framework has been successfully applied to study optimal boundary-control of blade-vortex interaction, which is a significant noise source for helicopters on approach to landing. In the model-problem presented here, the noise propogated toward the ground is reduced by 12dB.
An electrically programmable surface acoustic wave (SAW) correlator was recently completed from design through small scale production in support of low power space-based communications for NASA. Three different versions of this RF microsystem were built to satisfy design requirements and overcome packaging and system reliability related issues. Flip-chip packaging and conventional thick film hybrid assembly techniques are compared in the fabrication of this microsystem.
The apparent metal-insulator transition is observed in a high-quality two-dimensional electron system (2DES) in the strained Si quantum well of a Si/Si{sub 1-x}Ge{sub x} heterostructure with mobility {mu} = 1.9 x 10{sup 5} cm{sup 2}/V s at density n = 1.45 x 10{sup 11} cm{sup -2}. The critical density, at which the thermal coefficient of low T resistivity changes sign, is -0.32 x 10{sup 11} cm{sup -2}, a very low value obtained in Si-based 2D systems. The in-plane magnetoresistivity {rho}(B{sub ip}) was measured in the density range, 0.35 x 10{sup 11} < n < 1.45 x 10{sup 11} cm{sup -2}, where the 2DES shows the metallic-like behavior. It first increases and then saturates to a finite value {rho}(B{sub c}) for B{sub ip}>B{sub c} , with B{sub c} the full spin-polarization field. Surprisingly, {rho}(B{sub c})/{rho}(0)-1.8 for all the densities, even down to n = 0.35 x 10{sup 11} cm{sup -2}, only 10% higher than n{sub c}. This is different from that in clean Si metal-oxide-semiconductor field-effect transistors, where the enhancement is strongly density dependent and {rho}(B{sub c})/{rho}(0) appears to diverge as n {yields} n{sub c}. Finally, we show that in the fully spin-polarized regime, dependent on the 2DES density, the temperature dependence of {rho}(B{sub ip}) can be either metallic-like or insulating.
This article describes recent improvements in mapping a highly representative set of the world-wide scientific literature. The process described in this article extends existing work in this area in three major ways. First, we argue that a separate structural analysis of current literature vs. reference literature is required for R&D planning. Second, visualization software is used to improve coverage of the literature while maintaining structural integrity. Third, quantitative techniques for measuring the structural integrity of a map are introduced. Maps with high structural integrity, covering far more of the available literature, are presented.
A dynamic hohlraum is created when an annular z-pinch plasma implodes onto a cylindrical 0.014 g/cc 6-mm-diameter CH{sub 2} foam. The impact launches a radiating shock that propagates toward the axis at {approx}350 {micro}m/ns. The radiation trapped by the tungsten z-pinch plasma forms a {approx}200 eV hohlraum that provides X-rays for indirect drive inertial confinement fusion capsule implosion experiments. We are developing the ability to diagnose the hohlraum interior using emission and absorption spectroscopy of Si atoms added as a tracer to the central portion of the foam. Time- and space-resolved Si spectra are recorded with an elliptical crystal spectrometer viewing the cylindrical hohlraum end-on. A rectangular aperture at the end of the hohlraum restricts the field of view so that the 1D spectrometer resolution corresponds approximately to the hohlraum radial direction. This enables distinguishing between spectra from the unshocked radiation-heated foam and from the shocked foam. Typical spectral lines observed include the Si Ly{alpha} with its He-like satellites and the He-like resonance sequence including He{alpha}, He{beta}, and He{gamma}, along with some of their associated Li-like satellites. Work is in progress to infer the hohlraum conditions using collisional-radiative modeling that accounts for the radiation environment and includes both opacity effects and detailed Stark broadening calculations. These 6-mm-scale radiation-heated plasmas might eventually also prove suitable for testing Stark broadening line profile calculations or for opacity measurements.
Fluorescence correlation spectroscopy (FCS) is used to examine mobility of labeled probes at specific sites in supported bilayers consisting of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) lipid domains in 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC). Those sites are mapped beforehand with simultaneous atomic force microscopy and submicron confocal fluorescence imaging, allowing characterization of probe partitioning between gel DPPC and disordered liquid DOPC domains with corresponding topography of domain structure. We thus examine the relative partitioning and mobility in gel and disordered liquid phases for headgroup- and tailgroup-labeled GM1 ganglioside probes and for headgroup- and tailgroup-labeled phospholipid probes. For the GM1 probes, large differences in mobility between fluid and gel domains are observed; whereas unexpected mobility is observed in submicron gel domains for the phospholipid probes. We attribute the latter to domain heterogeneities that could be induced by the probe. Furthermore, fits to the FCS data for the phospholipid probes in the DOPC fluid phase require two components (fast and slow). Although proximity to the glass substrate may be a factor, local distortion of the probe by the fluorophore could also be important. Overall, we observe nonideal aspects of phospholipid probe mobility and partitioning that may not be restricted to supported bilayers.
We consider linear systems arising from the use of the finite element method for solving a certain class of linear elliptic problems. Our main result is that these linear systems, which are symmetric and positive semidefinite, are well approximated by symmetric diagonally dominant matrices. Our framework for defining matrix approximation is support theory. Significant graph theoretic work has already been developed in the support framework for preconditioners in the diagonally dominant case, and in particular it is known that such systems can be solved with iterative methods in nearly linear time. Thus, our approximation result implies that these graph theoretic techniques can also solve a class of finite element problems in nearly linear time. We show that the quality of our approximation, which controls the number of iterations in the preconditioned iterative solver, depends primarily on a mesh quality measure but not on the problem size or shape of the domain.
The authors explore various possible approaches for generating lowest order and higher order bases for modeling surface currents and their divergence for moment method application to integral equations. The bases developed are defined on curved triangular and quadrilateral elements. All the bases are conveniently defined in parent element coordinates, and each expansion function spans one or two patches.
This article examines how well one can predict the importance of a current paper (a paper that is recently published in the literature). We look at three factors--journal importance, reference importance and author reputation. Citation-based measures of importance are used for all variables. We find that journal importance is the best predictor (explaining 22.3% out of a potential 29.1% of the variance in the data), and that this correlation value varies significantly by discipline. Journal importance is a better predictor of citation in Computer Science than in any other discipline. While the finding supports the present policy of using journal impact statistics as a surrogate for the importance of current papers, it calls into question the present policy of equally weighting current documents in text-based analyses. We suggest that future researchers take into account the expected importance of a document when attempting to describe the cognitive structure of a field.
American Rock Mechanics Association - 40th US Rock Mechanics Symposium, ALASKA ROCKS 2005: Rock Mechanics for Energy, Mineral and Infrastructure Development in the Northern Regions
Bauer, Stephen J.; Munson, D.E.; Hardy, M.P.; Barrix, J.; McGunegle, B.
Stress measurements have been obtained from within the Norton Mine in support of site characterization activities intended to determine the in situ stress field around the mine. These results together with other measurements in the area permit an estimate of the principal stresses at the mine. Based on the most recent measurements, the maximum (σHmax) and minimum (σHmin) stresses acting in the horizontal plane are oriented nearly east-west and north-south, respectively, and their magnitudes are 5330 psi and 4100 psi, respectively. These values are expected to be essentially uniform within a few hundred feet vertically above and below the mine elevation. The stress acting in the vertical direction has a magnitude of 3270 psi at the mine level. This measured vertical stress is related to the overburden weight according to σv=1.26ρgh (where ρ is the overburden density, g acceleration of gravity, and h overburden depth). The measured vertical stress exceeds the stress calculated from overburden weight by a factor of 1.26. These in situ stresses are assumed to be principal stresses and, as a result, the vertical stress is the minimum principal stress. These measurements are generally consistent in magnitude and direction with two other much older sets of measurements taken in the mine and they are consistent with the east-west trend of the regional in situ principal stress direction. The average of all three sets of measurements, recent and old, in the mine give a maximum horizontal stress of 6110 psi, a minimum horizontal stress of 3630, and a vertical stress of 3030 psi. The directions of the mine excavation development, which normally are oriented according to the principal stresses, are also consistent with the current and past measurements.
Proceedings of the ASME/Pacific Rim Technical Conference and Exhibition on Integration and Packaging of MEMS, NEMS, and Electronic Systems: Advances in Electronic Packaging 2005